Title of Invention

"A CONJUGATE PAIR OF INTERMESHING ROTORS"

Abstract The invention provides for a conjugate pair of intermeshing rotors having helical lobes comprising helical crests and intervening grooves for rotation about parallel axes (A, B) within a working space of a screw rotor machine, each rotor has a tip circle (TF, TM), a pitch ckcle (PF PM), and a root circle (RFR, RMR), one rotor of each pair being a female rotor so that the major portion of each lobe of said female rotor is located inside said pitch circle of said female rotor, the other rotor being a male rotor formed so that the major portion of each lobe of said male rotor is located outside said pitch ckcle of said male rotor, the lobes of one rotor following the grooves of the other rotor to form a continuous sealing line between said pak of rotors, a first portion of each female lobe located generally between the tip ckcle (TF/12-l) and pitch ckcle (PF) of said female rotor containing a fkst segment (F5"-F7) having a large radius portion (F5"-F6) nearer said tip ckcle of said female rotor and a smaller radius portion (F6-F7) nearer said pitch ckcle of said female rotor. Figure 1
Full Text The present invention relates to a conjugate pair of intermeshing rotors.
While there is some commonality between gears and screw rotors, a major difference is in the fluid sealing requirements of screw rotors. As in the case of gears, screw rotors have pitch circles which represent locations of equal tangential velocity for conjugate pairs of rotors. The spiral grooves in the rotors are the locations of the volumes of gas which are trapped and compressed due to the co-action of a conjugate pair of rotors and an enclosing casing. Accordingly, the volumes of the spiral grooves are a major design consideration with their width, depth, length and number being design variables. The shape of the cross section of the spiral grooves includes the variables of width and depth as well as the shape requirements fro the driving/driven co-action between the conjugate pair of rotors. Additionally the conjugate pair must meet the sealing requirements as the line contact advances along the rotor profile in the driving/driven co-action and and as the rotor tips and end faces co-act with the enclosing casing. This line contact follows the perimeters of the rotor profiles and is therefore at a varying tangential speed and has significant radial components. Additionally, the shape and cross section of the spiral grooves must meet requirements for ease of manufacture and cutting tool life. One problem associated with conventional screw rotor designs is that the pressure angle and lobe thickness are inter-related. It is desirable to minimize the pressure angle, the angle of contact between the rotors in the contact zone near or at the pitch circle, to provide reduced contact loading. However, the reducing of the pressure angle has an attendant undesirable reduction in lobe thickness such that conventional designs represent a compromise between desired pressure angle and desired lobe thickness.
Assuming that each respective lobe tip of each rotor is in tangential contact with a root of the other rotor during a point in each revolution, the addendum of the lobes of one lobe will be co-incident to the dedendum of the lobes of the rotor as measured along a line connecting the centers of the two rotors. Ignoring running clearances, machining tolerances, wear, thermal expansion etc. there are three
nominal points of tangencs netween a conjugate pair of rotors, namely between the pitch circles and between the tip circle of each rotor and the root circle of the other rotor.
The present invention is directed to an improved configuration for a conjugate pair of screw rotors. Among the benefits provided by the present invention are: reduced viscous drag through the use of a departure angle; strengthened female lobes by controlling thickness along the pitch circle; opened root of male rotor to enhance manufacturability and tool life; a tortuous flow path for gas leaking from a high pressure thread; better control of root diameter; and control of the pressure angle independently of the other variables.
It is an object of this invention to increase the efficiency of a screw machine.
It is another object of this invention to provide conjugate screw rotor profiles having reduced leakage.
It is a further object of this invention to achieve the disclosed performance based objects while improving the manufacturability of the screw rotor profiles. These objects, and others as will become apparent hereinafter, are accomplished by the present invention.
Basically, the point of tangency of the tip circle ot the male rotor and the root ciicle of the female rotor is used as a starting point in ginerning the series of curves defning the male and female conjugate rotor profiles Adoronally, the pressure angle a independent of the female lobe thickness.
