CA1268747A - Screw rotors - Google Patents
Screw rotorsInfo
- Publication number
- CA1268747A CA1268747A CA000478391A CA478391A CA1268747A CA 1268747 A CA1268747 A CA 1268747A CA 000478391 A CA000478391 A CA 000478391A CA 478391 A CA478391 A CA 478391A CA 1268747 A CA1268747 A CA 1268747A
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- circular arc
- center
- tooth profile
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Abstract
ABSTRACT OF THE DISCLOSURE
Screw rotors having nonsymmetrical tooth profiles and used in a screw-type rotary compressor or expander.
The tooth profile of the female rotor is formed such that a line (H2-A2) is formed by a generated curve of a point A1 of the male rotor; a line (A2-B2) is formed by a circular arc having a point O7 as the center of the arc and a radius R7; a line (B2-C'2) is formed by an envelope developed by a circular arc (B1-C1) of the male rotor; a portion between points D'2 and E2 is formed by a circular arc having a point O1 as the center of the arc and a radius R1; a line (C'-D') is formed by a line smoothly connecting the lines (B2-C'2) and (D'2-E2); a line (E2-F2) is formed by a circular arc having a point O2 as the center of the arc and a radius R2; and a line (F2-G2) is formed by a circular arc having a point O8 as the center of the arc and a radius R8. The tooth profile of the male rotor is formed such that a line (H1-A1) is formed by a generated curve of a point H2 of the female rotor; a line (A1-B1) is formed by an envelope developed by the arc (A2-B2) of the female rotor; a line (B1-C1) is formed by a circular arc having a point O4 as the center of the arc and a radius R4; a line (C1-D1) is formed by a circular arc having the rotating center of the male rotor as the center of the arc and a radius R5; and lines (D1-E1), (E1-F1) and (F1-G1) are generated by arcs (D2-E2), (E2-F2) and (F2-G2) of the female rotor tooth profile, respectively. The screw rotors prevent abnormal noise and vibration of the compressor or expander and can be manufactured easily.
Screw rotors having nonsymmetrical tooth profiles and used in a screw-type rotary compressor or expander.
The tooth profile of the female rotor is formed such that a line (H2-A2) is formed by a generated curve of a point A1 of the male rotor; a line (A2-B2) is formed by a circular arc having a point O7 as the center of the arc and a radius R7; a line (B2-C'2) is formed by an envelope developed by a circular arc (B1-C1) of the male rotor; a portion between points D'2 and E2 is formed by a circular arc having a point O1 as the center of the arc and a radius R1; a line (C'-D') is formed by a line smoothly connecting the lines (B2-C'2) and (D'2-E2); a line (E2-F2) is formed by a circular arc having a point O2 as the center of the arc and a radius R2; and a line (F2-G2) is formed by a circular arc having a point O8 as the center of the arc and a radius R8. The tooth profile of the male rotor is formed such that a line (H1-A1) is formed by a generated curve of a point H2 of the female rotor; a line (A1-B1) is formed by an envelope developed by the arc (A2-B2) of the female rotor; a line (B1-C1) is formed by a circular arc having a point O4 as the center of the arc and a radius R4; a line (C1-D1) is formed by a circular arc having the rotating center of the male rotor as the center of the arc and a radius R5; and lines (D1-E1), (E1-F1) and (F1-G1) are generated by arcs (D2-E2), (E2-F2) and (F2-G2) of the female rotor tooth profile, respectively. The screw rotors prevent abnormal noise and vibration of the compressor or expander and can be manufactured easily.
Description
1~6874~
TITLE OF THE INVENTION:
SC~E~ ROTO~S
BAC~GROUND OF THE INVENTION
Field of the Invention The present invention relates to a pair of screw rotors used in a screw rotor machine for compressing or expanding a compressible fluid and supplying the compressed or expanded fluid and, more particularly, to a tooth profile curve thereof.
Description of the Prior Art Rotors having nonsymmetrlcal tooth profiles and used in a compressor or the like of a compressible fluid generally comprise a male rotor having helical lands with a major portion of each tooth profile outside the pitch circle thereof, and a female rotor having helical grooves with a major portion of each tooth profile inside the pitch circle thereof. Normally, the male rotor has a plurality of teeth, and the female rotor meshing therewith has a number of teeth slightly exceeding the 1~i87~7 number of teeth of the male rotor. The diameter of the tip circle of the male rotor is set to be substantially the same as that of the pitch circle of the female rotor.
A screw compressor or expander is constructed as follows. A pair of screw rotors of this type are rotatably housed inside a working space comprising two cylindrical bores formed in a casing. The cylindrical bores have parallel axes and have diameters equal to the outer diameter of the respective rotors to be arranged therein. The distance between the axes of the cylinders is shorter than the sum of the radii thereof, and the axial length of each cylindrical bore is the same as that of the rotors. The two end portions of the cylindrical bores are closed with end plates fixed to the casing.
Inlet and outlet ports for the fluid are formed at predetermined positions of the casing (Fig. 3(a) or 3(b)).
When the above assembly is used as a compressor, the female rotor is rotated counterclockwise while the male rotor is rotated clockwise. With respect to the concave tooth profile of the groove of the female rotorj a curve at the front side along the rotating direction is referred to as the leading side tooth profile, and that at the rear side along the rotating direction is referred to as the trailing side tooth profile. Similarly, with respect to the convex tooth profile of the land of the male rotor, that at the front side along the rotating direction is referred to as the leading side tooth profile, and that at the rear side along the rotating direction is referred to as the trailing side tooth profile.
When the above assembly 1s used as an expander, the names of the respective curves are reversed. However, in the description to follow, the respective tooth profile curves will be explained in accordance with the above definitions.
SUMM~RY OF THE IN~JENTION
It is, therefore, an object of the present invention to provide noveltoOth profiles which will not impair the advantages of the tooth profiles shown in E'igure l previously proposed by said Japanese Utility Model Registration No. 1432776; and which reduce the dis-advantages of these tooth profiles, i.e., increase the stroke volume, prevent rotor wear by changing portions of tooth profiles which form the sealing points for maintaining superior efficiency over a long period of time, increase the pressure angle for improving the i8~47 machining precision of the tooth profile and increasing the tool life, and facilitate easy formation of tools. To this end, the present inventio~ provides screw rotors comprising a male rotor having helical lands and a female rotor having helical grooves which mesh with each other and rotate about two parallel axes, a ma~or portion of each tooth profile of said female rotor being formed inside a pitch circle of said female rotor, and a major portion of each tooth profile of said male rotor being formed outside a pitch circle of said male rotor, characterized in that in tooth profile curves formed in a plane perpendicular to rotating axes of said rotors, a tooth profile of said female rotor is formed such that a portion connecting an outermost first point at a tip of an addendum and a second point located on the pitch circle is a first generated curve generated by a third point located on the pitch circle of the male rotor tooth proile; a portion between the second point and a fourth point is formed by a first circular arc having a first radius and a first center of an arc which is located on a line tangent to the pitch circle of the female rotor at ~he second point and located outside the concave of the groove; a portion between the fourth point and a fifth point is formed by a first envelope developed by a second circular arc which is a part of the male rotor tooth profile; a portion between a sixth point and a seventh point is formed by a third circular arc having a second radius and a second center of an arc located on a first straight line connecting rotating centers of said male and female rotors and outside the pitch circle of said female rotor; a portion between the fifth point and the sixth point is formed by one of a straight line and an approximate curve ,., ~
1~874~
connected with the first envelope at the fifth point and connected with the third circular arc at the sixth point; a portion between the seventh point and an eighth point is formed by a fourth circular arc connected with the third circular arc at the seventh point and having a third radius and a third center of an arc located on an extension of a second straight line connecting the second center of t,he third circular arc and the seventh point which line lntersecting at a first angle with the first straight line at a position opposite to the second center of the third circular arc with respect to the seventh point; and a portion between the eighth point and a ninth point is formed by a fifth circular arc connected with a sixth circular arc having a radius equal to the outer diameter of said female rotor and having a center of an arc on the rotating center of said female rotor at the ninth point and having a fourth radius and a fourth center of an arc located on a third straight line connecting the third center of the fourth circular arc and the eighth point and located inside the female rotor tooth profile; and a tooth profile of the male rotor is formed such that a portion connecting a tenth point located on a bottom land of a dedendum and the third point located on the pitch circle is a second generated curve generated by the first point located on the female rotor tooth profile, a portion between the third point and an eleventh point is a second envelope developed by the first circular arc of the female rotor tooth profile; a portion between the eleventh point and a twelfth point is formed by the second circular arc connected with the second envelope at the eleventh point and having a fifth radius and a fifth center of an arc located on a fourth straight line D
~87~7 - 5a -intersecting at a second angle with the firs~ straight line at the rotating center of said male rotor and located at a predetermined distance from the first straight line; a portion between the twelfth point and a thirteenth point is formed by a seventh circular arc having a sixth radius and a sixth center of an arc at the rotating center of said male rotor; a portion between the thirteenth point and a fourteenth point is formed by a third envelope developed by the third circular arc of the female rotor tooth profile; a portion between the fourteenth point and a fifteenth point is formed by a fourth envelope developed by the fourth circular arc of the female rotor tooth profile; a portion between the fifteenth point and a sixteenth point is formed by a fifth envelope developed by the fifth circular arc of the female rotor; and tooth profiles of said male and female rotors are formed by smoothly and tangentially connecting said arcs and curves.
