WO2005004175A1

WO2005004175A1 - Method for treating end of coil and bobbin used therefor

Info

Publication number: WO2005004175A1
Application number: PCT/JP2004/009399
Authority: WO
Inventors: Shinichi Sakai; Hisashi Morikawa; Makoto Mihara
Original assignee: Matsushita Electric Industrial Co., Ltd.
Priority date: 2003-07-04
Filing date: 2004-06-25
Publication date: 2005-01-13
Also published as: CN1806300A; JP2005026637A

Abstract

A method for treating the end portion of a coil which is wound around a bobbin 10 having a flange 11 and is lead out through the flange 11 to the outer surface, wherein the covered wire end 19 of the coil is locked with a provisional locking portion 21 installed at the flange and is supported in a raised condition with respect to the outer surface of the flange 11 and fusing is conducted with the electrodes 41, 42 for fusing which are disposed at a distance from the outer surface of the flange 11.

Description

DESCRIPTION

METHOD FOR TREATING END OF COIL AND BOBBIN USED THEREFOR

Technical Field The present invention relates to a method for treating a coil wound on a boosting transformer serving as a power source unit, for example, for an inverter-type high-frequency heating device.

Background Art A power source unit for an inverter-type high-frequency heating device contains, as shown in FIG. 6, a transformer unit 73 in which a transformer 72 is mounted on a printed circuit 71. The circuit of the transformer unit 73 will be described below with reference to FIG. 7. The output of a commercial power source 74 is full-wave rectified with a rectification circuit 75 such as a diode bridge or the like, converted into a high-frequency voltage by an inverter 76, and applied to a primary winding 77 of the transformer 72. As a result, a high-frequency high voltage of several kV is generated in a secondary winding 78 of the transformer 72. This high-frequency high voltage is rectified by a voltage-double rectification circuit 81 composed of a capacitor 79 and a diode 80. As a result, a high voltage is applied to a magnetron 82 which is a microwave generator. Furthermore, a heater winding 83 of the transformer 72 is connected to a filament 84 of the magnetron 82 for heating the filament 84. Further, the magnetron 82 generates microwaves under the effect of heating of the filament 84 and high voltage application. Referring to FIG. 8, the transformer 72 used in the aforementioned transformer unit 73 comprises a bobbin 85 having a primary winding 77, a secondary winding 78, and a heater winding 83 concentrically wound thereon, and has a structure in which cores 86 are inserted from both sides into the center of the bobbin 85. Further, this transformer 72, as shown in FIG. 9, comprises in the bottom portion thereof a primary winding connection pin 87, a secondary winding connection pin 88, a heater winding connection pin 89, and a ground connection pin 90. Those pins are inserted in the through holes of a printed substrate 71 prior to mounting and connected to the circuit pattern of the printed substrate 71 by soldering. In addition to the transformer 72, high- voltage components such as the capacity 79 and diode 80 and various components constituting a low-voltage circuits such as a control circuit are mounted on the printed substrate 71, as shown in FIG. 6. The transformer with the configuration shown in FIG. 7 is described, for example, in Patent Reference 1. [Patent Reference] JP-A-2001-189221. Due to the required miniaturization of high-frequency heating devices, the miniaturization of the transformer unit by size reduction of each component thereof has become an objective. On the other hand, in the transformers of the aforementioned inverter-type high-frequency heating device, it is important to inhibit the increase in heat generation in the coils caused by high frequency. Though using a wire of a large diameter can inhibit the increase in heat generation, increasing the weight of the coiled wire runs against the miniaturization trend. Therefore, it is advantageous to avoid the increase in the wire diameter by using a wire material with increased heat resistance. Further, a Litz wire which is an assembly of resin- coated