To meet the aforementioned objectives the invention provides for A conjugate pair of intermeshing rotor (14,16) having helical lobes comprising helical crests (14-1, 16-1) and intervening grooves (14-2,16-2) for rotation about parallel axes (A,B) within a working space of a screw rotor machine, each rotor has a tip circle (TF,TM), a pitch circle (PF,PM), and a root circle (RFR,RMR), one rotor of each pair being a female rotor (14) so that the major portion of each lobe of said female rotor is located inside said pitch circle of said female rotor, the other rotor being a male rotor (16) formed such that the major portion of each lobe of said male rotor is located outside said pitch circle of said male rotor, the lands of one rotor following the grooves of the other rotor to form a continuous sealing line between said pair of rotors, said lobes on said female rotor comprising at least eight segments, said lobes on said male rotor comprising at least eight segments, said lobes on said male rotor comprising at least eight segments which are conjugate to said female rotor segments, respectively, said female rotor segments starting at a first point coincident with a point on the female root circle and said conjugate male rotor segments starting at a corresponding first point coincident with a point on the male tip circle, said segments being characterized by:
a first segment on said male rotor comprising solely said first point only on said tip circle of said male rotor, and a first segment on said female rotor extending from said first female point on said female root circle to a second point radially inward of said female pitch circle and which is generated by said first point on male rotor when both of said rotors are rotated at the same pitch velocity; (POINT Ml ON MALE AND SEGMENT F1-F2 ON FEMALE)' a second segment on said female rotor comprising a circular are extending from the said second female rotor point and extending to a third point located radially outward at least to said pitch circle of said female rotor, and a second segment on said male rotor extending between said first male rotor point and a second male rotor point and which is generated by said second female segment when both of said rotors are rotated at the same pitch velocity; (SEGMENT F2-F3 ON FEMALE AND SEGMENT M1-M2 ON MALI:) a third segment on said female rotor comprising a circular are extending from said third female rotor point and extending to a fourth point located between said female rotor tip circle and said female rotor pitch circle and a third segment on said male rotor extending from said second male rotor point to a third male rotor point and which is generated by said third female segment when both of said rotors are rotated at the same pitch circle velocity;
(SEGMENT M2-M3 ON MALE AND SEGMENT F3-F4 ON FEMALE)
a fourth segment on said female rotor comprising a circular are extending from said fourth female rotor point and extending to a fifth female rotor point which is coincident with a point on said female tip circle, and a fourth segment on said male rotor extending from said third male rotor point to a fourth male rotor point which is coincident with a point on said male root circle, and said fourth male rotor segment which is generated by said fourth female segment when bodi of said rotors are rotated at the same pitch circle velocity; (SEGMENT F4-F5 ON FEMALE AND SEGMENT M3-M4 ON MALE)
a fifth segment on said female rotor comprising a circular are coincident with said female rotor tip circle and extending from said fifth female rotor point to a sixth female rotor point, and a fifth segment on said male rotor extending from said fourth male rotor point to a fifth male rotor point and which is generated by said fifth female segment when both of said rotors are rotated at the same pitch circle velocity; (SEGMENT F5-F5 ' ON FEMALE AND SEGMENT M4-M5 ON MALI:)
a sixth segment on said female rotor which extends from said sixth female rotor point on said tip circle of said female rotor to a seventh female rotor point located on or radially outward of said female rotor pitch circle comprising a curve of generally large radius in the outward end nearer said female rotor tip circle and having a generally smaller radius in the inward end nearer said female rotor pitch circle, and a sixth segment on said male rotor extending from said fifth male rotor point to a sixth male rotor point and which is generated by said sixth female segment when both of said rotors arc rotated at the same pitch circle velocity; (SEGMENT F5"-F7 ON FEMALE AND SEGMENT M5'-M7 ON MALI-:)
a seventh segment on said male rotor which extends from said sixth male rotor point to an seventh male rotor point which is coincident with a point on said tip circle of said male rotor and said seventh male rotor segment comprising a curve characterized by having a varying radius, and a seventh segment on said female rotor which extends from said seventh female rotor point to an eighth female rotor point which is coincident with a point on said female root circle and at least a portion of said eighth female rotor segment being generated by at least a portion of said seventh male rotor segment when both of said rotors are rotated at the same pitch circle velocity;
(SEGMENT M7-M9 ON MALE AND SEGMENT F7-F9 ON FEMALE)
