US1990750A

US1990750A - Variable volume pump and hydraulic transmission

Info

Publication number: US1990750A
Application number: US519571A
Authority: US
Inventors: Reginald J S Pigott
Original assignee: Gulf Research and Development Co
Current assignee: Gulf Research and Development Co
Priority date: 1931-03-02
Filing date: 1931-03-02
Publication date: 1935-02-12
Anticipated expiration: 1952-02-12

Description

Feb, 12, 1935. J 5 PIGQTT 1,990,750

VARIABLE VOLUME PUMP AND HYDRAULIC TRANSMISSION Filed March 2, 1931 6 Sheets-Sheet 1 Feb. 12, 1935. I js PIGQTT v 1,990,750

. VARIABLE VOLUME PUMP AND HYDRAULIC TRANSMISSION Feb. 12, 1 935. J 5 PIGOTT 1,990,750

I VARIABLE VOLUME PUMP AND HYDRAULIC TRANSMISSION Filed March 2, 1931 s Shets-Sheet 5 gwtwntoz Fb; 12 1935. R. J. s. PIGOTT 1,990,750

VARIABLE VOLUME- PUMP AND HYDRAULI C TRAN SMI S S I ON Filed March 2, 1931 -6 Sheets-Sheet 4 Feb. 12, 1935. R s plGOTT l990,750

VARIABLE VOLUME PUMP 'AND HYDRAULIC TRANSMISSION Filed March 2, 1951 s Sheets-Shae 5 Feb. 12, 1935, R. J. 5. QG TT VARIABLE VOLUME PUMP AND HYDRAULIC TRANSMISSION Filed March 2, 19:51 a Sheets-Sheei a Patented Feb. 12, 1935 VARIABLE VOLUME PUMP AND HYDRAULIC TRANSMISSION Reginald 'J. S. Pigott, Pittsburgh, Pa., assignor,

by mesne assignments, to Gulf Development Corporation, corporation of Delaware Research & Pittsburgh, Pa., a

Application March 2, 1931, Serial No; 519,571 27 Claims. (Cl. 103 -126) My invention relates to pumps for general use and applicable to hydraulic transmission systems.

The present invention includes improvements in the pumping mechanism shown in my prior Patent 1,742,215 of January 7, 1930 and has for an object the provision of a pump adapted to give a greater capacity per unit of occupied space.

' Another object of-the present invention is to materially increase the time for suction and discharge at any given rotational speed of the pump, thereby permitting the use of relatively low velocities of flow in the pump and thus reducing hydraulic shock losses.

A further object resides in the provision of' a pump having longer capillary passages and more teeth in contact at any one time than heretofore whereby leakage is considerably reduced.

A further object resides in the provision of a pump of the character referred to wherein the flow of fluid to the pump is substantially in the same direction as the rotation of the pump rotors whereby the fluid enters and leaves the rotors with practically no shock losses.

An additional object is to provide a pump which readily lends itself to manufacture, being simple and rugged in construction and comprising but a relatively few parts each of which may be economically machined.

Another object is to provide a variable volume pump including gears constituting the pumping elements and adapted to be moved more or less "into and out of mesh or engagement whereby to increase or decrease the capacity of the pump, simple and inexpensive means being provided to seal or cut off the portions of the gearsat any time out of mesh.

A further object is to provide a pump including a rotary shaft having bearings and packing, and means for increasing the flow of oil through the bearings of the pump shaft and at the same time relieving the pressure of the oil on the shaft packing.

Another object is to provide a pump which will be free of trapping and the noise and damage resulting therefrom.

Other objects and advantages of my present invention will appear from the more detailed description thereof.

The rotor combination or pumping elements of; my present invention consist of a pinion within an internal or ring gear, the latter having one tooth more than the former. .As herein hydraulic shock losses.

ing' drawings illustrating a preferred construcdisclosed the pinion is provided with eight teeth and the ring gear with nine. However, it is to be understood that the number of teeth on the pinion and ring gear permits of considerable variation. 5

An advantageous feature of the internal-external gear combination of one tooth difference,

is that this combination yields the maximum volume displacement per revolution for a given sized pinion and the suction and discharge 1o periods are each theoretically one-half revolution or 180 degrees. In all other teeth combinations, the suction and discharge periods are less than 180 degrees each, the teeth do not touch for a portion of the revolution, and a 'crescentr shaped filler is required to effect sealing. In the present construction the time for suction and discharge at any given rotational speed is very greatly increased over that of other designs. This permits the use of relatively low velocities of flow in the pump thereby reducing For a more detailed understanding of my invention, reference will be'had to the accompany- 25 tion adapted for use in the pumping of liquid and which will be described as applied to the pumping of oil. However, the invention is not to be construed as limited to 'the particular construction and use chosen for illustration but 30 that various changes and modifications may be made therein without departing from the spirit.

and scope of the invention as defined in the appended claims.

