US2262593A - Oil pump - Google Patents

Description

' Nov. 11, 1941'. 's. R. THOMAS EIAL Fiied July '1, 1939 s Sheets-Shet' 1 Q INVENTORS' ATTORNEY Ndv. 11, 1 941. s. R. THOMAS ETAL 2,262,593

OIL PUMP Filed July 1; 1939 s Sheets-Sheet 2 I I I JNVENTORS; Jaw a? ATTORNEY Nov. 11, 1941.

s. R THOMAS EI'AL OIL PUMP Filed July 1. 19:59

nvmvrozeg Jaw aw ATTORNEY.

Patented Nov. 11, 1941 UNITEDTSTATE PATENT. OFFICE on. PUMP Stanley R. Thomas, Lyons,- Mich., and John W. White, South Bend, Ind., assignors, by mesne assignments, of one-third to Stanley R. Thomas, Lyons, Mich;, and two-thirds to John W. White, South Bend, Ind.

Application July 1, 1939, Serial No. 282,398

17 Claims. (Cl. 103-161) i means of an inclined wobble plate or cam plate which swivels in its bearings throughvarious planes inclined to the axis of the pistons to produce variable travel of the pistons which are driven thereby. 1

Another design which has found common usage' comprises a plurality of cylinders having pistons which operate in a plane at right angles to the rotation of the cylinders; that is, the pistons are arranged in a radially extending position to cooperate with an enclosing ring which engages the ends of the pistons. The location of the ring is adjustable so that the axis thereof may be shifted off center with respect to the axis of the cylinder block, whereby the pistons are reciprocated through'each cycle of rotation to produce 'the desired pumping action. In this last type of construction, very complicated enclosing means is required for accommodating the shifting of the ring in order to vary the stroke of the pistons. This materially increases the outside limits of the housing for the pump, which results in increased cost, greater weight, and bearings of much larger design than are required by the pump of the present invention.

The present invention consists primarily in a modification of the principle underlyingthe latter mentioned type of pump referred to above in that a cylinder block is provided having radially extending pistons confined within an enclosing ring. However, in place of shifting the ringbodily in a plane at right angles to the axis of the cylinder block, in order to produce eccentricity between the axis of the ring and the axis of the cylinder block we employ a novel principle which, in the illustrated form of the invention, consists in maintaining the ring center on the center line of the cylinder block and rotating the same or tilting it to produce a variation in the stroke 01' the pistons as they are moved about the inner periphery of the ring. The tilting of the ring causes the pistons to move inwardly from a substantially intermediate position to an inner limiting position and. then outwardly to the same intermediate position through one-half of the rotating cycle, and to move from this intermediate position to an outward limiting position and back to the intermediate position in the opposite half of the rotating cycle. The degree of inclination of the ring with respect to the radial plane through the cylinder block determines the length of the piston stroke, and consequently determines the volume of liquid delivered by the pump. When the ring is moved into a plane at right angles to the axis of rotation of the cylinder block, maintaining its concentric relation thereto, no pumping action occurs due to the fact that the pistons are not moved during their cycle of rotation since the radial distance from the center of rotation to the ring is the same entirely around the inner circumference of the A further feature of the present invention resides in the provision of two sets of pistons in the cylinder block which may be arranged in staggered or parallel relationship and so constructed that a balanced thrust'against the bearings supporting the cylinder block is produced, thereby producing no stress upon such bearings. With two such banks of pistons, the ring is formed with either a double beveled, single convex double concave surface having its greatest depth intermediate the banks. By reason of this construction the pistons in the respective banks are moving in opposite directions, and consequently, a balanced pumping action is obtained,

since each bank of pistons is performingthe opposite functions from the associated pistons in the other bank. The radial and thrust loads on the bearing are therefore neutralized.

