JPWO2004001229A1

JPWO2004001229A1 - Screw rotor

Info

Publication number: JPWO2004001229A1
Application number: JP2004515457A
Authority: JP
Inventors: 俊敬阿部
Original assignee: Hokuetsu Industries Co Ltd
Current assignee: Hokuetsu Industries Co Ltd
Priority date: 2002-06-24
Filing date: 2002-06-24
Publication date: 2005-10-20
Anticipated expiration: 2022-06-24
Also published as: KR20050010753A; CN100351522C; CN1628216A; JP4271654B2; WO2004001229A1; AU2002346203A1

Abstract

スクリュロータの歯間の干渉がなく、シール性が良好で、加工が比較的容易であると共に、発生するブローホールを可及的に小さなものとすることができるスクリュロータを提供する。一対のスクリュロータのそれぞれの軸直角断面形状が、歯先面曲線１３’の両端Ａ，Ｂと、二の歯側面曲線１８’，１９’間に形成された角部１４，１５の一方１４を、軸直角断面形状において前記角部１４の突出方向に向かって曲率半径を漸減する形状と成すと共に、該角部１４から歯底面曲線１７’に至る歯側面曲線１８’の形状を、他方のスクリュロータに形成された前記角部１４が創成する曲線とする。There is provided a screw rotor that has no interference between the teeth of the screw rotor, has a good sealing property, is relatively easy to process, and can make a generated blow hole as small as possible. Each of the pair of screw rotors has a cross-sectional shape perpendicular to the axis, and both ends A and B of the tooth tip surface curve 13 'and one of the corner portions 14 and 15 formed between the two tooth side surface curves 18' and 19 '. In the cross-sectional shape perpendicular to the axis, the radius of curvature gradually decreases toward the protruding direction of the corner portion 14, and the shape of the tooth side surface curve 18 'extending from the corner portion 14 to the root surface curve 17' is changed to the other screw. It is set as the curve which the said corner | angular part 14 formed in the rotor creates.