D
1~~374~7 BRIEF DESCRIPTION OF ~ilE DRAWINGS
Various other objects, features ancl attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed descril)tion when considered in connection with the accompanying clrawings in which like reference characters designate like or corresponding parts through the several views and wherein:
Figures l(a), l(b) and 2(a) show tooth profile curves of conven-tional screw rotors, in which Figures l(a) and l(b) correspond to different phases of the tooth profiles disclosed in Japanese Utility Model Registration No. 1432776 as time elapses from Figure l(a) to Figure l~b~;
Figure 2(b) is a view for explaining a communication path formed in the conventional screw rotor shown in Figure 2(a);
Figures 3(a) and 3~b) are a side sectional view and a cross-section-al view of a rotor machine or a compressor using screw rotors according to the present invention;
Figure 4~a) to Figure 4~d) show the different meshing positions of a pair of tooth profile curves of the screw rotors of the present invention, in which the meshing phase shown in Figure 4~a) is shifted to that shown in Figure 4~b) and then to that shown in Figure 4~c), and Figure 4~d) is an en-larged view of Figure 4~c);
Figures 5 to 10 are enlarged views of parts of the tooth profiles in order to explain the characteristic features of the tooth profile curves of the screw rotors according to the present invention; and Figures lla, llb and llc ~with Figure 4c) are views illustrating the measuring method of the tooth profiles of the screw rotors according to the present invention.
1.26~747 DET~ILE~ DF.SCRIPTION OF Tl-lE PRF.FERRED EMBODIMEN'I`S
~ iss. l(a) and ltb) show the respec~ive tooth pxofile curves when the rotors are cut along a plane perpendicular to their rotating axes, i.e., the meshing sta.e between the screw rotors at the end face of each rotor along the longitudinal axes thereof. Fig. l(a) shows the phases of the tooth profiles of the two rotors immediately after the trailing side tooth profile curves of the male and female rotors have begun to contact each other. When the male rotor is rotated through about 20 thereafter, the phases as shown in Fig. l(b) are obtained wherein the highest portion of the tooth profile of the male rotor opposes the deepest portion of the groove of the tooth pro~ile of the female rotor.
The above tooth profiles are conventional ones which are used in, for example, screw compressor manufactured by Hokuetsu Industries Co., Ltd. (3apanese Utility Model Registration No. 1432776! and have the following characteristics.
Referring to Figs. l(a) and l(b), reference numeral 1 denotes a male rotor; and 2, a female rotor meshed therewith. The rotors l and 2 rotate about rotating centers 3 and 4 (centers of the pitch circles) inside cylindrical bores of a casing (not shown) in the direction indicated by arrows, respectively,so as to serve as a fluid compressor. Reference numerals 15 and 16, respectively, denote pitch circles of male rotor 1 and female rotor 2. A line connecting the rotating centers 3 and 4 passes a contact point 17 between the pitch circles 15 and 16, i.e., a pitch point 17.
The above-mentioned tooth profiles will be described with reference to Fig. ltb).
(1) Female Rotor Tooth Profile (i) Leading side curve: The leading side curve is formed such that it consists of a circular arc (11-12) which extends from a point 12 at the deepest tooth profile portion of the groove of the female rotor to an outermost end 10 of the tooth profile and has a radius r4 with respect to the pitch point 17 which is the center of ~'2~i~374'7 g the arc (11-12), the portion between points 11 and 10 and extending from the arc (11-12) is a straight line (10-11) passing through the rotating center 4 of the female rotor and being circumscribed the arc (11-12) having the radius r4, the curve between points 12 and 13 of the bottom land of the groove of the female rotor is a circular arc (12-13! which has a radius r2 with the rotating center 4 of the female rotor as the center of the arc, and a portion between points 10 and 14 on the outer diameter of the tip circle coincides with the pitch circle 16 of the female rotor.
(ii) Trailing side curve: The trailing side curve is formed such that the curve between points 13 and 14 at the trailing side of the groove of the female rotor is set as an epitrochoidal curve generated by a point 8 on the tooth profile of the male rotor.
TITLE OF THE INVENTION:
SC~E~ ROTO~S
BAC~GROUND OF THE INVENTION
Field of the Invention The present invention relates to a pair of screw rotors used in a screw rotor machine for compressing or expanding a compressible fluid and supplying the compressed or expanded fluid and, more particularly, to a tooth profile curve thereof.
Description of the Prior Art Rotors having nonsymmetrlcal tooth profiles and used in a compressor or the like of a compressible fluid generally comprise a male rotor having helical lands with a major portion of each tooth profile outside the pitch circle thereof, and a female rotor having helical grooves with a major portion of each tooth profile inside the pitch circle thereof. Normally, the male rotor has a plurality of teeth, and the female rotor meshing therewith has a number of teeth slightly exceeding the 1~i87~7 number of teeth of the male rotor. The diameter of the tip circle of the male rotor is set to be substantially the same as that of the pitch circle of the female rotor.
A screw compressor or expander is constructed as follows. A pair of screw rotors of this type are rotatably housed inside a working space comprising two cylindrical bores formed in a casing. The cylindrical bores have parallel axes and have diameters equal to the outer diameter of the respective rotors to be arranged therein. The distance between the axes of the cylinders is shorter than the sum of the radii thereof, and the axial length of each cylindrical bore is the same as that of the rotors. The two end portions of the cylindrical bores are closed with end plates fixed to the casing.
Inlet and outlet ports for the fluid are formed at predetermined positions of the casing (Fig. 3(a) or 3(b)).
When the above assembly is used as a compressor, the female rotor is rotated counterclockwise while the male rotor is rotated clockwise. With respect to the concave tooth profile of the groove of the female rotorj a curve at the front side along the rotating direction is referred to as the leading side tooth profile, and that at the rear side along the rotating direction is referred to as the trailing side tooth profile. Similarly, with respect to the convex tooth profile of the land of the male rotor, that at the front side along the rotating direction is referred to as the leading side tooth profile, and that at the rear side along the rotating direction is referred to as the trailing side tooth profile.
When the above assembly 1s used as an expander, the names of the respective curves are reversed. However, in the description to follow, the respective tooth profile curves will be explained in accordance with the above definitions.
SUMM~RY OF THE IN~JENTION
It is, therefore, an object of the present invention to provide noveltoOth profiles which will not impair the advantages of the tooth profiles shown in E'igure l previously proposed by said Japanese Utility Model Registration No. 1432776; and which reduce the dis-advantages of these tooth profiles, i.e., increase the stroke volume, prevent rotor wear by changing portions of tooth profiles which form the sealing points for maintaining superior efficiency over a long period of time, increase the pressure angle for improving the i8~47 machining precision of the tooth profile and increasing the tool life, and facilitate easy formation of tools. To this end, the present inventio~ provides screw rotors comprising a male rotor having helical lands and a female rotor having helical grooves which mesh with each other and rotate about two parallel axes, a ma~or portion of each tooth profile of said female rotor being formed inside a pitch circle of said female rotor, and a major portion of each tooth profile of said male rotor being formed outside a pitch circle of said male rotor, characterized in that in tooth profile curves formed in a plane perpendicular to rotating axes of said rotors, a tooth profile of said female rotor is formed such that a portion connecting an outermost first point at a tip of an addendum and a second point located on the pitch circle is a first generated curve generated by a third point located on the pitch circle of the male rotor tooth proile; a portion between the second point and a fourth point is formed by a first circular arc having a first radius and a first center of an arc which is located on a line tangent to the pitch circle of the female rotor at ~he second point and located outside the concave of the groove; a portion between the fourth point and a fifth point is formed by a first envelope developed by a second circular arc which is a part of the male rotor tooth profile; a portion between a sixth point and a seventh point is formed by a third circular arc having a second radius and a second center of an arc located on a first straight line connecting rotating centers of said male and female rotors and outside the pitch circle of said female rotor; a portion between the fifth point and the sixth point is formed by one of a straight line and an approximate curve ,., ~
1~874~
connected with the first envelope at the fifth point and connected with the third circular arc at the sixth point; a portion between the seventh point and an eighth point is formed by a fourth circular arc connected with the third circular arc at the seventh point and having a third radius and a third center of an arc located on an extension of a second straight line connecting the second center of t,he third circular arc and the seventh point which line lntersecting at a first angle with the first straight line at a position opposite to the second center of the third circular arc with respect to the seventh point; and a portion between the eighth point and a ninth point is formed by a fifth circular arc connected with a sixth circular arc having a radius equal to the outer diameter of said female rotor and having a center of an arc on the rotating center of said female rotor at the ninth point and having a fourth radius and a fourth center of an arc located on a third straight line connecting the third center of the fourth circular arc and the eighth point and located inside the female rotor tooth profile; and a tooth profile of the male rotor is formed such that a portion connecting a tenth point located on a bottom land of a dedendum and the third point located on the pitch circle is a second generated curve generated by the first point located on the female rotor tooth profile, a portion between the third point and an eleventh point is a second envelope developed by the first circular arc of the female rotor tooth profile; a portion between the eleventh point and a twelfth point is formed by the second circular arc connected with the second envelope at the eleventh point and having a fifth radius and a fifth center of an arc located on a fourth straight line D
~87~7 - 5a -intersecting at a second angle with the firs~ straight line at the rotating center of said male rotor and located at a predetermined distance from the first straight line; a portion between the twelfth point and a thirteenth point is formed by a seventh circular arc having a sixth radius and a sixth center of an arc at the rotating center of said male rotor; a portion between the thirteenth point and a fourteenth point is formed by a third envelope developed by the third circular arc of the female rotor tooth profile; a portion between the fourteenth point and a fifteenth point is formed by a fourth envelope developed by the fourth circular arc of the female rotor tooth profile; a portion between the fifteenth point and a sixteenth point is formed by a fifth envelope developed by the fifth circular arc of the female rotor; and tooth profiles of said male and female rotors are formed by smoothly and tangentially connecting said arcs and curves.
