US2111657A - Hydraulic pump or motor - Google Patents

Description

March 22, 1938 E. K. BENEDEK 2,111,657

HYDRAULIC PUMP OR MOTOR Filed May 22, 1934' s Sheets-Sheet 1 i ILEK K EENEDEK March 22, 1938. BENEDEK 2,111,657

- V HYDRAULIC PUM? 0R MOTOR Filed May 22, 1934 3 Sheets-Sheet 2 ELEKK .EENEEEK.

Patented Mar. 22, 1938 UNITEDSTATES PATENT OFFICE I ,nrnaanmzi ditr l on Moron Application May 22, 1934. Serial No. 726,962

9 Claims. (01. 103 -161) This invention ,relates to pumps or motors of the radialv piston type and more particularly to an improved design ,of pump or motor of theclass above referred to, which design is more eflicient, more positive in its-action and more compact in its structure.

Another object of this invention is the provision of a one piece hydrostatically balanced cylinder block or rotor, made of high grade alloy steel, so that the torque shaftmain driving or driven member as the case may bemay be forged out of the body of the rotor, and enable the machine when adapted to serve as a motor to transmit great torque at very low speeds. The objects include the provision of a motor which will transmit power at a speed identical with the speed of the driving pump and at reductions as great as in the ratio of 100:1 without any considerable decrease in efiiciency. v j

Another object of my invention is the provision, in a hydraulic motor or pump, of a rugged one piece body, comprising the valve head for inlet and exhaust fluid as well as the entirejmounting for a one piece twin cam designed 'for imparting reciprocating movements to radial pistons in a highly eflicient manner.

A further object is to provide for more accurately centering the piston carrying rotor-,cen- 40 tral valve and piston operating cams with ,each other to thereby reduce friction, vibration and fluid slip losses to the end of securing such operating efiiciency as will enable the mechanism to compete with well designed mechanical transmissions in this respect.

A further object is to provide, in a hydraulic motor, a novel arrangement of piston'reactance cams the surfaces of which may be 'more easily formed by standard machine tool equipment and which afiect the fiow characteristics of the motor in such manner that when'the -mechanism is used in connection with a variablespeed transmission, the motor speed will respond to changes in volume delivered by the pump gradually and without pressure fluctuation in the interconnecting piping of the pump and motor, or main transmission line. v

Another object. of my invention is the provision of cam surface arrangements controlling the pistons in their pressure and exhaust strokes and cooperating cross pin rollers reducing friction and play as much as practically possible for higher torque 'efliciency. v Another novel feature of my invention resides in the piston unit assembly, comprising anti-friction journal pins mounted in the piston heads, with paired rollers shrunk fitted to the pins with slight axial plearance between piston head and the rollers so that a slight transverse misalignment between the roller tracks and the axes of the pistons will be possible without any damage to the pump and so that the needle bearing for the pins may beheld in working relation to the pins and piston heads by the rollers without requiring special retainers, and so that the parts of the piston units may be very easily kept in one sub-assembly. j

Another object of the invention lies in the provision of a combination bearing, mounted in a special axially movable bearing housing, said housing being adapted to provide one of the exhaust cam profiles to operate the piston subassembly as well as to hold the rollers against I axial displacement.

A further important object of my invention is to provide transverse anti-friction or equivalent bearing means for the piston heads in the direction of radial reciprocation, so that the torque component of the radial piston load, acting transversely to the axis of the reciprocating piston will not materially reduce the efliciency of the machine.

Another specific object of my invention is the provision of a floating universal connection be tween the pistons and their'heads so that the turning force applied to the piston heads will not transmit transverse load to the radial pistons.