Description

本発明は、スクリュ圧縮機や真空ポンプその他のスクリュポンプなどのスクリュ流体機械に用いるスクリュロータに関し、より詳細には該スクリュロータの歯形に関する。
技術背景
近年、スクリュ圧縮機や真空ポンプの性能を向上させるため、スクリュロータの歯形についても多くの研究・開発がなされており、スクリュロータの歯形も複雑な曲線を組み合わせたものなど多種にわたっている。
このようなスクリュロータの歯形は、図１０（Ａ）に示すようにスクリュロータの軸線方向の断面における歯形を方形状とし、平坦な形状を成す歯先面１３及び歯底面１７が形成されていると共に、歯先面１３の軸線方向の両角部１４，１５から歯底面の両端部２４，２５に至る歯側面１８，１９が、軸線に対して直交するように形成されたスクリュロータ１０として、実開昭６３−１４８８４号公報に示されている。
前述のように、断面方形状の歯形を成す実開昭６３−１４８８４号公報に示すスクリュロータ１０においては、歯先が面（歯先面１３）として形成されているために、シリンダ内面とこの歯先面１３との間で行われるシールは面シールとなり密閉性が高く、その結果、一の作用空間において圧縮された流体が、シリンダの内壁とスクリュロータ１０の歯先面との隙間から低圧側に位置する他の作用空間に漏出することを好適に防止でき、圧縮効率を向上させることができる。
その一方で、このように形成されたスクリュロータ１０にあっては、図１０（Ｂ）に示すようにスクリュロータの軸直角断面における歯形を、歯先面１３の輪郭を成す歯先面曲線１３’と、歯底面１７の輪郭を成す歯底面曲線１７’と、前記歯先面曲線と前記歯底面曲線との間を連結し歯側面１８の輪郭を成す歯側面線１８’とを備え、前記歯側面線１８’をスクリュロータの外周方向に延びる直線状に形成すると共に、前記歯先面曲線１３’と前記歯側面線１８’との間に形成された角部１４を略直角状に形成している。
このような歯形を有する二つのスクリュロータ１０ａ，１０ｂが同期回転すると、２つのスクリュロータ１０ａ，１０ｂの歯が噛み合う際に角部１４が他方のスクリュロータに形成された歯側線１８’に干渉する。そのため、スクリュロータの角部１４を切り欠いて、このような干渉を防止することが行われている〔図１０（Ｃ）参照〕。
しかし、両スクリュロータ１０ａ，１０ｂが例えば図１０（Ｂ）に示す噛み合い状態にあるときに、図１０（Ｂ）中に破線で示すようにこの角部１４が切り欠かれた状態にあると、作用空間のシール性が低下し、スクリュロータ１０ａ，１０ｂの噛み合いにより本来それぞれ独立した室である作用空間Ａと作用空間Ｂとがこの切欠のために連通して圧縮された流体が低圧側に位置する作用空間に漏出する。そのため、この種のスクリュロータにあっては圧縮効率が低下するという問題を有する。
このような問題を解消するために、歯の干渉を防止しつつより良好なシール性を発揮するスクリュロータとして、特公昭６４−８１９３号公報に開示されているスクリュロータがある（図１１参照）。
このスクリュロータにあっては、図１１（Ｂ）に示すようにスクリュロータの軸直角断面における歯側面曲線１８’の形状を、当該スクリュロータと噛合する他方のスクリュロータの歯先面曲線１３’と歯側面曲線１８’とを連結した角部１４の一点の画くトロコイド曲線により形成し、略完全なシールを図ることができるよう構成されている。
確かに特公昭６４−８１９３号公報に示すスクリュロータにあっては、理論上略完全なシールを図ることができるが、この構成のスクリュロータにおいて完全なシール性を確保しようとすれば、角部１４は鋭利なエッジ状に形成されている必要がある。
しかし、角部１４を鋭利なエッジ形状に加工することは現実的には困難であり、例えばこのようなスクリュロータを切削加工により製造すると、角部１４に多量のバリが生じ、このバリを除去するために角部の面取り等を行うと、この面取りによりバリと共に角部１４のエッジ形状が削り取られるために、前述の切欠を設ける場合と同様に作用空間のシール性が低下する。
また、角部１４を鋭利な形状すると、この角部１４が噛合う他方のスクリュロータに形成する歯底面１７の端部２４を鋭利な形状を有する工具で加工しなければならず、この工具の鋭利な形状の部分は欠け易く、僅かな欠けや摩耗によっても正確にロータの切削が行えないものとなり交換や研ぎ直し等が頻繁に必要となる。
なお、特許第２９０４７１９号公報には、スクリュロータの軸直角断面における角部を円弧としつつシール性の向上を図ったスクリュロータが開示されている。
このスクリュロータは、二つのスクリュロータの角部１４，１４を円弧により形成し、この円弧を成す角部１４は当該スクリュロータと噛合する他方のスクリュロータの歯側面を成す歯側面曲線を創成している。
このように形成されたスクリュロータにあっては、両ロータ間に干渉が生じず、また、作用空間のシール性も向上する。
しかし、角部１４を前述のように円弧としていることから、シリンダ内壁の稜線３３部分に位置して両ロータの角部が対峙すると比較的大きなブローホールが形成され（図１２参照）、このブローホールを介して隣接する各作用空間が連通することから、圧縮した流体が低圧側に位置する作用空間に漏出し圧縮効率が低下するという問題点を有している。
なお、このような圧縮流体の漏れは、歯先面１３と歯側面１８との間に形成された角部１４においてのみ生じるものではなく、歯先面１３とシリンダ内壁３１間の隙間においても生じるものとなっている。
歯先面１３とシリンダ内壁３１間にはスクリュロータを回転させる為に最低限必要な隙間が設けられており、スクリュ流体機械の運転中であっても歯先面１３とシリンダ内壁３１とが接触しないようにスクリュロータの熱膨張量を考慮してシリンダの内径を設定している。しかしながら、スクリュロータの歯先面１３は回転軸芯に対して一様な熱膨張量ではなく、最も熱膨張量の大きい箇所に基づいてシリンダの内径を設定していることから、最も熱膨張量の大きい箇所以外の部分において歯先面１３とシリンダ内壁３１との隙間が大きく、この部分の隙間を介して流体の漏れが生じやすく、この部分において生じる漏れをも好適に防止し得る構造のスクリュロータを提供することができれば、真空ポンプ等のスクリュ流体機械の作業効率をより一層向上させることが可能となる。
そこで、本発明の目的は上記従来技術における欠点を解消するためになされたもので、両スクリュロータの歯間の干渉がなく、シール性が良好で、加工が比較的容易であると共に、発生するブローホールを実用上無視し得る程小さなものとすることができる歯形のスクリュロータを提供することを目的とする。The present invention relates to a screw rotor used in a screw fluid machine such as a screw compressor, a vacuum pump, and other screw pumps, and more particularly to a tooth profile of the screw rotor.
Technical Background In recent years, in order to improve the performance of screw compressors and vacuum pumps, many researches and developments have been made on the tooth profile of the screw rotor, and the tooth profile of the screw rotor covers various types such as a combination of complex curves.
As shown in FIG. 10 (A), the tooth profile of such a screw rotor has a tooth profile in a cross section in the axial direction of the screw rotor, and a tooth tip surface 13 and a tooth bottom surface 17 forming a flat shape are formed. In addition, as the screw rotor 10 formed so that the tooth side surfaces 18 and 19 extending from the both corners 14 and 15 in the axial direction of the tooth tip surface 13 to both end portions 24 and 25 of the tooth bottom surface are orthogonal to the axis, This is shown in Japanese Utility Model Laid-Open No. 63-14848.
As described above, in the screw rotor 10 shown in Japanese Utility Model Laid-Open No. 63-14848 having a tooth profile with a square cross section, the tooth tip is formed as a surface (tooth tip surface 13). The sealing performed between the tooth tip surface 13 is a surface seal and has high sealing performance. As a result, the fluid compressed in one working space is low pressure from the gap between the inner wall of the cylinder and the tooth tip surface of the screw rotor 10. It is possible to suitably prevent leakage into another working space located on the side, and compression efficiency can be improved.
On the other hand, in the screw rotor 10 formed in this way, the tooth profile in the cross section perpendicular to the axis of the screw rotor as shown in FIG. , A root surface curve 17 ′ that defines the contour of the tooth bottom surface 17, and a tooth side surface line 18 ′ that connects the tip surface curve and the root surface curve to define the tooth side surface 18, The tooth side surface line 18 ′ is formed in a straight line extending in the outer peripheral direction of the screw rotor, and the corner portion 14 formed between the tooth tip surface curve 13 ′ and the tooth side surface line 18 ′ is formed in a substantially right angle. are doing.
When the two screw rotors 10a and 10b having such tooth shapes rotate synchronously, the corner portion 14 interferes with the tooth side line 18 'formed on the other screw rotor when the teeth of the two screw rotors 10a and 10b mesh. . Therefore, the corner portion 14 of the screw rotor is cut away to prevent such interference [see FIG. 10C].
However, when the screw rotors 10a and 10b are in the meshing state shown in FIG. 10 (B), for example, if the corner 14 is cut out as shown by the broken line in FIG. 10 (B), The sealing performance of the working space is reduced, and the working space A and the working space B, which are originally independent chambers due to the engagement of the screw rotors 10a and 10b, communicate with each other due to this notch, and the compressed fluid is positioned on the low pressure side. Leaks into the working space. Therefore, this type of screw rotor has a problem that the compression efficiency is lowered.
In order to solve such problems, there is a screw rotor disclosed in Japanese Patent Publication No. 64-8193 as a screw rotor that exhibits better sealing properties while preventing tooth interference (see FIG. 11). .
In this screw rotor, as shown in FIG. 11B, the shape of the tooth side surface curve 18 ′ in the cross section perpendicular to the axis of the screw rotor is changed to the tooth tip surface curve 13 ′ of the other screw rotor meshing with the screw rotor. And the tooth side surface curve 18 'are formed by a trochoid curve formed by a single point of the corner portion 14 so that a substantially perfect seal can be achieved.
Surely, in the screw rotor shown in Japanese Patent Publication No. 64-8193, a theoretically perfect seal can be achieved. 14 needs to be formed in a sharp edge shape.
However, it is practically difficult to process the corner portion 14 into a sharp edge shape. For example, when such a screw rotor is manufactured by cutting, a large amount of burrs are generated at the corner portion 14 and the burrs are removed. Therefore, when the corner portion is chamfered, the edge shape of the corner portion 14 is removed together with the burr by this chamfering, so that the sealing performance of the working space is lowered in the same manner as in the case of providing the above-described notch.
Further, when the corner portion 14 has a sharp shape, the end portion 24 of the bottom surface 17 formed on the other screw rotor with which the corner portion 14 is engaged must be processed with a tool having a sharp shape. A sharply shaped portion is easily chipped, and even a slight chipping or wear makes it impossible to cut the rotor accurately and frequent replacement and sharpening are required.
Japanese Patent No. 2904719 discloses a screw rotor that improves the sealing performance while making the corners of the screw rotor perpendicular to the axis a circular arc.
In this screw rotor, the corner portions 14, 14 of the two screw rotors are formed by circular arcs, and the corner portions 14 forming the circular arcs create a tooth side curve that forms the tooth side surface of the other screw rotor that meshes with the screw rotor. ing.
In the screw rotor formed in this way, no interference occurs between the two rotors, and the sealing performance of the working space is improved.
However, since the corner portion 14 is an arc as described above, a relatively large blow hole is formed when the corner portions of both rotors are located at the ridge line 33 portion of the inner wall of the cylinder (see FIG. 12). Since the adjacent working spaces communicate with each other through the hole, the compressed fluid leaks into the working space located on the low pressure side, and the compression efficiency is lowered.
Such leakage of the compressed fluid does not occur only in the corner portion 14 formed between the tooth tip surface 13 and the tooth side surface 18 but also in a gap between the tooth tip surface 13 and the cylinder inner wall 31. It has become a thing.
A minimum gap is provided between the tooth tip surface 13 and the cylinder inner wall 31 to rotate the screw rotor. The tooth tip surface 13 and the cylinder inner wall 31 are in contact with each other even during operation of the screw fluid machine. The inner diameter of the cylinder is set in consideration of the amount of thermal expansion of the screw rotor. However, since the tip surface 13 of the screw rotor is not a uniform thermal expansion amount with respect to the rotational axis, the inner diameter of the cylinder is set based on the portion having the largest thermal expansion amount. The gap between the tooth tip surface 13 and the cylinder inner wall 31 is large in a portion other than the large portion, and fluid leakage is likely to occur through the gap in this portion, and the screw having a structure that can suitably prevent leakage occurring in this portion. If the rotor can be provided, the working efficiency of a screw fluid machine such as a vacuum pump can be further improved.
Accordingly, an object of the present invention is to solve the above-described drawbacks of the prior art, and there is no interference between the teeth of both screw rotors, the sealing property is good, the processing is relatively easy, and the problem occurs. An object of the present invention is to provide a screw rotor having a tooth profile in which a blow hole can be made so small as to be practically negligible.

