JP2002031142A - Bearing device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To realize a small size and a light weight with a structure capable of sufficiently ensuring a bearing rigidity. SOLUTION: A pair of outer rings 10a, 10a is engaged and fixed to a hub 4 in the state that axial inner end surfaces are abutted on each other. A pair of inner rings 8a, 8b is urged in an approaching direction to each other in the state that a gap is interposed between these inner rings 8a, 8a to impart a desired pre-load thereto and in this state, these inner rings 8a, 8a are engaged and fixed to a support shaft 3. The axial center of respective outer ring tracks 9, 9 provided on inner periphery surfaces of the respective outer rings 10a, 10a is deviated to a side at which the respective outer rings 10a, 10a are abutted on each other regarding the axial direction of the respective outer rings 10a, 10a. Respective retainers are made to a crown type retainer and main parts 17, 17 constituting the respective retainers 12, 12 are disposed near both axial ends of the bearing device 1a.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The bearing device according to the present invention comprises:
For example, a spindle motor incorporated in a magnetic, optical, or magneto-optical disk drive such as a hard disk drive (HDD), a flexible disk drive (FDD), a digital video disk (DVD), and a mini disk (MD), or a swing of the HDD. It is used by being incorporated into a swing support portion of an arm or a motor for an IC cooling fan.

[0002]

2. Description of the Related Art For example, an HDD used as a storage device of a computer rotates a hub around a support shaft fixed to a housing fixed to a frame or the like via a bearing device to which the present invention is applied. It is freely supported. One or more hard disks formed in a ring shape are connected to and supported on the inner peripheral edge of the hub, and rotate with the hub. Since the width of a track for recording data on the hard disk is extremely narrow, it is necessary to rotatably support the hub on the support shaft without causing a blur. For this reason, conventionally, as a bearing device provided between the outer peripheral surface of the support shaft and the inner peripheral surface of the hub, a pair of ball bearings is combined, and a preload is applied to each ball constituting each ball bearing. Those with sufficient bearing rigidity are widely used.

FIG. 7 shows an example of such a bearing device.
This shows the one described in Japanese Patent Application Laid-Open No. H10-155843. The bearing device 1 is incorporated in an HDD motor, and is provided on the outer peripheral surface of a distal end portion and an intermediate portion of a support shaft 3 having a base end portion fixed to a center portion of a housing 2 and an inner diameter side of a hub 4. A pair of ball bearings 6, 6 are provided between the inner diameter side cylindrical portion 5 and a part of the inner peripheral surface. That is, each of these ball bearings 6, 6 has an inner race 8 having an inner raceway 7 on the outer peripheral surface.
And an outer ring 10 having an outer ring track 9 on the inner peripheral surface, and balls 11, 11 provided in a plurality of rolls respectively between the inner ring track 7 and the outer ring track 9. Each of these balls 11,
11 is rotatably held by a retainer 12 formed in an annular shape. The inner rings 8, 8 are externally fitted and fixed to the front end portion and the intermediate portion of the support shaft 3 by tight fitting or bonding.

[0004] On the other hand, cylindrical projecting portions 13, 13 projecting in the axial direction from the axial end surfaces of the inner rings 8, 8 are formed at one axial end of the outer rings 10, 10, respectively. ing. Then, only the portions near the butting portions of the pair of outer rings 10 and 10 are internally fixed to the inner peripheral surface of the inner diameter side cylindrical portion 5 in a state where the tip surfaces of both the projecting portions 13 and 13 abut against each other. are doing. For this purpose, a plurality of ridges 14, 14 protruding toward the inner diameter side are formed on the entire inner circumference of the inner peripheral surface of the intermediate portion in the axial direction of the inner diameter side cylindrical portion 5. And each said protrusion part 13 and 13 is each said ridge 1
4 and 14, the inner fitting is fixed by tight fitting or bonding while being bridged.

