US2473234A

US2473234A - Helical asymmetrical thread forms for fluid devices

Info

Publication number: US2473234A
Application number: US505135A
Authority: US
Inventors: Joseph E Whitfield
Original assignee: Individual
Current assignee: Individual
Priority date: 1943-10-06
Filing date: 1943-10-06
Publication date: 1949-06-14
Anticipated expiration: 1966-06-14

Description

HELICAL A-SYMMETRICAL THREAD FORMS FOR FLUID DEVICES Filed Oct. 6, 1943 9 Sheets-Sheet 1 l' A ll' I ogg/gbe 'Sea/gy Zone aoes f 51 50' l www 22 Ww 6 l0 gg l I`IIIIIIIIII'IIIIII,

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June 14, 1.949. J. E wHn-FIELD HELICAL ASYMMETRICAL THREAD FORMS FOR FLUID DEVICES 9 Sheets-Sheet 2 Filed Oct. 6., 1943 June 14, 1949. J. E. WHITFIELD HELICAL ASYMMETRICAL THREAD FORMS FOR FLUID DEVICES 9 Sheets-Sheet 5 Filed 0017. 6, 1943 June 14, 1949. J. E. WHITFIELD HELICAL ASYMMETRICAL THREAD FORMS FOR FLUID DEVICES YV9 YSheets-Sheet 4 Filed Oct. 6, 1943 June 14, 1949. .1. E. WHITFn-:LD

HELICALASYMMETRICAL THREAD FORMS FOR FLUID DEVICES 9 lSheets-Sheet 5 Filed Oct. 6. 1943 g IN1/@MICR June 14, 1949. J. E. WHITFIELD 2,473,234

HELICAL ASYMMETRICAL 'I HREAD FORMS v FOR FLUID DEVICES A Filed'oct. 6, 194s l 9 sheets-sheet e M INVENTOR 2? if, BY

J. E. WHITFIELD HELICAL ASYMM Filed Oct. 6, 1943 '9 Sheets-@Sheet 7 June 14, 1949. E WHITFIELD 2,473,234

HELIGAL ASYMMETRIGAL THREAD FORMS FOR FLUID DEVICES Filed Oct. 6, 1943 9 Sheets-Sheet 8 IN VENTOR MEW June 14, 1949. f J E, WHITHELD 2,473,234

HELICAL A'SYMMETRICAL THREAD FORMS FOR FLUID DEVICES Filed Oct. 6, 1943 9 Sheets-Sheet 9 Patented June 14, 1949 UNITED STA-TE HELICAL ASYMMETRICAL- THREAD FORMS FR FLUID DEVECES Joseph E. Whitfield, Hamilton, ohio' Application October. 6, 1943, Serial No. 505,135

This invention relates generally to rotary screw pumps, motors, blowers, compressors, and similar fluid devices in which the rotary engaging members are provided with intermeshing complementary helical threads and operate in a casing having inlet and outlet openings. This invention is directed more particularly to the character and shape of the threads of the members.

The rotary members of uid devices of this character usually have two or more complementary helical threads and are rotatably supported in a casing with their axis parallel and with their complementary threads intermeshing. The threads and troughs or grooves are preferably formed to provide a continuous seal line between the rotary members and the crests or perimetral edges of the threads of the members seal with the walls of the casing. The threads thus cooperate with each other and with the Walls to form duid pockets that advance and move from one end of the casing to the other when themembers are rotated. To properly interengage and seal with one another and with the casing the complementary threads of one member have a right hand helical. twist while the threads of the other member have a left hand helical twist. Thus any fiow of uid from one end of the casing to the other passes through the troughs or grooves of the threaded members and when operating as a motor the fluid pressure on the thread or lobe surfaces propels them but when operating as a pump, blower cr compressor these surfaces propel the iiuid through the device.

It is preferable to construct threads on one member all or full addendum with the pitch circle being less than the root diameter. This member is commonly known as the rotor. To be complementary the threads on the other member are all. or full dedendum with the pitch circley being greater than the overall diameter of the member, This member is commonly referred to as the gate. This choice of the thread form is not necessary to produce an operative structure but has been found to be more desirable for this character of machine. Again the number of threads on the rotary members is a matter of choice. However it is beiieved that the most eicient construction is with two threads on the rotor and four threads on the gate which form is 'used for the purpose of describing this invention. Y

In the United States Letters Patent to 'Whit eld No. 2,287,716 the lobe surfaces of the rotor helical threads are generated or described bythe continuous crest edges of the helical gate threads'- and the curved troughs or grooves ofthe gate 28 Claims. (CI. 1133-128.)

are generated ordesoribedv by the-continuous crest edges of the helical-.threads of the rotor. thread form provides a continuous seal line between the members when they are assembled in intermeshing engagement and rotated. In the United States Letters Patent to Lysholm No. 2,12%,522 cnefiank. ofthe lobe of the rotor threads is generated while the opposite ank of the lobev is in the form` of a-'circular arc and the corresponding side of the cooperating groove of the gate is likewise made in the form of a circular arc of the same radius struck from a corresponding point on the' pitch circle of the latter. this disclosure it is said that the radius of curva ture is increased toward the root of the lobe of the rotor so that thecrest edge of the gate travels substantially iny contact with that part of the rotor lobesuriace. This structureY was found to require increased running tolerance' owing to the fact that the radius of curvatures are struck from points ony the'l pitch circles which become congruent when thefrotdr lobe is fully meshed with the gate. Ithas been determined that to increase the radius toward the roo't of the lobe will pro-'- Q ducean' inoperative mechanism as the additional metal on these surfaces creates an interference which' prevents the rotary member from rotating. There is no single radius that can produce a suitable curve that would provide a theoretically perfect seal prevent rotor' interference. Again imperfect seaiing also results from the increased radius of curvature and produces excess leakage between the members. It has been discovered that this portion of the lobe must be generated, or described1 by the continuous crest edge of the gate thread", as no single radius can produce a suitable curvel that would provide a theoretically perfectv seal andu prevent rotor interference.

