US3283996A - Screw rotor machine for elastic working fluid - Google Patents

Screw rotor machine for elastic working fluid Download PDF

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Publication number
US3283996A
US3283996A US394985A US39498564A US3283996A US 3283996 A US3283996 A US 3283996A US 394985 A US394985 A US 394985A US 39498564 A US39498564 A US 39498564A US 3283996 A US3283996 A US 3283996A
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Prior art keywords
rotor
rotors
female
pitch circle
male
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Expired - Lifetime
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US394985A
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English (en)
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Schibbye Lauritz Benedictus
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Svenska Rotor Maskiner AB
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Svenska Rotor Maskiner AB
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    • F—MECHANICAL ENGINEERING; LIGHTING; HEATING; WEAPONS; BLASTING
    • F04—POSITIVE - DISPLACEMENT MACHINES FOR LIQUIDS; PUMPS FOR LIQUIDS OR ELASTIC FLUIDS
    • F04C—ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT MACHINES FOR LIQUIDS; ROTARY-PISTON, OR OSCILLATING-PISTON, POSITIVE-DISPLACEMENT PUMPS
    • F04C18/00—Rotary-piston pumps specially adapted for elastic fluids
    • F04C18/08—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing
    • F04C18/12—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type
    • F04C18/14—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type with toothed rotary pistons
    • F04C18/16—Rotary-piston pumps specially adapted for elastic fluids of intermeshing-engagement type, i.e. with engagement of co-operating members similar to that of toothed gearing of other than internal-axis type with toothed rotary pistons with helical teeth, e.g. chevron-shaped, screw type