In the bearing device 1 constructed as described above, each of the inner rings 8, 8 is pressed in a direction approaching each other with a gap 16 interposed between the axial end faces, and the respective balls are pressed. A desired preload is applied to 11,11. And
With the preload applied in this manner, the hub 4 is rotatably supported around the support shaft 3 without backlash.
A hard disk (not shown) is fixed around the outer diameter side cylindrical portion 15 provided on the outer diameter side of the hub 4 and concentrically with the outer diameter side cylindrical portion 15.

[0006]

In recent years, there has been an increasing demand for devices (such as HDD motors) incorporating a bearing device used in a state where a preload is applied, in order to reduce the size and weight. In order to meet this demand, it is necessary to reduce the size and weight of the bearing device. On the other hand, in the case of the conventional bearing device 1 shown in FIG. 7 described above, the inner races 7, 7 are provided at the axially central portions of the outer peripheral surfaces of the inner races 8, 8, and the inner races 7, 7 are formed. The outer ring raceways 9, 9 are provided at positions on the peripheral surface that are offset toward both axial ends of the bearing device 1. That is, the axial center of each of the outer raceways 9, 9 is offset in the axial direction of each of the outer races 10, 10 to the side opposite to the position where these outer races 10a, 10a abut each other. Therefore, in the case of the conventional bearing device 1 described above, the axial length (pitch) between the plurality of balls 11 and 11 rows constituting each of the ball bearings 6 and 6 is described.
Therefore, it is difficult to reduce the size and weight of the bearing device 1 and thus the device incorporating the bearing device 1. In view of such circumstances, the present invention has been made to reduce the size and weight of a bearing device that can secure sufficient rigidity by applying a preload.

[0007]

The bearing device of the present invention has a pair of outer rings having outer ring raceways on the respective inner peripheral surfaces and a pair of outer races having inner ring raceways on the respective outer peripheral surfaces, similarly to the above-mentioned conventional structure. A pair of inner rings, a plurality of balls each of which is provided so as to freely roll between each of the inner ring raceways and each of the outer ring raceways, and a ball disposed between an inner peripheral surface of each of the outer races and an outer peripheral surface of each of the inner races. And a pair of cages for rollingly holding the balls. Then, the pair of outer rings is internally fitted and fixed to the outer member in a state where the opposing axial end surfaces are abutted with each other, and a gap is formed between the opposing axial end surfaces. The balls are pressed in the direction in which they approach each other with the balls interposed therebetween, so that the balls are externally fitted and fixed to the inner member while a desired preload is applied to the balls.

[0008] In particular, in the bearing device of the present invention, the axial center of each of the outer raceways is offset toward the side where the outer races meet in the axial direction of the outer races. Each of the retainers is a crown type retainer having a plurality of elastic pieces provided on one surface in the axial direction of an annular main portion and having a pocket between a pair of elastic pieces adjacent in the circumferential direction. The main part is arranged near both ends in the axial direction of the bearing device. Further, the axial end faces of the outer ring and the inner ring, which are located on both axial sides of the bearing device, are provided at substantially the same position in the axial direction.

[0009]

In the bearing device of the present invention configured as described above, the overall length in the axial direction can be sufficiently reduced in a structure in which the bearing rigidity can be sufficiently secured by applying a preload. Therefore, according to the present invention, the size and weight of the bearing device can be reduced. Further, since the overall length in the axial direction can be sufficiently reduced in this manner, the difference in the coefficient of linear expansion between the materials constituting the outer member or the inner member and each outer ring or each inner ring is large, Even when the temperature between the outer ring and each inner ring is different, distortion due to the difference in the amount of thermal expansion at the fitting and fixing portion of each member can be reduced. Therefore, the amount of change in bearing stiffness during use can be made extremely small.

