US2243874A

US2243874A - Rotary compressor

Info

Publication number: US2243874A
Application number: US44935A
Authority: US
Inventors: Lysholm Alf
Original assignee: Individual
Current assignee: Milo AB
Priority date: 1934-10-16
Filing date: 1935-10-14
Publication date: 1941-06-03
Anticipated expiration: 1958-06-03

Description

' June 3, 1941. A. LYSHOLM ROTARY COMPRESSOR Original Filed Oct. ,14, 1935 2 Sheets-Sheet 1 A. LYSHOLM ROTARY comknsson Original Filed 001:. 14. 1935 '2 sh m-sheet 2 IIIIIIIIII 4 IPTC 4 IN ENZOZ h 272% 71/ Pa'tented June 3,1941

sonar comranssoa Alf Lynch, Stockholm, Sweden, asslgnor to Aktiebolaget Milo, Stockholm, Sweden, a con poraiion of Sweden Application mm 14, 1935, Serial No. 44,935.. Renewed August 3, 1940. In Sweden October 1: Claims. (01. 230-150) The present invention relates to rotary compressors oi the axial flow screw or worm rotor type and has particular reference to compressors adapted to be operated at high speed and to compress relatively large volumes of air to subtantial pressure within the compressor. Such compressors are inherently reversible so as to be operable as motors and it is intended within the scope of this invention to include such use. but for the sake of simplicity of description, the apparatus forming the subject matter of this invention will hereinafter be described and claimed, but without limitation as to motor use, as compressor apparatus.

Amongst the several major objects of the invention are: to provide improved compressor ap-' paratus of the type described which is adapted to be operated at speeds such that the maximum relative speed between coacting rotor surfaces is substantially greater than that representing the maximum permissible speed for parts intended to operate with frictionally contacting surfaces and in which the rotor parts are most advantageously operated with clearance between cooperating rotors and between the rotors and thecasing; to provide improved apparatus of the above character which may be and is primarily intended to be operated with dry rotors, that is, without lubrication of the compressing surfaces of the rotors; to provide improved apparatus of the character described in which substantial compression may 'be effected in the apparatus itself, as distinguished from blower apparatus which depends upon discharge against a back pressure'to enable compression to be efiected; to provide improved apparatus of the type described in which continuous discharge of compressed medium is obtained; to provide improved compressor apparatus in which the phenomenon of"pumping is eliminated; and to provide compressor apparatus of the above described kind which is capable of operating with high efflciency because, among other factors, of novel form and construction of rotor parts and novel form and arrangement of inlet and outlet ports, as will hereinafter be more fully pointed out.

as for example, in the range of from 50 to 300 meters per second.

As mentioned above, in accordance with one phase of the invention, the rotors operate with a clearance relative to each other and to the Casing; r i

This clearance is preferably made as small as is practically possible in order to provide what may be advantageously referred to as "space packing between the relatively moving parts. Because of practical considerations it may in some instances be desirable to provide packing ribs or edges, particularly at the ends of the rotors, which ribs or edges may, due to expansion or minor irregularities, come into contact with relatively moving surfaces. In case of such contact these packing ribs or edges, if employed, will be very rapidly worn down without dama e to the apparatus to the point where any material frictional contact between parts is eliminated. the action being similar to that ofthe fine-packing edges of the ribs used in high speed turbine construction.-

. flowing into or out ofthe machines.

Other objects of theinvention will appear as the ensuing description proceeds:

With respect to the intended speed of operation, previously referred to, it is contemplated inaccordance with the present invention that the maximum relative speed of cooperating rotor parts be not less than 25 meters per second and preferably this speed is much greater in order to secure the maximum benefit from the invention,

The invention further contemplates in another of its phases the use, in combination with other features of construction tending to promote high efllciency of operation, rotor threads or lobes having special profile eharacteristicsresulting in the production of relatively short lines of contact or packing lines'between" the rotors and consequently relatively small areas-for leakage of fluid between adjacent working spaces in the apparatus. The preferred special form of such lobes will hereinafter be more fully described and constitutes, per se, the claimed subject matter of my continuation-impart application Serial No. 183,664, filed January 6, 1938'.

