The present invention relates generally to pumps, and more particularly to a miniature pump having a magnetically levitated impeller for a liquid cooling system for cooling an electronic package.
With the continued development of computer technology, electronic packages such as the CPUs are generating more and more heat that needs to be dissipated immediately to avoid damage to the circuitry. Conventional heat dissipating devices such as heat sink/fan combinations are not sufficiently effective at dissipating heat to cope with modern circuitry. Liquid cooling systems have thus been increasingly used in computer technology to cool these electronic packages.
A typical liquid cooling system comprises a heat absorbing unit for absorbing heat from a heat source, and a heat dissipating unit which is filled with liquid. The liquid exchanges heat with the heat absorbing unit, thereby taking away the heat of the heat absorbing unit as the liquid is circulated. Typically, a pump is used to circulate the liquid.
Generally, the pump comprises a housing having a bottom plate, a shaft having a bearing pivotably attached thereto, an impeller received in the housing and attached to the bearing, a magnetic coupling structure, and a motor. The shaft passes through the impeller and engages with the bottom plate of the housing. The magnetic coupling structure comprises an inner magnet mounted on the impeller and an outer magnet appropriately disposed on the motor outside of the pump housing. In operation, the motor rotates to drive the outer magnet to rotate therewith. The inner magnet receives the attractive force of the outer magnet, so that the inner magnet is caused to rotate at a high speed as a result of the high-speed rotation of the outer magnet, thus causing the impeller to rotate with high-speed. The impeller thus rotates with the inner magnet to circulate the liquid in the liquid cooling system, thereby taking away the heat. However, a problem existing in the conventional pump is that during the high-speed rotation of the pump there is friction between a bottom of the bearing and the bottom plate of the housing of the pump because the axial attract force of the outer magnet is applied on the impeller having the inner magnet, which causes damage to the pump housing. A way of reducing the friction between the bearing and the pump housing is that a wearable washer is mounted between the bearing and the bottom plate of the pump housing, however this can result in high levels of unwanted noise pollution.
Therefore, there is a need for a pump with a low-friction bearing
According to a preferred embodiment of the present invention, a miniature pump comprises a pump casing and a liquid circulating unit received in the pump casing. The pump casing comprises a hollow main body transversely forming a spacing plate and a partition wall separated from the spacing plate. The liquid circulating unit comprises a shaft mounted between the partition wall and the spacing plate, a bearing rotatably mounted mounted to the shaft, an impeller attached to the bearing to rotate therewith, a first pair of spaced magnetic spacers surrounding an upper portion of the shaft and positioned above the bearing, and a second pair of spaced magnetic spacers surrounding a lower portion of the shaft and positioned below the bearing. The two pairs of magnetic spacers suspend the impeller in a stable position in an axial direction of the pump when the impeller rotates so that the impeller is prevented from rubbing against the partition wall when the impeller rotates.
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:
Referring to
The pump casing 10 comprises a hollow main body 14, a top cover 12 hermetically attached to a top end 140 of the main body 14, and a bottom cover 16 attached to a bottom end 143 of the main body 14. A sealing ring 141 is disposed between the main body 14 and the top cover 12 to prevent liquid leakage. The top cover 12 forms an annular groove 120 at a bottom edge thereof for receiving the sealing ring 141 therein. An inlet 122 is formed on the top cover 12 for allowing liquid to enter the pump casing 10. An outlet 142 is formed on the main body 14 for allowing the liquid to exit the pump casing 10.
The main body 14 transversely forms an inner partition wall 144. This partition wall 144 effectively divides the inner space of the main body 144 into a top space 146 and a bottom space 148.
Referring also to
Referring to
The motor driving unit 30 is received in the bottom space 148 of the pump casing 10. The motor driving unit 30 is positioned on the bottom cover 16 and comprises a motor having a rotor 32. A second permanent magnet 320 is attached to the rotor 32 for rotating therewith, in a position corresponding to that of the first permanent magnet 261 with a flux gap formed therebetween. Like the first permanent magnet 261, the second permanent magnet 320 also has a ring flat body magnetized so as to have a plurality of alternating N and S poles along the ring body.
In operation, the rotor 32 of the motor driving unit 30 rotates so as to drive the second permanent magnet 320 to rotate therewith. The first permanent magnet 261 is driven to rotate with second permanent magnet 340 by the attractive magnetic force therebetween. The impeller 26 thus rotates with the first permanent magnet 261 to circulate the liquid in the liquid cooling system. In the present invention, the impeller 26 uses four annular magnetic spacers 21-24 to control its axial position, wherein the magnetic spacers 22, 23 are received in two opposite ends of the impeller 26 and rotate with the impeller 26, the magnetic spacers 21, 24 are respectively fixedly received in the spacing plate 126 and the partition wall 144. The magnetic spacers 21, 22 surround an upper portion of the shaft 25 without connection therewith and are positioned above the bearing 27. The magnetic spacers 21, 22 are spaced and opposite to each other, wherein the magnetic spacer 21 is received in the cap 1260 of the spacing plate 126 and the magnetic spacer 22 is received in an upper portion of the receiving room of the post 260. Each of the magnets 21, 22 has a north (N) pole and an opposite south (S) pole. The magnetic spacers 21, 22 are arranged so that the S pole of the magnetic spacer 21 opposes the S pole of the magnetic spacer 22. The like magnetic poles oppose each other so that a repulsive force F1 exists between the magnetic spacers 21, 22, which means the impeller 26 with the magnetic spacer 22 is pushed downwards with force F1 by the magnetic spacer 21. When the impeller 26 rotates, the impeller 26 acts on the liquid with centrifugal force. Simultaneously, the liquid acts on the impeller 26 with a corresponding force F. The force F has an upward component F4 where the liquid acts on the impeller 26 in an axial direction. The magnetic spacers 21, 22 are used to provide the downward force F1 to the impeller 26 to balance the upward axial force F4. The magnetic spacers 23, 24 surround a lower portion of the shaft 25 without connection therewith and are positioned below the bearing 27. The magnetic spacers 23, 24 are located so as to be separate and opposite to each other, the magnetic spacer 23 is received in a lower portion of the receiving room of the post 260 and the magnetic spacer 24 is received in the recess 1444 of the shaft support 1440. Each of the magnetic spacers 23, 24 has an N pole and an opposite S pole. The magnetic spacers 23, 24 are arranged so that the S pole of the second magnetic spacer 23 opposes the S pole of the magnetic spacer 24. Since like magnetic poles oppose each other so that a repulsive force F2 exists between the second magnets 23, 24, and the impeller 26 has an upward force F2 exerted on it by the magnetic spacer 21. When the impeller 26 rotates, an axial component force F3 pushes downward on the impeller 26 because of a magnetic interaction between the first permanent magnet 261 and the second magnet 320 of the motor driving unit 30. The magnetic spacers 23, 24 are used to provide the upward force F2 to the impeller 26 to balance the downward axial force F3 and the force G of gravity acting on the impeller 26. When the impeller 26 operates, total axial force acting on the impeller 26 is balanced, wherein the total axial force is illustrated by following equation:
F1+G+F3=F2+F4.
The four magnetic spacers 21-24 properly suspend the impeller 26 in a stable position in the axial direction such that a bottom of the impeller 26 has no contact with the partition wall 144, whereby a friction between the bottom of the impeller 26 and the partition wall 144 is prevented and noise pollution is considerably reduced.
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.