High voltage transformer for microwave oven and method of manufacturing therefor

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.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to high voltage transformers for 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.

2. Description of the Related Art

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.

FIG. 8is an exploded perspective view of a conventional high voltage transformer, whileFIG. 9is an enlarged cross sectional view taken generally along line IX—IX ofFIG. 8, showing a part of a secondary coil. As shown inFIG. 8, the conventional high voltage transformer, which is denoted120, has an I-shaped core121, and an E-shaped core123, both of which are made of silicon steel. A primary coil125is connected to an external power supply, (not shown) and a secondary coil129is connected to a magnetron (not shown). An insulating member or micasheet127made of a suitable insulating material is positioned between the primary and secondary coils125and129, and a heater coil131is positioned between the insulating member127and the secondary coil129. As illustrated, insulating member127may be formed as two separate parts.

Each of the primary and secondary coils125and129is covered with a respective insulating sheet or covering133for insulating the coils125and129from other components. As illustrated, the respective insulating sheets133can be formed of multiple parts. Beside the secondary coil129is installed a temperature sensor135for detecting temperature of the secondary coil129so as to protect the secondary circuit for the secondary coil129. The temperature sensor135is positioned inside the insulating sheet133enclosing the secondary coil129as shown in FIG.9. Alternately, sensor135can be fixed between the secondary coil129and the core121by a tape (not shown). Another insulating sheet137is positioned between the temperature sensor135and the secondary coil129so as to prevent the temperature sensor135from contacting the secondary coil129.

In the above-described conventional high voltage transformer for a microwave oven, because the temperature sensor135is fixed in position by the insulating sheet133enclosing the secondary coil129, the insulating sheet133can detach from the secondary coil129when the high voltage transformer120is in operation and the temperature of the high voltage transformer120can increase beyond a predetermined value. As a consequence, the temperature sensor135cannot 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 sensor135cannot 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 sensor135is fixed to the secondary coil129with 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

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.

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.

To accomplish these and other objects of the present invention, there is 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.

Preferably, the sensor accommodating portion is formed inside of the 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.

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.

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.

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.

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.

DETAILED DESCRIPTION OF THE INVENTION

Referring toFIG. 1which 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 housing1which includes a cooking chamber3and an electronic component compartment5. A door7provides access to the cooking chamber3, and a control panel9is installed in front of the electronic component compartment5. A plurality of electronic components are housed in the electronic component compartment5. These include a high voltage transformer20for generating high voltage when the microwave oven is supplied with power from a power supply (not shown), a high voltage capacitor11which is charged to a high voltage by the high voltage transformer20, and a magnetron13for generating microwaves and radiating the microwaves into the cooking chamber3when discharge of the high voltage capacitor11supplies the magnetron13with high voltage.

The transformer20is shown in more detail inFIGS. 2,3and4, wherein, as noted above,FIG. 2is an exploded perspective view of the high voltage transformer20ofFIG. 1,FIG. 3is an assembled perspective view of the high voltage transformer of FIG.2andFIG. 4is an enlarged cross sectional view taken generally along line IV—IV of FIG.3. As shown in various of these figures, the high voltage transformer20includes an I-shaped core21, and an E-shaped core23, (both of which are preferably made of silicon steel), a primary coil part30which is connected to the external power supply (not shown), and a secondary coil part40which is connected to the magnetron13. An insulator or micasheet27, made of a suitable insulating material, is positioned between the primary and secondary coil parts30and40, and a heater coil29is positioned between the insulator27and the secondary coil part40.

The primary coil part30includes an insulation molding part or molded insulation part31, and a primary coil (not shown) enclosed by the insulation part31. On the outer surface of the insulation molding part31is installed a pair of input terminals33for receiving power from the external power supply (not shown).