A further phase "of the invention contemplates the formation of the inlets and outlets of the apparatus in such a manner that the working medium is throttled as little as possible when Theworking spaces located between the lobes of the rotors will,.in the case of a compressor, first be closed and then be reduced with respect to the volume, and will finally, after the desired pressure has been attained, be opened toward the outlet. In ord r that the apparatus shall operate with as little us as possible, it is important, therefore, that the closing and the opening of the working spaces be effected as'quickly as possible.

' Primarily, this holds true for the connection of -the construction of the low pressure side.

ing medium is greater than at the low pressure side, while in most cases it is believed to be of advantage to make allowance for thisalso in' To obtain the object in'view, the limiting edges of the inlet opening, which is always in open and unregulated communication with the rotors,

If the inlet or the outlet be so arranged that i the working medium is supplied and discharged substantially at right angles-to the axes of the rotors, the edges of the outlet opening are arranged, according to the invention, in parallel to the helically extending edges of the threads. With axial or partially axial flow of the working medium, the axially opening and closing edges are arranged in'parallel to the edges obtained in a section of the rotors in a plane at right angles to the axis.

Further featuresof the invention will be described more in detail in the following portion of this specification, reference being had to the The compressor is driven from the shaft 446, Y

the movement of which is transmitted through ear wheels 442 and 444 to the rotor 2 which is arranged opposite the rotor 410, in such amanner that the two rotors do not touch one another at any point.

.In order to enable cooling of the rotors from the inside, the shafts are hollow and provided with concentric

internal tubes

446 and 448 respectively. For an internal cooling of the rotor ,4i6, cooling liquid is introduced through a nozzle 450 into the interior of the tube 446. The cooling liquid to begin with flows through the tube 446 in the direction of the arrow 452, then flows between the inner tube and the hollow shaft back in the opposite direction and enters in the direction of the

arrows

454, 456 into a space 466 closed by a cover 458, the liquid leaving this a space through an outlet opening not shown in the drawings, in order then to be cooled and again to be supplied to the cooling system.. As will be seen from the drawings, the intemal cooling of the rotor 412 takes place'in the same manner several embodiments illustrated 'in the accompanying drawings. Fig. 1 shows in axial longitudinal section one form of compressor, embodying the invention, viewed from the low pressure or inlet side;

Fig. 2 shows the rotors and part of the casing of the apparatus illustrated in Fig. 1; viewed from the high pressure or'outlet side; i

Fig. 3 is a section taken on the line 33 of Fi 1;

Fig. 4 is a plan view of a rotorof Fig. 1 showing the nature of the packing line between the rotors; I

Fig. 5 is a fragmentary view of apparatus similar to that shown in Fig. 1 but providing for Partial admission and discharge of fluid in axial direction;

Fig. 6 is'a more or less diagrammatic transverse view illustrating one suitable shape of axial discharge port provided by end plate structure of the kind shown in Fig. 5;

Fig. '1 is a similar view illustrative of suitable axial inlet port outline provided by such end plate structure; and

Fig. 8 is a fragmentary view illustrating a further form of axial discharge port'outline.

The compressor shown in Fig. 1 has two rotors 4H) and 2, which are surrounded by a casing part 4 adjacent to the peripheral portion of the rotors, said casing part being hollow to receive a cooling liquid. The rotors 4H! and 2 are made integral. with the shaft portions pertaining thereto, and are mounted in

roller bearings

8, 418 and 420, 422 respectively adapted to take up the radial pressure, and in ball bearin s 424 and 426 resp ctivelv adapted to take up the axial pfessure.- The roller bearings are carried by

easing parts

428 and 436 screwed to the part 4,. said casing parts limiting the working spaces of the compressor on both sides in an axial direction and being extended about the shafts of the rotors with the provision of

intermediate packings

432, 434, 436 and 436.

and therefore need not be further described.

