The present invention relates to a screw type fluid machine equipped with a screw rotor, such as a compressor, an air blower, and an expander.
In a screw compressor and such that compress a gas by making a pair of male and female rotors to be engaged with each other, a typical cause of performance degradation is an internal leakage. The internal leakage is a phenomenon in which a compressed gas flows backwards from a compression chamber formed between the male and female rotors to a compression chamber of lower pressure. Since suction of the gas is inhibited by the internal leakage and power loss occurs by recompression of a leakage gas, performance of the screw compressor and such is degraded. In the screw compressor and such, a series of continuous contact points are formed between the male and female rotors. The series of continuous contact points is called a meshing seal line. The meshing seal line has a function of sealing the compressed gas. A length of the meshing seal line is preferred to be short from a view point of reducing the internal leakage of the gas. Trials for suppressing the gas leakage from the meshing seal line are made by shortening the length of the meshing seal line formed between the male and female rotors as much as possible as a measure against the internal leakage.
As a second problem, there is a problem of a “blowhole”. In a screw rotor in which a female rotor has an addendum outside of a pitch circle and a male rotor has a dedendum inside a pitch circle, a blowhole is formed. The blowhole is formed among male and female rotors and a cusp line where bores formed in a casing are crossed. Through the blowhole, a gas leakage occurs. Formation of the blowhole is described with reference to
An internal wall of the casing bore b also has a gas sealing function of the compression chamber by being in contact with the male and female rotors. Hereinafter, a line of intersection between the internal wall of the casing bore b and the cross-section perpendicular to the axis is called a tip seal line c. A meshing seal line s formed between the male rotor 102 and the female rotor 104, and the tip seal line c formed at a rotor outer peripheral part are not connected and are discontinuous. The discontinuous part is called a blowhole, and is literally an open ceiling section. The blowholes are formed at two positions that are a suction side blowhole B1 and a compression side blowhole B2. The suction side blowhole B1 is formed between an upper cusp point Pk1 and the meshing seal line s. The compression side blowhole B2 is formed between a blowhole side closest point Ps of the meshing seal line s and a lower cusp point Pk2.
It is the compression side blowhole B2 which causes a problem from a viewpoint of performance of the screw compressor.
The applicant previously proposed a configuration of a screw rotor capable of reducing an area of the blowhole (Patent Document 1). The invention is to make a cross-section shape perpendicular to the axis from an addendum top center of the female rotor to a pitch circle on a side advancing against a rotation direction to be formed of three or more arcs, which reduces the blowhole area.
Patent Document 1: Japanese Patent No. 3356468
However, in general, in a fluid machine equipped with the screw rotor, a length of the meshing seal line and an area of the blowhole are in a conflicting relation. In other words, when the meshing seal line is made shorter, the blowhole area increases. Therefore, it is difficult to simultaneously achieve reduction in the meshing seal line length and reduction in the blowhole area. Since the internal leakage suppressing means disclosed in Patent Document 1 mainly reduces the blowhole area, it is necessary to consider an internal leakage suppressing means including shortening of the meshing seal line length.
The present invention, in view of the problem in the prior art, aims at achieving reduction in the meshing seal line length and further reduction in the blowhole area.
The present invention is applied to a screw-type fluid machine including a screw rotor having a problem of formation of a blowhole and including a male rotor and a female rotor that are engaged with each other and mutually rotate, wherein the female rotor has an addendum outside a pitch circle, the male rotor has a dedendum inside a pitch circle. To achieve the objective, in a screw-type fluid machine of the present invention, among contours of a blowhole formed among the male and female rotors and a cusp line formed in a casing, a female rotor side blowhole contour formed by the female rotor between a blowhole side closest point of the meshing seal line and the cusp line is composed of a plurality of contour elements, wherein the plurality of contour elements include at least two arcs.
In the present invention, tooth profiles of the male and female rotors are configured under a condition where the meshing seal line formed between the male rotor and the female rotor becomes equal to or less than a setting value. For instance, the tooth profiles of the male and female rotors are so configured that the meshing seal line becomes as short as possible in design. A compression side blowhole is formed among the male and female rotors and a lower cusp line. In the present invention, among the compression side blowhole contours, the female rotor side blowhole contour formed by the female rotor between the blowhole side closest point of the meshing seal line and the cusp line is made to be composed of a contour including at least two arcs. By including at least two arcs in the female rotor side blowhole contour, the blowhole area may be reduced. A tooth profile of the female rotor is obtained by mathematically transforming the blowhole contour formed by the female rotor. A tooth profile of the male rotor is generated corresponding to the tooth profile of the female rotor. A shape generation theory requires that a center of curvature of the obtained female rotor tooth profile is located inside the pitch circle.
The blowhole area reducing means described in Patent Document 1 is to find out a female rotor tooth profile capable of reducing the blowhole area by trial and error. On the other hand, the present invention is to find out a female rotor side blowhole contour capable of reducing the blowhole area at first, and to determine a tooth profile of the female rotor according to the contour. Therefore, a tooth profile of the female rotor capable of reducing the blowhole area may be selected without trial and error. Since tooth profiles of the male and female rotors are selected so that the meshing seal line becomes as short as possible in design in advance, shortening of the meshing seal line length and reduction in the blowhole area may be simultaneously achieved.
In the present invention, specifically, the female rotor side blowhole contour may be composed of a first arc connected to the blowhole side closest point of the meshing seal line, a second arc connected to the first arc, and a contour element composed of a curve extending between a terminating end of the second arc and the cusp line. Thereby, a contour capable of reducing the blowhole area may be formed.
