US20060292015A1

US20060292015A1 - Bearing unit and motor and electric apparatus having bearing unit

Info

Publication number: US20060292015A1
Application number: US11/450,340
Authority: US
Inventors: Kenichiro Yazawa; Takeshi Kaneko; Hiroshi Sato; Yoshiaki Kakinuma
Original assignee: Sony Corp
Current assignee: Sony Corp
Priority date: 2005-06-24
Filing date: 2006-06-12
Publication date: 2006-12-28
Also published as: JP2007002949A; CN100434737C; CN1884863A

Abstract

A bearing unit, including: a shaft; a first radial bearing configured to support the shaft in a circumferential direction; a second radial bearing disposed in a spaced relationship from the first radial bearing in an axial direction of the shaft configured to support the shaft in the circumferential direction; a thrust bearing configured to support one end of the shaft in a thrust direction; a spacer disposed between the first and second radial bearings; a housing in which the first and second radial bearings and the thrust bearing are disposed and which has an enclosed structure except a shaft insertion hole in which the shaft is fitted; and viscous fluid filled in the housing.

Description

CROSS REFERENCES TO RELATED APPLICATIONS

The present invention contains subject matter related to Japanese Patent Application JP 2005-185601 with the Japanese Patent Office on Jun. 24, 2005, the entire contents of which being incorporated herein by reference.

BACKGROUND OF THE INVENTION

1. Field of the Invention
This invention relates to a bearing unit for supporting a rotary shaft for rotation or for supporting a rotatable member for rotation on a shaft, and a motor and an electronic apparatus which have a bearing unit.
2. Description of the Related Art
Such a bearing unit for supporting a rotary shaft for rotation as shown in FIG. 15 is known in the past.
Referring to FIG. 15, the bearing unit 100 shown is used to support a rotary shaft 101 for rotation thereon. The bearing unit 100 includes a radial bearing 104 for supporting the rotary shaft 101 in a circumferential direction, a thrust bearing 110 for supporting one end of the rotary shaft 101 in a thrust direction, and a housing 105 in which the radial bearing 104 and the thrust bearing 110 are accommodated.
In the bearing unit 100, the radial bearing 104 cooperates with lubricating oil as viscous fluid filled in the housing 105 to form a dynamic pressure fluid bearing. A dynamic pressure generating groove 111 for generating dynamic pressure is formed on an inner circumferential face of the radial bearing 104 in which the rotary shaft 101 is fitted.
The housing 105 in which the radial bearing 104 and the thrust bearing 110 are accommodated includes a tubular housing body 106, a bottom closing portion 107 and an upper closing member 108. The bottom closing portion 107 is formed integrally with the housing body 106 so as to close up one end side of the housing body 106, and forms one end side portion. The upper closing member 108 is provided on the other end side of the housing body 106 on which the housing body 106 is open.
A shaft fitting hole 109 is provided at a central portion of the upper closing member 108, and the rotary shaft 101 supported for rotation on the radial bearing 104 accommodated in the housing 105 is fitted in the shaft fitting hole 109. The thrust bearing 110 is provided on the inner face side of the bottom closing portion 107 of the housing body 106. A bearing supporting portion 102 provided at the one end portion in the thrust direction of the rotary shaft 101 supported on the radial bearing 104 is supported for rotation on the thrust bearing 110.
The thrust bearing 110 is formed as a pivot bearing which supports the bearing supporting portion 102 of the rotary shaft 101, which has an end formed in an arcuate or tapering shape, at a point.
The housing 105 having the configuration described above is formed by attaching the radial bearing 104, thrust bearing 110 and rotary shaft 101 to the housing body 106 and then bonding the upper closing member 108 to the housing body 106 by a sealing portion 121.
The rotary shaft 101 is supported at the bearing supporting portion 102 on one end side thereof by the thrust bearing 110 and at an outer circumferential face of a shaft portion body 103 thereof by the radial bearing 104. Further, the rotary shaft 101 is supported on the attaching portion 120 side provided on the other side thereof by the housing 105 such that the attaching portion 120 side thereof projects from the shaft fitting hole 109 provided in the upper closing member 108 of the housing 105.
Further, a groove 116 is provided on the rotary shaft 101 between the bearing supporting portion 102 and the shaft portion body 103. An annular washer 115 serving as a coming off preventing member is provided in an opposing relationship to the groove 116 on the bottom closing portion 107. The washer 115 prevents the rotary shaft 101 from coming off from the housing 105. When the washer 115 is pushed by the bearing supporting portion 102 of the rotary shaft 101, it is deformed in a thrust direction to allow the bearing supporting portion 102 to be inserted into and thus attached to the groove 116.
Incidentally, the shaft fitting hole 109 is formed with an inner diameter a little greater than the outer diameter of the shaft portion body 103 so that the rotary shaft 101 fitted in the shaft fitting hole 109 may rotate without slidably contacting with the inner circumferential face of the shaft fitting hole 109. At this time, the shaft fitting hole 109 is formed such that a gap 112 of a distance x sufficient to prevent lubricating oil 113 filled in the housing 105 from leaking from within the housing 105 is formed between the circumferential face of the shaft fitting hole 109 and the outer circumferential face of the shaft portion body 103.
A tapering portion 114 is provided on the outer circumferential face of the rotary shaft 101 in an opposing relationship to the inner circumferential face of the shaft fitting hole 109. The tapering portion 114 is inclined so that the gap 112 formed between the outer circumferential face of the rotary shaft 101 and the inner circumferential face of the shaft fitting hole 109 increases toward the outer side of the housing 105. The tapering portion 114 forms a pressure gradient in the gap 112 formed between the outer circumferential face of the rotary shaft 101 and the inner circumferential face of the shaft fitting hole 109 to generate force which acts to draw the lubricating oil 113 filled in the housing 105 into the inside of the housing 105. Since, upon rotation of the rotary shaft 101, the lubricating oil 113 is biased so as to be drawn into the inside of the housing 105, the lubricating oil 113 enters the dynamic pressure generating groove 111 of the radial bearing 104 formed from a dynamic pressure fluid bearing with certainty to generate a dynamic pressure. Consequently, stabilized support of the rotary shaft 101 is implemented and besides leakage of the lubricating oil 113 filled in the housing 105 can be prevented.
In the bearing unit 100 having the configuration described hereinabove with reference to FIG. 15, the rotary shaft 101 is exposed at just one end thereof on the shaft fitting hole 109 side but is covered with the housing member except a small gap of the shaft fitting hole 109. Therefore, the bearing unit 100 can prevent leakage of the lubricating oil 113 to the outside of the housing 105. Further, since just the gap of the shaft fitting hole 109 forms a communicating portion to the outside, scattering of the lubricating oil which may be caused by an impact can be prevented thereby to retain the lubricating oil with certainty. Further, in the bearing unit 100, the rotary shaft 101 can be prevented from coming off from the housing 105 by the washer 115.
In short, since the bearing unit 100 can retain the lubricating oil 113 with certainty and prevent coming off of the rotary shaft 101, it can maintain the lubricating performance and the rotational performance to support the rotary shaft for rotation or support a rotary member for rotation on a shaft.
For such a bearing unit as described above, it is demanded to further reduce deflection and so forth of a rotary shaft to enhance the rotational performance. In order to reduce deflection and so forth of a rotary shaft to enhance the rotational performance, it is necessary to raise the rigidity. To raise the rigidity of a bearing unit can be implemented, for example, by increasing the length in an axial direction of a radial bearing which forms the bearing unit.
However, in the bearing unit 100 described above, the radial bearing which forms the bearing unit 100 is formed from a sintered member or the like, and there is a limitation to casting of the bearing unit 100 from a relationship between the diameter and the length in the axial direction. In this manner, the bearing unit has a limitation to increase of the rigidity and it is difficult to reduce deflection and so forth of a rotary member exceeding a predetermined condition.
A bearing unit similar to the bearing unit 100 described hereinabove with reference to FIG. 15 is disclosed in Japanese Patent Laid-open No. 2003-130043