With such a construction a further advantage is derived by reason of the fact that very simplified adjusting means can be employed for varying the angle of inclination of the ring. This eliminates the costly and involved constructions required with the eccentric displacement type pump, as well as reducing materially the size of pump required to produce a certain maximum volume under a certain predetermined pressure. 7

Still another feature of the present invention is the provision of a sump pumping arrangement associated with and driven directly from the rotor shaft of the pump, whereby oil or similar liquid being pumped by the mechanism can be withdrawn from the housing and returned into the suction line of the pump, thereby pre-' venting the housing from becoming tilled with oil which would materially retard the efllciency o! the pump as well as resulting in destruction. the oil and excessive heating within the pump.

Figure 2 is a sectional view at right angles through the pump shown in Figure 1;

Figure 3 is an end elevational view of' the pump shown in Figures 1 and 2;

Figure 4 is a detail view showing one manner of adjusting the volume delivery of the pump;

Figure 5 shows a modified form of control;

Figure 6 is a side view of the pump with. a portion broken away to show the pumping arrangement for withdrawing oil away from the base of the housing;

Figure 7 is a sectional view taken substantially on line 1-1 of Figure 6;

Figure 8 is a sectional view taken substantially on line 88 of Figure '7 Figure 9 is a sectional view through a modified ring structure; and

Figure 10 is a similar view through a still further modified ring.

7 Referring now in detail to the drawings, the pump comprises a housingconsisting of the two portions 5 and 6 which are piloted together, as indicated at I, and secured in fluid tight relation by means of the circumferential series of bolts 8. Preferably, the housing has a pair of boss por- Referring now again to therotor block l8, this block .has a plurality of cylinders and 32 formed therein, the cylinders 30 being arranged in one radial plane, and the cylinders 32 being v arranged in a second radial plane ofiset axially with respect to the first plane so as to form two banks of cylinders centered about the bearing sleeve 24. The cylinders 30 are opened at their inner ends to communicate with suitable port means 33 formed in radial alinement therewith in the sleeve member 24, the'po r't' members 33 in turn communicating through the tube 23 with helically shaped fluid passageways formed in the shaft 22, and which will be'described indetail hereinafter.

Disposed for radial reciprocatory movementin each of the'cylinder banks 30 and 32 are piston members 34, these piston members having axially recessed inner ends indicated at 35 in Figure 2.

tions 9 formed thereon which act as supporting feet and which may be counterbored to receive suitable cap screws for securing the same to any supporting surface. Extending into one end-of the housing through the housing member 6 is a driving shaft I0 which may be connected to an electric motor, or any other suitable means, which rotates the same, the shaft H1 being supported in the ball bearing assembly l2 secured in the opening formed in the housing member 6 and being sealed against leakage or the like by means of the packing means l3 engaging about the surface of the shaft and held in position by the retainer member [4 threaded to the projecting jpurnal portion of the housing member 6. The bearing is secured in position bymeans of abutment 'of the outer race against the retainer member I4 and abutment of the inner race against a shouldered portion I5 on the shaft. The inner end of the shaft is radially enlargedto provide two extending shoulders l6 which are adapted to be interlocked between spaced lugs l1 formed on the rotor block indicated generally at I8. The connection between the shaft [0 and the rotorv block I8 may be either rigid, flexible or a combination,

but is intended to secure the rotor block l8 with the shaft I 0 for conjoint rotation.

The opposite housing member 5 has an enlarged boss portion 20 which is provided with a journal portion adapted to receive the stub shaft -22 enclosed within the bronze sleeve 23, this sleeve being pressed overland suitably-welded to the shaft 22, and serving as a bearing surface upon which the bearing sleeve portion 24 of the rotor block I8 is supported for rotation under the influence of shaft l0. Theshaft .22 and tube 23 are rigidly fixed in the housing against rotation, the tube 23 being provided with opposed the cylinders and cleaned out whenever it is thought necessary or expedient. The outer ends of each of the pistons 34 are of spherical surface,

as indicated at 36, and are adapted to have bearing engagement with the frusto-conical surface 31 disposed at one side of the enclosing ring 38, this ring being of the double beveled type so that each bank of cylinders has engagement with either the angle surface 37 or the angle surface 39 of the ring. It is within the purview of the present invention to cant the pistons relative to the axis of shaft I!) if a longer stroke is desired.

