Motor

A motor includes a cylindrical or substantially cylindrical rotor unit configured to rotate about a rotation axis; a bearing unit arranged to rotatably support the rotor unit; a bearing holder arranged to hold the bearing unit; a disc-shaped or substantially disc-shaped base to which the bearing holder is fixed; a stator unit arranged inside the rotor unit and fixed to the bearing holder; and a circuit board arranged between the base and the stator unit and held by the stator unit. The circuit board is supported on the base through an insulative and flame-retardant vibration-preventing member.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to a motor for use in a blower or the like and, more particularly, to an improvement of a motor provided with a circuit board to which coils of a stator are connected.

2. Description of the Related Art

A centrifugal fan used as a blower for cooling electronic devices and so forth is configured such that, as a plurality of circumferentially-arranged blades is rotated by a motor about a rotation axis, axially-drawn air is radially discharged and then blown out from an exhaust port.

The centrifugal fan of this type generally has a configuration as disclosed in, e.g., Japanese Patent Application Publication No. 2005-256610. More specifically, an impeller including a ring-shaped hub extending radially outward from a rotor unit and a plurality of blades fixed to the hub and circumferentially arranged at the radial outer side of the rotor unit is fixed to the rotor unit having a substantially cylindrical portion rotating about a rotation shaft. A bearing unit for supporting the rotation shaft of the rotor unit is held inside of a bearing holder unit arranged in a base. A stator unit arranged on the inner circumference of the rotor unit is fixed to the outer surface of the bearing holder unit. A circuit board is arranged between the base and the stator unit.

In general, the circuit board is formed into a ring shape so as to be loosely fitted to the outer surface of the bearing holder unit. As disclosed in Japanese Patent Application Publication No. 2005-256610, tying pins implanted in an insulator of the stator unit are soldered to the circuit board, whereby the circuit board is supported on the stator unit. The coils of the stator unit are tied and connected to the tying pins. Thus, the coils are connected to the circuit board through the tying pins.

In the configuration in which the circuit board is supported by only the tying pins of the stator unit as set forth above, the circuit board tends to vibrate if the electromagnetic vibration generated in the stator unit is transferred to the circuit board. In addition, the circuit board may be vibrated when a part of the airflow generated by the rotation of the impeller flows around the circuit board. This may adversely affect the vibration and noise characteristics of the centrifugal fan as a whole.

A technology for solving the aforementioned problem is disclosed in, e.g., Japanese Patent Application Publication No. H07-075288. In Japanese Patent Application Publication No. H07-075288, a recess portion is formed in a counter intake port of a fan casing. A circuit board is arranged in the recess portion and is encapsulated with a resin sealant. With this structure, the circuit board is covered with the resin sealant and is fixed to the fan casing. It is therefore possible to obtain a vibration-free structure for the circuit board and to provide dustproof and waterproof effects.

In case of the configuration disclosed in Japanese Patent Application Publication No. H07-075288, however, the recess portion for the accommodation of the circuit board needs to be secured when encapsulating the circuit board with the sealant. If it is structurally impossible to provide the recess portion, a wall for covering the circuit board needs to be temporarily prepared in order to fill the sealant. This poses a problem in that the structure becomes complex. Moreover, a drying step needs to be performed after filling the sealant. Thus, there is a problem in that the number of required manufacturing steps grows larger and the installation becomes larger.

SUMMARY OF THE INVENTION

Preferred embodiments of the present invention are able to realize, with a simple structure and in a cost-effective manner, vibration prevention of a circuit board supported on a stator unit.

In accordance with a preferred embodiment of the present invention, a motor includes a cylindrical or substantially cylindrical rotor unit configured to rotate about a rotation axis; a bearing unit arranged to rotatably support the rotor unit; a bearing holder arranged to hold the bearing unit; a disc-shaped or substantially disc-shaped base to which the bearing holder is fixed; a stator unit arranged inside the rotor unit and fixed to the bearing holder; and a circuit board arranged between the base and the stator unit and held by the stator unit, wherein the circuit board is supported on the base through an insulative and flame-retardant vibration-preventing member.