D
1~~374~7 BRIEF DESCRIPTION OF ~ilE DRAWINGS
Various other objects, features ancl attendant advantages of the present invention will be more fully appreciated as the same becomes better understood from the following detailed descril)tion when considered in connection with the accompanying clrawings in which like reference characters designate like or corresponding parts through the several views and wherein:
Figures l(a), l(b) and 2(a) show tooth profile curves of conven-tional screw rotors, in which Figures l(a) and l(b) correspond to different phases of the tooth profiles disclosed in Japanese Utility Model Registration No. 1432776 as time elapses from Figure l(a) to Figure l~b~;
Figure 2(b) is a view for explaining a communication path formed in the conventional screw rotor shown in Figure 2(a);
Figures 3(a) and 3~b) are a side sectional view and a cross-section-al view of a rotor machine or a compressor using screw rotors according to the present invention;
Figure 4~a) to Figure 4~d) show the different meshing positions of a pair of tooth profile curves of the screw rotors of the present invention, in which the meshing phase shown in Figure 4~a) is shifted to that shown in Figure 4~b) and then to that shown in Figure 4~c), and Figure 4~d) is an en-larged view of Figure 4~c);
Figures 5 to 10 are enlarged views of parts of the tooth profiles in order to explain the characteristic features of the tooth profile curves of the screw rotors according to the present invention; and Figures lla, llb and llc ~with Figure 4c) are views illustrating the measuring method of the tooth profiles of the screw rotors according to the present invention.
1.26~747 DET~ILE~ DF.SCRIPTION OF Tl-lE PRF.FERRED EMBODIMEN'I`S
~ iss. l(a) and ltb) show the respec~ive tooth pxofile curves when the rotors are cut along a plane perpendicular to their rotating axes, i.e., the meshing sta.e between the screw rotors at the end face of each rotor along the longitudinal axes thereof. Fig. l(a) shows the phases of the tooth profiles of the two rotors immediately after the trailing side tooth profile curves of the male and female rotors have begun to contact each other. When the male rotor is rotated through about 20 thereafter, the phases as shown in Fig. l(b) are obtained wherein the highest portion of the tooth profile of the male rotor opposes the deepest portion of the groove of the tooth pro~ile of the female rotor.
The above tooth profiles are conventional ones which are used in, for example, screw compressor manufactured by Hokuetsu Industries Co., Ltd. (3apanese Utility Model Registration No. 1432776! and have the following characteristics.
Referring to Figs. l(a) and l(b), reference numeral 1 denotes a male rotor; and 2, a female rotor meshed therewith. The rotors l and 2 rotate about rotating centers 3 and 4 (centers of the pitch circles) inside cylindrical bores of a casing (not shown) in the direction indicated by arrows, respectively,so as to serve as a fluid compressor. Reference numerals 15 and 16, respectively, denote pitch circles of male rotor 1 and female rotor 2. A line connecting the rotating centers 3 and 4 passes a contact point 17 between the pitch circles 15 and 16, i.e., a pitch point 17.
The above-mentioned tooth profiles will be described with reference to Fig. ltb).
(1) Female Rotor Tooth Profile (i) Leading side curve: The leading side curve is formed such that it consists of a circular arc (11-12) which extends from a point 12 at the deepest tooth profile portion of the groove of the female rotor to an outermost end 10 of the tooth profile and has a radius r4 with respect to the pitch point 17 which is the center of ~'2~i~374'7 g the arc (11-12), the portion between points 11 and 10 and extending from the arc (11-12) is a straight line (10-11) passing through the rotating center 4 of the female rotor and being circumscribed the arc (11-12) having the radius r4, the curve between points 12 and 13 of the bottom land of the groove of the female rotor is a circular arc (12-13! which has a radius r2 with the rotating center 4 of the female rotor as the center of the arc, and a portion between points 10 and 14 on the outer diameter of the tip circle coincides with the pitch circle 16 of the female rotor.
(ii) Trailing side curve: The trailing side curve is formed such that the curve between points 13 and 14 at the trailing side of the groove of the female rotor is set as an epitrochoidal curve generated by a point 8 on the tooth profile of the male rotor.
(2) Male Rotor Tooth Profile (i) Leading side curve: The leading side curve is formed such that a curve (7-6) from a tip 7 of the male rotor tooth profile to a point 6 toward a point 5 at an innermost portion of the male rotor tooth profile is a circular arc which has with the contact point (pitch point) 17 between the pitch circles 15 and 16 of the two rotors as the center of the arc and a radius r3 which is smaller than the radius r4 by an amount required Sor 1~6874~7 rotation, and a curve (6-5) from the point 6 to the innermost portion 5 is an envelope which is developed by a line between points 10 and 11 of the female rotor.
(ii) Trailing side curve: The trailing side curve is formed such that a curve between points 7 and 8 at the trailing side of the male rotor tooth profile is a circular arc which has a radius r1 with the rotating center 3 ~f the pitch circle 15 of the male rotor as the center of the arc, a curve (8-g) between a point 8 and a point 9 at an innermost portion of the male rotor tooth profile is an epicycloidal curve generated by a point 14 at the outermost portion of the groove of the female rotor, a curve between points 9 and 5 of the bottom of the groove coincides with the pitch circle 15 of the male rotor, and the point 8 reaches the intersection, on the sealing line along the thread ridge, which is at the sealed side of the cylindrical bores of the working space of the compressor. The point 8 is determined to be distant from a line (X-axis) connecting the rotating centers 3 and 4 of the two rotors.
Since the conventional tooth profiles shown in Fig. l(b) are defined as described above have following advantages, (i) The blow hole between the working spaces can be set at substantially 0.
(iil In the tooth profiles shown in Fig. l(b), since the point 8 of the male rotor tooth profile is determined to be distant from the X-axis, the ratio of volume expansion of a space 18 defined at the contact portion between the tooth profiles of the male and female rotors upon rotation of the rotors is smaller than that obtained with the SRM tooth profiles (to be described later). Therefore, power loss due to a vacuum produced in the space 18 upon volume expansion is small.
Despite these advantages, the conventional tooth profiles have the following disadvantages:
(iii) The volume of the working space is small (a stroke volume is small).
(iv~ Since the bottom of the groove of the female rotor tooth profile has projections and recesses, a complete seal cannot be provided. The size measurement is difficult during machining. The cutter profile for machining the rotor also has projections and recesses and is complex and is inefficient in machining.
(v! Since the trailing side tooth profile curve is point-generated, the seal point wears easily and the sealing effect cannot be maintained over a long period of time.
(vi) Since the pressure angle of the tooth profile near the pitch circle is substantially 0, precise machining is difficult and the life of the machining tool is also short. The life of a hob tool is particularly short when screw rotors are hobbed.
: A contact surface 18' in the initial meshing phases of the tooth profiles shown in Fig. l(a) forms a space 18 in the phases shown in Fig. l(b~ in which the rotor 1 has rotated through about 20 from the state shown in Fig. l(a). Thus, the space 18 is exposed to vacuum by expanding and causes a power loss regardless of compression operation. For this reason, it is preferable to reduce the volume of trapped space 18. The tooth profile with the characteristics described above has a smaller ratio of volume expansion of the space 18 as compared to one to be described below.
For example, in one type of conventional tooth pro-file called the SRM tooth profile, the rotor used in a screw rotor machine as described in United States Patent No. 3,423,017 has the tooth profile as shown in Fig. 2.
The same reference numerals as in Figs. l(a) and l(b) denote the same parts in Fig. 2, and a detailed description thereof will be omitted. The meshing phases in Fig. 2 correspond to those in Figs. l(a) and l(b~.
Referring to Fig. 2, (1) Female Rotor Tooth Profile (i) Leading side curve: line (28-29); a circular 1?~87~'7 arc having a point 36 on a straight line (17-29) as the center of the arc and a radius r'l, and a circular arc (29-30) having a pitch point 17 as the center of the arc and a radius r'2.
(ii) Trailing side curve: line (30-31); an epitrochoidal curve generated by a point 23 on the male rotor tooth profile, line (31-32); a part of a line passing through the rotating center 4 of the male rotor, line (32-33); a circular arc having the center of the arc on the pitch circle 16, line (33-34~; a circular arc having the rotating center 4 as the center of the arc, and line (34-35); a circular arc having the center of the arc on the pitch circle 16.
(2) Male Rotor Tooth Profile (i) Leading side curve: line (21-22); an envelope developed by the arc (28-29) of the female rotor tooth profile, line (22-23); a circular arc having the pitch point 17 as the center of the arc and a radius r'2.
(ii) Trailing side curve: line (23-24); an epitrochoidal curve generated by a point 31 on the female rotor tooth profile, line (24-25!; a curve generated by a line (31-32), line (25-26); a circular axc having the center of the arc on the pitch circle 15, line (26-27); a circular arc having the rotating center 3 as the center 12~3747 of the arc, and line (27-21); an arc having the center on the pitch circle 15.
The volume of the space 18 in the SRM tooth profile which is to be exposed to vacuum is significantly larger than that in the tooth profile shown in Fig. l(b).
When both the male and female rotors are at the rotating positions shown in Fig. 2(a), they contact at three points 31, 30 and 69 so that the compressed fluid will not leak. Due to the presence of these three contact points, a space 73 is formed at the leading side (upper side from the X-axis in Fig. 2ta)) of the male rotor, while a similar space 18 is formed at the trailing side (lower side from the X-axis in Fig. 2(a)) of the male rotor. Assume that the space 18 is sealed by an end face 67 (Fig. 3(a)) at the inlet side ends of the rotors, and the male and female rotors continue to rotate in the direction indicated by the arrow in Fig. 2(a). Then, the volume of the space 18 is gradually increased, and the degree of vacuum inside the space 18 (to be referred to as a vacuum space) is increased. As compared to the tooth profile shown in Fig. l(b~, the size of the vacuum space is significantly larger. As for an end face 68 (Fig. 3(a)) at the outlet side ends of the rotors, immediately before the space 73 opens into the end face 68, it gradually decreases its volume as the two rotors 12~i~747 rotate and finally becomes substantially zero.
Therefore, .he gas trapped in the space 73 is compressed to an abnormal pressure. In a hydraulically-cooled rotary compressor, the lubricating fluid is injected into the working space for lubricating and cooling the contact and bearing portions. Therefore, the lubricating fluid being trapped inside the space 73 receives compression.