Definitions

  • a screw rotor machine for elastic working fluid is a machine which primarily comprises at least two coplanar, cooperating rotors provided with helical lands with a wrap angle of less than 360 and intervening grooves, and a housing enclosing the rotors.
  • the rotors are of male and female type which means that the lands of the male rotors have at least their major portions outside the pitch circle of the rotor and have substantially conyex flanks, and that the lands of the female rotor have at least their major portions inside the pitch circle of the rotor and have substantially concave flanks.
  • the housing enclosing the rotors is further provided with a working space substantially composed of two coplanar intermeshing bores, each sealingly enclosing a rotor, and provided with spaced low pressure and high pressure ports, of which at least their major portions are located, respectively, on opposite sides of the plane of the axes of the bores.
  • the rotors cooperate in such a way that a land of one rotor meshes with a groove of the cooperating rotor on the same side of the plane of the axes of the bores as the high pressure port is located whereby a chevronshaped chamber is formed between the rotors and the walls of the working space comprising a portion of a male rotor groove and a portion of a female rotor groove communicating therewith.
  • Each such chamber has its base ends located in a stationary transverse plane common for all chevron-shaped chambers and located at the high pressure port and its tip at the intermesh between the rotor lands of the different rotors.
  • the built-in volume ratio can be varied.
  • the ratio between the pressures in the chevronshaped chambers at said moment, the built-in pressure ratio can also be varied.
  • the built-in pressure ratio is, however, in addition to the built-in volume ratio also dependent on the ratio between the specific heats at constant pressure and at constant volume, respectively, the K-value, of the used elastic working fluid. This K-value varies between different gases which means that the builtin pressure ratio is different in one and the same machine in dependence on the gas used as working fluid.
  • the pressure distribution in the groove is thus such that the pressure in certain portions thereof is higher than the pressure in the port while in other portions it is lower than that in the port.
  • the flow between the groove and the high pressure port will then at the por tions of the groove in which there is an excess pressure in relation to the high pressure port be in the direction from the groove to the port and at the portions of the groove in which there is a pressure lower than that in the high pressure port in the direction from the port to the groove.
  • These flows cause an ununiform pressure distribution in the port resulting in turbulence and noise.
  • the flow conditions change due to the pressure equalization in the groove taking place during the continued revolving of the rotors.
  • the changes in the driving torque caused in this way are so large that under certain circumstances they cause a change of direction of the. torque acting on the female rotor, the driving torque of which normally is only a fraction of the corresponding torque of the male rotor, which means that the continuous driving contact between the elements transmitting torque to the female rotor is broken and results in strong clearly noticeable vibrations of the female rotor.
  • these torque transmitting elements are a synchronizing gearing connecting the male and female rotors
  • these vibrations can produce within the female rotor and especially within its shaft portion carrying the, synchronizing gear secondary vibrations substantially of torsional type of such an amplitude that seizing between the rotors and corresponding wear-takes place.
  • complete breakdowns of the rotors have occurred with synchronized as well as with unsynchronized rotors.
  • the present invention has for its object to solve this oscillation problem which, as stated above, substantially emanates from the pressure variations in the high pressure port and the invention is based on the fact that it has been established by tests that no oscillations of the mentioned type occur at a certain distribution of the driving torque of the machine between two cooperating male and female rotors.
  • the rotors In the standard profile (embodying the symmetrical circular profile disclosed in U.S. Patent No. 2,622,787) hitherto used the rotors have the same outer diameters and the male rotor is provided with four lands and the female rotor with six lands.
  • Each female rotor groove consists, when viewed in a transverse plane, of an inner portion limited by the pitch circle of the rotor and a circular are having its centre on the pitch circle and a radius which is 18% of the outer diameter of the rotor, and of an outer portion limited by the circumscribing circle and the pitch circle of the rotor and by addenda to the rotor lands limiting the groove said addenda being located outside the pitch circle and having a radial extent corresponding to 14.3% of the length of the chord to the pitch circle lying within the land separating two adjacent grooves.
  • the flow through the blow holes results in that the pressure in all chevron shaped chambers is about equal to the pressure in the high pressure port of the machine which means a considerable decrease of the efficiency of the machine.
  • the increase of the power transmission to the female rotor means an increased risk of wear of the rotors especially in machineswithout synchronizing gears. Tests have shown that a completely circular addendum brings about such a decrease of the efiiciency that such addenda cannot be used in practice but in special types of machines where the characteristics obtained by combination effects balance the decrease of the efficiency.
  • a type of machine in which the circular addendum for this reason is used is a two stage tandem compressor where it is essential to bring about so large differences between the displacement volumes of the first and the second stage that a pressure distribution between the stages can be obtained which is most favourable as regards efficiency.
  • Such a machine is shown in U.S. Patent 2,975,963.
