US2359513A

US2359513A - Variable volume pump

Info

Publication number: US2359513A
Application number: US460083A
Authority: US
Inventors: Eden Charles Howard; Edward E Stevenson
Original assignee: Individual
Current assignee: Individual
Priority date: 1942-09-29
Filing date: 1942-09-29
Publication date: 1944-10-03
Anticipated expiration: 1961-10-03

Description

Oct. 3, 1944. c. H. EDEN ETAL VARIABLE VOLUME PUMP Filed sept. 29, 1942 4 YSheets-Sheet l L l l Oct. 3, 1944. C` EDEN ET AL 2,359,513

#I VARIABLE VOLUME PUMP Filed Sept. 29, 1942 4 Sheets-Sheet 2 Jzyefzfars; 'lzarlfsifazl/ardlden, Ida/ard''feyewsan.

Oct. 3, 1944. Q H EDEN ErAL 2,359,513

VARIABLE VOLUME PUMP Filed Sept. 29, 1942 4 Sheets-Shea?Y 4 anfr Z'd'wrdlf 5760611.90.

ings.

Patented Oct. 3, 1944 UNITED. STATES PA sli-ica 2,359,513 VARIABLE VOLUME PUMP Charles Howard Eden and Edward E. Stevenson,

Los Angeles, Calif.

Application September `Z9, 1942, Serial No. 460,088

10 Claims.

pressure power transmission system such,y as is set out in our copending application, Ser. No.

334,558 led May l1, 1940. It will therefore be described as a pump and with reference to such a closed circuit system as is set o ut in that application, but without limitation thereto. In such systems, and in many other situations. there is desired a compact, positively acting pump of the rotary type having little or inappreciable slippage, high efficiency and long life; and also one that may be adjusted to diiferent capacities at high efciency.

How our present inventionI reaches the desired ends will be best understood from the following detailed description of the preferred and illusv trative design shown in the accompanying draw- In these drawings: Fig. 1 is a central longitudinal sectlon'of anillustrative and typical pumpstructure embodying vthe invention, the sections. through thetwo pump elements which are, shown in Figs. 4"and 5 being taken respectively on the lines designated I-I land Ia-Ia in those iigures;

Fig. 2 is an .end elevation, with parts in section on line 2-2 of Fig. 1, for illustrative purposes;

Fig. 3 is a cross section on line 3- -3l o f Fig. 1;

Fig. 4 a cross section on line 4-4 of Fig. 1;

Fig. 5 1s a cross section on line 5-5 of Fig. 1;

Fig. 6 is a developed diagrammatic view showing the shapes of the inlet and outlet ports;

Fig. 7 is a fragmentary perspective illustrating the formation of the ports which are showndiagrammatically in Fig. `6. d4,5

In the drawings a suitable main casing' is illustrated as made up of parts I and Il which are secured together, as by screws i2, und hold internally between them the ring I3 in which the two internally elliptic rings M and I are 50 set. Two such elliptic rlngs, with their cooperating pump pistons, 'comprise a pump set which will give a substantially continuous and uniform delivery of uid under pressure. The complete pump may comprise anysuitable num- 55 ber of these sets; we here prefer to show a single set, sufllcing to illustrate the invention.

AA rotor 2li is concentrically mounted on bearings 2|` and 22 within the casing, andls driven from a driving shaft 23 which projects into one` o0 arf end of the casingv and is mounted therein on.

bearing 24. The inner enlarged end 23a of shaft 23 hasa clutch or other suitable driving engagement with rotor 20, as indicated at 25. Rotor has an internal longitudinal bore 26 through .which a relatively non-rotatable but adjustable' distributor shaft 30 extends. This shaft contains inlet and outlet passages and ports and is adjustable lengthwise to change port registry with the cylinders in the rotor, all as vwill be described. The inner end of distributor shaft is carried in a bearing 3| which is carried in the enlarged-inner end of driving shaft 23, and the distributor shaft also supported at or near its outer end by havingv suitable bearing support in the bore 32 of a cylindric casing extension 33 which is secured to casing part l0 by suitable bolts or screws 34. The distributor shaft 30, and rotor 2li, are thus independently journalle'd or carried in the casing of the pump, so that the contacting surfaces of the distributor shaft and of bore26 of the rotor Rotor 20 is provided .with Atwo axially spaced i sets of radial cylinder bores 35, spaced and arrangedas is best shown in Figs. 1,4 and 5. Each cylinder' carries a" plunger or piston 36, preferably hardened and ground to a close' iit in the cylinder and having a rounded hardened end 36a adapted to engage and follow the concavef elliptic innersurface I 4a: or i5a of the two hardenedelliptic rings Il and l5. 'Ihe major axes of the two elliptic surfaces Ma and 15a as here shown preferably lie at right angles to each other,.as shown by Figs. 4 and 5. It will be well understood, without the necessity of further detailed description, how the two sets of pistons are 'reciprocate'd in their cylinders,vv when rotor 20 is revolved, by reason of their outer ends following the describedielliptic surfaces. The relative arrangement of the two sets of pistons is such (see Figs. 4 and 5) that each piston of one set. has a corresponding piston in the other set in other, the pistons will be slowly rotated about their own axis as they revolve, thusdistributing the lubricant and also distributing wear.

