US2441771A - Yieldable drive for rotors - Google Patents

Description

May 18, 1948. A. LYSHOLM YIELDABLE DRIVE FOR ROTORS Original Filed Ma 31, 1941 3 Sheets-Sheet 2 ATTORNEY May 18, 1948. A. LYSHOLM Patented May 18, 1948 All Lyslio memo Stockholm, assignments, to Jarvis 0.

Sweden, anignor, by Marble, Leslie ltLMen-ill, andlcrcy H.Batten,astrustees Original application May 31, 1941. Serial No.

Divided and this application March 11, 194:, Serial No. 419,429

4 Claims. (Cl. 14-411) This application is a division of-my co-pending application Serial No. 396,030, flied May 31, 1941, which matured into U. S. Patent No. 2,410,172 granted October 29, 1946.

The present invention relates to apparatus of the rotary screw wheel type and has particular reference to compressors of this type as disclosed in my United States Patents No. 2,174,522 and No. 2,243,874 granted October 3, 1939, and June 3, 1941, respectively. More particularly my invention relates to compressors of the aforesaid type adapted to be constructed in large sizes for the compression of relatively large volumes of gaseous fluid.

Apparatus'of the kind under consideration embodies working chambers defined by relatively moving rotor and casing parts which are out of contact with each other and the leakage from which is minimized by close clearances between the moving parts which may conveniently be referred to as "space packing." 'In order for such apparatus to operate with acceptable efficiency, the volume of fluid leaking from the working chambers through the space packing must be relatively small compared with the volume of fluid passing through the apparatus and this is essentially accomplished in the type of apparatus under consideration by operating the rotors at Y very high speeds, since the volume of fluid handled is substantially a direct function of the speed of operation while the volume of leakage through the space packing is relatively constant with respect to speed.

As noted above, the operation with eifective efficiency of compressors of the kind under consideration is dependent upon the maintenance of very close clearances between the relatively moving parts defining the working chambers. At the same time, due to the fact that the relative speed between these parts is very high and in most if not all instances the parts run dry, it is essential in order-not to damage the apparatus that the clearances be maintained to prevent damage to the apparatus through rubbing contact between the dry parts. Particularly in the case of large capacity compressors, these factors introduce a serious problem because of possible torsional deflection between the timing or synchronizing gears and the rotor parts, which would be sufiicient to destroy the close clearances and permit the rotors to come into contact with each other. The present inventioncontemplates improved rotor and gearing construction which will eflectively eliminate the possibility of such torsional deflection between the parts as to result in the desired clearances being destroyed.

The manner in which the above object and other and more detailed objects which will hereinafter appear, are attained, may best be understood from a consideration of the ensuing portion of this specification, taken in conjunction with the accompanying drawings, in which by way of example but without limitation suitable apparatus for carrying the invention into efiect is described and illustrated.

In the drawings:

Fig. 1 is a longitudinal section of a compressor embodying the invention, taken on the line i-i of Fig. 4;

Fig. la is a fragmentary section taken on the line io-iaofFig.1;

Fig. 2 is a section taken on Fi 1:

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

Fig. 4 is a section -'1;

Fig. 5 is a fragmentary view taken from the line 5-5 of Fig 1;

Fig. 6 is a fragmentary plan view looking from the line 6-6 of Figs. 1. and 4; and

Fig. 7 is a diagrammatic development illustra tive of certain features of construction.

Referring" now to the drawings, the compressor comprises a casing Ill consisting of a central barrel portion Illa and end closures lb and itc. In the embodiment illustrated, the central casing portion is shown with a jacket space i2 for cooling fluid. In the case of small compressors such jacketing may in some instances be omitted but ordinarily with large capacity compressors some form of cooling of the casing is desirable in order to prevent unequal expansion which adversely affects the maintenance of the desired close clearances.