The ring 38 is supported on anti-friction ball bearings 40 which are disposed between the ring and an outer retaining ring 42, whereby the ring 33 is free to rotate with respect to the ring 42 and is capable of free rotary movement by reason of the ball bearing assembly 40. The surfaces 31 and 39 of the ring 38 are very highly polished, and preferably are uniform in angle and size. When the ring is in its normal inoperative position as shown in Figure 2, the ends of the pistons in each bank of cylinders engage the beveled surfaces in such manner that no reciprocatory movement of the pistons is possible as they rotate by reason of the rotation of the rotor block l8. However, when the ring. 42 is' inclined slightly, as shown in dotted lines in Figure 2, the surface 31 of the enclosing ring 38 assumes a different relationship with respect to the pis-' tons so that as the pistons move about during the cycle of rotation, they are alternately forced inwardly by engagement with that portion of the periphery of the ring which has been moved closer to the center of rotation of the block' l8. The centrifugal force produced by the rotation of the block is suflicient as to ,urge the piston ends outwardly-and maintain them in constant abutting engagement with the mirface' of the ring 38. As a consequence, the stroke of the pistons varies directly in accordance with the degree of inclination of the ring 38; -=It will be the members 5 and 6, and is providedatopposite diametrical points with projecting trunnion members 44 and 45 which are retained in suitable trunnion journals formed in opposite halves of 4 the housing. The trunnions 44 and 45 support the ring 42 for rotation about an axis drawn through the center lines of the trunnions and passing through the center of the shaft 22, and consequently being co-incident with the axis of rotation of the rotor. Thus the center of the ring 42 is disposed at all times on 'the center line of the axis of rotation of the rotor, and at no time becomes eccentric therewith. The trunnions may be formed integral with the ring 42, or may be press fitted and welded thereto or secured in any other desired manner, and preferably the ring 42 is retained against any possibility of shifting of its center with respect to the center line of the shaft 22 by means of the bosses 45 formed in the housing members and providing for close limits of play of the ring 42 with respect to shifting laterally or in a direction axially of the trunnions.

If it is desired to have a fixed volume pump, it is obvious that the ring 42 may be fitted in the housing in a predetermined inclined position, eliminating the trunnions and any control means for varying the inclination. of the ring. This provides a very economical structure where variable control of volume is not desired.

In Figures 9 and 10 modified types of ring surfaces are provided, the ring 38' shown in Figure '9 comprising a single convex surface 39' so that line contact is established with the the piston ends. It will be apparent that the functioning of the mechanism remains the same with this type of surface. Inasmuch as the line of contact between the piston and ring in both types of ring 38 and 38' follows a sinuous path when the ring is inclined for pumping action, and there is a certain amount of creep between the ring and pistons, there is no possibility of grooving and no scufiing, and wear is divided over substantially the entire ring surface.

The ring 38" in Figure 10 is provided with double concave surfaces 4| which are so arranged with respect to the piston ends as to preserve this I line contact. The wear is still distributed so that no localized paths of wear are produced, and no scufiing action takes place since the pistons rotate on their axes as they are bodily rotated by the cylinder block.

The shifting of the ring may be accomplished in various wa'ysone example being shown in FiguresB and 4 in which the boss 4'Iv which forms one of the trunnion supporting journals for the trunnion is adapted to have an adjusting lever 48 fitted-over the projecting end of the trunnion shaft and moved into abutment therewith. The lever 48 has an end of the spring clamp type, indicated at 49, which may be tightened around the shaft'by means of the screw 50' to clamp the same rigidly to the trunnion shaft, the preferred form of the invention including the use of a key 52 for insuring that there will be no possibility of relative rotation between the trunnion shaft and the lever 48. 1

Adjacent its opposite end the lever 48 is provided with an arcuate laterally extending projection 53 which has the arcuate slot 54 formed therein and adapted to be engaged by the screw 55. On the side of the lever opposite the projection 53 there is a small'projection 56 which forms an indicator means adapted to be related to the dial 5! provided on the cylindrical portion of the pump housing-so that the lever 48 may be rotated by loosening the screw 55 to move the indicator boss 56 into any desired position with respect to the scale 51. Movement of the lever in this manner will effect a corresponding inclination of the ring 42 due to the keyed engagement between the trunnion shaft 45 and the opposite end of the lever whereby the ring 42 will be tilted to any desired position, one of which is shown in dotted lines in Figure 2. Thus an easy and inexpensive means for facilitating the variation in delivery volume of the pump is provided.