A gear pump casing element 40 4lies between' I the inner end of casing extension 33 and casing and is carried in the casing in the bearing 22 which has been previously mentioned and also in a bearing' 22a which is mounted in the casing extension 33. The gear element 4| is thus also journalled in the casing independently of distributor shaft Sii, so that the interfltting surfaces of those two parts are substantially relieved of all wear. Gear element 4I is rotatively interi- Iconnected to rotor 2u by any suitable means, such as the clutch indicated at 42. The other gear element 43 ofthe gear pump is mounted within casing 4U on a stud shaft M, as shown in Figs. 1 and 3. The inlet to the gear pump. which is also the initial inlet to the whole pump mechanism, is designated 5t in Figs. 1 and 3, being indicated in dotd lines in Fig. l. The outlet from the gear pump is designated 5|' in Figs. 2 and 3.`-

. From the gear pump outlet 5| a pipe or tubing arrangement 52 leads to two ports 53in casing extension' 33, which communicate with an annular channel 55 in the inner bore of 33 surrounding distributor shaft 30. Distributor shaft 30 has in it apair of diametrically opposed, longitudinal,A inlet passages 56, and another pair of diametrically opposed, longitudinal, outlet passages 5l. These passages are preferably ar- Figs. 2, 4 and 5. As illustrated, all these passages are formed as bores extending from the outer deft hand) end of distributor shaft 3o to the vicinity'of the inner (right hand) end of that shaft. The outlet passages 5l are open at the projecting outer end of the distributor shaft and may there connect with any suitable outlet piping or other distribution system as may be desired. In Fig. 2, the two outlet passages 5l 'are diametrically indicated as being'connected by lines 58 with a fluid pressure motor 59, and the exhaust of the fluid pressure motor is indicated as connected by line 60 with .theinitial pump intake 50; forming a closed circuit system.

The inlet passages 56 are communicated with the annular recess passage 55 by ports 6|, shown in Figs. 1 and 2, so located and of such lengththat the ports will remain in register with passage 55 throughout the longitudinal adjustment movement of distributor shaft 30. The inlet of fluid to inlet passages 56 being from the gear pump via passage 55 and ports 6I; the outer ends of the bored passages 58 are stopped in any suitable manner, as byjplugs such as shown at "sz in Fig. 1.

At the transverse plane of each of the piston and cylinder sets,"distributor shaftll is provided with a set of two inlet ports 85 and two outlet ports-68, these inlet and outlet ports registering respectively, with the inlet and

outletpassages

56 and 51 as is shown in Figs. l, 4 and 5, and their outer ends are at the outer or peripheral surface'ofdistrlbutor shaft 30, where their outer ends may be registered by. the cylinderports 35h during their rotation. These

ports

65 and 66 are,l

in one of their portions, of equal circumferential extent vabout the circumference of distributor shaft but in other portions these ports are ofunequal circumferential extent, as and for purposes which will be hereinafter described. Fig. 1 shows distributor shaft. 30 in such a longi tudinal position that the equal circumferential parts of the several ports'are in `.register with rotor cylinders 35, and the sections of Figs. 4 and 5 show those parts of the ports which are of equal circumferential extent. -The operation of the pump mechanism will first be explained as it is with the ports in the positions shown, and the optional method of operation which may be attained by shifting the distributor shaft longitudinally will then be explained.