SUMMARY OF THE INVENTION

There is a need for the present invention to provide a bearing unit and a motor and an electronic apparatus including a bearing unit by which the rigidity of a shaft can be raised to suppress deflection of the shaft and lubricating oil can be retained with certainty.
In order to attain the need described above, according to an embodiment of the present invention, there is provided a bearing unit including a shaft, a first radial bearing configured to support the shaft in a circumferential direction, a second radial bearing disposed in a spaced relationship from the first radial bearing in an axial direction of the shaft configured to support the shaft in the circumferential direction. Furthermore, a thrust bearing configured to support one end of the shaft in a thrust direction, a spacer disposed between the first and second radial bearings, a housing in which the first and second radial bearings and the thrust bearing are disposed and which has an enclosed structure except a shaft insertion hole in which the shaft is fitted, and viscous fluid filled in the housing.
According to another embodiment of the present invention, there is provided a motor including a stator, a rotor, and a bearing unit configured to support the rotor for rotation with respect to the stator, and for the bearing unit, the bearing unit of the first embodiment described above is used.
According to a further embodiment of the present invention, there is provided an electronic apparatus including a motor which includes a stator, a rotor, and a bearing unit configured to support the rotor for rotation with respect to the stator, and for the bearing unit, the bearing unit of the first embodiment described above is used.
With the bearing unit, motor and electronic apparatus, the rigidity of the shaft can be raised to reduce the deflection of the shaft, and the lubricating oil can be retained with certainty. Consequently, a good lubricating performance and a good rotational performance can be achieved.
The above and other objects, features and advantages of the present invention will become apparent from the following description and the appended claims, taken in conjunction with the accompanying drawings in which like parts or elements denoted by like reference symbols.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of an information processing apparatus to which the present invention is applied;
FIG. 2 is a sectional view taken along line A-A of FIG. 1;
FIG. 3 is a perspective view showing a heat radiation apparatus which uses a motor to which the present invention is applied;
FIG. 4 is a sectional view showing a configuration of the motor shown in FIG. 3;
FIG. 5 is a sectional view showing a bearing unit to which the present invention is applied;
FIG. 6 is a perspective view showing a dynamic pressure generating groove formed on an inner circumferential face of a radial bearing shown in FIG. 5;
FIG. 7 is a horizontal sectional view showing a spacer which is a component of the bearing unit of FIG. 5;
FIG. 8 is a horizontal sectional view showing another spacer which is a component of the bearing unit of FIG. 5;
FIG. 9 is a horizontal sectional view showing a further spacer which is a component of the bearing unit of FIG. 5;
FIG. 10 is a sectional view of an oil seal portion of the bearing unit of FIG. 5;
FIG. 11 is a sectional view showing a bearing unit of a comparative example for comparison with the bearing unit of FIG. 5;
FIG. 12 is a sectional view illustrating different variations of the volume variation amount and the liquid level of lubricating oil when the temperature of the bearing unit of FIG. 5 rises;
FIG. 13 is a sectional view illustrating different variations of the volume variation amount and the liquid level of lubricating oil when the temperature of the bearing unit of FIG. 5 drops;
FIG. 14 is a sectional view showing a maximum space volume of the oil seal portion of the bearing unit of FIG. 5; and
FIG. 15 is a sectional view showing a bearing unit in the related art.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