The secondary coil part40has a secondary coil41(seeFIG. 4) wound in the form of an annulus or ring, and a temperature sensor43(FIG. 4) for detecting temperature of the secondary coil41to protect the secondary circuit including secondary coil41. A variety of types of sensors can be used as the temperature sensor43as described below. The secondary coil part40also includes an insulation molding part45for insulating the secondary coil41from other components such as the temperature sensor43, the I-shaped core21, and the E-shaped core23. The insulation molding part45includes a sensor accommodating portion47in which the temperature sensor43is accommodated. As shown inFIG. 4, the temperature sensor43is placed in the sensor accommodating portion47adjacent to the secondary coil41and is molded together with the secondary coil41into an integral unit.

A thermostat is preferably used as the temperature sensor43which is molded together with the secondary coil41. The thermostat detects temperature of the secondary coil41and corresponding temperature values are 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 sensor43, one terminal49(FIGS. 2 and 3) of the thermostat is connected to one of the input terminals33installed in the primary coil part30and the other terminal50thereof (FIGS. 2 and 3) is connected to the external power supply (not shown). The secondary coil part40includes a pair of connection terminals51which are spaced from, and preferably disposed in opposition to, the temperature sensor43, and which are connected to other components in the electronic component compartment5.

In an alternative embodiment, a thermistor is used as a temperature sensor43. In this embodiment, the thermistor detects temperature of the secondary coil41and 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).

As indicated above,FIG. 5is 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), whileFIG. 6is an enlarged cross sectional view of the secondary coil part, taken generally line VI—VI of FIG.5.

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 transformer20ofFIG. 5includes a pair of cores21and23, and primary and secondary coil parts60and70. Between the coil parts60and70is installed an insulation member or micasheet27made of suitable insulating material. A temperature sensor80for detecting temperature of a secondary coil71(seeFIG. 6) in order to protect the secondary circuit is installed in the secondary coil part70. The secondary coil71of the secondary coil part70has an annular or ring shape and, as shown inFIG. 6, an insulation molding part73is provided for insulating the secondary coil71from other components including the pair of cores21and23. The insulation molding part73has a sensor accommodating portion75in which the temperature sensor80is accommodated. The sensor accommodating portion75is in the shape of a pocket formed by a curved generally L-shaped projection so that the temperature sensor43can be easily put into pocket portion75and taken out therefrom.

A thermostat or a thermistor may be used as the temperature sensor80to be accommodated in the pocket-shaped sensor accommodating portion75. 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 portion75, the method of connection will vary according to the capacity of the fuse to be installed.

Considering the latter point in more detail, where, for example, a small capacity fuse is installed adjacent to the secondary coil71, a pair of connector elements81connected to the respective terminals of the fuse are, as shown inFIG. 6, directly connected to corresponding connectors91installed at the PCB90. Where a large capacity (over10A) fuse is used (and this embodiment is not illustrated in the drawings), one terminal of the fuse is connected to either of the input terminals61associated with the primary coil part60and the other terminal thereof is connected to the external power supply.

FIG. 7is a flowchart showing the steps in a manufacturing process for either of the secondary coil part40or70. As shown inFIG. 7, the secondary coil part40is manufactured using the following process. A first step comprises preparation of a lower molder or mold in which the secondary coil41is 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 S1). Next, the secondary coil41is accommodated in the lower molder while maintaining a gap between the secondary coil41and the inner wall side of the lower molder (Step S2). The temperature sensor43is then positioned in the lower molder in spaced relation to the secondary coil41(Step S3). 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 S4). When this is done, molding material is poured into the assembled molders through the down and cross gates (Step S5). As a result, the insulating molding part45for the secondary coil41and the temperature sensor43are molded as an internal unit (Step S6). In this case, the sensor accommodating part47which accommodates the temperature sensor43is provided along with the insulation molding part45.

In the embodiment wherein the pocket-shaped sensor accommodating part75ofFIGS. 5 and 6is formed, the step of forming a pocket-shaped portion in the lower mold or molder is required, whereas the step of positioning the temperature sensor43in the lower mold or molder is not needed.

With this general manufacturing process, the insulation molding part45or73is molded in the secondary coil part40or70to provide insulation from the core and other components.

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.

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.

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.