Electrical fan

A electrical fan includes a frame (10) having a central tube (11), a bearing (30) received in the central tube, a stator (50) mounted around the central tube, and a rotor (70) being rotatably supported by a bearing in the stator. The frame defines an air inlet (19) and an air outlet (17) at two different sides thereof. The stator and the rotor expand radially along a direction from the air inlet to the air outlet. Fan blades (75) extend radially from the rotor. A hub (71) of the rotor has a streamline shaped outer surface. A stator core (511) of the stator is made by powder sintering technology.

CROSS-REFERENCES TO RELATED APPLICATION

This application is related to a co-pending application entitled “FERROMAGNETIC POWDER FOR DUST CORE”, invented by Chao-Nien Tung, Chuen-Shu Hou, Chih-Hao Yang and Lung-Wei Huang, assigned to the same assignee of this application and filed on Apr. 13, 2006 with Ser. No. 11/308,530. The disclosure of the co-pending application is wholly incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an electrical fan, and more particularly to a motor of such an electrical fan.

DESCRIPTION OF RELATED ART

With continuing development of the electronic technology, electronic packages such as CPUs (central processing units) are generating more and more heat that is required to be dissipated immediately. Electrical cooling fans are commonly used in combination with heat sinks for cooling the CPUs.

Referring toFIG. 8, a conventional electrical cooling fan includes a stator6, a rotor8rotatable with respect to the stator6, and a fan housing2receiving the rotor8and stator6therein. The stator6is approximately cylinder-shaped and typically includes a stator core62and stator coils64wound around the stator core62. The stator core62consists of layered yokes. Each yoke includes a ring shaped center portion and a plurality of pole members extending outwardly from the center portion for winding the coils thereon. To avoid the coils64from electrically contacting with the stator core62, upper and lower insulating frames66,68are used to cover the stator core62and electrically insulate the stator coils64from the stator core62. The rotor8includes an inverted U-shaped hub82surrounding the stator6. The hub82includes a flat, disc-shaped top wall81and a sidewall83extending downwardly from an outer-periphery of the top wall81. A plurality of fan blades86extends outwardly from the sidewall83, and a cylinder-shaped permanent magnet84adheres to an inner surface of the sidewall83of the hub82. A shaft88extends downwardly from a central portion of the top wall81into a bearing4mounted in the fan housing2. During operation of the cooling fan, an alternating magnetic field established by the stator6interacts with a magnetic field of the permanent magnet84to drive the rotor8to rotate, thereby generating an airflow by the fan blades86.

For enhancing the amount of airflow generated by the cooling fan, one way is to increase the size of the blades86. However, this way will increase the size of the cooling fan, which is disadvantageous in view of miniaturization requirement of electronic products. Another way is to reduce the diameter of the hub82. However, the yokes of the stator core62are formed by stamping silicon-steel sheets, each of which has a flat configuration and a predetermined diameter; thus, the size and the shape of the stator core62are almost fixed and difficult be altered. Due to the fixed size and shape of the stator6, the shape and size of the rotor8including the hub82are also almost fixed and difficult to be altered. For the conventionally-shaped hub82, a turbulent flow is produced in the area of an air inlet of the conventional electrical fan, which significantly affects the pressure and the speed of the airflow. Furthermore, the flat, disc-shaped top wall81of the hub82forms a barrier for the airflow through the fan, whereby flow rate of the airflow is adversely affected. Accordingly, the airflow provided by the conventional electrical fan cannot efficiently dissipate heat absorbed by a heat sink from a heat-generating electronic component away from the heat sink.

What is needed, therefore, is an electrical cooling fan having a relatively lager amount of airflow and a relatively smaller size.

SUMMARY OF INVENTION

According to a preferred embodiment of the present invention, an electrical fan comprises a fan housing having a central tube, a bearing received in the central tube, a stator mounted around the central tube, and a rotor being rotatably supported by the bearing in the central tube. The housing defines an air inlet and an air outlet at two different sides thereof. The stator and the rotor expand radially along a direction from the air inlet to the air outlet. The stator has a stator core which is made by powder sintering technology. The fan blades of the rotor have a larger size and thus can generate a larger amount of airflow. The hub of the rotor has a streamline shaped outer surface with the smallest diameter adjacent to the air inlet of the fan; the flowing resistance of the airflow is reduced and the turbulence flow and noise are generally avoided. Finally a larger amount of airflow with increased speed and pressure is generated, and the heat dissipating effectiveness of the electrical fan is improved.

Other advantages and novel features of the present invention will be drawn from the following detailed description of a preferred embodiment of the present invention with attached drawings, in which:

DETAILED DESCRIPTION

Referring toFIGS. 1 through 5, an electrical fan according to a first preferred embodiment of the present invention includes a rotor70, a stator50in respective to which the rotor70is rotatable, a frame10receiving the rotor70and the stator50therein, and a bearing30mounted in the frame10for supporting the rotor70to rotate.

The frame10is approximately cylinder shaped. An air inlet19and air outlet17are defined at two opposite sides of the frame10. An airflow generated by the electrical cooling fan flows from the air inlet19to the air outlet17. The frame10includes a base13adjacent to the air outlet17. A central tube11extends upwardly from a central portion of the base13. The central tube11defines a through hole111receiving the bearing30therein. An axial hole31is defined in the bearing30. A sealing cap15couples to and seals a bottom end of the central tube11.

The stator50is mounted around the central tube11. The stator50includes a stator core511, axial windings55wound on a tube52of the stator core511to establish an alternating magnetic field, and a PCB (printed circuit board)57electrically connecting with the windings55. To avoid the windings55from electrically contacting with the stator core511, an insulating layer (not labeled) is used to cover the tube52of the stator core511and electrically insulate the windings55from the stator core511.