The inlet of the compressor is designated by 462 and the outlet thereof by 464. The casing part 430 at the induction end of the compressor is provided with

radial bores

466, 466 extending from the rotor shafts outwardly and having for their object to prevent a sucking effect in the spaces located on the right of the

packings

434 and 436, andthus to prevent suction of lubricant into the compressor. The casing part 428 located at the pressure end of the compressor likewise has bores 41-0, 412 extending outwardly from the shafts, said bores being provided to prevent penetration of the compressed medium into the spaces containing the hearings, on the left of the

packings

432 and 436, and to lead oif pressure medium that may escape through any places that are not tight. In the clearance between the high pressure end of the rotor 4iil and the casing part- 428 there is provided one or more tightening edges 4' arranged either on the casing or on the end surface of the rotor, in order that a lower pressure shall prevail inside the tightening edge than outside the same.

As will be seen from Fig. 3, the two rotors in the present case are constructed as worms with three lobes. Rotors with three or more lobes are found to give the best results. With only two threads the compression will be intermittent and pulsating, and the compressor will a work with great outlet losses, it being difficult to losses will arise. The sizes of the two cooperating rotors are chosen so that the theoretical top circle 414 of the smaller rotor and the theoretical root circle of the greater rotor coincide with the pitch circle. While in Fig. 1 the clearances be-- tween the two rotors and between the rotors and the housings are indicated, the cooperating parts in the following figures are represented without any clearance to facilitate a betterconception of the processes in operation. In agreement with the explanations set forth introductorily it is then of course always supposed that a certain clearance of, for instance, 0.2 mm. is provided between the parts in question. For the sake of simplicity, the following description substantially pays regard only to the conditions such as they would be if there were no clearances. How conditions will actually be, is easily understood. however, when the clearances are conceived as being present.

The thread profiles shown by way of example in Fig. 3 have been obtained in the following manner. With a point A located on the root circle 416 of the larger rotor as a centre a circular line BC has been drawn, the radius r of which is equal to the height AC of the thread. Thus the one side act the one thread profile is obtained. n the top circle 414 of the small rotor a point D is determined; in such a manner that the points A and D will simultaneously. reach the connecting line for the centre points H and K of the rotors, the same thus meeting in the point'E. As in the present example the points A andD are located; on the pitch circle and therefore move at the same velocity, their distances from the point E. must always be equal. With D as a centre, a circular arc FG has been drawn, which has the same radius r as the arc BC and extends from the point of intersection F with the line DK to the point of intersection G with the top circle 414. Thus a line 0 of the profile of the thread space is obtained. From the profile lines a and 0 being obtained in the manner described, it follows that these lines coincide when points A and Dare in the point E. In this position points C and F thus also coincide, the same meeting on the connecting line I-lK between the centres of the rotors. From this it follows that the thread space in the said position'along the line F--G is entirely filled by a portion or. the thread profile a,

which is of importance with respect to the provision of a good tightening effect between the pressure and suction side of the "apparatus. As will be seen from the following description, the tightening line will be very short and will extend C1 to the intersection with the line L1 at 695, and then follows the line L1 to the point 495*. From here the track of the tightening line is repeated in the same manner as with the point 48$ as a starting point. If regard be paid to the clearances between the two rotors, the tightening line by reason of the curvature of the surfaces'a, b, c, d partly obtains a somewhat different extension, that is to say from 488 along the line 698 to 492 and from 492 along the line 500 to 656.

. Fig. 7 shows how the compression of the working medium takes place. It is assumed that air is to be compressed and that such air enters the induction side of the compressor through the inlet socket 462. Upon rotation of the rotors in the direction of the arrows drawn, air is entrained, without compression to begin with, into the spaces P and R, until the position shown in the drawing is reached, in which the points C, L and M coincide. Upon continued, rotation the lobe S penetrates into the space 1?, whereby the volume 01'. the space P is reduced and the pressure of the air enclosed therein is increased. As soon as the point G1 has reached over the point M, the two spaces P and R are brought into communication with each other, whereby an equalization of pressure is effected in these two spaces. Upon continued rotation the lobe T1 pro- Jects into the space R, and the compression proceeds, until the spaces P and R, diminishing in volume as they are displaced toward the pressure at the most over half of the periphery of the rotors, the losses due to leakage thus being considerably reduced;

