Patent Grant
7841832
1. Field of the Invention
The present invention relates to the correction of unbalance of rotation of a rotor of a fan.
2. Description of the Related Art
Currently, electronic devices are equipped with cooling fans for dissipating heat generated inside the electronic devices. The recent enhancement in performance of electronic devices has lead to an ever-increasing amount of internal heat generation, which inevitably calls for improvement of cooling characteristics of the fans. In order to improve cooling characteristics of the fans, air volume and static pressure of the fans need to be increased. For increasing the air volume and static pressure, the fans need to be run at higher speeds. Meanwhile, many electronic devices are used in homes and offices nowadays; for this reason, quiet operation of electronic devices is also demanded.
Noise during operation is caused mainly by an airflow generated by rotation of blades of the fan and making blade passing tones, and vibration associated with the rotation of the fan. As for the blade passing tones, the noise level can be reduced by optimization of the shape of the blades. There is, however, a limit to the reduction of this kind of noise, since the blade passing tones are naturally produced wherever an airflow is generated. On the other hand, the vibration can be reduced to a least possible degree by physically eliminating unbalance of rotation of a rotor.
The vibration value increases as the rotational speed of the fan increases. Since an impeller of the fan is a rotor, physically unbalanced rotation may be caused with respect to the rotation axis. In other words, eccentricity of center of gravity occurs with respect to the rotation axis. While zero is ideal for a value indicating the degree of unbalanced rotation (hereinafter, referred to an unbalanced amount), it is almost physically impossible. Therefore, there arises a need to provide correction of unbalance of rotation so as to bring the unbalance amount of the impeller with respect to the rotation axis, which is produced when the impeller is rotating, as close to zero as possible.
The vibration of the fan not only resonates with the housing of the electronic device and generates noises, but also may adversely affect other electronic components. This is a reason why the vibration of the fan needs to be reduced. And beside, the housing of the recent electronic device have become small in size, hence the installation space for the fan is restricted in the housing. It is required that a space be provided in the air intake area of the fan so as not to hinder entering of air, in order to maximize cooling performance of the fan.
A fan according to an embodiment of the present invention includes an impeller having a circular projected portion projecting radially inward from an upper end portion of a hub so as to cover the vicinity of the outer periphery of a lid of a rotor holder. A gap is formed between the circular projected portion and the rotor holder in the axial direction. In this configuration, a balance weight can be fixed to the circular projected portion, whereby the unbalance of rotation can easily be corrected.
Other features, elements, advantages and characteristics of the present invention will become more apparent from the following detailed description of preferred embodiments thereof with reference to the attached drawings.
Referring to
Referring to
The rotor holder 31 is supported on a base 12 via the shaft 32 in a rotatable manner. A substantially cylindrical bearing housing 1021 is disposed on a central portion of the base 12. Ball bearings 341 and 342 are fixed to two step portions provided on the inner peripheral surface of the bearing housing 1021. Each of the ball bearings 341 and 342 includes three members, i.e., an outer race, an inner race, and balls. The balls are arranged between the outer race and the inner race, and the balls roll there while being in contact with the outer race and the inner race.
In this configuration, the inner race freely rotates relative to the outer race. The shaft 32 is inserted into a space defined by the inner peripheral surfaces of the inner races of the ball bearings 341 and 342. In this manner, the shaft 32 and the ball bearings 341 and 342 form together a bearing portion. A coil spring 390 for applying a predetermined preload to the ball bearings 341 and 342 is disposed at a gap between the above-mentioned step portion and the ball bearing 342 in the axial direction.
An annular groove (not shown) centered on the rotation axis is formed in a portion close to a lower end or at the lower end of the shaft 32. A wire ring 391 is fitted into that annular groove to retain the shaft 32 within the ball bearing 342. The structure of the bearing portion is not limited to the above. For example, a sliding bearing such as an oil impregnated bearing may be used.