The principal object of this invention is to provide an improved asymmetrical thread structure which overcomes these disadvantages.

Another object is the provision of complementary asymmetrical rotor and gate thread structures wherein one side of the thread surface of the rotor is generated by the continuous crest edge of the gate and the other side is arcuatabeingsubstantially circular for the extent of the intereng'agement of the threads at their full mesh position and `generated from this circular surface to the root thereof by the continuous crest edge of the gate.

. Another object is the provision of complementary asymmetrical. rotor and gate thread structures wherein a portion of the adjacent lobe faces are constructed of matched and substantially circular surfaces having different radii.

Another object is the provision of a rotary screw device wherein the threads are asymmetrical to provide a leakage connection between adjacent pockets which acts as a balancing groove by connecting the advancing pockets to discharge before their leading edges are in port registration and vents to discharge the preceding pocket as it moves toward infinity.

Another object is the provision oi a rotary screw device having an asymmetrical thread form with a generated pressure face and a substantially circular suction face which seals the ends of the threads to the inlet when in the full mesh position and permits an enlarged discharge port opening in the casing.

Another object is the provision of a pair of rotors having complementary asymmetricai surfaces which form a radially disposed sealing band across'the arcuate thread surfaces which extends axially of the members on both sides of the full mesh position.

Other objects and advantages appear in the following description and claims.

In the accompanying drawings a practical embodiment illustrating the principles of this invention is shown wherein:

Fig. 1 is a longitudinal sectional view of the luid device comprising this invention.

Fig. 2 is an enlarged transverse sectional view of the asymmetrical thread structure with parts broken away illustrating the difference between this thread form and that of the generated symmetrical thread form.

Fig. 3 is a perspective view of the asymmetrical thread structure comprising this invention illustrating the leakage or balancing path between adjacent pockets, which path is created by the asymmetrical thread structure.

Fig. 3a is a view similar to Fig. 8 showing the rotor members at a different angle.

Fig. 3b is a view similar to Fig. 3 showing the opposite sides of the rotary members.

Figs. 4, 5, 6, 7, 8 and 9 are diagrammatic views showing the rotor and gate in a series of intermeshed positions when the latter is rotated in a clockwise direction.

Fig. 10 is a side elevation of elongated rotor and gate members in intermeshed relation.

Fig. 11 is a side elevation of the elongated rotor and gate members of Fig. 10 which have been separated to show the sealing line and the sealing band of the sealing engagement between the members when in intermeshed position.

Fig. l2 is a view showing the construction of the circular arcuate lobe and trough surfaces from centers on the pitch circles of the rotor and gate respectively.

Fig. 12a is a view showing the relative positions of the center points from which the circular arcuate lobe and trough surfaces are struck, which center points lie within the gate pitch circle in one instance and within the rotor pitch circle in another instance.

Fig. 13 is an exaggerated sectional view of the sealing band between the rotor and the gate.

Fig. 14 is an enlarged view of a rotor profile the crest of which is cylindrical.

Fig. 15 is a longitudinal view in section of the device illustrating the ultimate outlet port line.

Referring particularly to Fig. 1 of the drawings, the housing or casing i of the fluid device is provided with an integral end wall or head ll at the right end and a removable end wall or head I2 at the left end. The latter may be made in a single section but it is preferable to maize it in two parts to simplify the machining operations. rihe casing is divided into two parallel cylindrical chambers I3 and I4 disposed side by side and merging together forming a large chamber, the cross section of which is in the form oi a ligure 8. The intersection of the two chambers i3 and l forms sharp inwardly extending edges as indicated at l5 and I6 in Fig. 9. These edges wouid normally extend for the full length oi the chamber but are interrupted or cut away at diagonally opposite sides of the casing to provide for the inlet and outlet ports.

The end walls Il and l2 are provided with opposed bearing assemblies l1 and i3 axially aligned with their respective chambers i3 and lli for supporting the gate 2Q by its shaft 2l and the rotor 22 mounted on the hollow shaft 23 which in -turn is provided with an internal spline connection to receive the shaft 24. The shafts 2l and 23 extend beyond the bearing in the right end wall and have the timing gears 25 and 2G secured thereto. The diameters of these gears are determined by the thread ratio and pitch circles of the rotor and gate members which must be maintained in their proper phase relation during their operation. The shaft 24 is splined at the left end for connection with the hollow shaft 23. The other end of this shaft 24 extends beyond the timing gears and is splined to receive the pinion 21 which is employed to drive the rotary members when the device is operated as a pump or blower or to drive other mechanism when employed as a motor. The gears and bearing assemblies are covered by end plates 28 and provide for spaced bearing support for the pinion 21. A small portion of the cylindrical wall covering the pinion 2l is open for the purpose of connecting the meshing gear.