The point L limiting the thread space on the V otherv side is determined by the condition that the points L and C shall at the same time be in the point of intersection M for the two stop circles. The profile form'blocated between the points C and N is generated by the point L, that is to say, the point L touches the profile b all over its lengthfrom C to N. Finally the line dis generated by the point C from F to L. 'The direction of rotation of the rotors is indicated ythe arrows 418 and 4"- The expressions, points, and lines respectively used hereinbefore; are of. course adaptable only in the case of across section as shownin Fig. 3.

Considering the whole rotors, however, the point C, for example, makes a line. while the line a, for instance, makes a surface.

Fig. 4-shows the one rotor 4|! viewedin the direction of the arrow 48! in Fig. 3 to illustrate the tightening line, that is to say the line-along which the two rotors are at the least distance from each other. As will be found by a study end of the compressor, have been brought into communication with the outlet opening.

In the embodiment shown in Fig. 1, the entrance and the discharge of the air into and out of the compressor takes place substantially in a radial direction. When operating with large volumes it is often desirable, however, to cause the air at the same time to flow in'and out in an axial direction also. This could be attained, for instance, by removal of the casing parts limiting -the rotors in the axial direction and by suitably altering the inlet and outlet sockets. This, however, would require so long rotors that closed compression spaces would be formed without an axial limitation. The rotors may, however, be

made considerably shorter than .the pitch of the thread by arranging at the ends of the rotors special end plates or the, like, which only leave a definite inlet and outlet section open in the axial direction while completely; closing the remaining portion.

Fig. 5 iilustratesthe manner in which end plates 502 and ill! may be interposed to provide of Fig. 4, the tightening line on the surface b is 1 determined by the position of the line L, the portion 444, 485 of the tightening line being thus obtained. Then follows from I to 4" a portion parallel to the axis, which portion is formed by the cylindrical surfaces BB1 and no]. The theoretical tightening line, that is to say the line obtained without regard to the clearance between the rotors, then extends along the line G to I and then on the line of intersection of a plane at right angles to the axis with the surface a; to

e the intersection with the line C1 at 4.2. The

theoretical tightening line then follows the line "axial port openings at the ends of the rotors.

The contours of suitable end port openingsare illustrated in Figs. 6 to 8.

In the more or less diagrammatic Fig. 6 the rotors are taken as viewed in the axial direction from the pressure end. The greater portion of the end surfaces of the rotors is closed by the end plate "2, the shape of whichis obtained in the following manner.

To begin with, it is obvious that the spaces P1 and R1 must be closed until the desired final compression pressure has been attained. which it is assumed is with the rotors in the position shown in Fig. 6. The lines). a coincide with the root circles of the two rotors. An extension of the plate ll! iorwardly over the root circles would reduce the outlet area, but on the other hand and the suction side.

. on the left of said lines. line s results from the fact that the space P must shaped space which extends downwardly to the suction side and thus forms a non-desirable direct communication between the pressure side shown in Fig. 6, the rotors must be conceived as out along a plane extending through the line 490, 492 of Fig. 4, at right angles to the axis, the upper portion thereof being removed.- The end view from above of the lower portion then corresponds to the position shown in Fig. 6. It will then be understood, that the portion located between the point 492 and the line L1 is in direct communication with the suction side. To

close this communication the end plate is at this point caused to go further outwardly, the limiting line h being thus obtained. A closure is not necessary outside this line, inasmuch as the curved line 500 (Fig. 4) already tightens against v the suction side in said location.

Fig. 6 shows how large the axial outlet opening may be made. For practical reasons, that is To obtain the position On the other hand, this,

the compression they extend parallel to the,

thread edges C1 and L: (Fig. 7) ,which are designated as closing edges. In Fig. 1, these edges of the casing are denoted by 5! and H2. For a certain distance they follow the closing edges C1 and L2 respectively and are then united by a I casing edge 5. Fig. 1 is thus to be understood so that the portion of the rotors located to the left of the chain-dotted edges 5"), 5H and 512 is completely enclosed by the casing, while the portion to the right of these edges is directly connected with the inlet socket 462. The diagrammatic representation of the casing edges in Fig. 1 has been resorted to for the sake of clearness only.