As a result, as the rotors rotate, abnormal vibration or noise is generated and, in a worst case, the rotors wear or are damaged. In addition, a large drive torque is required for driving the compressor. Then, since an immoderate load is exerted on the rotors and the casing, a power loss is large and the life of bearings of the rotor shafts is shortened.
In order to solve this problem, Japanese Patent Application ~aid Open Gazette Nos. 58-214693 and 58-131388 propose means for preventing overcompression of a residual gas by forming a bypass hole 71 in a casing inner wall surface 70 at the outlet port side as shown in Fig. 2(b!, so that the residual gas and lubricating fluid are evacuated into another low-pressure working space through this bypass hole 71, or by forming a recess with a large volume at the position of the bypass hole 71.
However, these means render the structure of the compressor complex and expensive, and lowers the performance.
~2~87~17 The tooth profiles according to a pre_erred embodiment of the present invention will be described with reference to the accompanying drawings.
Figs. 3(a) and 3(b~ show a compressor of a compressible fluid having screw rotors according to the present invention assembied therein. Fig. 3(a) is a side sectional view alo~g the line A - A in Fig. 3(b), and Fig. 3(b) is a cross-sectional view along a line B - B in Fig. 3(al. Referring to Figs. 3(a) and 3(b), reference numeral 1 denotes a male rotor which is driven by a rotating shaft 40 coupled to a prime mover (not shown) and rotatably supported by bearings 44 and 45 mounted on end plates 42 and 43 by the rotating shaft 40 and a support shaft 41 extending symmetrically and coaxially with the rotating shaft 40 with respect to the rotor 1.
Reference numeral 2 denotes a 'emale rotor meshing with the male rotor 1. The rotor 2 is rotatably supported by the end plates 42 and 43 by supporting shafts extending coaxially with the female rotor 2. Reference numeral 46 denotes a ^asing surrounding the outer circumferences of l~t7,~7 the meshing rotors 1 and 2. The low-pressure side end plate 42 having an inlet port 47 and the high-pressure side end plate 43 having an outlet port 48 are coupled at the end faces of the casing 46 along its axial direction.
A working space 49 is defined by teeth of rotors, surfaces of grooves, inner surface of the casing and inner walls of the end plates. The working space 49 communicates the inlet port 47 and the outlet port 48 which respectively communicate with a low-pressure path 50 and a high-pressure path 51 for the working fluid formed in the casing 46. The sectional area of the working space 49 corresponds to a combined area of two parallel cylindrical spaces, the distance between the central axes of the two cylinders is smaller than the sum of the radii of the respective cylinders; the two cylinders have an overlapping portion and therefore have ridge lines 52 at which the inner walls thereof intersect as well shown in Fig. 3(b).
The female rotor 2 is provided with six helical grooves with a wrap angle of about 200 along the rotating axis (longitudinal axis) of the rotor 2. Major portions of the grooves are located inside the pitch circle of the rotor 2. The height of each tooth between adjacent grooves is slightly larger than the pitch - IX -circumference, and the profile of the grooves have inwardly concave curves.
The male rotor 1 is provided generally with four helical lands or teeth having a wrap angle of about 300 along the rotating axis (longitudinal axis) of the rotor 1. Each tooth has two flanks provided with generally convex profile, the major portion thereof is located outside the pitch circle and remainder thereof is located inside the pitch circle. Each two adjacent teeth define a groove for receiving a tooth of the rotor 2 between said flanks. The working space 49 has a V-shape. Upon rotation of the rotors, communication between the inlet port 47 of the low-pressure side end plate 42 and the working space 49 is shielded. Thereafter, as the meshing line (sealing line) of the tooth profiles of the two rotors shifts (relative to the rotation of the rotors!, the volume of the working space 49 is reduced to that before completely sealed. During this time, the fluid is adiabatically compressed and increased in pressure and temperature. When the working space communicates with the outlet port 48 formed in the high-pressure end plate 43, it supplies the compressed fluid to the side of the high-pressure path 51.
During this time, the cooled lubricating fluid is injected into the working space through a nozzle 53 in ~;~68747 ]9 order to lubricate meshing between the rotor teeth and groove surfaces, sliding surfaces between the inner wall of the casing and radial end surfaces of the teeth of rotors, between axial end faces of the rotors and inner side surfaces of the end plates, to seal the working space and to prevent a temperature increase due to the compression of tne fluid.
The present invention relates to tooth profiles of the rotors of the compressor for a compressible fluid.
Figs. 4(a), 4(b) and 4(c) show tooth profiles when the screw rotors of the present invention are cut along a plane perpendicular to the rotating axes. Referring to Figs. 4(a), g(b) and 4(c), reference numeral 1 denotes a male rotor; and 3, a rotating center of the male rotor l, i.e., the center of a pitch circle 15 of the male rotor tooth profile. The male rotor 1 meshes with a female rotor 2 and rotates about the rotating center 3 in the direction indicated by an arrow. Reference numeral 2 denotes a female rotor; and 4, a rotating center thereof, i.e., the center of a pitch circle 16 of the female rotor tooth profile. The rotor 2 meshes with the male rotor 1 and rotates about the rotating center 4 in the direction indicated by an arrow. Reference numeral 17 denotes a pitch point. Points 3, 17 and 4 are located on a straight line. The pitch circles 15 and 16 circumscribe 1~i8747 each other at the point 17. Reference numeral 18 denotes a vacuum space (vacuum producing space) formed between tooth profiles of rotors 1 and 2. Fig. 4(a) shows a phase immediately before the teeth and grooves of the two rotors start to mesh, and illustrates the blow hole formed between the teeth and inner wall of the casing.
Fig. 4(b) shows a phase wherein the rotor 1 has rotated through about 10 from the phase shown in Fig. 4(a) and the rotors contact at point 18' (upstream side along the rotating direction). Fig. 4(c~ shows a phase wherein the male rotor has rotated through another 20 and the tooth profiles mesh completely with each other. Fig. 4(d) is an enlarged view of the bottom of the groove of the female rotor and the tip of the male rotor. The following description of the tooth profiles will be made with reference to Figs. 4(c) and 4(d). Referring to -Figs. 4(c) to 4(d), the tooth profiles are set under the following conditions. Note that symbol Af denotes an addendum; and Dm, a dedendum. Point A1 located on the tooth profile is also a point on the pitch circle 15; and point A2 located on the tooth profile is also a point on the pitch circle 16.
(1) Female Rotor Tooth Profile (i) Trailing side curve: from the an outermost point toward the bottom of the groove, ~874~7 (a) line (H2-A2~; a curve generated by the point A
which is located on the male rotor tooth profile at a point that the profile is intexsecting with the pitch circle 15 and circumscribe line (A2-B2i at the point A2 located on the pitch circle 16 of the female rotor 2.
(b~ line (A2-B2); a circular arc having a radius R7 with a center of the arc 07 located on a straight line circumscribing the pitch circle 16 at the point A2 and outside the concave of the groove.
(ci line (B2-C2); an envelope developed by an arc (B1-Cl) which is a part of the male rotor tooth profile and tangentially connected with the line (A2-B2) at a point B2.
(d) line (C'2-D'2); a common tangent of an envelope (B2-C2) developed by the arc (Bl-C1) which is a part of the male rotor tooth profile (an extension thereof intersects with the line (3-4) at a point C2), and a circular arc (D'2-E1) having a radius R1 and a center of the arc l on the line (3-4) and outside the pitch circle 16. This line (C'2-D'2) can be a smooth curve similar to a circular arc having a radius R5.
(ii) Leading side curve: from the straight line (3-4) toward an outermost point, (e) line (D'2-E2~; a circular arc having a radius Rl and a center of the arc l located on the line (3-4) 12~8t74t;j~
and outside the pitch circle 16 The arc connects with a curve (E2-F2) at a point E2. One extension of the arc ~D'2-E2) intersects the line (3-4) at a point D2.
(f) line (E2-F2~; a circular arc having a radius R2 and a center of the arc 2 located at opposite to the point l on an extension of straight line (Ol-E2) which is intersecting the line (3-4) with an angle ~1 between the line (3-4) at the point l located outside the pitch circle 16 of the female rotor. The arc is convex toward the male rotor and connects with a line (F2-G2) at a point F2.
The angle 01 is 40 to 55 and satisfies an ine~uality 1.05 < (R1/(R5-PCR) _ 1.3. Note that PCR is the pitch circle radius of the male rotor.
The larger the value of R1/(R5-PCR) than 1 and the smaller the value of the angle a 1' the larger the pressure angle near the pitch circle of the tooth profile constituting the line (C2-E2) can be established (see Figs. 8 and 9). The closer the value of R1/(R5-PCR) to 1 and the larger the value of the angle 01' the larger the thickness of the tooth of the female rotor can be established.
In this embodiment, the pressure angle can be set to be sufficiently large, and the above ranges of R1 and 01 are set for assuring a tooth thickness with satisfactory strength.
(g! line (F2 G2); a circular arc having a radius R8 and a center of the arc 8 located on a straight line (02-F2) and outside the concave of the groove. The arc circumscribes the arc (E2-F2) at the point F2 and circumscribes~a circular arc having a radius equal to the outer diameter of the female rotor at a point G2.
(h) line (G2-H2); a circular arc having a radius the same as the outer diameter of the female rotor and has a length from 0.01 to 0.004 times PCD of the male rotor.
(2) Male Rotor Tooth Profile (i) Trailing side curve; from an innermost point to the tip, (j) line t~l-Al); a line generated by a point H2 located on the female rotor tooth profile. The line connects with an arc of the male rotor tooth bottom land at a point Hl.
(k) line (Al-Bl); an envelope generated by an arc (A2-B2) which is a part of the female rotor tooth profile. The envelope connects with a curve (Bl-Cl) at a point Bl, (Q~ line (Bl-Cl); a circular arc having a short radius R4 and a center of the arc 04 located on a radial ~2~874~7 line (3-Cl) extending from the rotating center of the male rotor and intersecting the line (3-4) at a point 3 with an angle ar5. The angle ~r5 is between 4 and 8 and is relatively large. For this reason, the center of the arc 0~ is distant from the line (3-4). The arc connects with a curve (Cl-Dl) at a point Cl.