an eighth segment on said male rotor comprising a circular are coincident with said male tip circle and extending from said seventh male rotor point to an eight male rotor point which is coincident with said first male rotor point for the subsequent male lobe, and an eighth segment on said female rotor extending from said eight female rotor point to a ninth female rotor point which is coincident with said first female rotor point for a subsequent female lobe, said eighth female rotor segment being generated by said eighth male rotor segment when both of said rotors are rotated at the same pitch circle velocity. (SEGMENT M9-M1 ON MALE AND SEGMENT F9-F1 ON FEMALE)
Brief Description of Accompanying Drawings:
Figure 1 is a transverse suction through a screw machine employing the present invention;
Figure 2 is a plot of the curve segments making up the female rotor;
Figure 3 is a plot of the curve segments making up the male rotor;
Figure 4 is an enlarged representation of the departure segment of the rotors of the present invention;
Figure 5 is an enlarged representation of the departure segment of the rotors of a PRIOR ART device;
Figure 6 is an enlarged portion of a modified segment of a female rotor;
Figure 7 is an enlarged portion of a second modified segment of a female rotor;
Figure 8 is an enlarged portion of a third modified segment of a female rotor;
Figure 9 is an enlarged portion of a fourth modified segment of a female rotor;
Figure 10 is an enlarged portion of a fifth modified segment of a female rotor;
Figure 11 is an enlarged portion of a sixth modified segment of a female rotor;
Figure 12 is an enlarged portion of a first modified segment of a male rotor;
Figure 13 is an enlarged portion of a second modified segment of a male rotor.
Figure 14 is an enlarged portion of a seventh modified segmeni of a female rotor; and
Figure 15 is an enlarged portion of a third modified segment of a male rotor which is conjugate to the Figure 14 configuration.
In Figure 1, the numeral 10 generally indicates a screw machine such as a screw compressor. Screw machine 10 has a casing 12 with overlapping bores 12-1 and 12-2 located therein. Female rotor 14 has a pitch circle, PF, and is located in bore 12-1. Male rotor 16 has a pitch circle, PM, and is located in bore 12-2. The axes indicated by points A and B are perpendicular to the plane of Figure 1 and are parallel to each other and are separated by a distance equal to the sum of the radius, RF, of the pitch circle, PF, of female rotor 14 and the radius, RM, cf the pitch circle, PM, of male rotor 16. The axis indicated by point A is the axis of rotation of female rotor 14 and the center of bore 12-1 whose diameter generally corresponds to the diameter of the tip circle, TF, of female rotor 14. Similarly, the axis indicated by point B is the axis of rotation of male rotor 16 and the center of bore 12-2 whose diameter generally corresponds to the diameter of the tip circle, TM, of male rotor 16. Neglecting operating clearances, the extension of the bore 12-1 through the overlapping portion with bore 12-2 will intersect line A-B at the tangent point with the root circle, RMR, of male rotor 16. Similarly, the extension of the bore 12-2 through the overlapping portion with bore 12-1 will intersect line A-B at the tangent point with the root circle, RFR, of female rotor 14 and this common point is labeled F, relative to female rotor 14 and M, relative to male rotor 16.
As illustrated, female rotor 14 has six lands, 14-1, separated by six grooves, 14-2, while male rotor 16 has five lands, 16-1, separated by five grooves 16-2. Accordingly, the rotational speed of rotor 16 will be 6/5 or 120% of that of rotor 14. Either the female rotor 14 or the male rotor 16 may be connected to a prime mover (not illustrated) and serve as the driving rotor. Other combinations of the number of female and male lands and grooves may also be used
The generation of the profiles of rotors 14 and 16 starts with common point, F1, M1, as shown in Figure 1. With reference to Figures 1-3, the curve F1-F2 on female rotor 14 is generated by point M, on the male tip as it rotates about axis B with both of rotors
14 and 16 having the same pitch circle velocity. Curve F1-F2 extends from the root of female rotor 14 to a point, F2, short of the female pitch circle, PF.
Curve F2-F3 is a circular arc on female rotor 14 and extends from point F, to the pitch circle PF. The center of curve F1-F3 is positioned such that curve F2-F3 both intersects curve F1-F2 and is tangent to curve F1-F2 at the point of intersection. The radius of curve F2-F3 is adjusted to provide a desired balance between minimum blow hole area, as it affects the angle at which curve F3-F4 intersects the pitch circle PF, described below, and ease of manufacturing since tool life decreases with a reduction in the radius of curve F2-F3.
Curve F2-F3 generates curve M1-M2 on male rotor 16. As noted above, point M1 generates curve F1-F2 so that F2 is a common point with point M, at one point in the rotation of the rotors. Curve M1-M2 represents the path swept out on male rotor 16 by curve F2-F3 as contact advances from F2 to F3 while both of rotors 14 and 16 are rotating at the same pitch circle velocity.