The male rotor i4 is mounted for rotation in bearings i5 and IS in the casing structure. For the same reasons that the casing is jacketed it is also desirable in the case of large units to cool the rotors and this is conveniently accomplished the line 2-2 of taken on the line 9-9 of by circulating a cooling fluid through the central or core portions of the respective rotors. One suitable arrangement for accomplishing this is shown in Fig. 1 wherein the male rotor I4 is shown provided with a hollow core. 14a. A hollow tube 20 is mounted at the axis of the rotor and is provided with one or more openings 22 adjacent to the end of the tube to provide communication between its interior and the hollow core space of the rotor surrounding the tube. One end of the tube 20 extends axially beyond the end of the rotor and is carried by a bearing 24 mounted in the casing structure. A Venturi tube 26 is provided at this latter end of the tube '20 and cooling fluid is supplied through the stationary nozzle 28 mounted in the casing structure. The injected cooling fluid travels through the hollow tube 20 and passes into the hollow rotor core through the ports 22, leaving the rotor through the annular channel 30 between the tube 20 and the end of the hollow core structure. Fluid discharged from channel 30 passes to the chamber 32 from which it may flow to any suitable cooling device for cooling and return through nozzle 28. Obviously other specific means for circulating cooling fluid may be employed, but the above described means provides a simple and eiiective way of accomplishing the desired cooling of the moving rotor. It is to be noted that in effecting such cooling it is advantageous to have one end of the rotor free of other mechanism so as to permit the advantageous placing of the cooling connections at the axis of the rotor. It will be understood that where such cooling is employed a similar arrangement will be used for cooling the female rotor. The female rotor 34 is mounted in bearings similar to bearings i6 and ill but not shown on the drawings, for rotation about an axis parallel to that of the male rotor.

The male rotor in the embodiment illustrated is provided with two sets of spiral lobes separated from each other at the center of the rotor by a space 36. One set of lobes 38, seen in Figs. 1 and 2, is inclined in one direction with respect to an axial plane while the other set of lobes 40, seen in Fig. l, is inclined in the opposite direction, in the manner of the teeth of a herringbone gear. In the embodiment illustrated, each set of lobes on the male rotor comprises four lobes and the profiles of these lobes are preferably in ac-- cordance with the disclosure of my aforesaid Patent No. 2,174,522.

The female rotor is provided with two sets of grooves separated axially by a space 36, these grooves also being spiral and inclined so that the two sets cooperate in intermeshing relation with the lobes 38 and 40, respectively. In the embodiment illustrated the grooves, of which the set cooperating with the lobes 38 are shown at 42 in Fig. 2, are five in number in each set, the pitch of the grooves being difierent from that of the cooperating lobes in order to permit the four lobes of each set to properly intermesh with the five grooves of the cooperating set. .The profile of the grooves is also preferably in accordance with the disclosure in my aforesaid Patent No. 2,174,522.

The cooperating rotors are synchronized or timed by suitable timing gears 44 and 44a mounted on the rotor shafts, as shown in Fig. 1a.

As will be observed from Fig. 1, timing gear 44 is carried by a hollow sleeve-like extension of the rotor core which is carried in the bearing I6. Although it is not essential to the invention, the power for driving the apparatus is preferably transmitted to the male rotor, for reasons which will hereinafter be more fully explained, and in accordance with the present invention the power is transmitted directly to the power receiving rotor through the shaft 46 which advantageously has some torsional and radial flexibility. This driving shaft, which is suitably keyed as at 48 to the rotor, extends through the sleeve carrying gear 44 to an outboard driving connection 50.

It will be noted that by means of this construction the timing gears are not in the path of power transmission from the source of power to the main body of the rotor and consequently the only torsional force tending to deflect the relatively small diameter journal part connecting the main body of the rotor with the timing gear is the torque transmitted through the timing gear in order to keep the rotors in properly synchronized relation.