Fig. 6 shows the rotors viewed from the pressure side at the moment when the air compressed in the working spaces P1 and R1 is brought into communication with the outlet.

The two working spaces are in open communicashape of the end plate requires another measure which will be described with reference to Fig. 8.

In the latter figure, the lobe profiles are drawn in a position which they reach immediately be fore they take the position shown in Fig. 6 As will appear from Fig. 8, the surfaces a, c and a portion of the surface d enclose a wedge-shaped space diminishing toward the suction end, which space upon the continued rotation of the rotors becomes smaller and smaller and finally on reaching the position shown in Fig. 6, disappears altogether. In order now to enable removal of the air quantity enclosed in this space, which quantity is completely enclosed on account of the position of the plate 504, and to prevent an inadmissible rise of the pressure in this space, an opening 506 is provided in the plate 504 in a suitable place, said opening connecting the space enclosed between a, c and d with the outlet of the compressor. Obviously, the opening 506 must have such a position as not to connect the space enclosed between b and d with the pressure side.

The end plate 503 provided on the suction side is preferably given the limitation shown by the lines stwv-z in Fig. 7, or some other sim ilar limitation, the plate then closing the part The extension of the be completely closed toward the suction side when the thread S commences to penetrate into this space or, in other words, when the compression is to commence in the space P. The other lines are selected so that direct communication between the suction side and the pressure side is prevented under all circumstances.

Instead of arranging special end plates, the casing parts '428 and 430 respectively shown in Fig. 1 and limiting the rotors on both sides in an axial direetion may be provided with suitably formed recesses, which facilitate the inflow and the outflow of the working medium in the axial or at leastpartly in the axial direction.

The edges of the casing closingthe spaces P and R are so arranged that in the beginning of compressor, so that the same pressure prevails in the same. The casing is enlarged at BIG and 5|8, so that the spaces P1 and R1 are opened and connected with the outlet as soon as the thread edges C and G1, which are designated as opening edges, pass beyond the position shown in the drawings. From this, the extension of the corresponding edges of the casing is obtained according to the invention in the manner illustrated in Fig. 2. The edge of the casing at 520 first follows the track of the opening lobe edge C to the intersection with the thread edge L, then extends on-the cylindrical main part of the lobe S for a distance 522 in parallel to the rotor shaft and then at 524 follows the opening lobe edge G1 to the pressure end of the compressor.

It will be seen from Fig. 2 that the working spaces P1 and R1 are opened later toward the pressure side and that the pressure of the comcasing edges 520, 522, 524 are brought toward the pressure end of the compressor. When combined radial and axial discharge is employed, it will be evident that as the casing edges 520, 522, and 524 limiting the radial portion of the discharge port are moved. toward the pressure end of the compressor, the limiting edges e and It should likewise be moved toward each other to correspond. The nature of this change may be ap- I the radial limiting lines of the discharge port v close together.

are relatively close together at the pressure end of the apparatus and accordingly the limiting lines e and k of the end port are correspondingly It will be apparent that where combined axial and radial port openings are employed, the limitingv edges of the two portions of the port should join each other without periphhowever, involves a loss in so far as a fall of the pressure will again take place to the desired final pressure upon the rise of the pressure. Accord- 7 ing to the invention this may be prevented by the outlet section being designed for a compression pressure, which is lower than the desired final compression pressure,.in such a manner that the final pressure will first adjust itself on account of the unavoidable subsequent compression after the outlet has been opened. Thus the reduction of the pressure and a corresponding loss may be avoided. For example, if air of atmospheric pressure is to be compressed to a pressure of 1.4 atmospheres, the edges of the casing are arranged in such a manner that the working spaces are opened toward the outlet when the compression amounts to 1.2 atmospheres.