wires such as enamel wires have been used as a primary winding of the transformer to suppress the increase in heat generation in the winding. A method for treating the end portion of the Litz wire, for example, comprises immersing the enamel wire in a lead- free-solder tank and peeling off the enamel coating from the surface, thereby soldering together the connection terminal and the inner conductor in an easy manner. However, when the aforementioned wire material with increased heat resistance is used for the Litz wire, the above-described end treatment method cannot be used because the enamel coating is not peeled off at a temperature of 500-550°C which is the melting temperature of the solder. Accordingly, a fusing welding process was considered as a replacement for the melt soldering process for mechanical and electric connection of the inner conductor and connection terminal by melting the electric coating (enamel film) . In the fusing process, while a pressure is applied with a pair of welding electrodes (electrodes for fusing) to a connection terminal locked to the covered wire end of the winding, an electric current is passed through the electrodes and the generated heat makes it possible to remove the insulating cover without peeling and to connect the wire to the connection terminal. Here, when fusing is conducted with respect to the winding that was wound around the bobbin, as shown in FIG. 10, first, the primary winding 77 is wound between two flanges 92, 95 located at a distance from each other in the axial direction of the bobbin 85, the covered wire end 87 is locked with the locking portion 91 formed at the outer surface of the flange 92 which is positioned at the outer side, and the primary winding 77 is fastened round the bobbin 85. As for the movement of the electrodes 93, 94 for fusing with respect to the covered wire end 87 of the primary winding 77 fastened round the bobbin 85, as shown in FIG. 11, due to space limitations, one electrode 93 is moved along the aforementioned flanges 92, 95 corresponding to the primary winding 77, and then moved from the vertical direction to the covered wire end 87 so as to apply a pressure to the covered wire end 87. On the other hand, the other electrode is moved from the vertical direction with respect to the outer surface of the flange 92 and disposed opposite the side surface of the first electrode 93 so as to sandwich the covered wire end 87 between the electrodes. Then fusing is conducted by fitting a contact terminal (not shown in the figures) from the outside onto the covered wire end 87 and passing an electric current to the electrodes 93, 94, while applying pressure with the two electrodes 93, 94 to the contact terminal. Thus, in the primary winding 77, the resin cover on the covered wire end 87 is softened under the effect of heat and applied pressure and pushed out form the end portion, thereby providing for mechanical and electrical connection of the inner conductor to the terminal . However, in the above-described method for treating the end portion of the primary winding (Litz wire) , because the spacing for the primary winding 77 between the two flanges 92, 95 is decreased following the miniaturization of the transformer 72, if the electrodes 93, 94 for fusing are miniaturized and reduced in width to satisfy the space limitations, an applied force generally exceeding 1000 N is necessary for a large number of Litz wires. Therefore, mechanical strength is reduced and there is a risk of buckling or deformation of one electrode 93 under the effect of a pushing force applied from the other electrode 94, as shown by a virtual line in FIG. 11, and the reliability can be reduced. When the primary winding 77 was taken off the locking portion 91 and fusing to the covered wire end 87 was conducted in a location without space limitations, the force fastening the primary winding 77 to the bobbin 85 was reduced and the primary winding could be unwound. As for the locking portion 91, as shown in FIG. 10, the distance from the component surface of the printed substrate 71 increased and the position of the distal end thereof could not be controlled, making the mounting difficult.

