Imported: 10 Mar '17 | Published: 27 Nov '08
USPTO - Utility Patents
A cooling fan includes a fan housing (10) having an upper tube (111) extending downwardly from a top side thereof and a lower tube (121) extending upwardly from a bottom side thereof, a ball bearing (20) being mounted in the upper tube, a sleeve bearing (30) being mounted in the lower tube, a stator (45) mounted around the lower tube, and a rotor (40). The rotor includes a hub (401) located between the ball bearing and the sleeve bearing and a shaft (50) extending through the hub. Two ends of the shaft are rotatably received in the ball bearing and the sleeve bearing, respectively.
1. Field of the Invention
The present invention relates to a cooling fan, and more particularly relates to a cooling fan having an improved bearing assembly.
2. Description of Related Art
With the continuing development of the electronic technology, electronic packages such as CPUs (central processing units) are generating more and more heat that requires immediate dissipation. Cooling fans are commonly used in combination with heat sinks for cooling CPUs.
Oftentimes, a cooling fan includes a blade set and a fan seat. The fan seat has a central tube portion integrally formed thereon. A pair of sleeve bearings are arranged in the tube portion. A coil is wound around the outside of the tube portion. The blade set is formed with a cap and fan blades connecting to the cap. A stainless steel rotary shaft supported by the pair of sleeve bearings at two opposite ends thereof is arranged within the cap. A magnet pushed by magnetic force of the coil is fixed to the cap and is driven to rotate by the coil so that the fan blades can produce an airflow. Since the aforesaid stainless steel rotary shaft is arranged on the sleeve bearings to rotate, after rotating for a period of time, the rotary shaft and the bearings will experience wear due to leaking of lubricating oil contained therebetween. Thus, the lifetime of the fan will be reduced. In order to improve the lifetime of the fan, wear-tolerable ball bearings for point contact have been developed. However, the manufacturing process for ball bearings requires precision-grinding and a high polish, and thus the ball bearings are more expensive, which results in higher expense.
For the foregoing reasons, therefore, there is a need in the art for a cooling fan which overcomes the above-mentioned problems.
According to a preferred embodiment of the present invention, a cooling fan includes a fan housing having an upper tube extending downwardly from a top side thereof and a lower tube extending upwardly from a bottom side thereof, a ball bearing being mounted in the upper tube, a sleeve bearing being mounted in the lower tube, a stator mounted around the lower tube, and a rotor. The rotor includes a hub located between the ball bearing and the sleeve bearing, and a shaft extending through the hub. Two ends of the shaft are rotatably received in the ball bearing and the sleeve bearing, respectively.
Other advantages and novel features of the present invention will be drawn from the following detailed description of the preferred embodiments of the present invention with attached drawings, in which:
Referring to FIGS. 1 through 4, a cooling fan according to a preferred embodiment includes a fan housing 10, a ball bearing 20 and a sleeve bearing 30, a rotor 40, and a stator 45 in respective to which the rotor 40 is rotatable.
The fan housing 10 includes a lower portion 12 and an upper portion 11 mounted on the lower portion 12. Each portion 11, 12 of the housing 10 includes a base 119, 129 and a tube 111, 121 extending perpendicularly from a central portion of the base 119, 129. The upper tube 111 extends downwardly from the base 119 of the upper portion 111 of the housing 10. An upper central hole 112 extends through the upper tube 111 for receiving the ball bearing 20 therein. The lower tube 121 extends upwardly from the base 129 of the lower portion 12 of the housing 10. The lower tube 121 has a top end being open and a bottom end being closed. A lower central hole 122 is defined in the lower tube 121 for receiving the sleeve bearing 30 therein. An annular recess 125 communicating with the lower central hole 122 is formed on an inner circumference of the top end of the lower tube 121 with a diameter larger than that of the lower central hole 122. Thus the top end of the lower tube 121 has an inner diameter larger than that of the other portion of the lower tube 121. An annular protrusion extends inwardly from the inner circumference of the bottom end of the lower tube 121, and thus forms a step 124 in the lower central hole 122 at the bottom end of the lower tube 121.
The stator 45 includes a stator core 451 with coils wound thereon to establish an alternating magnetic field, and a PCB 452 (printed circuit board) with electronic components mounted thereon being electrically connected with the coils to control electrical current flowing through the coils. The rotor 40 includes a hub 401 forming a shaft seat at a central portion thereof, a plurality of fan blades 402 extending radially and outwardly from an outer periphery of the hub 401, a magnet 41 adhered to an inner side of the hub 401 and confronting the coils of the stator 45, and a shaft 50 extending through the shaft seat of the rotor 40. Two ends (i.e., top and bottom ends) of the shaft 50 respectively extend to upper and lower sides of the hub 401. An annular slot 501, 502 is respectively defined on the shaft 50 near the top and bottom ends thereof. An annular notch 503 is defined in a circular circumference of a middle of the shaft 50, under the hub 401.