The bearing assemblies Il and I8 are provided with lubricating circuits including passageways, seals and oil slingers for directing the flow of the lubricant therethrough. Inwardly adjacent the lubricant seals the walls H and l2 are provided with vents leading from uid seals around the shafts to the atmosphere directly discharging the lubricant and the motivating iiuid to prevent any intercommunication between these fluids.

-The bearings and timing gear assembly are similar to that shown and described in Patent 2,287,716 and the manner in which the rotary members are mounted is disclosed in application Serial No. 480,792, filed March 27, 1943, now

VPatent 2,442,254, issued May 25, 1948.

The gate member 20 used for the purpose of this disclosure has four threads or teeth which follow a left hand helix and which are preferably all or full dedendum as shown in Figs. 2, 3 and 4. The pitch circle 38 ci the gate is greater 'in diameter than the overall diameter of the gate itself.

The rotor member 22 is provided with only two threads or teeth which follow a right hand helix and which are preferably all or full addendum. The pitch circle 3i of the rotor is smaller in diameter than the root diameter oi the rotor. This choice of pitch circles provides smooth and slightly lleted corners at the root of the rotor threads.

These rotary members thus have a thread ratio of two to one which is the same ratio for the diameters of the pitch circles and the number of teeth on the timing gears. As previously stated, the number and ratio of threads is a matter of choice but the two to one thread form shown herein is preferable.

The rotor threads preferably extend 'through substantial-ly 180 uniform helix angle while the gate threads extend through substantially a 90o` helix and these rotary members operate within their respective chambers i3 and i4 with a running clearance between the side and end walls of these chambers and between the rotary members themselves. This running clearance is sumcient to permit the members to freely rotate under an overload with the closest possible clearance. that allows for thermal expansion due to the generation of heat inthe transformation of energy within the device or by reason of the teni perature of the uid medium.

Referring particularly to Fig. 2, the left side of the lober of the rotor 22 is generated from the root surface 32 up along the i"ace 33 to the left crest edge 34. From this-edge across the crest to 4l? the surface is circular, being struck from the axis of' the rotor, andl from ill down the right side ofthe rotor lobe the surface. 35 is substantially circuiar' to the vicinity of the point 35 which is adjacent the crest edge of the gate. The center ci this circularsuriace may be located on the pitch circle or on either side thereof as described with reference to Figs. l2 to 14. From the vicinity of the point 316 the lobe surface 3l is generated tol the. base of the root 32.

The trough of the` gatei 2li' being substantially complementary to the form of the rotor threads has a generated surfaceV 38Y from the crest to the point 34 and a substantially circular arcuate surface 39' on the other side extending between the

points

34 and 36 or' to the edge of the gate crest which is also described with reference to Figs. 12 to 14.v

From the pointl 4B'- on the right dank, equivalent to the point 34, to the point 35 may be said to provide an asymmetrical thread `form. However the choice of a substantially circular arcuate section for a portion of the thread flank in creases the thickness of the tooth on that side which results in the whole of thek right flank be'- ing asymmetrical with respect to the longitudi-A nal axis of the tooth as shown in Fig. 2, even though a portion is a generated surface. This is' clearly shown bythe dotted symmetrical thread flank di which extends from the crest lil to the thread root 32. The width of the rotor thread' crest of this symmetrical form lies between the poi-nts 3d and l and may be considered too wide for' this thread form which could be remedied by extending of the gate.

If the substantially circular arcuate surface elli were extended it would follow the dotted line fifi' to the thread root of the rotor. Thus the spacek between this line and the generated surface 3l represents the additional material required on this il'ank of the lobe to prevent the formation-v of a leakage path between the members. By requiring that portion of the ank designated by the reference number 3l to be generated by the adjacent crest edge of the gate a continuous sea-lk is provided. between the rotary members, othere wise this space would always provide a break the seal line causing a directleakage from the inlet to the outlet which ordinarily represents considerable differential in. pressure. Since this? leakage path interrupts the seal line and` is be.`` tween the rotary members themselves it is: not affected by the'extent or location. of the inlet and the generated flanks closer to the center surfaces produce a ridge at point @il an inter-v ference is created which prevents the members from rotating and the seal line therebetween is broken.

The height of the rotor threads is thus limited by the selection of the circular surface 35, whether its center is located on the pitch circle or on either side thereof. as the rotor thread crest 34 to 40 must coincide with the circular surface 35 to form a smooth continuous lobe surface.

This thread form also produces a second leakage path between adjacent pockets which to be avoided materially limits the size of the outlet port opening when the substantially circular arcuate lobe surface 34 to 36 of the rotor is used as the pressure face. On the other hand. the portsY may be reversed and the generated surface of the. rotor is used as the pressure face, thus restricting the inlet but not the outlet por-t. This choice is made by decidi-ng which direction the device is to rotate.