Other objects and novel features will appear from the-following description relating to the accompanying drawings. The essential novel characteristics are set forth in the claims. Referring briefly to the drawingsz= Fig. 1 is a longitudinal sectional view of my novel pump or motor, taken substantially along the line Il on Fig. 2 and showing. the central valve pintle and the impeller shaft in elevation only; Fig. 2 is a transverse sectional view taken substantially along the line 2-4 of Fig. 1, showing the crosshead guide flange of the rotor and also the pistons in side elevation for clearness of illustration;

Fig. 3 is a partial sectional view of a modified piston unit and cross head assembly with an anti-frictionally guided crosshead and two part piston including a universal floating connection between the piston parts. This view corresponds to the showing of any one of the pistons and guides therefor shown on Fig. 2;

Fig. 4 is a sectional view taken on line 4-4 in Fig. 3;

Fig. 5 is a transverse sectional view taken on line 5-5 in Fig. 1, showing the communication of one of the main passages for fluid in the ma.- chine with passages in the valvepintle;

Fig. 6 is a sectional view similar to Fig. 5, taken partially through the lin5--5, but centrally offset to show the communicating passages between the other main passage and the pintle; and Fig. 7 is a section taken as indicated on Fig. 3.

Referring in detail to the drawings, the pump or motor disclosed for illustration comprises a generally cylindrical unitary rotor unit 2 adapted to be made as a forging preferably from Nitralloy or tungsten carbide steel or equivalent wear resisting metal and having an impeller shaft I forged integrally with the main body of the rotor. The cylindrical body portion of the rotor 2 is provided with a central flange portion 3, and has an axial bore at 4, to receive a stationary central valve pintle 5. The rotor and pintle mutually support each other by reason of two sets of axially spaced pilot roller needle bearings 8 and 9 respectively, which ride directly on accurately finished and shouldered or undercut surfaces of the pintle and rotor requiring no special retainers or. cages. The needle rollers 8 are axially retained in an undercut annular channel in the reduced end of the pintle and the rollers 9 are axially retained at one end by the adjacent relative enlargement ill of the pintle and oppositely by the wall of a counterbore in the rotor or if desired a retainer ring (not shown)- in the bottom of the counterbore. The bearings 8 and 9 will positively mount and center the rotor on the pintle and be lubricated by oil necessarily escaping between the adjacent surfaces of the rotor and pintle, between the bearings, these surfaces however being in snug hydraulic fit and preferably lapped. The mounting provides a considerable span between the two bearings for the axial stability of the rotor against lateral vibration of the crosshead flange 46 of the rotor.

The pintle 5, has an enlarged end Ill which is supported in the central hub portion 33 of a main casing section 32 of the machine and the rotor is supported in part by the pilot bearing arrangement just described and also preferably by one or more very sturdy anti-friction bearings, one only (39) being shown and this being supported in a main bearing housing 35 fitted to the casing section 32 as will be later described. The hearing 39 may be retained in the bearing housing by a casing closure cap 42, and the casing parts or sections just referred to are screwed or bolted e. g. together forming in effect one rigid casing unit when assembled. the pintle is very firmly secured in the hub portion 33 of the main casing part as by heavy press fit.

The bearing 9 and the main bearing 39 distribute the greater portion of the operating torque pressures between them and the small needle bearings at 8 by reason of their location on the rigidly mounted pintle have only to steady The enlarged end I 0 of the rotor hence may be small, as shown, in proportion to the bearing 39. In case of extremely severe service at low speed and high torque for the motor, I may provide another high torque pressure bearing opposite the bearing 39 surrounding the end of the rotor radially opposite the bearing 9 to support said end of the rotor, and unload-the pilot bearing 9 from any substantial transverse force imposed by the torque. This modification would necessitate the inlaying of the left hand exhaust stroke cam. shoulders 30 in the respective casing sections 32 and 35 so that the bearing may be axially removable. Hence it is important to obviate the necessity for such outer bearing at the inner end of the rotor when possible.

