Asymmetric double screw rotor assembly

Details Asymmetric double screw rotor assembly Asymmetric double screw rotor assembly

2000-08-17

2001-11-06

Denion, Thomas (Department: 3748)

Rotary expansible chamber devices

Interengaging rotating members

Helical or herringbone

C418S194000

Reexamination Certificate

active

06312242

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 for use in a vacuum pump, air compressor, water or oil pump, or any of a variety of fluid media to regulate the pressure of a fluid passing through.
FIG. 1
shows a double screw rotor assembly constructed according to U.S. Pat. No. 5,667,370 discloses another structure of double screw rotor assembly. According to this design, the meshed screw rotors
83
and
84
have same tooth height H″, and the pitch is made gradually reduced in direction from the input side toward the output end
801
(P
1
>P
2
). Because of P
1
>P
2
, the volume of air chamber
830
or
840
is getting smaller during transmission, causing pressure to be relatively increased. Therefore, when compressed and transmitted to the output end
801
, less pressure difference occurs on the output end, preventing a reverse flow of air and high noise. However, because of different pitches and pressure angles are defined at different elevations, the fabrication process of the screw rotors
83
and
84
is complicated, resulting in a high manufacturing cost.
FIG. 2
shows still another structure of double screw rotor assembly, which was filed by the present applicant under U.S. application Ser. No. 09/372,674. According to this design, two symmetric screw rotors
91
and
92
are meshed together and mounted in a compression chamber inside a casing, each comprising a spiral thread around the periphery. The thread has a tooth height H made gradually reduced from the input side
901
toward the output end
90
. The threads of the screw rotors
91
and
92
define an uniform pitch P. The volumes of the air chambers
910
and
920
reduce gradually from the input side
901
toward the output end
90
, so that pressure can be gradually increased during the transmission process, preventing a high consumption of power and high noise. Because an uniform pitch P is provided and the height H is made gradually reduced from the input side
901
toward the output side
90
, the outer diameter D has the shape of an invertedly disposed cone, and the inner root diameter d has the shape of a regular cone. This design complicates the fabrication of the rotors
91
and
92
.
SUMMARY OF THE INVENTION
The present invention has been accomplished to provide an asymmetric double screw rotor assembly, which eliminates the aforesaid drawbacks. It is main object of the present invention to provide an asymmetric double screw rotor assembly, which is easy and inexpensive to b e manufactured. According to the present invention, the asymmetric double screw rotor assembly comprises a casing, the casing having an inside wall defining a receiving chamber, an inlet, and an outlet, and two screw rotors meshed together and mounted in the receiving chamber inside the bushing. The screw rotors include a first screw rotor and a second screw rotor. The first screw rotor and the second screw rotor each have at least one spiral thread raised around the respective periphery. The tooth tip of the at least one spiral thread of each screw rotor defines an outer diameter disposed in contact with the inside wall of the casing. Each spiral thread of each screw rotor has two side walls. A root of tooth of each spiral thread of each screw rotor defines an inner root diameter. The at least one spiral thread of each screw rotor defines a pitch, and defines with the inside wall of the casing at least one air chamber in the respective pitch. The outer diameter of the first screw rotor and the inner root diameter of the second screw rotor are uniform. The inner root diameter of the first screw rotor gradually increases from the inlet of the casing toward the outlet. The outer diameter of the second screw rotor reduces gradually in direction from the inlet of the casing toward the outlet. Based on the aforesaid design, the fabrication of the first screw rotor and the second screw rotor is easy and inexpensive. The inner root diameter of the first screw rotor can be made linearly increased in direction from the inlet of the casing toward the outlet, and the outer diameter of the second screw rotor can be made linearly reduced in direction from the inlet of the casing toward the outlet. Alternatively, the inner root diameter of the first screw rotor and the outer diameter of the second screw rotor can be increased or reduced non-linearly, for example, curved inwards or outwards.


REFERENCES:
patent: 2939745 (1960-06-01), Carlsmith et al.
patent: 3814557 (1974-06-01), Volz
patent: 5667370 (1997-09-01), Im
patent: 6176694 (2001-01-01), Fang et al.
patent: 384355-A (1932-12-01), None
patent: 01-237384-A (1989-09-01), None
patent: 1437575-A (1988-11-01), None

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