This second leakage path is caused by the crest .l edgev 23 of the" gate abruptly approaching or leaving the arcuate. surface 3d in the vicinity of point d'4 on the rotor lobe, which is approximately 15 from the full mesh position as shown in Fig. 6,

depending upon the direction of rotation of the members. The extent of this leakage path with reference to a symmetrical thread form is from the point la of Fig. 6 to the point :it of Fig. 5, which on a symmetrical thread form would represent the right thread crest of the rotor lobe.

If Figs, 4 to 9 are read in the reverse order theyr simulate different sections of the same rotor and gate members reading from left to right in Fig. 10' in accordance with the relative rotary positionk of the rotor and gate members. Actually Fig. 9 may represent the transverse section of the members at il, 9 of Fig. 1o and Fig. 8 the transverse section at l, 8 and so on. Thus if the rotor and gate members are revolving as indicated by the arrows of Figs. l and 4 to 10 this V-shaped leakage path precedes the engagement of the gate crest edge with the circular arcuate surface of the rotor lobe and is shown at il@ in Flgs. 3 and 3a.

This' leakage path does not occur in the symmetrical thread form as the crest edges of the gate meet and leave the crest edges oi the rotor at the juncture of the chambers il and i2 which are designated by the reference numerals I5 and I5 but in the asymmetrical thread form this leakage takes place within the boundary of the chamber walls and occurs only on the circular arcuate or right side of the rotor and gate members. The left side being wholly generated has no leakage path.

In Fig. 4 the crest edge di oi the gate is at the root of the generated lobe surface and is about to travel up along said surface as the members rotate. When the members reach the position shown in Fig. 5 the gate crest @3 would engage the rotor lobe at'fiii if-v the thread' forms 7 were symmetrical and wholly generated on both sides, but here a considerable gap 4t is shown.

As the members rotate to the position shown in Fig. 6 the edge 43 engages the lobe surface in the vicinity of the point 44 and the gate crest edge 4l is in the vicinity of the point 48 on the generated lobe surface. In Fig. 'l the members are in their full mesh position as shown in Fig. 2. Between the positions shown in Figs. 6 and 7 the mating circular

arcuate surfaces

35 and 39 of the rotor and gate respectively are in substantial contact, thus providing a wide sealing line during this portion of the intermeshing engagement between the members. The cross section of this sealing zone is shown at 5% in the enlarged view of Fig. 13 wherein the seal is produced by the running clearance between the gate and the rotor which is normally from l to 20 thousandths of an inch. The borderline Zones l on either side of the .sealing zone 59, defined by the

points

36 and 44, have substantially the same clearance dimension as the running clearance so they also aid in extending the eifective width of this band seal. In a front View the

points

36 and 44 lie in parallel transverse planes on the rotor thread flank which form the boundary lines of the sealing Zones 5i, as shown in Fig. 11.

In Fig. 8 the gate crest #il is about to leave the generated rotor crest at the chamber intersection i5 and in Fig. 9 the gate crest 43, which has remained in engagement with the generated rotor lobe surface since passing point 44, has reached the thread root of the rotor. The positions of the rotor and gate as the crest of the latter engages the root surface of the former are not shown. However the cylindrical root surface of the rotor is larger in diameter than its pitch -circle and is therefore greater than the cylindrical crests of the gate threads. Thus the gate crests have a combined rolling and sliding action across the root surfaces of the rotor.

The sealing line 52 between the gate and rotor is shown on the members in Fig. 11. This sealing line is the opposite hand on the gate than on the rotor. Starting from the left end of the rotor the seal line 53 is parallel with the axis of the rotor as it travels across the root surface 32 to the base of the lobe. The sealing line then travels up across the face 3l of the lobe as shown at 54 following the continuous crest edge 43 of the gate to the vicinity of the point tri on the rotor lobe as shown in Fig. 6. The sealing line then changes into a band that extends from the line 54 across the lobe surface 35 to the crest edge 34 of the rotor lobe. The borderline zones 5l of this band are bounded by the parallel transverse planes in which the points 36 and it lie. The width of this sealing band is determined by the extent of substantial sealing engagement between the substantially circular arcuate surfaces of the gate and rotor. If they do not remain in contact for an appreciable angle of rotation the band is correspondingly narrow.

The sealing line then continues back along the crest edge Sli of the rotor lobe as indicated at 55 to the position where it intersects the crest edge 4l of the gate which would be at the juncture I5 of the chambers I3 and i4. The seal line then follows the gate crest edge 4'! down across the generated face 33 of the rotor lobe as shown at 5G to the rotor root surface where it continues parallel with the axis of the rotor as originally indicated at 53 and thus completing one complete cycle of the sealing line.

If the generated surface 3l were not provided between the vicinity of the point 3B to the root surface 32 of the rotor, the whole of the sealing line section 54 would be omitted. This would create the leakage path formerly described between the generated line 3l and the dotted circular line ft2 in Fig. 2. By providing the generated suriace 3l on the rotor lobe and arranging it so that the generated surface and circular arcuate surface 35 overlap between the points 36 and 44 a continuous seal with a wide sealing band is produced. This is an important advantage of this invention.

if the rotor member of Fig. l0 is turning in the direction of the arrow 5l the sealing line will move from left to right in Fig. 11. The same eiiect may be had by moving the vertical edge of a sheet of paper from right to left over the figure. The generated lobe surface 33 of the rotor becomes, the pressure surface due to this direction of rotation which would require the outlet port to be on the rear side of the rotor and gate member as viewed in Figs. 3, B a and 10.