In the drawings:

Fig. 1 is a longitudinal sectional view of the variable volume pump in substantially full volume position, but with the gear and pinion about one-sixteenth inch out of mesh;

Fig. 2 is a sectional view on the line 2-2 of Fig. 1;

Figs. Sand 4 are sectional views taken on the lines 3-3 and 4-4 of Figure 1 respectively;

Fig. 5 is a sectional view of the follower member taken on the line 5-5 of Figure .2;

Fig. 6 is a section on the line 6-6 of Figure 5;

Fig. 7 is a perspective view partly in section and showing the pinion and ring gears partially disengaged and in approximately the half-volume position;

Fig. 8 "is a plan view of the variable volume pump as shown in Figures 1 to 7;

Fig. 9 is a vertical longitudinal section of a constant volume motor or pump; and

Fig. 10 is a transverse sectional view on the line 10-10 of Figure 9.

Referring more particularly to the drawings and to the variable volume pump of Figs. 1 to 8, at 1 is shown the pump casing provided at its upper portion with a suction inlet 2 and a discharge outlet 3 for the introduction and discharge respectively of the oil or other fluid being pumped. The ends of the casing are closed by means of a front head 4 having spud 5 and rear head 6 having spud '7 the latter spud being the larger in diameter and disposed eccentrically with respect to the spud 5. Disposed within the casing and adapted for rotation therein is an internal or ring gear 8 having teeth 9 and tooth spaces 10, the gear forming with the casing' 1 and a follower hereinafter described, the suction passage 11 and a discharge passage 12 communicating respectively with inlet 2 and outlet 3. The interior of the ring gear communicates with the suction and discharge passages by means of circumferentially'spaced ports 13 disposed between the teeth of the gear. A pinion 14 having teeth 15 is disposed within and adapted for engagement with gear 8 and is fixed by means of key 18 to shaft 17i which is driven from any suitable prime mover or source of power in the direction indicated by the arrow in Figure 2. A packing gland 18 and packing nut 19 are provided for shaft 17 while at 20 and 21 respectively are shown roller and thrust bearings for'the pinion.

The pinion is made with one tooth less than the ring gear which is mounted eccentric to the pinion by about one-half the tooth depth so that, as best shown in Figure 2, the teeth of the gear are fully engaged at the top, and just clear. the tips of the pinion teeth at the bottom. In the particular modification of the invention illustrated in the drawings, the pinion and gear are provided with eight and nine teeth respectively but the exact number is not important as long as the gear has one more tooth than the pinion. The arrangement is such that the gear and pinion mesh deeply overa considerable are at the top. At the bottom of the device, the tips of the gear and pinion teeth contact or maintain small clearance continuously for a space of about two and one-half gear teeth so that sometimes three and at other times two teeth are simultaneously in contact or at close clearance at the tips.

The front spud 5 extends inward to the side of thepinion 14 and is concentric with gear 8 to fit snugly inside the top of gear teeth 9 when the gear is moved to the left (Fig. 1) or in the direction of head 4. The rear spud 7 likewise extends inward to the side of the pinion and is of the same outside diameter as the pinion and concentric therewith.

Mounted for sliding movement within the easing is an annular follower member 22, the intermediate side portions of which, as best shown in Figure 5, are cut out to form with the casing and gear 8 the suction passage 11, communicating with inlet 2, and discharge passage 12, communicating with outlet 3, thereby leaving an upper abutment 23 and a lower abutment 24. The rearward end of follower member 22 (Figs. 1 and 7) is bored to fit snugly over spud 7 and is adapted for sliding movement thereon. The distance from the cut out portion or surface of the follower to the rear edge thereof opposite head 6 is equal to the length of spud 7 and the right hand side (Fig. 1) of ring gear 8 abuts against surface 25 of the follower. When gear 8 and pinion 14 are in full mesh, the follower member is all the way over to the rear end of the casing and against head 6.

The forward end of follower 22 is bored to receive gear 8 for rotation within the

abutments

23 and 24 and against vertical surface 25 and horizontal surface 25' and is closed by an annular follower plate 26 held within the forward end of the follower member by a retaining ring 27, the follower plate 26 fitting snugly over and slidable on spud 5 and forming the front wall of the pumping chamber enclosing the gear and pinion. The follower member and plate form a front balancing chamber 28 with head 4 and when the follower is moved forward, a rear chamber 29 is formed between the head 6 and the rearward end of the follower. A feather or key 22' is provided between the casing and the follower member for preventing rotation of the follower within the casing and on which the follower slides longitudinally.

From the structure Just described, it will be seen that, ring gear 8 fitting snugly within the follower member and plate and pinion 14 being fixed to rotary shaft 17, movement of the follower member frontwise toward head 4 will slide the gear partially out of engagement with the pinion, depending upon the extent of sliding movement of the follower, while movement of the follower member rearward toward head 6 will bring the gear back into full mesh with the pinion.

