Abstract:
A high voltage transformer for a microwave oven includes a core, and primary and secondary coils. An insulation molding part encloses at least a part of the secondary coil and has a sensor accommodation portion formed therein. A temperature sensor is accommodated in the sensor accommodating portion for detecting temperature of the secondary coil. The sensor accommodating portion can be formed inside of the insulation molding part together with the temperature sensor, or formed outside of the insulation molding part in a pocket shape. With either configuration, the temperature sensor can be positioned at the correct sensor position, thereby improving the detecting accuracy of the temperature sensor. In addition, it is easy to repair and/or replace the temperature sensor.

Description:
CROSS REFERENCE TO RELATED APPLICATION  
       [0001]    The present application is a divisional of application Ser. No. 09/543,865 filed on Apr. 5, 2000. 
     
    
     
       BACKGROUND OF THE INVENTION  
         [0002]    1. Field of the Invention  
           [0003]    The present invention relates to high voltage transformers for  
           [0004]    microwave ovens and manufacturing methods therefor, and more particularly, to an improved high voltage transformer for a microwave oven including a core, and primary and secondary coils, and an improved manufacturing method therefor.  
           [0005]    2. Description of the Related Art  
           [0006]    A typical microwave oven comprises a casing or housing having a cooking chamber and an electronic component compartment, a door for the cooking chamber, and a control panel installed in front of the electronic component compartment. A plurality of electronic components are housed in the electronic component compartment. These electronic components include a high voltage transformer for generating high voltage when the microwave oven is supplied with power from a power supply, a high voltage capacitor which is charged to a high voltage by the high voltage transformer, and a magnetron for generating microwaves and radiating the microwaves into the cooking chamber when discharge of the high voltage capacitor supplies the magnetron with high voltage.  
           [0007]    [0007]FIG. 8 is an exploded perspective view of a conventional high voltage transformer, while FIG. 9 is an enlarged cross sectional view taken generally along line IX-IX of FIG. 8, showing a part of a secondary coil. As shown in FIG. 8, the conventional high voltage transformer, which is denoted  120 , has an I-shaped core  121 , and an E-shaped core  123 , both of which are made of silicon steel. A primary coil  125  is connected to an external power supply, (not shown) and a secondary coil  129  is connected to a magnetron (not shown). An insulating member or micasheet  127  made of a suitable insulating material is positioned between the primary and secondary coils  125  and  129 , and a heater coil  131  is positioned between the insulating member  127  and the secondary coil  129 . As illustrated, insulating member  127  may be formed as two separate parts.  
           [0008]    Each of the primary and secondary coils  125  and  129  is covered with a respective insulating sheet or covering  133  for insulating the coils  125  and  129  from other components. As illustrated, the respective insulating sheets  133  can be formed of multiple parts. Beside the secondary coil  129  is installed a temperature sensor  135  for detecting temperature of the secondary coil  129  so as to protect the secondary circuit for the secondary coil  129 . The temperature sensor  135  is positioned inside the insulating sheet  133  enclosing the secondary coil  129  as shown in FIG. 9. Alternately, sensor  135  can be fixed between the secondary coil  129  and the core  121  by a tape (not shown). Another insulating sheet  137  is positioned between the temperature sensor  135  and the secondary coil  129  so as to prevent the temperature sensor  135  from contacting the secondary coil  129 .  
           [0009]    In the above-described conventional high voltage transformer for a microwave oven, because the temperature sensor  135  is fixed in position by the insulating sheet  133  enclosing the secondary coil  129 , the insulating sheet  133  can detach from the secondary coil  129  when the high voltage transformer  120  is in operation and the temperature of the high voltage transformer  120  can increase beyond a predetermined value. As a consequence, the temperature sensor  135  cannot be securely disposed at its optimum or desired position with respect to the secondary coil, and under conditions such as those outlined above, the temperature sensor  135  cannot precisely detect the temperature of the secondary coil. In addition, with this conventional configuration, the efficiency of insulation is not optimal. Further, because the temperature sensor  135  is fixed to the secondary coil  129  with the insulating sheet, or in the non-illustrated embodiment, to the fixing tape, the insulating sheet or the fixing tape must be removed by hand for inspecting, repairing or replacing the sensor, thereby decreasing the efficiency of any such inspection, repair or replacement.  