In the following, an information processing apparatus to which the present invention is applied is described.
Referring to FIG. 1, the information processing apparatus to which the present invention is applied is a personal computer of the notebook type. The computer 1 includes a display section 2 for displaying a result of an information process and so forth, and a computer body 3 including a built-in information processing section which performs an arithmetic operation process of various kinds of information. A keyboard 5 is provided on the upper face side of the computer body 3 for inputting an operation instruction of the computer 1 or inputting various kinds of information therefrom. The computer body 3 has a heat radiation apparatus 4 provided in the inside thereof. The heat radiation apparatus 4 has a cooling apparatus for radiating heat generated from an information processing circuit such as a CPU, a disk apparatus and so forth disposed in the computer body 3 to cool the inside of the computer body 3.
The heat radiation apparatus 4 built in the computer body 3 is accommodated in a housing 6 which forms the computer body 3 as shown in FIG. 2. Referring to FIG. 3, the heat radiation apparatus 4 includes a base 7 made of a metal material, a motor 10 attached to the base 7, a fan 8 for being driven to rotate by the motor 10, a fan case 9 accommodated in the fan 8, and a heat sink 11.
The base 7 is formed in a substantially L shape as shown in FIG. 3. A heat generating element 12 is attached to a face 7 a on one end side of the base 7 formed in a substantially L shape. The heat generating element 12 generates heat when it is energized like a central processing unit (CPU). The heat generating element 12 is attached to the face 7 a of the base 7 through a heat transmitting seal 12 a.
The motor 10 and the fan case 9 in which the fan 8 for being driven to rotate by the motor 10 is accommodated are attached to a substantially central portion of the face 7 a of the base 7. A circular intake port 13 is formed in the fan case 9 such that it opens the position corresponding to a central portion of the fan 8 which is driven to rotate by the motor 10. An opening 14 is provided at a position of the bottom face side of the housing 6 opposing to the intake port 13 provided in the fan case 9 such that it is communicated with the intake port 13. Further, an exhaust port 15 for exhausting air taken in through the intake port 13 to the outside is provided in the fan case 9.
The heat sink 11 is secured to the face 7 a of the base 7 on the other end side. The heat sink 11 is a corrugate-shaped or fin-shaped heat sink and is made of a metal material which is superior in heat radiating property such as, for example, aluminum. Also the base 7 and the fan case 9 are preferably made of aluminum or iron which is a metal which is superior in heat radiating property.
On the base 7 to which the heat generating element 12 is attached and also the heat radiation apparatus 4 and the heat sink 11 which radiate heat generated from the heat generating element 12 are attached, a plurality of mounting holes 7 b into which screws which are used to attach the base 7 in the housing 6 are to be inserted are provided. The base 7 is attached in the housing 6 by securing screws for fixation, which are inserted in the mounting holes 7 b, to bosses 16 provided in the inside of the housing 6 as shown in FIG. 2.
The heat sink 11 is disposed at a position at which it is opposed to a through-hole 17 formed in a side wall of the housing 6 as seen in FIGS. 2 and 3 when the base 7 is attached in the housing 6.
The heat radiation apparatus 4 configured in such a manner as described hereinabove takes in, when the motor 10 is driven to rotate the fan 8 in the direction indicated by an arrow mark R1 in FIG. 3, the air outside the apparatus through the opening 14 formed in the housing 6 and further takes the air into the fan case 9 through the intake port 13. The air taken in the fan case 9 by rotation of the fan 8 flows in the direction indicated by an arrow mark D2 in FIGS. 2 and 3 and further flows in the direction indicated by another arrow mark D3 in FIG. 3 so as to flow through the heat sink 11. Then, the air is exhausted to the outside of the housing 6 through the through-hole 17.
Incidentally, the heat generated when the heat generating element 12 attached to the base 7 is driven is transmitted to the heat sink 11 attached to the base 7 through the base 7 formed from a metal material having a superior heat radiating property. At this time, air taken in from the outside of the housing 6 by the fan 8 of the heat radiation apparatus 4 rotated by the motor 10 flows along and between the fins of the heat sink 11 and radiates the heat transmitted to the heat sink 11 to the outside of the housing 6 through the through-hole 17.
Referring now to FIG. 4, the motor 10 which is used in the heat radiating apparatus and to which the present invention is applied includes a rotor 18 and a stator 19.
The stator 19 is provided integrally on the top plate 9 a side of the fan case 9 in which the fan 8 rotated by the motor 10 is accommodated together with the motor 10. The stator 19 includes a stator yoke 20, a bearing unit 30 to which the present invention is applied, a coil 21, and a core 22 on which the coil 21 is wound. The stator yoke 20 may be of the type which is formed integrally with the top plate 9 a of the fan case 9, that is, may be formed from part of the fan case 9, or may alternatively be formed as a separate member from the fan case 9. The stator yoke 20 is formed, for example, from iron. The bearing unit 30 is secured by force fitting or adhesion or by force fitting and adhesion in a holder 23 formed in a cylindrical shape at a central portion of the stator yoke 20.
It is to be noted that the holder 23 in which the bearing unit 30 is force fitted is formed in a cylindrical shape integrally with the stator yoke 20.
The core 22 on which the coil 21 to which driving current is supplied is wound is attached to an outer peripheral portion of the holder 23 formed integrally on the stator yoke 20 as seen in FIG. 4.
The rotor 18 which cooperates with the stator 19 to form the motor 10 is attached to a rotary shaft 31 supported for rotation on the bearing unit 30 such that it rotates integrally with the rotary shaft 31. The rotor 18 includes a rotor yoke 24, and the fan 8 which rotates integrally with the rotor yoke 24 and has a plurality of blades 25. The blades 25 of the fan 8 are formed integrally with the rotor yoke 24 by outsert molding on an outer peripheral face of the rotor yoke 24.
A ring-shaped rotor magnet 26 is provided on an inner circumferential face of a cylindrical portion 24 a of the rotor yoke 24 in an opposing relationship to the coil 21 of the stator 19. The rotor magnet 26 is a plastic material having the S poles and the N poles magnetized alternately in a circumferential direction, and is secured to the inner peripheral face of the rotor yoke 24 by a bonding agent.
The rotor yoke 24 has a boss portion 27 provided at a central portion of a flat plate portion 24 b thereof and having a through-hole 27 a provided at a central portion thereof. The boss portion 27 is force fitted in a mounting portion 31 c provided on the free end side of the rotary shaft 31 supported on the bearing unit 30 to attach the rotor yoke 24 for integral rotation to the rotary shaft 31.
In the motor 10 having such a configuration as described above, driving current is supplied to the coil 21 on the stator 19 side in a predetermined energization pattern from a driving circuit section provided on the outside of the motor 10. When the driving current is supplied in this manner, the rotor 18 rotates integrally with the rotary shaft 31 by an action between a magnetic field generated by the coil 21 and a magnetic field from the rotor magnet 26 of the rotor 18 side. As the rotor 18 rotates, also the fan 8 attached to the rotor 18 and having the blades 25 rotates integrally with the rotor 18. As the fan 8 rotates, air outside the apparatus is taken in the direction indicated by the arrow mark D1 in FIGS. 2 and 3 through the opening 14 formed in the housing 6 and flows in the direction indicated by the arrow mark D2. Then, the air flows in the heat sink 11 and is exhausted to the outside of the housing 6 through the through-hole 17, whereupon the air radiates heat generated by the heat generating element 12 to the outside of the computer body 3 thereby to cool the inside of the computer body 3.