Abutments

23 and 24, in which gear 8 rotates, form a seal between suction passage 11 and discharge passage 12 at the top and bottom of the casing respectively while further scaling is effected between the suction and discharge passages by contact of the ring gear with the surfaces of the upper and lower abutments in which it rotates, the abutment 24 extending over an are great enough to span a little more than one tooth space 10 plus two gear ports 13 and the abutment 23 extending over an area about half that of abutment 24. A further seal is effected between the suction and discharge passages by contact between the teeth of the pinion and ring gear which, as already explained, mesh for a considerable are at the top of the casing while the tips of the teeth contact adjacent the bottom of the casing. A further seal around the periphery of the gear is formed by surface 25' in which the gear rotates, surface 25, and the inner face of plate 26. The surfaces 25' of the follower form a bearing completely around the ring gear.

It will further be seen from the construction thus far described that, when the gear 8 and pinion 14 are partially disengaged, the rear faces of the pinion teeth 15 are bounded by spuds 7. The tops or crests of the pinion teeth 15 out of engagement with the gear 8 are bounded and sealed by the rearward cylindrical portion of the follower member which snugly fits over the spud 7.

The toothed spaces of the pinion 14 are sealed from one another longitudinally of the pinion axis by the rearward bore of the follower member 22 when the gear is moved longitudinally of the pinion or out of engagement therewith. Also the front faces of the pinion teeth are partly covered by the spud 5, and where not thus covered are in communication over the spud 5 with the corresponding pockets ortooth spaces 10 between the ring gear teeth, and consequently the inner face of the plate 26. Similarly the ring gear pockets 10 are bounded on the front end of the follower plate 26 on the tips of the teeth by the spud 5 and the pockets so formed are in communication at the rear end with the engaged portion of the teeth and the pockets between the teeth of the pinion.

Each of these pockets is in communication with its own engaged tooth but not with any other pocket or any other tooth. Consequently, while these pockets are alternately under the suction and discharge pressure they can notbe simultaneously under both, and as the liquid to be pumped is incompressible it swings freely around the pump.

As previously described the spuds 5 and. 7 are cylindrical in shape and the latter is larger in diameter than the former. If the spud 7 were superimposed on Fig. 2 it would cover the area of 'a circle scribed about the tips of the pinion teeth 15. If the spud '5 were superimposed on Fig. 2 it would cover the area of a circle scribed about the tips of the ring gear teeth 9. Due to their being disposed 'eccentrically these spud circles would become tangent to each other at the bottom of the pinion where the pinion teeth 15 ride upon the crest of the ring gearv teeth 9, which is the'point of maximum disengagement.

The difference in the area of these spud circles would be a lunar shaped figure starting at the point of common tangency and extending therearound, being thickest at the top of the pinion or at the full mesh position.

A portion of this differential of the areas of the spud faces plays an important part in controlling the volume delivered by the rotating the pinion, which is fixed from axial-movement.

In-approaching this description from another view point the

spuds

5 and 7 may be looked upon as two differential stationary pistons dis-.- posed opposite to one another. The lower side of said pistons are tangent to a common horizontal plane. The plate 26 and the rear'cylindrical end of the follower 22 may be looked upon as being movable cylinders which are assembled in one unit and are slidably operable longitudinally of the

spuds

7 and 5 respectively. The cylinder (the plate 26) operating on the smaller piston (the spud '7) will have a larger area exposed to the internal pressure of the mechanism than does the other cylinder (the rear end of the follower member 22) which differential area causes the cylinder unit to move to the left in Fig. 1 when-a pressure is developed within the pump. The rotating gears mounted within the cylinder unit between the differential cylinders seal, with the

abutments

23 and 24, the

intake from the discharge side .of the mechanism and the actual useful differential area of the pistons is the half lunar shaped area of the cylinder plate 26 exposed to the discharge pres-- sure of the pump. The function of these differential 'spud faces will be enlarged upon after a more detailed discussion is had regarding some of the associated parts of the follower memben.

Attention is particularlydi'rected to the simplicity of the structuralparts employed in my improved pump; In thisconnection it will be noted that thepump includes but relatively few parts each of which in its manufacture ineludes or requires only simple machine operaions.

Essentially the pump includes but the casing.

or cylinder v1, the heads 4 and 6 carrying the

spuds

5 and 7 respectively, the pinion and the ring gear and the shaft for the pinion, and the follower structure. These parts, since they comprise for the most part only cylindrical surfaces, may obviously be completed 'or finished by a simple-machine operation.

The follower may be manufactured without the use of complicated or expensive machining operations and it and the plate 26 with the spud 5 perform the added function of sealing or en-' closing those portions of the pinion and ring gear which at any time may be exposed due to ,the gears not being fully in mesh, as when the pump is set to.deliver less than its full volume.

For the most part the follower obviously comprises cylindrical surfaces which may be easily machined and the follower does not include projecting fingers or the like to seal or fill any exposed portions of the pinion or ring gear.