Disclosure of Invention With the foregoing in view, it is an object of the present invention to provide a method for treating the end portion of a coil by which fusing is conducted in a position which is not subject to space limitations and unwinding of the wire material is prevented. In order to attain the above-described object, the method for treating an end portion of a coil in accordance with the present invention is a method for treating an end portion of a coil which is wound around a bobbin having a flange and lead out through said flange to the outer surface of the bobbin, characterized in that it comprises the steps of locking the covered wire end of the coil in a raised condition with respect to the outer surface of the flange and fusing with the electrodes disposed at a distance from the outer surface of the flange. With this configuration, the covered wire end of the coil is locked in a raised condition and unwinding of the coil from the bobbin is prevented. Further, because the covered wire end of the coil is set in a raised condition with respect to the outer surface of the flange, the electrodes for fusing can be disposed so that the distal ends thereof face each other in a position which is not subject to space limitations, fusing can be conducted even without miniaturizing and reducing the width of the electrodes, and buckling or deformation caused by the decrease in mechanical strength can be avoided. Further, in the method for treating an end portion of a coil in accordance with the present invention, at least the covered wire end of the last turn of the coil is locked with a provisional locking portion in a raised condition with respect to the outer surface of the flange. With such a configuration, the covered end portion of the coil is reliably held in a raised condition and the covered end portion can be disposed in an almost central portion between a pair of electrodes. Therefore, fusing can be reliably conducted. The bobbin in accordance with the present invention comprising flanges and a coil wound therearound, in that a provisional locking portion is provided at the outer surface of the flange for locking the covered wire end of the coil that was lead out through the flange to the outer surface of the flange in a raised condition with respect to the outer surface of the flange. With such a configuration, the covered wire end of the coil is provided in a raised condition by the provisional locking portion provided at the outer surface of the flange of the bobbin and is disposed during fusing in a position at a distance from the side surface of the flange, which is not subject to space limitation. Further, in the bobbin in accordance with the present invention, a locking portion for fixing the terminal which is connected by fusing the covered wire end of the coil is further provided at the outer surface of the flange. With such a configuration, since the terminal connected to the end portion of the coil protrudes beyond the peripheral edge of the flange because of the locking portion, mounting thereof on the printed substrate of the transformer can be conducted in a very simple manner.

Brief Description of Drawings FIG. 1 is a perspective view illustrating the external appearance of the transformer unit employed in an embodiment of the present invention. FIG. 2 is a perspective view illustrating the external appearance of the transformer shown in FIG. 1. FIG. 3 is a perspective view illustrating the external appearance of the bobbin in the transformer prior to fusing. FIG. 4 is an enlarged view of the main portion of the bobbin in the transformer during fusing. FIGS. 5A and 5B are perspective views illustrating the external appearance of a connection terminal employed for the end portion of the coil; FIG. 5A is an example of the terminal which is externally fitted from the axial direction of the coil wire, FIG. 5B is an example of the terminal which is externally fitted from the side of the coil. FIG. 6 is a perspective view illustrating the external appearance of a power source unit of the conventional high- frequency heating device. FIG. 7 is a circuit diagram of the power source unit shown in FIG 6. FIG. 8 is a cross-sectional view of the transformer shown in FIG. 6. FIG. 9 is an perspective view illustrating the external appearance of the transformer unit shown in FIG. 6, as shown from below. FIG. 10 is an perspective view illustrating the external appearance of the bobbin used in the power source unit of the conventional high-frequency heating device. FIG. 11 is an enlarged cross-sectional view illustrating the coil end portion of the bobbin shown in FIG. 10.