The dotted line 43a extending from 11.4 on the band seal in Fig. l1 represents the approximate position that the crest edge 43 of the gate would be if the upper portion of the rotor lobe were generated in place of being a substantially circular arcuate surface. The line 43a is thus a continuation of the seal line 54 and represents the lobe face boundary of the V-shaped leakage path ri.

Thus if the rotor is rotating in the direction of the arrow 5l the sealing band 5D will move to the right on Fig. 10 and this V-shaped leakage path 46 will permit the previous pocket, which lies to the right of the seal lines 5B and 55, to escape to the outlet until the band 50 reaches the wall of the right casing head ll and the entrapped iilnd between the seal lines 55 and 5S and the dotted line 53 is relatively small but must be vented by a groove or cut away portion on the end of the rotor. However a materially greater portion of the fluid would be trapped if the thread form were symmetrical and the seal line extended along the dotted line 43.

If the rotor member is turned in the direction opposite to that of the arrow 5'! or in the direction of the arrow 59 in Fig. 11 the circular arcuate lobe surface of the rotor becomes the pressure surface and the discharge or outlet is on the near side of the members in Fig. 3bI and to the right or toward the removable head l2. The seal line is the same as that shown in Fig. ll but is moving toward the right of the figure. Thus the forward tip of the next succeeding pocket, between the seal lines 55 and 5E, opens up before the band sealing zone 5H runs out by reaching the end of the rotor member, at which time the pocket is completely run out, which condition limits the extent of the outlet port in the end wall I2. On this side of the members there is no leakage path to aid in discharging the pocket that is running out and the pointed end of the sealing line section 5t and 56 precedes the band 50. Thus the ends of the rotor members must be provided with offset sealing plates or end abutments to seal the space between 55 and 5G and a groove to permit the large volume between the sealing lines 54, 5G and 55 to escape to discharge as the pocket runs out. In view of this fact it is better to rotate these members as indicated by the arrow 5l and use the generated lobe face as the pressure face.

As previously stated, the leakage path 46 connects the adjacent pockets as viewed in Figs. 3,

l1 previously explained this crest edge 43 comes into sealing engagement with the rotor lobe surface 35 at point @d and continues in sealing enga-geu ment until it reaches the root of the rotor lobe. This is an important feature of this invention.

As shown in the construction view of Fig. 12 the center points Ella to 31e on the rotor pitch circle 3i slightly lag the corresponding points Sta to 38e on the gate pitch circle 3c and in no position are these sets of points congruent.

The circular surface of the gate thread trough is shown in its progressed rotary positions as indicated by the solid lines 39 from A to E struck from the corresponding positions of their respective centers Sila to 38e. In like manner the circular surface 35 of the rotor thread flank is shown in its corresponding rotary positions as indicated by the heavy broken lines 35 from A to E each of which is struck from the progressive centers 3io to Sie on the pitch circle 3l. With proper selection of the radii these circular surfaces become substantially congruent and form a substantially single line as indicated by these arcs which show the different relative positions of these mating circular surfaces for different de grees of rotation of the members. When these arcuate surfaces are constructed and then lappezi in by rotating the surfaces in contact with a fine abrasive it is obvious that the high spots are removed and the surfaces become substantially true mating surfaces which do not have the same length of radius nor are they truly circular, but in no case will their difference be as great as the normal running clearance of the blower. These particular distinguishing features provide a great improvement over thread forms of this character.

In Fig. 12 the centers Bla, and 3de of the cir cular surfaces 35 and 39 on the rotor lobe and. gate trough are on their respective pitch circles. However these centers need not always be located on the pitch circles 3c and 3| but may be placed on circles within either pitch circle and these circles may or may not be tangent.

The circles upon whichV these centers travel may be defined as the gate or rotor circle of the radius describing the circular surface on the gate thread trough or the rotor thread flank. These circles are shown in Fig. 12a where the gate circle '8 of the radius describing the circular surface 39 on the gate thread lies within the gate pitch circle 3B and the corresponding rotor circle 'li of the radius describing the circular surface 35 on the rotor thread flank is tangent thereto. The centers of the

circular surfaces

35 and 35 are ita and 'Ha respectively and they progress to me and 'ile as the members rotate in the direction of the arrow El of Fig. 12a. with the gate centers leading the rotor centers which rotation is in the opposite direction to that of Fig. 12.

The rotor circle 13 of the radius describing the circular surface on the rotor thread flank produces another thread form. This circle is within the rotor pitch circle 3l and the corresponding gate pitch circle 12 is tangent thereto.

Thus three distinct thread forms are illustrated by Figs. 12 and 12a. In the first the center points of the radii describing the circular surfaces on the threads of the members lie on the pitch circles and in the other two forms these centers lie on the gate and rotor circles which are alternately within the pitch circles of their respective members. Other thread forms may be constructed by using a combination of these center points. Thus the center point 75a on the gate circle 'f may be used with the center point 'la on the rotorv pitch circle 3i. Again the center point 'ida Imay be used with 13a of the rotor circle As another combination the center point a on the gate pitch circle 3U may be used with the center point '53a on the rotor circle i3. Other combinations may be made with the centers on these three gate and rotor circles together with the changing of the relative positions of the two centers from a leading to a lagging position to obtain different thread forms and different widths of the sealing band with varying degrees of sealing or running clearance between the members. These structural features provide an important object cf this invention.