         SUMMARY OF THE INVENTION  
         [0010]    To solve the above discussed problems, it is an object of the present invention to provide a high voltage transformer for a microwave oven in which a temperature sensor is securely positioned at its desired position relative to a secondary coil, thereby improving the detecting accuracy of the temperature sensor, and to provide a method of manufacturing such a transformer.  
           [0011]    It is another object of the present invention to provide a high voltage transformer, and a manufacturing method therefor, wherein the associated temperature sensor can be installed and removed in a simple manner so as to permit the sensor to be easily repaired or replaced.  
           [0012]    To accomplish these and other objects of the present invention, there is  
           [0013]    provided a high voltage transformer for a microwave oven including a core, and primary and secondary coils, wherein the high voltage transformer further comprises an insulation molding part which encloses at least a part of said secondary coil and which includes a sensor accommodating portion, and a temperature sensor disposed or accommodated in said sensor accommodating portion for detecting temperature of the secondary coil.  
           [0014]    Preferably, the sensor accommodating portion is formed inside of the  
           [0015]    insulation molding part, and the temperature sensor is one of a thermostat and a thermistor. Advantageously, when a thermistor is used, a safety device such as a fuse is also employed.  
           [0016]    In an alternative preferred embodiment, the sensor accommodating portion has the shape of a pocket, or is otherwise shaped, so that the temperature sensor can be easily put into, and taken out of, the sensor accommodating portion, and the temperature sensor comprises one of a thermostat, a thermistor and a fuse.  
           [0017]    According to a further aspect of the present invention, there is provided a method for manufacturing a high voltage transformer for a microwave oven, the transformer including a core, primary and secondary coils, and a temperature sensor for detecting temperature of the secondary coil and the method including the steps of: accommodating the secondary coil and the temperature sensor in a molder member; molding the secondary coil and the temperature sensor accommodated in the molder member into an insulating molding part accommodating the temperature sensor, and enclosing at least part of the secondary coil such that the temperature sensor is fixed in position relative to the secondary coil.  
           [0018]    Advantageously, the molding step comprises molding a temperature sensor accommodating portion into the molding part in which the temperature sensor is accommodated. In a beneficial implementation, the sensor and the secondary coil are molded together such that the sensor is disposed directly adjacent to the secondary coil. Advantageously, the external sensor accommodating portion is formed as a pocket defining member on an outside surface of the insulating molding part. Preferably, the temperature sensor is one of a thermostat and a thermistor.  
           [0019]    According to another aspect of the present invention, there is provided a manufacturing method of a high voltage transformer for a microwave oven, the transformer including a core, primary and secondary coils, and a temperature sensor for detecting temperature of the secondary coil, and the method comprising the steps of: providing a molder member for forming an insulating molding part including an external sensor accommodating portion; disposing the secondary coil in the molder member; and molding the secondary coil in the molder member to form the insulating molding part with at least a part of the secondary coil molded therein and to form the external sensor accommodating portion in spaced relation to the secondary coil so as to permit placement of the temperature sensor into, and removal of the sensor from, the sensor accommodating portion. Preferably, the temperature sensor is one of a thermostat, a thermistor and a fuse. 
       
    
    
     BRIEF DESCRIPTION OF THE DRAWINGS  
       [0020]    The present invention will be better understood, and the various  
         [0021]    objects and advantages thereof will be more fully appreciated, from the following description of the invention, taken in conjunction with the accompanying drawings, in which:  
         [0022]    [0022]FIG. 1 is an exploded perspective view of a microwave oven including a high voltage transformer according to the present invention;  
         [0023]    [0023]FIG. 2 is an exploded perspective view, drawn to an enlarged scale, of the high voltage transformer of FIG. 1;  
         [0024]    [0024]FIG. 3 is an assembled perspective view of the high voltage transformer of FIG. 2;  
         [0025]    [0025]FIG. 4 is an enlarged cross sectional view taken generally along line IV-IV of FIG. 3, showing a portion of the secondary coil part;  
         [0026]    [0026]FIG. 5 is a flowchart of a manufacturing process of the secondary  
         [0027]    coil of FIG. 4.  
         [0028]    [0028]FIG. 6 is an enlarged perspective view of a high voltage transformer including a secondary coil part according to another preferred embodiment of the present invention;  
         [0029]    [0029]FIG. 7 is an enlarged cross sectional view taken generally along line VII-VII of FIG. 6 showing a portion of the secondary coil.  
         [0030]    [0030]FIG. 8, which was described above, is a perspective view of a conventional high voltage transformer; and  
         [0031]    [0031]FIG. 9, which was also described above, is an enlarged cross sectional view taken generally along line IX-IX of FIG. 8 showing a portion of the secondary coil part. 