(m) line (Cl-Dl); a circulàr arc having a point 3 as the center of the arc and a radius R5. The arc (Cl-Dl) connects with a the curve (Dl-El) at a point Dl.
(ii) ~eading side curve; from the tip to an innermost point, (n) line tDl-El); an envelope generated by the arc (D2-E2) which is a part of the female rotor tooth profile (can be approximated by (D'2-E2)). The envelope connects with a curve (El-Fll at a point El. The envelope contacts with the arc (D'2-E2) of the female rotor tooth profile at the point D'2.
(o) line (El-Fl); an envelope generated by the arc (E~-F2) which is a part of the female rotor tooth profile. The envelope connects with a curve (Fl-Gl~ at a point Fl.
(p) line (Fl-Gl); an envelope generated by the arc (F2-G2) which is a part of the female rotor tooth profile. The envelope connects with an arc of the rotor bottom land at a point Gl.
37~7 (q) line (G~ ); an arc forming the male rotor bottom land.
Advantages:
Due to the above characteristics of the tooth profiles of the screw rotors of the present invention, the following effects are obtained.
(1) Since the center 04 of the arc lB1-C1) having the radius R4 is located on the radial line (3-C1) extending from the rotating center 3 of the male rotor, referring to Fig. 5, the angle el formed between a line tangent to the arc ~Bl-C1) at the point Cl and a line ~Q perpendicular to the line (3-4) at the point C1 can be set to be smaller than an angle ~'1 which is formed in the same manner when the center 04 is located on the radial line extending from the pitch point 17. In addition, the trailing side tooth profile of the male rotor is largely separated from the line (3-4) connecting the rotating centers of the t~o rotors and approaches the female rotor trailing side tooth profile curve. The space 18 can therefore be decreased.
(2) Since the angle ~r5 is set to be relatively large, the center 04 of the arc IB1-C1 ) located on the extension of radial line (3-C1) which is intersecting the line (3-4) with the angle 9r5 is largely distant from the ~2~q4~
line (3-4). Therefore, the space 18 can further be decreased.
As can be seen from Figs. 4(b) and 4(c), since the volume expansion ratio of the space 18 is small, the power loss due to the vacuum formation is small.
Further, in the tooth profiles shown in Fig. 2(a), gas and lubricating fluid trapped in the space 73 appeared in the leading side of the male rotor are overcompressed due to the decrease of the volume of the space 73 upon rotation of the rotors when the output port is closed immediately before the end of the output stroke.
According to the present invention, a space 75 which corresponds to the space 73 may be appeared as shown in Figs. 4(c) and 4(d) during the compression stroke.
However, since the line (Bl-Cl) of the male rotor tooth profile is a circular arc having the radius R4 and the center of the arc 04 on the line (3-Cl) intersecting at the point 3 with the line (3-4l at the angle ~r5 of 4-8 and the center of the arc 04 is distant from the line (3-4), and further, the line (C'2-D'2) of the female rotor tooth profile is the common tangent of the envelope (B2-C2~ developed by the arc (Bl-Cl) which is a part of the male rotor tooth profile and the arc (D'2-E1) having the radius Rl or the circular arc having the radius R5 and the line (Dl-El) of the male rotor tooth profile is the envelope developed by the arc (D'2-E2) which is a part of the female rotor tooth profile, the sealed volume of the space 75 can be minimized. In addition, the space 75 is communicated with the input side of the working space due to the separation of the portions of the envelope of the male and female rotors from each other upon rotation of the rotors, the appearance of the space 75 is practically ineffective for the performance of the compressor.
As stated heretofore, when the outlet port is closed immediately before the end of the output stroke, the compressed gas and lubricating fluid are not trapped inside the space 75. Accordingly, overcompression of gas and liquid which accompanies noise and abnormal vibration can be prevented. In addition, a bypass hole (see reference numeral 71 in Fig. 2(b)) described in Japanese Patent Application Laid Open Gazette Nos. 58-214693 and 58-131383 need not be formed. The present invention can provide a simple and inexpensive compressor.
(3~ Since the curve (B2-C2), the curve (Dl-El~, the curve (El-Fl~, the curve (Fl-Gl~ and the curve (Al-Bl) are the envelopes developed by the arc (Bl-Cl), the arc (D2-E2), the arc (E2-F2), the arc (F2-G2) an~ the arc q~7 (A2-B2), respectively, the sliding surfaces of the teeth provide surface contact and will not wear.
(4) Referring to Fig. 6, since the sliding surfaces of the teeth provide surface contact, when a lubricating fluid E is supplied, lubricating and sealing effects can be improved by the wedging effect.
In this manner, the wear resistance and the seal can be improved, and a lowering of efficiency after the use of screw rotors over a long period of time can be prevented.
(5) Referring to Fig. 7, since the curve (A2-B2) is the circular arc having the center of the arc 07 outside the concave of the groove of the female rotor, as compared to a tooth profile wherein the curve (B2-C2) is extended to a circle having a radius equal to the outer diameter (4-H'2) or a line connecting the center 4 and the point B2 to the circle having a radius equal to the outer diameter, the bottom of the profile of a cutter cutting the tooth profile of the rotors is tend to be widened, and the pressure angle can be increased.
Therefore, machining precision of the teeth is improved, and the tool life can be extended.
(6) Since the curve (H2-A2) is a curve generated by the point A1 located on the male rotor tooth profile curve, the pressure angle ~2 can be set to be larger than the pressure angle ~', which is obtained when the curve (A2-B2! is extended to the circle having a radius equal to the outer diameter (4-H'2). Therefore, the machining precision of the teeth can be improved, and the tool life can be prolonged.
(7) Referring to Fig. 8, the curve (D2-E2) is the circular arc having the center of the arc l located outside the pitch circle 16 of the female rotor, the pressure angle ~3 at the point E2 can be set to be larger than the pressure angle ~'3 which is obtained when the center of the arc (D2-E2) is located at the pitch point 17, and the pressure angle of the tooth profile constituting the arc (D2-E~) can be set to be large.
(8) Referring to Fig. 9, since the curve (E2-F2) is the circular arc having the center of the arc 2 located on the extension of line (O1-E2) and opposite to the center l the arc (D2-E2) with respect to the point E2, as compared with the case wherein the center of the arc (E2-F2) is located at a point 2 at the same side with the center l of the arc (D2-E2), the pressure angle at the point F on the tooth profile can be set to be large (L~4 > L~ ' 4) and the pressure angle of the curve constituting the curve (E2-F2) can be set to be large.
Therefore, the damage to the side surface of the hob cutter during hobbing of the rotors can be prevented, the ~874'7 tool life can be prolonged, and the machining precision of rotors is improved.
(9) Referring to Fig. 10, since the curve (F2-G2) is the circular arc having the center of the arc 8 located outside the concave of the groove of the female rotor, as compared to the case wherein the arc ~E2-F2~ is directly e~tended to a point G'2 located on the circle having the radius equivalent to the outer diameter instead of forming the curve (F2-G2), the pressure angle 35 at the point G2 on the tooth profile curve can be set to be large (L~5 > L~ ' 5) and the pressure angle of the curve (F2-G2) can be increased.
~ 10) Since the addendum Af and the dedendum Dm are incorporated, the space vo~ume between the teeth of the rotor can be increased and the volume of the working space can be significantly increased.
In this manner, the volume of the working space can be increased for increasing the volume of the input air, the pressure angle of the tooth profile can be set to be large, the machining precision of teeth can be improved, and the tool life can be prolonged.
(11) In the conventional tooth profiles, a discontinuous point of the tooth profile at the tip of the male rotor 1 is provided as a sealing point with the tooth profile of the female rotor 2 (see reference 374 ~t numeral 8 in Fig. l(b), and reference numeral 23 in Fig. 2). However, although the sealing point is an important point, since it is a discontinuous point, it cannot be precisely measured by a slide caliper, a micrometer, three-dimensional measurement and the like due to the spherical shape of the tip of a filler f.
Referring to Figs. ll(b) and ll(c), when the tooth profile has a discontinuous point, even if the same point is measured, the contact point with the filler f is not stable and the correct position of the discontinuous point cannot be determined. In the tooth profile of the present invention, since the sealing point on the rotor l is set to a point located on the arc (Bl-Cl) which is a continuous curve as shown in Fig. ll(a), the above problem is resolved and correct measurement can be performed~ Accordingly, a correct tooth curve can be easily machined.
According to the tooth profile curves of the present invention, the vacuum producing space is prevented from being large while retaining advantages of the prior art technique. Meanwhile, the tooth profile of the sealing point provides a surface contact between a cylinder and a spherical surface to obtain a wedging effect of a l~bricating fluid to achieve efficient sealing and lubrication. The wear of the rotors is reduced, and the sealing with high efficiency are prolonged. The volume of the working space is increased due to incorporation of the addendum Af and the dedendum Dm.
Since the pressure angle near the pitch circle of the tooth profile is set to be relatively large, machining by a tool is easy, and machining precision is improved. In addition, since a cutter need not have a sharp corner, manufacture of the tool is easy and it can be used over a long period of time.
The life of a hobbing tool can be prolonged, and hobbing is facilitated.
Even though an addendum and a dedendum are incorporated, the blow hole shown in Fig. 4~a) is negligible, small.
In summary, the present invention provides screw rotor tooth profiles which allow easy machining, have increased volumes and have excellent durability and efficiency.
The table below shows the radius R and angle ~ at each section of the tooth profile according to the present invention. PCD represents radius of the pitch circle of the male rotor.