As in my prior patent, above referred to, in the present construction variations in volume being pumped are effected by varying the extent of engagement of the teeth and the greater the degree of engagemenathe greater will be the pumping capacity of the device at constant speed. In the present construction, it will be seen that pressure inside the tooth spaces between the gear and pinion on the discharge side of the pump acts on the portionof the inner surface of the follower plate 26 which represents the diiferential between the spud areas and tends to force ring gear 8 out of mesh with of discharge. This tendency of the follower member to slide the ring gear out of mesh with the pinion is checked and the follower member is moved to vary'the capacity of the pump at constant speed by cons ruction now to be de-- scribed.

As best shown iii-Figs. 5 and 6, a valve chamber 30 is formedwithin upper abutment 23 of follower member 22 .and is provided with

ports

31, 32, and 33. Port 31, through passage 34,

connects-the valve chamber with the discharge .oted by the link 41 to the casing and having guide 42 fixed to the casing and upon which arm 40 may be locked in any desired position by .the wing nut and bolt 43.

The enlargement 39 of the pilot valve fills the valve chamber substantially pressure tight and in thenormal setting of the valve, the enlargement 39 is disposed directly opposite and just covering balancing port 32 which communicates with balancing chamber 28 through passage 35.

pinion 14 thereby tending to reduce the volume As best shown in Figure '5, pressure supply port 31, connected with the discharge side of the pump through passage 34, is disposed to the left of piston 39 while exhaust port 33, communicating with the suction side of the pump, is disposed to the right of piston 39.

In this normal setting of thepilot valve, it will be seen that any movement of the follower to the left or toward head 4, caused by the internal pressure in the pumping chamber working against the follower plate 26 by reason of the differential between the areas of the faces of the spuds, will cause port 32 to be slightly uncovered on the left of piston 39 thereby admitting pressure to balancing chamber 28 from the discharge side of the pump or passage 12 through passage 34, port 31, partialh open port 32, and passage 35. It should be noted that the area of the follower member 22 and the follower plate 26' exposed to the balancing chamber 28 is considerably larger than the area exposed to the internal pressure of the pump or the tooth spaces on the discharge side of the pump, which area may be represented as onehalf of the differential between the spud areas as above explained. It is thus evident that the pressure required in the balancing chamber 28 to balance the internal pressure of the pump need not be equal to the actual internal pressure of the pump because of the difference between these two effective areas. In this way, the different pressures applied on both sides of follower plate 26 may be made to balance and the follower and ring gear maintained in any desired setting with respect to the pinion since there is always more pressure available for use in the balancing chamber than is necessary.

Assuming the pump to be in the substantially full volume position of Figure 1, and it is desired to decrease the output of the pump or the volume being pumped, pilot valve 36 is moved to the left or toward head 4 by means of operat ing handle 40 so that piston 39 will be moved leftwise out of alignment with port 32 thereby establishing communication between balancing chamber 28 and suction passage 11 through passage 35, port 32, valve chamber 30, and port 33. The balancing pressure within balancing chamber 28 will thus be dropped and the follower member 22 will move forward in the direction of front head 4 by reason of the internal pressure within the pumping chamber acting upon the pumping chamber side of the follower plate 26 and such forward movement of the follower member will continue until port 32 is again covered by piston 39 whereupon communication between balancing chamber 28 and suction passage 11 will be cut oil. and the follower will come to rest at the new setting. Such movement of the follower member slides ring gear 8 laterally out of mesh with pinion 14 thereby decreasing the width of the engaging portions of the gear and pinion teeth and correspondingly decreasing the output of the pump.

'If it is desired to again increase the volume of liquid being pumped, pilot valve 36, is now moved rearward in the direction of rear head '6 by means of the operating handle and port 32 uncovered on the left side of piston 39. In this manner discharge passage 12 is placed in communication with balancing chamber 28 through passage 34, port 31, valve chamber 30, port 32 and passage 35. Thus pressure isadmitted to balancing chamber 28 from the discharge side of the pump through the passages and ports just noted and this pressure will naturally build .by touching at their tips.

up against the balancing chamber side of the follower plate 26 (which is of larger area than the area under pressure in the pumping chamber) until it overbalances the pressure within the pumping chamber on the opposite side of follower plate 26. The follower member 22 and gear 8 'will thus be moved rearward toward head 6 until port 33 is again brought in alignment with and closed by piston 39 thereby shutting off further supply of pressure from the discharge side of the pump to balancing chamber 28. Such rearward movement of the follower member and ring gear with respect to the pinion will increase the engaging portions of the gear and pinion and thereby increase the volume of liquid being pumped.

From the foregoing it will be seen that the follower will chase up.the pilot valve after each movement of the latter until the device comes back to the balanced position, that is, with the piston 39 closing port 32 and the total pressures on both sides of plate 28 being substantially equal. In this way the follower and ring gear can be moved under load when the pump is in operation without anyeffort and requires no mechanical locking in position except fixing the position of the pilot valve.