Referring to FIGS. 4 and 5, the bearing unit 30 on which the rotary shaft 31 of the motor 10 described above supported for rotation includes a rotary shaft 31 is disposed a first radial bearing 32 for supporting the rotary shaft 31 in a circumferential direction, and a second radial bearing 33 disposed in a spaced relationship from the first radial bearing 32 in an axial direction for supporting the rotary shaft 31 in a circumferential direction. The bearing unit 30 further includes a thrust bearing 34 for supporting one end of the rotary shaft 31 in a thrust direction, a spacer 35 disposed between the first radial bearing 32 and the second radial bearing 33, a housing 37, and lubricating oil 38 as viscous fluid fitted in the housing 37. The housing 37 accommodates the first radial bearing 32, spacer 35, second radial bearing 33 and thrust bearing 34 in the inside thereof and has a closed structure except a shaft fitting hole 45 in which the rotary shaft 31 is fitted.
The spacer 35 is formed so that the variation of the liquid level of the lubricating oil 38 filled in the housing 37 when the volume lubricating oil 38 is expanded or contracted by a temperature variation remains within a range within which the shaft fitting hole 45 of the housing 37 is formed.
Referring to FIG. 5, the rotary shaft 31 includes a shaft portion body 31 a supported at an outer circumferential face thereof by the first and second radial bearings 32 and 33 and a bearing supported portion 31 b formed in an arcuate or tapering shape on one end side of the shaft portion body 31 a and supported by the thrust bearing 34. The rotary shaft 31 further includes a mounting portion 31 c provided on the other end side of the shaft portion body 31 a and having a rotary member such as, for example, the rotor 18 of the motor 10, attached thereto. The rotary shaft 31 further includes a groove 31 d provided between the bearing supported portion 31 b and the shaft portion body 31 a for preventing coming off of the rotary shaft 31. The rotary shaft 31 is supported at the bearing supported portion 31 b thereof by the thrust bearing 34, at an outer circumferential face of the shaft portion body 31 a thereof by the first and second radial bearings 32 and 33, and at the mounting portion 31 c thereof, which projects from the shaft fitting hole 45, by the housing 37. Further, a washer 51 serving as a shaft coming off preventing member is provided at a position of the rotary shaft 31 corresponding to the groove 31 d.
The first and second radial bearings 32 and 33 are each formed in a cylindrical shape from a sintered metal material and disposed in a spaced relationship from each other in the axial direction. The first and second radial bearings 32 and 33 cooperate with the lubricating oil 38 filled in the housing 37 to form a dynamic pressure fluid bearing, and first and second dynamic pressure generating grooves 39 and 40 are formed on inner circumferential faces of the first and second radial bearings 32 and 33 through which the rotary shaft 31 is fitted, respectively.
Referring to FIG. 6, each of the first and second dynamic pressure generating grooves 39 and 40 is formed such that a pair of V-shaped grooves 39 a or 40 a successively appear in a circumferential direction on the inner face of the first radial bearing 32 or 33. Each of the first and second dynamic pressure generating grooves 39 and 40 is formed such that one end side of the pair of V-shaped grooves 39 a or 40 a is directed in a direction R2 of rotation of the rotary shaft 31. Further, the first and second dynamic pressure generating grooves 39 and 40 are formed in pair in parallel to each other at upper and lower portions in the axial direction of the first and second radial bearings 32 and 33 which form a cylindrical shape. It is to be noted that, although the first and second dynamic pressure generating grooves 39 and 40 are provided on the first and second radial bearings 32 and 33, respectively, such that they make a pair in parallel to each other, the manner of provision of dynamic pressure generating grooves is not limited to this. For example, a pair of dynamic pressure generating grooves may be provided in parallel to each other at upper and lower locations in the axial direction on each of the first and second radial bearings 32 and 33 such that totaling two pairs of dynamic pressure generating grooves are provided. In other words, the number and the size of the dynamic pressure generating grooves to be provided on the first and second radial bearings 32 and 33 are suitably selected depending upon the size, length and so forth of the first and second radial bearings 32 and 33. It is to be noted that the firsthand second radial bearings 32 and 33 may otherwise be formed from brass, stainless steel or a high molecular material.
In the first and second radial bearings 32 and 33 formed as a dynamic pressure fluid bearing, when the rotary shaft 31 fitted in the first and second radial bearings 32 and 33 continuously rotates in the direction indicated by the arrow mark R2 in FIG. 6 around the center axis CL, the lubricating oil 38 filled in the housing 37 flows in the first and second dynamic pressure generating grooves 39 and 40. Thereupon, the lubricating oil 38 generates a dynamic pressure between the outer circumferential face of the rotary shaft 31 and the inner circumferential face of the first and second radial bearings 32 and 33 and supports the rotating rotary shaft 31. The dynamic pressure generated in this instance decreases the coefficient of friction between the rotary shaft 31 and the first and second radial bearings 32 and 33 to a very low level thereby to achieve smooth rotation of the rotary shaft 31.
Since the first and second radial bearings 32 and 33 are disposed in a spaced relationship from each other in the axial direction, if the distance between the first and second radial bearings 32 and 33 is increased, then the rigidity of the rotary shaft 31 can be raised. As a result, deflection of the rotary shaft 31 can be suppressed and the rotational performance can be enhanced.
The thrust bearing 34 is formed as a pivot bearing which supports the bearing supported portion 31 b of the rotary shaft 31, which is formed in an arcuate or tapering shape, at a point.
Referring to FIGS. 5 and 7, the spacer 35 is formed in a substantially cylindrical shape and disposed between the first and second radial bearings 32 and 33. The spacer 35 is formed with an outer diameter with which it can be accommodated in the housing 37 with an outer periphery thereof contacting with the housing 37. Further, the spacer 35 is formed with an inner diameter which is a little greater than the outer diameter of the rotary shaft 31 and with which it does not contact with the rotary shaft 31, that is, with which a predetermined gap is left between the spacer 35 and the rotary shaft 31. The predetermined gap between the inner circumferential face of the spacer 35 and the outer circumferential face of the rotary shaft 31 functions as a communicating path for establishing communication between a region in which the first radial bearing 32 is provided and another region in which the second radial bearing 33 is provided as hereinafter described. Further, a plurality of flow paths 49 for the lubricating oil 38 are formed on a portion of the spacer 35 on the housing 37 side, that is, on the outer circumferential face of the spacer 35 as shown in FIG. 7. The flow paths 49 are formed along the axial direction of the rotary shaft 31 on the outer circumferential face of the spacer 35 and have a shape which is cut in a substantially semicircular shape, that is, in a D-cut shape, along a cross section perpendicular to the rotary shaft 31. Thus, the flow paths 49 serve as communicating paths for establishing communication between the region in which the first radial bearing 32 is provided and the region in which the second radial bearing 33 is provided. The flow paths 49 are provided at six locations spaced equally from each other on the outer circumferential face of the spacer 35 on the cross section perpendicular to the rotary shaft 31.