上記目的を達成するために本発明のスクリュロータは、一対のスクリュロータ１０ａ，１０ｂをねじれ方向を逆にして噛合させて回転し、流体を吸入しかつ吐出するスクリュ機械に使用されるスクリュロータにおいて、
前記一対のスクリュロータ１０（１０ａ，１０ｂ）のそれぞれの軸直角断面における歯形は、スクリュロータ１０（１０ａ，１０ｂ）の回転軸芯Ｏを中心とする所定径（ｒ_１）の円弧から成り歯先面１３の輪郭を成す歯先面曲線１３’と、前記歯先面曲線１３’と同心で前記歯先面曲線１３’よりも小径（ｒ_２）の円弧から成り歯底面１７の輪郭を成す歯底面曲線１７’と、前記歯先面曲線１３’と歯底面曲線１７’との間に形成された歯側面１８，１９の輪郭を成す二の歯側面曲線１８’，１９’とを備え、
前記歯先面曲線１３’の両端と、前記二の歯側面曲線１８’，１９’との間に形成された角部１４，１５の一方１４を、前記歯先面曲線１３’の一端Ａと前記歯側面曲線１８’の一端Ｇ間を連結する曲線Ａ−Ｇにより形成し、
前記歯先面曲線１３’の一端Ａと前記歯側面曲線１８’の一端Ｇ間を連結する前記曲線Ａ−Ｇを、前記歯先面曲線１３’の一端Ａから前記角部１４の突出方向に向かって曲率半径を漸減する形状を成すと共に、該角部１４から前記歯底面曲線１７’に至る前記歯側面曲線１８’を、他方のスクリュロータに形成された前記角部１４，１５の一方１４が創成する曲線としたことを特徴とする（請求項１：図６参照）。
また、本発明の別のスクリュロータ１０（１０ａ，１０ｂ）にあっては、前述の角部１４の構成に代え、又は前述の角部１４の構成と共に、少なくとも一方、好ましくは双方のスクリュロータ１０（１０ａ，１０ｂ）の前記歯先面曲線１３’を前記スクリュロータ１０（１０ａ，１０ｂ）の回転軸芯を中心として９０〜１８０°の範囲に形成したことを特徴とする（請求項２及び請求項３）。
前記角部１４，１５の一方１４の軸直角断面形状は、楕円、放物線、双曲線である二次曲線により構成することができ（請求項４）、楕円の場合にはその一部により前記角部１４を形成しても良い（請求項５）。
さらに、前記角部１４，１５の一方１４の軸直角断面形状は、該角部１４の突出方向に向かって曲率半径を漸減する二次曲線上の複数の点を連結することにより形成された、前記二次曲線に近似した曲線により形成することもできる（請求項６）。In order to achieve the above object, a screw rotor according to the present invention is a screw rotor used in a screw machine that rotates by meshing a pair of screw rotors 10a and 10b with their torsional directions reversed to suck and discharge fluid. ,
The tooth profile of each of the pair of screw rotors 10 (10a, 10b) in a cross section perpendicular to the axis is an arc having a predetermined diameter (r ₁ ) centered on the rotational axis O of the screw rotor 10 (10a, 10b). Tooth surface curve 13 ′ that defines the contour of the surface 13, and a tooth that is concentric with the tooth surface curve 13 ′ and is formed by an arc having a smaller diameter (r ₂ ) than the tooth surface curve 13 ′ A bottom surface curve 17 ', and two tooth side surface curves 18', 19 'defining the tooth side surfaces 18, 19 formed between the tooth tip surface curve 13' and the tooth bottom surface curve 17 ',
One end 14 of the corners 14 and 15 formed between both ends of the tip surface curve 13 'and the second tooth side surface curves 18' and 19 'is connected to one end A of the tip surface curve 13'. Formed by a curve AG connecting one end G of the tooth side curve 18 ',
The curve A-G connecting one end A of the tooth tip curve 13 'and one end G of the tooth side curve 18' is extended from one end A of the tooth tip curve 13 'in the protruding direction of the corner portion 14. One of the corner portions 14, 15 formed on the other screw rotor is formed so that the radius of curvature gradually decreases and the tooth side surface curve 18 'extending from the corner portion 14 to the root surface curve 17' is formed. (1) (see FIG. 6).
Further, in another screw rotor 10 (10a, 10b) of the present invention, at least one, preferably both of the screw rotors 10, instead of the configuration of the corner portion 14 described above or together with the configuration of the corner portion 14 described above. The tip surface curve 13 'of (10a, 10b) is formed in a range of 90 to 180 ° centering on the rotational axis of the screw rotor 10 (10a, 10b). Item 3).
The cross-sectional shape perpendicular to the axis of one of the corner portions 14 and 15 can be constituted by an elliptical, parabolic, or hyperbolic quadratic curve (Claim 4). 14 may be formed.
Further, the cross-sectional shape perpendicular to the axis of one of the corner portions 14 and 15 is formed by connecting a plurality of points on a quadratic curve that gradually decreases the radius of curvature toward the protruding direction of the corner portion 14. It can also be formed by a curve approximated to the quadratic curve.

図１は、本発明のスクリュロータを備えた真空ポンプの断面平面図。
図２は、図１の正面断面図。
図３は、図２のＩＩＩ−ＩＩＩ線断面図。
図４は、スクリュロータの要部断面正面図。
図５は、スクリュロータの軸直角断面図。
図６は、スクリュロータの角部の拡大図。
図７は、歯先面の軸線方向横断幅と歯先面曲線の形成長さの関係を示す説明図。
図８は、本発明のスクリュロータの加工方法を示す概略説明図。
図９は、本発明のスクリュロータの加工方法を示す概略説明図。
図１０は、従来のスクリュロータを示し、（Ａ）は軸線方向断面図、（Ｂ）は、角部の干渉状態を示す軸直角方向断面図、（Ｃ）は干渉を防止するための切欠が設けられた状態を示す軸直角方向断面図。
図１１は、従来の別のスクリュロータを示し、（Ａ）は軸線方向断面図、（Ｂ）は軸直交方向断面における角部の拡大図。
図１２は、従来のスクリュロータにおいて形成されるブローホールの説明図。FIG. 1 is a cross-sectional plan view of a vacuum pump provided with the screw rotor of the present invention.
FIG. 2 is a front sectional view of FIG.
3 is a sectional view taken along line III-III in FIG.
FIG. 4 is a cross-sectional front view of the main part of the screw rotor.
FIG. 5 is a cross-sectional view perpendicular to the axis of the screw rotor.
FIG. 6 is an enlarged view of a corner portion of the screw rotor.
FIG. 7 is an explanatory diagram showing the relationship between the axial transverse width of the tooth tip surface and the formation length of the tooth tip surface curve.
FIG. 8 is a schematic explanatory view showing a screw rotor processing method according to the present invention.
FIG. 9 is a schematic explanatory view showing a screw rotor machining method according to the present invention.
10A and 10B show a conventional screw rotor, where FIG. 10A is an axial sectional view, FIG. 10B is an axial perpendicular sectional view showing an interference state at a corner, and FIG. 10C is a notch for preventing interference. FIG. 4 is a cross-sectional view in the direction perpendicular to the axis showing the state of being provided.
11A and 11B show another conventional screw rotor, where FIG. 11A is an axial sectional view, and FIG. 11B is an enlarged view of a corner portion in an axial orthogonal cross section.
FIG. 12 is an explanatory view of a blow hole formed in a conventional screw rotor.