Best Mode for Carrying Out the Invention The method for treating the end portion of a coil of the preferred embodiment of the present invention and a bobbin used therefore will be described below with reference to the appended drawings. In the present embodiment the explanation will be conducted with respect to a bobbin for a transformer of a high-frequency heating device and to the treatment of the end portion of the coil wound around the bobbin. As shown in FIG. 1, a transformer unit 1 which serves as a power source unit of a high-frequency heating device (simply referred to hereinbelow as "power source unit") has a structure in which a switching element 3b and a rectifying element 3a such as a diode bridge provided with a heat sink 4, a high-voltage component 5 such as a capacitor or a diode, a low-voltage circuit such as a control circuit (not shown in the figure) , and a transformer 6 are mounted on a printed substrate 2. The transformer 6 comprises a bobbin 10 having wound therearound a primary winding 13, a secondary winding 16 , and a heater winding 17. In the bobbin 10, the primary winding 13 is wound between the opposing flanges 11, 12, and the secondary winding 16 and heater winding 17 are independently wound concentrically with the primary winding 13 between the opposing flanges 14, 15. A core (not shown in the figure) is inserted so as to pass through the center of the bobbin 10. In the outer surface of the flange 11 at the side of the primary winding 13 forming the bobbin 10, as shown in FIG. 2, there are formed a lead-out groove 20a for pulling out the covered wire end 18 of the first turn of the primary winding 13 to the outside and a flange 20b for similarly pulling out the covered wire end 19 of the last turn of the primary winding 13 to the outside. At the outer periphery of the flange 20b for pulling out the covered wire end 19, as shown in FIG. 3, there is formed, continuously with the flange 20b, a protruding provisional locking portion 21 composed of a pair of elastic locking pieces. The provisional locking portion 21 has a function of removing restrictions placed on the space for fusing by locking the covered wire end 19 in a raised condition with respect to the outer source of the flange 11, as shown in FIG. 4, when fusing is employed for the covered wire end 19 and a function of holding the covered wire end, so as to avoid the relaxation of the winding force of the primary winding 13, and preventing the unwinding from the bobbin 10. Returning to FIG. 2, at the outer surface of the flange 11, there are further provided locking portions 22, 23 for fixedly disposing the connection terminals 24, 25 connected to the end portions of the primary winding 13 by fusing at the peripheral edge of the flange 11. The locking portions 22, 23 cause the connection terminals 24, 25 to protrude along the outer surface of the flange 11 and facilitate the insertion of the connection terminals 24, 25 into the through holes formed in the electric pattern when the transformer 6 is mounted on the printed circuit 2. A method for treating the end portion of the coil will be explained below. In the present embodiment, the explanation will be conducted with respect to a method for treating the end portion by which the connection terminal 25 is connected by fusing to a covered wire end 19 of the last turn of the primary winding 13. First, the primary winding 13 is obtained by winding the necessary number of turns between the flanges 11, 12 of the bobbin 10. Then, as shown in FIG. 3, the covered wire end 19 of the last turn is passed through the flange 20b and pulled out to the outer surface of the flange 11. The pulled-out covered wire end 19, as shown in FIG. 4, is then locked by the provisional locking portion 21 in a raised condition with respect to the outer surface of the flange 11. As has already been described hereinabove, locking the covered wire end 19 by the provisional locking portion 21 makes it possible to prevent the primary winding 13 from unwinding from the bobbin 10. The reason why only the covered wire end 19 of the last turn was selected as the object of the end portion treatment is that the primary winding 13 is wound over the first turn thereby always preventing it from unwinding. A cable connection portion 25a of the connection terminal 25 shown in FIG. 5 is fitted from the axial or side direction on the covered wire end 19 held in a raised condition and fused thereto. The fusing is carried out with a pair of electrodes 41, 42 for fusing. A pair of electrodes 41, 42 are disposed opposite each other so as to sandwich the covered wire end 19 in a raised condition thereof in a position withdrawn from the outer surface of the flange 11, the electrodes 41, 42 are moved toward each other so that the distal ends thereof come close to each other and apply pressure to the covered wire end 19, the electric cable connection portion 25a of the connection terminal 25 (not shown in the figure) is collapsed, and an electric current is passed to heat the covered wire end 19. The electric current first flows from the electrodes 41, 42 to the terminal 25, the distal ends of the electrodes 41, 42 and the connection terminal 25 (not shown in the figure) generate heat, and the temperature of the conductor of the covered wire end 19 which is in contact with terminal rises. Because the insulating cover which covers the conductor has thermal plasticity, it is softened under the effect of heat and applied pressure and pressed out from the electric cable connection portion 25a, thereby providing for a conductive connection of the conductor and the terminal 25. Once fusing has been completed, the primary winding 13 is bent along the outer surface of the flange 11, as shown in FIG. 2, the connection terminal 25 