Title:
MULTIPLE LEAD SCREW COMPRESSOR
United States Patent 3807911


Abstract:
A rotor structure is disclosed for a fluid compressor of the character having a pair of complementary, intermeshing rotatable rotors for transferring and compressing a fluid from an inlet into the compressor to an outlet from the compressor. The rotor includes helical land and intervening helical groove means for intermeshing with complementary helical land and groove means of a complementary rotor. The helical land and groove means includes a first portion having a first constant helix angle and a second portion having a second constant helix angle which is different from the first helix angle. The two helical portions are disposed on shaft means and meet in a transition area intermediate the opposite ends of the shaft means and in which area the lands and grooves are disposed in mating relationship. One of the helical portions is integral with the shaft means, and the other helical portion is defined by a separate component adapted to be mounted on the shaft means and suitably interconnected with the one helical portion.



Inventors:
CAFFREY T
Application Number:
05/359665
Publication Date:
04/30/1974
Filing Date:
05/14/1973
Assignee:
DAVEY COMPRESSOR CO,US
Primary Class:
Other Classes:
418/201.1
International Classes:
F04C18/08; (IPC1-7): F01C1/16; F04C1/10; F04C17/12
Field of Search:
418/9,197,201,202,203
View Patent Images:
US Patent References:
3424373VARIABLE LEAD COMPRESSOR1969-01-28Gardner
2975963Rotor device1961-03-21Nilsson
2804260Engines of screw rotor type1957-08-27Nilsson et al.
2691482Method and apparatus for compressing and expanding gases1954-10-12Ungar
2652192Compound-lead screw compressor or fluid motor1953-09-15Chilton
2586842Drilling apparatus1952-02-26McCallum
2369539Displacement apparatus1945-02-13Delamere
1597411Rotary pump1926-08-24Kinney



Foreign References:
GB210088A1925-05-21
Primary Examiner:
Croyle, Carlton R.
Assistant Examiner:
Vrablik, John J.
Attorney, Agent or Firm:
Meyer, Tilberry & Body
Parent Case Data:


This is a continuation, of application Ser. No. 168,023 filed Aug. 2, 1971.
Claims:
I claim

1. In a rotary fluid compressor of the character comprising a housing having laterally communicating cylindrical chambers in which a pair of intermeshing male and female rotors are disposed for progressively compressing fluid between an inlet port at one end of said chambers and an outlet port at the other end of said chambers, said rotors having corresponding inlet and outlet ends with respect to said inlet and outlet ports, said male rotor having arcuately convex helical lands and said female rotor having complementary arcuately concave helical grooves, said lands and grooves being cooperable in response to rotation of said male and female rotors to progressively and continuously compress fluid between said inlet and outlet ports within a total wrap angle of the lands and grooves less than 360°, and wherein the discharge port opens into said chambers peripherally of and laterally therebetween at the discharge ends of the rotors and the lead of said lands and grooves adjacent said outlet port is less than the lead of said lands and grooves adjacent said inlet port, the improvement comprising: said male and female rotors each including structurally separate first and second portions having helical lands and grooves, said first portions extending along said rotors from said inlet ends of the rotors to a transition plane intermediate said inlet and outlet ends and transverse to the axes of said rotors, said second portions extending along said rotors from said transition plane to said outlet ends, the lands and grooves in said first portions having a constant lead, and the lands and grooves in said second portions having a constant lead which is less than the constant lead of said first portions, and means interconnecting said first and second portions of said rotors for the lands and grooves thereof to engage in mating relationship at said transition plane, said rotors including shaft means, one of said first and second portions being integral with said shaft means and the other of said first and second portions being apertured to receive said shaft means, the ends of said first and second portions at said transition plane having pairs of axially aligned recesses therein, at least one of the recesses of the pair in said other portion extending completely through said other portion, and the recess in said one portion aligned therewith being internally threaded, said interconnecting means including a pin in the other of the aligned recesses in said one and other portions and a threaded fastener extending through said one recess into threaded engagement with said threaded recess.

2. The improvement according to claim 1, wherein the ratio of the leads of said first portions to the leads of said second portions is approximately 3 to 1.