In the period between the commencement of the opening and the obtaining of full opening, a further compression will then take place from 1.2 to 1.4 atmospheres.

The apparatus described above may also be operated as a motor, for instance as a steam or gas motor. In this case the supply of driving medium is effected through the socket 454, and the expanded driving medium escapes atlBZ, the direction of rotation of the rotors being then opposed to that of the rotors when they operate as a compressor. It is possible, however, to use the machine both as a compressor and as a motor with the same direction of rotation, but in such case the sockets 462 and! have to be exchanged, that is to say, the working medium flows through the machine in the same direc' tion independently of whether it operates as a compressor or as a motor. I

The invention is not limited to the embodi ments shown herein merely by way of example,

but may be formed constructively in various ways. Obviously, the invention may be applied also to double-acting rotors, in which the working.

medium consumes or gives off work in parallel streams. The invention is also independent of the number of cooperating rotors.

What I claim is:

1. A compressor of the rotary screw type including a casing having an inlet and an outlet for the medium to be compressed, a male rotor and a female rotor mounted for rotation in said casing, said rotors having intermeshing lobes and grooves, respectively cooperating with each other and with the internal surface of the casing to form'compression spaces which are progressively displaced axially of the compressor upon rotation of said rotors, each of said compression spaces registering successively with said inlet and with said outlet in different positions of rotation of the rotors and decreasing in volume during the interval between registration with the inlet and registration with the outlet, there being radial clearance to provide radial space packing between the rotors and the casing, and means connecting said rotors for maintaining the surfaces of the intermeshing lobes in peripheral spaced relation to provide space packing between said surfaces, said compressor being constructed for normal operation of the rotors at a speed such that the peripheral rotor speed at the place of greatest rotor diameter in the compressor is greater than maximum permissible speed between frictionally contacting sliding surfaces.

2. A compressor of the rotary screw type including a casing having an inlet and an outlet for the medium to be compressed, a male rotor and a female rotor mounted for rotation in said and with the internal surface of the casing to form compression spaces which are progressively displaced axially of the compressor upon rota tion of said rotors, each of said compression spaces registering successively with said inlet and with said outlet in different positions of rotation of the rotors and decreasing in volume during the interval between registration with the inlet and registration with the outlet, there being radial clearance to provide radial space packing between the rotors and the casing, and means connecting said rotors for maintaining the surfaces of the intermeshing lobes in peripheral spaced relation to provide space packing between said surfaces, said compressor being constructed for normal operation of the rotors at a speed such that the eripheral rotor speed at the place of greatest rotor diameter in the compressor is within a range the lower limit of which is of the order of fifty meters per second and the upper limit of which is of the order of three hundred meters per second.

3. A compressor of the rotary screw type including a casing having an inlet and an outlet for the medium to be compressed, a male rotor and a female rotor mounted for rotation about parallel axes in said casing, said rotors having a plurality of lobes and an efiective length less than the pitch of the lobes, said lobes intermeshing and cooperating with each other and with the internal surface of the casing to form compression spaces which are progressively displaced axially of the compressor upon rotation of said rotors, said surfaces including an end wall surface defining the outlet ends of said spaces, "each the outlet, there being radial clearance to provide radial space packing between the rotors and the casing, and means connecting said rotors for -maintaining the surfaces of the intermeshing lobes in peripheral spaced relation to provide space packing between said surfaces.