Assuming the counter-clockwise direction ofl rotation indicated by the arrows in Figs. i and 5, the pistons 38 of the two piston sets will move outwardly during rotation through the quadrants indicated A and will be forced inwardly during rotation through the quadrants indicated l5. In

4 the aspects shown in Figs. 4 and 5, the inlet ports 65 are of such circumferential extent that'the ini ner ends of cylinders will register with them -ranged in the relative arrangement shown in f during the travel of pistons 35 throughout quadrantsvA. Thus, during the travels' of the vpistons and cylinders through quadrants A the pistons may move out and are moved out by the fiuid pressure which is initially raised by the' gear pump. The several cylinders of each set thus take-in fluid during their travels throughout quadrants n.

During and throughout the piston travel through quadrant B they are moved inwardly by the elliptic track engaged by their outer ends; and outlet ports 66 are, in the aspect shown in Figs. 4 and 5. so sized and locatedthat cylinders 35 register with those outlet ports throughout I travel through quadrants B. The fluid which` has been taken into the cylinders during travel through quadrants A is `forced out under pressure during travel through quadrants B, through theoutlet ports 56 and outlet passages 51 and f thence to the high pressure side of whatever distributing lines are used (for instance through the lines 58 to thekiiuid pressure motor 59) If the pump mechanism is being used in a closed circuit system, such as here indicated, the'exhaust from motor 59, or any other device which is energized by the pump pressure,ilows through the return une soto the mami intake su of the gear pump. The gear pump is operated at the same speed as the piston pump elements, and it is' designed to be of a capacity to supply the full cawith the inner ends of the twosets of rotor cylc' inders 35. The inner open-ends of the cylinders may thus be regarded as ports, registering with the shaft ports, and leading to the piston mechanism can'ied by the rotor. The inner ends of cylinders are preferably vfreduced to form paclty of the rotary piston elements at some suitable and relatively low pressure, say 20 or 25 lbs. per sq. in. The pressure raised by the gear pump is suillcient to insure that the piston cylinders each take afull charge of fluid during their intake strokes, and also sumcient, at least with the aid of centrifugal force, to move the pistons outwardly during their intake strokes.

Although the pumping capacity of the .gear pump may be made, as nearly as may be, Just equal to the capactiy of the cylinder and piston elements, it is preferable to design the gear Inlet and outlet ports and communicate, 75 pump for a'slight over-capacity in order to be previously takenv in. This expelled portion is sure that the gear pump has the-desired full capacity of the piston and cylinder elements. And that slight over-capacity, if present, may be taken care of by the by-pass arrangements which are hereinafter described. In themode of operation which has so far been described, the pump will deliver at its maximum capacity per revolation.

Distributor shaft 30 is rotationally stationary but longitudinally movable,.being splined in the casing extension 35 "by the arrangement-shown at 1D. The outer end of shaft 30 is screw-threaded as shown at H and an internally threaded worm wheel 'l2 engages threads 1|. Worm -wheel l2 has end thrust in one direction .against a bearing 1.3 which is set in a member 'Il which forms the end portion of casing extension 33; and may have end thrust bearing in the opposite direction against a similar bearing, but ishere shown as bearing simply against a bracket'16 attached to member 14. A worin' 11 is mounted in 4bearcompressed back into the inlet passages communicating with the inlet port, and is taken care of by the by-pass arrangement to be described.

Each outlet port 66 has. corresponding extensions 66a toward the right of lesser circumferential extent than the main.port, 66. In this particular instance the circumferential, extent of a. port extension 66a is such that each cylinder is inregistry with the port extension durl Ving the latter part of` each outlet' quadrant B.

Consequently, in this mode of operation of the l pump, each piston expels only about one-half its full capacity into the outlet passages of the pump; and the resultant over-all pumping c'apacity of the pump as a whole is .thus reduced to about one-half its full capacity per revolu tion. The shapes and spacings of the adjacent edges 65h' and 66h of the inlet and outlet ports -are such that the cylinder ports do not register with both 6 5 and 66 at thesame time, and such ingsv 18 carried by member 1I, and a hand wheel 'I6 typifies any suitable. means of rotating worm 11. By rotating the hand wheel distributor shaft may be moved longitudinally. In Fig. 1 it is shown in'its limiting right-hand position with relation to the other parts of the pump mechanlsm. It may be moved to the left through a distance about equal to the, diameter of cylinders 35. When so moved towardtheeleft the portions of the

ports

65 and 66 which are directly shown in Figs. 4 and 5 are moved out of the plane of rotationof cylinders and therefore out'of registry with the cylinders, and the portions of the several portsl which lie to the right in Fig. lare brought into registry with the cylinders 35.