つぎに、本発明の実施形態について添付図面を参照しながら以下説明する。なお、以下に示す実施形態にあっては、本発明のスクリュロータ１０を真空ポンプ１に使用した例を示しているが、本発明のスクリュロータ１０は真空ポンプ１用のスクリュロータとしてのみではなく、スクリュ圧縮機やその他のスクリュポンプなど、スクリュ流体機械全般に適用可能である。
〔真空ポンプの全体構成〕
図１において、１は本発明のスクリュロータ１０（１０ａ，１０ｂ）を備えた真空ポンプの一構成例であり、この真空ポンプ１は、ケーシング３０内に前述のスクリュロータ１０（１０ａ，１０ｂ）を二本、回転可能に収容している。
このケーシング３０の内部には、二本のスクリュロータ１０ａ，１０ｂを噛み合い状態で収容するシリシダ３１が形成されていると共に、各スクリュロータ１０ａ，１０ｂのロータ軸１１が軸受３２により回転可能に支承されている。
スクリュロータ１０ａ，１０ｂのうち、駆動側ロータ１０ａのロータ軸１１には、モータやエンジン、その他の駆動源（本実施形態にあってはモータ４０）の出力軸４１が直接、又は増速機、その他の動力伝達手段を介して連結されている。
本実施形態にあってはモータ４０の出力軸４１がこの駆動側ロータ１０ａのロータ軸１１と直接連結されており、モータ４０の回転に伴って駆動側ロータ１０ａが回転すると共に、この駆動側ロータ１０ａの回転によりこれに噛合する被動側ロータ１０ｂが回転するよう構成されている。
この駆動側ロータ１０ａと被動側ロータ１０ｂとの同期した回転は、各スクリュロータ１０ａ，１０ｂのロータ軸１１に設けられたタイミングギヤ１２の噛合により行われ、両スクリュロータ１０ａ，１０ｂが微少間隔を以て噛合するよう構成されている。
前述のシリンダ３１が形成されたケーシング３０の外壁には、スクリュロータ１０ａ，１０ｂの一端側に位置して流体を導入するための導入口４２と、他端側に位置して流体を吐出する吐出口４３がそれぞれ前記シリンダ３１内の空間に連通して形成されており、前記駆動側スクリュロータ１０ａを回転すると、前記タイミングギヤ１２の噛合により被動側スクリュロータ１０ｂが反対方向に回転し、スクリュロータ１０ａ，１０ｂの噛合により形成された作用空間内に流体が前述の導入口４２を介して導入され、この導入された流体がスクリュロータ１０ａ，１０ｂ間に形成された作用空間内をスクリュロータ１０ａ，１０ｂの他端側に向かって搬送される際に体積収縮されて圧縮された後、前述の吐出口４３より吐出される。
スクリュロータ１０（１０ａ，１０ｂ）を収納するシリンダ３１は、図３に示すように二本のスクリュロータ１０ａ，１０ｂを噛み合い状態で収容することができるよう、断面略８の字形状を成し、駆動側ロータ１０ａを収容する室を成す内壁と、被動側ロータ１０ｂを収容する室を成す内壁との境界位置において稜線３３が形成されている。
なお、図１〜図３に示す実施形態にあっては、同一の歯形を有する２本のスクリュロータをねじれ方向を逆にして噛み合わせた状態でシリンダ内に収容したものを図示しているが、このスクリュロータ１０（１０ａ，１０ｂ）の歯形形状は各スクリュロータ１０ａ，１０ｂにおいて異なるものであってもよく、噛合した状態において回転可能なものであればその形状は図示の例に限定されない。
また、同様に図示の例では、各スクリュロータ１０ａ，１０ｂには１条のスクリュのみが形成されている例を示しているが、各スクリュロータ１０ａ，１０ｂは２条以上のスクリュが形成された多条ロータや、各スクリュロータ１０ａ，１０ｂの条数を異ならせても良い。
〔スクリュロータ〕
以上のように構成された真空ポンプ１に使用される本発明のスクリュロータ１０は、図４に示すようにスパイラル状のスクリュ歯形がリード角αで形成されている。
本発明のスクリュロータは、図４に示すようにその軸線方向の断面において歯側面１８，１９の一方１８は、スクリュロータの軸線Ｘに対して直交方向を成す線Ｙに対して図４中左側に僅かに陥没する湾曲形状に形成されており、従って歯先面１３と歯側面１８との連結位置にあたる角部１４，１５の一方１４はスクリュロータ１０の軸線方向における断面において僅かに鋭角を成し、この鋭角を成す角部１４に続く歯側面１８は歯底面１７から外周方向に向かってオーバーハング状に傾斜している。
また、他方の角部１５は、スクリュロータ１０の軸線方向の断面において僅かに鈍角を成し、この角部１５に続く歯側面１９は、歯底面１７に向かって傾斜する傾斜面を形成している。
このように形成されたスクリュロータ１０の軸直角断面における歯形は、図５に示すようにスクリュロータの軸芯Ｏを中心とした半径ｒ_１の円弧から成る歯先面曲線１３’、スクリュロータの軸芯Ｏを中心とし、歯先面曲線の円弧よりも小径の半径ｒ_２の円弧から成る歯底面曲線１７’と、この二つの曲線との間に形成する歯側面曲線１８’，１９’により略その形状が画成されている。
歯先面曲線１３’の両端と歯側面曲線１８’，１９’との間に形成された前述の角部１４，１５のうち、鋭角的に形成された角部１４は、図６において実線で示すように歯先面曲線１３’の一端Ａから、歯側面曲線１８’の一端Ｇを繋ぐ曲線Ａ−Ｇにより形成されている。
この角部１４の軸直角断面形状を成す曲線Ａ−Ｇは、歯先面曲線１３’の端部Ａから角部１４の突出方向に向かって曲率半径を漸減する形状、例えばこの条件を満たす二次曲線により形成されており、本実施形態にあっては、この曲線中、もっとも曲率半径が小さく形成された頂部Ｆ’を長軸の一端をとする楕円の一部から成る曲線Ａ−Ｇにより角部１４の断面形状としている。
なお、この曲線Ａ−Ｇから成る角部１４の形状は、前述の楕円に限定されるものでなく、歯先面曲線１３’の一端Ａから角部１４の突出方向に向かって曲率半径を漸減する形状の曲線と成るものであれば如何なる形状であっても良い。前述の例では、二次曲線、具体的には楕円の一部としているが、この角部１４の形状は、歯先面曲線１３’の端部Ａから角部１４の突出方向に向かって曲率半径を漸減する形状であれば必ずしも二次曲線のように頂部Ｆ’を中心として対称の形状を成すものである必要はない。また、前述の二次曲線の例では楕円の他、例えば放物線、双曲線等として得られた曲線又はその一部により構成しても良い。
また、角部１４を成す曲線は、正確に楕円、その他の二次曲線を画いたものである必要はなく、この二次曲線上の任意の点を複数取り、この点間を滑らかに連結する曲線により繋いで連続させた、二次曲線に近似した曲線として形成する等、その形状は実施形態のものに限定されない。
このように角部１４を歯先面曲線１３’の端部Ａから角部１４の突出方向に向かって曲率半径を漸減する曲線、特にこのような二次曲線により形成することにより、スクリュロータ１０の熱膨張に際しても角部１４がシリンダ３１の内壁に接触し難いものとなり、その結果歯先面１３とシリンダ３１内壁間の隙間δｔを可及的に狭くすることが可能となる。
また、角部１４の軸直角断面形状を円弧状とする従来のスクリュロータ１０と比較した場合において、形成されるブローホールを可及的に小さなものとすることができる。
この点につき、前述のような角部１４を突出方向に向かって曲率半径を漸減する軸直角断面形状にすることにより歯先面１３とシリンダ３１内壁間の隙間を狭くすることができる点について図５及び図６を参照して説明すれば、この種のスクリュロータ１０にあっては、運転時に発生する流体の圧縮熱によりスクリュロータが熱膨張することを考慮して、スクリュロータ１０の歯先面１３とシリンダ３１の内壁間にはこの熱膨張によるスクリュロータ１０の熱膨張量を考慮した隙間δｔが設けられている（図６参照）。
しかし、この歯先面１３とシリンダ３１内壁間に設けられた隙間δｔは、この隙間δｔを広く取る程歯先面１３とシリンダ３１内壁間におけるシール性が低下することから、この隙間δｔは可及的に狭いものとすることが好ましい。
ところで、真空ポンプの運転時には作用空間内の流体が圧縮作用により発熱し、スクリュロータにより画成される作用空間の表面が前記流体により加熱され、スクリュロータが熱膨張する。このときスクリュロータの中で最も熱膨張量の大きい箇所は作用空間に面していて回転軸芯から最も遠くに位置する角部１４であるが、この角部１４を成す曲線Ａ−Ｇは、この角部の突出方向に向かって曲率半径を漸減する形状を成すために、歯先面曲線１３’の一端Ａから先端方向に向かうに従い徐々にシリンダ３１内壁から離間する形状になっている。ゆえに、これにより最も熱膨張による影響を受けやすい角部１４においては、隙間δｔに加えて隙間δｔ’が存在している。
そのため、この隙間δｔ’において角部１４における外周方向への熱膨張量の増加分を補償し得るものとすれば、歯先面１３とシリンダ３１内壁間の隙間δｔは、歯先面曲線１３’の一端Ａにおける変形量を最大値として考慮すれば良いものとなり、その結果、歯先面１３とシリンダ３１の内壁間の隙間δｔは、可及的に狭めることができる。
これに対して、従来技術において紹介したように、角部１４の軸直角断面形状を円弧とする場合において、本願スクリュロータ１０の角部１４における突出長さと同程度の突出長さを確保しようとすれば、図６中破線で示すように歯先面曲線１３’の端部は、より角部１４の先端側の位置であるＡ’迄延長する必要がある。そして、歯先面１３とシリンダ３１内壁間に形成すべき隙間δｔは、このＡ’における外周方向への熱膨張量を考慮して決定する必要がある。
しかし、角部１４の突出方向先端側にある端部Ａ’は、曲線Ａ−Ｇよりも外周方向に位置していて前述の点Ａに比較して作用空間に近く、作用空間の熱影響を受けやすいことから熱膨張量の大なる部分で、この端部Ａ’における変形量を基準として決定された隙間δｔは必然的に広くなる。このことから、シリンダ３１の内径も大きくなって、端部Ａ‘以外の歯先面１３とシリンダ３１内壁との隙間が大きくなって、この隙間を介して流体の漏れが生じやすい。
その一方で、本願のスクリュロータ１０と同様に、歯先面曲線１３’の端部を図６中の点Ａとし、この点Ａにおいて歯先面曲線１３’と接し、かつ、歯側面曲線１８’と接する円弧（図６中の一点鎖線）により角部１４を形成すると、角部１４の切欠は極めて大きくなり、噛合するスクリュロータ１０ａ，１０ｂの角部１４，１４間に形成されるブローホールが大きくなる結果、実用に耐え得ないスクリュロータとなる。
このように、本発明のスクリュロータ１０にあっては、歯先面１３とシリンダ３１内壁間の隙間δｔを可及的に狭くすることができることにより、該部分におけるシール性の向上が図られているが、歯先面１３とシリンダ３１内壁間におけるシール性を向上させるためには、好適には前述の構成に代えて、又は前述の構成と共に、歯先面曲線１３’をスクリュロータ１０の回転軸芯を中心として全外周（３６０°）に対して９０〜１８０°となる歯形とする。
最外周を半径ｒ_１とするスクリュロータ１０に形成された歯形の歯先面１３を平面上に展開した状態を想定すると、この歯先面１３は、リード角αで傾斜する斜辺を有する直角三角形Δの斜辺と、この斜辺に平行な直線間に形成された帯状部分で表すことができる。
ここで、前述の帯状部分を円筒に巻き付けた際、前記直角三角形の斜辺により形成されるつる巻き線のリードをＲとすると、このリードＲは、
Ｒ＝２πｒ_１ｔａｎα
となる。
そして、ロータの軸直角断面において９０°から１８０°の範囲であらわれる歯先面曲線１３’の長さは、
２πｒ_１／４≦歯先面曲線の長さ≦２πｒ_１／２
の範囲となり、スクリュロータ１０の軸線方向における歯先面１３の横断幅Ｒ’は、
πｒ_１ｔａｎα／２≦Ｒ’≦πｒ_１ｔａｎα
すなわち、歯先面１３の軸線方向の横断幅Ｒ’はリードＲの１／４から１／２の長さとなる。
このように、ロータの軸直角断面において、歯先面１３を成す歯先面曲線が９０°から１８０°の範囲であらわれる形状の歯形とすることにより、歯先面１３の幅をリード長に対して一定幅確保することかでき、歯先面１３とシリンダ内壁間におけるシール性が向上する。
すなわち、軸直角断面においてあらわれる歯先面曲線１３’が、スクリュロータ１０の回転軸芯を中心として全周（３６０°）に対して９０°以下となる場合には、歯先面１３のロータ軸線方向における横断幅Ｒ’がリードＲの１／４以下の長さとなり、歯先面１３の幅が狭く、歯先面１３とシリンダ内壁面間における十分なシール性を発揮することができないものとなるが、前述のように歯先面曲線１３’を９０°〜１８０°の範囲で形成することにより、この部分におけるシール性を向上させることができると共に、前述の角部１４の形状と組み合わせる場合には、歯先面１３とシリンダ３１内壁間の隙間δｔを可及的に狭くすることができることと相俟って該スクリュロータ１０を使用したスクリュ流体機械の作業効率は飛躍的に向上する。
図６において、曲線Ａ−Ｇと歯底面曲線１７’とを結ぶ歯側面曲線１８’（図６中の曲線Ｇ−Ｈ）は、軸直角方向断面における歯側面１８の輪郭を示しており、この歯側面曲線１８’は、両ロータを同期回転させた際に、当該スクリュロータに噛合する前述の形状に形成された他方のスクリュロータの角部１４を成す曲線Ａ−Ｇが創成する曲線に形成されている。
このように歯側面曲線１８’を、回転するスクリュロータの角部１４を構成する曲線Ａ−Ｇが創成する曲線としたことにより、一方のスクリュロータの角部１４と、他方のスクリュロータの歯側面１８間において作用空間がシールされているとき、一方のスクリュロータの角部１４を成す曲線Ａ−Ｇのいずれかの位置と、他方のロータの歯側面曲線１８’のいずれかの位置間において作用空間がシールされるために、シール性が良好である。
〔製造方法〕
以上のスクリュロータは、一例として図８及び図９に示すように回転するカッタにより切削加工される。この切削加工において、カッタ回転軸３の軸芯４は、所定のねじれ角を有する歯溝の形成方向、すなわち歯形のリード角αに対応してワークの回転軸芯７に対して角度α傾斜されており、このカッタ回転軸３にシングルカッタをスペーサ２と共に取り付けている。
シングルカッタのカッタ回転中心Ｏｃは、カッタ回転軸３に長さＬのスペーサ２を設けているため、スペーサ２を設けることなく取り付けた場合のカッタ回転中心Ｏｃ’に対して図中右方向にＬだけオフセットしている。従って、カッタの回転中心の移動方向の延長線は、ワークの回転軸芯７の下方に所定距離ずれた位置を通過するよう設定されている。
このように、回転中心Ｏｃがオフセットされたカッタによるスクリュロータの製造方法について説明すると、まず、カッタ回転軸３に沿って右方向にオフセットしたシングルカッタを切り込み量に応じた分、ワーク６の回転軸芯７に対して直交方向にワーク６側に移動する。その後、シングルカッタをカッタ回転軸３により回転させる。そのときワーク６は、ワーク軸９の回転軸芯７上であってシングルカッタよりも左側の加工開始位置で待機している。
次に、ワーク６をその回転軸芯７を中心として回転させながら回転軸芯に沿って図中左側から右側へ移動させる。
ワークが加工終了位置まできたら、シングルカッタをワークから一旦離し、ワークをワーク軸９に沿って加工開始位置まで左側に戻す。
次にまた、シングルカッタをワーク６の回転軸芯に対して直交方向に切り込み量に応じた分ワーク側に送り、その後シングルカッタをカッタ回転軸により回転させる。
次に、ワーク６をその回転軸芯７を中心として回転させながら前記回転軸芯７に沿って図中左側から右側へ移動させる。
ワーク６が加工終了位置まできたら、シングルカッタをワーク６から一旦離し、ワーク６をワーク軸９に沿って加工開始位置まで左側に戻す。
以上の動作を所望の歯形が得られるまで繰り返し行うことで、スクリュ歯形の歯溝を加工している。
このように、回転中心Ｏｃをオフセットしたカッタを使用することにより、シングルカッタを切り込み量に応じてワーク側に移動させていっても、カッタの回転中心の移動方向の延長線上にワークの回転軸芯が配置されていないので、歯側面１８，１９が傾斜しているスクリュロータの歯溝をカッタの回転軸芯を水平方向に傾斜させることなく加工することができる。もっとも、本発明のスクリュロータ１０は前述の方法による加工に限定されず、カッタの回転軸芯を水平方向に傾斜させた既知の加工装置により製造しても良い。
なお、スクリュロータは所定のリード角αを有することから、前述のカッタの角部１４を切削する部分を、所定径の円弧状に形成すれば、軸直角方向の断面においてスクリュロータ１０の角部１４の形状を角部１４の突出方向に向かって曲率半径を漸減する楕円形状とすることが容易にできる。
また、角部を切削する部分の形状を円弧とする切削刃は、製造や研ぎ直し作業が比較的容易であると共に、円弧状に形成された切削工具は、鋭角的に形成された切削工具に比較して欠けや摩耗が生じ難く長寿命となり、比較的長期に亘り正確にロータの切削を行うことができる。さらに、角部切削する部分の形状を円弧とする切削刃は、角部に切削によるバリが発生しないことから、バリを除去する作業が不要となり、バリ取り作業によって角部が削り取られ作用空間のシール性が低下することがない。
以上説明した本発明の構成により、本発明の歯形形状を備えたスクリュロータにあっては、スクリュロータ間の完全なシール線を得ることができ、また、ブローホールを可及的に小さなものとすることができた。その結果、シール性の向上されたスクリュロータを提供することができた。
また、歯先面とシリンダ内壁間の隙間を可及的に狭くすることができると共に、軸直角断面に現れる歯先面曲線を、スクリュロータの全周に対して９０°〜１８０°とすることにより、歯先面とシリンダ内壁間におけるシール性を向上させることができた。
