Rotary expansible chamber devices – Interengaging rotating members – Each tapered
Reexamination Certificate
2000-06-08
2001-07-10
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Interengaging rotating members
Each tapered
C418S149000, C418S107000
Reexamination Certificate
active
06257854
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to fluid machinery for controlling a fluid pressure, and more particularly to a double screw rotor assembly, which uses pressure difference to adjust the clearance automatically, so as to reduce the consumption of starting power. The double screw rotor assembly of the invention can be used in vacuum pumps, air compressors, water or oil pumps, or other fluid media.
FIG. 1
shows a double screw rotor assembly manufactured by KASHIYAMA INDUSTRIES, LTD., and designed for use in a vacuum pump. This structure of double screw rotor comprises two screw rotors
81
and
82
meshed together. Because the screw rotors
81
and
82
have a constant pitch P′ and constant height of tooth H′, the volume of air chamber
810
or
820
does not change while air is transferred from the inlet to the output end
80
, a significant pressure difference occurs and causes a reverse flow of air, high noises, and waste of energy.
U.S. Pat. No. 5,667,370 discloses another structure of double screw rotor assembly. According to this design, as illustrated in
FIG. 2
, the meshed screw rotors
83
and
84
have same height of tooth H″, and the pitch is made gradually reduced in direction from the input side toward the output side
801
(P
1
>P
2
). Because of P
1
>P
2
, the volume of air chamber
830
or
840
is reduced during transmission, and the pressure in these chambers would be increased gradually. Therefore, when the air cambers were compressed and transmitted to the output end
801
, less pressure difference occurs, the reverse flow of air would be reduced and so as to the noise. However, because of different pitches and pressure angles are defined at different rotor section, the fabrication process of the screw rotors
83
and
84
are complicated, resulting in a high manufacturing cost.
FIG. 3
shows still another structure of double screw rotor assembly, which was filed to USPTO for a patent by the present applicant under application Ser. No. 09/372,674. According to this design, two screw rotors are meshed together and mounted in a compression chamber inside a casing, each comprising a spiral thread around the periphery. The thread has a height H made gradually reduced from the input side to the output side
90
. The threads of the screw rotors define a constant pitch P in order to be manufactured easily. The volumes of the air chambers
910
and
920
reduce gradually from the input side toward the output side, so the pressure can be increased gradually during transmission of air, the consumption of operation power and noise can be reduced. Because a uniform pitch P is provided and the height H is made gradually reduced from the input side toward the output side
90
, the outer diameter D has the shape of an invertedly disposed cone, and the inner diameter d has the shape of a regular cone.
According to the aforesaid second and third prior art designs, much starting power is required when starting the double screw rotor assembly. As illustrated in
FIG. 3
, the pressure (i.e. the atmospheric pressure) in all air chambers
910
and
920
, pressure Pi at the input side, and pressure Po at the output side, at the initial stage are the same. Because the volumes of the air chambers
910
and
920
are gradually reduced during rotary motion of the screw rotors, the pressure Pmax near the output side surpasses the pressure P
0
(=the atmospheric pressure) at the output side when starting the double screw rotor assembly. Therefore, much more power and electric current are required to drive the rotors
91
and
92
to conquer the flow pressure of all air chambers
910
and
920
. A certain period of time after starting, the flow pressure at the input side
901
is gradually reduced (for example, being drawn into a vacuum state), causing the flow pressure in the air chambers
910
and
920
near the input side
901
to be gradually reduced, and hence the power consumed is gradually reduced to the level of the rated working power. Because high working power is required when starting the double screw rotor assembly, high current, noise and vibration occur at the initial state when starting the screw rotors, resulting in an unstable operation.
FIG. 4
shows another prior art design constructed according to U.S. Pat. No. 5,533,887. According to this design, a movable case is sliding in a fixed case, however the spring at the top of the movable case is not adjustable, and the presence of the gap
22
C which is left between the movable case and the fixed case for enabling the movable case to slide in the fixed case which may cause air leakage directly from the high pressure area to the low pressure area, thereby causing a low working efficiency. Further, if the process gas condensed in the gap between movable and fixed cases, the movable case may be jammed at some position, and the bypass mechanism failed.
In view of the drawbacks of the aforesaid prior art designs, there is a strong demand for a high performance double screw rotor assembly that requires low starting power, and can be conveniently adjusted to fit different manufacturing requirement.
SUMMARY OF THE INVENTION
The present invention has been accomplished to provide a double screw rotor assembly, which eliminates the aforesaid drawbacks. It is one object of the present invention to provide a double screw rotor assembly, which reduces starting power and starting electric current automatically by adjusting the pre-loading spring to control the flow leakage, so as to prevent a motor overload, and to achieve a stable operation. It is another object of the present invention to provide a double screw rotor assembly, which achieves a high performance by preventing a leakage during its operation. According to one aspect of the present invention, the double screw rotor assembly comprises a casing having a receiving chamber; an inlet and an outlet; a bushing axially movably mounted in the receiving chamber inside the casing, the bushing having an inside wall defining a receiving chamber, and an outside wall fitting the inside wall of the casing; guide means to guide axial movement of the bushing relative to the casing; a O-ring disposed between the top wall of the bushing and the casing; two screw rotors meshed together and mounted in the receiving chamber inside the bushing; and pre-loading adjustable spring means mounted between the bushing and the casing and imparting an axial spring force to the bushing relative to the casing, wherein the adjustable spring means pushes the bushing away from the casing to increase the gap between the inside wall of the bushing and the tooth tip of each spiral thread of the screw rotors before rotation of the screw rotors, and the bushing is forced by a pressure difference between the inlet and the outlet to conquer the axial spring force from the adjustable spring means and to force the O-ring against the casing after rotation of the screw rotors, thereby causing the gap between the inside wall of the bushing and the tooth tip of each spiral thread of the screw rotors to be gradually reduced. According to another aspect of the present invention, spring, hydraulic cylinder, pneumatic cylinder, elastomer, or any other equivalent means can be used for the adjustable spring means. According to still another aspect of the present invention, the guide means comprises at least one sliding groove formed on the outside wall of the bushing, and at least one guide rib respectively formed integral with the inside wall of the casing and coupled to the at least one sliding groove on the bushing. The O-ring can be made of rubber, or any suitable equivalent sealing material. The sliding groove and the guide rib can be made having any of a variety of designs that facilitate stable movement of the bushing relative to the casing. Further, the outer diameter of the thread of each screw rotor can be made linearly or non-linearly reduced from the inlet toward the outlet, having a convex or concave profile.
REFERENCES:
patent: 2707441 (1955-05-01), Drenn
Fang Hong-Sheng
Liu Ming-Hsin
Tsai Cheng-Chan
Denion Thomas
Industrial Technology Research Institute
Rabin & Champagne, P.C.
Trieu Theresa
LandOfFree
Double screw rotor assembly having means to automatically... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Double screw rotor assembly having means to automatically..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Double screw rotor assembly having means to automatically... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2493952