     
    
     DETAILED DESCRIPTION OF THE INVENTION  
       [0032]    Preferred embodiments of the present invention will now be described with reference to the accompanying drawings.  
         [0033]    Referring to FIG. 1 which is, as noted above, an exploded perspective view of a microwave oven including a high voltage transformer according to a first embodiment of the present invention, the microwave oven comprises a casing or housing  1  which includes a cooking chamber  3  and an electronic component compartment  5 . A door  7  provides access to the cooking chamber  3 , and a control panel  9  is installed in front of the electronic component compartment  5 . A plurality of electronic components are housed in the electronic component compartment  5 . These include a high voltage transformer  20  for generating high voltage when the microwave oven is supplied with power from a power supply (not shown), a high voltage capacitor  11  which is charged to a high voltage by the high voltage transformer  20 , and a magnetron  13  for generating microwaves and radiating the microwaves into the cooking chamber  3  when discharge of the high voltage capacitor  11  supplies the magnetron  13  with high voltage.  
         [0034]    The transformer  20  is shown in more detail in FIGS. 2, 3 and  4 , wherein, as noted above, FIG. 2 is an exploded perspective view of the high voltage transformer  20  of FIG. 1, FIG. 3 is an assembled perspective view of the high voltage transformer of FIG. 2 and FIG. 4 is an enlarged cross sectional view taken generally along line IV-IV of FIG. 3. As shown in various of these figures, the high voltage transformer  20  includes an I-shaped core  21 , and an E-shaped core  23 , (both of which are preferably made of silicon steel), a primary coil part  30  which is connected to the external power supply (not shown), and a secondary coil part  40  which is connected to the magnetron  13 . An insulator or micasheet  27 , made of a suitable insulating material, is positioned between the primary and secondary coil parts  30  and  40 , and a heater coil  29  is positioned between the insulator  27  and the secondary coil part  40 .  
         [0035]    The primary coil part  30  includes an insulation molding part or molded insulation part  31 , and a primary coil (not shown) enclosed by the insulation part  31 . On the outer surface of the insulation molding part  31  is installed a pair of input terminals  33  for receiving power from the external power supply (not shown).  
         [0036]    The secondary coil part  40  has a secondary coil  41  (see FIG. 4) wound in the form of an annulus or ring, and a temperature sensor  43  (FIG. 4) for detecting temperature of the secondary coil  41  to protect the secondary circuit including secondary coil  41 . A variety of types of sensors can be used as the temperature sensor  43  as described below. The secondary coil part  40  also includes an insulation molding part  45  for insulating the secondary coil  41  from other components such as the temperature sensor  43 , the I-shaped core  21 , and the E-shaped core  23 . The insulation molding part  45  includes a sensor accommodating portion  47  in which the temperature sensor  43  is accommodated. As shown in FIG. 4, the temperature sensor  43  is placed in the sensor accommodating portion  47  adjacent to the secondary coil  41  and is molded together with the secondary coil  41  into an integral unit.  
         [0037]    A thermostat is preferably used as the temperature sensor  43  which is  
         [0038]    molded together with the secondary coil  41 . The thermostat detects  
         [0039]    temperature of the secondary coil  41  and corresponding temperature values are  
         [0040]    received by a controller (not shown). The thermostat is automatically turned off when the detected temperature is above a predetermined value. Where the thermostat is used as the sensor  43 , one terminal  49  (FIGS. 2 and 3) of the thermostat is connected to one of the input terminals  33  installed in the primary coil part  30  and the other terminal  50  thereof (FIGS. 2 and 3) is connected to the external power supply (not shown). The secondary coil part  40  includes a pair of connection terminals  51  which are spaced from, and preferably disposed in opposition to, the temperature sensor  43 , and which are connected to other components in the electronic component compartment  5 .  
         [0041]    In an alternative embodiment, a thermistor is used as a temperature sensor  43 . In this embodiment, the thermistor detects temperature of the secondary coil  41  and the corresponding detected temperature values are received by the controller (not shown). However, since the thermistor is not turned off even though the detected temperature is above a predetermined value, it is preferable to use the thermistor along with one or more other components which function as a temperature responsive safety device (e.g., a fuse).  
         [0042]    As indicated above, FIG. 5 is an enlarged perspective view of a high voltage transformer in which a secondary coil part according to a secondary embodiment of the present invention is installed on a printed circuit board (PCB), while FIG. 6 is an enlarged cross sectional view of the secondary coil part, taken generally line VI-VI of FIG. 5.  