The flow paths 49 cooperate with the predetermined gap between the inner circumferential face of the spacer 35 and the outer circumferential face of the rotary shaft 31 to allow the lubricating oil 38 to flow well into the first and second dynamic pressure generating grooves 39 and 40 of the first and second radial bearings 32 and 33. In other words, the flow paths 49 and the gap described hereinabove can suppress floating of the rotary shaft 31 by allowing flows of the lubricating oil 38 in an appropriate direction to be produced between the first and second dynamic pressure generating grooves 39 and 40 and the rotary shaft 31.
The spacer 35 is formed with such a size that, when the volume of the lubricating oil 38 enclosed in the bearing unit 30 which has the dynamic pressure fluid bearing increases or decreases as a result of a temperature variation, the variation of the volume remains within a space defined by the oil seal section formed at an upper portion of the bearing unit 30 and the rotary shaft 31, that is, within the shaft fitting hole 45. Then, the spacer 35 formed in a dimension adaptable to the expansion and contraction of the lubricating oil 38 by a temperature variation can prevent air from entering the lubricating oil 38 and prevent the lubricating oil 38 from leaking out to the outside of the housing.
In particular, the spacer 35 can reduce the volume of the lubricating oil 38 to be filled in the bearing unit 30 as hereinafter described, and the lubricating oil 38 can be retained with certainty by reducing the variation amount of the volume of the lubricating oil 38 with respect to the temperature variation.
It is to be noted that the spacer which forms the bearing unit 30 is not limited to the spacer 35 formed in such a manner as described above. In particular, any element may be used as the spacer if it is disposed between the first and second radial bearings 32 and 33 and decreases the volume of the lubricating oil 38 filled in the bearing unit 30.
For example, the spacer which forms the bearing unit 30 may be a spacer 35 a formed in a cylindrical shape and having a substantially hexagonal cross section as shown in FIG. 8. The spacer 35 a having a substantially hexagonal cross section is disposed between the first and second radial bearings 32 and 33 similarly to the spacer 35. The spacer 35 a has an outer peripheral face formed with a size with which it can be accommodated in the housing 37 and has an inner diameter a little greater than the outer diameter of the rotary shaft 31 while it does not contact with the rotary shaft 31. In other words, the spacer 35 a is formed with a predetermined gap left from the rotary shaft 31. The spacer 35 a cooperates with the inner circumferential face of the housing 37 to form a plurality of flow paths 49 a for the lubricating oil 38. The flow paths 49 a serve as communicating paths for establishing communication between the region in which the first radial bearing 32 is provided and the region in which the second radial bearing 33 is provided.
Further, the spacer which forms the bearing unit 30 may be a spacer 35 b which has such a substantially cylindrical shape as shown in FIG. 9 and has a plurality of through-holes formed in the axial direction. The spacer 35 b having the through-holes formed therein is disposed between the first and second radial bearings 32 and 33 similarly to the spacer 35. The spacer 35 b has an outer diameter having a size with which it can be accommodated in and contact with the housing 37 and has an inner diameter a little greater than the outer diameter of the rotary shaft 31 while it does not contact with the rotary shaft 31. In other words, the spacer 35 b is formed with a predetermined gap left from the rotary shaft 31. The through-holes formed in the spacer 35 b serves as communicating paths 49 b in which the lubricating oil 38 flows. The flow paths 49 b are formed as through-holes which extend in the axial direction and are formed substantially on a circle in an equally spaced relationship from each other at a predetermined position in the thicknesswise direction of the spacer 35 b on a cross section perpendicular to the rotary shaft 31. The flow paths 49 b serve as communicating paths for establishing communication between the region in which the first radial bearing 32 is provided and the region in which the second radial bearing 33 is provided.
Each of the flow paths 49 a and 49 b formed in the spacers 35 a and 35 b, respectively, cooperates with the predetermined gap between the inner circumferential face of the spacer 35 a or 35 b and the outer circumferential face of the rotary shaft 31 to allow the lubricating oil 38 to circulate well into the first and second dynamic pressure generating grooves 39 or 40 of the first radial bearing 32 or second radial bearing 33. In other words, the flow paths 49 a and 49 b and the gap described hereinabove can suppress floating of the rotary shaft 31 by allowing flows of the lubricating oil 38 in an appropriate direction to be produced between the first and second dynamic pressure generating grooves 39 and 40 and the rotary shaft 31.
Referring back to FIG. 5, the housing 37 includes a housing body 42, a bottom closing portion 43, and an upper closing portion 44. The housing 37 has such a shape that it accommodates and surrounds the first and second radial bearings 32 and 33 each formed in a cylindrical shape and disposed in a spaced relationship from each other in the axial direction. The housing body 42 is disposed on the outer side of the first and second radial bearings 32 and 33. The bottom closing portion 43 closes up a lower opening on one side of the housing body 42. The upper closing portion 44 closes up an upper opening formed on the opposite side to the lower opening of the housing body 42. The housing body 42 has a tubular shape and is formed from a metal material. Further, the upper closing portion 44 and the bottom closing portion 43 are formed from a metal material similarly to the housing body 42.
The shaft fitting hole 45 is provided at a central portion of the upper closing portion 44. The rotary shaft 31 supported for rotation by the first and second radial bearings 32 and 33 accommodated in the housing 37 is fitted in the shaft fitting hole 45.
The thrust bearing 34 is disposed at a central portion on the inner face side of the bottom closing portion 43. The bearing supported portion 31 b is provided at one end portion in a thrust direction of the rotary shaft 31 supported on the first and second radial bearings 32 and 33 and is supported for rotation by the thrust bearing 34.
The housing 37 having the configuration described hereinabove is formed from the housing body 42 in which the first and second radial bearings 32 and 33 and the spacer 35 are accommodated, and the upper closing portion 44 and a bottom closing portion 43. The housing body 42, upper closing portion 44 and bottom closing portion 43 are integrated with each other by sealing portions 46 formed by laser welding to join the upper closing portion 44 and the bottom closing portion 43 together. The housing 37 has an enclosed structure except the shaft fitting hole 45 by sealing the joined portions from the outside with the sealing portions 46.
