Rotary expansible chamber devices – Interengaging rotating members – Helical or herringbone
Reexamination Certificate
1999-11-18
2001-07-10
Denion, Thomas (Department: 3748)
Rotary expansible chamber devices
Interengaging rotating members
Helical or herringbone
Reexamination Certificate
active
06257855
ABSTRACT:
BACKGROUND OF THE INVENTION
The invention relates to a screw fluid machine such as screw compressors, screw vacuum pumps and the like, and particularly to a screw fluid machine suitable for reducing noises.
In a twin screw compressor among screw fluid machines, it has become a significant problem to prevent noises generated by a phenomenon called “tooth separating vibration”. With such twin screw fluid machines, a male rotor is made on a drive side, and lobe faces of a female rotor and the male rotor are made to come into contact with each other to drive the female rotor. Apart from this, non-contact type screw fluid machines have been often used, in which timing gears are provided on axial ends of each of the male rotor and the female rotor to mesh with each other to transmit torque. In addition, the lobe faces of the timing gears, which transmit torque, also continue to contact with each other.
Depending upon lobe profiles of the rotors and a condition of pressures acting on the lobe faces of the rotors, circumstances may happen, in which a gas torque acting on the female rotor temporarily becomes negative (here, a gas torque acting in a direction for promoting rotation is made negative), whereby there is generated a state, in which two lobe faces in torque transmitting relationship will move in relatively opposite directions. When the transmission torque again becomes positive, the lobe faces having been temporarily spaced apart from each other come to collide with each other. This phenomenon is called as tooth separation, and large vibrations and noises resulted from such repetitive tooth separation and collision are called as “tooth separating vibration”.
Since large vibrations and great noises are caused by tooth separation, there have been suggested some methods of preventing the tooth separation. For example, Japanese Patent Unexamined Publication No. 5-195972 defines some conditions on lobe profiles, a rotation transmission error between rotors, and between moments of inertia on the respective rotors and rotor lobe faces, in order to prevent a transmission torque from the male rotor to the female rotor from becoming negative. Japanese Patent Unexamined Publication No. 2-252991 describes another example for preventing the tooth separation. In this example, configuration of lobe faces of a screw rotor is defined so that a transmission torque from a male rotor to a female rotor always becomes negative.
However, Japanese Patent Unexamined Publication No. 5-195972 mentioned above defines the conditions for prevention of tooth separation but does not disclose any concrete rotor configuration for satisfying the conditions, and so it is unclear what rotors can realize tooth separation. Also, Japanese Patent Unexamined Publication No. 2-252991 takes no account of gas pressure conditions such as suction pressure, discharge pressure, the kind of a gas being compressed and the like, and so satisfactory results can not be always obtained in a general use where the gas pressure conditions are changed.
BRIEF SUMMARY OF THE INVENTION
The invention has been made in view of the disadvantages in the above-described prior art, and has its object to provide a lobe profile configuration of a screw rotor, with which tooth separating vibration is hard to generate even under various gas pressure conditions. Further, it is another object of the invention to realize a screw fluid machine, which can be operated in a quiet manner under a variety of operating conditions.
In order to achieve the objects mentioned above, a first feature of the invention provides a screw fluid machine comprising a male rotor having helical lobes on an outer periphery thereof, a female rotor adapted to mesh with the male rotor to compress a working gas and having helical lobes on an outer periphery thereof, and a casing adapted to receive both the rotors, and wherein a integrating value of a transmission torque from the male rotor to the female rotor for a single lobe of the female rotor is positive.
In order to achieve the objects mentioned above, a second feature of the invention provides a screw fluid machine comprising a male rotor having helical lobes on an outer periphery thereof, a female rotor adapted to mesh with the male rotor to compress a working gas and having helical lobes on an outer periphery thereof, and a casing adapted to receive both the rotors, and wherein lobe profiles of the respective rotors are defined so that a radius at a point of contact on a leading surface side of the female rotor becomes smaller than both of radii at two points of contact on a trailing surface side when the male rotor and the female rotor are a relative positional relationship, in which three points, at which the female rotor contacts with the male rotor or at which the male rotor and the male rotor are disposed nearest to each other, are formed.
In order to achieve the object mentioned above, a third feature of the invention provides a screw fluid machine comprising a male rotor having helical lobes on an outer periphery thereof, a female rotor adapted to mesh with the male rotor to compress a working gas and having helical lobes on an outer periphery thereof, and a casing adapted to receive both the rotors, and wherein lobe profiles of the respective rotors are defined so that a integrating value at a point of contact on a trailing surface side becomes larger than a integrating value at a point of contact in a leading surface side when integrating a radius of a point of contact of the female rotor with respect to a section of an angle of rotation until point of contacts disappear on the trailing surface side after a maximum radius point of the male rotor and a minimum radius point of the female rotor are disposed nearest to each other. Preferably, the number of male rotor lobes is five and the number of the female rotor lobes is six.
In order to achieve the object mentioned above, a fourth feature of the invention provides a screw fluid machine comprising a female rotor having helical lobes, a male rotor adapted to mesh with the male rotor and having helical lobes, and a casing adapted to receive the pair of the rotors, and wherein, when a leading surface in cross section perpendicular to an axis of the female rotor is divided into a first range between a lobe bottom and a point of inflection and a second range between the point of inflection and a lobe tip, a configuration of the leading surface inverts a sign of positive and negative of curvature before and behind the point of inflection and a curvature distribution of the lobe profile generally increases in the first range.
Preferably, in the fourth feature, the curvature between the lobe bottom and the point of inflection continuously increases in the first range, the curvature distribution of lobe profile monotonously increases in the first range, the curvature distribution of lobe profile in the first range includes at least one point of discontinuity, and the curvature distribution of lobe profile in the first range has a range of a constant curvature.
More preferably, in the first feature, when a leading surface in cross section perpendicular to an axis of the female rotor is divided into a first range between a lobe bottom and a point of inflection and a second range between the point of inflection and a lobe tip, a configuration of the leading surface inverts a sign of positive and negative of curvature before and behind the point of inflection and a curvature distribution of the lobe profile generally increases in the first range. Then, it is desired that the number of male rotor lobes is five and the number of the female rotor lobes is six.
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Aoki Masakazu
Hida Takeshi
Kameya Hirotaka
Nozawa Shigekazu
Urashin Masayuki
Antonelli Terry Stout & Kraus LLP
Denion Thomas
Hitachi , Ltd.
Trieu Theresa
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