Table R1 ~ 0.33 - 0.4 PCD
R2 0 9 - 1.2 PCD
R40.05 - 0.07 PCD
R50.8 - 0.85 PCD
R70.2 - 0.3 PCD
~r54 - 8
(ii) Trailing side curve: The trailing side curve is formed such that a curve between points 7 and 8 at the trailing side of the male rotor tooth profile is a circular arc which has a radius r1 with the rotating center 3 ~f the pitch circle 15 of the male rotor as the center of the arc, a curve (8-g) between a point 8 and a point 9 at an innermost portion of the male rotor tooth profile is an epicycloidal curve generated by a point 14 at the outermost portion of the groove of the female rotor, a curve between points 9 and 5 of the bottom of the groove coincides with the pitch circle 15 of the male rotor, and the point 8 reaches the intersection, on the sealing line along the thread ridge, which is at the sealed side of the cylindrical bores of the working space of the compressor. The point 8 is determined to be distant from a line (X-axis) connecting the rotating centers 3 and 4 of the two rotors.
Since the conventional tooth profiles shown in Fig. l(b) are defined as described above have following advantages, (i) The blow hole between the working spaces can be set at substantially 0.
(iil In the tooth profiles shown in Fig. l(b), since the point 8 of the male rotor tooth profile is determined to be distant from the X-axis, the ratio of volume expansion of a space 18 defined at the contact portion between the tooth profiles of the male and female rotors upon rotation of the rotors is smaller than that obtained with the SRM tooth profiles (to be described later). Therefore, power loss due to a vacuum produced in the space 18 upon volume expansion is small.
Despite these advantages, the conventional tooth profiles have the following disadvantages:
(iii) The volume of the working space is small (a stroke volume is small).
(iv~ Since the bottom of the groove of the female rotor tooth profile has projections and recesses, a complete seal cannot be provided. The size measurement is difficult during machining. The cutter profile for machining the rotor also has projections and recesses and is complex and is inefficient in machining.
(v! Since the trailing side tooth profile curve is point-generated, the seal point wears easily and the sealing effect cannot be maintained over a long period of time.
(vi) Since the pressure angle of the tooth profile near the pitch circle is substantially 0, precise machining is difficult and the life of the machining tool is also short. The life of a hob tool is particularly short when screw rotors are hobbed.
: A contact surface 18' in the initial meshing phases of the tooth profiles shown in Fig. l(a) forms a space 18 in the phases shown in Fig. l(b~ in which the rotor 1 has rotated through about 20 from the state shown in Fig. l(a). Thus, the space 18 is exposed to vacuum by expanding and causes a power loss regardless of compression operation. For this reason, it is preferable to reduce the volume of trapped space 18. The tooth profile with the characteristics described above has a smaller ratio of volume expansion of the space 18 as compared to one to be described below.
For example, in one type of conventional tooth pro-file called the SRM tooth profile, the rotor used in a screw rotor machine as described in United States Patent No. 3,423,017 has the tooth profile as shown in Fig. 2.
The same reference numerals as in Figs. l(a) and l(b) denote the same parts in Fig. 2, and a detailed description thereof will be omitted. The meshing phases in Fig. 2 correspond to those in Figs. l(a) and l(b~.
Referring to Fig. 2, (1) Female Rotor Tooth Profile (i) Leading side curve: line (28-29); a circular 1?~87~'7 arc having a point 36 on a straight line (17-29) as the center of the arc and a radius r'l, and a circular arc (29-30) having a pitch point 17 as the center of the arc and a radius r'2.
(ii) Trailing side curve: line (30-31); an epitrochoidal curve generated by a point 23 on the male rotor tooth profile, line (31-32); a part of a line passing through the rotating center 4 of the male rotor, line (32-33); a circular arc having the center of the arc on the pitch circle 16, line (33-34~; a circular arc having the rotating center 4 as the center of the arc, and line (34-35); a circular arc having the center of the arc on the pitch circle 16.
(2) Male Rotor Tooth Profile (i) Leading side curve: line (21-22); an envelope developed by the arc (28-29) of the female rotor tooth profile, line (22-23); a circular arc having the pitch point 17 as the center of the arc and a radius r'2.
(ii) Trailing side curve: line (23-24); an epitrochoidal curve generated by a point 31 on the female rotor tooth profile, line (24-25!; a curve generated by a line (31-32), line (25-26); a circular axc having the center of the arc on the pitch circle 15, line (26-27); a circular arc having the rotating center 3 as the center 12~3747 of the arc, and line (27-21); an arc having the center on the pitch circle 15.
The volume of the space 18 in the SRM tooth profile which is to be exposed to vacuum is significantly larger than that in the tooth profile shown in Fig. l(b).
When both the male and female rotors are at the rotating positions shown in Fig. 2(a), they contact at three points 31, 30 and 69 so that the compressed fluid will not leak. Due to the presence of these three contact points, a space 73 is formed at the leading side (upper side from the X-axis in Fig. 2ta)) of the male rotor, while a similar space 18 is formed at the trailing side (lower side from the X-axis in Fig. 2(a)) of the male rotor. Assume that the space 18 is sealed by an end face 67 (Fig. 3(a)) at the inlet side ends of the rotors, and the male and female rotors continue to rotate in the direction indicated by the arrow in Fig. 2(a). Then, the volume of the space 18 is gradually increased, and the degree of vacuum inside the space 18 (to be referred to as a vacuum space) is increased. As compared to the tooth profile shown in Fig. l(b~, the size of the vacuum space is significantly larger. As for an end face 68 (Fig. 3(a)) at the outlet side ends of the rotors, immediately before the space 73 opens into the end face 68, it gradually decreases its volume as the two rotors 12~i~747 rotate and finally becomes substantially zero.
Therefore, .he gas trapped in the space 73 is compressed to an abnormal pressure. In a hydraulically-cooled rotary compressor, the lubricating fluid is injected into the working space for lubricating and cooling the contact and bearing portions. Therefore, the lubricating fluid being trapped inside the space 73 receives compression.
As a result, as the rotors rotate, abnormal vibration or noise is generated and, in a worst case, the rotors wear or are damaged. In addition, a large drive torque is required for driving the compressor. Then, since an immoderate load is exerted on the rotors and the casing, a power loss is large and the life of bearings of the rotor shafts is shortened.
In order to solve this problem, Japanese Patent Application ~aid Open Gazette Nos. 58-214693 and 58-131388 propose means for preventing overcompression of a residual gas by forming a bypass hole 71 in a casing inner wall surface 70 at the outlet port side as shown in Fig. 2(b!, so that the residual gas and lubricating fluid are evacuated into another low-pressure working space through this bypass hole 71, or by forming a recess with a large volume at the position of the bypass hole 71.
However, these means render the structure of the compressor complex and expensive, and lowers the performance.
~2~87~17 The tooth profiles according to a pre_erred embodiment of the present invention will be described with reference to the accompanying drawings.
Figs. 3(a) and 3(b~ show a compressor of a compressible fluid having screw rotors according to the present invention assembied therein. Fig. 3(a) is a side sectional view alo~g the line A - A in Fig. 3(b), and Fig. 3(b) is a cross-sectional view along a line B - B in Fig. 3(al. Referring to Figs. 3(a) and 3(b), reference numeral 1 denotes a male rotor which is driven by a rotating shaft 40 coupled to a prime mover (not shown) and rotatably supported by bearings 44 and 45 mounted on end plates 42 and 43 by the rotating shaft 40 and a support shaft 41 extending symmetrically and coaxially with the rotating shaft 40 with respect to the rotor 1.
Reference numeral 2 denotes a 'emale rotor meshing with the male rotor 1. The rotor 2 is rotatably supported by the end plates 42 and 43 by supporting shafts extending coaxially with the female rotor 2. Reference numeral 46 denotes a ^asing surrounding the outer circumferences of l~t7,~7 the meshing rotors 1 and 2. The low-pressure side end plate 42 having an inlet port 47 and the high-pressure side end plate 43 having an outlet port 48 are coupled at the end faces of the casing 46 along its axial direction.
A working space 49 is defined by teeth of rotors, surfaces of grooves, inner surface of the casing and inner walls of the end plates. The working space 49 communicates the inlet port 47 and the outlet port 48 which respectively communicate with a low-pressure path 50 and a high-pressure path 51 for the working fluid formed in the casing 46. The sectional area of the working space 49 corresponds to a combined area of two parallel cylindrical spaces, the distance between the central axes of the two cylinders is smaller than the sum of the radii of the respective cylinders; the two cylinders have an overlapping portion and therefore have ridge lines 52 at which the inner walls thereof intersect as well shown in Fig. 3(b).
The female rotor 2 is provided with six helical grooves with a wrap angle of about 200 along the rotating axis (longitudinal axis) of the rotor 2. Major portions of the grooves are located inside the pitch circle of the rotor 2. The height of each tooth between adjacent grooves is slightly larger than the pitch - IX -circumference, and the profile of the grooves have inwardly concave curves.
The male rotor 1 is provided generally with four helical lands or teeth having a wrap angle of about 300 along the rotating axis (longitudinal axis) of the rotor 1. Each tooth has two flanks provided with generally convex profile, the major portion thereof is located outside the pitch circle and remainder thereof is located inside the pitch circle. Each two adjacent teeth define a groove for receiving a tooth of the rotor 2 between said flanks. The working space 49 has a V-shape. Upon rotation of the rotors, communication between the inlet port 47 of the low-pressure side end plate 42 and the working space 49 is shielded. Thereafter, as the meshing line (sealing line) of the tooth profiles of the two rotors shifts (relative to the rotation of the rotors!, the volume of the working space 49 is reduced to that before completely sealed. During this time, the fluid is adiabatically compressed and increased in pressure and temperature. When the working space communicates with the outlet port 48 formed in the high-pressure end plate 43, it supplies the compressed fluid to the side of the high-pressure path 51.
During this time, the cooled lubricating fluid is injected into the working space through a nozzle 53 in ~;~68747 ]9 order to lubricate meshing between the rotor teeth and groove surfaces, sliding surfaces between the inner wall of the casing and radial end surfaces of the teeth of rotors, between axial end faces of the rotors and inner side surfaces of the end plates, to seal the working space and to prevent a temperature increase due to the compression of tne fluid.
