1.  Field of the Invention
The present invention relates to a cooling fan, and more particularly to a magnetically assembled cooling fan.  The cooling fan has a thrust bearing provided on the bottom of a shaft, such that there is no limitation to the types of the bearings provided around the shaft.  Furthermore, the cooling fan has an elongated metal plate provided below the permanent magnet that is installed in the fan assembly, such that the assembly of the fan assembly is achieved by the attraction between the metal plate and the permanent magnet. 
2.  Description of Related Art
With reference to FIG.  5, the conventional brushless cooling fan has a fan assembly (70), a stator assembly (60), a circuit board (65) and a housing (50) for receiving the fan assembly (70), the stator assembly (60) and the circuit board (65).  The stator assembly (60) has a first conjugated plate (62), a second conjugated plate (63), a coil (64) securely received between the first and the second conjugated plates (62, 63) and a sleeve (61) with which the first and second conjugated plates (62, 63) and the coil (64) are securely mounted on the bottom face (51) of the housing (50).  The fan assembly (70) has a seat (71), a shaft (73) firmly mounted on the seat (71) and an annular permanent magnet (75) securely installed inside the fan assembly (70).  Since the principle of operation of this type of brushless cooling fan is well known in the art, a detailed description is omitted.  With reference to FIG.  6, during assembly, the shaft (73) is inserted through the first conjugated plate (62), the coil (64), the ball bearing (611), the pad (612) and the self-lubricating bearing (613) within the sleeve (61), the second conjugated plate (63) and the circuit board (65) into the housing (50).  The portion of the shaft (73) extending into the housing (50) is then clamped by a fastener (731).  Therefore, the rotation of the shaft (73) is affected by the tightness of the fastener (731) to the shaft (73).  If the fastener (731) clamps the shaft (73) so tight that the rotation of the shaft (73) is difficult, the heat dissipation efficiency of the cooling fan is low.  If the fastener (751) is not tight enough, the fan assembly (70) will move up and down within the housing (50) during operation.  Furthermore, the design as previously described limits the first type of bearing chosen within the sleeve (61) to a ball bearing (611), then the self-lubricating bearing (613).  The price for a ball bearing (611) is several times larger than that of a self-lubricating bearing (613).  Thus, if there is no limitation to the type of the bearing, the cost for manufacturing the cooling fan will surely be greatly reduced. 
To overcome the shortcomings, the present invention tends to provide an improved cooling fan assembly to mitigate and obviate the aforementioned problems.