The configurations and relative extents of the port extensions 65a' and 66a, and their effect upon the functioning of the pump, may best be -understood from consideration of Figs. 6 and 7.

that any pump capacity intermediate full and half may be had by moving the distributor shaft appropriately.

The gear pump, which is rotating at even speed with the rotor and 'piston assembly, pumps a xed volume of fluid to the piston intake ports per revolution. To take care of the fractional volume which is pumped back into the intake ports by the pistons in the last described mode of operation, and also to take care of any slight excess volume of the pump in theilrst described mode of operation, a suitable by-pass system' may be employed. For instance a bypass with a 'loaded valve may be installed, leading from any suitable point in the passages between the gear pump and the rotorcylinders, to the initial in- Fig. 6 is a diagrammatic development of the sexies of ports and Fig. 7 is a fragmentary pros' pective illustrative of' the port formation. In

Fig-6 the relative direction of rotation (of the rotor and cylinders with reference ,to the ports),

is indicated by the arrow, andthe successive quadrants of normal intake and out-put are indicated by the letters A and B. The portions of the ports which have been previously described and which in Fig. 1 lie on 'the section lines 4 1 and 5-5 are those portions of the `several ports which lie toward the left in Fig. 6 and are` designated by the numerals and 66. Each inlet port 65 has an extension 65a toward the right (in a direction axial of distributor shaft 30) and this inlet port extension is also extended in the direction of rotation by an amount, in this particular instance,A equal to something less than half the effective registering Vlength of port 65. Thus, the port extension '65a reaches over into the immediately succeeding outlet quadrant B far enough that when a cylinder in its rotation has passed completely out of register with port extension .6 5athat cylinder and its piston is,l

in this particular instance, nearly halfway through the succeeding outlet quadrant andzthe.

piston is accordingly in about the middle of its fluid expulsion or compression stroke. Thus, in the operation ofthe pump when port extension 65a1is in register with v thecylindera each cyl'- inder takes in1 its full charge of fluid during the intake quadrant A and then during a portion of ciency'is not large when the pump is operating at less than full capacity.

Although the described structure is such, and the relatively rotating parts are `so journalled, that a' very close lit may be made and maintained between the distributor shaft and "the 'l other parts to reduce or preclude leakage, suitend of the distributor shaft to preclude leakage able packing glands are Provided at 85 on driving shaft 23 and at 86 on the left hand or outer of any uid from the whole pump mechanism. The packing gland at 85 makes 'the right-hand end of the pumpfluid-tight. The packing gland at 66 makes the left-hand end of the pump iluidtight and, in particular, prevents any leakage l toward the left along shaft 30 from the annular passage 55. Leakage toward thel right'from annular passage 55 is precluded by the.` close fit .that is maintained,between shaft 30 and gear element 4I. And any leakage that may occur the succeeding expulsionquadrant B itfexp'els" a proportionate part of the iluid which has been along or aroundthe shaft within the limited space between gear element `4I and packing gland 66 is of no consequence as that leakage only` has egress through the ports l6I which lead intov the'inlet passages-56.

With the'whole pump mechanism thus packed to prevent'over-all-leakage, the space Sv between rotor 20 and outer casing liI-H may have a sure a slow passage of fluid, usually oil, to the l 'outer piston ends and to rings i4 and i5, toiinsure lubrication. At the operating speeds and pressures for which the mechanism is designed and intended, centrifugalforce alone, or that force plus the intake pressure, may force the pistons out, even though all leakage pressure is held at packings 85 and 86. If, however, in any case the operating speeds and pressures are too low to move the pistons out positively, leakage from space S may beallowed, either by not using one or both packings 85 and 86, or byconnecting space S either with the intake or discharge of the gear pump. For instance a' small pressure venting passage may be provided at (Fig. l) to vent space S either to atmospheric pressure or tothe intake pressure of the gear pump. .For

instance, the whole pump mechanism may commonly be set in an oil reservoir from which the gear pump intakes and into which the exhaust from motor 59 discharges; and vent I0!) may simply discharge into that reservoir. In such an arrangement the intake pressures on -the pistons 36 will always positively force them out no matter how small centrifugal force may be.

If the gear pump is omittedfrom the mechanism and the piston pump elements used alone, the initial intake pressure to the pistons 'may be maintained high enough` either in a closed or open system, to insure full outward movement of the pistons and the taking of full charges.