The ball bearing 20 is arranged in the upper tube 111. As a conventional ball bearing, the ball bearing 20 includes an annular inner ring 21, an annular outer ring 23 and a plurality of balls 22 sandwiched between the inner and outer rings 21, 23. An outer diameter of the outer ring 23 is substantially the same as a diameter of the upper central hole 112 of the upper tube 111, and an inner diameter of the inner ring 21 is approximately the same as the diameter of the shaft 50. The sleeve bearing 30 is arranged in the lower tube 121. A bearing hole 31 is defined in the sleeve bearing 30. A plurality of grooves 32 are defined in an outer surface of the sleeve bearing 30. The grooves 32 communicate with the bearing hole 31.
During assembly, the upper and lower portions 11, 12 of the housing 10 are stacked together and face towards each other. A space is defined in the housing 10 between the two portions 11, 12. The stator 45 is received in the space and mounted around the lower tube 121 of the lower portion 12 of the housing 10. The ball bearing 20 and the sleeve bearing 30 are respectively mounted into the central holes 112, 122 of the upper and lower tubes 111, 121. The rotor 40 is arranged between the two tubes 111, 121 with the hub 401 mounted around the stator 45. The top end of the shaft 50 of the rotor 40 extends through the ball bearing 20 and the upper tube 111. An upper locking ring 81 is arranged on the upper tube 111 and engaged into the slot 501 of the top end of the shaft 50 to limit movement of the shaft 50 along an axial direction thereof. The bottom end of the shaft 50 extends through the sleeve bearing 30 into the bottom end of the lower tube 121. A wear pad 90 made of highly abrasion-resistant material is arranged in the bottom end of the lower tube 121 facing and supportively engaging with the bottom end of the shaft 50. A lower locking ring 80 is arranged on the step 124 of the lower tube 121 and located between the bottom end of the sleeve bearing 30 and the protrusion of the lower tube 121. The lower locking ring 80 engages into the slot 502 of the bottom end of the shaft 50 thus limiting movement of the shaft 50 along the axial direction thereof.
The ball bearing 20 has a height approximately the same as or a little smaller than that of the upper tube 111. A conical-shaped coil spring 60 is arranged between the ball bearing 20 and the hub 401 for providing the ball bearing 20 and the hub 401 with a preset engaging pressure therebetween, thus ensuring that the ball bearing 20 remains stationary relative to the hub 401 in the axial direction of the shaft 50. A top end of the spring 60 abutting against the inner ring 21 of the ball bearing 20 has a diameter relatively smaller than that of a bottom end of the spring 60 abutting against the hub 401. The sleeve bearing 30 has a height lower than that of the lower tube 121. The sleeve bearing 30 consists of porous material made of sintered metal or the like, and is impregnated with lubricating oil. A bearing clearance defined between the sleeve bearing 30 and the shaft 50 is also filled with lubricating oil. An oil retaining ring 70 is arranged in the recess 125 of the top end of the lower tube 121 and located above the notch 503 of the shaft 50 for preventing leakage of the lubricating oil from the sleeve bearing 30. An oil buffer 100 is thus defined among the oil retaining ring 70, the sleeve bearing 30, the lower tube 121 and the shaft 50 for receiving the lubricating oil provisionally. The oil buffer 100 communicates with the bearing hole 31 and the grooves 32 of the sleeve bearing 30; thus, the lubricating oil received in the oil buffer 100 can flow back to the sleeve bearing 30 through the grooves 32.
During operation, the rotor 40 is driven to rotate by the interaction of the alternating magnetic field established by the stator 45 and the magnetic field of the magnet 41 of the rotor 40. Due to the support of the ball bearing 20 and the sleeve bearing 30 arranged on the top and bottom ends of the shaft 50, rotation of the shaft 50 is smooth and stable. The two bearings 20, 30 are respectively fixed in place and thus are spaced from each other; the lubricating oil of the sleeve bearing 30 cannot flow into the ball bearing 20 and thus interference between the two bearings 20, 30 is avoided. Use of the ball bearing 20 thus gives a longer operational lifespan to the cooling fan. The sleeve bearing 30 can reduce the cost of the cooling fan as it is cheaper. Thus the bearing assembly of one ball bearing 20 and one sleeve bearing 30 can achieve a relatively low cost and a relatively high performance at the same time, thus improving the life-span of the cooling fan and reducing the cost of the cooling fan.
It is understood that the invention may be embodied in other forms without departing from the spirit thereof. Thus, the present example and embodiment are to be considered in all respects as illustrative and not restrictive, and the invention is not to be limited to the details given herein.