また、このようなシール性を向上させる角部の形状は、切削工具の該当個所を円弧状にすることにより極めて容易に形成することができると共に、切削工具の該部分を鋭利な形状とする場合に比較して寿命をも延ばすことができ、切削工具が切れなくなったり、加工精度が確保できなくなり工具交換をするまでに多数のスクリュロータの加工ができ、工具交換の作業が少なくなる。Next, embodiments of the present invention will be described below with reference to the accompanying drawings. In the embodiment shown below, an example in which the screw rotor 10 of the present invention is used for the vacuum pump 1 is shown, but the screw rotor 10 of the present invention is not only used as a screw rotor for the vacuum pump 1. It can be applied to all screw fluid machines such as screw compressors and other screw pumps.
[Overall configuration of vacuum pump]
In FIG. 1, reference numeral 1 denotes a configuration example of a vacuum pump provided with the screw rotor 10 (10 a, 10 b) of the present invention. The vacuum pump 1 includes the above-described screw rotor 10 (10 a, 10 b) in a casing 30. Two are rotatably housed.
The casing 30 is formed with a siricid 31 for accommodating the two screw rotors 10a and 10b in mesh with each other, and the rotor shaft 11 of each of the screw rotors 10a and 10b is rotatably supported by a bearing 32. ing.
Of the screw rotors 10a and 10b, the rotor shaft 11 of the drive-side rotor 10a has a motor, an engine, and an output shaft 41 of another drive source (the motor 40 in the present embodiment) directly or a speed increaser. It is connected via other power transmission means.
In the present embodiment, the output shaft 41 of the motor 40 is directly connected to the rotor shaft 11 of the drive-side rotor 10a, and the drive-side rotor 10a rotates with the rotation of the motor 40. The driven rotor 10b that meshes with the rotation of 10a is configured to rotate.
The synchronized rotation of the drive-side rotor 10a and the driven-side rotor 10b is performed by meshing of timing gears 12 provided on the rotor shafts 11 of the screw rotors 10a and 10b, and the screw rotors 10a and 10b are spaced at a slight interval. It is comprised so that it may mesh.
On the outer wall of the casing 30 in which the above-described cylinder 31 is formed, an inlet 42 for introducing a fluid located on one end side of the screw rotors 10a and 10b, and a discharge for discharging the fluid located on the other end side. The outlets 43 are respectively formed in communication with the space in the cylinder 31. When the drive side screw rotor 10a is rotated, the driven side screw rotor 10b is rotated in the opposite direction by the engagement of the timing gear 12, and the screw rotor is rotated. A fluid is introduced into the working space formed by the meshing of 10a and 10b through the introduction port 42, and the introduced fluid is passed through the working space formed between the screw rotors 10a and 10b. When being transported toward the other end of 10b, the volume is shrunk and compressed, and then discharged from the discharge port 43 described above.
The cylinder 31 for accommodating the screw rotor 10 (10a, 10b) has a substantially 8-shaped cross section so that the two screw rotors 10a, 10b can be accommodated in an engaged state as shown in FIG. A ridge line 33 is formed at a boundary position between an inner wall that forms a chamber that houses the drive-side rotor 10a and an inner wall that forms a chamber that houses the driven-side rotor 10b.
In the embodiment shown in FIG. 1 to FIG. 3, two screw rotors having the same tooth profile are shown accommodated in a cylinder in a state where they are meshed with their twist directions reversed. The tooth profile of the screw rotor 10 (10a, 10b) may be different in each of the screw rotors 10a, 10b, and the shape is not limited to the illustrated example as long as it can rotate in a meshed state.
Similarly, in the illustrated example, each screw rotor 10a, 10b has an example in which only one screw is formed, but each screw rotor 10a, 10b has two or more screws formed. The number of strips of the multi-row rotor and the screw rotors 10a and 10b may be different.
[Screw rotor]
The screw rotor 10 of the present invention used in the vacuum pump 1 configured as described above has a spiral screw tooth profile formed at a lead angle α as shown in FIG.
As shown in FIG. 4, the screw rotor of the present invention has one of the tooth side surfaces 18, 19 in the cross section in the axial direction, and the left side in FIG. 4 with respect to the line Y perpendicular to the axis X of the screw rotor. Accordingly, one of the corner portions 14 and 15 corresponding to the connecting position of the tooth tip surface 13 and the tooth side surface 18 forms a slightly acute angle in the cross section in the axial direction of the screw rotor 10. The tooth side surface 18 following the corner portion 14 forming an acute angle is inclined in an overhang shape from the tooth bottom surface 17 toward the outer peripheral direction.
Further, the other corner portion 15 forms a slightly obtuse angle in the axial section of the screw rotor 10, and the tooth side surface 19 following the corner portion 15 forms an inclined surface inclined toward the tooth bottom surface 17. Yes.
Tooth profile in the thus formed cross section perpendicular to the shaft of the screw rotor 10, the tooth crest curve 13 consisting of an arc of a radius r ₁ around the axis O of the screw rotor, as shown in FIG. 5 ', of the screw rotor A root surface curve 17 ′ composed of an arc having a radius r _{2 having} a radius r ₂ smaller than the arc of the tooth tip surface curve centered on the axis O and tooth side surface curves 18 ′ and 19 ′ formed between the two curves. The shape is defined.
Among the aforementioned corner portions 14 and 15 formed between both ends of the tooth tip surface curve 13 'and the tooth side surface curves 18' and 19 ', the corner portion 14 formed acutely is a solid line in FIG. As shown, it is formed by a curve A-G connecting one end A of the tooth tip curve 13 'to one end G of the tooth side curve 18'.
The curve A-G forming the cross-sectional shape perpendicular to the axis of the corner portion 14 is a shape in which the radius of curvature gradually decreases from the end portion A of the tooth tip surface curve 13 'toward the protruding direction of the corner portion 14, for example, two satisfying this condition. In this embodiment, the apex F ′ formed with the smallest radius of curvature is a curve A-G composed of a part of an ellipse having one end of the major axis. The cross-sectional shape of the corner portion 14 is used.
Note that the shape of the corner portion 14 formed by the curve A-G is not limited to the above-described ellipse, and the radius of curvature gradually decreases from one end A of the tooth tip surface curve 13 ′ toward the protruding direction of the corner portion 14. Any shape can be used as long as it is a curved line. In the above-described example, a quadratic curve, specifically, a part of an ellipse is used, but the shape of the corner 14 is a curvature from the end A of the tooth tip curve 13 ′ toward the protruding direction of the corner 14. If the shape has a gradually decreasing radius, it is not always necessary to form a symmetric shape with the top F ′ as the center like a quadratic curve. Moreover, in the example of the above-mentioned quadratic curve, you may comprise in addition to an ellipse, for example, a curve obtained as a parabola, a hyperbola, etc., or a part thereof.