The stator core511includes a top wall51on a front end of the tube52and a sidewall53extending downwardly from an outer periphery of the top wall51. The sidewall53is arc-shaped with a diameter thereof gradually increased along a direction from the front end to a rear end of the tube52(better seen inFIG. 5). In other words, a distance between the sidewall53and the tube52is gradually increased along a direction from the air inlet19to the air outlet17. The sidewall53expands radially along the direction from the air inlet19to the air outlet17. The top wall51is flat and ring-shaped and defines a circular hole510in a central portion for extension of the central tube11of the frame10therethrough. The tube52of the stator core511extends downwardly from an outer edge of the circular hole510of the top wall51and defines a central hole520communicating with the circular hole510of the top wall51. A space is defined between the tube52and the sidewall53and expands radially along the flowing direction of the airflow. A plurality of slots530is defined in the sidewall53of the stator core511for the cooling fan to start smoothly.

The rotor70covers the stator50therein and has a profile generally conforming the profile of the stator core511. The rotor70includes an arc-shaped hub71forming a shaft seat72at a central portion, a shaft77received in the shaft seat72and extending downwardly thereof to be rotatably received in the bearing30, a plurality of fan blades75extending radially from an outer periphery of the hub71, and a permanent magnet73adhered to an inner wall of the hub71to establish a magnetic field. The hub71more specifically has a hemispherical shape. The permanent magnet73has a top wall731with a shape of a flat ring, confronting the top wall51of the stator core511. Furthermore, the permanent magnet73has an arc-shaped sidewall732confronting the sidewall53of the stator core511. The hub71has an outer diameter gradually increasing along the flowing direction of the airflow. The lower portion of the hub71adjacent to the air outlet17has a diameter relatively larger than that of the upper portion of the hub71adjacent to the air inlet19. The hub71converges to a point at the top end thereof. In other words, an outer surface of the hub71is approximately streamline shaped. Thus, the turbulent flow occurring at the inlet of the conventional electric fan can be avoided in the present invention and the flowing resistance of the airflow is reduced. The hub71occupies a space which is not larger than ⅔ of that of the hub82of the conventional electrical fan ofFIG. 8when the hub82has a diameter the same as that of the hub71measured at a bottom end thereof. Thus the blades75of the rotor70can have a relatively lager size than that of the blades86of the conventional electric fan ofFIG. 8when the electrical fan in accordance with the present invention and the conventional fan has the same size. Accordingly, the amount of airflow generated by the fan blades75is greatly increased.

When the cooling fan assembly is assembled together, the axial hole31of the bearing30receives the shaft77therein to support the rotor70to rotate. During operation, the axial windings55wound around the tube52establish the alternating magnetic field interacting with the magnetic field of the permanent magnet73of the rotor70to drive the rotor70to rotate. The rotating fan blades75of the rotor70generate airflow to dissipate heat of a heat source. For the larger size of the fan blades75, a relatively larger amount of airflow is generated by the electrical fan of the present invention. As the airflow flows through the electrical fan to the heat source, the flowing resistance is low for the streamline shaped outer surface of the hub71. Also the turbulent flow and noise are generally avoided. The speed and pressure of the airflow are increased. After leaving the air outlet17, the larger amount of airflow with increased speed and pressure blows onto the heat source and takes away the heat of the heat source effectively. Thus, the flow rate of the airflow and the heat dissipating effectiveness of the electrical cooling fan are improved.

FIG. 6illustrates an alternative embodiment of the present invention. Except for the stator650and rotor670, other parts of the cooling fan in accordance with this second embodiment have substantially the same configuration with the cooling fan of the previous first preferred embodiment. In this embodiment, the stator core of the stator650has a shape of a truncated cone. The hub671and the permanent magnet673of the rotor670each has a truncated-conical shape generally corresponding to that of the stator core. The volume of the truncated-cone shaped hub71is approximately ⅓ of that of the hub of the conventional electrical fan. Thus the fan blades675have a larger size and can generate an airflow with a higher flow rate.

Referring toFIG. 7, it illustrates a third embodiment of an electrical cooling fan in accordance with the present invention. In this embodiment, the hub771of the rotor770has a configuration of a hemi-ellipsoid. The stator750has a shape corresponding to the rotor770. In this design, the volume of the hub771can be further decreased, whilst the size of the fan blades775further increases. Also the fan blades775of the rotor770can generate a relatively larger amount of airflow.

Also the stator core and the hub can be formed in other shapes if each of which has a profile with a small diameter at the front end thereof adjacent to the air inlet19of the electrical fan and a large diameter at the rear end near the air outlet17of the electrical fan. Such design not only reduces the flowing resistance of the airflow, but also decreases the volume of the hub and finally improves the amount of airflow. To form the stator core of the present invention, which has a complex configuration than the conventional stator, the stator core is made by powder sintering technology wherein a particle of powder for forming the stator has a Core-Shell structure. Such a Core-shell structure of the powder can reduce the eddy current loss of the stator core. The Core-Shell structure of the powder has a core portion for generating magnetic force, and a shell portion for providing bond for interconnecting the core portions of the powder together. The electrical resistance of the shell portions is greater than that of the core portions. Details regarding the Core-Shell structure of the powder for forming the stator core of the present invention can be referred to the co-pending application entitled “FERROMAGNETIC POWDER FOR DUST CORE”. In the preferred embodiments as disclosed above, the stator core511is integrally formed. Alternatively, the tube52can be formed separately and then assembled to the other part of the stator core511.