It is to be noted that, while the housing body 42, upper closing portion 44 and bottom closing portion 43 are formed from a metal material, they may otherwise be formed from a synthetic resin material and integrated with each other by welding. Where, for example, a synthetic resin material having a superior lubricating property is used as the material for the housing 37, a comparatively great contact angle can be achieved. As a result, since leakage of the lubricating oil 38 under centrifugal force is suppressed, the heightwise dimension of the shaft fitting hole 45 can be reduced.
Incidentally, the shaft fitting hole 45 of the housing 37 is formed with an inner diameter a little greater than the outer diameter of a fitted portion 31 e of the rotary shaft 31, which is a portion fitted in the shaft fitting hole 45, so that the fitted portion 31 e may rotate without slidably contacting with the inner circumferential face of the shaft fitting hole 45. At this time, the shaft fitting hole 45 is formed such that a gap 47 of a distance c sufficient for the lubricating oil 38 filled in the housing 37 to be prevented from leaking from the inside of the housing 37 is provided between the inner circumferential face of the shaft fitting hole 45 and the outer circumferential face of the fitted portion 31 e of the rotary shaft 31. The upper closing portion 44 in which the shaft fitting hole 45 is formed so that the gap 47 which prevents leakage of the lubricating oil 38 filled in the housing 37 is formed between the shaft fitting hole 45 and the rotary shaft 31 in this manner forms an oil seal section.
Further, a tapering portion 48 is provided on the outer circumferential face of the rotary shaft 31 which opposes to the inner circumferential face of the shaft fitting hole 45. The tapering portion 48 is inclined such that the gap 47 formed between the outer circumferential face of the rotary shaft 31 and the inner circumferential face of the shaft fitting hole 45 increases toward the outside of the housing 37. The tapering portion 48 forms a pressure gradient in the gap 47 formed by the outer circumferential face of the rotary shaft 31 and the inner circumferential face of the shaft fitting hole 45 so that force to draw the lubricating oil 38 filled in the housing 37 into the insider of the housing 37 is generated. Since the lubricating oil 38 tends to be drawn into the inside of the housing 37 upon rotation of the housing 37, the lubricating oil 38 enters with certainty into the first and second dynamic pressure generating grooves 39 and 40 of the first and second radial bearings 32 and 33 formed as a dynamic pressure fluid bearing and generates a dynamic pressure. Consequently, stabilized support of the rotary shaft 31 is implemented, and besides, leakage of the lubricating oil 38 filled in the housing 37 can be prevented.
The lubricating oil 38 is filled such that it is opposed from the inside of the housing 37 to the gap 47 which is formed by the tapering portion 48 formed on the rotary shaft 31 and the inner circumferential face of the shaft fitting hole 45. In particular, the lubricating oil 38 is filled into the gap in the housing 37 and further impregnated into the first and second radial bearings 32 and 33 made of a sintered metal. The lubricating oil 38 enters the first and second dynamic pressure generating grooves 39 and 40 provided on the first and second radial bearings 32 and 33 which form a dynamic pressure fluid bearing to generate a dynamic pressure.
In order to fabricate the bearing unit 30 configured in such a manner as described above, the first radial bearing 32 is attached to the housing body 42 first, and then the spacer 35 is attached, whereafter the second radial bearing 33 is attached. Then, the washer 51 and the thrust bearing 34 are attached to the bottom closing portion 43, and then the housing body 42 described above is attached to the bottom closing portion 43, whereafter the upper closing portion 44 is attached. Then, at a location between the housing body 42 and the upper closing portion 44 and another location between the housing body 42 and the bottom closing portion 43, sealing portions 46 are formed by laser welding to integrate the housing 37. Then, the rotary shaft 31 is inserted into the housing 37 integrated in this manner.
In the bearing unit 30, the tapering portion 48 is provided which is inclined such that the distance c of the gap 47 formed between the outer circumferential face of the rotary shaft 31 and the inner circumferential face of the shaft fitting hole 45 increases toward the outside of the housing 37. Therefore, a pressure gradient is formed in the distance c of the gap 47 formed by the outer circumferential face of the rotary shaft 31 and the inner circumferential face of the shaft fitting hole 45, and force which tends to draw the lubricating oil 38 filled in the housing 37 into the inside of the housing 37 is generated. In other words, in the bearing unit 30, the gap 47 formed between the outer circumferential face of the rotary shaft 31 and the inner circumferential face of the shaft fitting hole 45 prevents the lubricating oil 38 from being scattered by the surface tension seal.
In the bearing unit 30 having the configuration described above, since it has the configuration that the first and second radial bearings 32 and 33 are disposed in a spaced relationship from each other in the axial direction, the rigidity of the rotary shaft 31 can be raised thereby to reduce the deflection of the rotary shaft 31 by assuring a great distance between the first and second radial bearings 32 and 33. In other words, the bearing unit 30 to which the present invention is applied can raise the rigidity higher than a rigidity which has been a limit from a relationship of formation of a radial bearing, and implements enhancement of the rotational performance in the past.
Further, in the bearing unit 30 to which the present invention is applied, the spacer 35 is disposed between the first and second radial bearings 32 and 33. Therefore, the overall volume of the lubricating oil 38 increases by an amount of the space between the first and second radial bearings 32 and 33 which has a bad influence when the first and second radial bearings 32 and 33 are disposed in a spaced relationship from each other in the axial direction. Consequently, a problem of variation of the liquid level by a temperature variation and like problems can be prevented.
Here, it is described in detail that the problem of a temperature variation can be prevented by the provision of the spacer 35. In order to make a comparison with the above-described bearing unit 30 to which the present invention is applied, description is given of a bearing unit 60 of a comparative example which does not include a spacer. It is to be noted that, in the description of the bearing unit 60 of the comparative example, like elements to those of the bearing unit 30 described hereinabove are denoted by like reference characters, and overlapping description of them is omitted herein to avoid redundancy.
Referring to FIG. 11, the bearing unit 60 includes a rotary shaft 31, a first radial bearing 32 for supporting the rotary shaft 31 in a circumferential direction, and a second radial bearing 33 disposed in a spaced relationship from the first radial bearing 32 in an axial direction for supporting the rotary shaft 31 in a circumferential direction. The bearing unit 60 further includes a thrust bearing 34 for supporting one end of the rotary shaft 31 in a thrust direction, a housing 37 which accommodates the first radial bearing 32, second radial bearing 33 and thrust bearing 34 therein, and lubricating oil 68 as viscous fluid filled in the housing 37.
The lubricating oil 68 is filled in the gap in the housing 37 such that it is opposed to the gap 47 formed by the tapering portion 48 and the inner circumferential face of the shaft fitting hole 45 similarly to the lubricating oil 38 described hereinabove.
