Patent Application
20110070081
1. Technical Field
The present disclosure relates generally to cooling fans, and more particularly to an axial fan with a fan housing which can be easily fabricated.
2. Description of Related Art
Cooling fans are commonly used in combination with heat sinks for cooling electronic components, such as CPUs. Normally, the heat sink is arranged on the electronic component to absorb heat therefrom, while the cooling fan is arranged on the heat sink to produce forced airflow flowing through the heat sink to take away the heat.
Generally, the cooling fan includes a stator, a rotor rotatably supported by the stator, and a fan housing surrounding the rotor for guiding the forced airflow through the heat sink. The fan housing usually has a rectangular or annular profile. An inner surface of the fan housing facing the rotor is cylindrical, to avoid interference of the rotor and the fan housing during rotation of the rotor. The fan housing is usually made of plastic, by a process of injection molding. During the molding process, after the fan housing is molded in a mold, it is difficult to separate the fan housing from the mold because the inner surface of the fan housing is cylindrical. As a result, the fan housing is liable to sustain abrasion of the inner surface thereof and/or deformation during the removal process.
What is need, therefore, is a cooling fan which can overcome the above limitations.
The drawing is a cross-sectional view of a cooling fan according to an exemplary embodiment.
The drawing shows a cooling fan according to an exemplary embodiment, the cooling fan including a fan housing 12, a stator 20, a rotor 14, and a pair of bearings 129.
The fan housing 12 is annular (or cylindrical) and hollow. An air inlet 121 is formed at a top of the fan housing 12, and an air outlet 123 is formed at a bottom of the fan housing 12 opposite to the air inlet 121. The fan housing 12 has an inner surface 124 surrounding the rotor 14. The inner surface 124 converges (tapers) slightly in a downward direction, i.e., the inner surface 124 of the fan housing 12 slants towards a central axis O of the fan housing 12 from top to bottom. Put another way, the inner surface 124 of the fan housing 12 expands slightly in an upward direction away from the central axis O of the fan housing 12, with an inner space 126 surrounded by the inner surface 124 correspondingly expanding slightly in the upward direction. Accordingly, the air inlet 121 at the top of the fan housing 12 is a little larger than the air outlet 123 at the bottom of the fan housing 12.
Since the inner surface 124 of the fan housing 12 expands upwardly along the central axis O, after the fan housing 12 is molded in a mold, it is relatively easy to separate the fan housing 12 from the mold by moving the mold in an upward direction along the central axis O of the fan housing 12. Furthermore, during the separation process, friction between the inner surface 124 of the fan housing 12 and the mold is avoided. Thus the quality of the fan housing 12 obtained should be good. In order to maintain the cooling capability of the cooling fan and still facilitating separation of the fan housing 12 from the mold, a first angle θ1 between the inner surface 124 and the central axis O of the fan housing 12 is in the range of 0.3˜3 degrees.
A base 125 is received in the fan housing 12, and is arranged at the air outlet 123. A central tube 128 extends upwardly from a center of the base 125. A central hole 30 extends through the central tube 128, such that top and bottom ends of the central tube 128 are open. That is, the central hole 30 is a through hole. In addition, an annular recess 32 communicating with the central hole 30 is formed at an inner periphery of each of the top and bottom ends of the central tube 128. Each recess 32 has a diameter exceeding that of the central hole 30. Thus the top and bottom ends of the central tube 128 have an inner diameter exceeding that of a middle portion of the central tube 128.
The stator 20 is mounted around the central tube 128 of the base 125. The stator 20 includes a stator core 22 with coils 24 wound thereon to establish an alternating magnetic field, and a PCB (printed circuit board) 26 electrically connected with the coils 24 to control electrical current flowing through the coils 24.
The rotor 14 includes a hub 146 forming a shaft seat 147 at a central portion thereof, a plurality of rotary blades 142 extending radially and outwardly from an outer periphery of the hub 146, a magnet 148 adhered to an inner surface 124 of the hub 146 and facing the coils 24 of the stator 20, and a shaft 144 extending downwardly from the shaft seat 147 of the rotor 14. The shaft 144 defines an annular notch 140 at a distal end thereof.
Each of the rotary blades 142 has an outer edge 145 confronting the inner surface 124 of the fan housing 12. The outer edge 145 of each rotary blade 142 is approximately parallel to the inner surface 124 of the fan housing 12. That is, the outer edge 145 of the rotary blade 142 slants towards the central axis O of the fan housing 12 from top to bottom. A second angle θ2 between the outer edge 145 of the rotary blade 142 and the central axis O of the fan housing 12 is equal to the first angle θ1 between the central axis O and the inner surface 124 of the fan housing 12. Thus a distance between the outer edge 145 of the rotary blade 142 and the inner surface 124 of the fan housing 12 is constant from top to bottom.
As shown in the drawing, a height of the outer edge 145 of the rotary blade 142 as measured parallel to the central axis O of the fan housing 12 is designated as H, a first distance between a bottom end of the outer edge 145 of the rotary blade 142 and the central axis O of the fan housing 12 is designated as R1, and a second distance between a top end of the outer edge 145 of the rotary blade 142 and the central axis O of the fan housing 12 is designated as R2. The second distance R2 is slightly larger than the first distance R1, and the second angle θ2 between the outer edge 145 of the rotary blade 142 and the central axis O should satisfy the equation: θ2=tan−1((R2−R1)/H).
The bearings 129 are received in the top and bottom recesses 32 of the central tube 128, respectively, and surround the shaft 144. When assembled, the rotor 14 is received in the inner space 26 and surrounded by the inner surface 124, with the shaft 144 extending through the bearings 129. Thus the shaft 144 of the rotor 14 is rotatably supported by the pair of bearings 128. A locking ring 40 is arranged in the bottom recess 32 of the central tube 128 and engages in the notch 140 of the shaft 144 to limit movement of the shaft 144 along an axial direction thereof. A coil spring 50 is arranged between the bottom bearing 129 and the central tube 128 for applying a preset engaging pressure between the rotor 14 and the top bearing 129, thereby ensuring that the top bearing 129 remains stationary relative to the hub 146 in the axial direction of the shaft 144.
During operation, the rotor 14 is rotated by the interaction of the alternating magnetic field established by the stator 20 and the magnetic field of the magnet 148 of the rotor 14. The rotary blades 142 thus produce forced airflow to take away heat generated in an application environment that employs the cooling fan. Since the distance between the outer edge 145 of each rotary blade 142 and the inner surface 124 and the fan housing 12 is uniform from top to bottom, during rotation of the rotor 14, interference of the rotor 14 and the fan housing 12 is avoided, and the cooling fan can operate smoothly and quietly.
It is to be understood, however, that even though numerous characteristics and advantages of embodiments have been set forth in the foregoing description, together with details of the structures and functions of the embodiments, 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 disclosure to the full extent indicated by the broad general meaning of the terms in which the appended claims are expressed.
| Number | Date | Country | Kind |
|---|---|---|---|
| 200910307441.5 | Sep 2009 | CN | national |
