Rolling bearing

Details Rolling bearing Rolling bearing

2001-02-22

2004-01-13

Footland, Lenard A. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C384S513000, C384S516000, C384S523000

Reexamination Certificate

active

06676297

ABSTRACT:

TECHNICAL FIELD
A rolling bearing according to this invention is incorporated into a rotation supporting section which is installed outdoors and may be driven at low temperatures, such as for example, a propeller shaft of a vehicle, or a rotation shaft of an electric motor, to thereby prevent the occurrence of harmful vibration or noise even at low temperatures.
BACKGROUND ART
In order to dampingly support for example, a middle portion of a propeller shaft of a vehicle under a floor of the vehicle, a rotation supporting unit
1
as shown in
FIG. 1
is used. This rotation supporting unit
1
supports a rolling bearing
3
via a buffer material
4
and a housing
5
, on the inner diameter side of a support bracket
2
. Of these, the buffer material
4
is formed from a material having a large internal loss, such as rubber, so as to be freely displaceable in the radial direction (vertical direction in
FIG. 1
) and in thee axial direction (lateral direction in FIG.
1
). The housing
5
is formed by fitting and combining elements
6
a
,
6
b
respectively formed in a cylindrical shape, for fittingly supporting an outer ring
7
of the rolling bearing
3
on the inside.
The rolling bearing
3
, being a deep groove ball bearing, comprises an inner ring
9
having an inner ring raceway
8
on an outer peripheral surface thereof, an outer ring
7
having an outer ring raceway
10
on an inner peripheral surface thereof, and a plurality of rolling bodies (balls)
11
,
11
arranged rollably between the inner ring raceway
8
and the outer ring raceway
10
. The rolling bodies
11
,
11
are rollably held by a retainer (not shown), respectively. Also, grease is filled into a space
12
existing between the outer peripheral surface of the inner ring
9
and the inner peripheral surface of the outer ring
7
, in which the rolling bodies
11
,
11
are arranged, and openings on the opposite ends of this space
12
are respectively sealed by ring-shaped seal rings
13
,
13
. Such a rolling bearing
3
constitutes the rotation supporting unit
1
described above, in such a manner that the outer ring
7
is supported under the floor of the vehicle via the housing
5
and the buffer material
4
, and the inner ring
9
on the outside is fittingly secured to the middle portion of the propeller shaft
14
.
The rotation supporting unit
1
for a propeller-shaft described above, or a rotation supporting apparatus incorporated in an electric motor installed outside, is used in a low temperature environment in the winter season. In the case of the rotation supporting unit
1
used under such a low temperature environment and lubricated by grease, when the temperature in the portion of the rolling bearing
3
is still low just after startup, abnormal vibration often occurs, and it is known that when the vibration is conspicuous, offensive noise to the ear occurs due to this abnormal vibration. In particular, it is known that under an environment of −10° C. or less, the offensive noise occurs conspicuously.
The mechanism in which such a noise occurs was elucidated in a paper “Research Regarding Abnormal Vibration of Ball Bearings” described in Nihon Machinery Society Paper, Vol. 63, No. 616 (Chapter C), pp 250~256, issued in December 1997. According to this paper, the above described mechanism is such that self-excited vibration of the rolling body becomes a cause of the above described abnormal vibration.
For example, if a rotation supporting unit
1
for supporting the middle portion of a propeller shaft
14
as shown in
FIG. 1
is considered, when an axial force is applied to the rolling bearing
3
due for example to a change in the operating conditions, external disturbances, or friction in a joint portion disposed at the end of the propeller shaft, axial slippage occurs in each abutting portion between the rolling surface of the respective rolling bodies
11
,
11
and the inner ring race
8
and the outer ring race
10
. This generates a shear rate in the oil film of the grease intervening in each abutting portion. When this shear rate exceeds a certain value, the shear stress decreases, and the grease acts as a negative resistance. That is to say, there is a relationship expressed by an equation of equilibrium in the lubricant film: dp/dx=d&tgr;/dy, between the pressure p of the oil film in the grease and the shear stress &tgr; of the oil film. As is obvious from this relation, as the shear stress &tgr; of the oil film decreases, the pressure p of the oil film also decreases, to generate the self-excited vibration of the respective rolling bodies
11
,
11
whose rolling surface abuts against the oil film. It is made clear in the paper “Simulation Regarding Nonlinear Vibration of Ball Bearings” described in Nihon Machinery Society Lecture Paper, No. 985-2, pp 269, issued in October 1998, that the frequency of such self-excited vibration becomes a multiple of the rotational frequency.
When the self-excited vibration occurs in the respective rolling bodies
11
,
11
with the above described mechanism, the film thickness of the grease existing in the inner ring raceway
8
, the outer ring raceway
10
and the rolling surface portion of the respective rolling bodies
11
,
11
becomes uneven over the circumference, depending on the traveling tracks based on the rotation movement and revolution movement of the respective rolling bodies
11
,
11
. In other words, an undulation (bank of grease) is formed by the grease on the surface portion of the inner ring raceway
8
and the outer ring raceway
10
and on the rolling surface portion of the respective rolling bodies
11
,
11
, respectively. The banks of grease formed in this manner cause radial and axial vibrations, in the same manner as undulations originally existing on the inner ring raceway
8
, the outer ring raceway
10
or the rolling surface of the respective rolling bodies
11
,
11
.
If the frequency of the self-excited vibration of the rolling bodies coincides with the vibration frequency resulting from the banks of grease, vibration is promoted. Moreover, if the frequency of the self-excited vibration of the rolling bodies and the vibration frequency resulting from the banks coincide with the vibration frequency resulting from undulations originally existing (not the banks of grease, but originally existing) on the inner ring raceway
8
, the outer ring raceway
10
or the rolling surface of the respective rolling bodies
11
,
11
, vibration is further promoted to become large. Vibration which has grown in such a manner resonates with a member circumjacent to the rolling bearing
3
, thereby resulting in offensive noise to the ear.
Abnormal vibration and noise described above occurs in the first place, based on the self-excited vibration of the rolling bodies and this self-excited vibration grows due to the banks of grease. Accordingly, in order to eliminate the above described banks of grease or to reduce the strength thereof so that the self-excited vibration does not grow to an abnormal vibration, grease having a low viscosity may be used. However, even with such a measure, it is difficult to obtain a sufficient effect at extremely low temperatures, as low as −10° C. Moreover, if grease having such a low viscosity that abnormal vibration does not occur even at such an extremely low temperature is used, the grease tends to leak through the above described respective seal rings
13
,
13
. Furthermore, grease having a low viscosity has a weak oil film holding power at the rolling contact portion, and in many cases, it is not always satisfactory from the standpoint of lubricating ability. As a result, when grease having a low viscosity is used, it becomes difficult to favorably maintain the lubricating condition of the rolling bearing
3
for a long period of time.
The present invention addresses the above situation, and realizes a rolling bearing which hinders growth of the self-excited vibration of the rolling bodies to an abnormal vibration, without using a special grease, and which has sufficient durabili

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