The outer diameters of the rotors and the lobes thereon are made so that clearance is provided between the rotors and the inner surfaces of the casing which encloses them and also between the intermeshing portions of the rotors. This clearance is made as small as practical to provide what may be conveniently termed space packing for the compression spaces formed between the cooperating parts, and a primary function of the timing or synchronizing gears is to maintain the rotors in such properly timed relationship that clearance between them is maintained. Due to the space packing and resultant lack of rolling or sliding contact between the relatively moving rotor and casing parts, the rotors may be operated, and in accordance with the present invention are intended to be operated dry and at relatively very high speeds of rotation. When space packing is employed, high rotating speeds are required in order to obtain suitably high efliciency of operation.

When the rotor profiles are made in accordance with the preferred design disclosed in my aforesaid Patent No. 2,174,522, the torque transmitted through the timing gears is relatively only a small fraction of the total torque, amounting in most instances to not over about 15% of the latter. For reasons not germane to the present invention, the torque transmitted through the timing gears is negative rather than positive when the input power is applied to the male rotor, since the fluid forces acting on the sides of the grooves and lobes when the compressor is in operation tend to make the female rotor rotate at a higher speed, or overrun, the male rotor. Since the driving torque is transmitted directly to the main body of the rotor in accordance with the present construction, it will be evident that the clearance between the rotors may be most effectively maintained since the parts connecting the rotors to effect synchronization therebetween are subject to very little torque and consequently are not subject to such torsional deflection as might permit the rotors to turn relative to each other to an extent destroying the clearance therebetween.

As will be noted from Fig. 2, the pitch lines of the rotors lie on the root circle of the male rotor and at the cylindrical envelope of the female rotor, respectively, or closely adjacent thereto, and as employed in this specification and the appended claims the terms male rotor and female rotor are intended to define rotors having this general characteristic with respect to their pitch circles as distinguished from rotors of the well known Roots or similar type which have their pitch lines located intermediate the apexes and roots of the lobes and which may be characterized generally as twin rotors;

Referring now more particularly to Figs. 1, 3, and 5, the casing ends are provided with inlet passages 52 and 54 which terminate in inlet ports 56 and 58, respectively, in the two end walls at the opposite ends of the rotors. These ports and their cooperating inlet passages are formed to provide for substantially axial admission of air to the ends of the grooves in the rotors as the latter pass these ports.

As will be seen more particularly from Fig. 3, the portion of the inlet port 56 for direct axial admission of fluid is defined by line the area of. the port portion defined by this line in the end wall constituting the major area of the port. It is not essential, however, that this constitute the entire inlet port area and as will be seen from Fig. 1, it may be desirable in the interests of providing a smoothly curved inlet passage to have a small portion of the inlet port extend axially inwardly from the end wall. In the embodiment illustrated there is a small axially extending port portion defined by the lines 9 and h in Fig. but it. will be apparent from a-consideration of Figs. 1, 3, and 5 that this relatively small port portion will not materially affect the general character of fiow of the fluid into the apparatus, which fiow can be said to be axial in nature.

It will be understood that the port 58 at the opposite end of the compressor will have the same outline as port 56.

The casing is provided with a partition 60 intermediate its ends which projects radially inwardly to fill the space 36 between the two sets of lobes on each rotor and to provide end wall surfaces 62 and 64 which define the outlet ends of the working chambers in certain positions of rotation of the rotors. This partition does not extend peripherally entirely around the rotors as will be more clearly seen from Fig. 4 in which the edge defining the peripheral extent of this partition is indicated by the line The outlet port is indicated generally at 66, this port being located in the casing intermediate its ends and as will be observed from Figs. 1 and 4, this port extends axially along each of the two sets of rotor lobes and is further in direct communication with the portion of the space 36 lying above the partition EU so that the outlet port is in both radial and axial communication with the working spaces. In Fig. 6 the edges defining the radially communicating portions of the port are indicated by the lines kr--s-pand tu,vw, respectively.