[0010]

1 to 4 show an example of an embodiment of the present invention. The bearing device 1a of the present invention has outer ring raceways 9, 9 on the respective inner peripheral surfaces thereof, and a pair of outer rings 10a, each of which can be internally fitted and fixed to the hub 4 as an outer member.
10a, and inner ring raceways 7, 7 on the respective outer peripheral surfaces,
A pair of inner races 8a, 8a, each of which can be externally fitted to and fixed to the support shaft 3, which is an inner member, and a plurality of the respective inner races 7, 7 and each of the outer races 9, 9, which can roll freely. And the balls 11, 11 provided between the inner races of the outer races 10a, 10a and the outer races of the inner races 8a, 8a. And a pair of retainers 12 and 12. And, the bearing device 1a
When the pair of outer rings 10a and 10a are used, the pair of outer rings 10a and 10a are placed in the axial direction (the term "inside in the axial direction" refers to the sides of the outer rings 10a and 10a and the inner rings 8a and 8a that face each other.
The outside refers to the side of each outer ring 10a, 10a and each inner ring 8a, 8a that does not face each other. same as below. 3.) With the end faces abutting against each other, the hub 4 is internally fitted and fixed to the hub 4 by interference fitting or bonding. At the same time, the pair of inner rings 8
A desired preload is applied to the balls 11, 11 by pressing the a and 8a in directions approaching each other with a jig (not shown) while the gap 16 is interposed between the inner end surfaces in the axial direction. In this state, the pair of inner rings 8a, 8a is externally fitted to the support shaft 3 by tight fitting or bonding. Also, in the case of this example, the diameter d of each of the balls 11, 11
₁₁ (FIG. 2) is set to 0.5 mm.

In particular, in the case of the present invention, each of the cages 1
A plurality of elastic pieces 18 are provided on one surface of an annular main portion 17 in the axial direction, and two
The pockets 19, 1 between the elastic pieces 18
9 and a crown type cage. In the case of this example, each of the retainers 12, 12 is made of a synthetic resin such as polyamide 66.

In the case of the present invention, the axial center of each of the outer raceways 9, 9 is offset toward the side where the outer races 10a, 10a abut each other in the axial direction of the outer races 10a, 10a. I have. Thus, the axial center and the respective outer rings 10a of the respective outer ring raceways 9, 9, the axial length between the axially outer end face of 10a and L _1, and the axial center of the respective outer ring raceways 9,9 each outer ring 10a, an axial length between the axially inner end face of 10a when the L ₂ (FIG. 1), and L _1> L _2. Further, an axial length L between the axial inner end surfaces of the inner rings 8a, 8a and the axial centers of the inner ring raceways 7, 7 formed on the outer peripheral surfaces of the inner rings 8a, 8a.
₃ is an outer raceway 9 formed on an axial inner end surface of an outer race 10a provided around the inner race 8a and an inner race surface of the outer race 10a.
It is smaller than the axial length L ₂ between the axial center of the (L ₃ <L _2).

In the case of the present invention, each of the cages 1
The main parts 17 and 17 constituting the parts 2 and 12 are arranged near both ends in the axial direction of the bearing device 1a. In addition, each outer ring 10
The axially outer end surfaces of the inner rings 8a and 8a are provided at substantially the same position in the axial direction. Note that the substantially same position does not deviate in the axial direction than the sum of the deviation caused by applying the predetermined preload to the balls 11 and 11 and the dimensional tolerance required for processing. In this case, this deviation is set to 0.25 mm or less. This shift is 0.
If it is 25 mm or less, it can be considered that they are almost at the same position. The end faces of the main portions 17, 17 of the cages 12, 12 are positioned at the median of the allowable dimensions of the respective members, and
Although they do not protrude axially outward from the outer end surfaces of the inner rings 8a, 8a, they may slightly protrude in the axial direction depending on the finished product. Further, in the case of the present example, a part of each of the balls 11, 11 is
a, 8a, on the side where the gap 16 exists than the inner end face,
It is slightly projected in the axial direction.