The pintle 5 in order to provide balanced hydrostatic load condition and proper distribution for any oval shaped cam is provided with four diametrically opposite ports as at II, I2, I3 and I4 respectively, which ports will in proper time intervals successively communicate with the radial rotary ports 23 of the piston cylinders 24 of the pistons 25. Thus it will be seen that the working fluid will simultaneously occupy and cause pressure film spread around ports I2 and I3, or about I I and I4 whichever may be the pressure ports. The axial conduits I2a and I3a will create communication between internal ports I2 and I3 and inlet ports I8 and I! respectively to the inlet pressure main 22. The opposite port 2I will discharge the fluid of the other ports I I and I4 through their discharge passages Na and Ma through distributing discharge channel I9 Fig. 5 which is axially spaced from and functions oppositely to the inlet e. g. distributing channel 20.

Cylinder block 2 is provided with a radial series of individual bores 24 which are fitted with pistons 25. Each piston is provided with an enlarged head as at 26, and a transverse bore to carry cross pins 3|, which are anti-frictionally mounted in the heads 26 in capillary needle rollers or their equivalent as at 21. The heads may be cylindrical in cross section or non-circular as desired and in any event the heads are flattened in the transverse plane of the rotor common to all the pistons, to reduce the axial extent of the cross pin assemblies and for reduction of their supporting span.

Since the pins 3i and the associated piston crossheads are rotating at substantial speeds and under considerable centrifugal force at the upper speed limit it will be clear that the capillary bearing means such as 21 have definite advantage over non-capillary bearings by holding the lubricating fluid in between and around the needles thus eliminating Wear, so common in cases of rigid, non-capillary bearings for this purpose. Another inherent advantage of the needle rollers is in their rotation, and flexibility. Since the piston load is acting always in one direction, the loaded needles try to escape their responsibility and thus new needles come under the load, and thereby automatic wear equalization takes place in the bearings, and subsequent longer life of the cross pins 3I and the needles 21 will be obtained.

Each crosshead 26 is guided in a radial cylindrical or non-circular guide space 46b formed in the flange 46, and, in case the machine is adapted to serve primarily as a motor, the tangential forces will be preferably transmitted between the sides of the crosshead and complementary noncircular (planar or prismatic e. g.) guide surfaces 46a of the guide flange 46.

Each cross pin after having been mounted in needles 2'! will have secured thereto a pair of rollers or other suitable cam followers as at 28, which will be permanently fixed to the respective ends of the pins 3| as by heavy shrink fit with appropriate axial clearance between both sides of the piston heads 26 and the rollers 28, so that any transverse misalignment of the roller guides and/or the piston guides will be taken up without friction or strain on the structure; and so that the needles, pistons and cam followers .will be simply and permanently retained as a convenient sub-assembly unit for ease in handling, say during It will .be observed that in the illustrated embodiment of the invention the reactance means comprises axially separable side members 32 and 35 respectively formed with inner trackways -30 and a member 29 curve of my motor, and draw the cam profile for intervening between said side members and providing the outer trackways for the rollers 28, the bolts 45 serving to secure the side members 32 and 35 and the intervening member 29 in assembled relation. The reactance engaging rollers 21 on the protruding ends of the cross-pins 3| lie respectively between the radially disposed side faces of the piston head portions and the adjacent radially extending portion of the reactance side members. The rollers 21 act to retain the roller bearing elements 21 within the piston head bores, the arrangement being such as to facilitate assembly of the parts as well as to provide a compact smooth-running structure.