The curve F3-F4 is a circular arc on female rotor 14 and its length or angular range is adjusted such that the male portion it generates, M2-M3, falls inside the pitch circle, PM, of male rotor 16. The center of curve F3-F4 is positioned such that curve F3-F4 both intersects curve F2-F3 and is tangent to curve F2-F3 at the point of intersection. Curve F3-F4 influences the blow hole area, which is a leakage area defined by the cusp between bores 12-1 and 12-2 and rotors 14 and 16, and by minimizing the blow hole area, the leakage area, and therefore the leakage, is reduced which helps to improve the efficiency of screw machine 10. The radius of curve F3-F4 is adjusted to provide a desired balance be'.uecn minimum blow hole area and ease of manufacturing
Curve M2-M3 is generated by curve F3-F4 on the female rotor 14 and represents the clearance path swept out on male rotor 16 by curve F3-F4 as contact advances from F3 to F4 while both of rotors 14 and 16 are rotating at the same pitch circle velocity.
The curve F4-Fs on female rotor 14 is a circular arc extending from point F4 to its intersection with the tip circle TF (bore 12-1) at point F5. The radius and position of curve F4-F5 is adjusted so that curve F4-F5 is both coincident with and tangent to curve F3-F4 at the point of intersection, F4, and so that it is tangent to the tip circle TF (bore 12-1) at point F5.
Curve M3-M4 on the male rotor is generated by curve F4-F5 and represents the path swept out on male rotor 16 by curve F4-Fs as contact advances from M3 to M4 while both of rotors 14 and 16 are rotating at the same pitch circle velocity.
Curve F5-F5 is a circular arc extending along the tip circle TF (bore 12-1) of female rotor 14. Curve F,-F, generates curve M4 - M5 as contact advances from F5 to F5' while both of rotors 14 and 16 are rotating at the same pitch circle velocity. Since curve F5 - F5' is a circular arc on the tip circle TF (bore 12-1) of the female rotor 14 and is thus centered on the female rotor center A, the resulting curve M4 - M5 is also a circular arc which is centered on the male rotor center B and which is the root circle RMR of male rotor 16. These qualities of M4 - M5 make it particularly suited for easy generation and inspection and provides better control of the male root for manufacturability.
Points F5" and Ms correspond to points F5 and M5, respectively, located on an adjacent rotor lobe face and will be used as starting points for describing the other portions of the profiles of rotors 14 and 16. Straight line, or curve of infinite radius, F5"-F6 extends from F5" on the tip of female rotor 14 at an angle, A,, with respect to a tangent at female tip circle TF (bore 12-1) at Fs. Line F5-F6 extends to a point short of the female pitch circle P,. The angle A, is the female rotor departure angle and it provides the benefit of reducing viscous drag.
Curve M5-M6 on male rotor 16 is generated by line F5"-F& and represents the path swept out on male rotor 16 by line F5 -F6 as contact advances from M5 to M6 while both of rotors 14 and 16 are rotating at the same pitch circle velocity.
Curve F6-F7 is a circular arc on female rotor 14. Line F5"-F6 and curve Fs-F7 coact to: (1) control the thickness, t, of the lobes of female rotor 14 as measured along the pitch circle, PF, and which is controlled to maintain stiffness of the female lobe tip 14-1 to reduce deflection during machining; (2) to provide sufficient room at the base 16-2 of the male lobe so that a large, strong cutting tool may be used to improve the accuracy and speed of machining; and (3) to make the leak path more tortuous.
Curve M6-M7 on male rotor 16 is generated by curve F6-F7 and represents the path swept out on male rotor 16 by curve F6-F7 as contact advances from M6 to M7 while both of rotors 14 and 16 are rotating at the same pitch circle velocity.
Curve M7-M8 on male rotor 16 is an involute of a circle at the desired pressure angle. The male pitch circle, PM, and female pitch circle, PF, meet at a common point called the pitch point and have a common tangent at the pitch point. At any contact point between the male and female rotor profiles, or conjugate profiles, a common normal can be drawn between the contact point and the pitchpoint. The angle between this common normal at the contact point and the common tangent at the pitchpoint is called pressure angle.
Curve F7-F8 on female rotor 14 is also an involute of a circle at the desired pressure angle. For both rotors, the involute base circle is smaller than but proportional to the pitch circles P1 and PM of the female rotor 14 and the male rotor 16, respectively. Thus the two involutes are inherently conjugate and one surface need not be generated by the other Points F- and F8 are not on the same side of pitch circle, Pf, but one of the points can be located on the pitch circle. The transmission of torque between the driving and driven rotors occurs at, or near, the pitch circle with some sliding but
primarily with rolling contact between the rotors. Point F7 has been illustrated as located on pitch circle Pr.