         [0043]    This embodiment is similar to that described above and hence, description of parts which correspond to those in the high voltage transformer according to the first embodiment of the present invention will be dispensed with or only briefly made reference to. The high voltage transformer  20  of FIG. 5 includes a pair of cores  21  and  23 , and primary and secondary coil parts  60  and  70 . Between the coil parts  60  and  70  is installed an insulation member or micasheet  27  made of suitable insulating material. A temperature sensor  80  for detecting temperature of a secondary coil  71  (see FIG. 6) in order to protect the secondary circuit is installed in the secondary coil part  70 . The secondary coil  71  of the secondary coil part  70  has an annular or ring shape and, as shown in FIG. 6, an insulation molding part  73  is provided for insulating the secondary coil  71  from other components including the pair of cores  21  and  23 . The insulation molding part  73  has a sensor accommodating portion  75  in which the temperature sensor  80  is accommodated. The sensor accommodating portion  75  is in the shape of a pocket formed by a curved generally L-shaped projection so that the temperature sensor  43  can be easily put into pocket portion  75  and taken out therefrom.  
         [0044]    A thermostat or a thermistor may be used as the temperature sensor  80  to be accommodated in the pocket-shaped sensor accommodating portion  75 . More preferably, a fuse is used which provides automatic cut off of current flow when the temperature is above a predetermined value. Where the fuse is installed in the sensor accommodating portion  75 , the method of connection will vary according to the capacity of the fuse to be installed.  
         [0045]    Considering the latter point in more detail, where, for example, a small capacity fuse is installed adjacent to the secondary coil  71 , a pair of connector elements  81  connected to the respective terminals of the fuse are, as shown in FIG. 6, directly connected to corresponding connectors  91  installed at the PCB  90 . Where a large capacity (over  10 A) fuse is used (and this embodiment is not illustrated in the drawings), one terminal of the fuse is connected to either of the input terminals  61  associated with the primary coil part  60  and the other terminal thereof is connected to the external power supply.  
         [0046]    [0046]FIG. 7 is a flowchart showing the steps in a manufacturing process for either of the secondary coil part  40  or  70 . As shown in FIG. 7, the secondary coil part  40  is manufactured using the following process. A first step comprises preparation of a lower molder or mold in which the secondary coil  41  is to be accommodated, and an upper molder, or mold which is to be assembled to the lower molder and in which a down gate and a cross gate are formed (Step S 1 ). Next, the secondary coil  41  is accommodated in the lower molder while maintaining a gap between the secondary coil  41  and the inner wall side of the lower molder (Step S 2 ). The temperature sensor  43  is then positioned in the lower molder in spaced relation to the secondary coil  41  (Step S 3 ). Next, the upper molder and the lower molder are combined with each other, i.e., brought together or assembled to form a complete mold (Step S 4 ). When this is done, molding material is poured into the assembled molders through the down and cross gates (Step S 5 ). As a result, the insulating molding part  45  for the secondary coil  41  and the temperature sensor  43  are molded as an internal unit (Step S 6 ). In this case, the sensor accommodating part  47  which accommodates the temperature sensor  43  is provided along with the insulation molding part  45 .  
         [0047]    In the embodiment wherein the pocket-shaped sensor accommodating part  75  of FIGS. 5 and 6 is formed, the step of forming a pocket-shaped portion in the lower mold or molder is required, whereas the step of positioning the temperature sensor  43  in the lower mold or molder is not needed.  
         [0048]    With this general manufacturing process, the insulation molding part  45  or  73  is molded in the secondary coil part  40  or  70  to provide insulation from the core and other components.  
         [0049]    Because the temperature sensor is enclosed by the insulation molding portion, or is positioned in the pocket-shaped sensor accommodating portion, the temperature sensor can be firmly and securely located adjacent to the secondary coil, thereby improving the detecting accuracy of the temperature sensor.  
         [0050]    In the embodiment wherein the sensor accommodating portion is formed in a pocket shape, the sensor can be easily put into, or taken out from, the sensor accommodating portion, and therefore, it is easier to repair and replace the temperature sensor.  
         [0051]    Although the present invention has been described in connection with preferred embodiments thereof, it will be appreciated by those skilled in the art that additions, modifications, substitutions and deletions not specifically described may be made therein without departing from the spirit and scope of the invention.