Patent Application
20070122293
1. Field of the Invention
The present invention generally relates to a motor equipped with a coil, more particularly, relates to a heat dissipating structure of the motor to dissipate heat generated by the armature.
2. Description of the Related Art
With numerous fans and drive motors for heat dissipation, disk drives, and like applications being installed in electronic devices, high speed motor operation is being demanded, in part because the demand for high speed data transfer and high heat dissipating capacity is increasing. A motor which rotates at a high speed is one answer to this need. In such a motor, however, a large electric current flows into a coil of an armature of the motor, and the coil generates considerable heat. The heat may substantially compromise reliability and endurance of the motor since a copper wire used for the coil has a temperature limit and the generated heat influences bearing life.
A motor having a heat dissipating structure is one answer to the demand for high-speed motor operation. One example of such a structure for an axial fan is to provide outside air into an impeller cup which accommodates a coil via a through hole on an upper surface of the impeller cup. In this structure, however, air which flows into the impeller cup via the through hole is limited. With such limited air flow, only limited heat will be dissipated from the coil of the motor.
In order to overcome the problems described above, preferred embodiments of the present invention provide a motor having a structure that dissipates heat generated by an armature (e.g., a coil of the armature) of the motor in an effective manner.
According to a preferred embodiment of the present invention, an electric motor used for a fan includes a shaft, a stator core having a plurality of teeth, a coil having a looped wire at each of the teeth, a circuit board arranged axially below the stator core, a heat dissipating layer arranged on an axially upper surface of the circuit board extending along the upper surface of the circuit board, and a thermal conductive member arranged between the coil and the heat dissipating layer so as to be in contact with both. By virtue of this configuration, heat generated by the coil is diffused to the heat dissipating layer via the thermal conductive member and is dissipated from the heat dissipating layer.
According to another preferred embodiment of the present invention, the circuit board includes a protruding portion arranged radially outside an impeller cup of the motor. According to yet another preferred embodiment of the present invention, at least a portion of the heat dissipating layer is arranged on the protruding portion. In case that the motor according to a preferred embodiment of the present invention is used for a fan, the heat may be actively dissipated from the heat dissipating layer arranged radially outside the impeller cup by air flowing thereto.
Other features, elements, steps, processes, characteristics and advantages of the present invention will become more apparent from the following detailed description of preferred embodiments of the present invention with reference to the attached drawings.
Referring to FIGS. 1 to 10, a motor according to preferred embodiments of the present invention will be described in detail. It should be understood that in the following description, when positional relationships among and orientations of the different components are described as being such as top/bottom, up/down or left/right, positional relationships and orientations that are in the drawings are indicated, and positional relationships among and orientations of the components once having been assembled into an actual device are not indicated. Meanwhile, in the following description, an axial direction indicates a direction parallel to a rotation axis, and a radial direction indicates a direction perpendicular to the rotation axis.
Referring to
The fan 10 includes a frame 12 having a bearing housing 121 at a middle portion thereof. The bearing housing 121 has a substantially cylindrical shape with a base connected to the frame 12. A radial bearing 34 is press-fitted and supported within the bearing housing 121. The radial bearing 34 includes a through hole extending in the axial direction at a middle portion thereof, and the shaft 32 is inserted into the through hole. In the present preferred embodiment of the present invention, the radial bearing 34 is an oil-impregnated bearing made of porous material (e.g., a sintered material impregnated with lubricating oil). It should be noted, however, a roller bearing (e.g., a ball bearing) or the like may be used instead of the radial bearing 34.
Four ribs 13 are arranged in a circumferentially equally spaced manner. Each of the four ribs 13 extends radially between the frame 12 and a housing 1. However, the fan 10 may include any suitable number of ribs 13.
The housing 1 radially surrounds the impeller 21 and defines an air-flow passage 11 through which air flow generated by the rotation of the impeller 2 passes. The housing 1 has a substantially square shape on its upper and lower end portions, and has a substantially circular shape at its middle portion, whose diameter is substantially the same as a length of a side of the square. Therefore, each of the upper and bottom ends of the housing 1 includes flange portions 14 protruding radially outwardly at four corners of each of the upper and lower end of the housing 1. Each of the flange portions 14 includes a mounting hole 141 for mounting the fan 10 on an electronic device. For example, a screw or the like may be inserted into the mounting hole 141 and tightened so as to mount the fan on the electronic device.
A rotor yoke 31 is arranged on a radially inner circumferential surface of the impeller cup 20 to reduce leakage of magnetic flux to outside of the fan 10. A rotor magnet 33, of which a radially inside portion is multipolar-magnetized, is arranged on a radially inner side of the rotor yoke 31. The impeller cup 20, the impeller 2, the rotor yoke 31, and the rotor magnet 33 define a cup portion 22.