Then, where the volume of the lubricating oil 38 or 68 of the oil seal section is represented as oil seal section volume Vb and the volume of the lubricating oil 38 or 68 filled in the housing 37 other than the oil seal section is represented as seal lower portion volume Va, the overall volume of the lubricating oil 38 or lubricating oil 68 filled in the bearing unit 30 or 60 at a room temperature is represented by V which is the sum total of the oil seal section volume Vb and the seal lower portion volume Va as given by the following expression (1):
V=Va+Vb (1)
Here, when the temperature varies by ΔT° C., the volume of the lubricating oil 38 or 68 varies by a volume variation amount ΔV represented by the following expression (2): $\begin{matrix} \begin{matrix} Δ V = (1 + αΔ T) \cdot V - V \\ = αΔ T \cdot V \end{matrix} & (2) \end{matrix}$
where α is the volume expansion coefficient of the lubricating oil. It is to be noted that FIG. 12 illustrates a relationship between the volume variation amount ΔV and the liquid level of the lubricating oil 38 or 68. In FIG. 12, reference character SN denotes the liquid level of the lubricating oil at a room temperature, and SH denotes the liquid level of the lubricating oil when the temperature rises by ΔT° C. Meanwhile, FIG. 13 illustrates a relationship between the volume variation amount ΔV and the liquid level of the lubricating oil 38 or 68 when the temperature drops by ΔT° C. In FIG. 13, reference character SN denotes the liquid level of the lubricating oil at a room temperature, and SL denotes the liquid level of the lubricating oil when the temperature droops by ΔT° C.
Then, where the maximum space volume of the oil seal section is represented by Vc, it is necessary to set the maximum space volume Vc so as to satisfy the following expression (3):
Vc−Vb>ΔV (3)
The reason is that, if the expression (3) is not satisfied, then when the temperature is high, that is, when the temperature rises by ΔT° C., the lubricating oil 38 or 68 leaks out from the seal section, that is, the bearing unit 30 or 60.
On the other hand, it is necessary to set the oil seal section volume Vb so as to satisfy the following expression (4):
Vb>ΔV (4)
The reason is that, if the expression (4) is not satisfied, then when the temperature is low, that is, when the temperature drops by ΔT° C., the lubricating oil 38 or 68 is excluded from the lubricating oil 38 or 68 and air is mixed into the inside of the bearing unit from the outside.
In order for the expressions (3) and (4) given above to be satisfied to obtain an appropriate liquid level of the lubricating oil 38 or 68 when the temperature varies, it is necessary to make the maximum space volume Vc of the oil seal section great and/or to make the voltage variation amount ΔV small.
In order to make the maximum space volume Vc great, it is necessary to expand the shaft fitting hole 45 and the distance c of the rotary shaft 31 and/or to make the height t of the shaft fitting hole 45 high. However, if the distance c is expanded, then when an impact applies, a problem that the lubricating oil is likely to be scattered occurs, and if the height t of the shaft fitting hole 45 is made high, then another problem that the heightwise dimension of the entire bearing unit becomes great occurs.
With the bearing unit 30 to which the present; invention is applied, the overall volume V of the lubricating oil at a room temperature is smaller by an amount equal to the volume of the spacer 35 than that of the bearing unit 60 of the comparative example described hereinabove. Therefore, the volume variation amount ΔV can be reduced, and such problems as described above can be eliminated.
In particular, the bearing unit 30 to which the present invention is applied includes the spacer 35 formed with a size which can absorb expansion and contraction of the lubricating oil 38 caused by a temperature variation. Therefore, when the temperature of the lubricating oil 38 varies, the variation of the liquid level of the lubricating oil 38 can be restricted within the range within which the shaft fitting hole 45 is formed. Consequently, mixture of air into the lubricating oil 38 and leakage of the lubricating oil 38 to the outside of the housing can be prevented.
In other words, since the bearing unit 30 to which the present invention is applied includes the spacer 35 disposed between the first and second radial bearings 32 and 33, the volume variation amount ΔV of the lubricating oil 38 by temperature variation can be reduced. Therefore, leakage of the lubricating oil 38 to the outside of the bearing unit 30 when the temperature rises can be prevented, and mixture of air into the lubricating oil 38 by a drop of the liquid level of the lubricating oil 38 from the oil seal section when the temperature drops can be prevented. Consequently, such problems of deterioration of the rotational performance, lubricating performance and so forth by leakage of the lubricating oil and mixture of air into the lubricating oil can be prevented. In other words, the bearing unit 30 to which the present invention is applied makes it possible for the lubricating oil 38 to be retained with certainty in the unit.
Further, with the bearing unit 30 to which the present invention is applied, since the volume variation amount ΔV of the lubricating oil 38 by a temperature variation can be reduced, the dimension of the oil seal section in the axial direction, that is, the height t of the shaft fitting hole 45, can be suppressed to its minimum value. Consequently, the dimension of the bearing unit in the axial direction can be suppressed to a small dimension, and miniaturization of the apparatus can be achieved.
Consequently, with the bearing unit 30 to which the present invention is applied, since the rotary shaft 31 is formed with enhanced rigidity, it is possible to reduce the deflection of the rotary shaft 31 and retain the lubricating oil 38 with certainty thereby to obtain a good lubricating performance and a good rotational performance.
Further, with the bearing unit 30 to which the present invention is applied, since the flow paths 49 for the lubricating oil 38 are formed in the spacer 35 disposed between the first and second radial bearings 32 and 33, the oil is circulated readily in the inside of the dynamic pressure fluid bearing. Therefore, a flow of the lubricating oil 38 in an appropriate direction is produced between the first and second dynamic pressure generating grooves 39 and 40 of the first and second radial bearings 32 and 33 and the rotary shaft 31, and consequently, floating of the rotary shaft 31 can be suppressed. As a result, the bearing unit 30 to which the present invention is applied can prevent such a situation that, as a result of floating of the rotary shaft 31, the liquid level of the lubricating oil 38 drops and the air is mixed into the lubricating oil 38.
In this manner, the bearing unit 30 to which the present invention is applied can achieve a good lubricating performance and a good rotational performance, which enhance the universal use and the selectivity of the bearing unit and raise the degree of freedom in design of products which use the bearing unit.
Further, since the motor and the electronic apparatus to which the present invention is applied include the bearing unit 30 described above, they can achieve a good rotational performance with the reduced deflection and so forth of the rotary shaft 31 and with a good lubricating performance for a long period of time.
The bearing unit to which the present invention is applied can be applied not limited as a bearing for a motor of a heat radiating apparatus or a spindle motor of a disk drive, and also as a bearing for various motors.
Further, the bearing unit to which the present invention is applied can be used widely not limited for motors, and also for various mechanisms which include a rotary shaft and other mechanisms which support a part which rotates with respect to a shaft.
It should be understood by those skilled in the art that various modifications, combinations, sub-combinations and alterations may occur depending on design requirements and other factors insofar as they are within the scope of the appended claims or the equivalents thereof.