To balance the pressure in chamber 29 at the rear of follower member 22, this chamber is simply connected to suction passage 11 by a balancing port 44 which permits oil or other liquid being pumped to,freely enter or leave chamber 29 as the volume of this chamber is increased or decreased by movement of the follower. A relief port 45 is provided in valve chamber 30 behind front balancing piston 38, this port connecting with suction passage 11 for releasing or admitting liquid from behind piston 38 and also for completely balancing the valve 36 so that there is no end thrust thereon.

For cooling and lubricating the

bearings

20 and 21, spuds 5 and '1 are provided respectively with passages 46 and 4'1 leading from the bearings to the exterior of the casing and adapted to be connected back to the suction side of the pump by means of pipes 50, as best shown in Figs. 2, '7 and 8. The arrangement illustrated takes all the pressure ofi the shaft packing 18 and also provides a definite pressure drop from the pump pressure spaces through the bearings which permits a flow of oil through the bearings back to the suction side of the pump. Oil flows from the pumping chamber through

bearings

20 and 21, passages 46 and 47, and pipes 50 back to the suction side of the pump, without exerting full pressure on packing 18.

In the pump structure described and illus trated, it will be seen that the device is sealed against leakage without packing by reason of the relatively close clearances. Sealing between the ring gear and pinion teeth is accomplished in the usual manner of rotary gear type pump by the pressure of the teeth upon each other. For all combinations of external-internal gears of one tooth difference, it will be seen that if the tooth depth is twice the eccentricity, the teeth will seal at the disengaged or bottom position The ring gear is sealed at its outer periphery by the

follower abutments

23 and 24, and the bearing surfaces 25' and both the gear and pinion are sealed on their ends by contact with

spuds

5 and 7, follower member 22, and follower plate 26. As distinguished from the pump structure of my prior patent above referred to, it will be observed that in the present design there are at least two line contacts on the teeth in series between the suction and discharge sides, of the pump whereas in the construction of my prior patent only one such contact'was maintained. Theleakage in the present construction is therefore less than in that of my patent referred to.

Referring now to the constant volume motor or pump shown in Figs. 9 and 10 wherein parts corresponding to elements of Figs. 1 to 8 are designated by corresponding primed reference numerals, 1? is the casing provided at its upper portion with an inlet 2' and outlet 3 for the introduction and discharge respectively of the liquid handled. The ends of the casing are closed by means of heads 4 and 6'. The internal or ring gear 8' and pinion 14' aredisposed within the casing and adapted to be rotated therein by means of shaft 17', but since there is no necessity for variable volume, the

gears are not arranged to slide axially in or out of full mesh, but are maintained constantly in full mesh. The follower and associated mechanism for sliding one of the gears axially rela-. tive to the other are therefore omitted, and the constructionsimplified to this extent.

End plates 26' are fastened within flanges or extensions 8 in the ring gear by snap rings 27' forming a closure for the tooth spaces 10 by contact with the side faces of pinion '14. The extended flanges 8 may 'be used as a journal bearing running in casing 1, or may serve, as shown in Fig. 8, as outer races for roller bearings 20, a form of construction preferred when handling clean fluids. .The spuds and I serve to support the inner races for the roller bearings 20, as well as those for the pinion roller bearings 20. Suction passage 11 is sealed from discharge passage 12 by means of abutment 23' at the top and abutment 24' at the bottom,

,, these abutments being integral with the casing as shown.

When used. as a pump, the action is precisely the same as that for the variable volume pump, except that since the gears are always in full mesh, the volume discharged is constant for any given speed.

When used as a motonin conjunction with the variable volume pump, as a hydraulic variable speed transmission, the inlet 2 is supplied with" pressure liquid from the variable volume pump; the discharge3'. being at low pressure, delivering liquid back to the suction of the variable volume pump. Since the area of the teeth of the pinion and ring gear opposite the bottom abutment 24', where the gears are fully out of mesh and exposed to the difierence of pressure between inlet and outlet, is greater than that'opposite the top abutment 23', where the gears are fully in. mesh, by the area of one full tooth, a continuous torque is developed that causes rotation of the gears. When used in combination, as a hydraulic transmission, the ratio of rotational speed of the motor to that of the variable volume pump is substantially inversely proportional to the ratio of volume displacement of constant volume motor per revolution, to that of the variable volume pump, at whatever mesh position axially the latter may be. i

As in the variable volume pump, passagesflfi and .47 are provided in the constant volume pump or motor and these lead back to the suction side of the pumpso that oil may circulate through pinion roller bearings 20 without exer ing full pressure on shaft packing 18'. Also as laterally and very rapidly the full face With the radial ports 13 and 13' in the variable volume pump, the lower abutment 24 spans a little more than one tooth space and two gear ports 13 while the upper abutment 23' is about half the size of the lower abutment. The upper abutment is made smaller for a purpose'hereinafter described. As" indicated by the arrows, the direction of rotation in Fig. 10 is opposite that of Fig.2..