Further, the curve forming the corner portion 14 does not have to be an ellipse or other quadratic curve accurately, and a plurality of arbitrary points on the quadratic curve are taken and the points are smoothly connected. The shape is not limited to that of the embodiment, such as a continuous curve connected by a curve or a curve approximated to a quadratic curve.
Thus, the screw rotor 10 is formed by forming the corner portion 14 by a curve that gradually decreases the radius of curvature from the end A of the tooth tip surface curve 13 ′ toward the protruding direction of the corner portion 14, particularly such a quadratic curve. Also during the thermal expansion, the corner portion 14 is difficult to contact the inner wall of the cylinder 31, and as a result, the gap δt between the tooth tip surface 13 and the inner wall of the cylinder 31 can be made as small as possible.
Further, when compared with the conventional screw rotor 10 in which the cross-sectional shape perpendicular to the axis of the corner portion 14 is an arc shape, the blow hole formed can be made as small as possible.
Regarding this point, the gap between the tooth tip surface 13 and the inner wall of the cylinder 31 can be narrowed by forming the corner portion 14 as described above into a cross-sectional shape perpendicular to the axis in which the radius of curvature gradually decreases in the protruding direction. 5 and FIG. 6, in this type of screw rotor 10, the tooth tip of the screw rotor 10 is taken into consideration that the screw rotor is thermally expanded by the compression heat of the fluid generated during operation. A gap δt is provided between the surface 13 and the inner wall of the cylinder 31 in consideration of the amount of thermal expansion of the screw rotor 10 due to this thermal expansion (see FIG. 6).
However, since the clearance δt provided between the tooth tip surface 13 and the inner wall of the cylinder 31 decreases as the clearance δt increases, the sealing performance between the tooth tip surface 13 and the inner wall of the cylinder 31 decreases. It is preferable to make it as narrow as possible.
By the way, when the vacuum pump is operated, the fluid in the working space generates heat due to the compression action, the surface of the working space defined by the screw rotor is heated by the fluid, and the screw rotor is thermally expanded. At this time, the portion having the largest thermal expansion amount in the screw rotor is the corner portion 14 that faces the working space and is farthest from the rotation axis, and the curve AG that forms this corner portion 14 is In order to form a shape in which the radius of curvature gradually decreases toward the protruding direction of the corner portion, the shape is gradually separated from the inner wall of the cylinder 31 as it goes from the one end A of the tooth tip surface curve 13 ′ toward the tip end direction. Therefore, a gap δt ′ is present in addition to the gap δt at the corner 14 that is most susceptible to thermal expansion.
Therefore, if it is possible to compensate for the increase in the amount of thermal expansion in the outer circumferential direction at the corner portion 14 in this gap δt ′, the gap δt between the tooth tip surface 13 and the inner wall of the cylinder 31 becomes the tip surface curve 13 ′. Therefore, the amount of deformation at one end A can be considered as the maximum value, and as a result, the gap δt between the tooth tip surface 13 and the inner wall of the cylinder 31 can be reduced as much as possible.
On the other hand, as introduced in the prior art, when the cross-sectional shape perpendicular to the axis of the corner portion 14 is an arc, an attempt is made to secure a projection length similar to the projection length at the corner portion 14 of the screw rotor 10 of the present application. In this case, as shown by a broken line in FIG. 6, the end portion of the addendum surface curve 13 ′ needs to be extended to A ′ that is a position on the tip end side of the corner portion 14. The gap δt to be formed between the tooth tip surface 13 and the inner wall of the cylinder 31 needs to be determined in consideration of the amount of thermal expansion in the outer peripheral direction at this A ′.
However, the end portion A ′ on the front end side in the protruding direction of the corner portion 14 is located in the outer peripheral direction with respect to the curve AG and is closer to the working space than the point A described above, and the thermal effect of the working space is reduced. The gap δt, which is determined based on the deformation amount at the end A ′, is inevitably wide at the portion where the thermal expansion amount is large because it is easily received. For this reason, the inner diameter of the cylinder 31 is also increased, and a gap between the tooth tip surface 13 other than the end portion A ′ and the inner wall of the cylinder 31 is increased, and fluid is likely to leak through the gap.
On the other hand, like the screw rotor 10 of the present application, the end portion of the tooth tip surface curve 13 ′ is set as a point A in FIG. When the corner portion 14 is formed by a circular arc in contact with '(dotted line in FIG. 6), the notch of the corner portion 14 becomes extremely large, and the blow hole formed between the corner portions 14 and 14 of the screw rotors 10a and 10b that mesh with each other. As a result, the screw rotor cannot be practically used.
Thus, in the screw rotor 10 of the present invention, the gap δt between the tooth tip surface 13 and the inner wall of the cylinder 31 can be made as narrow as possible, so that the sealing performance at the portion is improved. However, in order to improve the sealing performance between the tooth tip surface 13 and the inner wall of the cylinder 31, the tooth tip surface curve 13 ′ is preferably rotated by rotating the screw rotor 10 in place of or in addition to the above configuration. The tooth profile is 90 to 180 ° with respect to the entire outer periphery (360 °) with the shaft core as the center.
Assuming that the tooth tip surface 13 of the tooth profile formed on the screw rotor 10 having the outermost radius r ₁ is developed on a plane, the tooth tip surface 13 is a right triangle having a hypotenuse inclined at a lead angle α. It can be represented by a slanted side of Δ and a belt-like portion formed between straight lines parallel to the hypotenuse.
Here, when the above-mentioned belt-like portion is wound around a cylinder, if the lead of the helical winding formed by the hypotenuse of the right triangle is R, this lead R is
R = 2πr ₁ tan α
It becomes.
The length of the addendum curve 13 ′ that appears in the range of 90 ° to 180 ° in the cross section perpendicular to the axis of the rotor
2.pi.r _1/4 length of ≦ tooth crest curve ≦ 2.pi.r _1/2
The transverse width R ′ of the tooth tip surface 13 in the axial direction of the screw rotor 10 is
πr ₁ tan α / 2 ≦ R ′ ≦ πr ₁ tan α
That is, the transverse width R ′ of the tooth tip surface 13 in the axial direction is ¼ to ½ of the lead R.
Thus, in the cross-section perpendicular to the axis of the rotor, the tooth tip surface curve forming the tooth tip surface 13 has a shape that appears in the range of 90 ° to 180 °, thereby making the width of the tooth tip surface 13 relative to the lead length. Thus, a certain width can be secured, and the sealing performance between the tooth tip surface 13 and the cylinder inner wall is improved.