The enlarged profile of the rotor lobe shown in 14 illustrates the relation of different portions of the thread surfaces. The gate trough surface is made up of the generated surface 38 and the circulararcuate surface 39 which imperceptibly merge together forming a smooth continuous surface but the mating lobe surfaces of the rotor define the crest edge 3d which emphasizes one margin between the different rotor lobe surfaces. As previously stated the generated sur- 'face 3?, begins at the root surface 32 and extends up the side of the lobe, merging with the circular surface in the vicinity of the point 365. The complete circle of the circular arcuate surface 35 is shown in Fig. 14 as having the radius r and the generated surface 3l merges with this surface at 3e. rhe generated surface 3? and the arcuate surface form the same surface between points 35 and it and begin to digress on the remote sides of these points. The crest edge 43 of the gate engages this common surface at point di! and stays in engagement until it reaches the root of the generated surface 37 but when the gate crest edge i3 reaches the vicinity of point 35, which is on one boundary line of the borderline sealing zones 5l, the mating circular surfaces 55 and 39 begin to leave each other. The length of the borderline sealing zones 5l, on each side of the zone 5i), may thus be represented by the arcuate distance between the crest 3d and the point 44 on one side and the point 35 on the other side.

As previously stated, the circular surface 35 extends to the point but the lobe surface is made cylindrical between the

points

34 and 40 which are equidistant from the axis 66 of the thread forms, as indicated by the small circle 61 in Fig. 14. The arc 68 struck between the points 34 and l0 using the axis of the rotor as the center with the radius R, which is the radius of the chamber It, lies slightly within the circular surface 35. But this short arc 68 is substantially the same as the arc of the same length on the surface 35 and they appear to merge imperceptibly at the point lill. Thus the thread form is symmetrical from the point 59 on the thread axis 65 in both directions to the points 34 and 4U.

In the structure illustrated in Fig. 14 the center 3io of the circular surface 35 is located on the pitch circle 3l below the thread axis 66 and this surface has the radius of r. If the circle of the same radius r is struck from the point 3B it will substantially intersect the point 4U on one side and the root of the generated surface 3l on the other side where it intersects the root surface 32 of the rotor.

When these surfaces are formed and the radius ofthe circular arcuate surface 3Q of the gate is made less than the radius r its center full mesh position would be on the pitch circle 30 at point Sta slightly above the point 3|a and the thread axis 66 in Fig. 14. The rotary members may then be assembled on Iadjustable .axes and operated with their mating surfaces in engagement to lap them in. Theseflapped surfaces thus change from circular to substantially circular surfaces and produce true thread forms that when provided with approximately -fifteen thousandths of an inch running clearance form a good seal for fluids such as air. This clearance is suil'icient to prevent contact under heavy load and high temperature conditions. Thermal eX- pansion merely decreasesthis running clearance and increases the resistance to leakage.

In view of the fact that the inlet is closed prior to the development of the largest pocket volume and since the leakage path or fluid connection 4B begins to open simultaneously with the closing of the inlet, there can be no pressure generation due to a decreased pocket volume between registration with the inlet and outlet ports. Thus liquid as well as gases may be pumped by this device when the generated lobe surface is used at the pressure surface. If the rotors are turned in the opposite direction using the` substantially circular surfaces as the pressure faces the device is less efcient than a symmetrically generated lobe surface since the pockets cannot be closed to the inlet until after the formation of the largest pocket volume and the leakage path or fluid pocket connection 46 creates an inletv blowback if the inlet port is positioned at the ultimate por-t outline Thus the most eii'lcent operation and utility of this thread form is obtained when the generated surface 33 is employed as the pressure surface of the rotor lobe. This is an important feature of this invention.

I claim:

1. In a fluid device of the character described the combination of a housing having iiuid inlet and outlet openings, a rotor member and a gate member rotatably disposed in parallelism in said housing and having mating substantially complementary inter-meshing helical threads and troughs, the crests of the gate threads being cylindrical and bounded on each side by continuously extending helical edges, the crests of the rotor threads being arcuate and bounded on one side by a continuously extending helical edge, one flank of the rotor thread and the corresponding side of the gate thread being generated by the adjacent continuous crest edges of the gate and rotor respectively, the other flank of the rotor thread being generated from the root to part way up the flank by the adjacent continuous crest edge of the gate, the remainder of the gate thread trough and the connecting portion of the rotor thread flank between the generated surfaces being of different radii fro-rn each other and each being substantially circular in a plane normal to the axes of the members to form substantially complementary mating surfaces.

2.. The structure of claim l characterized in that the substantially circular surfaces are lapped in creating slightly changing radii on these gate and rotor surfaces.

3. The structure of claim 1 characterized in that. the complementary matingl surfaces are constructed to provide a continuous -seal line between the members, a part of which is formed by the substantially circular surfaces Which provide a sealing zone of material width for the full ex'- tent of the substantiallycircular surfaces` 4,. The structure,v of claim l characterized in that, the radius of theI substantially' circular surface, of the. gate, threadg is less in; length than i4 .the radius' of the substantially circular surface of the rotor thread.