3. The improvement according to claim 1, wherein the wrap angle of each of said first and said second portions is approximately 135°.

4. In a rotary fluid compressor of the character comprising a housing having laterally communicating cylindrical chambers in which a pair of intermeshing male and female rotors are disposed for progressively compressing fluid between an inlet port at one end of said chambers and an outlet port at the other end of said chambers, said rotors having corresponding inlet and outlet ends with respect to said inlet and outlet ports, said male rotor having arcuately convex helical lands and said female rotor having complementary arcuately concave helical grooves, said lands and grooves being cooperable in response to rotation of said male and female rotors to progressively and continuously compress fluid between said inlet and outlet ports within a total wrap angle of the lands and grooves less than 360°, and wherein the discharge port opens into said chambers peripherally of and laterally therebetween at the discharge ends of the rotors and the lead of said lands and grooves adjacent said outlet port is less than the lead of said lands and grooves adjacent said inlet port, the improvement comprising: said male and female rotors each including structurally separate first and second portions having helical lands and grooves, said first portions extending along said rotors from said inlet ends of the rotors to a transition plane intermediate said inlet and outlet ends and transverse to the axes of said rotors, said second portions extending along said rotors from said transition plane to said outlet ends, the lands and grooves in said first portions having a constant lead, and the lands and grooves in said second portions having a constant lead which is less than the constant lead of said first portions, and means interconnecting said first and second portions of said rotors for the lands and grooves thereof to engage in mating relationship at said transition plane, said rotors including shaft means, said first portions being integral with said shaft means and said second portions being apertured to receive said shaft means, the ends of said first and second portions at said transition plane having pairs of axially aligned recesses therein, at least one of the recesses of the pair in said second portion extending completely through said second portion, and the recess in said first portion aligned therewith being internally threaded, said interconnecting means including a pin in the other of the aligned recesses in said first and second portions and a threaded fastener extending through said one recess into threaded engagement with said threaded recess.

5. The improvement according to claim 4, wherein the lead of said first portion is approximately three times the lead of said second portion and the wrap angle of each said portions is approximately 135°.

Description:
This invention relates to the art of helical screw-type compressors and, more particularly, to helical screw or rotor components for such compressors.

Rotary screw-type compressors have been provided heretofore and generally include a pair of intermeshing, complementary rotors positioned within a compressor housing, and means for rotating the intermeshed rotors relative to one another. The compressor housing includes an inlet opening into which fluid such as air, flows and an outlet opening through which compressed fluid flows as a result of rotation of the intermeshing rotors which operate to transfer and compress the fluid from the inlet to the outlet of the compressor. Compressors of this type are employed for compressing gases which, during transfer and compression, move axially along the rotors. Such rotary screw compressors may be operated dry or wet. In wet operated compressors, liquid is introduced into the compression chamber to effect a seal between the rotors. Dry compressors, on the other hand, rely upon extremely close tolerances between intermeshing lands and grooves of the rotors to effect a seal therebetween. The introduction of liquids into the compression chamber of a screw compressor, of course, provides for additional sealing between the rotor components and serves further to dissipate the heat of compression. The compression ratio which can be realistically achieved under dry operation is about 3:1 or 4:1 whereas a wet operated compressor may have a compression ratio of up to 8:1 or 9:1.

Prior art screw compressors of the above character have generally been constructed with constant lead helical lands and intervening grooves on the complementary intermeshing rotors. Such construction limits the efficiency and performance of the compressors, especially at higher compression ratios. In this respect, the discharge velocity from a screw compressor having constant lead rotors is undesirably high if the discharge ports are correctly sized. When the outlet port is enlarged in an effort to lower the velocity, back flow occurs which requires additional work to be done by the compressor. Efforts have been made in the past to provide rotary screw-type compressors with rotors having lands and grooves which continuously vary in lead from one end of the rotor to the other. While such rotor components may provide for increasing the discharge area of a compressor to relieve backflow and the resultant overworking of the compressor, it remains that a continuously variable lead rotor is both extremely difficult and expensive to manufacture.