In the case of the bearing device of the present invention configured as described above, sufficient rigidity of the bearing can be secured by applying a desired preload to the balls 11, 11 as described above. Further, according to the present invention, the overall length in the axial direction can be sufficiently reduced. Next, the reason will be described. First, as a first reason, in the case of the present invention, the axial center of each of the outer raceways 9, 9 is set on the side where the outer races 10a, 10a abut each other in the axial direction of the outer races 10a, 10a. We are biased. Also, the inner races 8a, the axially inner end face of 8a and respective inner rings 8a, an axial length L ₃ between the axial center of the inner ring raceway 7, 7 formed on the outer peripheral surface of 8a,
It is smaller than the axial length L ₂ between the axial center of the outer ring raceway 9 formed on the inner peripheral surface of the outer ring 10a and the axially inner end face of the outer ring 10a provided around of the inner ring 8a ( L ₃ <L ₂ ). On the other hand, in the case of the conventional structure shown in FIG. 7, the center of each outer raceway 9, 9 in the axial direction is
With respect to the axial direction of each outer ring 10,
They were biased to the opposite side of the 10's butting.
When the axial center of each outer raceway 9, 9 is provided at the same position as the axial center of each outer race 10, 10, as in the bearing device 1b of the comparative example shown in FIG. Although the overall length in the axial direction can be reduced to some extent,
It cannot be said that it can be made small enough. That is, in the structure shown in FIG. 5, each of the inner rings 8, 8 and each of the outer rings 10,
The inner end portions of the inner rings 8, 8 and the outer rings 10, 10, which are indicated by oblique lattices at the inner end portions in the axial direction of 10, respectively, still remain as omissible portions.

Taking such points into consideration, in the case of the present invention, the axial center of each of the outer raceways 9, 9 is set to the axial direction of each of the outer races 10a, 10a.
10a are offset to the side where they abut each other. Also, the inner end faces of the inner rings 8a, 8a in the axial direction and the inner rings 8
a, an axial length L ₃ between the axial center of the inner ring raceway 7, 7 formed on the outer peripheral surface of 8a, the axially inner end face and the outer ring 10a of the outer ring 10a provided around the said inner ring 8a It is smaller than the axial length L ₂ between the axial center of the outer ring raceway 9 formed on the inner peripheral surface (L ₃ <L _2). Because of this,
The axial length of the inner ends of the outer races 10a, 10a and the inner races 8a, 8a can be reduced, for example, by the axial length of the portion indicated by the oblique lattice in FIG. Therefore,
According to the present invention, the axial length of each of the outer rings 10a, 10a and the inner rings 8a, 8a in the axial direction can be reduced, and the overall length of the bearing device 1a in the axial direction can be reduced.

Next, according to the present invention, the total length in the axial direction is sufficient.
As a second reason, in the case of the present invention,
The retainers 12, 12 are connected to the annular main portions 17, 17.
Along with providing a plurality of elastic pieces 18 on one surface in the axial direction,
A pair of elastic pieces 18, 18 adjacent in the circumferential direction
It is a crown type retainer with pockets 19 and 19 between them,
In addition, each of the main parts 17, 17 is arranged in the axial direction of the bearing device 1a.
It is located near both ends. In contrast, shown in FIG.
As in the second comparative example, a main part provided in each of the cages 12 and 12
17, 17 are provided near the center in the axial direction of the bearing device 1c.
Therefore, the total length cannot be sufficiently shortened. What happens above
The minimum axial thickness L of each main part 17, 17 ₁₇Are the above
In order to secure the rigidity of the cages 12, 12
Need to be This is because the small shaft
The same applies to the receiving device. And each said main part 1
The minimum required value of the minimum wall thickness of 7, 17
8, shoulder portions 20a and 20b provided on both axial sides of the outer peripheral surface.
Of the axial length, the length is on the inner diameter side of each of the main portions 17 and 17.
Axial length L of the existing shoulders 20b, 20b_20b Required
It is larger than the minimum value. Each of these shoulders 20a,
The axial length of 20b is the strength of these shoulders 20a, 20b.
It is necessary to secure the degree. Therefore, the structure shown in FIG.
In the case of, based on the existence of each of the main parts 17, 17, 1
Axial length L between pairs of balls 11, 11 rows₁₁Is large
Has become.