In the configuration, a curve connecting the terminating end of the second arc and the cusp line may be composed of a third arc connected to the terminating end of the second arc and a fourth arc extending between a terminating end of the third arc and the cusp line. In this way, by configuring the female rotor side blowhole contour by four different arcs, a contour capable of reducing the compression side blowhole area may be formed.
Alternatively, the curve extending between the terminating end of the second arc and the cusp line may be composed of a first parabola connected to the terminating end of the second arc and a second parabola connecting a terminating end of the first parabola and the cusp line. In this way also, a contour capable of reducing the compression side blowhole area may be formed.
Alternatively, the curve extending between the terminating end of the second arc and the cusp line may be composed of one cubic curve. In this way also, a contour capable of reducing the compression side blowhole area may be formed.
In the present invention, at a connection point between contour elements composed of an arc, a parabola, or a cubic curve, tangents of the contour elements on both sides across the connection point may have a same gradient. In this way, different curves may be smoothly connected while reducing the blowhole area.
According to the present invention, shortening of the meshing seal line length and further reduction in the blowhole area may be simultaneously achieved, and an internal leakage of the screw-type fluid machine may be effectively suppressed.
Embodiments of the present invention will now be described in detail with reference to the accompanying drawings. It is intended, however, that unless particularly specified, dimensions, materials, shapes, relative positions and the like of components described in the embodiments shall be interpreted as illustrative only and not limitative of the scope of the present invention.
A first embodiment of the present invention is described on the basis of
The female rotor side blowhole contour R3 is formed by four arcs C1 (Ps to P1), C2 (P1 to P2), C3 (P2 to P3), and C4 (P3 to P4). A starting end of the arc C1 is a blowhole side closest point Ps of the meshing seal line s, and a starting end of the arc C2 is connected to a terminating end of the arc C1. A starting end of the arc C3 is connected to a terminating end of the arc C2, and a starting end of the arc C4 is connected to a terminating end of the arc C3. A terminating end of the arc C4 is connected to the lower cusp line k2 at the intersection P4.
A center of the arc C1 is O1, and a curvature radius is r1. A center of the arc C2 is O2, and a curvature radius is r2. A center of the arc C3 is O3, and a curvature radius is r3. A center of the arc C4 is O4, and a curvature radius is r4. At a connection point of each arc, tangents of the arcs on both sides across the connection point have a same gradient, and the both tangents are overlapped. Thus, at the connection point of each arc, the arcs on both sides are smoothly connected. The curvature radius r1 and r4 are set at diameters significantly larger than the curvature radius r2 and r3. Thereby, formation of a blowhole contour capable of reducing the compression side blowhole B2 becomes easy.
As illustrated in
A tooth profile of the female rotor is obtained by mathematically transforming the female rotor side blowhole contour R3. A tooth profile of the male rotor is generated corresponding to the tooth profile of the female rotor. Part of the tooth profile of the female rotor at the cross-section perpendicular to the axis thus obtained is illustrated in
In
According to the present embodiment, a female rotor side blowhole contour R3 capable of reducing an area of the compression side blowhole B2 is to be found first, and then a tooth profile of the female rotor is determined according to the female rotor side blowhole contour R3. Therefore, a tooth profile of the female rotor capable of reducing compression side blowhole area B2 may be selected without trial and error, and an area of the compression side blowhole B2 may be further reduced than Patent Document 1. Since a curvature radius r1 of the arc C1 connected to the blowhole side closest point Ps of the meshing seal line s and a curvature radius r4 of the arc C4 connected to the intersection P4 are set at diameters significantly larger than the curvature radiuses r2 and r3 of the other arcs, formation of the female rotor side blowhole contour that reduces the area of the compression side blowhole B2 becomes easy.
A second embodiment of the present invention is described with reference to
The female rotor side blowhole contour R4 of the present embodiment is formed by replacing the arcs C3, and C4 of the first embodiment with the parabolas C5, and C6. Similar to the first embodiment, at a connection point of each arc and each parabola, tangents of arcs on both sides across the connection point have the same gradient, and the both tangents are overlapped. In this way, by configuring the female rotor side contour R4 with the two arcs C1 (Ps to P1) and C2 (P1 to P2), and two parabolas C5 (P2 to P3) and C6 (P3 to P4), an area of the compression side blowhole B2 may be reduced. Since, at the connection points of the arc C1 and C2 and parabolas C5 and C6, the tangents of the arcs on both sides across the connection points have the same gradients, different curves may be smoothly connected.
Next, a third embodiment of the present invention is described with reference to
The female rotor side blowhole contour R5 of the present embodiment is formed by replacing the arcs C3 and C4 of the first embodiment with the cubic curve C7. Similar to the first embodiment, at a connection point of each arc and each parabola, tangents of arcs on both sides across the connection point have the same gradient, and both tangents are overlapped. The other configurations are the same as the first embodiment. It is apparent from
Next, results obtained by actually designing screw rotors according to the specifications of the first to third embodiments, and measuring lengths of the meshing seal lines s and areas of the compression side blowholes B2 of the designed screw rotors are explained. Table 1 of
According to the present invention, in a screw rotor that is applied to a rotary machine such as a screw compressor, a meshing seal line length and a blowhole area may be reduced than those in the prior art, and thus an internal leakage may be suppressed and performance may be further improved.
Number | Date | Country | Kind |
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2012-212086 | Sep 2012 | JP | national |
Filing Document | Filing Date | Country | Kind |
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PCT/JP2013/075003 | 9/17/2013 | WO | 00 |
Publishing Document | Publishing Date | Country | Kind |
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WO2014/050632 | 4/3/2014 | WO | A |
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Number | Date | Country | |
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20150211517 A1 | Jul 2015 | US |