Curve M,-M, is a circular arc on the tip circle TM (bore 12-2) of male rotor 16. Curve F9-F1 on female rotor 14 is generated by curve M9-M1 and represents the path swept out on female rotor 14 by curve M9-M1 as line contact advances from F, to F, while both rotors 14 and 16 arc rotating at the same pitch circle velocity. Since curve M9-M1 is a circular arc on the tip circle TM (bore 12-2) of male rotor 16 and is thus centered on the male rotor center B, the resulting curve F9-F1 is also a circular arc which is centered on the female rotor center A and which is the root circle RFR of the female rotor 14. These qualities of curve F, - F, make it particularly suited for easy generation and inspection which provides better control of the female root for manufacturability.
The curve M8-M9 on male rotor 16 is a curve of variable length and radius which bridges the gap between points M8 and M9 while approaching point M9 at departure angle A2 with respect to a tangent at tip circle TM (bore 12-2) of male rotor 16. Curve M8-M9 may be a generalized involute or made up of two or more curves such as arcs of circles with different radii. Curve F8-F9 on female rotor 14 is generated by curve M8-M9, and represents the path swept out on female rotor 14 by curve M8-M9 as line contact advances from F8 to F9, while both of rotors 14 and 16 are rotating at the same pitch circle velocity.
Alternatively, the curve F8-F9 on female rotor 14 may be a curve of variable length and radius which bridges the gap between points F8 and F, while approaching point F9 at an angle which will control departure angle A, with respect to a tangent at tip circle TM (bore 12-2) of male rotor 16 at point M9. Curve FK-F., may be a generalized involute or made up of two or more curves such as arcs of circles with different radii. Curve M8-M9 on male rotor 16 is generated by alternative curve F8-F9 and represents
the path swept out on male rotor 16 by alternative curve F8-F9 as line contact advances from M8 to M, while both rotors 14 and 16 are rotating at the same pitch velocity.
The curves F5"-F6, M5-M6. F6-F7, M5-M7, M8-M9, and F8-F9 coact to provide control of the pressure angle independently of other profile variables such as female and male departure angles A, and A-,, respectively, and the female lobe thickness, t, among others.
Referring now to Figure 4, points W and X would correspond to points F5 and F5' of female rotor 14 and points M1 and M9 of male rotor 16, respectively. The departure angle A, for female rotor 14 and A, for male rotor 16 is located between a tangent to curve W-X at point X and the departure segment S which is the portion of rotor 14 or 16 starting at point X and corresponding to line F5 -F6 on female rotor 14 and curve M8-M9 on male rotor 16. It will be noted that departure segment S moves rapidly away from the bore which will be 12-1 for rotor 14 and 12-2 for rotor 16. Accordingly, since oil film 100 is dependent upon a close distance between adjacent parts, its length is reduced and restricted essentially to the region of small clearance which essentially corresponds to the surface defined between W and X and a little past X. The reduced length of oil film 100 results in a reduced viscous shear stress area and thus reduced overall drag.
Referring now to Figure 5, points Y and Z correspond to points W and X in Figure 4. Departure segment S has a PRIOR ART configuration and starts essentially tangent to, and for considerable distance remains close to, the rotor bore 12-1, 12-2. The oil film 100 which develops is much longer than oil film 100 and results in a greater viscous drag as the rotor tip moves relative to the bore as compared to the configuration of Figure 4.
As noted above, the present invention permits control of the pressure angle independently of other profile variables such as female and male departure angles A,
and A,, respectively, and the female lobe thickness, t, among others. Accordingly, the rotor profiles described above may be modified in order to achieve a desired design feature.
Segment F5-F6 of Figure 2 is described above as a straight line or a curve of infinite radius. In reality, taking manufacturing tolerances and the length of F5"-F6 into account, there would be no practical difference if F5-F6 is a straight line or a curved segment where the radius is very large, and there would be no perceived difference in the drawings in the absence of distortion at a very greatly magnified scale. Segment F5 -F6 becomes a point where there is tangency with the tip circle at F5" and where A, becomes 0c.
Referring now to Figure 6, straight or very large radius segment F5"-F6 has been replaced by large radius segment F5-F6, which is tangent to female rotor tip circle TF (bore 12-1) at F5. Curved segment F6-1-F7 is of a smaller radius than curved segment F5 -F6.,. The advantage of this embodiment is that A1, the female rotor departure angle is made 0' while still allowing for independent control of the pressure angle and the female lobe thickness, t. Segments F5 -F6-1 and F6-1-F7 will generate modified segments corresponding to M5 -M6 and M6-M7, respectively, on male rotor 16 as described with respect to Figures 1-3.