That is, in the structure shown in FIG. 6, a desired preload is applied to each of the balls 11, 11 by pressing the pair of inner rings 8, 8 in a direction to approach each other. In a state where the inner races 8 and 8 are externally fitted and fixed to the support shaft 3 (see FIG. 1), based on changes in the internal gaps of the constituent members of the bearing device 1c, each of the balls 11, 11 and each of the outer races 10, 10 and A load is applied to the inner rings 8, 8 in a direction indicated by a chain line α in FIG. Accordingly, of the pair of shoulders 20a, 20b provided on both sides in the axial direction of the outer peripheral surfaces of the inner rings 8, 8, the balls 1
Axial outer shoulder 20 loaded by 1, 1
Since a and 20a are close to the point of application of this load, their strength is more likely to be insufficient than the strength of the axially inner shoulders 20b and 20b. For this reason, the axially outer shoulders 20a,
The axial length L20a of _20a needs to be sufficiently large to secure the strength. On the other hand, the axially inner shoulder 2
Since 0b and 20b do not receive the load from the balls 11 and 11, there is no need to particularly increase the axial dimension _L20b . However, even if the axial dimension L20b of the inner shoulders 20b, _20b is shortened in the structure shown in FIG. 6, based on the presence of the main parts 17, 17, the pair of balls 11,
11 can not be reduced axial length L ₁₁ between between rows of, it not can also reduce the size of the bearing apparatus 1c.

On the other hand, in the case of the present invention, the main parts 17 and 17 constituting each of the cages 12 and 12 are connected to the bearing device 1.
a is disposed near both ends in the axial direction. Therefore, in the case of the present invention, each of these main parts 17, 17 is connected to a pair of balls 11, 1
By eliminating the portion between the one row, the axial length L ₁₁ ′ between the pair of balls 11, ₁₁ (FIG. 1)
The can be made smaller than the axial length L ₁₁ shown in FIG. However, in the present invention, each of the main parts 17, 17 is connected to the bearing device 1a.
Of the balls 11, 1
The axial length of the outer part in the axial direction is larger than the axial length of the inner part in the axial direction. That is, each of the main parts 1
Even when the bearings 7 and 17 are arranged near both ends in the axial direction of the bearing device 1a, compared with the case where the respective main parts 17 and 17 are arranged near the center in the axial direction of the bearing device 1c, the respective main parts 17 and 17 are arranged.
The axial length between the center of the axial end face and the balls 11, 11 of _{17 (L 17 + d 11/} 2) can not be a small. Also, considering that the inner rings 8 (or 8a) are brought closer to each other for applying a preload, even when the main parts 17, 17 are arranged near both ends in the axial direction of the bearing device 1a, the main parts 17, The thickness of the gap 16 formed between the axial end faces of the inner rings 8 (or 8a) or the cages 12 and 12 as compared with the case where the bearing 17 is disposed near the axial center of the bearing device 1c. d ₁₆ cannot be reduced.

