Relevant subject matter is disclosed in copending U.S. patent application filed on the same date and having a same title with the present application, and copending U.S. patent application filed on the same date and having a title “ferromagnetic powder for dust core”, both of which are assigned to the same assignee with the present application.
The present invention relates generally to motors, and more particularly to a motor stator for use in a brushless motor, such as a fan motor.
It is well known that rotary motors are widely used to drive devices such as cooling fans, hard disc drives, etc. A rotary motor includes therein two important components—stator and rotor. The rotor rotates relative to the stator due to a magnetic interaction between them. For example, in a computer system, a fan motor is used to drive an impeller of a cooling fan so as to produce airflows flowing towards a heat generating electronic component such as a central processing unit (CPU) whereby the CPU is cooled. The impeller is affiliated to the rotor of the fan motor and moves continuously to generate the airflows due to rotation of the rotor.
Therefore, it is desirable to provide a motor stator wherein one or more of the foregoing disadvantages may be overcome or at least alleviated.
The present invention relates to a motor stator for use in a brushless motor such as a fan motor. The motor stator includes a hollow cylinder, a stator winding and upper and lower magnetic pole plates. The stator winding is axially wound around the hollow cylinder along an axial direction of the hollow cylinder. The upper and lower magnetic pole plates are disposed at opposite sides of the stator winding. At least one of the upper and lower magnetic pole plates has a plurality of projecting fins extending from a periphery thereof. The upper and lower magnetic pole plates are made from a ferromagnetic powder with a plurality of particles each having a core-shell structure with a central core and an outer shell coated on the central core. The central core is made of a magnetic material and is used for providing magnetic property for the upper and lower magnetic pole plates. The outer shell has a higher electrical resistance than the central core and is used for increasing insulation and enhancing interconnection between the particles of the ferromagnetic powder.
Other advantages and novel features of the present invention will become more apparent from the following detailed description of preferred embodiment when taken in conjunction with the accompanying drawings, in which:
With reference also to
The illustrated motor stator 10 can be suitably used as a stator for a brushless motor, such as a fan motor, thereby substituting for the conventional stator prepared from laminated silicon steel sheets. The upper and lower magnetic pole plates 12, 18 and the hollow cylinder 19, with cooperation of the stator winding 16, generate a magnetic field for rotating a rotor which is rotatably mounted to the motor stator 10. The hollow cylinder 19 operates to receive shaft, ball bearings or sleeve bearings, or other necessary accessories of the formed brushless motor of which the motor stator 10 is a part. The projecting fins 122, 182 formed on the upper and lower magnetic pole plates 12, 18, alternated with each other and provided with slanted edges at free sides thereof, are used to effectively guide rotation of the rotor.
In order to electrically insulate the stator winding 16 from the upper and lower magnetic pole plates 12, 18 and the hollow cylinder 19, an outer surface of each of these components 12, 18, 19 may be coated with a layer of electrical insulating material, in which case the stator winding 16 may be directly wound on an outer circumference of the hollow cylinder 19 and the insulating member 14 can be omitted, thereby simplifying the structure of the motor stator 10.
According to the first embodiment, the upper and lower magnetic pole plates 12, 18 each have a plurality of projecting fins formed thereon. Alternatively, the projecting fins may be formed at only one of the upper and lower magnetic pole plates 12, 18, and the other magnetic pole plate 12 or 18 is not provided with projecting fins.
In order to electrically insulate the stator winding 26 from the upper and lower magnetic pole plates 22, 28 and the hollow cylinders 224, 284, an outer surface of each of these components 22, 28, 224, 284 may be coated with a layer of electrical insulating material, in which case the stator winding 26 may be directly wound on outer circumferences of the hollow cylinders 224, 284 and the insulating member 24 can be omitted, thereby simplifying the structure of the motor stator 20.
According to the second embodiment, the upper and lower magnetic pole plates 22, 28 each have a plurality of projecting fins formed thereon. Alternatively, the projecting fins can be provided at only one of the upper and lower magnetic pole plates 22, 28, and the other magnetic pole plates 22 or 28 is not provided with projecting fins.
With reference to
In order to electrically insulate the stator winding 36 from the upper and lower magnetic pole plates 32, 38 and the hollow cylinder 39, an outer surface of each of these components 32, 38, 39 may be coated with a layer of electrical insulating material, in which case the stator winding 36 may be directly wound on an outer circumference of the hollow cylinder 39 and the insulating member 34 can be omitted, thereby simplifying the structure of the motor stator 30.
According to the third embodiment, the upper and lower magnetic pole plates 32, 38 each have a plurality of projecting fins formed thereon. Alternatively, the projecting fins can be provided at only one of the upper and lower magnetic pole plates 32, 38, and the other magnetic pole plates 32 or 38 is not provided with projecting fins.
In order to electrically insulate the stator winding 46 from the upper and lower magnetic pole plates 42, 48 and the hollow cylinders 424, 484, an outer surface of each of these components 42, 48, 424, 484 may be coated with a layer of electrical insulating material, in which case the stator winding 46 may be directly wound on outer circumferences of the hollow cylinders 424, 484 and the insulating member 44 can be omitted, thereby simplifying the structure of the motor stator 40.