4. A compressor of the rotary screw type including a casing having an inlet and an outlet for the medium to be compressed, a male rotor and a female rotor mounted for rotation about parallel axes in said casing, said rotors'having a plurality of lobes and an effective length less than the pitch of the lobes, said lobes intermeshing and cooperating with each other and with the internal surface of the casing to form compression spaces which are progressively displaced axially of the compressor upon rotation of said rotors, said surface including axially spaced end wall surfaces for defining the axial ends of said spaces, each of said compression spaces registering successively with said inlet and with said outlet in different positions of rotation of the rotors and decreasing in volume during the in- 5. A compressor of the rotary screw type including a casing having an inlet and an outlet and cooperating with each other and with the internal surface of the casing to form compression spaces which are progressively displaced axially of the compressor upon rotation of said rotors, said surfaces including an end wall surface defining the outlet ends of said spaces, each of said compression sp'aces registering successively with said inlet and with said outlet in different positions of rotation of the rotors and decreasing in volume during the interval between registration with the inlet and registration with the outlet, there being radial clearance to provide radial space packing between the rotors and the casing, and means connecting said rotors for maintaining the surfaces of the intermeshing lobes in peripheral spaced relation to provide space packing between said surfaces, said outlet comprising a port arranged partly in the end wall defining the outlet ends of said spaces and partly in the peripheral wall adjacent to said outlet ends and said inlet comprising a port arranged for radial admission of fluid to'sai'd spaces adjacent to the inlet ends of said spaces.

6. A compressor of the rotary'screw type in-' cluding a casing having an inlet and an outlet for the medium to be compressed, a plurality of cylindrical rotors mounted for rotation about parallel axes in said casing, 'said rotors having a plurality'of lobes and an effective length less than the ,pitch of the lobes, said lobes intermeshing and cooperating with each other and with the internal surface of the casing to form compression spaces which are progressively displaced axially of the compressor upon rotation of said rotors, said surfaces including an end wall surface defining the outlet ends of said spaces, each and means connecting said rotors for maintaining, the surfaces of the intermeshing lobes in perlpheral spaced relation to provide space packing between saidsurfaces, said inlet comprising a port arranged partly in the casing end wall at the inlet end of the compressor and partly in the peripheral casing wall adjacent to said inlet end and i said outlet comprising a port arranged partly in said end wall surface defining the outlet ends of said spaces and partly in the peripheral casing wall adjacent to the outlet ends of said spaces.

7. A compressor of the rotary screw type indecreasing in volume during the interval between A registration with the inlet and registration with the outlet, there being radial clearance to provide radial space packing between the rotors and the casing, and means connecting said rotors for, maintaining the surface of the intermeshing lobes in peripheral spaced relation to provide space packing between said surfaces, said outlet comprising a port having irregular outline arranged to substantially register with the rotor edges defining each compression space at the instant of cluding a casing having an inlet and an outlet 1 for the medium to be compressed, a plurality of cylindrical rotors mounted for rotation about parallel axes in said casing, said rotors having a plurality of lobes and an effective length less 7 placed axially of the compressor upon rotation of said rotors, said surfaces including an end wall surface defining theoutlet ends of said spaces,

each of said compression spaces registering successively with said inlet and'withsaid outlet in different positions of rotation of the rotorsand connection of 'the said space with said outlet.

8.. A compressor of the rotary screwtype including a casing having an inlet and an outlet for the medium to be'compressed, a plurality of cylindrical rotors mounted for rotation about parallel axes in said casing, said rotors having a plurality of lobes and an effective length less than the pitch of the lobes, said lobes intermesh- 'ing and cooperating with each other and with decreasing in volume during the interval between registration with the inlet and registration with the outlet, there being radial clearance to provide radial space packing between the rotors and the casing, and means connecting said rotors for maintaining the surfaces of the intermeshing lobes in peripheral spaced relation to provide space packing between said surfaces, said outlet comprising a port for radial discharge of fluid from said spaces adjacent to the outlet end of the compressor and. having limiting edge portions arranged substantially parallel with respect to the edges of the rotor lobes which define the peripheral limits of said compression spaces,

said portions being located so as to register substantially simultaneously with the respective rotor edges to which they are substantially parallel.