On the other hand, the axial end faces of the inner races 8 (or 8a) on the side where the main parts 17, 17 are not provided,
The axial length between the balls 11 and 11 is the axial direction necessary to secure the strength of the shoulder portion 20a (or 20b ') of each inner ring 8 (or 8a) existing in the portion. Length L
_20a (or L _20b ′). Looking at each figure in consideration of such points, in the case of the structure shown in FIG. 6 described above, the axially outer sides of the inner rings 8, 8 which are present on the side where the main parts 17, 17 are not provided. A load is applied to the shoulders 20a, 20a by the balls 11, 11 based on the preload application. For this reason, despite the absence of the main portions 17 around the respective peripheral portions, the axially outer shoulder portions 20a, 20a
Must be increased in the axial length _L20a . This leads to an increase in the size of the bearing device 1c by increasing the axial length on both the inner and outer sides of each of the balls 11, 11. On the other hand, in the case of the present invention, each of the inner rings 8a, 8
The load is not applied to the shoulders 20b ', 20b' on the inner side in the axial direction of "a". Therefore, in the present invention, each of the main parts 1
There is no need to particularly consider the prevention of interference between the inner rings 7 and 17 and the inner rings 8a,
The axial length L _20b ′ of the shoulders _{20 b} ′, _{20 b} ′ on the inner side in the axial direction of the inner ring 8 a of each inner ring 8 constituting the structure shown in FIG.
8 axial length L of the axially outer shoulders 20a, 20a
_20a ( _L20b '< _L20a ). In the case of the present invention, the axial outer end faces of the outer rings 10a, 10a and the axial outer end faces of the inner rings 8a, 8a are provided at substantially the same position in the axial direction. Each of the main parts 17, 17 has an axial dimension _L20a 'for maintaining strength.
Are arranged around the shoulder 20a ', which is enlarged, so that the respective end faces can be provided at substantially the same positions as the outer end faces of the outer rings 10a, 10a and the inner rings 8a, 8a. As a result, according to the present invention, each of the inner rings 8a, 8a
Axial length L of the axially inner shoulders 20b ', 20b'
The difference δ (= L _20a −) between _20b ′ and the axially outer shoulders 20a of the inner races 8 constituting the structure shown in FIG.
L _20b ′), which is almost equal to twice (2δ).
The total length in the axial direction of “a” can be reduced.

It should be noted that in the case of the present invention,
Each outer ring 1 to which a load is applied by each ball 11, 11
Shoulders 21 ', 21' provided on the inner side in the axial direction of 0a, 10a
Axial length L of_{twenty one}′ Are the respective constituents of the structure shown in FIG.
The shoulders 21, 21 provided on the inner side in the axial direction of the outer races 10, 10
Axial length L_{twenty one}Smaller than (L_{twenty one}´ <L_{twenty one})Become. However
However, in the case of the present invention, each of the shoulders 21 ', 21'
The inner end faces are butted against each other. Therefore, these
Axial length L of each shoulder 21 ', 21'_{twenty one}´ in each of the above
Of the shoulders 20b ', 20b' on the inner side in the axial direction of the wheels 8a, 8a.
Axial length L_{20 b} ', The length of half of the gap 16 (d₁₆/
2) plus the length (L_{twenty one}´ = L_20b '+ D
₁₆/ 2), axially outer shoulders of the inner rings 8, 8 shown in FIG.
20a, length L in the axial direction of 20a_20a At least the length equivalent to
Can be secured. Moreover, from each of the balls 11, 11,
The load applied to each of the shoulders 21 ′, 21 ′ is
Acting in the direction of pressing the shoulders 21 ′, 21 ′ against each other.
And are offset by each other. Therefore, each of the shoulders 21, 21
There is no shortage of strength.

For the reasons described above, according to the present invention, the overall length in the axial direction can be made sufficiently small, and the size and weight of the bearing device 1a can be reduced. Further, since the overall length in the axial direction can be sufficiently reduced in this manner, the hub 4 or the support shaft 3 and the outer rings 10a, 10a or the inner rings 8a,
8a and the outer rings 10a and 10a and the inner rings
Even when the temperatures of the members a and 8a are different from each other, the distortion based on the difference in the amount of thermal expansion between the fitting and fixing portions of the members 4, 3, 10a and 8a can be reduced. Therefore, the amount of change in bearing stiffness during use can be made extremely small.