That is, when the tooth tip surface curve 13 ′ appearing in the cross section perpendicular to the axis is 90 ° or less with respect to the entire circumference (360 °) around the rotation axis of the screw rotor 10, the rotor axis of the tooth tip surface 13. The transverse width R ′ in the direction is ¼ or less of the lead R, the width of the tooth tip surface 13 is narrow, and sufficient sealability between the tooth tip surface 13 and the cylinder inner wall surface cannot be exhibited. However, when the tip surface curve 13 ′ is formed in the range of 90 ° to 180 ° as described above, the sealability at this portion can be improved and the shape of the corner portion 14 is combined. In combination with the fact that the gap δt between the tooth tip surface 13 and the inner wall of the cylinder 31 can be made as small as possible, the working efficiency of the screw fluid machine using the screw rotor 10 is dramatically improved.
In FIG. 6, a tooth side surface curve 18 ′ (curve GH in FIG. 6) connecting the curve A-G and the root surface curve 17 ′ shows the contour of the tooth side surface 18 in a cross section perpendicular to the axis. The tooth side surface curve 18 ′ is formed into a curve created by a curve AG forming the corner portion 14 of the other screw rotor formed in the above-described shape that meshes with the screw rotor when both rotors are rotated synchronously. Has been.
In this way, the tooth side surface curve 18 'is a curve created by the curve AG forming the corner portion 14 of the rotating screw rotor, whereby the corner portion 14 of one screw rotor and the teeth of the other screw rotor are formed. When the working space is sealed between the side surfaces 18, between any position of the curve AG forming the corner portion 14 of one screw rotor and any position of the tooth side curve 18 ′ of the other rotor. Since the working space is sealed, the sealing property is good.
〔Production method〕
The above-described screw rotor is cut by a rotating cutter as shown in FIGS. 8 and 9 as an example. In this cutting process, the shaft core 4 of the cutter rotating shaft 3 is inclined at an angle α with respect to the rotating shaft core 7 of the workpiece corresponding to the formation direction of the tooth groove having a predetermined twist angle, that is, the lead angle α of the tooth profile. A single cutter is attached to the cutter rotating shaft 3 together with the spacer 2.
Since the cutter rotation center Oc of the single cutter is provided with the spacer 2 having the length L on the cutter rotation shaft 3, the cutter rotation center Oc is L in the right direction in the drawing with respect to the cutter rotation center Oc 'when the spacer 2 is not installed. Is just offset. Accordingly, the extension line in the moving direction of the rotation center of the cutter is set so as to pass through a position shifted by a predetermined distance below the rotation axis 7 of the workpiece.
In this way, the manufacturing method of the screw rotor using the cutter with the rotation center Oc offset will be described. First, the rotation of the workpiece 6 is performed by the amount corresponding to the cutting amount of the single cutter offset rightward along the cutter rotation shaft 3. It moves to the workpiece 6 side in a direction orthogonal to the axis 7. Thereafter, the single cutter is rotated by the cutter rotating shaft 3. At that time, the workpiece 6 is waiting at the machining start position on the rotation axis 7 of the workpiece shaft 9 and on the left side of the single cutter.
Next, the workpiece 6 is moved from the left side to the right side in the drawing along the rotation axis while rotating the workpiece 6 around the rotation axis 7.
When the workpiece reaches the machining end position, the single cutter is once separated from the workpiece, and the workpiece is returned to the left side along the workpiece axis 9 to the machining start position.
Next, the single cutter is fed to the workpiece side in the direction orthogonal to the rotation axis of the workpiece 6 according to the cut amount, and then the single cutter is rotated by the cutter rotation shaft.
Next, the work 6 is moved from the left side to the right side in the drawing along the rotation axis 7 while rotating the workpiece 6 around the rotation axis 7.
When the workpiece 6 reaches the machining end position, the single cutter is once separated from the workpiece 6, and the workpiece 6 is returned to the left side along the workpiece axis 9 to the machining start position.
By repeating the above operation until a desired tooth profile is obtained, the tooth profile of the screw tooth profile is processed.
As described above, by using the cutter with the rotation center Oc offset, even if the single cutter is moved to the workpiece side according to the cut amount, the rotation axis of the workpiece is on the extension line in the moving direction of the rotation center of the cutter. Since the core is not disposed, the tooth groove of the screw rotor in which the tooth side surfaces 18 and 19 are inclined can be processed without inclining the rotating shaft core of the cutter in the horizontal direction. However, the screw rotor 10 of the present invention is not limited to the processing by the above-described method, and may be manufactured by a known processing apparatus in which the rotation axis of the cutter is inclined in the horizontal direction.
Since the screw rotor has a predetermined lead angle α, if the portion for cutting the above-mentioned corner portion 14 of the cutter is formed in an arc shape with a predetermined diameter, the corner portion of the screw rotor 10 in the cross section perpendicular to the axis. The shape of 14 can be easily formed into an elliptical shape in which the radius of curvature gradually decreases toward the protruding direction of the corner portion 14.
In addition, a cutting blade having a circular arc shape at the corner cutting portion is relatively easy to manufacture and regrind, and a cutting tool formed in an arc shape is a sharp cutting tool. In comparison, chipping and wear are unlikely to occur and the life is long, and the rotor can be accurately cut for a relatively long time. Furthermore, a cutting blade having a circular arc shape at the corner cutting portion does not generate burrs due to cutting at the corners, so that there is no need to remove the burrs. Sealing performance does not deteriorate.
With the configuration of the present invention described above, in the screw rotor having the tooth profile of the present invention, a complete seal line between the screw rotors can be obtained, and the blow hole can be made as small as possible. We were able to. As a result, a screw rotor with improved sealing performance could be provided.
In addition, the gap between the tooth tip surface and the cylinder inner wall can be made as narrow as possible, and the tooth tip surface curve appearing in the cross section perpendicular to the axis is 90 ° to 180 ° with respect to the entire circumference of the screw rotor. As a result, the sealability between the tooth tip surface and the inner wall of the cylinder could be improved.
In addition, the shape of the corner portion that improves the sealing performance can be formed very easily by making the corresponding portion of the cutting tool into an arc shape, and the portion of the cutting tool is sharpened. In comparison with the above, the life can be extended, the cutting tool can not be cut, the processing accuracy cannot be ensured, and a large number of screw rotors can be processed before the tool is replaced.