A stationary part 3 is arranged radially outside of the bearing housing 121. The stationary part 3 includes a stator core 35, coils 37, an insulator 36, a circuit board 38, and a thermal conductive member 39. The stator core 35 includes a plurality of teeth, and radially-inward-tip ends of the teeth radially face the rotor magnet 33 with a gap maintained therebetween. The teeth and both axial side surfaces of the stator core 35 are covered by the insulator 36. A looped wire is provided on each of the teeth so as to form a coil 37 thereon. A circuit board 38 supplying an electric current to the coil 37 to control rotation of the impeller 2 is arranged at a bottom end portion of the stationary part 3 (i.e., on the insulator 36 at a bottom end portion of the stator core 35). Electronic components and circuit patterns (not shown in
Upon providing electricity from an external power source to the coil 37 via electronic components (e.g., an IC and a Hall element arranged on the circuit board 38), a magnetic field is generated around the stator core 35. The magnetic field interacts with another magnetic field generated by the rotor magnet 33, and torque which rotates the impeller 2 centered about the shaft is generated. The magnetic field changes slightly based on the rotation of the rotor magnet, and the Hall element detects the change in the magnetic field. Based on the signal from the Hall element, the IC switches the output voltage such that the impeller 2 rotates stably. Upon rotation of the impeller 2, the fan 10 takes air from an upper end opening of the air-flow passage 11 and discharges air from a bottom end opening thereof.
Referring to
As shown in
The heat dissipating layer 381 is circumferentially divided into a number of areas, each of which corresponds to a coil 37 arranged on each of the teeth. The coil 37 and the heat dissipating layer 381 are arranged so as to axially face each other with the thermal conductive member 39 arranged axially therebetween. The thermal conductive member 39 is in contact with the coil 37 and the heat dissipating layer 381 such that heat generated by the coil 37 is diffused to the heat dissipating layer 381. For the purpose of heat diffusion, it is advantageous that the thermal conductive member 39 has a wide contacting area with the coil 37 and the heat dissipating layer 381. In the present preferred embodiment, the thermal conductive member 39 includes a gelled material such as a thermal-conductive silicone resin, including silicone oil as a base oil and a high thermal conductive material (i.e., alumina). The thermal-conductive silicone resin is deformed along shapes of the coil 37 and the heat dissipating layer 381. By virtue of this configuration, the thermal conductive member 39 may have a wide contacting area with both the coil 37 and the heat dissipating layer 381.
It should be noted, however, that the thermal conductive member 39 may be other than a gelled material. Taking workability into account, the thermal conductive member 39 may be a tape-like member (e.g., a thermal tape formed by applying pressure-sensitive adhesives with a filler on a supporting substrate such as polyimide film, fiberglass mat, aluminum foil, etc.). The thermal conductive member 39 may include any material having high thermal conductivity. However, it should be noted that the coil 37 and the heat dissipating layer 381 should be electrically isolated to prevent short circuiting the coil 37. In the present preferred embodiment, even in case that the coil 37 and the heat dissipating layer 381 are electrically connected, short circuiting of the coils does not occur since the heat dissipating layer 381 is circumferentially divided.
As shown in
The coil 37 generates heat in accordance with the electric resistance thereof and an amount of the electricity provided thereto. In the present preferred embodiment, the heat generated by the coil 37 is diffused to the heat dissipating layer 381 via the thermal conductive member 39. The greater an area from which the heat is dissipated from the heat dissipating layer 381, the greater the heat will automatically dissipate into the air. In addition, the air flow generated by the impeller 2 is provided to the heat dissipating layer 381 such that the heat diffused to the heat dissipating layer 381 is actively dissipated. Therefore, it is possible to provide more electricity to the motor to rotate the motor at a greater speed compared to a conventional motor.
Referring to FIGS. 6 to 10, a second preferred embodiment of the present invention will be described in detail. In the description that follows, similar configurations described in the first preferred embodiment are labeled with the same reference numerals in the explanation that follows. In the second preferred embodiment of the present invention, the motor is used for a fan.
A fan 100 includes an impeller 2a having a plurality of impeller blades 21a. The impeller 2a is rotatably driven when electricity is supplied to the fan 100. As shown in
The fan 100 includes a frame 12 having a bearing housing 121 at a middle portion thereof. The bearing housing 121 has a substantially cylindrical shape with a base connected to the frame 12. A radial bearing 34 is press-fitted and supported within the bearing housing 121. The radial bearing 34 includes a through hole extending in the axial direction at a middle portion thereof, and the shaft 32 is inserted into the through hole. In the present preferred embodiment, the radial bearing 34 is an oil-impregnated bearing made of porous material (e.g., a sintered material impregnated with lubricating oil). It should be noted, however, a roller bearing (e.g., a ball bearing) or the like may be used instead of the radial bearing 34.
As shown in
A rotor yoke 31 is arranged on a radially inner circumferential surface of the impeller cup 20a to reduce leakage of magnetic flux to the outside of the fan 100. A rotor magnet 33, of which a radially inside portion is multipolar-magnetized, is arranged on a radially inner side of the rotor yoke 31. The impeller cup 20a, the impeller 2a, the rotor yoke 31, and the rotor magnet 33 define a cup portion 22.
