DC fan motor and method of manufacturing same

[0002] The present invention relates to a DC fan motor that forces cold air to circulate inside of a freezer or a refrigerator as well as other DC fan motors for a ventilating fan or the like, and particularly to a downsized DC fan motor having a DC power source, and a method of manufacturing the same.

[0003] Freezing equipment, such as a refrigerator, is high power consuming equipment for household use; therefore, its power savings is desired. In freezing equipment, the compressor has the highest power consumption. The fan motor that forces cold air to circulate inside of the freezing equipment increases the workload of the compressor, which lowers the temperature inside of the freezing equipment, because the fan motor itself generates heat. For this reason, power savings of a fan motor is important for power savings of freezing equipment.

[0004] Prior Art 1

[0005] A shaded-pole AC fan motor 1 shown in FIG. 13 has conventionally been used as a fan motor for freezing equipment because of the following advantages: the motor can directly operate on an AC power source, has a small number of components, and is inexpensive. This AC fan motor 1 has a high power consumption of 9 to 10 W, a power loss of approximately 90% and generates heat at a temperature of approximately 40° C. Moreover, having a thickness of approximately 48 mm, this AC fan motor is relatively large.

[0006] Prior Art 2

[0007] A DC fan motor 2 shown in FIG. 15 has conventionally been used as a fan motor for freezing equipment instead of AC fan motor 1 because motor 2 has an advantage of requiring a low power consumption. An AC-DC conversion power source 3 is attached to the outside of DC fan motor 2 in order to supply DC power to DC fan motor 2. When motor driving power is obtained by AC-DC conversion power supply 3, voltages are stepped down via a resistor or transformer and thus a power loss is produced. In addition, motor 2 requires a lead connecting DC fan motor 2 and AC-DC conversion power source 3 and this causes the motor to have a more complicated structure and a larger size.

[0008] It is an object of the present invention to provide a DC fan motor for freezing equipment or a ventilating fan that has a compact structure as a whole and a small power loss and to provide a method of manufacturing the same.

[0009] A DC fan motor in accordance with the present invention has a stator including a stator core, and a rotor placed in the stator core. The stator has the following components: a printed circuit board; the stator core having stator coils; an AC power source connector; a rectifier circuit that rectifies input AC power to obtain high DC voltage; a step-down circuit that obtains DC low voltage from the DC high voltage; a heat shock absorber fixedly attached to the printed circuit board; and a control circuit that controls the stator coils. These components are molded into one body to form a stator using a molding material. The DC high voltage from the rectifier circuit is supplied to the stator coils as a driving power source and the DC low voltage from the step-down circuit is supplied to the control circuit as a control power source. The present invention thus provides a compact DC fan motor for freezing equipment or the like with small power loss and low power consumption and that has a rectifier circuit and a control circuit integrated therein.

[0010] FIG. 1 is a perspective view of a DC fan motor in accordance with a first exemplary embodiment of the present invention.

[0011] FIG. 2 is a partially sectional side view of the same DC fan motor.

[0012] FIG. 3 is a schematic electrical connection diagram of the same DC fan motor.

[0013] FIG. 4 is a perspective view of a rotor of the same DC fan motor.

[0014] FIG. 5 is a perspective view of a stator core of the same DC fan motor.

[0015] FIG. 6 is a perspective view of a stator coil of the same DC fan motor.

[0016] FIG. 7 is a perspective view of an end of the wound stator coil.

[0017] FIG. 8 is a perspective view of an AC power source connector of the same DC fan motor.

[0018] FIG. 9 is a perspective view of wiring of a printed circuit board of the same DC fan motor.

[0019] FIG. 10 is a detailed circuit diagram of the same DC fan motor.

[0020] FIG. 11 is a cross sectional view of a mold having an upper part and a lower part that is used for molding a stator of the same DC fan motor.

[0021] FIG. 12 illustrates a bearing frame having an oil impregnated bearing of the same DC fan motor.

[0022] FIG. 13 is a perspective view of a conventional AC fan motor.

[0023] FIG. 14 is an electrical connection diagram of a refrigerator using a conventional DC fan motor.

[0024] FIG. 15 is a perspective view of a conventional DC fan motor.