9. A compressor of the rotary screw type including a casing having an inlet and an outlet for the medium to be compressed, a plurality of cylindrical rotors mounted for rotation about parallel axes in said casing, said rotors having a plurality of lobes and an effective length less than the pitch of the lobes, said lobes intermeshing and cooperating with each other and with the internal surface of the casing to form compression spaces which are progressively displaced axially of the compressor upon rotation of said rotors, said surfaces including an end wall surface defining the outlet ends of said spaces, each of said compression spaces registering successively with said inlet and with said outlet in different positions of rotation of the rotors and decreasing in volume during the ini terval between. registration with the inlet and" registration with the outlet, there being radial clearance to provide radial space packing be tween the rotors and the casing, and means connecting said rotors for maintaining the surface of the intermeshing lobes in'peripheral spaced relation to provide space packing between said surfaces, said outlet comprising a port for radial and axial discharge, of fluid from said spaces at the outlet ends thereof and the limiting edges of said port having portions formed and locatedto provide substantially simultaneous discharge ing and cooperating with each other and with the internal surface of the casing to form compression spaces which are progressively displaced axially of the compressor upon rotation of said rotors, said surfaces including end wall surface defining theoutlet ends of said spaces, each of said compression spaces registering successively with said inlet and with said outlet in' diflerent positions of rotation of the rotors and decreasing in volume during the interval between registration with the inlet and registration with the outlet, there being radial clearance to provide radial space packing between the rotors and the casing, and means connecting said rotors for V maintaining the surfaces of the intermeshing lobes in peripheral spaced relation. to provide space packing between said surfaces, said inlet comprising a port for radial admission of fluid to said spaces and having edge portions substantially parallel to the iting the peripheral extent of said spaces.

11. A compressor of the rotary screw type including a casing having an inlet and an outlet for the medium to be compressed, a male rotor and a female rotor mounted for rotation about parallel axes in said casing, said rotors having a plurality of lobes and an eifective length less than the pitch of the lobes, said lobes intermeshing and cooperating with each other and with the internal surface of the casing toform compression spaceswhich are progressively displaced axially of the compressor upon rotation of said rotors, said surfaces including an end wall surface deflning the outlet ends of said spaces, each of said compression spaces registering successively with said inlet and with said outlet in different positions of rotation of the rotors and decreasing in volume during the interval between registration with the inlet and registration with the outlet, there being radial clearance to provide radial space packing between the rotors and the casing, and means connecting said rotors for maintaining the surfaces of the intermeshing lobes in peripheral spaced relation to provide space packing between said surfaces, said inlet comprising a port for, axial and radial admission of fluid to said spaces and'having edge portions formed in part substantially parallel to the edges of the rotors limiting said compression spaces and arranged for substantial simultaneous admission of fluid in axial and radial directions to said spaces. I

e es of the rotors limand end wall surfaces in the casing to form compression spaces which are progressively displaced axially of the compressor upon rotation of said rotors, each of said compression spaces registering successively with said inlet and with said outlet in different positions of rotation of the rotors and decreasing in volume during the interval between registration with the inlet and registration with the outlet, there being radial clearance to provide radial space packing between the rotors and the casing, and means connecting said rotors for maintaining the surfaces of the intermeshing lobes in peripheral spaced relation to provide space packing between said surfaces, said outlet comprising a port the area and dimensions of which permit commencement of discharge of compressed fluid from the compression spaces into the outlet at a pressure less than the desired final pressure of discharge from the compressor.

13. A compressor of the rotary screw type including a casing having an inlet and an outlet for the medium to be compressed, a plurality of rotors mounted for rotation in said casing, said rotors having a plurality of lobes and grooves the rotors and the casing and means connecting and an effective length of the order of the pitch of the lobes, said lobes and grooves intermeshing and cooperating with each other and with the internal surface of the casing to form compression spaces which are progressively displaced axially of the compressor upon rotation of said rotors and said lobes and grooves having asymmetrically shaped profiles to provide a shorter line of approximate contact therebetween than is obtainable with profiles of symmetrical shape, each of said compression spaces registering successively with said inlet and with said outlet in different positions of rotation of the rotors and decreasing in volume during the interval between registration with the inlet and registration with the outlet, there being radial clearance between said rotors for maintaining the surfaces of the cooperating lobes and grooves in peripheral spaced relation, said inlet comprising a port arranged at least in part for radial admission of fluid to said compression spaces at the inlet end of the compressor and said outlet comprising a port arranged at least in part for radial discharge of the fluid from said compression spaces at the outlet .end of the compressor.

ALF LYSHOLM.