The pressure path of the piston sub-assembly unit is formed of a unitary cam forging having symmetrical working profiles about the transverse meridian of the unit and these working profiles are generated simultaneously by appropriate machine tools and with one setting, so that the rotational axes of the cam follower rollers and rotor will be parallel at all times in any angular position of the rollers with the rotational axis of the rotor 2 for smoother and more silent running with minimum rolling resistance and losses. Made in this fashion one roller of a given cross pin never has to drag the other of the same pair as might be the case if the cam tracks were separately formed or mounted in inaccurate angular position with respect to each'othezgi. e. with a The character of the pressure cams is such'that the relative piston strokes remain substantially of pure harmonic nature since the entire profile is made up of circular sections, thus the resultant reception and discharge of fluid by the motor will be substantially the same in character at all deliveries as the res Variable Displacement Pumps etc., Transactions of A. S. M. E. for February, 1934, pagev 89, which furnishes a 10 pitch harmonic above the horizontal axis which axis carries the time scale for a complete revolution. The Y axiswill carry the resultant velocity scale which, as is well known is identical with the delivery per second curve. Thus a velocity resultant curve for the 5 plunger pump gives a resultant curve. Then I assume said resultant curve as the resultant delivery each revolution of a piston in such manner that the resultant velocity for such profiles will be substantially identical with the resultant velocity of the pump. The result gives the profile shown in Fig. 2,v which can be composed or built up of two different distinct curvatures in four sections. Thus instead of a true elliptical cam, anoval-shaped cam results with a ratio of not less than 1.25 to 1 between the major and minor axes of the oval-for low speed and great reduction ratios such as :1 and commercial efficiency. A larger ratio between the major and minor axes of the oval is recommended to obtain better torque characteristics at low speed rather than better speed characteristics at higher speed. Thus it will be noted that the peaks of my cams are circles of the radius 1', whereas the less curved I or above the speed of the driving pump. Such" modified form is disclosed in my copending application 749,745, filed October 24, 1934, which shows my novel pump and motor, comprising an adjustable oval cam to provide a hydrostatically balanced pump or motor of the variable displacement type.

The practical advantages in manufacture of my novel cam are very apparent. The ends of the cam may be ground by a grinding wheel of the radius 7', one after the other by appropriate shift of the Work, which will leave plenty of space to finish the sections of the radius R with the same grinding wheel. But even in case of using a master cam for finishing and grinding with a small wheel say of the size of the rollers 28, by grinding the profiles continuously along the periphery, the operation will be much easier and more accurate due to the true circular characteristics of the cam sections.

The inner or exhaust earns 30 (contours parallel with line 29a not shown in Fig. 2) are integral with the respective casing parts, as illustrated in Fig. 1, this being entirely satisfactory in case the machine is designed to serve as a motor wherein the rollers are constantly under outwardly acting forces only. Preferably the end walls of the casing have'portions disposed along side opposite faces of the barrel flange which portions are formed with rabbeted under-cuts in the zones of the associated rollers as shown in Fig.. 1. These under cuts provide inner cam tracks for the rollers 28, the tracks having radially extending track edge portions immediately alongside the outer marginal portions of the rollers with operating clearance only between the track edge portions and the rollers. However, these cams may be made of separate, hardened and ground rings having contours parallel with the pressure cams and inserted into the end walls of the casing when the device is used as a pump 39 and thus the inner ring lll absolutely concentric with the pintle 5 for the purpose of providing substantially frictionless performance of the valving functions of the pintle 5 and barrel bore 4 respectively. Closing the casing I provide a shaft end cover 42 having a retainer shoulder 43 to lock the inner bearing ring 40 against the shoulder 31 of the housing member 35. The inner ring 40 is locked against the rotor 2 by an appropriate lock nut 4| either threaded or pressed on the shaft end of the rotor forging. Coupling bolts 44 and 45 as shown secure the housing 35 and cover 42 in their respective assembled relation to the adjacent casing parts.

Figs. 3, 4, and 7 show the two-part pistoncrosshead earlier referred to, including improved bearing supports for anti-frictionally guiding the crossheads of the pistons under the transverse driving forces of the crossheads in the rotor. Since in a motor, each crosshead 26 Fig. 3, has to carry large radial and transverse pressures simultaneously, I propose to provide a pair of transversely opposite bearing surfaces as at 46a in guide flanges 46' of the rotor, adapted to receive needle bearings 49. Lips 50 retain the needles in their operating relation. The needle elements are insertable through a pair of transverse holes as at 46b formed by cutting away the lips 50 as by an appropriate bore, which will allow filling the needles into the needle spaces.