Another manner in which such tilting action may be provided is shown in Figure 5 in which the ring 42' is provided with an arcuate threaded portion, indicated at 60, adapted to be engaged by the threaded portion 62 of a transverse shaft 63 extending through the two housing members 5 and B. On its opposite ends the shaft 63 is provided with suitable hand wheel means 64 which are pinned to the shaft, as indicated at 65, to facilitate controlling the rotation of the shaft 63. Rotating either one of the hand wheels 64 will result in the threads 62 engaging the cor-' able indicator means may be formed on the housing to be correlated with a suitable marking on one or both of the hand wheels so that rotation of the .hand wheel will indicate to the operator the position of the ring 42 and the pumping capacity of the pump when the ring is in such position.

It will be noted that when the ring 42 is in the position shown in Figure 2 in full lines, the bear ing ring 38 is in a neutral position concentric with the shaft 22, and as the cylinder housing I8 rotates about the surface of the tube 23 the ring 38 will rotate freely with the pistons and there will be no pump discharge. The bevel surfaces 31 and 39 at this time engage the rounded ends of the pistons at a point slightly offset with respect to the longitudinal center line of the piston, and consequently as the pistons bear against the ring 38 this point of contact will have a tendency to rotate the pistons in one direction or the other, thereby in effect producing a lapping action on the pistons within the cylinders.

As the ring 42 is tilted on the trunnions from the position' shown'in full lines in Figure 2 to that shown in dotted lines, the pistons in the right hand bank of cylinders above the trunnlons will be free to move outwardly into the position shown in dotted lines, while the corresponding pistons in the other'bank of cylinders will be forced inwardly into the position shown in dotted lines. It will therefore at once be apparent that tilting of the ring 42 produces a pumping action which is controlled by the amount of tilt imparted to the ring. Thus; in the position shown in dotted lines, the cylinder 34 on the right hand side of the rotor housing will be starting its delivery stroke inasmuch as it will be forced radially inwardly of its cylinder as it proceeds about its cycle of rotation so that when it reaches a position from' that shown, it will be'i'n its innermost position or at a point at which it has discharged all of the fluid within the cylinder, and will be initiating its suction stroke due to its centrifugal force, tending to throw it out against the surface 31 of the ring 38.

' Similarly, the left hand piston shown in full and dotted lines in Figure 2 will be forced into its dotted line position upon shifting of the ring, 'and will thus be starting its suction stroke, this particular piston moving radially outwardly of the cylinder through 180 of its rotation to draw fluid from the suction line 21 and through the port 25'and the cut-in passage 65 of the shaft 22 and thence outwardly through the port in the bearing sleeve into the inner ends ofthe cylinders.

Considering now the particular valve arrangement for controlling the delivery of liquid to the cylinders and the discharge of liquid therefrom, the shaft 22 including the sleeve 23 has a particularly novel type of porting arrangement in view of the fact that while one of the banks of cylinders is discharging, the other bank is filling, and the adjacent ports in the same plane must therefore beperforming opposite functions. The shaft 22 is provided with the milled passageways 65 and 66, the passageway 66 communicating with the outlet port 28 through the passageway 26 in the tube 23. These passageways are shown at the left hand end of Figure 2 as'being 90 out of the plane of the remainder of Figure 2 for the sake. of clarity. The tube 23 is provided with transversely extending slotted portions 61 and 68 which are disposed in alinement with the respective banks of cylinders and with the respectiveports 33 in the bearing sleeve 24...