Claims

1. A bearing unit, comprising:

a shaft;

a first radial bearing configured to support said shaft in a circumferential direction;

a second radial bearing disposed in a spaced relationship from said first radial bearing in an axial direction of said shaft configured to support said shaft in the circumferential direction;

a thrust bearing configured to support one end of said shaft in a thrust direction;

a spacer disposed between said first and second radial bearings;

a housing in which said first and second radial bearings and said thrust bearing are disposed and which has an enclosed structure except a shaft insertion hole in which said shaft is fitted; and

viscous fluid filled in said housing.

2. The bearing unit according to claim 1, wherein:

said spacer is formed such that, when the volume of said viscous fluid filled in said housing is expanded or contracted by a temperature variation, the variation of the liquid level of said viscous fluid remains within a range within which said shaft insertion hole of said housing is formed.

3. The bearing unit according to claim 1, wherein:

said spacer has a flow path for said viscous fluid formed therein.

4. A motor, comprising:

a stator;

a rotor; and

a bearing unit configured to support

said rotator for rotation with respect to said stator;

said bearing unit including:

a shaft;

a spacer disposed between said first and second radial bearings;

viscous fluid filled in said housing.

5. An electronic apparatus, comprising:

a motor including a stator;

a rotor; and

a bearing unit configured to support said rotator for rotation with respect to said stator;

said bearing unit including:

a shaft;

a spacer disposed between said first and second radial bearings;

viscous fluid filled in said housing.