The crosspins 3| Figs. 3, 4, and 7 are carried as previously described on needle rollers 21' but the piston proper 25' has its individualcrosshead as at 25a, and'a reaction cap 25b. The mating thrust surfaces of the crosshead 25a and the cap are spherical and the pistons and heads have slight clearance as at 250 for lateral self-alignment of the pistons.

This two-part piston crosshead arrangement has great significance not only from the viewpoint of efllciency but also obviously from the standpoint of manufacturing and handling the parts. From the viewpoint of efliciency the separation of the normal function of the piston 25' from the torque exertion of the croshead 26 means that transverse wear of the crosshead will not affect the pistcn'to cause it to wear its cylinder, and thus even after considerable wear of the crosshead guide the piston will still be highly efllclent in delivering its required capacity. Moreover since the needle bearing suport 49 facilitates radial movement of the piston assembly it is evident that the tangential or torque component of the crosshead forces and thus the turning moment of the motor will be greater, which means a more efficient machine. I

The spherical mating surface of the piston crosshead proper 25a. and the reaction cap 251) provide perfect alignment for the pistons 25 in their cylinder bores irrespective of slight misalignment of the bores and corresponding crosshead guides 46a further insuring greater efiiciency by reducing wear and strain.

The operation of the machine as a motor is as follows: Assuming a clockwise revolution for the rotor 2 as viewed in Fig. 2, it is necessary to provide pressure fluid for the outgoing pistons, thus ports Ila and Ma must conduct the pressure fluid for such rotation. The pressure fluid being substantially incompressible, the pistons are forced to move outwardly and thus due to the angle of incidence of the associated piston axes with the cam tracks 29a, the rollers 28 are forced to roll clockwise on the pressure tracks as will be obvious. The work being equal to the force times the travel, the useful work exerted by each piston, will be proportional to the working pressure times the working stroke of the pistons. Thus to obtain definite starting impulse it is necessary to impart definite speed to the pistons per unit time. This has been done in my motor by the relative travel of the pistons in the oval cam, which, as explained above, is constructed to have a minimum ratio of 1.25 to 1 between its major and minor axes. The relative slope of the cam will determine the rolling friction and thus the rolling drag of the motor. The greater the above ratio, the greater the torque efliciency will be. Another factor is the rolling friction of the rollers. Due to my anti-friction mounting of the crosspins in needle rollers, this rolling friction is brought substantially to its minimum value. The third factor of efficiency is the rolling track friction of the rollers 28 in the cam surfaces which I reduce as much as practicable by using very hard surfaces obtainable by Nitralloy or tungsten carbide steel. Finally the floating piston arrangement and the anti-friction thrust hearings in the crosshead guides as at 49 will enhance the hydraulic efli? ciency by the reduction of radial friction between the crossheads 26' and the guide blocks 46. In the above stated use the inner cam track surfaces 30 are only called upon to steady the inward movement of the pistons, the outer cam tracks actually accomplishing the work of exhausting the fluid through the ports l2 and I3 and communicating passages I211, I311, etc. in the pintle.

In operating as a pump (which may require the above suggested modifications of the inner cam track surfaces) the action is simply reversed from that above described, the ports II and I4 being suction ports assuming clockwise rotation (Fig. 2) of the impeller shaft and rotor and the ports I! and I3 becoming the pressure ports.

It will be noted that when my device operates as a pump, it will be highly eflicient due to its hydrostatically balanced nature. This means, that great pressure can be allowed to build up without putting any load on the central elements of the pump, in fact its mechanical efficiency will be independent of the pressure, with the exception of the rolling friction of the rollers which will increase in proportion with the pressure.