The present invention relates to tooth profiles of the rotors of the compressor for a compressible fluid.
Figs. 4(a), 4(b) and 4(c) show tooth profiles when the screw rotors of the present invention are cut along a plane perpendicular to the rotating axes. Referring to Figs. 4(a), g(b) and 4(c), reference numeral 1 denotes a male rotor; and 3, a rotating center of the male rotor l, i.e., the center of a pitch circle 15 of the male rotor tooth profile. The male rotor 1 meshes with a female rotor 2 and rotates about the rotating center 3 in the direction indicated by an arrow. Reference numeral 2 denotes a female rotor; and 4, a rotating center thereof, i.e., the center of a pitch circle 16 of the female rotor tooth profile. The rotor 2 meshes with the male rotor 1 and rotates about the rotating center 4 in the direction indicated by an arrow. Reference numeral 17 denotes a pitch point. Points 3, 17 and 4 are located on a straight line. The pitch circles 15 and 16 circumscribe 1~i8747 each other at the point 17. Reference numeral 18 denotes a vacuum space (vacuum producing space) formed between tooth profiles of rotors 1 and 2. Fig. 4(a) shows a phase immediately before the teeth and grooves of the two rotors start to mesh, and illustrates the blow hole formed between the teeth and inner wall of the casing.
Fig. 4(b) shows a phase wherein the rotor 1 has rotated through about 10 from the phase shown in Fig. 4(a) and the rotors contact at point 18' (upstream side along the rotating direction). Fig. 4(c~ shows a phase wherein the male rotor has rotated through another 20 and the tooth profiles mesh completely with each other. Fig. 4(d) is an enlarged view of the bottom of the groove of the female rotor and the tip of the male rotor. The following description of the tooth profiles will be made with reference to Figs. 4(c) and 4(d). Referring to -Figs. 4(c) to 4(d), the tooth profiles are set under the following conditions. Note that symbol Af denotes an addendum; and Dm, a dedendum. Point A1 located on the tooth profile is also a point on the pitch circle 15; and point A2 located on the tooth profile is also a point on the pitch circle 16.
(1) Female Rotor Tooth Profile (i) Trailing side curve: from the an outermost point toward the bottom of the groove, ~874~7 (a) line (H2-A2~; a curve generated by the point A
which is located on the male rotor tooth profile at a point that the profile is intexsecting with the pitch circle 15 and circumscribe line (A2-B2i at the point A2 located on the pitch circle 16 of the female rotor 2.
(b~ line (A2-B2); a circular arc having a radius R7 with a center of the arc 07 located on a straight line circumscribing the pitch circle 16 at the point A2 and outside the concave of the groove.
(ci line (B2-C2); an envelope developed by an arc (B1-Cl) which is a part of the male rotor tooth profile and tangentially connected with the line (A2-B2) at a point B2.
(d) line (C'2-D'2); a common tangent of an envelope (B2-C2) developed by the arc (Bl-C1) which is a part of the male rotor tooth profile (an extension thereof intersects with the line (3-4) at a point C2), and a circular arc (D'2-E1) having a radius R1 and a center of the arc l on the line (3-4) and outside the pitch circle 16. This line (C'2-D'2) can be a smooth curve similar to a circular arc having a radius R5.
(ii) Leading side curve: from the straight line (3-4) toward an outermost point, (e) line (D'2-E2~; a circular arc having a radius Rl and a center of the arc l located on the line (3-4) 12~8t74t;j~
and outside the pitch circle 16 The arc connects with a curve (E2-F2) at a point E2. One extension of the arc ~D'2-E2) intersects the line (3-4) at a point D2.
(f) line (E2-F2~; a circular arc having a radius R2 and a center of the arc 2 located at opposite to the point l on an extension of straight line (Ol-E2) which is intersecting the line (3-4) with an angle ~1 between the line (3-4) at the point l located outside the pitch circle 16 of the female rotor. The arc is convex toward the male rotor and connects with a line (F2-G2) at a point F2.
The angle 01 is 40 to 55 and satisfies an ine~uality 1.05 < (R1/(R5-PCR) _ 1.3. Note that PCR is the pitch circle radius of the male rotor.
The larger the value of R1/(R5-PCR) than 1 and the smaller the value of the angle a 1' the larger the pressure angle near the pitch circle of the tooth profile constituting the line (C2-E2) can be established (see Figs. 8 and 9). The closer the value of R1/(R5-PCR) to 1 and the larger the value of the angle 01' the larger the thickness of the tooth of the female rotor can be established.
In this embodiment, the pressure angle can be set to be sufficiently large, and the above ranges of R1 and 01 are set for assuring a tooth thickness with satisfactory strength.
(g! line (F2 G2); a circular arc having a radius R8 and a center of the arc 8 located on a straight line (02-F2) and outside the concave of the groove. The arc circumscribes the arc (E2-F2) at the point F2 and circumscribes~a circular arc having a radius equal to the outer diameter of the female rotor at a point G2.
(h) line (G2-H2); a circular arc having a radius the same as the outer diameter of the female rotor and has a length from 0.01 to 0.004 times PCD of the male rotor.
(2) Male Rotor Tooth Profile (i) Trailing side curve; from an innermost point to the tip, (j) line t~l-Al); a line generated by a point H2 located on the female rotor tooth profile. The line connects with an arc of the male rotor tooth bottom land at a point Hl.
(k) line (Al-Bl); an envelope generated by an arc (A2-B2) which is a part of the female rotor tooth profile. The envelope connects with a curve (Bl-Cl) at a point Bl, (Q~ line (Bl-Cl); a circular arc having a short radius R4 and a center of the arc 04 located on a radial ~2~874~7 line (3-Cl) extending from the rotating center of the male rotor and intersecting the line (3-4) at a point 3 with an angle ar5. The angle ~r5 is between 4 and 8 and is relatively large. For this reason, the center of the arc 0~ is distant from the line (3-4). The arc connects with a curve (Cl-Dl) at a point Cl.
(m) line (Cl-Dl); a circulàr arc having a point 3 as the center of the arc and a radius R5. The arc (Cl-Dl) connects with a the curve (Dl-El) at a point Dl.
(ii) ~eading side curve; from the tip to an innermost point, (n) line tDl-El); an envelope generated by the arc (D2-E2) which is a part of the female rotor tooth profile (can be approximated by (D'2-E2)). The envelope connects with a curve (El-Fll at a point El. The envelope contacts with the arc (D'2-E2) of the female rotor tooth profile at the point D'2.
(o) line (El-Fl); an envelope generated by the arc (E~-F2) which is a part of the female rotor tooth profile. The envelope connects with a curve (Fl-Gl~ at a point Fl.
(p) line (Fl-Gl); an envelope generated by the arc (F2-G2) which is a part of the female rotor tooth profile. The envelope connects with an arc of the rotor bottom land at a point Gl.
37~7 (q) line (G~ ); an arc forming the male rotor bottom land.
Advantages:
Due to the above characteristics of the tooth profiles of the screw rotors of the present invention, the following effects are obtained.
(1) Since the center 04 of the arc lB1-C1) having the radius R4 is located on the radial line (3-C1) extending from the rotating center 3 of the male rotor, referring to Fig. 5, the angle el formed between a line tangent to the arc ~Bl-C1) at the point Cl and a line ~Q perpendicular to the line (3-4) at the point C1 can be set to be smaller than an angle ~'1 which is formed in the same manner when the center 04 is located on the radial line extending from the pitch point 17. In addition, the trailing side tooth profile of the male rotor is largely separated from the line (3-4) connecting the rotating centers of the t~o rotors and approaches the female rotor trailing side tooth profile curve. The space 18 can therefore be decreased.
(2) Since the angle ~r5 is set to be relatively large, the center 04 of the arc IB1-C1 ) located on the extension of radial line (3-C1) which is intersecting the line (3-4) with the angle 9r5 is largely distant from the ~2~q4~
line (3-4). Therefore, the space 18 can further be decreased.
As can be seen from Figs. 4(b) and 4(c), since the volume expansion ratio of the space 18 is small, the power loss due to the vacuum formation is small.
Further, in the tooth profiles shown in Fig. 2(a), gas and lubricating fluid trapped in the space 73 appeared in the leading side of the male rotor are overcompressed due to the decrease of the volume of the space 73 upon rotation of the rotors when the output port is closed immediately before the end of the output stroke.
According to the present invention, a space 75 which corresponds to the space 73 may be appeared as shown in Figs. 4(c) and 4(d) during the compression stroke.
However, since the line (Bl-Cl) of the male rotor tooth profile is a circular arc having the radius R4 and the center of the arc 04 on the line (3-Cl) intersecting at the point 3 with the line (3-4l at the angle ~r5 of 4-8 and the center of the arc 04 is distant from the line (3-4), and further, the line (C'2-D'2) of the female rotor tooth profile is the common tangent of the envelope (B2-C2~ developed by the arc (Bl-Cl) which is a part of the male rotor tooth profile and the arc (D'2-E1) having the radius Rl or the circular arc having the radius R5 and the line (Dl-El) of the male rotor tooth profile is the envelope developed by the arc (D'2-E2) which is a part of the female rotor tooth profile, the sealed volume of the space 75 can be minimized. In addition, the space 75 is communicated with the input side of the working space due to the separation of the portions of the envelope of the male and female rotors from each other upon rotation of the rotors, the appearance of the space 75 is practically ineffective for the performance of the compressor.
As stated heretofore, when the outlet port is closed immediately before the end of the output stroke, the compressed gas and lubricating fluid are not trapped inside the space 75. Accordingly, overcompression of gas and liquid which accompanies noise and abnormal vibration can be prevented. In addition, a bypass hole (see reference numeral 71 in Fig. 2(b)) described in Japanese Patent Application Laid Open Gazette Nos. 58-214693 and 58-131383 need not be formed. The present invention can provide a simple and inexpensive compressor.