is locked with the locking portion 23, and the end portion treatment process is completed. It does not matter that" the primary winding 13 is separated from the provisional locking portion 21 at this time because the terminal 25 is fixed by the locking portion 23 and held at the outer surface of the flange 11. In other words, the provisional locking portion 21 can be interpreted as provisional locking means for temporary locking the covered wire end 19 for conducting fusing. The covered wire end 18 of the first turn of the primary winding 13 is treated in a similar manner and the connection terminal 24 is locked by the locking portion 22. With the method for treating the end portion of the coil of the above-described embodiment, the covered wire ends 18, 19 of the primary winding 13 were locked in a raised condition with respect to the outer surface of the flange, and fusing thereof was conducted with the electrodes 41, 42 for fusing that were similarly disposed at a distance from the outer surface of the flange 11. As a result, unwinding of the primary winding 13 from the bobbin 10 can be prevented and a sufficient operation space can be ensured for the electrodes 41, 42 for fusing. Moreover, because the electrodes 41, 42 can be disposed opposite each other along the same line as that of the pressure application direction, buckling and deformation owing to miniaturization and width reduction can be prevented. Further, because the primary winding 13 is held in a raised condition, while at least the covered wire end 19 of the last turn is locked with the provisional locking portion 21, the fusing position is constantly stabilized, the operability can be improved, and the fusing accuracy can be increased. Further, with the bobbin 10 of the present embodiment, because the provisional locking portion is provided at the outer surface of the flange 11 and the provisional locking portion 21 can lock the covered wire end 19 of the primary winding 13, unwinding of the primary winding 13 can be prevented, and the primary winding 13 can be disposed in a position which does not hinder fusing, by locking the covered wire end 19 in a raised condition. Further, because the locking portions 22, 23 for fixing the connection terminals 24, 25 are provided at the bobbin 10, and the locking portions 22, 23 protrude from the peripheral edge of the flange 11, the insertion of the connection terminal 24, 25 into the circuit pattern during connection to the circuit pattern of the printed substrate 2 can be facilitated and mounting of the transformer 6 can be conducted in an easy manner. Further, the present invention is not limited to the above-described embodiment, and appropriate modifications and changes can be made without departing from the essence of the present invention. Further, materials, shapes, dimensions, and forms of the constituent elements can be set arbitrarily and no limitation is placed thereon. Industrial Applicability With the method for treating the end portion of the coil in accordance with the present invention, when the coil and the connection terminal are connected during the manufacture of a transformer, the electrodes for fusing are disposed in a position separated from the outer surface of the flange, thereby providing for sufficient operation area. Therefore, fusing can be advantageously conducted without causing buckling or deformation caused by miniaturization or width reduction of the electrodes. Therefore, the coil and connection terminal can be mechanically and electrically connected by fusing by using a wire material with increased heat resistance for the coil, and using the wire material with increased heat resistance makes it possible to miniaturize the transformer. Further, with the bobbin in accordance with the present invention, the provisional locking portion and locking portion are installed by using the outer surface of the flange and the provisional locking portion holds the distal end portion of the coil wound around the bobbin in a raised condition with respect to the outer surface of the flange. Therefore, the coil can be prevented from unwinding from the bobbin and the fusing position can be stabilized thereby providing for effective fusing. Further, because the locking portion fixedly disposes the connection terminal installed at the distal end of the coil along the outer surface of the flange, the insertion of the connection terminal into the circuit pattern is facilitated, and mounting of the transformer on the printed substrate can be conducted in an easy manner.

Claims

1. A method for treating an end portion of a coil which is wound around a bobbin having a flange and is lead out through said flange to the outer surface of said bobbin, the method comprising the steps of: locking a covered wire end of said coil in a raised condition with respect to the outer surface of said flange; and fusing said covered wire end with electrodes disposed at a distance from the outer surface of said flange.

2. The method for treating an end portion of a coil according to claim 1, wherein at least the covered wire end of last turn of said coil is locked with a provisional locking portion in a raised condition with respect to the outer surface of said flange.

3. A bobbin comprising: a flange; a coil wound around said bobbin; and a provisional locking portion provided at an outer surface of said flange for locking a covered wire end of said coil that was lead out through said flange to -the outer surface of said flange in a raised condition with respect to the outer surface of said flange.

4. The bobbin according to claim 3, wherein a locking portion for fixing a terminal which is connected by fusing the covered wire end of said coil is further provided at the outer surface of said flange.