Backflow advantageously is relieved in accordance with the present invention by employing rotors or screws having helical lands and intervening grooves which have a different helix angle or lead at the intake end of the rotor from the lead thereof at the discharge end. By this arrangement, it is possible to provide a discharge port for a screw compressor which is approximately 2.25 times the size of the discharge port of a compressor of comparable size employing rotors having a constant lead. Moreover, such a rotor is structurally simple and reasonably inexpensive to produce relative to a continuously varying lead rotor.

Accordingly, it is an outstanding object of the present invention to provide a rotor component for screw-type fluid compressors which provides for increasing the efficiency of a constant lead screw compressor of a given size by permitting enlargement of the discharge port thereof to achieve a reduction in discharge velocity without backflow and resultant additional work by the compressor.

A further object of the present invention is the provision of a rotor component of the above character which includes helical lands and intervening grooves in portions having different leads and in each of which portions the lead is constant along the length thereof.

Yet another object of the present invention is the provision of a rotor component of the above character which is reasonably simple and inexpensive to manufacture.

Still another object of the present invention is the provision of a screw compressor rotor of the above character wherein the two helical portions are defined by separate components, each having helical lands and intervening grooves and wherein the lead of each portion is constant along its length, thus facilitating the manufacture thereof.

Still another object of the present invention is the provision of a rotor of the above character wherein the separate portions are adapted to be readily interconnected to define a rotor component having helical lands and intervening grooves in portions having different leads, and which portions are interconnected in a manner whereby they meet in a transition area in which the lands and grooves of the two portions are disposed in mating relationship.

The foregoing objects will in part be obvious and in part more fully pointed out hereinafter in conjunction with the following description of the drawing of a preferred embodiment and in which:

FIG. 1 is a plan view, partially in section, illustrating a rotary screw-type compressor having a pair of rotor components made in accordance with the present invention;

FIG. 2 is a sectional elevation of the compressor of FIG. 1, the section being taken along line 2--2 in FIG. 1;

FIG. 3 is a plan view of a male rotor made in accordance with the present invention;

FIG. 4 is a plan view of a female rotor made in accordance with the present invention;

FIG. 5 is a view in cross-section of the rotor illustrated in FIG. 3, the section being taken along line 5--5 in FIG. 3; and

FIG. 6 is a schematic projection of complementary male and female rotors made in accordance with the present invention.

Referring now to the drawings in greater detail wherein the showings are for the purpose of illustrating preferred embodiments of the invention only and not for limiting the same, a rotary screw-type compressor assembly 10 is illustrated in FIGS. 1 and 2 which is comprised of a housing 12 having an inlet port 14 at one end thereof and an outlet port 16 at the other end thereof. Housing 12 includes cylindrical chambers 18 and 20 in which male and female rotor components 22 and 24, respectively, are disposed. Male rotor 22 is provided with shaft means including shaft portions 26 and 28 at opposite ends thereof. Similarly, female rotor 24 is provided with shaft means including shaft portions 30 and 32 at opposite ends thereof. The shaft means of rotors 22 and 24 are suitably associated with housing 12 in a manner to support the rotors for rotation within the housing in intermeshing relationship. One of the shaft portions such as shaft portion 28, for example, projects outwardly of housing 12 for suitable interconnection thereof with suitable drive means which is not illustrated. The intermeshing relationship between rotors 22 and 24 provides for rotor 24 to be rotated in response to rotation of rotor 22 through shaft portion 28. It will be understood, however, that shaft portion 32 could be extended exteriorly of housing 12 and that shaft portions 28 and 32 could be suitably interconnected such as by gear means to achieve rotation of rotor 24.

Male rotor 22, as best illustrated in FIGS. 2 and 3, includes helical land means 34 and intervening helical groove means 36. The helical land means of the male rotor are in the form of lobes having convex outer side surfaces 40. In accordance with the present invention, the helical land means and intervening groove means of the male rotor is defined by two portions designated A and B which meet in transition area designated by line E.