A stator 3 is supported at an outer periphery of the bearing housing 1021. The stator 3 mainly includes a stator core stack 35, coil windings 37, and an insulator 36. The stator core stack 35 is formed by stacking a plurality of thin plates. The stator core stack 35 has a plurality of magnetic pole teeth projecting radially outward from the rotation axis. The insulator 36 made of insulating material surrounds the stator core stack 35 so as to electrically insulate the upper and lower ends and the individual magnetic pole teeth of the stator core stack 35 from each other. The coil windings 37 are arranged around each of the magnetic pole teeth via the insulator 36.
At a lower end portion of the stator 3 is attached the circuit board 38. The circuit board 38 includes a circuit that controls the rotation of the impeller 2. In the circuit board 38, at least one electronic component (not shown) is mounted on a printed board. A leading end of the coil winding 37 is electrically connected to the electronic component of the circuit board 38, thereby constituting a rotation control circuit. The circuit board 38 is secured at a position below the insulator 36. When the coil winding 37 is energized with an electric current supplied from an external power source through the electronic component including an IC (integrated circuit) and/or a Hall element, a magnetic field is generated on the stator core stack 35.
The impeller 2 includes a substantially cylindrical hub 22 about the rotation axis and a plurality of blades 21 radially arranged around the external surface of the hub 22. The blades 21 are turned about the rotation axis so as to produce an airflow. A rotor holder 31 is provided on the inner circumferential surface of the hub 22, and a rotor magnet 33 is attached to the inner surface of the rotor holder 31. The rotor holder 31 reduces leakage flux toward the outside of the fan 1. The rotor magnet 33 is magnetized such that a plurality of magnetic poles are alternately arranged on the inner peripheral surface thereof in the circumferential direction. The shaft 32 fastened at the center of the rotor holder 31 is inserted through the ball bearings 341 and 342, so that the rotor magnet 33 and the stator core stack 35 are arranged to face each other in a radial direction perpendicular to or substantially perpendicular to the rotation axis. When an electric current flows through the coil windings 37, the magnetic field is generated from the stator core stack 35 and interacts with a magnetic field produced by the rotor magnet 33 so as to generate rotary torque about the rotation axis. The rotary torque is applied to the impeller 2, thereby rotating the impeller 2 about the rotation axis. The Hall element (not shown) detects changes in the magnetic flux of the rotor magnet 33 during rotation, based on which a drive IC controls the rotation, so that the impeller 2 can be rotated stably. When the impeller 2 is driven and rotated, the blades 21 push out air toward one end side in the axial directions and an airflow is thus produced in the axial direction.
The base 12 is disposed to axially face the circuit board 38. The base 12 is formed into a generally disk-like shape having almost the same diameter as the outer diameter of the circuit board 38. The base 12 is coupled to a housing 10 with a plurality of ribs 13. In this preferred embodiment, four ribs 13 are provided. The ribs 13 extend radially outward from the base 12 and are coupled to the housing 10 at their distal ends (i.e., their radially outer ends). Please note that the number of the ribs 13 is not limited to four. For example, three or five ribs 13 may be provided. In this preferred embodiment, the four ribs 13 are regularly arranged in the circumferential direction.
The housing 10 is formed so as to enclose the impeller 2 from the outer side in the radial direction. An air channel 11 is formed at the inner side of the housing 10. The air channel 11 serves as an air passage of the airflow generated by the rotation of the blades 21. The housing 10 is in the form of a substantially rectangular frame whose outer periphery at both the axially upper and lower ends is substantially square shape, when viewed in the axial direction. At corners of the axially upper and lower ends of the housing 10, flanges 14 are arranged to protrude outward in the radial direction. A mounting hole 14a is formed in each of the flanges 14. The mounting hole 14a is used for insertion of an attachment such as a screw in mounting the fan 1 to a device.
An annular portion 221 as a weight adjustment portion is provided to protrude radially inward at an upper end portion of the hub 22.
The rotor of the fan 1 of this preferred embodiment mainly includes the blades 21, the hub 22, the rotor holder 31, the rotor magnet 33, and the shaft 32. The blades 21 and the hub 22 are formed integrally by injection molding of a resin. The rotor holder 31 is formed by press work. These components may rotate in an unbalanced manner at least with respect to the rotation axis.