[0025] Embodiment 1

[0026] FIG. 1 is a perspective view of a DC fan motor in accordance with a first exemplary embodiment of the present invention, and FIG. 2 is a partially sectional side view of the same DC fan motor. As shown in FIGS. 1 and 2, a stator core 8 having stator coils 7 is attached to a printed circuit board 6. Printed circuit board 6 has the following components in a space outside of stator core 8: a rectifier circuit 16 comprising diodes 10, a smoothing capacitor 11, and other circuit elements; a step-down circuit 15; and a control circuit 18 comprising a magnetic pole detecting element 12, a driver element 13, and other circuit elements. Printed circuit board 6 also has, at the edge thereof, an AC power source connector 14 attached thereto. FIG. 3 is a schematic electrical connection diagram of the DC fan motor in accordance with this embodiment. AC power supplied from an AC power source 22 via AC power source connector 14 is converted into DC high voltage by rectifier circuit 16 comprising diodes 10 and smoothing capacitor 11. Step-down circuit 15 steps down the DC high voltage to DC low voltage. Printed circuit board 6 has wiring 17 for supplying the DC high voltage from rectifier circuit 16 directly to stator coils 7 as a driving power source and wiring 19 for supplying the DC low voltage from the step-down circuit to control circuit 18 as a control power source. Printed circuit board 6, stator core 8, AC power source connector 14, step-down circuit 15, rectifier circuit 16, and control circuit 18 are molded into one body using molding material 20, such as unsaturated polyester. A Rotor 9 is placed in a hollow space formed by stator core 8, and is rotatably held by bearings placed at both ends of the hollow space to construct the DC fan motor in accordance with this embodiment. Bearing frames 21 are directly press-fitted into the ends of the hollow space with a press-fit force of 50 to 200 Kgf. More specifically, as shown in FIG. 4, rotor 9 is made of a plastic magnet material formed into a cylindrical shape and has a plurality of N and S magnetic poles along the outer circumference thereof Stator core 8 is made of a ring-like core 8cand T-shaped poles 8a, as shown in FIG. 5. Stator core 8 is assembled in the following steps: mounting stator coils 7 onto poles 8a; placing poles 8ainside of ring-like core 8c; temporarily press-fitting the proximal ends of poles 8ainto connecting recesses 8bprovided in ring-like core 8cfor distortion prevention, and connecting them by firmly press-fitting. As stator coils 7 shown in FIG. 6, fine electric wire 7a(0.08 mm in diameter in this embodiment) made of copper is used because a DC high voltage (DC 141 V obtained by rectification of a commercial power source of AC 100V in this embodiment) is applied to the wire. Electric wire 7ais wound around a coil bobbin 7bmade of polyamide resin. An end 7d of the wire is wound around a terminal pin 7cattached to coil bobbin 7b, and soldered to the pin 7c. In this manner, stator coils 7 are constructed. Since stator coils 7 can be wound separately prior to the assembly of stator core 8, the winding operation is easy. Therefore, even when the electric wire of stator coils 7 is very fine, breaks in the wire made during the winding operation can be reduced. Moreover, since terminal pins 7calso serve as the legs for mounting stator core 8 onto printed circuit board 6, no other mounting members are required. This simplifies the mounting structure. As shown in FIG. 7, end 7dof the winding of stator coil 7 is folded and bundled a plurality of times, twisted three to five times, wound around terminal pin 7c, and soldered thereto for connection.

[0027] Therefore, even with stator coil 7 of a very fine wire, breaks in the wire made when end 7dof the winding is wound around terminal pin 7cfor connection are prevented because end 7dof the winding is reinforced. As shown in FIG. 8, AC power source connector 14 has two or three annular grooves 14balong the outer periphery of an electrically insulating shell 14afor housing terminals therein. These annular grooves 14bmake the insulating distance along the face longer and thus improve the insulating characteristics of AC power source connector 14. Annular grooves 14balso stabilize AC power source connector 14 onto printed circuit board 6 because molding material 20 enters into annular grooves 14b. As shown in FIG. 9, on printed circuit board 6, a heat shock absorber 6a, such as a quick-dry silicon bond is attached to a soldered connection of an arbitrary component, for example, an FET element, for the purpose of improved workability. The heat shock absorber can prevent an expansion and breaking of a soldered connection between each component and printed circuit board 6, which are caused by the heat applied during molding, and thus stabilizes the connection.