Although the whole mechanism has beendescribed as functioning to compress a fluid, acting as a pumpthe same mechanism may be used as a lmotor simply by inverting its operation. If pressure fluid be applied at the high pressure side of the. mechanism (at what has been described as the high pressure outlet) and a lower pressure be maintained at the low pressurey side (that has been described as the initial inlet of the pump) the course of fiuid'through the mechanism will be reversed and the mechanism will act as a motor to deliver` power at shaft v23.v In such use the gear pump unit may if desired be dispensed with, as it also'may in some circumstances when using the mechanism as a pump.

But if, as a motor, the gear unit is retained, a

two-stage mechanism results, just as there are two stages in the described pump.

Further the mechanism is applicable, either as pump or motor, to lgas fluid as well as liquid. The illustrated form has been particularly designed for use with liquid, but the mechanism is nation, although preferred, is merely 'illustres tlve of various and well known forms of rotary pump or motor mechanisms that' maybe used. In other aspects however, a unit having alternating intake and expulsion `strokes forms a characteristic part of the invention; and the described mechanism is preferred.

We claim:

1. A fluid pressure mechanism which includes a rotor having an axial bore, a port at the bore surface, and mechanism which takes and expels fluid through said port during revolution of the port through successive vangles of rotation, and which includes a relatively' non-rotating axial distributor shaft with an inlet `and an outlet port at the shaft periphery adapted to be registered successively by the rotor port, characterized further in that: the distributor shaft is longitudinally movable, the-several distributor ports l have two parts which lie respectively in two longitudinally spaced planes normal of the shaft axis, the parts of the portswhich lie in one said plane being substantially equal in circumferential extent-and the parts of the ports which lie in the other plane being one relatively longer and one relatively shorter in circumferential extent.

2. A fluid pressure mechanism which includes a rotor having an axial bore, a port at the bore surface, and mechanism which takes and expels iiuid through said port during revolution of the port through successive angles of rotation, and which includes-a relatively non-rotating axial vdistributor shaft with an linlet and an outlet port at the shaft peripheryadapted to be registered successively by .the rotor port, charactershorter. e

` ing, a rotor with fluid pressure piston mechanism and having an internal non-rotative longitudinally movable distributor shaft with inlet and outlet passages and ports communicating with the rotor mechanism; the combination of a rotary gear pump of two gear velements one of which is journalled in the casing concentrically about the distributor shaft in a position longitudinally spaced from the rotor, rotary coupling means between said gear element and the Vrotor independent of the distributor shaft, and a conduit connecting the outlet of the gear pump and the inlet passage'of the distributor shaft, the distributor shaft being longitudinally movable through both theV rotor and said concentrically journalled gear. 4. In a fluid pressure mechanism, a. casing, a central longitudinal distributor shaft non-rotatively mounted in the casing for longitudinal movement therein, a rotor journalled in the casing concentrically about 'the' distributor shaft,

, piston mechanism associated with the rotor, the

dis'tributorshaft having longitudinal inlet and outlet passages and transverse ports communieating with the proton a gear pump of two gear elements mounted in the-casing, journals supporting one' of the gear elements in Athe casing concentrically about the distributor shaft and in av position longitudinally spaced from the rotor, means rotatively-coupling the rotor and said gear element independently of the distributor shaft, anda conduitconnecting the outlet of the gear pump with the inlet passage of the 'distributor shaft, the distributor shaft being longitudinally movable through .both the vrotor and said concentrically journalled gear.

5. In fluid pressure mechanism, la casing, a central longitudinal distributor shaft mounted in the casing to be non-rotative but longitudinally movable, a centrally bored rotor journalled in the casing concentrically about thedistributor shaft to rotate thereabout in a fixed radial plane, said rotor having ports at its central bore surface which bore surface iits the central distributor shaft closely, the distributor shaft having longitudinal inlet and outlet passages and having inlet and outlet ports at its periphery adapted to be registered by the rotor ports, each of the shaft ports having two parts cf different circumferential extent adapted selectively to be moved into registery with the rotor ports by longitudinal.

movement of the distributor shaft, and means for moving the distributor shaft longitudinally.