The unbalanced rotation in this application means a state in which the rotation axis of the rotor is not coincident with the center of gravity of the rotor. When the rotor is rotated with its rotation axis not coinciding with the center of gravity of the rotor, the center of gravity thereof rotates around the rotation axis. As the distance increases between the center of gravity and the rotation axis, the unbalance amount becomes larger. The unbalance amount is expressed as a product of the amount of weight unbalance (weight: g) and a distance between the rotation axis and a position causing unbalanced rotation (distance from the rotation axis in the radial direction: cm); therefore, the unbalance amount is indicated mainly in a unit of g·cm. For example, assuming that the rotor has a unbalance amount of 1.0 g·cm, it is possible to reduce the unbalance amount to 0 g·cm theoretically by placing a balance weight of 1.0 g at a position of 1.0 cm away from the rotation axis in the radial direction such that the balance weight is located on the opposite side of the rotation axis to the position causing unbalance. The unbalance amount is typically corrected such that a balance weight is added at a position axisymmetric to the position which causes unbalanced rotation so as to compensate for unbalance of rotation.
Rotors cannot always be manufactured in stable dimensions with reliable precision according to changes in processing conditions and environment in mass-production lines. Unbalance amounts, therefore, vary depending on individual rotors. It is physically impossible to manufacture components with the unbalance amount of 0 g·cm in mass-production. Various efforts are, however, made to reduce the unbalance amount as much as possible in processing rotors. When two or more rotors rotating in an unbalance manner are combined into one, those rotors are arranged to minimize total unbalance of rotation of a resultant rotor. The unbalance of rotation, however, may not be improved even through the rotors are combined such that their unbalance amounts are counterbalanced, since there is a possibility that the rotors to be combined are not precisely coaxial. Consequently, it is not possible to bring the unbalance amount to 0 g·cm in a case of forming a rotor by combining processed components used in mass production.
In this preferred embodiment, the unbalance of rotation is corrected by attaching the balance clip 40 to the annular portion 221 as the weight adjusting portion, as described above. In particular, more than one balance clips 40 are attached for correcting unbalance of rotation of a rotor with which the unbalance amount is large. The balance clip 40 is made of an anti-corrosive metallic material such as stainless steel. Since the metallic material has a larger specific gravity than resin and the like, unbalance of rotation can be corrected with small volume. It should be noted that the material of the balance clip 40 is not limited to the metallic material including stainless steel, and may be altered appropriately.
The balance clip 40 of this preferred embodiment is formed into an approximately U-shape, as shown in
In this preferred embodiment, the blades 21, the hub 22, the rotor holder 31, the rotor magnet 33, and the shaft 32 construct an impeller assembly, which is a rotor. The impeller assembly is loaded onto a balance measuring device (a measuring device for measuring the unbalance amount with respect to the rotation axis of a rotor) for measurement of the unbalance amount of the impeller assembly. The balance measuring device indicates a direction and a magnitude of unbalance of rotation. More specifically, the balance measuring device indicates, as the direction of the unbalance of rotation, an angle of the position about the rotation axis when a predetermined point is assumed to be 0 degree. The magnitude of the unbalance is indicated as the aforementioned unbalance amount in unit of g·cm. Based on the measurement result, at least one balance clip 40 is attached to the annular portion 221. Then, the impeller assembly is again loaded onto the balance measuring device. A specified value is preliminarily set for the unbalance amount of the impeller assembly, and the above-described steps are repeatedly performed on the impeller assembly until the measured unbalance amount comes below the specified value. If the impeller assembly has a unbalance amount smaller than the specified value in the state where the balance clip 40 is not attached, the balance clip 40 need not be attached.
The U-shaped balance clip 40 is fitted onto the annular portion 221 outward in the radial direction. Restoring force is generated in the directions opposite to the separating directions of the tips of the opening of the U-shape when they are pulled apart from each other. The upper and lower surfaces of the annular portion 221 are pinched with the balance clip 40 by this restoring force.
The balance clip 40 is attached to the annular portion 221 as described above, so that unbalance of rotation of the rotor is corrected.