Figure 7 illustrates a second modified female rotor profile. Specifically, points F5 and F7 are connected through three curved segments, rather than two segments. Segment F5 -F6-2, is a small radius portion intersecting the female rotor tip circle TF (bore 12-1). Segment F6-2-F6-3 is a large radius segment and segment F6-3-F7 is a small radius segment. The angle A, is the female rotor departure angle and is measured between a tangent to point F,,_, and the female rotor tip circle T8 (bore 12-1). Segments F5 -F6-2 F6-2-F6-3and F6-3-F7 will generate modified segments corresponding to the portion between M5 and M7 on male rotor 16. The advantage of the embodiment of Figure 7 is the elimination of the sharp corner at F5 which otherwise
might be difficult to produce with certain manufacturing processes such as finish milling or grinding of the lobes and tip diameter in a single operation.
Figure 8 illustrates a third modified female rotor profile. Specifically, points F5 and F7 are connected through three curved segments. Segment F5 -F6-4 is a large radius portion intersecting the female rotor tip circle TF (bore 12-1). Segment F6-4-F6-5 is a curved segment having a smaller radius than segment F5 -F6-4 Segment F6-5 -F7 is a curved segment having a smaller radius than segment F6-4-F6-5. Segments F5 -F6-4, F6-4-F6-5 and F6-5-F7 will generate modified segments corresponding to the portion between M5 and M7 on male rotor 16. The advantage of the embodiment of Figure 8 is the increased flexibility in the independent selection of female lobe thickness, pressure angle and the radius of segments F6-4-F6-5 and F6-5 - F7 which replace segment F6-F7 in the Figure 2 embodiment and which may be restricted in certain desired ranges based on manufacturing requirements.
Figure 9 illustrates a fourth modified female rotor profile. Specifically, points Fs and F7 are connected through a single varying radius curve, such as an involute, which reduces in radius in going from point F5" to point F7. Segment F5"-F7 will generate a modified segment corresponding to the portion between M5 and M7 on male rotor 16. The advantage of the embodiment of Figure 9 is the extension of the width of the contact band where a constant pressure angle is maintained.
Other variations are the cases where either curve Mg-M9 or curve F8-F9 is made up of two or more curses, one of said curves may be located on a portion of curve M8-M9 and another of said curves may be located on curve F8-F9 both of said curves being located so as not to be conjugate with each other.
Figure 10 illustrates a fifth modified female rotor profile. Specifically, points Fs and F9 are connected through two curves. The two curves are F8 - F9 and F8 - F9 which are each arcs of circles. Segments F8 - F9 and F8 - F9 will coact to generate a modified
segment corresponding to segment M8 - M9 on male rotor 16. The advantage of the embodiment of Figure 10 is an alternate method of generating curves F8-F9and M8-M9 of Figures 2 and 3. respectively, by substituting simplified arcs of circles on the female rotor in place of the more complex generalized involute.
Figure 11 illustrates a sixth modified female rotor profile. Specifically, points F8 and F9 are connected through two curves. The two curves are F8 - F8" which is a curve of continuously varying radius, such as an involute, and F8" - F9 which is an arc of a circle. Segments F8-F9. and F8-F9, coact to generate a modified segment M8-M9 on male rotor 16. The advantage of the embodiment of Figure 11 is an alternate method of generating curves F8-F9,and M8-M9 of Figures 2 and 3 by substituting a simplified arc of a circle and a lower order involute on the female rotor in place of the more complex generalized involute.
Figure 12 illustrates a first modified male rotor profile. Specifically, points M8 and M9 are connected through two curves. Curves M8-M9 and M8-M9 are each arcs of circles tangent at their common point M8. The advantage of the embodiment of Figure 12 is an alternate method of generating curves F8-F9 and M8-M9 of Figures 2 and 3 by substituting simplified arcs of circles on the male rotor in place of the more complex generalized involute.
Figure 13 illustrates a second modified male rotor profile. Specifically, points M8 and M9 are connected through two curves. Curve M8 and M9 is an arc of a circle and curve M8-M9 is a curve of continuously varying radius such as an involute. The two curves are tangent at their common point M8". The advantage of the embodiment of Figure 13 is an alternate method of generating curves F8-F9 and M8-M9 of Figures 2 and 3 by substituting a simplified arc of a circle and a lower order of involute on the male rotor in place of the more complex generalized involute.
Figures 14 and 15 depict conjugate segments on a female and male rotor, respectively. The Figure 14 modification differs from the Figure 2 embodiment in that points F7 and F, are connected through a single curve of continuously varying radius, such as a generalized involute. Similarly, the Figure 15 modification differs from the Figure 3 embodiment in that points M7 and M9 are connected through a single curve of continuously varying radius, such as a generalized involute. The advantage of the embodiments of Figures 14 and 15 is the elimination of the transition at the points F8 and M8 and the associated sudden change in radius of curvature which in some cases might otherwise add complexity to the design.