5. The structure of claim 1 characterized in that the pitch circle of the rotor -is smaller than its cylindrical root surface and the pitch circle of the gate is greater than its overall diameter, and the radius of the substantially circular surface of the gate thread the center of which lies on its pitch circle is less in length than the radius of the substantially circular surface of the rotor thread the center of which lies on its pitch circle.

6. In a fluid device of the character described the combination of a housing having fluid inlet and outlet openings, a rotor member and a `gate member rotatably disposed in parallelism in said housing and having mating substantially complementary intermeshing helical threads and troughs, the crests of the threads of both members being cylindrical, one side of the rotor crest and both sides of the gate crest being bounded by .continuously extending helical edges, one flank of the rotorthread and the corresponding side of the gate thread being generated by the adjacent continuous crest edges of the gate and rotor respectively, the other flank of the rotor thread being generated from the root to part away up the dank by the adjacent continuous crest edge of the gate, the remainder of the gate and rotor thread surfaces being connected by surfaces of different radii from each other which are substantially circular in a plane normal to the axes of the members to form substantially complementary mating surfaces.

7. The structure of claim 6 characterized in that the substantially circular surfaces are formed with different and changing radii.

8. The structure of claim 6 characterized in that the complementary mating surfaces are constructed to provide a continuous seal line between -the members, a part of which is formed by the rotor thread crest together with the substantially circular surfaces which provide a sealing zone of material width for the full extent of the circular sealing surfaces.

9. The structure of claim 6 characterized in that the radius of the substantially circular surface of the gate thread is less in length than the radius of the substantially circular surface of the rotor thread.

l0. The structure of claim 6 characterized in that the pitch circle of the rotor is smaller than its cylindrical root surface and the pitch circle of the gate is greater than its overall diameter, and the radius of the substantially circular surface of the gate thread the center of which lies on its pitch circle is less in length than the radius of the substantially circular surface of the rotor thread the center of which lies yon its pitch circle.

1l. In a fluid device of the character described the combination of a housing having a plurality of parallel cylindrical chambers closed at their ends and which intersect to form a common chamber, a rotary member operable in each chamber and having running clearance with the walls of the chamber, the adjacent rotary members cooperating as a rotor and a gate and provided with substantially complementary interimeshing helical threads with crests and troughs which mate and cooperate with each other and the walls of the chambers to form uid sealed pockets that progress from one end of the housing to the other when the members are rotated,

`inlet and outlet port openings diagonally disposed from one another in opposite sides of the housing, the pressure flank of the rotor thread and the corresponding side of the gate thread being generated by the continuous crest edges of the gate and rotor respectively, the suction ank oi the rotor thread and the corresponding side of the gate thread being generated from the root to part Way up the flank by the adjacent continuous crest edge of the gate, the remainder of the gate thread and the connecting portion of the rotor thread between the generated surfaces being of different radii from each other and each being substantially circular in a plane normal to the axes of the members which produces a iiuid connection between successive adjacent pockets on the discharge side of the housing thereby limiting the extent of a possible inlet port opening and providing a restricted discharge prior to the registry of the succeeding pockets to the outlet opening.

12. The structure of claim 11 characterized in that the outlet port opening is constructed to permit the pocket that is running out to discharge through the fluid connection until the ends of the members reach their full meshed position when the pocket runs out.

13. The structure of claim 1 characterized in that the radius of a portion of the substantially circular surface on the gate thread trough the center of which lies on its pitch circle, is out of y phase and is less in length than the radius of a portion of the substantially circular surface on the rotor thread dank the center of which lies on its pitch circle, which provides a sealing zone of material width for the full extent of the Substantially circular surfaces.

14. The structure of claim 1 characterized in that the gate circle of the radius describing a portion of the substantially circular surface on the gate thread trough lies within the gate pitch circle, and the rotor circle of the radius describing a portion of the substantially circular surface on the rotor thread flank is tangent to the gate circle.

15. The structure of claim 1 characterized in that the gate circle of the radius describing a portion of the substantially circular surface on the gate thread trough lies within the gate pitch circle, and the rotor circle of the radius describing a portion of the substantially circular surface on the rotor thread flank is tangent to the gate circle, the radius of a portion of the substantially circular surface on the gate thread trough is out of phase and is less in length than the radius of a portion of the substantially circular surface on the rotor thread flank to provide a sealing zone of material width for the full extent of the substantially circular surfaces.

16. The structure of claim 1 characterized in that the rotor circle of the radius describing a portion of the substantially circular surface on the rotor thread flank lies within the rotor pitch circle, and the gate circle of the radius describing a portion of the substantially circular surface on the gate thread trough is tangent to the rotor circle.

17. The structure of claim 1 characterized in that the rotor circle of the radius describing a portion of the substantially circular surface on the rotor thread flank lies Within the rotor pitch circle, and the gate circle of the radius describF ing a portion of the substantially circular surface on gate thread troughs is tangent to the rotor circle, the radius of a portion of the substantially circular surface on the gate thread 1d trough is out of phase and is less in length than the radius of a portion of the substantially circular surface on the rotor thread flank to pro- Vide a sealing zone of material width for the full extent of the substantially circular surfaces.

