Rolling bearing and rolling bearing device

Details Rolling bearing and rolling bearing device Rolling bearing and rolling bearing device

2001-10-05

2003-06-10

Footland, Lenard A. (Department: 3682)

Bearings

Linear bearing

Alternating roller; or antifriction bearing for auto seat

C384S447000, C384S619000

Reexamination Certificate

active

06575631

ABSTRACT:

BACKGROUND OF THE INVENTION
The present invention relates to a bearing which is capable of receiving a radial load, axial loads in two directions, and a moment load. The bearing may be used in several applications, such as an industrial machine, a robot, a medical instrument, a semiconductor/liquid crystal manufacturing apparatus, an optical instrument, an opto-electronic instrument, and so on.
As such, the present invention also relates to a rolling bearing device to be utilized in the spindle of a machine tool or another general high-speed rotation machine.
The present invention further relates to a rolling bearing for a compressor pulley.
Conventionally, as a bearing which is capable of receiving a radial load, axial loads in two directions, and a moment load, there are known a cross roller bearing and a four-point contact ball bearing. In the conventional cross roller bearing, between an inner race
100
and an outer race
200
, there is incorporated a cylindrical-shaped roller
300
(see FIG.
94
). On the other hand, in the conventional four-point contact ball bearing, between an inner race
100
and an outer race
200
, there is incorporated a ball
400
(see FIG.
95
).
However, in the conventional cross roller bearing and four-point contact ball bearing, there are found the following problems to be solved.
(1) In the case of the cross roller bearing, since a rolling element is a cylindrical-shaped roller
300
and the rolling contact surface
301
of the roller
300
is line contacted with a raceway groove
500
, there is produced large torque.
(2) In the case of the four-point contact ball bearing, because a rolling element is a ball, when the bearing receives a pure axial load or when an axial load is dominant over a radial load, the four-point contact ball bearing produces smaller torque than the cross roller bearing of the same size.
On the other hand, when a radial load is dominant over an axial load or when the bearing receives a pure radial load, each ball
400
is contacted with a raceway groove
500
at four points
401
,
401
,
401
and
401
and, therefore, there occurs large spin slippage between the ball
400
and raceway groove
500
, which results in large torque.
As the bearing to be used in the high-speed rotation machine such as the machine tool spindle, there has been employed in the prior art an angular ball bearing or a four-point contact ball bearing, as shown in
FIGS. 96
to
98
, for its high speed and axial rigidity. Reference numeral
900
designates a rotation shaft.
In
FIG. 96
, the radial load is borne by two cylindrical roller bearings
600
, and axial loads in the two directions are borne or the axial displacements are restricted by two angular ball bearings
700
.
In
FIG. 97
, the four angular ball bearings
700
bear the radial loads together with one cylindrical roller bearing
600
while bearing the axial loads in the two direction or restricting the axial displacements.
In
FIG. 98
, the radial load is borne by the two cylindrical roller bearings
600
as in
FIG. 96
, but the axial loads in the two directions are borne or the axial displacements are restricted by one four-point ball bearing
800
, as shown in FIG.
99
.
In these Figures: reference numeral
801
designates an outer race; numeral
802
an inner race; numeral
803
a rolling element; and numeral
804
a retainer.
The prior arts thus far described have the following problem.
In the structures of
FIGS. 96 and 97
using the angular ball bearing
700
, this one angular ball bearing
700
can bear only the axial load in one direction. In order to bear the axial loads in the two directions, therefore, it is customary to employ two or more angular ball bearings
700
in combination.
However, the bearing to be used in the high-speed rotation machine such as the machine tool spindle is demanded to have a high precision and therefore has a high price. As the number of angular ball bearings
700
to be arranged becomes the larger, moreover, the axial size of the bearing device becomes the larger therefore, the bearing device and accordingly the entire system cannot be made compact to cause a problem that the cost rises for the entire device.
In the structure employing the four-point contact ball bearing shown in FIG.
98
and
FIG. 99
, moreover, the single bearing can bear the radial load, the axial loads in the two directions, and the moment load so that the single four-point ball bearing
800
can realize the functions of the two angular ball bearings. Therefore, this structure has merits of a compact size and a low cost. Where the radial load is dominant over the axial loads or where a pure radial load is borne, however, the individual balls
803
of the four-point contact ball bearing
800
make contacts at four points with the races
801
and
802
. Therefore, the balls
803
spin largely to cause a problem that a small spin wear performance cannot be attained. This problem is made especially serious by the action of the centrifugal force, especially in the case of the machine tool rotating at a high speed.
In order to improve the spin wear performance even a little, moreover, the clearance between the bearings is usually set positive. As a result, the rigidity of the bearings is lowered to exert adverse effects on the rigidity of the entirety of the bearing system for supporting the rotation shaft.
SUMMARY OF THE INVENTION
The present invention aims at solving the above problems found in the conventional cross roller bearing and four-point contact ball bearing. Accordingly, it is an object of the invention to provide a rolling bearing which can control spin slippage between a rolling element and a raceway groove and can reduce rolling resistance to realize low torque, thereby being able to receive a radial load, axial loads in two directions, and a moment load.
In attaining the above object, according to the invention, there is provided a rolling bearing, wherein a plurality of rolling elements are incorporated between a pair of races, each of the two races has a raceway groove defined by two raceway surfaces each having a radius larger than the radius of each of the rolling elements, the outside diameter of each rolling element serving as the rolling contact surface thereof has a curvature in the axial direction of the rolling element as well, the mutually adjoining ones of the rolling elements are arranged in such a manner that they cross each other alternately, and the outside diameter of each rolling element is always contacted at two points with the raceway surfaces of one of the races as well as with the raceway surfaces of the other.
The above-mentioned object can also be achieved by a rolling bearing comprising:
a first race and a second race, each having at least one raceway surface; and
a plurality of rolling elements rotatably disposed between the first race and the second race, each of the rolling elements having a rolling contact peripheral surface defined by rotating a curved bus line about a rotation axis of the rolling element, the curved bus line having a predetermined curvature that is smaller than a radius of the at least one raceway surface,
wherein the rolling contact peripheral surface of each of the rolling elements always contacts one point on each of the at least one raceway surface of the first race and the at least one raceway surface of second race, and wherein mutually adjoining rolling elements are arranged in a circumferential direction of the rolling bearing such that their rotation axes alternately cross one another.
One embodiment of the rolling bearing according to the present invention, each of the rolling elements may include at least one flat surface.
Another embodiment of the rolling bearing according to the present invention, each of the rolling elements may include two mutually opposing and flat-surfaces
In the rolling bearing according to the present invention, it is advantageous that each of the rolling elements is a top and bottom cut-shaped ball which is formed by cutting upper and lower portions of a ball so as to define

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