Method of constructing a self-aligned, rigid spherical...

Details Method of constructing a self-aligned, rigid spherical... Method of constructing a self-aligned, rigid spherical...

1998-10-21

2001-03-06

Footland, Lenard A. (Department: 3682)

Bearings

Rotary bearing

Antifriction bearing

C029S898042

Reexamination Certificate

active

06196726

ABSTRACT:

FIELD OF THE INVENTION
The present invention pertains to a bearing assembly that is equally well-suited for use in self-aligning and rigid shaft supporting applications. More particularly, the bearing assembly of the invention permits one bearing bushing to be employed in both applications that permit self-aligning pivoting movement of the support for a rotating shaft and applications that rigidly support a rotating shaft, thereby eliminating the need to inventory two different types of bearings for these two different applications.
DESCRIPTION OF THE RELATED ART
Self-aligning bearing assemblies are often used in environments where the bearing assembly provides support from a structure to a rotating shaft while permitting a limited degree of shaft pivoting movement relative to the supporting structure. A typical application of this type is found on the output shaft of an electric motor, although self-aligning bearing assemblies are employed in various other applications. This illustrative environment of the prior art self-aligning bearing assembly is shown in drawing
FIGS. 1-3
.
The typical prior art self-aligning bearing assembly is comprised of a bearing seat
10
, a bearing bushing
12
, a retaining ring
14
, and a sealing cap
16
.
In the application shown in
FIGS. 1-3
, the bearing seat
10
is formed as part of an end shield
18
of an electric motor housing. The bearing seat
10
is cast integrally with the housing end shield
18
. Aluminum is often employed in casting the bearing seat and the end shield. The bearing seat has a shaft opening
20
through its center. When the end shield
18
is assembled to an electric motor (not shown) the rotor shaft of the motor will pass through the shaft opening
20
. A bearing land surface
22
supports the bearing bushing
12
in sliding engagement extends around the shaft opening
20
. In some bearing seats the land surface extends as a single continuous surface around the shaft opening, and in other bearing seats the land surface is actually formed as several separate surfaces that are spacially arranged around the shaft opening. In the illustrative prior art shown in
FIGS. 1-3
, the bearing land surface
22
is shown as three separate surface sections spacially arranged around the shaft opening
20
. In cross-section, the land surfaces
22
have a concave configuration. Together the land surfaces
22
define a cup or socket shape with the shaft opening
20
at the bottom, center of the socket shape.
Referring to
FIG. 2
, the prior art bearing bushing
12
has a semi-spherical forward end
24
and a cylindrical rearward end
26
. A shaft bore
28
extends axially through the center of the bushing. The interior diameter of the shaft bore
28
is sized to securely mount the motor shaft for rotation in the bore. The semi-spherical forward end
24
of the bushing is defined by the spherical shape of the bushings bearing surface
30
that mates in sliding engagement with the land surfaces
22
of the bearing seat. The shape of the bearing surface
30
is complimentary to the curvature of the bearing seat land surfaces
22
. This enables the bearing bushing
12
to pivot to a limited extent on the bearing land surfaces. The bearing bushing
12
is often constructed of powdered metal iron graphite that is a softer material than the aluminum employed in constructing the bearing seat
10
. The powdered metal of the bearing bushing is also porous which enables the bearing surface
30
to retain lubricant which enhances its ability to pivot on the bearing seat land surfaces
22
.
The method of assembling the prior art self-aligning bearing assembly is shown in FIG.
1
. The motor end shield
18
is shown placed face down with the interior surface
32
, or that surface that would face the stator and rotor of the electric motor, facing upwardly. The bearing seat
10
is shown at the center of the end shield
18
. The bearing bushing
12
is placed in the bearing seat
10
with the bearing surface
30
of the bushing resting on the land surfaces
22
of the bearing seat. A tooling pilot shaft
34
is inserted through the shaft bore
28
of the bushing. The retaining ring
14
functions somewhat like a Belleville spring and is placed over the shaft and press-fit into a cylindrical collar
38
of the bearing seat that extends upwardly from the land surfaces
22
. Projecting tabs
40
of the retainer engage against the interior surface of the cylindrical collar
38
and hold the retaining ring in its position pressed downwardly into the cylindrical collar. A center ring
42
of the retainer passes around the cylindrical rearward end
26
of the bearing bushing and engages against an annular shoulder
44
of the bearing bushing that separates the cylindrical rearward end
26
from the semi-spherical forward end
24
. When inserted completely into the cylindrical collar
38
, the center ring
42
of the retaining ring
36
exerts a biasing force against the annular shoulder
44
of the bearing bushing that forces the bearing surface
30
of the bushing into engagement with the land surfaces
22
of the bearing seat. This biasing force also produces the correcting or centering force on the bearing bushing
12
that urges the bearing bushing
12
to return to a position where a center axis passing through the bearing bushing shaft bore
28
is aligned coaxially with a center axis passing through the bearing seat shaft opening
20
. In completing the construction of the prior art self-aligning bearing assembly, a lubricant may be applied within the cylindrical collar
38
of the bearing seat
10
and then the sealing cap
16
is press-fit into the cylindrical collar
38
to retain the lubricant and complete the assembly of the self-aligning bearing assembly.
A primary benefit provided by the self-aligning bearing assembly is that the motor end shield
18
does not have to be perfectly aligned with the center axis of the electric motor rotor and stator when the end shield is assembled to the motor, i.e., the center axis (not shown) of the end shield bearing seat shaft opening
20
does not have to be perfectly aligned with the center axes of the electric motor rotor and the electric motor stator. If these axes are not perfectly aligned when the end shield
18
is assembled to the electric motor, the bearing bushing
12
will pivot slightly on the bearing seat land surfaces
22
to compensate for the misalignment and thereby support the motor shaft for rotation in the end shield
18
without having the end shield perfectly oriented relative to the shaft.
In the construction of electric motors, there are applications where the motor end shield must be properly positioned relative to the shaft In these applications, the end shield itself is used to orient the motor shaft relative to the environment in which the motor is used For example, where the electric motor is used to power a transmission such as a gearing transmission, the motor end shield would typically be connected directly to the supporting structure, i.e., the casing of the gearing transmission. If the motor shaft was improperly oriented relative to the motor end shield, for example if the shaft center axis was not perfectly aligned with the center axis of the end shield shaft opening, then the shaft would not be perfectly aligned with the center axes of the gears employed in the gearing transmission attached to the motor end shield. This would result in gears of the transmission not properly meshing with each other and often produced accelerated and uneven wearing of the gear teeth. Similar problems would also occur in other environments. For example, if the motor were powering a belt and pulley transmission, the center axis of the drive pulley mounted on the motor shaft would not be aligned parallel with the driven pulley of the transmission. This would also result in accelerated wear of the belt connected between the drive and driven pulleys. Also, if the motor were used to power a pump, the misalignment of the motor shaft and the pump shaft could cause pump seals to wear and leak. Th

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