Rotary kinetic fluid motors or pumps – Smooth runner surface for working fluid frictional contact
Reexamination Certificate
2001-06-20
2002-10-22
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Smooth runner surface for working fluid frictional contact
Reexamination Certificate
active
06468030
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a turbo-molecular pump for evacuating gas with a rotor that rotates at a high speed, and more particularly to a turbo-molecular pump having a radial turbine blade pumping section in a casing.
2. Description of the Related Art
FIG. 12
of the accompanying drawings shows a conventional turbo-molecular pump having a radial turbine blade pumping section in a casing. As shown in
FIG. 12
, the conventional turbo-molecular pump comprises a rotor R and a stator S which are housed in a casing
10
. The rotor R and the stator S jointly make up an axial turbine blade pumping section L
1
and a radial turbine blade pumping section L
2
. The stator S comprises a base
14
, a stationary cylindrical sleeve
16
vertically mounted centrally on the base
14
, and stationary components of the axial turbine blade pumping section L
1
and the radial turbine blade pumping section L
2
. The rotor R comprises a main shaft
18
inserted in the stationary cylindrical sleeve
16
, and a rotor body
20
fixed to the main shaft
18
.
Between the main shaft
18
and the stationary cylindrical sleeve
16
, there are provided a drive motor
22
, and upper and lower radial bearings
24
and
26
provided above and below the drive motor
22
. An axial bearing
28
is disposed at a lower portion of the main shaft
10
, and comprises a target disk
28
a
mounted on the lower end of the main shaft
18
, and upper and lower electromagnets
28
b
provided on the stator side. Further, touchdown bearings
29
a
and
29
b
are provided at upper and lower portions of the stationary cylindrical sleeve
16
.
With this arrangement, the rotor R can be rotated at a high speed under
5
-axis active control. The rotor body
20
in the axial turbine blade pumping section L
1
has disk-like rotor blades
30
integrally provided on an upper outer circumferential portion thereof. In the casing
10
, there are provided stator blades
32
disposed axially alternately with the rotor blades
30
. Each of the stator blades
32
has an outer edge clamped by stator blade spacers
34
and is thus fixed. Each of the rotor blades
30
has a wheel-like configuration which has a hub at an inner circumferential portion thereof, a frame at an outer circumferential portion thereof, and inclined blades (not shown) provided between the hub and the frame and extending in a radial direction. Thus, the turbine blades
30
are rotated at a high speed to make an impact on gas molecules in an axial direction for thereby evacuating gas.
The radial turbine blade pumping section L
2
is provided downstream of, i.e. below the axial turbine blade pumping section L
1
. In the radial turbine blade pumping section L
2
, the rotor body
20
has disk-like rotor blades
36
integrally provided on an outer circumferential portion thereof in the same manner as the axial turbine blade pumping section L
1
. In the casing
10
, there are provided stator blades
38
disposed axially alternately with the rotor blades
36
. Each of the stator blades
38
has an outer edge clamped by stator blade spacers
40
and is thus fixed.
Each of the stator blades
38
is in the form of a follow disk, and as shown in
FIGS. 13A and 13B
, each of the stator blades
38
has spiral ridges
46
which are formed in the front and backside surfaces thereof and extend between a central hole
42
and an outer circumferential portion
44
, and spiral grooves
48
whose widths are gradually broader radially outwardly and which are formed between the adjacent ridges
46
. The spiral ridges
46
on the front surface, i.e. upper surface of the stator blade
38
are configured such that when the rotor blade
36
is rotated in a direction shown by an arrow A in
FIG. 13A
, gas molecules flow inwardly as shown by a solid line arrow B. On the other hand, the spiral ridges
46
on the backside surface, i.e. lower surface of the stator blade
38
are configured such that when the rotor blade
36
is rotated in a direction shown by the arrow A in
FIG. 13A
, gas molecules flow outwardly as shown by a dotted line arrow C. Each of the stator blade
38
is usually composed of two half segments, or three or more divided segments. The stator blades
38
are assembled by interposing the stator blade spacers
40
so that the stator blades
38
alternate with the rotor blades
36
, and then the completed assembly is inserted into the casing
10
.
With the above configuration, in the radial turbine blade pumping section L
2
, a long evacuation passage extending in zigzag from top to bottom between the stator blades
38
and the rotor blades
36
is constructed within a short span in the axial direction, thus achieving high evacuation and compression performance without making the radial turbine blade pumping section L
2
long in the axial direction.
In the radial turbine blade pumping section L
2
, the outer diameter D
1
of the rotor at its portion facing the inner circumferential surface of the stator blade
38
is set to the same dimension in all stages, and the inner diameter D
2
of the stator (outer diameter of the spiral ridge-groove section) at its portion facing the outer circumferential surface of the rotor blade
36
is set to the same dimension in all stages.
However, in the case of the conventional turbo-molecular pump having the radial turbine blade pumping section L
2
, as shown in
FIG. 14
, the gap G
1
between the stator blade
38
located at the first stage in the radial turbine blade pumping section L
2
and the rotor blade
30
located immediately above this first-stage stator blade
38
and at the lowermost stage in the axial turbine blade pumping section L
1
is constant. Therefore, the cross-sectional area of the flow passage extending along the upper surface of the stator blade
38
toward the inner circumferential side of the stator blade
38
, i.e. the inner circumferential side of the radial turbine blade pumping section L
2
decreases drastically in proportion to the radius of the stator blade
38
. Consequently, the gas is prevented from flowing smoothly to the inner circumferential side of the radial turbine blade pumping section L
2
to cause stagnation of the gas. Further, when the gas turns its flow direction from the axial direction to the radial direction, the gas cannot be smoothly flowed to be stagnated, thus lowering the evacuation performance of the pump.
SUMMARY OF THE INVENTION
The present invention has been made in view of the above drawbacks in the conventional turbo-molecular pump. It is therefore an object of the present invention to provide a turbo-molecular pump which can create smooth gas flow therein and prevent the evacuation performance from lowering.
According to a first aspect of the present invention, there is provided a turbo-molecular pump comprising: a casing; a stator fixedly mounted in the casing and having stator blades; a rotor rotatably provided in the casing and having rotor blades, the rotor blades alternating with the stator blades; and a radial turbine blade pumping section having a spiral ridge-groove section provided on at least one of surfaces, facing each other, of the stator blade and the rotor blade; wherein at least one of the stator blade and the rotor blade which are located at a first stage of the radial turbine blade pumping section has such a shape that the at least one of the stator blade and the rotor blade is smaller in thickness in a direction of gas flow.
With the above arrangement, at least one of the cross-sectional area of the flow passage defined between the stator blade at the first stage in the radial turbine blade pumping section and the rotor blade located immediately above this first-stage stator blade and at the lowermost stage in the axial turbine blade pumping section and the cross-sectional area of the flow passage defined between the rotor blade at the first stage in the radial turbine blade pumping section and the stator blade located immediately above this first-stage rotor blade and at the lowermost stage in the axial turbin
Armstrong Westerman & Hattori, LLP
Ebara Corporation
Look Edward K.
Nguyen Ninh
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