  • screw compressors For compression of gases where it is of importance that the gas must not be polluted by liquid, screw compressors are used which operate dry without injection of cooling liquid into the working space.
  • the practical upper limit of the built-in pressure ratio is about 5:1 owing to the thermal deformation of the rotors and the housing in spite of the most intense cooling possible of the rotors and the housing by a cooling fluid completely separated from the working fluid and passing through cooling channels.
  • Compressors for this purpose are normally owing to the desired condensing and evaporating temperature designed for a built-in pressure ratio of about 3:1 and usually for a built-in pressure ratio not exceeding 5 :1.
  • FIG. 1 shows a vertical section through a screw rotor compressor along the line 11 in FIG. 2.
  • FIG. 2 shows a cross section of the compressor shown in FIG. 1 along the line 22 in FIG. 1.
  • FIG. 3 shows another cross section of the compressor shown in FIG. 1 along the line 3-3 in FIG. 1.
  • FIG. 4 shows a horizontal section of the compressor shown in FIG. 1 with the rotors removed, the section being taken along the line 44 in FIG. 1.
  • FIG. 5 is a diagram showing the volume of a chamber when opening against the high pressure port plotted against the axial extent of the high pressure port.
  • FIG. 6 shows the cross section of a pair of cooperat' ing rotors mounted in the machine.
  • FIG. 6a shows on a larger scale the addendum of a female rotor land located outside the pitch circle of the rotor.
  • FIG. 6b shows on a larger scale the dedendum at the bottom of a male rotor groove located inside the pitch circle of the rotor.
  • FIG. 7 shows a vertical section through another screw compressor according to the invention.
  • FIG. 8 shows a vertical section through a third screw compressor according to the invention.
  • the screw compressor shown in FIGS. 1 to 4 comprises a casing 10, in which a working space 12 is provided in the shape of two intersecting cylindrical bores with parallel axes.
  • the casing is further provided with a low pressure channel 14 and a high pressure channel 16 for the working fluid which communicate with the working space 12 through the low pressure port 18 and the high pressure port 20, respectively.
  • the low pressure port 18 is located entirely in the low pressure end wall 22 of the working space 12 and substantially on one side of the plane containing the axes of the bores (FIG. 2).
  • the high pressure port is located partly in the high pressure end wall 24 and partly in the barrel wall 26 of the working space 12 and entirely on the side of the plane containing the axes of the bores opposite to the low pressure port (FIGS. 3 and 4).
  • two cooperating rotors In the working space 12 two cooperating rotors, one male rotor 28 and one female rotor 30, are located with their axes coaxial with the axes of the bores.
  • the rotors are journalled in the casing 10 but for the sake of simplicity the bearings carrying the rotors are omitted.
  • the rotors 28, 30 are further connected through a synchronizing gear 32 of the gear wheel type.
  • the male rotor 28 is provided with an external shaft 34 projecting from the casing 10.
  • the male rotor 28 is provided with four helical lands 36 with intervening grooves 38 which have a wrap angle of about 300.
  • the female rotor 30 is provided with six helical lands 40 with intervening grooves 42 which have a wrap angle of about 200.
  • the flanks of the male rotor lands 36 are composed of three main portions, viz.
  • the flanks of the female rotor lands 40 are correspondingly composed of two different portions, viz. an inner portion between the points 58 and 54 located inside the pitch circle 48 of the female rotor and circular around a centre located on the pitch circle 48 of the female rotor with a radius which is 18.7% of the outer diameter of the female rotor, and an outer portion between the points 54 and 60 located outside the pitch circle 48 of the female rot-or with a radial extent 62-60 the length of which is about 25.4% of the length of the chord to the pitch circle 48 of the female rotor lying Within a female rotor land 40 and the end points of which are the point 54 and an equally located point 64 on an adjacent female rotor land flank.
  • the inner portion 52-56 of the male rotor land flank is shaped in such a way that it continuously seals against the outer portion 54-60 of the female rotor land flank, when said portion passes into or out of the dedendum of the male rotor groove 38 lying inside the pitch circle 50 of the rotor.
  • the tips of the rotor lands are shaped in such a way that the male rotor land 36 is slightly cut away on both sides of its outermost portion 44 so that only a thin sealing edge is left, and the radially outermost portion 60 of the addendum of the female rotor land 40 is also shaped as a thin sealing edge, a corresponding groove being provided at the innermost portion 56 of the bottom of the male rotor groove 38.
  • the female rotor has lands with profiles consisting of circular portions lying inside the pitch circle of the rotor with addendum portions connecting the circular portions and lying outside the pitch circle of the rotor
  • the male rotor has grooves with profiles having circular portions lying outside the pitch circle of the rotor connected by dedendum portions at the bottoms of the grooves complementary in shape to the addendum portions of the female rotor lands.
  • the low pressure port 18 is so shaped that the rotor grooves communicating therewith are open over their whole length when the communication is broken so that the complete displacement volume of the machine is always utilized.
  • the high pressure port 20 which as said above comprises a portion located in the high pressure end wall 24 and a portion located in the barrel wall 26 is, however, shaped in such a way that the rotor grooves 38, 42 when they start to communicate with the high pressure port 20 have a considerably smaller volume than that corresponding to completely open grooves.
  • the high pressure port 20 is shaped in such a Way that its edges in the barrel wall 26 as well as in the high pressure end wall are substantially parallel with the portions of the lands limiting the grooves when the communication with the grooves commences.