In most previous designs of rotary pump, especially gear forms, difllculty has developed due to trapping of liquid between the teeth at the point of deepest engagement or full mesh due to inability to vent the liquid fully therefrom. Unless such liquid is relieved up to the .point where the volume between the teeth becomes a minimum, extremely heavy pressures aredeveloped between the gears, making it impossible to prevent damage to the bearings and gears. In rotary pumps consisting of a pinion and internal gear differing by one or more teeth, but having the inlet and outlet ports opposite the lateral faces or sides of the gears, 'it has been found dimcult to eliminate such trapping completely inasmuch as the liquid must travel width of the teeth in order to escape.

opening practically the entire width of the teeth, the. path for relief of oil is short and itis possible to completely avoid trapping by suitable placement of the entering edges 48 and 48'-of the top abutments 23 and 23' respectively. For this purpose, it has been found desirable to set these entering edges 48 and 48' at least opposite the point of deepest engagement of the teeth where the volume between the pinion and ring gear has become minimum. For very high speeds and viscous liquids such as oil, it is desirable to set the abutment edges 48 and 48' even further forward in the direction of rotation by an amount not exceeding one-half the port width. The amount of such forward setting is determined by the rotational speed and the viscosity of the liquid pumped. By reference to Figs. 2 and 10, it will be seen that the arrangement of the sealing abutments 23 and .23 is. such that

ports

13 and 13 between the gear, teeth are in communication with the discharge passages 12 and 12' respectively from the point of zero mesh at the bottom up to and including the point of maximum mesh at the top. Theports are pro.-

gressively closed by the upper sealing abutment as the gear rotates around the casing and it will be noted that the port of the tooth space in full mesh with a pinion tooth is only partially closed by the abutment 23 or 23'. The port is fully closed by the upper abutment'only after its corresponding tooth space has been in maximum or deepest engagement whereby, as already ex plained, the liquid is vented from the space of minimum volume and. trapping avoided. By the time the port has rotated around to the position of complete closure by abutment 23.0r 23', its

corresponding tooth space has been relieved of preferred embodiments herein chosen for illustration but that various changes and modifications may be made therein without departing from the spirit and scope of the invention as hereinafter claimed.

Having thus described my invention, what I claim is:-

1. A rotary pump comprising a casing, an internal gear within said casing and forming suetion and discharge passages therewith, a pinion adapted to mesh with and having one tooth less than said gear, circumferentially spaced openings in said gear, a follower forming in combination with the casing and the gear a seal between said suction and discharge passages and adapted to slide said gear relative to said pinion, and means for moving said follower.

2. In a rotary pump, a pump casing having suction and discharge passages, a movable follower member forming a seal between the sucition and discharge passages and having a ring gear mounted for rotation therein, a pinion adapted to mesh with and having one tooth less than said ring gear, a follower plate forming with said member a pumping chamber enclosing said gear and pinion, and means for balancing pressure on opposite sides of said plate.

3. A rotary pump comprising a casing having a suction passage and a discharge passage, a slidable ring gear within said casing, a fixed pinion in mesh with and having one tooth less than said gear, a movable follower member forming a seal between said suction and discharge passages and adapted to slide said gear, circumferentially spaced ports in said gear, a follower plate fixed to said member and forming a balancing chamber with a wall of said casing, said plate also forming with said member a pumping chamber enclosing said gear and pinion, and means in said member for alternately establishing communication between said discharge passage and balancing chamber and between the latter and said suction passage.

4. A rotary pump comprising a casing, a movable follower member and plate forming a balancing chamber and a pumping chamber in said casing, a ring gear in said pumping chamber and movable with said follower member and plate, a fixed pinion meshing with and having one tooth less than said gear, means for supplying fluid to and discharging fluid from said balancing chamber, and supply and discharge openings for said pumping chamber.

5. A rotary pump comprising a casing, a movable follower member and plate forming a balancing chamber and a pumping chamber in said casing, a ring gear in said pumping chamber and movable with said follower member and plate, a fixed pinion meshing with and having one tooth less than said gear, suction and discharge passages communicating with said pumping chamber, and means in said follower member for supplying fluid from said discharge passage to said balancing chamber and for discharging fluid from said balancing chamber into said suction passage.

6. A rotary pump comprising a casing having a front head and spud and a rear head and spud, a non-rotatable annular follower member slidable onsaid rear spud, an annular plate fixed to said follower member and slidable on said front spud, and forming one end of a pump chamber in the follower, a ring gear mounted for rotation in said follower member and slidable therewith, a fixed pinion between said spuds meshing with and having one tooth less than said gear, and means in said follower member for balancing pressure on opposite sides of said plate.

7. A rotary pump comprising a casing having a front head and spud and a rear head and spud, a non-rotatable annular follower member slid- 'ble on said rear spud, an annular plate fixed to said follower member and slidable on said front spud, a ring gear mounted for rotation in said follower member and slidable therewith, a fixed pinion between said spuds meshing with and having one tooth less than said gear, and means for moving said follower member.