(3~ Since the curve (B2-C2), the curve (Dl-El~, the curve (El-Fl~, the curve (Fl-Gl~ and the curve (Al-Bl) are the envelopes developed by the arc (Bl-Cl), the arc (D2-E2), the arc (E2-F2), the arc (F2-G2) an~ the arc q~7 (A2-B2), respectively, the sliding surfaces of the teeth provide surface contact and will not wear.
(4) Referring to Fig. 6, since the sliding surfaces of the teeth provide surface contact, when a lubricating fluid E is supplied, lubricating and sealing effects can be improved by the wedging effect.
In this manner, the wear resistance and the seal can be improved, and a lowering of efficiency after the use of screw rotors over a long period of time can be prevented.
(5) Referring to Fig. 7, since the curve (A2-B2) is the circular arc having the center of the arc 07 outside the concave of the groove of the female rotor, as compared to a tooth profile wherein the curve (B2-C2) is extended to a circle having a radius equal to the outer diameter (4-H'2) or a line connecting the center 4 and the point B2 to the circle having a radius equal to the outer diameter, the bottom of the profile of a cutter cutting the tooth profile of the rotors is tend to be widened, and the pressure angle can be increased.
Therefore, machining precision of the teeth is improved, and the tool life can be extended.
(6) Since the curve (H2-A2) is a curve generated by the point A1 located on the male rotor tooth profile curve, the pressure angle ~2 can be set to be larger than the pressure angle ~', which is obtained when the curve (A2-B2! is extended to the circle having a radius equal to the outer diameter (4-H'2). Therefore, the machining precision of the teeth can be improved, and the tool life can be prolonged.
(7) Referring to Fig. 8, the curve (D2-E2) is the circular arc having the center of the arc l located outside the pitch circle 16 of the female rotor, the pressure angle ~3 at the point E2 can be set to be larger than the pressure angle ~'3 which is obtained when the center of the arc (D2-E2) is located at the pitch point 17, and the pressure angle of the tooth profile constituting the arc (D2-E~) can be set to be large.
(8) Referring to Fig. 9, since the curve (E2-F2) is the circular arc having the center of the arc 2 located on the extension of line (O1-E2) and opposite to the center l the arc (D2-E2) with respect to the point E2, as compared with the case wherein the center of the arc (E2-F2) is located at a point 2 at the same side with the center l of the arc (D2-E2), the pressure angle at the point F on the tooth profile can be set to be large (L~4 > L~ ' 4) and the pressure angle of the curve constituting the curve (E2-F2) can be set to be large.
Therefore, the damage to the side surface of the hob cutter during hobbing of the rotors can be prevented, the ~874'7 tool life can be prolonged, and the machining precision of rotors is improved.
(9) Referring to Fig. 10, since the curve (F2-G2) is the circular arc having the center of the arc 8 located outside the concave of the groove of the female rotor, as compared to the case wherein the arc ~E2-F2~ is directly e~tended to a point G'2 located on the circle having the radius equivalent to the outer diameter instead of forming the curve (F2-G2), the pressure angle 35 at the point G2 on the tooth profile curve can be set to be large (L~5 > L~ ' 5) and the pressure angle of the curve (F2-G2) can be increased.
~ 10) Since the addendum Af and the dedendum Dm are incorporated, the space vo~ume between the teeth of the rotor can be increased and the volume of the working space can be significantly increased.
In this manner, the volume of the working space can be increased for increasing the volume of the input air, the pressure angle of the tooth profile can be set to be large, the machining precision of teeth can be improved, and the tool life can be prolonged.
(11) In the conventional tooth profiles, a discontinuous point of the tooth profile at the tip of the male rotor 1 is provided as a sealing point with the tooth profile of the female rotor 2 (see reference 374 ~t numeral 8 in Fig. l(b), and reference numeral 23 in Fig. 2). However, although the sealing point is an important point, since it is a discontinuous point, it cannot be precisely measured by a slide caliper, a micrometer, three-dimensional measurement and the like due to the spherical shape of the tip of a filler f.
Referring to Figs. ll(b) and ll(c), when the tooth profile has a discontinuous point, even if the same point is measured, the contact point with the filler f is not stable and the correct position of the discontinuous point cannot be determined. In the tooth profile of the present invention, since the sealing point on the rotor l is set to a point located on the arc (Bl-Cl) which is a continuous curve as shown in Fig. ll(a), the above problem is resolved and correct measurement can be performed~ Accordingly, a correct tooth curve can be easily machined.
According to the tooth profile curves of the present invention, the vacuum producing space is prevented from being large while retaining advantages of the prior art technique. Meanwhile, the tooth profile of the sealing point provides a surface contact between a cylinder and a spherical surface to obtain a wedging effect of a l~bricating fluid to achieve efficient sealing and lubrication. The wear of the rotors is reduced, and the sealing with high efficiency are prolonged. The volume of the working space is increased due to incorporation of the addendum Af and the dedendum Dm.
Since the pressure angle near the pitch circle of the tooth profile is set to be relatively large, machining by a tool is easy, and machining precision is improved. In addition, since a cutter need not have a sharp corner, manufacture of the tool is easy and it can be used over a long period of time.
The life of a hobbing tool can be prolonged, and hobbing is facilitated.
Even though an addendum and a dedendum are incorporated, the blow hole shown in Fig. 4~a) is negligible, small.
In summary, the present invention provides screw rotor tooth profiles which allow easy machining, have increased volumes and have excellent durability and efficiency.
The table below shows the radius R and angle ~ at each section of the tooth profile according to the present invention. PCD represents radius of the pitch circle of the male rotor.
Table R1 ~ 0.33 - 0.4 PCD
R2 0 9 - 1.2 PCD
R40.05 - 0.07 PCD
R50.8 - 0.85 PCD
R70.2 - 0.3 PCD
~r54 - 8
Claims
PROPERTY OR PRIVILEGE IS CLAIMED IS DEFINED AS FOLLOWS:
1. Screw rotors comprising a male rotor having helical lands and a female rotor having helical grooves which mesh with each other and rotate about two parallel axes, a major portion of each tooth profile of said female rotor being formed inside a pitch circle of said female rotor, and a major portion of each tooth profile of said male rotor being formed outside a pitch circle of said male rotor, characterized in that in tooth profile curves formed in a plane perpendicular to rotating axes of said rotors, a tooth profile of said female rotor is formed such that a portion connecting an outermost first point at a tip of an addendum and a second point located on the pitch circle is a first generated curve generated by a third point located on the pitch circle of the male rotor tooth profile; a portion between the second point and a fourth point is formed by a first circular arc having a first radius and a first center of an arc which is located on a line tangent to the pitch circle of the female rotor at the second point and located outside the concave of the groove; a portion between the fourth point and a fifth point is formed by a first envelope developed by a second circular arc which is a part of the male rotor tooth profile; a portion between a sixth point and a seventh point is formed by a third circular arc having a second radius and a second center of an arc located on a first straight line connecting rotating centers of said male and female rotors and outside the pitch circle of said female rotor; a portion between the fifth point and the sixth point is formed by one of a straight line and an approximate curve connected with the first envelope at the fifth point and connected with the third circular arc at the sixth point; a portion between the seventh point and an eighth point is formed by a fourth circular arc connected with the third circular arc at the seventh point and having a third radius and a third center of an arc located on an extension of a second straight line connecting the second center of the third circular arc and the seventh point which line intersecting at a first angle with the first straight line at a position opposite to the second center of the third circular arc with respect to the seventh point; and a portion between the eighth point and a ninth point is formed by a fifth circular arc connected with a sixth circular arc having a radius equal to the outer diameter of said female rotor and having a center of an arc on the rotating center of said female rotor at the ninth point and having a fourth radius and a fourth center of an arc located on a third straight line connecting the third center of the fourth circular arc and the eighth point and located inside the female rotor tooth profile; and a tooth profile of the male rotor is formed such that a portion connecting a tenth point located on a bottom land of a dedendum and the third point located on the pitch circle is a second generated curve generated by the first point located on the female rotor tooth profile, a portion between the third point and an eleventh point is a second envelope developed by the first circular arc of the female rotor tooth profile; a portion between the eleventh point and a twelfth point is formed by the second circular arc connected with the second envelope at the eleventh point and having a fifth radius and a fifth center of an arc located on a fourth straight line intersecting at a second angle with the first straight line at the rotating center of said male rotor and located at a predetermined distance from the first straight line; a portion between the twelfth point and a thirteenth point is formed by a seventh circular arc having a sixth radius and a sixth center of an arc at the rotating center of said male rotor; a portion between the thirteenth point and a fourteenth point is formed by a third envelope developed by the third circular arc of the female rotor tooth profile; a portion between the fourteenth point and a fifteenth point is formed by a fourth envelope developed by the fourth circular arc of the female rotor tooth profile; a portion between the fifteenth point and a sixteenth point is formed by a fifth envelope developed by the fifth circular arc of the female rotor; and tooth profiles of said male and female rotors are formed by smoothly and tangentially connecting said arcs and curves.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000478391A CA1268747A (en) | 1984-04-07 | 1985-04-04 | Screw rotors |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| JP59069699A JPS60212684A (en) | 1984-04-07 | 1984-04-07 | Screw rotor |
| JP69699/SHO59(1984) | 1984-04-07 | ||
| CA000478391A CA1268747A (en) | 1984-04-07 | 1985-04-04 | Screw rotors |
Publications (1)
| Publication Number | Publication Date |
|---|---|
| CA1268747A true CA1268747A (en) | 1990-05-08 |
Family
ID=25670642
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000478391A Expired - Lifetime CA1268747A (en) | 1984-04-07 | 1985-04-04 | Screw rotors |
Country Status (1)
| Country | Link |
|---|---|
| CA (1) | CA1268747A (en) |
-
1985
- 1985-04-04 CA CA000478391A patent/CA1268747A/en not_active Expired - Lifetime
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