  • the high pressure port In order to define the size of the high pressure port it is sufiicient to speak only about the position of the point 66 where the edge of the barrel wall sealing against the tip of the male rotor land 36 crosses of the point 66 from the low pressure end wall as is clearly shown in the diagram of FIG. Where the volume of the groove portions forming a discharging chevron shaped chamber expressed in percentage of the total volume of the two grooves is shown as a function of the distance from the low pressure end wall of the point 66 expressed in percentage of the total distance between the low pressure and high pressure end walls.
  • the ratio of the total volume of the grooves to the volume of the chevron shaped chamber when opening against the high pressure port is called the built-in volume ratio of the machine, 6.
  • the mean pressure in the chevron shaped chamber when it opens against the high pressure port can be calculated by means of the built-in volume ratio and the Ic-VEtlLlB of the working fluid defined already in the introduction to the specification.
  • the ratio of the mean pressure in the chevron shaped chamber when it opens against the high pressure port to the pressure in the grooves completely filled by working fluid when communicating with the low pressure port, the built-in pressure ratio can thus be calculated from the formula
  • the machine operates in the following way.
  • the rotors are rotated by a motor (not shown) through the shaft 34 projecting from the casing 34 and through the synchronizing gear 32 connecting the rotors.
  • Working fluid is sucked in through the low pressure channel 14 and the low pressure port 18 into the Working space 12 where it flows into the portions of the rotor grooves 38, 42 which are open against the low pressure port 18 so that the grooves are filled with working fluid to their whole length.
  • the working fluid is then moved circumferentially 'by the rotors. During this movement a female rotor land 40 first enters the male rotor groove 38 and a male rotor land 36 then also enters the female rotor groove 42.
  • a chevron shaped chamber composed of two communicating grooves which is sealed against the high pressure port 20 as well as against the low pressure port 18 and the volume of which continuously decreases during the rotation of the rotors.
  • the pressure in the chamber increases in the first hand at the intermesh between a land and the cooperating groove. The pressure initiated in this way is then transmitted through the rotor grooves in the direction towards the high pressure ends of the rotors.
  • the compressor shown in FIG. 7 differs from the one shown in FIG. 1 only by the fact that the synchronizing gear 32 connecting the rotors has been omitted so that the torque transmission between the rotors is obtained by direct flank contact therebetween.
  • the compressor shown in FIG. 8 differs from the one shown in FIG. 1 only by the fact that the synchronizing gear 32 connecting the rotors has been omitted so that the torque transmission between the rotors is obtained by direct flank contact therebetween, and by the fact that the compressor is provided with openings 68 in the casing 10 for injection under pressure of a liquid supplied from a pressure liquid source, not shown, close to the intersection line between the bores of the working space 12 on the same side of the plane of the axes of the bores as the hi h pressure port 20, whereby on one hand an improved cooling and sealing is obtained within the compressor and on the other a liquid film is obtained on the rotor flanks contacting each other.
  • a screw rotor machine for elastic working fluid comprising two coplanar intermeshing male and female rotors having helical lands with a wrap angle of less than 360 and intervening grooves and a casing enclosing said rotors in sealing relationship to provide working space for the fluid, said lands having profiles comprising substantially circular portions on the male flanks lying outside the pitch circle of the male rotor and substantially circular portions on the female flanks lying inside the pitch circle of the female rotor, each of the lands of the female rotor further having an addendum portion extending outside the pitch circle of the female rotor, the radial extent of said addendum being within the range of from 18% to 37.5% of the length of the chord of the portion of the pitch circle of the female rotor lying Within the land and the bottom portion of each of the grooves of the male rotor having a dedendum portion lying inside the pitch circle of the male rotor and having a profile complementary to that of said addendum portions of the female rotor land.
  • a screw rotor machine as defined in claim 1 in which the rotors and the high and low pressure ports communicating With the working space are so formed and dimensioned in relation to each other that the built-in pressure ratio for the elastic working fluid is less than 5 to 1.
  • a pair of cooperating rotors comprising a male rotor and a female rotor having helical lands with a wrap angle of less than 360 and intervening grooves, said lands having profiles comprising substantially circular flank portions on the male flanks lying outside the pitch circle of the male rotor and substantially circular portions on the female flanks lying inside the pitch circle of the female rotor, each of the lands of the female rotor further having an addendum portion extending outside the pitch circle of the female rotor, the radial extent of said addendum portion being within the range of from 18% to 37.5% of the length of the chord of the portion of the pitch circle of the female rotor lying within the land and the bottom portion of each of the grooves of the male rotor having a dedendum portion lying inside the pitch circle of the male rotor and having a profile complementary to that of said addendum portions of the female rotor lands.
  • Rotors as defined in claim 8 in which the male rotor has four lands and the female rotor has six lands with intervening grooves and the portions of the female rotor grooves lying inside the pitch circle of the female rotor are defined by profiles comprised of circular arcs having their centers on the pitch circle of the female rotor and a radius the length of which is approximately 18.7% of the outer diameter of the female rotor.