According to the motor of a preferred embodiment of the present invention, the circuit board held by the stator unit is arranged between the base provided with the bearing holder and the stator unit fixed to the bearing holder. The circuit board is supported on the base through an insulative and flame-retardant vibration-preventing member. Therefore, the vibration-preventing effect of the circuit board is remarkably increased. There is no need to use a complex structure required in filling a resin sealant. It is not necessary to perform a drying step. A vibration-preventing measure can be provided with a simple configuration. In particular, it is possible to safely support the circuit board because the vibration-preventing member is insulative and flame-retardant.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

Hereinafter, preferred embodiments of the present invention will now be described with reference to the drawings which form a part hereof. In the description of the present preferred embodiments, for the sake of convenience, the up-down direction in the respective drawings will be referred to as an “up-down direction”. However, the up-down direction is not intended to mean the direction available in an actual installation state. In the description of the present preferred embodiments, the direction parallel or substantially parallel to the rotation axis will be referred to as an “axial direction”. The radius direction about the rotation axis will be referred to as a “radial direction”. The present invention is not limited to the preferred embodiments described below but may be appropriately modified without departing from the scope proving the effects of the present invention.

FIG. 1is a section view schematically showing the configuration of a centrifugal fan provided with a motor according to a preferred embodiment of the present invention. As shown inFIG. 1, the centrifugal fan preferably includes a cylindrical or substantially cylindrical rotor unit2arranged to rotate about a rotation axis J, a stator unit3arranged inside the rotor unit2and a plurality of blades52arranged along the circumferential direction of the rotor unit2. In this regard, the rotor unit2preferably includes a cylindrical or substantially cylindrical closed-top rotor holder21, a field magnet22fixed to the inner surface of a sidewall portion of the rotor holder21, and a shaft23fixed to the central portion of the rotor holder21so as to rotate about the rotation axis J.

A ring-shaped connecting portion51extending radially outward from the rotor unit2is preferably fixed to the rotor unit2. A plurality of blades52arranged along the circumferential direction of the rotor unit2at the radial outer side of the rotor unit2is fixed to the connecting portion51. The connecting portion51and the blades52together define an impeller5. The impeller5is configured to rotate together with the rotor unit2. In the present preferred embodiment, the blades52are preferably arranged on the outer circumferential surface of the rotor unit2in a mutually spaced-apart relationship. In this connection, it is only necessary that the ring-shaped connecting portion51has a function of fixing the blades52along the circumferential direction of the rotor unit2. No particular restriction is imposed on the manner in which the connecting portion51is fixed to the rotor unit2.

The rotor unit2is preferably rotatably supported by a bearing unit4through the shaft23. The bearing unit4is fixed to the bearing holder6. The bearing holder6is preferably defined together with a disc-shaped or substantially disc-shaped base7as a monolithic member. However, the bearing holder6and the base may alternatively be provided by separate members if so desired. In the present preferred embodiment, the base7is preferably defined by a bottom portion of a lower case81of a housing8arranged to accommodate the motor1including the rotor unit2and the stator unit3and the impeller5. The bearing unit4is preferably provided by ball bearings, but any other desirable type of bearing could be used. The housing8preferably has a snail-like or substantially snail-like shape when seen in a plan view and includes a lower case81and an upper case82fitted to each other. A circular or substantially circular intake port9is defined in the substantially central portion of the upper case82. As can be noted inFIG. 2which shows the lower case81, an exhaust port10which opens frontward is preferably defined on the side surface of the housing8. The base7of the lower case81is preferably provided by a circularly depressed shape in the central region of the bottom portion of the lower case81by arranging a ring-shaped protrusion portion51ain the bottom portion of the lower case81.

The stator unit3fitted to the outer circumference of the bearing holder6is arranged inside the rotor unit2. The stator unit3preferably includes a stator core31including a plurality of salient poles, upper and lower insulator portions32aand32barranged to cover the upper and lower surfaces of the stator core31and the inner surfaces of slots, and a coil33wound around the respective salient poles of the stator core through the insulator portions32aand32b. The outer circumferential surfaces of the respective salient poles of the stator core31face the inner circumferential surface of the field magnet22of the rotor unit2across an air gap.

A disc-shaped or substantially disc-shaped circuit board11arranged to control the rotation of the motor1is preferably arranged between the base7and the stator unit3. The circuit board11preferably has a disc-like or substantially disc-like shape. An aperture to which the bearing holder6is loosely fitted is preferably defined in the central portion of the circuit board11. A plurality of tying pins34is preferably embedded in the lower insulator32bof the stator unit3. The end portions of the coil33are preferably tied to the tying pins34. The respective tying pins34are inserted into the connecting holes of the circuit board11and are, for example, soldered to the circuit board11. Thus, the circuit board11is supported on the stator unit3. The end portions of the coil33are preferably electrically connected to a conductive pattern on the circuit board11through the tying pins34. Various kinds of electronic components or elements defining a motor control circuit are preferably mounted on the lower surface of the circuit board11.