18. The structure of claim 1 characterized in that the gate circle of the radius describing a portion of the substantially circular surface on the gate thread trough lies within the gate pitch circle, and the rotor circle of the radius describing a portion of the substantially circular surface on the rotor thread flank is spaced from the gate circle sufficiently to produce a defined clearance between the mating substantially circular thread surfaces of the members.

19. The structure of claim 1 characterized in that the gate `circle of the radius describing a portion of the substantially circular surface on the gate thread trough lies within the gate pitch circle, and the rotor circle of the radius describing a portion of the substantially circular surface on the rotor thread flank is spaced from the gate circle sufliciently to produce a defined clearance between the mating substantially circular thread surfaces of the members, the radius of a portion of the substantially circular surface on the gate thread trough is out of phase and is less in length than the radius of a portion of the substantially circular surface on the rotor thread flank to provide a sealing zone of material width for the full extent of the substantially circular surfaces.

20. The structure of claim 1 characterized in that the rotor circle of the radius describing a portion of the substantially circular surface on the rotor thread flank lies Within the rotor pitch circle, and the gate circle of the radius describing a portion of the substantially circular surface on the gate thread trough is spaced from the rotor circle sufciently to produce a defined clearance between the mating substantially circular thread surfaces of the members.

2l. The structure of claim 1 characterized in that the rotor circle of the radius describing a portion of the substantially circular surface on the rotor thread flank lies within the rotor pitch circle, and the gate circle of the radius describing a portion of the substantially circular surface on the gate thread trough ls spaced from the rotor circle sufficiently to produce a defined clearance between the mating substantially circular thread surfaces of the members, the radius of a portion of the substantially circular surface on the gate thread trough is out of phase and is less in length than the radius of a portion of the substantially circular surface on the rotor thread flank to provide a sealing zone of material Width for the full extent of the substantially circuiar surfaces.

22. The structure of claim 1 characterized in that the radius of a portion of the substantially circular surface of the thread of one member is less in length than the radius of a portion of the substantially circular surface of the thread of the other member, and the center of curvature of one substantially circular surface leads the center of curvature of the other substantially circular surface when said members are rotated.

23. The structure of claim 6 characterized in that the radius of a portion of the substantially circular surface of the thread of one member is less in length than the radius of a portion of the substantially circular surface of the thread of the other member, and the center of curvature of one substantially circular surface leads the 17 center of curvature of the other substantially circular surface when said members are rotated.

24. The structure of claim 11 characterized in that the inlet port opening is constructed to seal each pocket the same instant that the threads of the rotary members create the fluid connection to said pocket on the discharge side of the device.

25. In a fluid device of the character described the combination of a housing having a plurality of parallel cylindrical chambers closed at their ends and which intersect to form a common chamber, a rotary member operable in each chamber and having running clearance with the walls of the chamber, the adjacent rotary members constructed as a rotor and a gate and provided with substantially complementary intermeshing helical threads with crests and troughs which cooperate with each other and with the Walls of the housing to form uid sealed pockets that progress from one end of the housing to the other when the members are rotated, one ank of the rotor thread and the corresponding side of the gate thread being generated by the continuous crest edges of the gate and rotor respectively, the other flank of th'e rotor thread being generated from the root to part way up the iiank by the adjacent continuous crest edge of the gate, the remainder of the gate thread and that portion on the rotor thread lbetween the generated surfaces being substantially circular in a plane normal to the axes of the members, iiuid inlet and outlet openings diagonally disposed from one another in the opposite sides of the housing, the edges of each port opening in the side walls of the housing matching the crests of the threads of the rotary members at 'its respective ultimate port opening, and each pocket being sealed by the wall of the housing denning one port opening at the same instant that it is opened to the other port opening.

26. The structure of claim 25 characterized in that the generated flank of the rotor is employed as the pressure iiank, and with the exception that the employed voutlet port opening is less in extent than its corresponding ultimate port opening, thereby restricting the discharge of uid from the pockets.

27. In a fluid device of the character described, the combination of a housing having a plurality of closed parallel cylindrical chambers which intersect to form a common chamber, a rotary member operable in each cylindrical chamber and having running clearance with the walls of the chamber, the adjacent rotary members constructed as a. rotor and a gate and provided with substantially complementary intermeshing helical threads with crests and troughs which cooperate with each other and with the walls of the housing to form fluid sealed pockets that progress from one end of the housing to the other when the members are rotated, one flank of the rotor thread and the corresponding side of the gate thread being generated by the continuous crest edges of the gate and rotor respectively, the other iiank of the rotor thread being generated from the root to part way up the ank by the adjacent continuous crest edge of the gate, the remainder of the gate thread` and that portion on the rotor thread betweenthe generated i surfaces being substantially circular in a plane normal to the axes of the members, and diagonally disposed inlet and outlet port openings in the sides of the housing wherein the employed outlet port opening extends in eect, due to the thread form, from the deiined ultimate port line in the side wall of the housing toward the end of the housing where the pockets run out.

28. The structure of claim 27 characterized in that the employed outlet port opening extends from the apex of the dened ultimate port line toward the end of the housing where the pockets run out.

JOSEPH E. WHITFIELD.

REFERENCES CITED The following references are of record in the 40 file of this patent:

UNITED STATES PATENTS