Claims

In a screw rotor used in a screw machine that rotates by meshing a pair of screw rotors while reversing the twisting direction, and sucking and discharging fluid,
The tooth profile of each of the pair of screw rotors in a cross section perpendicular to the axis is a tooth tip surface curve formed of an arc of a predetermined diameter centered on the rotational axis of the screw rotor and defining the tooth tip surface, and the tooth tip surface curve A concentric tooth base curve composed of an arc having a smaller diameter than the tooth tip surface curve and defining the tooth bottom surface, and two teeth forming the tooth side surface contour formed between the tooth tip surface curve and the tooth bottom surface curve With side curves,
One of the corners formed between both ends of the tooth surface curve and the second tooth side surface curve is formed by a curve connecting one end of the tooth surface curve and one end of the tooth side surface curve. ,
The curve connecting one end of the addendum surface curve and one end of the addendum surface curve is a curve that gradually decreases the radius of curvature from one end of the addendum surface curve toward the protruding direction of the corner portion, and The screw rotor, wherein the tooth side surface curve extending from the corner portion to the root surface curve is a curve created by one of the corner portions formed on the other screw rotor.

In a screw rotor used in a screw machine that rotates by meshing a pair of screw rotors while reversing the twisting direction, and sucking and discharging fluid,
The tooth profile of each of the pair of screw rotors in a cross section perpendicular to the axis is a tooth tip surface curve formed of an arc of a predetermined diameter centered on the rotational axis of the screw rotor and defining the tooth tip surface, and the tooth tip surface curve A concentric tooth root curve formed by an arc having a smaller diameter than the tooth tip surface curve and defining the root surface, and two tooth side contours formed between the tooth tip surface curve and the tooth bottom curve. Tooth side curve,
The corner portion formed on the other screw rotor, the tooth side surface curve extending from one of the corner portions formed between both ends of the tooth tip surface curve and the second tooth side surface curve to the tooth bottom surface curve. Along with the curve created by one of the
At least one of the screw rotors is characterized in that the tooth tip curve is formed in a range of 90 to 180 ° centering on the rotational axis of the screw rotor.

In a screw rotor used in a screw machine that rotates by meshing a pair of screw rotors while reversing the twisting direction, and sucking and discharging fluid,
The tooth profile of each of the pair of screw rotors in a cross section perpendicular to the axis is a tooth tip surface curve formed of an arc of a predetermined diameter centered on the rotational axis of the screw rotor and defining the tooth tip surface, and the tooth tip surface curve A concentric tooth root curve formed by an arc having a smaller diameter than the tooth tip surface curve and defining the root surface, and two tooth side contours formed between the tooth tip surface curve and the tooth bottom curve. Tooth side curve,
One of the corners formed between both ends of the tooth surface curve and the second tooth side surface curve is formed by a curve connecting one end of the tooth surface curve and one end of the tooth side surface curve. ,
The curve connecting one end of the addendum surface curve and one end of the addendum surface curve is a curve that gradually decreases the radius of curvature from one end of the addendum surface curve toward the protruding direction of the corner portion, and The tooth side surface curve from the corner portion to the root surface curve is a curve created by one of the corner portions formed on the other screw rotor, and
The screw rotor, wherein at least one of the screw rotors has the tooth tip curve formed in a range of 90 to 180 ° centering on a rotation axis of the screw rotor.

The screw rotor according to any one of claims 1 to 3, wherein one of the corners is formed by a quadratic curve.

The screw rotor according to any one of claims 1 to 3, wherein one of the corners is formed by a part of an ellipse.

A cross-sectional shape perpendicular to the axis of one of the corners approximates the quadratic curve formed by connecting a plurality of points on a quadratic curve that gradually decreases the radius of curvature toward the protruding direction of the corner. The screw rotor according to any one of claims 1 to 3, wherein the screw rotor is a curved line.