A stationary part 3 is arranged radially outside of the bearing housing 121. The stationary part 3 includes a stator core 35, coils 37, an insulator 36, a circuit board 38, and a thermal conductive member 39. The stator core 35 includes a plurality of teeth, and radially-inward-tip ends of the teeth radially face the rotor magnet 33 with a gap maintained therebetween. The teeth and both axial side surfaces of the stator core 35 are covered by the insulator 36. A looped wire is provided on each of the teeth so as to form a coil 37 thereon. A circuit board 38 supplying an electric current to the coil 37 to control rotation of the impeller 2a is arranged at a bottom end portion of the stationary part 3 (a bottom end portion of the stator core 35 (i.e., insulator 36)). Electronic components and circuit patterns (not shown in
Upon providing electricity from an external power source to the coil 37 via electronic components (e.g., an IC and a Hall element arranged on the circuit board 38), a magnetic field is generated around the stator core 35. The magnetic field interacts with another magnetic field generated by the rotor magnet 33, and torque which rotates the impeller 2a centered about the shaft is generated. The magnetic field changes slightly based on the rotation of the rotor magnet, and the Hall element detects the change in the magnetic field. Based on the signal from the Hall element, the IC switches an output voltage such that the impeller 2a rotates stably. Upon rotation of the impeller 2a, the fan 100 takes air from an air inlet 41 and discharges air from the air-outlet 42 via the air-flow passage 43.
As previously described with respect to
The heat dissipating layer 381 is circumferentially divided into a number of areas each of which corresponds to a coil 37 arranged on each of the teeth. The coil 37 and the heat dissipating layer 381 are arranged so as to axially face each other with the thermal conductive member 39 arranged axially therebetween. The thermal conductive member 39 is in contact with the coil 37 and the heat dissipating layer 381 such that heat generated by the coil 37 is diffused to the heat dissipating layer 381. For the purpose of heat diffusion, it is advantageous that the thermal conductive member 39 has a wide contacting area with the coil 37 and the heat dissipating layer 381. In the present preferred embodiment, the thermal conductive member 39 includes a gelled material such as a thermal-conductive silicone resin, including silicone oil as a base oil and a high thermally conductive material (i.e., alumina). The thermal-conductive silicone is deformed along the shapes of the coil 37 and the heat dissipating layer 381. By virtue of this configuration, the thermal conductive member 39 may have a wide contacting area with both the coil 37 and the heat dissipating layer 381.
It should be noted, however, that the thermal conductive member 39 may be a material other than a gelled material. Taking workability into account, the thermal conductive member 39 may be a tape-like member (e.g., a thermal tape formed by applying pressure-sensitive adhesives with a filler on a supporting substrate such as polyimide film, fiberglass mat, and aluminum foil, etc.). The thermal conductive member 39 may include any material having a high thermal conductivity. However, it should be noted that the coil 37 and the heat dissipating layer 381 should be electrically isolated to preventing short circuiting the coil 37. In the present preferred embodiment, even in case that the coil 37 and the heat dissipating layer 381 are electrically connected, short circuiting of the coils does not occur since the heat dissipating layer 381 is circumferentially divided.
As shown in
The coil 37 generates heat in accordance with the electric resistance thereof and an amount of the electricity provided thereto. In the present preferred embodiment, the heat generated by the coil 37 is diffused to the heat dissipating layer 381 via the thermal conductive member 39. The greater an area from which the heat is dissipated from the heat dissipating layer 381, the greater the heat will automatically dissipate into the air. In addition, the air flow generated by the impeller 2a is provided to the heat dissipating layer 381 such that the heat diffused to the heat dissipating layer 381 is actively dissipated. Therefore, it is possible to provide more electricity to the motor to rotate the motor at a greater speed compared to a conventional motor.
In the description of the first and second preferred embodiments, the brushless DC motor preferably includes a plurality of blades such that the brushless DC motor is used for a fan. It should be noted, however, the scope of the present invention is not limited to a fan. A brushless DC motor having a structure in which heat generated by the coil 37 is diffused to the heat dissipating layer 381 via the thermal conductive member 39 may be used for other devices than a fan (e.g., a brushless DC motor used as a disk driving motor and the like).
In the description of the first and second preferred embodiments, the brushless DC motor is preferably an inner-rotor type motor. It should be noted, however, the present invention is applicable to an outer-rotor type brushless DC motor (i.e., a brushless DC motor in which a rotor magnet is arranged axially outward of the stator core 35 with a gap maintained therebetween).
While the present invention has been described with respect to preferred embodiments, it will be apparent to those skilled in the art that the disclosed invention may be modified in numerous ways and may assume many embodiments other than those specifically set out and described above. Accordingly, it is intended by the appended claims to cover all modifications of the present invention which fall within the true spirit and scope of the invention.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2005-344744 | Nov 2005 | JP | national |