The passageways 65' and 66 comprisegrooves milled in the shaft 22 and extend longitudinally of the shaft to the first bankof cylinder ports 33, and then each of the passageways assumes the lead of a spiral thread around the shaft 180 to the port on, the opposite side where- .by the ports are staggered to take the combined discharge or suction of both banks." The tube 23 which is pressed over the shaft 22 closes the passageways 65 and 66 for the major portion of i their,length, but has formed therein the de1iv-, cry and suction openings 61. and 88, there being a delivery and suction opening for-each bank of radial ports 33 "so' that actually four slots corto provide such 'a'construction since one of the V banks of cylinders is discharging while the other 5 ilar parts have been givencorresponding refpump; are retained, but certain modifications have been made in order to provide for withdrawing excessive oil from the housing and returningit to the suction line of the pump. Simerence numerals in this figure.

In this form of the invention, the housing member 6' has a cylindrically flanged hub por-- tion 10 within which is mounted the ball hearing assembly 12 for supporting the drive shaft 13. Suitable sealing means. 14 are provided in the end of the flange portion 18, and are retained in position by means of the retaining member 15. The shaft 13 is provided with an eccentric collar portion 16 intermediate the bearing support 12 and the winged portion l6 by which the shaft is secured for conjoint rotation with the cylinder block 18. This eccentric cam portion 16 on the shaft is adapted to be engaged by the spring pressed plunger 11 carried in an extending boss portion 18 on the housing member 6'. The plunger 11 is adapted to reciprocate within the cylinder 19upon rotation of the shaft 13, and is pressed into contact with the eccentric surface of the shaft by means of the coil spring 88 which is seated at its base in a' recess in a threaded closure plug 82 closing the lower end of the cylinder. The plunger," is adapted to 1 act as a pump producing a suction injthe transverse passageway 83 formed adjacent the base of the housing. member 6'. This suction is adapted to open the spring pressed valve 84 and through the passageway 85 withdraws oil from within the lower portion of the housing through the passageway 85 past the valve 84 and into the passageway 83. Upon downward movement of the piston 11, a pressure is exerted on the liquid within the passageway 83, and since the valve bank is filling, and adjacent ports in the same f plane must therefore be providing opposite functions.

It should also be noted that when the ring'31 is tilted to producegpumping action, the contact;

between the rounded piston end and the ring surface is varied with respect to the center of j the piston, thereby providing for equalized wear 1 on the piston heads and eliminating. any possibility of causing flat'spots, scufling, or grooving therein, such as may be produced in pumps previous types. r The same variation of path'occurs on the ring '1 surface, since the'pistons have a sinuous line contact path therewith when the ring is inclined.

Also, the creepage between the ring and pistons serves to .widen this path so that substantially all Considering now the structures shown in Fign; member 5. as'shown in Figure 3, to provide a vertically extending passageway 92 leading up to the inlet 84 is closed under pressure, the valve 86 is adapted to open against the pressure of spring 81,

allowing this liquid to pass through the valveing sump through the passageway 85, and upon opposite movement of the piston, is discharged under pressure through the valve 86 to the passageway 88. The passageway 88 extends beneath'the housing to the opposite end thereof and into the boss portion 90 formed in thehous- The boss portion 98 is drilled,

opening 21. The upper end of this passageway is closed'by means of the cap screw 93. Intermediate the ends of the passageway 92 a suitable pressure release valve 94 is provided which is normally closed, but which under excessive pressure in the passageways 88 and- 9|] will-open to by-pass a portion of the liquid back to the housing. This, valve 94 allows that portion of the liquid which the suction line is not capable of carrying to be discharged back to the housing from the the housing will have only a certain predetermined amount of liquid therein, since liquid above 0 this point will be withdrawn by means of the the ring surface is contacted; preventing any flat spots, scufling or grooving.

pumping action described. This allows the pump to run cooler, prevents excessive wear or heating, and prevents destruction of the liquid.

As is well known in the majority of hydraulic pumping systems using variable delivery pumps,

there is usually a companion motor connected to both the suction and discharge lines. This motor is sometimes built in the same case, but may be remotely located. In such cases, the pump usually incorporates the variable discharge feature, while the motor has a fixed power takeoff mechanism for effecting the rotation of the pistons. It is therefore to be understood that while the present invention has been illustrated and described in connection with a pump, it can also be used as a motor with the ring placed in a fixed position so that the mechanism may be used as a motor equally as well as a pump.