8. A rotary pump comprising a casing having a front head and a spud and a rear head and spud, the spuds being disposed within the casing and directed toward each other, a non-rotatable annular follower member slidable on one of said spuds, an annular plate fixed to said follower member and slidable on the other of said spuds, a ring gear mounted for rotation in said member and slidable therewith, a fixed pinion between said spuds meshing with said gear, means for moving said member to move said gear and thereby vary the engagement between the gear and pinion, said follower member being adapted to seal the portion of the pinion at any time out of mesh with the gear, and said other spud and said annular plate being adapted to seal the portion of the gear at any time out of mesh with the pinion.

9. In a rotary pump, the combination of a pinion, an internal gear in engagement with said pinion, and adapted for sliding movement with respect thereto, and means for sliding said gear to vary the extent of mesh of the gear with said pinion, said means partially enclosing, entirely supporting and forming the bearing for said gear.

10. In a rotary pump, the combination of a pinion, an internal gear in engagement with and having one more tooth than said pinion, and means movable axially with respect to the easing and the pinion and for varying the extent of the engagement between pinion and gear, said means partially enclosing, and entirely supporting said gear, and forming suction and discharge ports.

11. A rotary pump comprising a casing, an annular follower slidable axially therein, and forming suction and discharge passages therewith, an internal gear within said follower, means for sealing said suction and discharge passages, openings in said gear between adjacent teeth thereof, and a pinion adapted to mesh with and having one less tooth than said gear.

12. A rotary pump comprising a casing, an annular follower member slidable longitudinally within said casing and forming a suction passage and a discharge passage therewith, an internal gear within said follower member and supported thereby, means for sealing said suction passage from said discharge passage, openings in said gear between adjacent teeth thereof, a pinion adapted to mesh with and having one tooth less than said gear, and means for sliding said follower to vary the extent of engagement between said gear and pinion.

13. In a rotary pump, the combination of a pinion, an internal gear in engagement therewith and having one tooth more than the pinion, a follower member movable axially of the pinion and partially enclosing and entirely supporting the gear and adapted to slide the gear '15. A rotary pump comprising a casing, a

movable follower member and plate forming a single balancing chamber and a pumping chamber in said casing, a ring gear in said pumping chamber supported by said follower member and movable with said follower member and plate, a fixed pinion meshing with and having one tooth less than said gear, suction and discharge passages communicating with said pumping chamber, a valve chamber in said follower member communicating with said suction and discharge passages and with said balancing chamber, and a valve movable in said valve chamber, movement of said valve relative to said follower member causing variation 'of fluid pressure in 'ripheral ports between.

said balancing chambensaid variation of fluid pressure causing said follower member to move in the same direction as said valve and with the same amount of movement. v

16. In a liquid pump, a ring gear having peeach two consecutive teeth, a pinion having one tooth less than the ring gear and operating therein, a suction chamber open to the ports on one side of the ring gear, a discharge chamber open to the ports on the opposite side of the ring gear, and an abutment arrangedto cut off each port as it passes out of registration with the suction chamber and to open said port as it passes into registration with the discharge chamber, said abutment being extended was to cut oii" the port. while the toothed space corresponding to the port and defined by consecutive teeth of the gear and pinion is expanding and so as to open said port while said toothed space is contracting.

1'7. In a liquid pump, a ring gear having peripheral .po'rts between each two consecutive teeth, a pinion having cne tooth less than the ring gear and operating therein, a suction chamber open to the ports on one side of the ring gear, a discharge chamber open to the ports on the opposite side of the ring gear, and an abutment sealing off the outer end of each port as it passes from .the discharge chamber, but only after the pinion tooth cooperating with the port has'entered into its fullest engagement with the ring gear teeth sealing oft the'inner end of the port, the seal being maintained continuously by the driving contact of the corresponding teeth of the pinion and the ring gear through the whole distance through which the abutment seals the outer end of the port.

18. In a liquid pump, a ring gear having peripheral ports between. each two consecutive teeth, a pinion having one tooth less than the ring gear and operating therein, a suction chamber open to the ports on one side of the ring gear, a discharge chamber open tothe ports on the opposite side of the ring gear, an

abutment arranged to cut off each port as it passes out of registration with the suction chamber and to open said port as it passes into registration with the discharge chamber, said abutment being extended so as to cut off the port while the toothed space corresponding to the port and defined by consecutive teeth of the gear and pinion is expanding and so as to open said port while said toothed space is contracting to a volume equal to or greater than that which it had at the point of seal-off from the suction,

chamber, and an abutment sealing off the outer end of each port as it passes from the discharge chamber, but only after the pinion tooth cooperating with the port has entered into its fullest engagement with the ring gear teeth sealing off the inner end of the port, the seal being maintained continuously by the driving contact of the corresponding teeth of the pinion and the ring gear through the whole distance, through which the abutment seals the outer end" of the port.