The radial compactness of my motor, the one piece mounting casing, the axial compactness, the hydrostatically balanced action of the pintle and rotor, the pilot bearing supported rotor forged as a single block from high grade steel with integral torque shaft, the compact piston sub-assembly units with capillary needle roller mountings to maintain capillary lubrication of the crosshead pins, the unitary extra hard and directly supported pressure and exhaust cams, the axially self -aligning pistons, and the novel two-part piston and crosshead structure of Figs. 3, 4 and 7 are all novel features which taken in combination simultaneously result in a plurality of advantages of great importance in operating efficiency and long wearing qualities of hydraulic pumps and motors utilizing the principles of the invention.

Having thus described my invention, I claim: 1. In a pump or motor of the character described, a substantially cylindrical casing, a stationary pintle centrally secured in said casing, a rotor having valving cooperation with the pintle, a radial series of cylinder bores in said rotor, a piston for each cylinder, a crosshead for each piston, a plurality of radial extensions forming crosshead guiding surfaces surrounding said rotor and disposed in the plane of said bores, mechanical bearing means interposed between the guiding surfaces of the extensions and the crossheads to resist the transverse'reactions of the crossheads, a secondary crosshead associated with each piston, having a planar radially inwardly disposed surface and a spherical outwardly disposed surface, a cap associated with thesecondary crosshead, having a planar outwardly disposed surface and a spherical surface mating with said spherical surface of the secondary crosshead, and an openingin the piston crosshead substantially closely engaging the said planar surfaces of the secondary crosshead and cap thereof and reactance means operatively associated with the crossheads for reciprocating the pistons.

2. In a rotary radial piston pump or motor, a rotatable barrel having a plurality of radial cylinders, valve means for the cylinders, a radial flange on the barrel in the zone of the cylinders, a stationary reactance surrounding the barrel and comprising a pair of parallel cam tracks arranged at opposite faces of the flange to accommodate the passage of a portion of the flange therebetween, pistons in said cylinders respectively, radial guideways in said flange and aligned respectively with the cylinders for accommodating and guiding outer end portionsof the pistons for radial reciprocation, cross pins rotatably mounted in the outer end portions of the pistons, each cross pin extending parallel to the barrel axis beyond the lateral faces of outer end portions of the associated piston, rollers fixedly secured on the ends of said cross pin and rotatable as a unit therewith and in rolling engagement with the tracks, said rollers having end portions lying partially in said radial guideway of the associated piston and prevented thereby from skewing.

3. In a rotary radial piston pump or motor a rotatable barrel having a plurality of radial cylinders, valve means therefor and a radial flange means on the barrel in the zone of the cylinders, a reactance surrounding the barrel and comprising a pair of parallel reactance tracks arranged at opposite faces of the flange means and accommodating the flange therebetween, pistons in said cylinders respectively,-radial guide-ways in said flange means and aligned respectively with the cylinders for accommodating and guiding the outer end portions of the pistons for radial reciprocation, transverse thrust means carried by the outer end portion of each piston and extending parallel to the barrel axis beyond the lateral faces of the outer end portions of the associated piston, rollerson the ends of said thrust means and in rolling engagement with the tracks, said rollers having end portions lying partially in the radial guideway of the associated piston and prevented thereby from skewing.

4. In a rotary radial piston pump or motor, a rotatable barrel having a plurality of radial cylinders, valve means for the cylinders, pistons in the cylinders respectively, parallel, stationary elliptical cam tracks surrounding the barrel, and means carried by the pistons, respectively, for anti-frictionally rolling on said tracks for cooperating the tracks and pistons, said means comstrain said rollers and pin from skewing,