[0028] Next, the electrical circuit of the DC fan motor of this embodiment is detailed with reference to FIG. 10. As shown in FIG. 10, rectifier circuit 16 performs full-wave rectification of AC 100 V using a plurality of diodes 10 to obtain a DC high voltage of 141 V, smoothes the voltage using smoothing capacitor 11, and supplies the DC high voltage directly to stator coils 7. Control circuit 18 has the following components: hall element 23 for detecting a magnetic pole of the rotor; comparator 24 for comparing the output of hall element 23; digital transistor 25 incorporating a resistor that inverts the output of comparator 24; controlling transistor 26 that is inserted into the energization circuit of stator coils 7 and has a control gate for receiving the output of comparator 24; and controlling transistor 27 that has a control gate for receiving the output of digital transistor 25. Step-down circuit 15 steps down the voltage using capacitor 36 and voltage-dividing circuit 28 and feeds the obtained DC low voltage of half-wave rectification to control circuit 18 as a control power source. As illustrated in FIG. 10, reference numeral 29 shows a varistor and reference numeral 30 shows a Zener diode. With this structure, DC high voltage is supplied to stator coils 7, stator coils 7 are controlled by control circuit 18, and the DC fan motor rotates as desired. Generally, DC fan motors consume less power than AC fan motors. In addition, supplying DC high voltage from rectifier circuit 16 directly to stator coils 7 can provide a DC fan motor having smaller power loss and lower power consumption. Control voltage is supplied to control circuit 18. However, since the control voltage is low and the power consumption of the transistors is low, their effects on the power consumption of the entire DC fan motor are extremely small. Consequently, the DC fan motor of this embodiment has an extremely low power consumption, i.e. approximately ¼ of that of a conventional AC fan motor. In addition, since printed circuit board 6, which has stator core 8, step-down circuit 15, rectifier circuit 16, and control circuit attached thereto, is not placed outside of the motor as external circuitry but is integrated with the motor in one body, the DC fan motor can be constructed compactly with an entire thickness of approximately 35 mm.

[0029] Embodiment 2

[0030] FIG. 11 is a cross sectional view of a mold having upper part 31 and lower part 32 that are used for molding a stator of a DC fan motor in accordance with the present invention. The DC fan motor of the present invention is manufactured in the following steps: a) mounting stator core 8, AC power source connector 14, step-down circuit 15, rectifier circuit 16, and control circuit 18 onto printed circuit board 6 as shown in FIG. 2, and connecting circuits so that DC high voltage obtained by rectifying AC power source using rectifier circuit 16 is supplied to stator coils 7 as a driving power source and DC low voltage stepped down from the DC high voltage is supplied to control circuit 18 as a control power source; b) molding the above-mentioned printed circuit board 6, stator core 8, AC power source connector 14, rectifier circuit 16, and control circuit 18 into one body using molding material 20 where the mold has an upper part 31 and a lower part 32 to construct a stator of the DC fan motor; and c) inserting rotor 9 into stator core 8, press-fitting bearing frames 21 into the molded stator and assembling these components so that bearings in bearing frames 21 rotatably hold the rotor 9. During this molding step, the molding pressure is approximately 60 kg/cm²and the heating temperature is 120° C. The molding pressure may cause a warp or distortion to thin printed circuit board 6 placed in the mold and thus a connection between each component and the wiring network on printed circuit board 6 may come off or deteriorate. In this embodiment, either upper part 31 or lower part 32 of the mold has a plurality of pins 33 projected so that the tips of the pins are in proximity to one side of printed circuit board 6 to be molded. Therefore, pins 33 prevent warps or distortions of printed circuit board 6 caused by the molding pressure, and the connection between each component and the wiring network on printed circuit board 6 will not come off or deteriorate.

[0031] Although the DC fan motor in accordance with each of these embodiments is for freezing equipment, this DC fan motor can be also used for a relatively small ventilating fan. In addition, this motor can be used as a DC fan motor for cooling electronic devices, such as a personal computer. The bearings inside of bearing frames 21 used in each of the above embodiments can be an oil impregnated bearing as shown in FIG. 12. With the bearing shown in FIG. 12, a molded resin pipe 35 and a frame cover recover the oil from an oil-impregnated felt 34 so that the oil does not leak outside.