19. In a rotarypump having an inlet and an outlet, the combination of a rotary pinion, an internal rotary gear to transfer liquid-from the inlet to the outlet and arranged to mesh with and slide longitudinally of the pinion to vary the extent of engagement therebetween, a nonrotary follower member arranged to slide the gear and seal the portion of the pinion out of mesh with the gear, and means for moving the follower member.

20. In a rotary pump, the combination of a pair of rotors comprising an internal gear having cireumferentially spaced suction and discharge ports in the periphery thereof and a pinion in mesh with said gear, an annular follower shiftable axially of the pinion and having opposed surfaces of unequal eifective area, the lesser surface being exposed to the discharge pressure of the pump, said gear being supported for rotation in said follower and arranged to be shifted therewith, and means whereby the pressure exerted against the follower surface of larger area is varied to shift the follower and gear and thus regulate the output capacity of the pump.

21..In a rotary pump, the combination with a casing having an inlet and an outlet, an internal gear in said casing and a pinion meshing therewith, said gear and pinion being arranged to transfer fiuid from the inlet to the outlet of the pump, of a member mounted in said casing and arranged to slide axially .of the pinion, thegear being rotatably mounted on said member, said member having opposed surfaces of unequal effective area, the lesser of V which is exposed to discharge pressure of said pump, and means comprising a valve and passages in said member controlled by said valve and arranged to shift said member by varying 'the pump, of a member mounted in said casing and arranged to slide axially of the pinion, the gear being rotatably supported by said member, said member having opposed surfaces of unequal effective area, the lesser of which is exposed to discharge pressure of said pump, passages in said member connecting the end of the casing wherein the pressure is effective against the surface of the member having larger efiective area to the outlet and to the inlet of the pump, a valve in said.member arranged by movement relative to the member to selectively open and close said passages, the valve member being so arranged that when the valve has been adjusted to open one of said passages, the resulting pressure variation in said end of the casing will cause the member to shift and close the valve.

23. In a rotary pump, the combination with a casing having an inlet and an outlet, an internal gear element in said casing and a pinion element meshing therewith, said elements being arranged to transfer fluid from the inlet to the outlet, of a member mounted in said casing and arranged to slide. in said casing, one of said elements being rotatably mounted on said member and arranged to slide therewith, said member having opposed surfaces of unequal effective area, the lesser of which is exposed to the discharge pressure of the pump, and means comprising a valve and passages in said member controlled by said valve and arranged to vary the pressure effective against the surface of larger area of said member whereby to regulate the extent of engagement between said elements.

24. In a rotary pump, the combination with a casing having an inlet and an outlet, an internal gear element in said casing and a pinion element meshing therewith, said elements being arranged to transfer fluid from the inlet to the outlet, of a member mounted in said casing and arranged to slide in said casing, one of said elements being rotatably mounted on said member and arranged to slide therewith, said member having opposed surfaces of unequal effective area, the lesser of which is exposed to the discharge pressure of the pump, and means whereby the pressure effective against the surface of larger area may be varied whereby to move the member and thereby regulate the extent of engagement between said elements.

25. In a rotary pump, the combination with a casing having an inlet and an outlet, an internal gear element in said casing and a pinion element meshing therewith, said elements being arranged to transfer fluid from the inlet to the outlet, of a member mounted in said casing and arranged to slide in said casing, one of said elements being rotatably mounted on said member and arranged to slide therewith, said member having opposed surfaces of unequal effective area, the lesser of which is exposed to the discharge pressure of the pump, and means comprising a valve and passages in said member controlled by said valve and arranged to maintain the pressure effective against the surface of larger area of said member for holding the gears in fixed relation.

26. A rotary pump comprising a casing having an inlet and an outlet, an internal gear within said casing and having portions of its periphery exposed to said inlet and outlet and arranged for both rotary and axial movement, oppositely arranged spuds within the casing, one spud being greater in diameter than the other, a pinion rotatably mounted between the spuds and arranged to mesh with said gear, and means actuated by the pressures generated within the pump for maintaining the extent of the engagement of the pinion and gear controlled by the difference between the exposed areas of the spuds.

27. In a liquid pump, a ring gear having peripheral ports between each two consecutive teeth, a pinion having one tooth less than the ring gear and operating therein, a suction chamber open to the ports on one side of the ring gear for the greater portion of its semicircumferential extent, a discharge chember open to the ports on the opposite side of the ring gear for the greater portion of its semicircumferential extent, and an abutment, arranged to cut off each port as it passes out of registration with the suction chamber and to open said port as it passes into registration with the discharge chamber, said abutmentbeing extended so as to cut off the port while the toothed space corresponding to the port and defined by consecutive teeth of the gear and pinion is expanding and so as to open said port while said toothed space is contracting.

REGINALD J. S. PIGOTI