It is also to be noted that the pistons are free to roll with the ring and to rotate around their respective axes due to the relative .slip between the two units. This rotation of the piston is fractional as it reverses itself each half revolution of the pump. There is therefore no sliding between the two members, nor any possibility of localized wear.

We are aware that various changes may be made in certain details of the invention herein shown and described, and we therefore do not intend to be limited except as defined by, the scope and spirit of the appended claims.

We claim: I

1. A variable displacement pump including a rotating cylinder'block, radially directed pistons 'therein,,and means inclined at an angle to the plane of said pistons including a trunnion mounted ring having a frusto-conical ring rotatably mounted therein the frusto-conical ring being'engageable by the ends of said pistons to j reciprocate said pistons.

3. A pump comprising a rotating cylinder blockhaving a series of radially directed pistons,

a rotating ring encircling said pistons and having a frusto-conical surface continuously engaged intermediate its ends by the ends of said pistons, and means for tilting said ring While retaining its center coincident with the axis of rotation of saidblock for varying the stroke of said pistons, said last-named means being limited to tilt said ring in such manner that said piston ends never pass beyond the defining ends of said ring surface whereby said pistons make only one complete stroke during each complete revolution of said cylinder block.

1 4. A pump comprising a rotating cylinder block having a series of radially directed pistons, a rotatable ring encircling saidpistons and having a convex internalannular surface engaged by the ends of said pistons, and means for tilting said ring while retaining its center coincident with the axis of rotation of said block for varying the stroke of said pistons.

5. A pump comprising a rotating cylinder block having a series of radially directed pistons,

venting axial displacement therebetween and means for tilting said ring member while retaining its center coincident with the axis of rotation of said block for varying the stroke of said ally directed pistons in axially spaced relation,

ring means having oppositely beveled annular surfaces extending radially and axially outwardly from a medial plane and 'engageable by the ends of said pistons, an outer ring-shaped race member including bearing means mounting said ring means for rotation, trunnions for said race member, and means for tilting said race member on said trunnions to vary the'inclination of said ring means for varying the stroke of said pistons, said inclination being such that each bank of pistons engages only one beveled surface between the large and small ends thereof.

'7. A pump comprising a housing, a cylinder block therein havingradially directed pistons, means for rotating said block, a ring trunnioned in said housing, a second ring rotatably supported in said first ring and having a frustoconical internal annular surface engaged by the ends of said pistons, and means for tilting the first ring within such limits as to vary the radial distance between said second ring and the axis of rotation of said block to vary the stroke of said pistons while maintaining said surface in such position that each piston makes only one stroke per revolution of said cylinder block.

8. In combination, a pump housing, a rotating cylinder block therein having radially directed pistons, a ring trunnioned in said housing, a second ring rotatably carried in said first n'ng encircling said block and having an inner annular double tapered wear surface engaged by the ends of said pistons, and means for tilting said rings with respect to the plane of said pistons to vary the reciprocatory movement thereof, said means comprising a projecting trunnion on said first ring, an arm for rotating the same having an arcuate slotted portionLand means for securing said arm in selected rotated position on said housing through said slotted portion.

9. In combination, a housing, a shaft projecting thereinto and having a sleeve pressed thereover, opposed milled longitudinal grooves in the shaft connected externally of the housing to respective suction and discharge ports, each groove terminating-within the housing in a spiral end portion extending a substantial distance about the shaft, axially spaced pairs of transverse slots in the tube alined with the respective ends of said spiral end portions of the grooves, a cylinder block rotatable about said tube and having axially spacedradially directed banks of cylinders, port means in the inner ends of said cylinders adapted to open into the respective slots, pistons in said cylinders, and means confining said pistons and adjustable to vary the a ring encircling said pistons and having an internalannular frusto-conical section surface engaged by the ends of said pistons, and arranged to vary'the radial distance therefrom to said block when tilted with respect thereto, an enclosing ring member having ball bearing means mounting said ring for rotation therein but prestroke thereof. a