5'. In a rotary radial piston double pumping cycle hydraulic pump-or motor a rigid casing hav-- ing a circumferential wall and end walls, a valve pintle mounted in one end wall and extending into the casing, a rotatable barrel anti-frictionally mounted on'double thrust bearings in the opposite end wall of the casing coaxial with and fitting the pintle, said barrel having a plurality of radial cylinders, pistons in the cylinders respectively, a radial flange in the barrel in the zone of the cylinders, said cylinders being in valving cooperation with the pintle, radial guideways in the barrel flange aligned with the cylinders respectively and in guiding engagement with the outer end portions of the pistons, cross pins rotatably mounted in the pistons and extending therebeyond parallel to the axis of rotatiomrollers carried on the ends of the cross pins, a pair of stationary elliptical cam tracks for the rollers in the casin in surrounding relation to the barrel and disposed alongside opposite faces of the flange, the end walls of the casing having portions lying alongside the flange, said portions respectively being formed with rabbeted undercuts in the zones of the associated rollers to provide inner cam tracks for the rollers having radially extending track edge portions alongside the outer marginal portions of the rollers with operating clearance only between said track edge portions and said marginal portions of the rollers.

6. In a rotary, radial piston pump or motor, including a barrel having a radial cylinder, valve means therefor, a radial flange on the barrel in the zone of the cylinder, a piston in the cylinder, said flange having parallel radial guideways fore and aft of the piston, a cross head on the piston reciprocable radially in the guideways, and reactance means operatively connected to the piston head for reciprocating the sameconsequentupon relative rotation of the barrel and reactance, means for anti-frictionally guiding the head in the guideways and for transmitting torque be tween the head and barrel comprising parallel planar bearing faces on the guideways, undercut guide flanges along the lateral marginal limits thereof, free cageless rollers extending transversely of the bearing faces with their end portions in the undercuts of the guide flanges, and constrained thereby from displacement laterally of the guideways, said cross head having fore and aft portions received between the guide flanges, having planar end faces in cooperation with the portions of the rollers exposed between the flanges.

7. In a rotary radial piston pump or motor, a

rotatable barrel having a plurality of radial cylinders and a radial flange in the zone of the cylface, the other-member having a planar surface,

a cap interposedbetween the members and having surfaces matingsaid surfaces thereof, and a. recess in the crosshead member accommodating the piston and secondary head member, and means for holding the members and interposed cap in assembled condition.

8. In a rotary radial piston pump or motor, including a rotor, radial cylinders and cooperat-' ing pistons carried thereby, reactance means for reciprocating the pistons, valve means for the cylinders, operating head portions respective to the pistons, each of said head portions having a bore extending parallel to the axis of the rotor, a thrust pin received in the bore and protruding therefrom at each end, free elongated roller elements intermediate the thrust pin and bore wall and substantially coextensive axially with the bore wall, said rollers being spaced apart circumferentially of the bore a capillary distance only Iromeach other for free individual rolling action, reactance engaging rollers fixedly secured on each end of the pin and forming a unitary roller structure therewith cooperable with the reactance means, said reactance rollers lying in closely spaced face to face relationto the ends of said bore and being of greater diameter than the bore for retaining the free roller elements therein while permitting limited floating movement of the pin axially of the bore.

9. In a rotary radial piston pump or motor, a rotor; radial cylinders and cooperating pistons carried thereby; operating head portions on the pistons respectively and having radially disposed side faces; each of said head portions having a bore extending parallel to the axis of the rotor; a plurality of thrust pins one received in each bore and protruding therefrom at each end;

elongated roller bearings intervening between each thrust pin and the associated bore wall and substantially coextensive axially with the bore wall; reactance means surrounding said cylinders and including inner and outer trackways on opposite sides of the piston head portions, said reactance means comprising axially separable side members respectively providing said radially extending portions and said inner trackways, a member intervening between said side members and surrounding said pistons and cylinders and providing said outer trackways, and means for securing said side members and said member in assembled relation; reactance engaging rollers on the protruding ends of said thrust pins and lying respectively between the side faces of the piston head portions and the adjacent reactance side member and lying between and being adapted for rolling engagement with said inner and outer trackways, said rollers being secured to said pins on each end thereof, each pin and associated two secured rollers forming a unitary roller structure, said rollers lying in face-to-face relation to the ends of the associated bores and. being of greater diameter than said bores for retaining the elongated roller bearings in operative position within the bores.

ELEK K. BENEDEK.

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