We claim:
1. A conjugate pair of intermeshing rotor (14,16) having helical lobes
comprising helical crests (14-1, 16-1) and intervening grooves (14-2,16-2)
for rotation about parallel axes (A,B) within a working space of a screw
rotor machine, each rotor has a tip circle (TF,TM), a pitch circle
(PF,PM), and a root circle (RFR,RMR), one rotor of each pair being a
female rotor (14) so that die major portion of each lobe of said female
rotor is located inside said pitch circle of said female rotor, the other
rotor being a male rotor (16) formed such that the major portion of each lobe of said male rotor is located outside said pitch circle of said male rotor, the lands of one rotor following the grooves of the other rotor to form a continuous sealing line between said pair of rotors, said lobes on said female rotor comprising at least eight segments, said lobes on said male rotor comprising at least eight segments, said lobes on said male rotor comprising at least eight segments which are conjugate to said
female rotor segments, respectively, said female rotor segments starting
at a first point coincident with a point on the female root circle and said
conjugate male rotor segments starting at a corresponding first point
coincident with a point on the male tip circle, said segments being
characterized by:
a first segment on said male rotor comprising solely said first point
only on said tip circle of said male rotor, and a first segment on said
female rotor extending from said first female point on said female
root circle to a second point radially inward of said female pitch circle and which is generated by said first point on male rotor when both of said rotors are rotated at the same pitch velocity; (POINT Ml ON MALE AND SEGMENT F1-F2 ON FEMALE) a second segment on said female rotor comprising a circular are extending from the said second female rotor point and extending to a third point located radially outward at least to said pitch circle of said female rotor, and a second segment on said male rotor extending between said first male rotor point and a second male rotor point and which is generated by said second female segment when both of said rotors are rotated at the same pitch velocity; (SEGMENT F2-F3 ON FEMALE AND SEGMENT M1-M2 ON MALE) a third segment on said female rotor comprising a circular are extending from said third female rotor point and extending to a fourth point located between said female rotor tip circle and said female rotor pitch circle and a third segment on said male rotor extending from said second male rotor point to a third male rotor
point and which is generated by said third female segment when both of said rotors are rotated at the same pitch circle velocity; (SEGMENT M2-M3 ON MALE AND SEGMENT F3-F4 ON FEMALE)
a fourth segment on said female rotor comprising a circular are extending from said fourth female rotor point and extending to a fifth female rotor point which is coincident with a point on said female tip circle, and a fourth segment on said male rotor extending from said third male rotor point to a fourth male rotor point which is coincident with a point on said male root circle, and said fourth male rotor segment which is generated by said fourth female segment when both of said rotors are rotated at the same pitch circle velocity; (SEGMENT F4-F5 ON FEMALE AND SEGMENT M3-M4 ON MALE)
a fifth segment on said female rotor comprising a circular are coincident with said female rotor tip circle and extending from said fifth female rotor point to a sixth female rotor point, and a fifth segment on said male rotor extending from said fourth male rotor point to a fifth male rotor point and which is generated by said fifth female segment when both of said rotors are rotated at the same pitch circle velocity; (SEGMENT F5-F5 ' ON FEMALE AND SEGMENT M4-M5 ON MALE)
a sixth segment on said female rotor which extends from said sixth female rotor point on said tip circle of said female rotor to a seventh female rotor point located on or radially outward of said female rotor pitch circle comprising a curve of generally large radius in the outward end nearer said female rotor tip circle and having a generally smaller radius in the inward end nearer said female rotor pitch circle, and a sixth segment on said male rotor extending from said fifth male rotor point to a sixth male rotor point and which is generated by said sixth female segment when both of said rotors are rotated at the same pitch circle velocity; (SEGMENT F5"-F7 ON FEMALE AND SEGMENT M5'-M7 ON MALE7)
a seventh segment on said male rotor which extends from said sixth male rotor point to an seventh male rotor point which is coincident with a point on said tip circle of said male rotor and said seventh male rotor segment comprising a curve characterized by having a varying radius, and a seventh segment on said female rotor which extends from said seventh female rotor point to an eighth female rotor point which is coincident with a point on said female root circle and at least a portion of said eighth female rotor segment being
generated by at least a portion of said seventh male rotor segment when both of said rotors are rotated at the same pitch circle velocity; (SEGMENT M7-M9 ON MALE AND SEGMENT F7-F9 ON FEMALE)
an eighth segment on said male rotor comprising a circular are coincident with said male tip circle and extending from said seventh male rotor point to an eight male rotor point which is coincident with said first male rotor point for the subsequent male lobe, and an eighth segment on said female rotor extending from said eight female rotor point to a ninth female rotor point which is coincident with said first female rotor point for a subsequent female lobe, said eighth female rotor segment being generated by said eighth male rotor segment when both of said rotors are rotated at the same pitch circle velocity. (SEGMENT M9-M1 ON MALE AND SEGMENT F9-F1 ON FEMALE)
2. The rotors as claimed in claim 1 wherein said seventh male rotor segment contains two or more different arcs of circles.
3. A conjugate pair of intermeshing rotors substantially as herein described with reference to and as illustrated by the accompanying drawings.