In the case of the present embodiment, each of the retainers 12,
Each of the pockets among the main portions 17, 17 constituting
19, the minimum thickness L of the portion corresponding to 19₁₇Is 0.1 mm
Larger than 0.2 mm. Each of the above
Minimum thickness L of main parts 17, 17 ₁₇Within this range
The reason is that the shaft of the bearing device 1a is secured while ensuring sufficient durability.
This is to make the overall length in the direction sufficiently small. That is,
Minimum thickness L of each of the main parts 17, 17₁₇, 0.2 mm or more
In the case of
It is difficult to reduce the overall length in the axial direction compared to
It becomes difficult. Also, the minimum thickness L of each of the main parts 17, 17 is described.
₁₇Is set to 0.1 mm or less, each cage 12, 1
2 cannot be sufficiently secured. For example, the minimum
Thickness L₁₇Is 0.1 mm, the inner and outer wheels 8a,
5000a for 10a^-1 When rotating the
Retainers 12,12 act on each of these retainers 12,12
It could not withstand the centrifugal force and some parts were deformed. Because of this
Minimum thickness L₁₇When 0.1 mm is used, use rotation speed
5000min^-1 Must be kept below. these
In consideration of this, in the case of this example, each of the cages 12, 1
2 of the main portions 17, 17, the pockets 19, 19
Thickness L of the part corresponding to₁₇In the above range (0.1
mm <L₁₇<0.2 mm). In addition, the ball 11, 11
Diameter d₁₁Above minimum wall thickness L₁₁Ratio (L₁₇/ D₁₁)
Is in the range of 0.2 to 0.4 (0.2 <L ₁₇/ D₁₁<
0.4).

Further, in the case of the present embodiment, each of the cages 1
A part of each of the balls 11, 11 held by 2 and 12 is slightly protruded in the axial direction from the inner end surfaces of the inner rings 8a, 8a to the side where the gap 16 exists. For this reason, in the case of the present example, the axial length L ₄ between each of the balls 11, 11 is set.
Can be reduced, and the overall length of the bearing device 1a in the axial direction can be further reduced.

In general, in a bearing device in which a pair of ball bearings are combined and a plurality of balls constituting each of the ball bearings are used by applying a preload thereto, each of the balls is applied to each outer ring and each inner ring. The direction of the applied load is inclined with respect to the center axis of the bearing device. For this reason, in general, the diameters of the shoulder portions provided on the inner peripheral surface of each of the outer rings and the pair of shoulder portions provided on both sides in the axial direction of the outer peripheral surface of each of the inner rings are made different. Then, even when the balls are pressed against one of the pair of shoulders, the balls are reliably prevented from riding on the one shoulder. On the other hand, in the case of this example, the inner peripheral surface of each outer ring 10a, 10a and each inner ring 8
The diameters of the shoulders 20a ', 20b', 21 ', and 22 provided on each of the axial sides of the outer peripheral surfaces of the a and 8a are substantially the same. The reason for this is that, in the present invention, since the present invention is applied to an extremely small bearing device having an inner diameter of 2 mm and an outer diameter of 9 mm, as described above, each of the outer rings 10a, 10a
This is because if the diameters of the shoulders 20a ', 20b', 21 ', 22 provided on the inner ring 8a and the inner rings 8a, 8a are different from each other, the working of the bearing device 1a becomes difficult. Also, in such a very small bearing device 1a, since the load based on the preload applied to the balls 11, 11 is relatively small, the outer rings 10a, 10a and the inner rings 8a,
8a, a pair of shoulders 20a, 20b,
Even if the diameters of the balls 21 'and 22 are substantially the same, the balls 1 are attached to the shoulders 20a' and 21 'on the side to which the load is applied.
1 and 11 never get on.

