Double row bearing

Details Double row bearing Double row bearing

2000-11-07

2003-04-01

Lavinder, Jack (Department: 3683)

Bearings

Rotary bearing

Antifriction bearing

Reexamination Certificate

active

06540406

ABSTRACT:

BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a double row bearing, and more particularly to a dual row bearing used for a spindle motor for a precision instrument.
2. Description of the Related Art
As shown in
FIG. 1
, a conventional dual row bearing as one of the double row bearings includes a shaft
101
, a pair of inner rings
102
and
103
disposed in an axially separated manner from each other on the shaft
101
, a pair of outer rings
104
and
105
coaxially surrounding the inner rings
102
and
103
, two rows of balls
110
and
111
arranged circumferentially on the raceway surfaces
106
and
107
formed in the outer surfaces of the inner rings
102
and
103
and the raceway surfaces
108
and
109
formed in the inner surfaces of the outer rings
104
and
105
. A circular spacer
112
is provided between the outer rings
104
and
105
in the conventional dual row bearing. Annular grooves
113
are formed in those portions of the shaft
101
which correspond to the inner surfaces of the inner rings
102
and
103
. After the annular grooves
113
have been filled with adhesive, a predetermined preload is applied from one of the inner rings
102
and
103
(in
FIG. 1
, the left side inner ring
102
) towards the other of the inner rings
102
and
103
(in
FIG. 1
, the right side inner ring
103
) and the inner rings
102
and
103
are bonded to the shaft
101
.
When the inner rings
102
and
103
, the outer rings
104
and
105
and the balls
110
and
111
are made of bearing steel, the outer rings
104
and
105
expand more largely than the inner rings
102
and
103
as the temperature of the dual row bearing mounted on a component of a machine or an instrument is raised, since the inner diameter of the outer rings
104
and
105
is larger than the outer diameter of the inner rings
102
and
103
. Thus, the radial space between the outer surfaces of the inner rings
102
and
103
and the inner surfaces of the outer rings
104
and
105
increases due to the temperature rise of the bearing.
Since the balls
110
and
111
between the inner rings
102
and
103
and the outer rings
104
and
105
have much smaller diameters than the outer diameter of the inner rings
102
and
103
and the inner diameters of the outer rings
104
and
105
, the increase of the diameter of the balls
110
and
111
is less than the increased distance between the outer surfaces of the inner rings
102
and
103
and the inner surfaces of the outer rings
104
and
105
caused by elevation of the temperature.
This reduces the pushing forces between the balls
110
and the raceway surface
106
of the inner ring
102
and the raceway surface
108
of the outer ring
104
and between the balls
111
and the raceway surface
107
of the inner ring
103
and the raceway surface
109
of the outer ring
105
, or, in some cases, the balls
110
and
111
are separated from the raceway surfaces
106
and
107
and/or the raceway surfaces
108
and
109
.
When the pushing forces are lowered, the preload of the bearing is remarkably reduced. Or, when the balls
110
and
111
are separated from the raceway surfaces
106
and/or
108
and/or
107
and/or
109
, the preload is diminished and the bearing cannot function well.
Since the bearing of this type is very small, its heat capacity is very small. Thus, when this bearing is used in a spindle motor, the bearing is much influenced by heat generated due to the electric consumption power of the coil of the spindle motor, heat generated in the bearing by friction or the like and/or by heat from an external heat source.
The raceway surfaces
106
and
107
of the inner rings
102
and
103
are finished extremely accurately. However, when bonded to the shaft
101
, the inner rings
102
and
103
are deformed and sometimes their dimensional accuracy is deteriorated. For instance, the roundness of the raceway surface of the inner rings
102
and
103
sometimes changes from 0.1 &mgr;m at the finished state to 0.5 &mgr;m to 1 &mgr;m or more in a bonded state to the shaft
101
. Further, when the inner rings
102
and
103
are bonded to the shaft
101
in an inclined state, the inclination cannot be corrected. This deteriorates the assembly accuracy of the bearing.
Further, this bearing is of a radial type. Thus, when a load which causes an axial relative movement between the shaft
101
and the outer rings
104
and
105
and particularly when such axial relative movements are repeated, it is not desirable to use such bearing.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a double row bearing in which a preload does not change quickly even if the temperature of the bearing changes whereby the bearing keeps a high performance characteristic.
Another object of the present invention is to provide a double row bearings having high assembly accuracy.
A further object of the present invention is to provide a double row bearing which has a long service life and which can be used stably even if it is in a condition in which an axial load is applied to the bearing.
In order to achieve the objects of the present invention, there is provided a double row bearing which has a shaft, outer ring means coaxially surrounding the shaft and relatively rotatable therearound. The outer ring means has one end portion and the other end portion.
A first annular raceway surface is formed in the inner peripheral surface in said one end portion of the outer ring means, and an annular inner ring surrounds the shaft between the shaft and said one portion of the outer ring means. A second annular raceway surface is formed in the outer peripheral surface of the inner ring so as to radially face the raceway surface. A row of balls are received by the first and second raceway surfaces and arranged circumferentially thereof.
A preloading member is mounted on the shaft at the end of said one end portion of the outer ring means, and elastic means is provided between the inner ring and the preloading member. The preloading member is fixed to the shaft in a position in which the preloading member presses the elastic means towards the inner ring to apply a predetermined preload to the inner ring through the elastic means.
The elastic means can comprise at least one belleville spring.
Alternatively, the elastic means can comprise at least one gear-shaped spring having tooth sections inclined towards the inner ring.
Alternatively, the elastic means is made of elastic rubber.
A space can be formed between the end of said one end portion of the outer ring means and said one end of the inner ring so that at least a part of the preloading member enters the space. The preloading member can be bonded to said shaft.
An annular groove filled with adhesive is formed in the outer peripheral surface of the shaft. Axial slots filled with adhesive can be formed in the area of the outer peripheral surface of the shaft at an end portion of the shaft and arranged so as to be separated circumferentially of the shaft.
It is preferred that the shaft comprises a first cylindrical shaft portion inserted into the inner ring and a second cylindrical shaft portion formed integrally and coaxially with the first shaft portion and having an outer diameter substantially equal to the diameter of the inner peripheral surface of the other end portion of the outer ring means, wherein a third annular raceway surface is formed in the inner peripheral surface of the other portion of the outer peripheral surface of the outer ring means, a fourth annular raceway surface is formed in the outer peripheral surface of the second shaft portion so as to radially face the third annular raceway surface, and another row of balls are disposed between the other portion of the outer ring means and the second shaft portion so as to be received by the third and fourth annular raceway surfaces arranged circumferentially thereof.
Preferably, a first outer ring is formed by said one end portion of the outer ring means and a second outer ring is formed by t

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