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  • Engineering & Computer Science (AREA)
  • Mechanical Engineering (AREA)
  • General Engineering & Computer Science (AREA)
  • Applications Or Details Of Rotary Compressors (AREA)
  • Rotary Pumps (AREA)
  • Rotary-Type Compressors (AREA)
US394985A 1963-09-12 1964-09-08 Screw rotor machine for elastic working fluid Expired - Lifetime US3283996A (en)

Applications Claiming Priority (1)

Application Number Priority Date Filing Date Title
SE9983/63A SE303170B (enrdf_load_stackoverflow) 1963-09-12 1963-09-12

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US (1) US3283996A (enrdf_load_stackoverflow)
JP (1) JPS504886B1 (enrdf_load_stackoverflow)
BE (1) BE652892A (enrdf_load_stackoverflow)
DE (1) DE1428270B2 (enrdf_load_stackoverflow)
GB (1) GB1084465A (enrdf_load_stackoverflow)
SE (1) SE303170B (enrdf_load_stackoverflow)

Cited By (8)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3640649A (en) * 1969-09-23 1972-02-08 Jan Edvard Persson Screw rotors
US3692441A (en) * 1971-05-20 1972-09-19 Pavel Evgenievich Amosov Screw rotor machine for compressible media
US4504203A (en) * 1983-01-18 1985-03-12 Delta Screw Nederland B.V. Apparatus adapted for use as a screw compressor for motor
US5078583A (en) * 1990-05-25 1992-01-07 Eaton Corporation Inlet port opening for a roots-type blower
US5083907A (en) * 1990-05-25 1992-01-28 Eaton Corporation Roots-type blower with improved inlet
US20050244294A1 (en) * 2004-04-28 2005-11-03 Kabushiki Kaisha Toyota Jidoshokki Screw fluid machine
US20080168961A1 (en) * 2007-01-12 2008-07-17 Gm Global Technology Operations, Inc. Intake assembly with integral resonators
US20240287990A1 (en) * 2023-02-27 2024-08-29 Carrier Corporation Screw compressor and refrigeration system having it

Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2486770A (en) * 1946-08-21 1949-11-01 Joseph E Whitfield Arc generated thread form for helical rotary members
US2622787A (en) * 1947-07-16 1952-12-23 Jarvis C Marble Helical rotary engine
US2975963A (en) * 1958-02-27 1961-03-21 Svenska Rotor Maskiner Ab Rotor device
US3179330A (en) * 1960-08-30 1965-04-20 James Howden And Company Ltd Rotary engines and compressors

Patent Citations (4)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US2486770A (en) * 1946-08-21 1949-11-01 Joseph E Whitfield Arc generated thread form for helical rotary members
US2622787A (en) * 1947-07-16 1952-12-23 Jarvis C Marble Helical rotary engine
US2975963A (en) * 1958-02-27 1961-03-21 Svenska Rotor Maskiner Ab Rotor device
US3179330A (en) * 1960-08-30 1965-04-20 James Howden And Company Ltd Rotary engines and compressors

Cited By (9)

* Cited by examiner, † Cited by third party
Publication number Priority date Publication date Assignee Title
US3640649A (en) * 1969-09-23 1972-02-08 Jan Edvard Persson Screw rotors
US3692441A (en) * 1971-05-20 1972-09-19 Pavel Evgenievich Amosov Screw rotor machine for compressible media
US4504203A (en) * 1983-01-18 1985-03-12 Delta Screw Nederland B.V. Apparatus adapted for use as a screw compressor for motor
US5078583A (en) * 1990-05-25 1992-01-07 Eaton Corporation Inlet port opening for a roots-type blower
US5083907A (en) * 1990-05-25 1992-01-28 Eaton Corporation Roots-type blower with improved inlet
US20050244294A1 (en) * 2004-04-28 2005-11-03 Kabushiki Kaisha Toyota Jidoshokki Screw fluid machine
US20080168961A1 (en) * 2007-01-12 2008-07-17 Gm Global Technology Operations, Inc. Intake assembly with integral resonators
US7779822B2 (en) * 2007-01-12 2010-08-24 Gm Global Technology Operations, Inc. Intake assembly with integral resonators
US20240287990A1 (en) * 2023-02-27 2024-08-29 Carrier Corporation Screw compressor and refrigeration system having it

Also Published As

Publication number Publication date
DE1428270B2 (de) 1980-01-17
JPS504886B1 (enrdf_load_stackoverflow) 1975-02-25
GB1084465A (en) 1967-09-20
BE652892A (enrdf_load_stackoverflow) 1964-12-31
DE1428270A1 (de) 1970-01-08
DE1428270C3 (enrdf_load_stackoverflow) 1980-09-11
SE303170B (enrdf_load_stackoverflow) 1968-08-19

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