Documents:

1139-del-2004-abstract.pdf

1139-del-2004-claims.pdf

1139-del-2004-complete specification(granted).pdf

1139-del-2004-correspondence-others.pdf

1139-del-2004-correspondence-po.pdf

1139-del-2004-description (complete).pdf

1139-del-2004-drawings.pdf

1139-del-2004-form-1.pdf

1139-del-2004-form-19.pdf

1139-del-2004-form-2.pdf

1139-del-2004-form-3.pdf

1139-del-2004-gpa.pdf

1139-del-2004-petition -137.pdf


Patent Number 244207
Indian Patent Application Number 1139/DEL/2004
PG Journal Number 48/2010
Publication Date 26-Nov-2010
Grant Date 23-Nov-2010
Date of Filing 16-Jun-2004
Name of Patentee CARRIER CORPORATION
Applicant Address CARRIER PARKWAY, P.O BOX 4800, SYRACUSE, NEW YORK 13221, U.S.A.
Inventors:
# Inventor's Name Inventor's Address
1 KESHAVA BASAVAPATNA KUMAR 161 NATSISKY FARM ROAD, SOUTH WINDSOR, CONNECTICUT 06074, U.S.A.
2 JAMES WILLIAM BUSH 11 ACADEMY STREET, SKANEATELES, NEW YORK 13152-1201, USA.
PCT International Classification Number F01C 1/08
PCT International Application Number N/A
PCT International Filing date
PCT Conventions:
# PCT Application Number Date of Convention Priority Country
1 09/087,576 1998-05-29 U.S.A.