Portion A extends from the inlet end of the compressor toward transition area E, and portion B extends from transition area E toward the outlet end of the compressor. The helical land and groove means of portions A and B each have a constant lead throughout the length thereof and, as is best illustrated in FIG. 3, the lead of portion A is greater than the lead of portion B. Preferably, the lead ratio of portion A to portion B is approximately 3:1. It will be appreciated, however, that the lead ratio can be of any value greater or lesser than 3:1 and is limited only by manufacturing or strength considerations. The inner ends of portions A and B are interrelated in transition area E in a manner whereby the helical land and groove means of portions A and B are disposed in mating relationship. Thus, continuous but angularly related helical land and groove means are provided which extend along the length of the rotor component.

In conjuction with the lead ratio of the helical land and groove means of portions A and B, it is desirable to maintain the total wrap angle thereof at less than 360°. More particularly, it is preferred that the total wrap angle be approximately 270°. The total wrap angle, of course, is the angle circumscribed by the helical land and intervening groove means of both portions between the longitudinally opposite ends thereof. Similarly, portion A has a wrap angle which is defined by the angle circumscribed by the helical land and groove means thereof in extending from the ends thereof adjacent shaft portion 28 to transition area E, and portion B has a wrap angle which is defined by the angle circumscribed by the helical land and groove means thereof in extending from transition area E to the ends thereof adjacent shaft portion 26. In the preferred embodiment herein illustrated, portions A and B have a lead ratio of 3:1, as mentioned above, and the wrap angle of the helical land and groove means of each portion is approximately 135°.

The structure of female rotor 24 is, of course, complementary to that of male rotor 22. In this respect, with reference to FIGS. 2 and 4 of the drawing, the female rotor includes helical land means 42 and intervening helical groove means 44. Helical land means 42 are complementary to helical groove means 36 of the male rotor and, accordingly, helical land means 42 include concave outer side surfaces 46. Similarly, helical groove means 44 are complementary to helical land means 34 of male rotor 22. Thus, rotors 22 and 24 are adapted to be disposed in side by side intermeshing relationship.

The helical land and groove means of female rotor 24 include portions C and D corresponding respectively to portions A and B of male rotor 22. Portions C and D of the helical land and groove means are interrelated in a transition area therebetween denoted by line F. The transition areas of rotors 22 and 24, of course, coincide in location relative to the opposite ends of the rotors. Since the helical land and groove means of the male and female rotors are complementary, it will be appreciated, that the helical land and groove means of portion C have a lead corresponding to that of portion A of male rotor 22, and that the helical land and groove means of portion D have a lead corresponding to the lead of portion B of male rotor 22. Further, it will be appreciated that the lead ratio of portion C to portion D, the wrap angles of each portion and the total wrap angle will correspond with that of the male rotor, or vice versa.

The rotor members may be formed or produced in any suitable manner and preferably, are constructed in the manner illustrated in FIG. 5. In this respect, a male rotor 50 is illustrated which includes shaft means 52 carrying helical land and intervening helical groove means 54 defined by helical land and groove means portions 56 and 58. Portion 56 is integral with shaft means 52, and portion 58 is defined by a separate component suitably interconnected with portion 56. In the particular embodiment illustrated, portion 58 is an annular component having helical land and groove means in the outer surface thereof and having a cylindrical aperture 60 therethrough which is adapted to receive a cylindrical portion 62 of shaft means 52 which projects from the corresponding end of land and groove portion 56. Portion 58 is interconnected with portion 56 by bolt means 64, or the like, which extends through aperture 65 in portion 58 and has a threaded inner end disposed in a cooperatively threaded recess 66 in portion 56. Further, means is provided to assure that portion 58 is oriented relative to portion 56 so that the helical land and groove means of the two portions are disposed in mating relationship in the transition area therebetween defined by a line of juncture G. In this respect, portions 56 and 58 may be provided with a recess 68 and aperture 70, respectively, adapted to be aligned to receive a suitable dowel pin 72. It will be appreciated, of course, that recess 68 and aperture 70 are provided in the corresponding portions 56 and 58 so as to assure proper alignment of the lands and grooves of the two portions upon insertion of dowel 72 thereinto. After proper positioning is thus assured, aperture 65 and recess 66 can be provided in the corresponding portions 58 and 56, and bolt means 64 inserted thereinto to complete the assembly.

