Rotary expansible chamber devices – Interengaging rotating members – Helical or herringbone
Reexamination Certificate
1999-03-31
2001-06-12
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Interengaging rotating members
Helical or herringbone
C418S002000, C073S261000
Reexamination Certificate
active
06244844
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to fluid displacement apparatus, and more particularly, to fluid displacement apparatus employing helical rotors.
BACKGROUND OF THE INVENTION
Helical-rotor fluid displacement apparatus, such as screw pumps and helical-rotor volumetric flow meters, have been used for many years. Generally, such apparatus include one or more helical rotors arranged within a conformal chamber having an input port and an output port. The rotor (or rotors) and an inner surface of the chamber typically define a displacement volume that moves along the axis of the rotor as the rotor turns, thus moving fluid from one port of the chamber to another.
Many variations on this basic design have been proposed. For example, U.S. Pat. No. 1,191,423 to Holdaway, U.S. Pat. No. 1,233,599 to Nuebling, U.S. Pat. No. 1,821,523 to Montelius, U.S. Pat. No. 2,079,083 to Montelius, U.S. Pat. No. 2,511,878 to Rathman, U.S. Pat. No. 4,078,653 to Suter, U.S. Pat. No. 4,405,286 to Studer and U.S. Pat. No. 5,447,062 to Kopl et al. describe various positive displacement flow meter and pump apparatus utilizing one or more helical rotors. Another example of a helical-rotor volumetric flow meter is the Birotor™ line of positive displacement flow meters produced by Brooks Instrument, assignee of the present invention.
In helical-rotor fluid displacement apparatus such as flow meters or pumps, the dynamic characteristics of the rotors can significantly affect performance of the apparatus. For example, it is generally desirable for a helical-rotor flow meter used in petroleum flow metering applications have a rugged structure, low vibration levels, low pressure drop, wide operational flow range and high reliability. Each of these characteristics can be affected by the mechanical configuration of the helical-rotors in the apparatus. Certain rotor configurations, including some used in the conventional apparatus referred to above, may limit performance or exhibit reduced reliability. Accordingly, there is a continuing need for improved helical-rotor fluid displacement apparatus.
SUMMARY OF THE INVENTION
In light of the foregoing, it is an object of the present invention to provide improved helical-rotor positive displacement apparatus.
It is another object of the present invention to provide positive displacement flow meter apparatus with enhanced operational flow range, reduced vibration and increased reliability.
It is yet another object of the present invention to provide improved helical rotors for use in positive displacement apparatus such as volumetric flow meters or pumps.
These and other objects, features and advantages are provided according to the present invention by positive displacement apparatus including a housing defining a chamber in which parallel first and second helical rotors are meshed. Each of rotors includes a cylindrical body portion with a helical groove therein, and a helical tooth portion extending radially from the cylindrical body portion and running adjacent the helical groove. Preferably, a first tooth surface (e.g., a leading surface) lies in the helical groove and extends onto the helical tooth portion, and a second tooth surface (e.g., a trailing surface) extends away from the cylindrical body portion and onto the helical tooth portion, opposite the first tooth surface, with the first tooth surface defining an epitrochoid curve in radial cross section and the second tooth surface defining an epicycloid curve in radial cross section. The housing preferably has an inner surface that conforms to a boundary of a swept volume defined by the meshed rotors, forming a capillary seal between portions of third tooth surfaces of the rotors and the inner surface of the housing. This capillary seal, in conjunction with a capillary seal supported between meshed portions of the tooth portions of the rotors, defines a displacement volume that moves parallel to the axes of the rotors as the rotors turn. Clearances between the rotors are preferably maintained by meshed first and second timing gears that are coaxially mounted at ends of respective ones of the first and second rotors.
Rotor forms provided according to the present invention can provide improved dynamic performance, which in turn can provide advantageous operating characteristics in devices in which the rotors are used. For example, a rotor form according to the present invention can offer higher maximum rotational speed, reduced vibration and higher swept volume per revolution in comparison to conventional designs. These advantageous characteristics can mean higher throughput, lower pressure drop and wider operational flow range in devices such as flow meters.
In particular, according to one embodiment of the present invention, a fluid displacement apparatus includes a housing defining a chamber therein having a first port and a second port. First and second helical rotors with opposing pitches are meshed within the chamber, in fluid communication with the first and second ports. A respective one of the first and second helical rotors includes a cylindrical body portion having a helical groove therein and a helical tooth portion extending radially from the cylindrical body portion adjacent the helical groove. The first and second helical rotors are arranged such that respective longitudinal axes of the first and second helical rotors are parallel to one another and a helical tooth portion of one of the first and second helical rotors engages a helical groove of another of the first and second helical rotors, such that the first and second helical rotors are operative to rotate within the chamber and provide fluid transport between the first and second ports parallel to the longitudinal axes.
In another embodiment according to the present invention, a respective one of the first and second helical rotors has a first tooth surface lying within the helical groove and extending onto the helical tooth portion and a second tooth surface extending from the cylindrical body portion onto the helical tooth portion opposite the first tooth surface. The first tooth surface preferably includes an epitrochoid-derived surface, i.e., a surface defining an epitrochoid curve in radial cross section. The second tooth surface preferably includes an epicycloid-derived surface, i.e., a surface defining an epicycloid curve in radial cross section.
According to another embodiment of the present invention, the cylindrical body portion defines a pitch circle in radial cross section. The first tooth surface defines, in radial cross section, a compound curve including two opposing hypocycloid segments extending from a hub portion of the cylindrical body portion to the pitch circle and a first epicycloid segment extending radially from the pitch circle. The second tooth surface defines, in radial cross section, a second epicycloid segment extending radially from the pitch circle, opposite the first epicycloid segment.
In yet another embodiment of the present invention, rotation of the first and second rotors defines a swept volume, and the housing includes an inner surface conforming to a boundary of the defined swept volume. Opposing portions of the first and second helical rotors and portions of the third tooth surfaces confronting the inner surface of the housing may define a displacement volume that moves parallel to the axes of the first and second rotors as the first and second helical rotors rotate within the chamber. A respective one of the first and second helical rotors may include a third tooth surface disposed between the first and second tooth surfaces. The first and second helical rotors are preferably arranged such that portions of the third tooth surfaces are spaced apart from the inner surface of the chamber a distance that supports a capillary seal between portions of the third tooth surfaces and the inner surface of the chamber. The first and second rotors also are preferably arranged such that a capillary seal is supported between opposing portions of the first and second helical rotors. Respective first an
Denion Thomas
Emerson Electric Co.
Myers Bigel Sibley & Sajoec
Trieu Theresa
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