As viewed in Fig. 6, the apex line of one of the male rotor lobes 38 appears at 380, and that of one of the rotor lobes 40 appears at 40a. Likewise, 42a (see also Fig. 4) indicates the edge of one of the female grooves 42. In the normal operation'of the apparatus, the direction of movement of the rotor grooves and lobes will be as indicated by the arrows in Fig. 6 as they pass the outlet port and it will be noted that the port line kr is angularly related to the apex line 38a of the male rotor and further that the line s--p is angularly related to the line 42a defining the edge of the female rotor groove. These port edges are so arranged that the poropened up progressively as the rotors revolve,

from the outlet ends of the working spaces axially toward their inlet ends, until full communication between the working spaces and the outlet port for radial discharge from such spaces is established. In the position of the rotors shown in Fig. 6, the port has been opened for radial discharge along the entire length of the -port from the groove space 42 lying behind the edge 42a and from the space 38b lying behind the apex line 38a. Obviously the action is similar with respect to the port edges t-u and 12-10 which cooperate with the Working spaces formed on the axially opposite side of the central partition 60.

In the operation of the hereinbefore described apparatus as a compressor, the working spaces are filled substantially axially of their length and progressively from the inlet toward the outlet ends thereof as the inlet endsof the spaces pass their respectively cooperating inlet port. Moreover, these spaces increase in volume to their maximum from their inlet toward their outlet as the rotors revolve during the portion of the cycle when the spaces are in communia cation with the inlet port, as will be more readily apparent from a consideration of Fig. 7 in which a working space 381), lying between two apex lines 38a, and a female rotor working space 42, are shown in diagrammatic development.

The direction of rotation of the rotors as seen in this view is as indicated by the arrows 68. The lines defining the peripheral limits of the inlet port are'indicated at ab and e-f, respectively, these lines corresponding to the similarly designated lines appearing in Fig. 3. At the opposite ends of the working spaces the outlet end closing wall is indicated which corresponds to the portion of the partition 60 lying below the line lm-no in Fig. 4.

As seen in Fig. 7, the working spaces open up progressively from left to right as the male rotor lobes progressively roll out of their cooperating grooves and the flow of air or other working fluid into these spaces is generally in the direction of the arrows 10. Because of the fact that the speed of rotation is relatively very high, a depressed pressure is created due to suction as the working spaces open up and this in turn induces a relatively high velocity of flow generally axially of the working spaces. As these spaces progressively open up to their full volume, the ends of the spaces are determined by the end Wall at their outlet ends and this wall may be said to extend generally transversely of the axes of the spaces, although as will be observed from Fig. '7 the wall does not extend transversely at right angles to these axes. The high velocity column of fluid moving into the working spaces from the generally axially directed inlet produces what is in efiect an elastic'piston moving toward the outlet ends of the spaces and when the spaces open up to their full axial length, this moving column is stopped by the outlet end wall. Due, however, to the fact that the column is elastic, flow through the inlet port continues after flow has ceased at the outlet ends of the spaces. I have discovered that if the speed of operation of the rotors and the peripheral extent of the inlet port are properly related to the length of the working spaces, the volumetric 'efflciency of the apparatus may be enhanced by taking advantage of a phenomenon resulting from the impact of the high velocity fluid piston striking the outlet end wall as the spaces open up to their full length. When this occurs under high velocity conditions, a fluid pressure wave is created which moves in the working spaces back toward their inlet ends in the direction of the arrows 12. This pressure wave moves approximately with the velocity of -sound and if the working spaces are kept in communication until approximately the time when this pressure wave reaches the inlet ends of the spaces, the net result is to produce what may conveniently be termed a ramming effect which enables the spaces to be filled with fluid at a pressure as high or higher than the pressure of the atmosphere or other fluid body from which the fluid entering the spaces is derived. As a consequence of this, a greater weight of fluid may be packed into the working spaces than corresponds to their actual volumetric displacement at inlet pressure and thus the capacity of a compressor of given size may be increased as compared with the capacity of a compressor which is not designed to make use of this ramming effect. The exact peripheral extent of the axially opening inlet required to achieve this desired result will be different with different specific compressor designs but in each instance, having in mind the substantially fixed speed of travel of the pressure wave created during the inlet period, the required peripheral extent of the inlet port is readily determinable for rotors having working spaces of given length and design to operate with a given normal peripheral speed. In all cases, however, if the desired effect is to be obtained, the peripheral extent of the inlet port must be such that the working space in the male rotor remains in communication with the inlet port until after such space has opened up to its full axial extent and full volume. By reference to Fig. '7 it will be seen that the working space 381) in the male rotor comes into communication at the outlet end with the working space formed by groove 42 in the female rotor before the male lobe has rolled completely out of the groove and thereby opened up the groove to its full volumetric capacity. Due to this open communication between the two spaces, the pressure wave created by impact against the end wall moves toward the inlet ends of both of the communicating spaces. Therefore, in order to secure the desired result it is not essential that the groove in the female rotor be kept in communication with the inlet port until after the groove in this rotor has reached its maximum volume. Also, it is desirable to so locate the lines ab and e-f defining the peripheral limits of the inlet port that communication between the inlet port and the working spaces in both rotors is cut off simultaneously as indicated by the relative positions of these lines in Fig. '7 with respect to the edges of the working spaces formed in the rotors.