A rotor constructed as illustrated in FIG. 5 is very economical to produce in that the shaft means and portion 56 of the helical land and groove means of the rotor can be turned or otherwise produced as an integral unit, while portion 58 having helical land and groove means of a different lead which is constant along its entire length can readily be turned or otherwise produced as a separate element or component. Thereafter, it is only necessary to position portion 58 on the shaft means and against portion 56, orient the two portions for the land and groove means thereof to mate, fix the positions thereof by means of the dowel pin and interconnect the two portions by bolt means 64.

While the foregoing rotor structure has been described in conjunction with a male rotor, it will be appreciated that the female rotor is produced in the same manner. Further, it will be appreciated that means other than a dowel pin can be employed to assure proper alignment of the helical lands and grooves of the two portions of the rotor. In this respect, for example, the projecting portion of the shaft and the opening in the separate component through which the shaft portion projects could be provided with aligned keyway means adapted to receive a key element which would properly orient the two rotor portions. Further, the projecting portion of the shaft could be provided with a flat and the opening through the separate component could be provided with a flat side interrupting the cylindrical contour thereof and which flat side would cooperate with the flat on the shaft to properly align the rotor portions. Still further, although the helical land and groove means of portion 56 of the rotor is illustrated as being integral with shaft means 52, portion 56 could also be a separate component from the shaft means suitably interconnected therewith. It is also contemplated that portions 56 and 58 could be separate portions each integral with a corresponding shaft portion. In this instance, the two rotor portions would be suitably interconnected with the helical land and groove means thereof in mating relationship and the shaft portions thereof would together define shaft means for the rotor unit.

In use, complementary male and female rotor elements are disposed in a compressor housing in intermeshing relationship with one another and with high lead portions A and C thereof toward the compressor inlet and low lead portions B and D thereof toward the compressor outlet. In a manner well known, fluid such as air enters the compressor inlet and is transferred therefrom to the compressor outlet by being captured in pockets or cells defined by the helical land and groove means of the rotating male and female rotors together with the chambers in which the rotors are disposed. During such transfer, the pockets in which the fluid is trapped gradually decrease in volume whereby the fluid is gradually compressed and is ultimately exhausted through the compressor outlet under high pressure and velocity.

The working relationship of male and female rotors made in accordance with the present invention is schematically illustrated in FIG. 6. In this respect, male rotor 22 has helical land and groove means portions A and B of different leads and in which the helical land and groove means of the two portions are disposed in mating relationship. The helical lands of the male rotor are numbered 1 through 4. Similarly, female rotor 24 has helical land and groove means portions C and D having different leads corresponding, respectively, to the leads of portions A and B of the male rotor. Further, the helical lands and grooves of portions C and D are disposed in mating relationship. The grooves of female rotor 24 are numbered 1 through 6. The space between lines 73 and 74 of male rotor 22 together with the space between lines 75 and 76 of female rotor 24 define the width of the compressor inlet. If the leads of the helical land and groove means of the rotors were constant throughout the lengths thereof the compressor outlet would have a width designated by lines 78. However, by providing the portions of the rotors adjacent the outlet of the compressor with helical land and groove means having a lead which is less than that of the portions adjacent the inlet end of the compressor, a compressor outlet of greater width or size as designated by lines 80, advantageously is provided for. The small outlet opening necessitated by the use of constant lead rotors produces an undesirably high output velocity from the compressor, and if the outlet is enlarged to decrease the velocity there is a resultant backflow which disadvantageously results in imposing additional work on the compressor and thus decreasing its efficiency. The low lead feature provided for the outlet ends of the male and female rotors in accordance with the present invention allows for the size of the discharge opening to be increased to reduce the output velocity of the compressor without the resultant backflow and loss of efficiency.

While considerable emphasis has been placed herein on the structure of the rotors being such that the male rotor has four helical lands and intervening grooves and the female rotor has six helical lands and intervening grooves, it will be appreciated that other well known rotor configurations and ratios may be employed.

As many possible embodiments of the present invention may be made and as many possible changes may be made in the embodiment herein set forth, it is to be distinctly understood that the foregoing description of the preferred embodiment is to be interpreted merely as illustrative of the present invention and not as a limitation.