6. In fluid pressure mechanism, a casing, a central longitudinal distributor shaft mounted in face which bore surface nts the central distributor shaft closely, the distributor shaft having longitudinal inlet and outlet passages and having inlet and outlet ports at its periphery adapted to be registered by the rotor ports, each of the shaft ports having two parts of different circumferential extent adapted selectively to be moved into registry with the rotor ports by longitudinal movement of the distributor shaft, lmeans for moving the distributor shaft longitudinally, a gear pump of two gear elements mounted inthe casing, one of said gear elements having an axial bore fitting the distributor'shaft closely but movably, journals for said gear element in the casing concentric with the shaft, a coupling between that gear element and the rotor, and a conduit connecting the outlet of the gear pump with the inlet passage of the distributor shaft.

'7. In fluid pressure mechanism, a casing, a central longitudinal distributor shaft mounted in the casing to be non-rotative but longitudinally movable, a rotor having. a central bore closely cylinders in a common radial plane with their inner ends open at the rotor bore, radially reciprocating pistons associated with the rotor and the casing so as to move radially inwardly and outwardly during successive angles of rotation, the

distributor shaft 'having longitudinal inlet and outlet passages reaching lto the'vicinity of the plane of the Arotor and having inlet and outlet ports at its periphery, each of the shaft ports inner ends open at the rotor bore, radially reciprocating pistons associated with the rotor and the casing so as to move radially inwardly and outwardly during successive angles of/rotation, the distributor shaft having longitudinal inlet the plane of the rotor and having inlet and outlet having two parts of different circumferential n the casing to be non-rotative but longitudinally .movab1e, 'a' rotor having a central bore closely but movably fitting the distributor shaft, the rotor being journalled in thecasingconcentri cally about the distributor shaft and constrained to lrotate in a fixed plane, the rotor having radial cylinders in a common radial plane with their ports at vits periphery, each of the shaft ports having two parts of differentcircumferential extent adapted selectively to be moved into the plane of rotation of the rotor cylinders bylongitudinal movement of the shaft, means for moving the distributor shaft longitudinally, a gear pump of two gear elements mounted in the casing, one of said gear elements having an axial bore fitting the distributor shaft closely but movably, journals for said gear element in the casing concentric with the shaft, a coupling between that gear element and the rotor, and a conduit connecting the outlet of the gear pump with the inlet passage of the distributor shaft.

9. In fluid pressure mechanism, a casing, av

central longitudinal distributor shaft mounted in the easing to be' non-rotative but longitudinally movable, a rotor having a central bore closely but movably tting the, distributor shaft, the rotor being Journalled in the casing concentrically about the distributor shaft.4 and constrained to rotate in a fixed plane, the rotor having radial cylinders in a common radial plane with their invner ends open at the rotor bore, radially recip shaft having one end within the casing in the vicinity of the rotor and its opposite end projecting from one end of the casing, a power 'shaft entering the casing at the first mentioned end of the distributor shaft and rotatively directly,

coupled with the rotor, a packing gland in the casing surrounding the power shaft, a packing gland in the casing surroundingthe. distributor shaft near its projecting end, and means applied to the projecting end of the distributor shaft for moving it longitudinally.

10. In` fluid pressure mechanism, a casing, a

central longitudinal vdistributor shaft .mounted in the casing to be non-rotative but longitudinally movable, a rotor having a central bore closely but movably fitting the distributor shaft, the rotor being journalled inthe casing concentrically about the distributor shaft and constrainedl to rotate in a fixed plane, the rotor having radial cylinders in a common radial plane` 'with their inner ends open at the rotor bore, radially reciprocating pistons associated with the rotor and the casing so as to move radially inwardly and outwardly during successive angles of rotation, the distributor shaft having longitudinal inlet and outlet passages reaching to the vicinity of the plane of the rotor and having in.. let and outlet ports at its periphery, each of the shaft ports having two parts of different circum- A ferential extent adapted selectively to be moved into the plane of rotation of the rotor cylinders by longitudinal movement of the shaft, the distributor shaft having oneend within the casing in the vicinity of the rotor and its opposite end the casing surrounding the distributor shaft near its projectinga end, means applied to the projecting end of the distributor shaft for moving it longitudinally, a gear pump of two gear elements mounted in the casing, one of said gear elements having an axial bore fitting the distributor shaft closely but movably, journals mounting said gear element in the casing concentric with the distributor shaft and'longitudmally adjacent the side of the rotor that lies toward the projectingend of the distributor shaft, a direct coupling between that gear element and the rotor, a lateral port in the distributor shaft extending from its longitudinal inlet passage toits periphery at a" point between said gear element and the endl of the casing from which-the distributor shaft projects, an annular passage in the casing registered by said last mentioned port. and-a conduit *I connecting the outlet of the gear pump with the annular passage.