The rotor holder 31 is press-fitted into the hub 22 to be secured on the inner surface of the hub 22. With the rotor holder 31 press-fitted in the hub 22, a gap 50 is formed between the upper surface of the rotor holder 31 and the lower surface of the annular portion 221, as shown in
In this preferred embodiment, the steel sheet of about 0.2 mm in thickness is used for forming the balance clip 40. The balance clip 40 preferably has a thickness in the order of about 0.2 mm in terms of mass per volume and strength of the balance clip 40. The gap 50, therefore, needs to have a size not less than about 0.2 mm in order to physically allow the balance clip 40 to be fitted onto the annular portion 221. In view of work ability, the gap 50 preferably has a margin in size for fitting the balance clip 40 onto the annular portion 221. The size of the gap 50 will be described later.
A portion of the upper surface of the lid of the rotor holder 31, which axially faces the annular portion 221, is arranged lower in axial height than another portion thereof. The axial height of the impeller assembly is dependent on the dimensions of the stator 3 to be housed within the rotor holder 31 on the inner surface side. Namely, the rotor holder 31 is designed to have a minimum possible size that allows the stator 3 to be housed therein. The axial height of the rotor holder 31 needs to be set such that the rotor holder 31 does not contact the coil windings 37 at a portion where the rotor holder 31 is located axially above the coil windings 37. However, the rotor holder 37 may have an axial height lower than that of the coil windings 37 in the radially outside of the rotor holder 37 because the rotor holder 37 does not come into contact the coil windings 37. And besides, with the height thus made lower, the annular portion 221 does not protrude excessively from the upper surface of the impeller assembly axially upward.
Referring to
In the fan 1 used for cooling the interior of the housing of an electronic device, the mass of the impeller assembly is smaller in comparison with large fans. Hence, the fan 1 has a smaller unbalance amount than those of large fans, and thus requires a smaller amount of correction of unbalance of rotation. The diameter of the impeller assembly is not more than 150 mm in most of the fan 1; therefore, the balance clip 40 needs to be attached at a position radially inward of the diameter of 150 mm. As shown in
In a case where the balance clip 40 is attached to the hub 22 at a position 50 mm in diameter, the mass of the balance clip 40 necessary for correcting unbalance of rotation is obtained by dividing the unbalance amount to be corrected by the radius. First, the unbalance amount to be corrected is calculated by subtracting a target unbalance amount from the uncorrected unbalance amount, i.e., 0.3 g·cm−0.2 g·cm. Next, the mass of the balance clip 40 required for the correction of the unbalance amount is calculated by dividing the unbalance amount to be corrected by a distance from the rotation axis to the position at which the balance clip 40 is to be attached, i.e., 0.1 g·cm/25 mm=0.04 g. The balance clip 40 is formed in the order of about 0.025 g in mass per piece in consideration of fine adjustment of unbalance of rotation. Thus, in the case described above, two pieces of the balance clip 40 are used for correcting unbalance of rotation.
When it is already known that the unbalance amount to be corrected is large, either of a balance clip 40 made of a material with a large specific gravity or a balance clip 40 large in size is used. The method of this preferred embodiment is applicable not only to the correction for the impeller assembly having the above dimensions but also for impeller assemblies having other dimensions.
The balance clip 40 used in this preferred embodiment is about 0.025 g in mass as described above; therefore, if a stainless steel of 0.2 mm in thickness is used as a material, the balance clip 40 is to have an approximate U-shape of about 0.3 mm in the radial direction and about 2.0 mm in the axial direction, in the state where the balance clip 40 is attached to the annular portion 221. In the case where the balance clip 40 is fitted in the axial direction with respect to the impeller, it is necessary for the structure for attachment of the balance clip to have a size of 3.0 mm or more in the axial direction. In the case where the balance clip 40 is fitted onto the annular portion 221 outwardly in the radial direction and the gap 50 is sized in 1.0 mm or more, it is necessary for the structure for attachment of the balance clip to have a size of at least about 3.0 mm in the axial direction. Hence, it is possible to make the impeller assembly shorter in the axial direction by sizing the gap 50 in 1.0 mm or less.