Further, in the case of this embodiment, each of the inner rings 8a,
8a axial length L_8aOf each ball 11, 11
Diameter d₁₁Ratio (d₁₁/ L_8a) And the outer rings 10a, 10a
The axial length L of a_10a Of each ball 11, 11
Diameter d₁₁Ratio (d₁₁/ L_10a ) And 0.71,
0.65 and 0.6 or more (d₁₁/ L_8a, D ₁₁
/ L_10a ≧ 0.6). Each such ratio (d₁₁/
L_8a, D₁₁/ L_10a ) Is the diameter of each ball 11, 11
0.5mm or less, with built-in crown type cage
Significantly larger than the bearing device used
No. As described above, in this example, each of the above ratios (d₁₁/ L_8a, D₁₁/ L
_10a The reason for increasing the value of) is the diameter of each of the balls 11, 11 described above.
d₁₁Is constant, the axial direction of the bearing device 1a is not
This is to make the overall length sufficiently small.

As described above, according to the present invention, in a structure in which bearing rigidity can be sufficiently secured by applying a preload,
Compact and lightweight. For example, in the case of the present example, the minimum thickness L ₁₇ of the main parts 17, 17 constituting these cages 12, 12 is ensured while ensuring the durability of the cages 12, 12.
Is as small as possible, the axial length of the bearing device 1a can be reduced to 1.6 mm or less. When the present invention is carried out, it is not always necessary to use an outer ring divided into two. If the manufacture and the assembly are not troublesome, a single outer ring having a double row of outer ring tracks on the inner peripheral surface may be used.

[0027]

Since the bearing device of the present invention is constructed and operates as described above, it is possible to reduce the size and weight of the structure in which sufficient bearing rigidity can be ensured by applying a preload. Furthermore, the amount of fluctuation in bearing stiffness during use can be made very small.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view illustrating an example of an embodiment of the present invention.

FIG. 2 is an enlarged view of the upper half of FIG. 1;

FIG. 3 is a perspective view showing the cage taken out.

FIG. 4 is an illustration of the structure of FIG.
A sectional drawing.

FIG. 5 is a diagram similar to FIG. 2, showing a first example of a comparative example, used to explain a first reason that the effects of the present invention are produced.

FIG. 6 is a view similar to FIG. 2, showing a second example of a comparative example, also used for explaining the second reason.

FIG. 7 is a sectional view showing an example of a conventional structure.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 1a-1c Bearing device 2 Housing 3 Support shaft 4 Hub 5 Inside diameter cylindrical part 6 Ball bearing 7 Inner ring track 8, 8a Inner ring 9 Outer ring track 10, 10a Outer ring 11 Ball 12 Cage 13 Projection 14 Projection 15 Outer diameter Side cylindrical part 16 Gap 17 Main part 18 Elastic piece 19 Pocket 20a, 20b, 20a ', 20b' Shoulder 21, 21 'Shoulder 22 Shoulder

Claims (2)

[Claims] 1. An outer ring raceway on each inner peripheral surface.
A pair of outer races, a pair of inner races each having an inner raceway on an outer peripheral surface thereof, a plurality of balls provided in a rolling manner between the inner raceways and the outer raceways, respectively; A pair of cages disposed between an inner peripheral surface and an outer peripheral surface of each of the inner rings to hold each of the balls in a freely rolling manner; By abutting the inner rings on the outer member and pressing the pair of inner races in a direction approaching each other while leaving a gap between the axial end surfaces facing each other, In the bearing device which is externally fitted and fixed to the inner member in a state where a desired preload is applied to each ball, the axial center of each of the outer raceways is on the side where these outer races abut each other with respect to the axial direction of the outer races. Each cage is biased, and each cage is an annular main part. A crown-shaped retainer having a plurality of elastic pieces provided on one surface in an axial direction and having a pocket between a pair of elastic pieces adjacent to each other in a circumferential direction, wherein the main part is formed at both axial ends of the bearing device. A bearing device, wherein the axial end faces of the outer ring and the inner ring, which are located on both sides in the axial direction of the bearing device, are provided at substantially the same position in the axial direction. 2. The bearing device according to claim 1, wherein one outer ring having a double-row outer ring raceway on the inner peripheral surface is used instead of the pair of outer rings.