While in order to provide a suitable disclosure of a compressor to which the present invention s pp i a th p ting and ramming characteristics of the compressor herein illustrated by way of example have been described in some detail, it is to be understood that the invention herein claimed is not limited in its application to compressors embodying these features but is equally applicable generally to screw wheel compressors of the kind in which inter-meshing rotors It will be understood that the present inven-' tion is not limited to the specific structural embodiment herein disclosed by way of example, but is to be considered as including all forms of apparatus falling within the scope of the appended claims.

What is claimed:

1. In a rotary screw wheel apparatus, a casing having axially spaced walls, a plurality of intermeshing rotors having main body portions located between said walls, extensions on said rotors passing through one of said walls, synchronizing gears on said extensions on the side of said one of said walls remote from said body portions of the rotors, at least one of said extensions being hollow, and a rotor driving connection passing through said hollow extension for transmitting power directly from an external source to the main body portion of the rotor torsionally independently of said hollow extension.

2. In a rotary screw wheel apparatus, a casing having axially spaced walls, a plurality of intermeshing rotors having main body portions located between said walls, extensions on said rotors passing through one of said walls and providing bearings for rotatably supporting said rotors, synchronizing gears on said extensions on the side of said one of said walls remote from said body portions of the rotors, at least one of said extensions being hollow, and a rotor driving connection passing through said hollow extension for transmitting power directly from an external source to the main body portion of the rotor torsionally independently of said hollow extension.

3. In a rotary screw wheel apparatus, a casing having axially spaced walls, a plurality of intermeshing rotors having main body portions located between said walls, extensions on said rotors passing through one of said walls, bearings located outside the wall through which said extensions pass and cooperating with the extensions to rotatably support the rotors, synchronizing gears on said extensions outside said bearings, at least one of said extensions being hollow, and a rotor driving connection passing through said hollow extension for transmitting power directly from an external source to the main body portion of the rotor, said driving connection being torsionally independent of said hollow extension.

4. In a rotary screw wheel apparatus, a casing having axially spaced walls, a plurality of intermeshing rotors having main body portionsv located between said walls, extensions on said rotors passing through one of said walls, bearings located outside the wall through which said extensions pass and cooperating with the extensions to rotatably support the rotors, synchronizing gears on said extensions outside said bearings, at least one of said extensions being hollow, and a rotor driving connection passing through said hollow extension for transmitting power directly from an external source to the main body portion of the rotor, said driving connection comprising a shaft member connected at its inner end to the main body portion of the 9 rotor and having an external diameter iete than the internal diameter or the hollow extension to provide clearance for permitting the shaft member to move tonionnliy and radially 1ndependently of said extension.

AL? LYSHOIM;

REFERENCES 0111111 The following references are of record in the me of this patent:

1 UNITED sm'rzs PATENTS Number Nnme Date as..- nnnnn we a.

1,001,676 Ostenreen AU. 29. 1911 ll Number Number Great Britain 069.29, 1931

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