A plurality of (for example, preferably three, in the present preferred embodiment) vibration-preventing members12arranged in a mutually spaced-apart relationship is interposed between the lower surface of the outer periphery portion of the circuit board11and the upper surface of the base7. The circuit board11is supported on the base7through the vibration-preventing members12. Each of the vibration-preventing members12is preferably defined by joining two insulative and flame-retardant rubber sheets12aand12b, for example. Each of the vibration-preventing members12is preferably fixedly secured to the circuit board11through the use of, for example, an adhesive agent12capplied on the rubber sheet12a. The upper rubber sheet12aof each of the vibration-preventing members12is preferably made of, for example, a relatively soft rubber material and is, e.g., about 1 mm in thickness. The lower rubber sheet12bis preferably made of, for example, a rubber material softer than the upper rubber sheet12aand is, e.g., about 2 mm in thickness. The adhesive agent12cis preferably made of a soft material identical or substantially identical to the upper rubber sheet12aand is about 0.3 mm to about 0.4 mm in thickness, for example. As a result of joining the rubber sheets12aand12b, it is possible to obtain a vibration absorption range of, e.g., about 400 Hz to about 1500 Hz, so as to realize a wide vibration absorption characteristic.

The stator unit3is fixed to the bearing holder6in a position having a predetermined height and the vibration-preventing members12are preferably interposed in a slightly contracted state between the circuit board11supported on the stator unit3and the base7. As a consequence, the lower surface of the lower rubber sheet12bof each of the vibration-preventing members12is pressed against the upper surface of the base7. The lower rubber sheet12bis firmly fixed to the base7by the self-bonding force of the lower rubber sheet12b. Needless to say, the lower surface of the lower rubber sheet12bmay also be fixed to the upper surface of the base7using an additional adhesive agent if so desired.

In the centrifugal fan configured as above, if an electric current begins to be supplied to the coil33of the stator unit3, the rotor unit2is rotated by the electromagnetic interaction between the respective salient poles of the stator core31excited by the coil33and the field magnet22. The impeller5is rotated together with the rotor unit2. As the impeller5rotates, air is drawn from the intake port9and is centrifugally moved in the circumferential direction along with the rotation of the blades52. The air is moved along the inner surface of the circumferential wall of the housing8and is blown outward from the exhaust port10.

During this operation, electromagnetic vibration is induced between the rotor unit2and the stator unit3. In the stator unit3supported on the bearing holder6, the vibration is transferred to the circuit board11supported by the tying pins34. Since the circuit board11is supported on the base7by the three vibration-preventing members12, the vibration acting on the circuit board11is absorbed by the respective vibration-preventing members12and is restrained or substantially restrained from being transferred to the base7.

FIGS. 3A, 3B, 4A, and 4Bare Campbell diagrams respectively showing the vibration measured in a conventional centrifugal fan not provided with the vibration-preventing members12and the vibration measured in a centrifugal fan according to preferred embodiments of the present invention provided with the vibration-preventing members12.FIGS. 3A and 4Ashow the vibration of the conventional centrifugal fans not provided with the vibration-preventing members12.FIGS. 3B and 4Bshows the vibration of the centrifugal fans of preferred embodiments of the present invention provided with the vibration-preventing members12.FIGS. 3A and 3Billustrate the axial vibration measured in a location corresponding to the top plate of the upper case82of the housing8near the intake port9.FIGS. 4A and 4Billustrate the radial vibration measured in a location corresponding to the sidewall of the housing8. A Campbell diagram indicates the vibration amplitude with the size of a circle by taking the frequency in a vertical axis, the rotation speed in a horizontal axis, and the rotation order in a tilt axis. With the Campbell diagram, it is possible to visually confirm the rotation order, the rotation speed and the frequency of the portion where the vibration amplitude is large. As is apparent inFIGS. 3A, 3B, 4A, and 4B, the provision of the vibration-preventing members12makes it possible to significantly reduce the axial vibration and the radial vibration.

The use of the vibration-preventing members12produced by joining two rubber sheets12aand12bdiffering in hardness from each other makes it possible to effectively suppress or substantially suppress the vibration in the wide frequency band before and behind the audible frequency region. Moreover, the use of the insulative and flame-retardant vibration-preventing members12preferably enables the vibration-preventing members12to directly support the circuit board11. This makes it possible to obtain a remarkable vibration-preventing effect with a simple configuration.

While the present invention has been described on the basis of the above preferred embodiments, the aforementioned preferred embodiments are not limitative but may be modified in many different forms. For example, the motor applied to the centrifugal fan has been described in the aforementioned preferred embodiments. However, the motor can be applied to not only an axial flow fan but also to different kinds of motors in which a circuit board is supported by a stator unit in a similar manner as is the case in the aforementioned configuration.