The gap 50 between the annular portion 221 and the rotor holder 31 in the axial direction is used as a space into which the balance clip 40 is inserted. It is thus necessary that the gap 50 be maintained at a uniform size in the state where the impeller 2 and the rotor holder 31 are combined. For this purpose, a plurality of seats 2213 are arranged at regular circumferential intervals beneath the annular portion 221, as shown in
The balance clip 40 cannot be fitted at the position where the seat 2213 is formed in the annular portion 221. Thus, position-indicating projections 2214 are formed on the upper surface of the annular portion 221 at the positions where the seats 2213 are formed, as shown in
The blades 21, the hub 22 and the annular portion 221 are integral with one another through injection molding of a resin. The resin injection molding is carried out with two molding dies, i.e. an upper molding die and a lower molding die. The upper molding die and the lower molding die are brought into contact with each other to form a closed space therebetween. A molten synthetic resin is injected into the closed space, the upper and lower dies are opened and separated from each other, the resin that has been solidified in the shape of the closed space is ejected and taken out, and thus a molded product is obtained. In this preferred embodiment, the closed space is formed in the shape of the impeller 2, so that the impeller 2 is molded therein.
It is necessary to provide a gate for injecting resin into molding dies to carry out resin injection molding. The gate is formed at the boundary portion between the inside and the outside of the molding die, and upon opening of the molding dies, the resin inside the molding die and the resin outside the molding die are cut in the gate. In the resin injection molding, therefore, a gate cutting mark 2215 is left on the side of the molded product. Generally, the gate cutting mark 2215 is disposed in a portion where high dimensional accuracy is not required. If the gate cutting mark 2215 is formed on the surface of the blade 21, for example, a turbulent flow is likely to occur in the air flow because of the gate cutting mark 2215 on the surface of the blade 21 during the rotation of the impeller 2, which will become a cause of noise. If the gate cutting mark 2215 is formed in a portion where high dimensional accuracy is required, such as for positioning, a dimensional distortion may be caused by the gate cutting mark 2215 in the positioning, which may bring about a structural problem. In this preferred embodiment, therefore, the gate cutting mark 2215 is formed on five out of the ten position-indicating projected portions 2214, as shown in
The annular portion 221 is formed such that the upper end surface thereof is positioned lower than the upper end surface of the hub 22 so as not to let the balance clip 40 project from the upper end surface of the hub 22 in the state where the balance clip 40 is attached to the annular portion 221. With this structure, when a component, which does not belong to the fan 1, is disposed on the upper end surface side of the hub 22 of the fan 1, the balance clip 40 can be prevented from touching the component disposed outside the fan 1, should external impact force be accidentally applied to the fan 1 and the hub 22 bounce out to touch the component. Further, since the balance clip 40 is fitted outwardly in the radial direction, the balance clip 40 will not fly out to the outside in the radial direction even when centrifugal force acts on the balance clip 40 with the rotation of the impeller 2.
Referring to
The cross-sectional shape of the annular portion 221 is not limited to above-described structure. For examples a tapered portion 2217 may be formed such that an axial thickness of the annular portion 221 is gradually reduced radially outward, as shown in
Alternatively, the increased-thickness portion 2211 may be arranged on the lower surface of the annular portion 221, i.e., the surface which axially faces the rotor holder 31, as shown in
The projections may be so provided on both of the upper and lower surface side of the annular portion 221 such that the wall-like portion between the projection and the adjacent non-projecting portion is formed on each of the upper and lower surfaces, as shown in
An inclined surface 221, which is at an angle to the radial direction and the axial direction, is formed between the radially inner end of the annular portion 221 and the lower surface thereof, as shown in
A plurality of projected portions 2217 are arranged on the annular portion 221 around the rotation axis in the circumferential direction, as shown in
The description has been made on an axial flow fan (a fan in which air is taken and released in the axial direction) in the present embodiment. The present invention is, however, not limited thereto, and is applicable to a centrifugal fan (a fan in which air is taken in the axial direction and is released in the radial direction), as shown in
While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.
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