Rotary kinetic fluid motors or pumps – Smooth runner surface for working fluid frictional contact
Reexamination Certificate
2000-03-29
2001-09-18
Look, Edward K. (Department: 3745)
Rotary kinetic fluid motors or pumps
Smooth runner surface for working fluid frictional contact
C415S222000, C417S423400
Reexamination Certificate
active
06290457
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a vacuum pump, and more specifically to a vacuum pump having rotor blades arranged on an inlet port side.
2. Description of the Related Art
Vacuum pumps are widely used in, for example, systems for discharging a gas within a chamber and for evacuating the chamber in semiconductor production devices. Such vacuum pumps include those entirely comprised of blades and those comprised of blades and thread groove portions.
FIGS. 6A-6C
depict the structures of conventional vacuum pumps.
FIG. 6A
is a top plan view showing part of a conventional vacuum pump,
FIG. 6B
is a partial cross-sectional view showing a conventional vacuum pump with a straight inlet port, and
FIG. 6C
is a partial cross-sectional view showing a conventional vacuum pump with a constricted inlet port.
These vacuum pumps comprise a stator
70
fixed to an interior of a casing
10
, and a rotatable rotor
60
. The stator
70
and the rotor
60
are formed with axially stepped portions of blades, constituting a turbine.
In vacuum pumps having such a structure, the rotor
60
is rapidly rotated with a motor at several tens of thousand rpm under a normal state, so that the vacuum pumps may be evacuated (exhausted).
Such vacuum pumps are used to discharge gas molecules in such a manner whereby rotation of the rotor
60
allows the gas molecules sucked from an inlet port
16
to be struck in a direction of rotation of rotor blades
62
. Depending upon the difference between an amount of the molecules flowing toward the outlet port
17
and the amount of molecules flowing back to the inlet port
16
from the outlet port
17
due to a pressure difference between the inlet port
16
and the outlet port
17
, a final discharge amount, i.e., a discharge capability of the pump is determined.
However, the gas molecules within a molecular flow region are reflected in a direction perpendicular with respect to an impinging wall surface (impinging surface) regardless of an angle incident to the wall surface. This urges most of the molecules accelerated in the vicinity of the tip ends of the rotor blades
62
to advance in its tangential direction (a direction vertical to the rotor blades
62
). On the other hand, the inner wall of the casing
10
is shaped into a cylinder, and is expanded in a direction of advancing the molecules (tangential direction) depending upon its curvature. Therefore, the gas molecules impinging on the tip ends of the rotor blades
62
may often impinge on the inner wall of the casing
10
.
If portions where the rotor blades
62
are arranged have axially constant inner diameters in the casing
10
, most of the molecules that accelerate in the vicinity of the tip ends of the rotor blades
62
then impinge on the casing
10
, and are reflected in a direction vertical to the wall surface of the casing
10
, thereby decelerating in flowing directions. This causes the gas molecules that decelerate in flowing directions (an axial direction) to stay in the vicinity of the tip ends of the rotor blades
62
, thereby reducing the discharge flow rate along with a partially increased pressure. This deteriorates discharge capabilities.
This tends to occur at the uppermost rotor blade to which no certain momentum in a discharge direction is yet applied by the rotor blades
62
or in the vicinity of the tip end of the second rotor blade
62
with less momentum.
Consider a turbomolecular pump of the type shown in
FIG. 6C
, in which the inner diameter of the casing is narrowed at the inlet port side so as to be constricted to a predetermined bore size at the inlet port side (an upstream side) above the uppermost rotor blade
62
in order to attach the casing to a flange with a smaller bore size than the outer diameter of the rotor blades. The gas molecule flow in a molecular flow region is highly straightforward while the gas molecules enter only into substantially the same range as the port size of the inlet port
16
. Therefore, the uppermost rotor blade
62
has the problem that the gas molecules are not likely to flow around its tip end (outer peripheral side) with a high flow rate and high discharge efficiency. Hence, the tip end of the uppermost rotor blade
62
is dead space for the gas molecules introduced from the inlet port
16
, resulting in less discharging of the gas molecules from the inlet port, and is often used to prevent backflow. The discharging effects are deteriorated.
In order to avoid such disadvantages, it is conceivable that a change ratio of the inner diameter of the constriction of the casing
10
is reduced to increase the gas molecules flowing around the tip end of the uppermost rotor blade
62
from the inlet port. However, an increased distance from the inlet port
16
to the uppermost rotor blade
62
brings less conductance, resulting in no improved discharge rate (effective discharge rate) at the inlet port
16
of the pump.
SUMMARY OF THE INVENTION
The present invention has been made in order to solve the above problems associated with aforementioned conventional vacuum pumps, and an object of the present invention is to provide a vacuum pump with less loss at the tip ends of rotor blades arranged on an inlet port side so that the discharge capabilities may be enhanced.
The present invention provides a vacuum pump comprising: a casing having an inlet port for sucking a gas; rotatable rotor blades arranged in multiple stages and received in the casing; and stator blades fixed between the rotor blades, the rotor blades being rotated to transport the gas, wherein the casing includes a cylindrical portion having a larger inner diameter than the inner diameter of the inlet port and a conical portion continuously connecting the cylindrical portion to the inlet port, and wherein each of the rotor blades comprises a plurality of blades extending radially outwardly such that an uppermost rotor blade of the above-described multiple rotor blades on the inlet port side is located in a position corresponding to the conical portion, thus attaining the above object.
Further according to the vacuum pump of the present invention, the shape of the radially outward end of the uppermost rotor blade is inclined at the same angle as an inclination angle of the conical portion.
Still further according to the vacuum pump of the present invention, a second rotor blade of the above-described multiple rotor blades is further located in a position corresponding to the conical portion.
Still further according to the vacuum pump of the present invention, the rotor blade is located so that an upper portion on the inlet port side than a center of the rotor blade in a vertical direction is positioned in the conical portion.
REFERENCES:
patent: 5618167 (1997-04-01), Hirakawa et al.
patent: 5688106 (1997-11-01), Cerruti et al.
patent: 5695316 (1997-12-01), Schutz et al.
patent: 5924841 (1999-06-01), Okamura et al.
patent: 5971725 (1999-10-01), de simon et al.
Kabasawa Takashi
Nonaka Manabu
Adams & Wilks
Look Edward K.
McAleenan James M
Seiko Instruments Inc.
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