According to the fourth embodiment, the upper and lower magnetic pole plates 42, 48 each have a plurality of projecting fins formed thereon. Alternatively, the projecting fins may be provided at only one of the upper and lower magnetic pole plates 42, 48, and the other magnetic pole plates 42 or 48 is not provided with projecting fins.
Each of the above-mentioned magnetic pole plates 12, 18, 22, 28, 32, 38, 42 and 48 is integrally made from ferromagnetic powder by, for example, powder metallurgy technique, wherein the powder metallurgy technique is a process of making parts by pressing powdered particles in die presses.
The magnetic material used for the central core 52 is typically selected from a soft magnetic material of high magnetic permeability and low magnetic loss, such as soft magnetic metals, amorphous iron-based magnetic powder, pure iron powder, iron-based powder compositions, soft magnetic non-metals and the like. For example, magnetic powder such as iron, sendust, ferrosilicon, permalloy, supermalloy, iron nitride, iron-aluminum alloys and iron-cobalt alloys may be suitable for the central core 52. Among these magnetic materials mentioned above, iron or iron-based powders having high saturation magnetization are preferred when the powders are used to prepare the stator core consisting of the upper magnetic pole plate 12 (22, 32, 42) and the lower magnetic pole pate 18 (28, 38, 48) as a substitute for the conventional stator core prepared from silicon steel laminations.
The outer shell 54 of the particle 50 is made from such materials as to enable the outer shell 54 to have an electrical resistance that is higher than that of the central core 52 for the purpose of reducing an eddy current loss associated with the stator core made from the ferromagnetic powder. In this embodiment, such materials include, without limitation, metal composites and piezoelectric materials.
As an example, the particle 50 of the core-shell structure is prepared by employing a diffusion/precipitation mechanism, based on powder sintering process. Specifically, the soft magnetic material for the central core 52 such as iron is melted firstly and the coating material as used to form the outer shell 54 is then added to the melted magnetic material to form a mixture. By using an atomizing or pulverization method, small powder is accordingly prepared from the mixture. Then the obtained powder is sintered at a temperature of about 300° C. to about 900° C. to cause the coating material contained in the powder to become supersaturated and accordingly precipitate out from the remaining magnetic material in the powder. As such, the precipitated coating material forms as the outer shell 54 for the particle 50 and the magnetic material forms as the central core 52 for the particle 50.
In another example, the central core 52 is previously obtained by, for example, an atomizing method from a soft magnetic material such as iron. A thin layer of film having a higher electrical resistance than the central core 52 is then deposited on the outer surface of the core 52, wherein the film operates as the outer shell 54. Such deposition method may be physical vapor deposition (PVD) or chemical vapor deposition (CVD). The material used for depositing of the film may be ferrites, piezoelectric materials, ferroelectric materials or ceramic materials.
As the ferromagnetic powder described above is used to produce the magnetic pole plates 12, 18, 22, 28, 32, 38, 42 and 48, the ferromagnetic powder is pressure molded at a high temperature, for example, in the range of 300 to 800 centigrade degrees. After the ferromagnetic powder is molded into a semi-finished product, the compact can be desirably annealed to release the strain induced during the pressure molding process to obtain a final product for the magnetic pole plates 12, 18, 22, 28, 32, 38, 42 and 48.
Alternatively, these magnetic pole plates 12, 18, 22, 28, 32, 38, 42 and 48 can be made from the ferromagnetic powder by metal injection molding. Specifically, the ferromagnetic powder is mixed with a binder such as wax-polymer binder and then is injected into a mold. After molding, the wax-polymer binder is removed, usually by heat, and then the structure is sintered in a manner similar to powder metallurgy.
The central core 52 and the magnetic layer 56 in the ferromagnetic powder provide the necessary magnetic property for the magnetic pole plates 12, 18, 22, 28, 32, 38, 42 and 48 made from the ferromagnetic powder, while the outer shell 54 or the binder 58 operates to improve a bonding strength between the particles 50 (50a, 50b) as the ferromagnetic powder is pressure molded into the magnetic pole plates 12, 18, 22, 28, 32, 38, 42 and 48. The outer shell 54 or the binder 58 permits adjacent ferromagnetic particles 50 (50a, 50b) to strongly bond together. The outer shell 54 and the binder 58 also enhance insulation between adjacent ferromagnetic particles 50 (50a, 50b), thereby decreasing the eddy current loss for the final products. Therefore, the motor stator 10 (20, 30 or 40) made from the above-illustrated ferromagnetic powder exhibits a high magnetic flux density, low eddy current loss, as well as high mechanical strength.
The motor stator 10 (20, 30 or 40) can be suitably used as a substitute for the conventional motor stator having a stator core made from laminated silicon steel sheets. In the conventional motor stator, the silicon steel sheets for the stator core are typically prepared by stamping silicon steel sheets, in which case the material yield is extremely low since waste material is unavoidable from the stamping operation. By using the powder metallurgy process or the metal injection molding process, the material yield is 100%, and it is possible to produce stator cores with relatively complex shapes.
It is to be understood, however, that even though numerous characteristics and advantages of the present invention have been set forth in the foregoing description, together with details of the structure and function of the invention, the disclosure is illustrative only, and changes may be made in detail, especially in matters of shape, size, and arrangement of parts within the principles of the invention to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
Number | Date | Country | Kind |
---|---|---|---|
200510035128.2 | Jun 2005 | CN | national |