10. In combination, a housing, ashaft fixed in the housing and having a sleeve assembled integrally thereover, opposed longitudinal grooves in said shaft, radial ports in said sleeve for connecting said grooves to respective suction and discharge ports, the inner ends of said grooves terminating in spiral end portions extending a substantial distance about the shaft, axially spaced pairs of slots in said sleeve alined with opposite ends of said spiral end portions, a cylinder block rotatable on said sleeve and said pistonsand having an annular frusto-con- 1v ical wear surface engaged by the ends of said pistons to impart one stroke to each piston per 1. revolution of said block, and means for inclining said ring with respect to the'axis of said block while maintaining it concentric therewith to varythe stroke of said pistons, the pistons having sinuous off-center line contact with said surface so as to rotate the pistons fractionally in opposite directions during each revolution, said pistons and surface having relative creepage whereby the cumulative wear on both pistons and ring is a. substantial area over the surfaces of each.

12. In combination, a housing, a rotating cylinder block therein having a plurality of radially directed pistons, a rotatable ring encircling said pistons and having an axially and radially inclined wear surface engaged by the ends of said pistons, and means for shifting the plane of said ring angularly relative to said block to vary the 3 stroke of said pistons, each-of said pistons having a spherical end portipn engaging said inclined surface at-a point radially offset from the axis of the piston to produce sinuous off-center 1 line contact with said surface when said ring shifted angularly so as to rotate the pistons fractionally in opposite directions during each revolution, said pistons and surface having relative creepage whereby the cumulative wear on I both pistons and ring is the surfaces of each. 7

13. A pump'comprising a housing, a rotating cylinder block therein having two axially spaced 1 banks of radially directed pistons therein, a 1'0 tatable reactance ring trunnioned in said housing and having symmetrical annular oppositely beveled reactance surfaces extending axially and radially outwardly away from each other, each of said, surfaces being engageable by the ends of onlyone bank of pistons, and means for tiltwhereby each of said pistons makes one stroke per revolution of said block and at no time engages the other reactance surface.

14. A pump comprising a rotatable cylinder block having two axially spaced banks of radij ally directed pistons therein, a reactance ring a substantial area over trunnioned for tilting movement relative the axis of said block and having two symmetrical annular reactance surfaces respectively engaged by the ends of each bank of pistons, said'reactance surfaces being of smallest diameter at the medial radial plane of said ring, and means for tilting said ring to vary the stroke of said pistons, while maintaining said plane intermediate the banks of pistons.

15. A reactance ring for a variable delivery pump of the radial piston type comprising a ball bearing assembly including inner and outer races, and a series of ball bearings therebetween,

said inner race having a symmetrical oppositely j beveled'internal surface adapted to form sepa'' jecting trunnions journalling said assembly for tilting movement thereabout.

16. In a variable delivery pump, a stationary supporting shaft, a block rotatable thereon and having a plurality of axially spaced banks of radially acting pistons, said shaft having suc-' tion and discharge passageways extending therethrough to a point adjacent said block and arranged with respectively ,ofiset radially directed suction and discharge ports extending to the surface of said shaft in alinement with the respective banks of pistons, and a freely rotatable ring encircling said block and having oppositely directed ,frusto-conical inner annular surfaces respectively engaged by the pistons, said ring being ,tiltable relative to the axis of said block for causing said pistons to function substantially in 7 banks of radial cylinders, pistons reciprocable in said cylinders, separate suction .and discharge passageways in said shaft extending to a point adjacent said block, each bank having its own tive to the discharge passageway, whereby reing said ring to vary the stroke of said pistons inlet and discharge ports between the radial inner end of said cylinders and said passageways,

said ports being so arranged that the respective inlet ports of the two banks are oppositely disposed in axially spaced relation along the shaft relative to the suction passageway and the .discharge parts are correspondingly arranged relaspective diagonally opposite cylinders are simultaneously connected to the same passageway through the diagonally offset arrangement of the"

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