Bearings – Rotary bearing – Fluid bearing
Reexamination Certificate
2001-11-29
2004-03-02
Footland, Lenard A. (Department: 3682)
Bearings
Rotary bearing
Fluid bearing
Reexamination Certificate
active
06698930
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a foil gas bearing which is used in a small gas turbine, a compressor, and the like. In particular, the present invention relates to a foil gas bearing which comprises top foils having a sufficient stiffness to reliably support a rotary shaft.
2. Description of the Related Art
It has been well known that a foil gas bearing is sometimes used as a bearing for supporting a rotary shaft of a gas turbine, a compressor, an expander, and the like. Foil gas bearings are classified into leaf-foil-type gas bearings and bump-foil-type gas bearings.
In the leaf-foil-type gas bearing, a plurality of top foils support the rotary bearing while they are supported by back springs. The top foil is provided in a rotary shaft retainer under conditions in which one end contacts the rotary shaft and the other end is fixed to the rotary shaft retainer, and the one end is more forward than the other end in a rotary direction of the rotary shaft. Specifically, the leaf-foil-type gas bearing will be explained referring to U.S. Pat. No. 4,195,395.
FIG. 15
shows the conventional leaf-foil-type gas bearing described in U.S. Pat. No. 4,195,395. In
FIG. 15
, reference number
1
denotes a rotary shaft, and
2
denotes a leaf-foil-type gas bearing. The rotary shaft
1
is supported by the bearing
2
. The bearing
2
comprises a tube shaped rotary shaft retainer
3
and a support ring
4
which is fixed to the inside of the rotary shaft retainer
3
. Plural slots
5
are formed around the inside of the support ring
4
. A plate shaped top foil
6
is fixed to the support ring
4
under the conditions in which one end is fixed to the slot
5
and the vicinity of the other end contacts the surface of the rotary shaft
1
; that is, the top foil
6
is curved so as to partially contact around the rotary shaft
1
, and the other end is more forward than the one end in a rotary direction of the rotary shaft
1
. Each top foil
6
is supported by a support spring
7
which is fixed to the slot
5
from the outside of the top foil
6
in a radial direction of the rotary shaft
1
.
The bump-foil-type gas bearing comprises a top foil and a bump foil in a corrugated plate shape. The bump-foil-type gas bearing supports the rotary shaft using the top foil and the bump foil. The bump-foil-type gas bearing will be explained referring to Japanese Patent Application, Examined Second Publication No. Hei 01-47649 (Japanese Patent Application, Unexamined First Publication No. Sho 59-093515).
FIG. 16
shows the conventional bump-foil-type gas bearing disclosed in the Japanese Patent Application, Examined Second Publication No. Hei 01-47649. As shown in
FIG. 16
, a rotary shaft
11
is provided in a rotary shaft retainer
10
. Around the rotary shaft
11
, a ring shaped top foil
12
is provided. In addition, between the top foil
12
and the rotary shaft retainer
10
, a bump foil in a corrugated plate shape
13
is provided. When the rotary shaft
11
rotates at high speed, air in a space between the rotary shaft
11
and the top foil
12
is involved in a rotation of the rotary shaft
11
, and thereby, the rotary shaft
11
floats. In addition, the bump foil
13
has a resiliency, and therefore it exerts damping effects.
In the latter, when the rotary shaft
11
is displaced, the bump foil
13
rubs on the inside of the rotary shaft retainer
10
, and thereby a frictional force is generated. Due to the frictional force, the damping effects can be obtained. In order to increase the frictional force, it is necessary to increase the rubbing distance over which the bump foil
13
rubs on the inside of the rotary shaft retainer
10
. In addition, in order to increase the rubbing distance, it is necessary to substantially transform the bump foil
13
. Due to this, a problem occurs in that the stiffness of the bump foil
13
decreases.
In the former, similar to the latter, in order to increase the damping effects by increasing the rubbing distance between the top foil
6
and the rotary shaft
1
, it is necessary to increase the length of the top foil
6
. In order to support the top foil
6
having a large length, a support spring
7
having a large length is needed. As a result, a problem occurs in that the stiffness of the support spring
7
decreases.
In addition, in conventional foil gas bearings, in order to decrease the frictional force which is caused by contacting the rotary shaft
1
or
11
and the top foil
6
or
12
when the operation starts or stops, the surface of the rotary shaft
1
or
11
is chrome plated and a calcination film containing fluororesin as a main component is formed on the surface of top foil
6
or
12
. However, since the maximum allowable temperature of the calcination film containing fluororesin is low, such as about 200° C., it is difficult to use foil gas bearings comprising the top foils which are coated with the calcination film with elements for gas turbines which are subjected to high temperatures.
The present invention has been realized in consideration of the matters mentioned above, and an object of the present invention is to provide a foil gas bearing which has sufficient damping effects due to a frictional force and a sufficient stiffness to support the rotary shaft.
In addition, another object of the present invention is to provide a foil gas bearing in which a back spring for preventing the displacement of the rotary shaft has a sufficient stiffness to prevent damages to the back spring; and in which a frictional force which is generated by the contact between the rotary shaft and the top foil when the operation starts or stops, decreases.
In addition, another object of the present invention is to provide a foil gas bearing in which the back spring for preventing the displacement of the rotary shaft is easily mounted into the rotary shaft retainer with a high precision, and thereby a bearing clearance between the rotary shaft and the top foil is maintained precisely, and in which the bearing clearance can be adjusted after assembly.
Furthermore, another object of the present invention is to provide a foil gas bearing which has a high maximum allowable temperature and an improved heat resistance, and which can be used for the elements of gas turbines which are subjected to high temperatures.
SUMMARY OF THE INVENTION
In order to achieve the above objects, the present invention provides a foil gas bearing comprising a rotary shaft retainer for retaining a rotary shaft, and a back spring for preventing the displacement of the rotary shaft, which is provided between the rotary shaft and the rotary shaft retainer. Plural protrusions are formed at one element which is either the rotary shaft retainer or the back spring. Plural recesses are formed at the other element, which is either the back spring or the rotary shaft retainer, at places which correspond to the protrusions, and the protrusions partially fit into the recesses.
According to the foil gas bearing, when the rotary shaft is displaced in a radial direction or in a thrust direction thereof, the protrusion which is formed at the back spring (or the rotary shaft retainer) fits the recess which is formed at the rotary shaft retainer (or the back spring). Due to this, a frictional force is generated, and the frictional force has damping effects on the displacement of the rotary shaft. In addition, when a recess and a protrusion fit, a tensile force or a compressive stress is generated at the back spring. Specifically, when the back spring comprises the protrusions, a tensile force is generated. In contrast, when the back spring comprises the recess, a compressive stress is generated. Thereby, the stiffness of the back spring is improved and it is possible to oppose the displacement of the rotary shaft.
In the foil gas bearing, it is preferable to further have a top foil for preventing the displacement of the rotary shaft in the radial direction thereof, which is provided between the rotary shaft and the back spring.
According to the foil gas
Akizuki Yukio
Makino Takero
Matsui Akihiko
Footland Lenard A.
Mitsubishi Heavy Industries Ltd.
Wenderoth , Lind & Ponack, L.L.P.
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