US2753810A - Pump or motor - Google Patents

Description

July 10, 1956 B. F. QUINTILIAN 2,753,810

PUMP OR MOTOR Filed Jan. 30, 1953 5 Sheets-Sheet 1 INVENT OR Barf/w/omew F Ou/n/i/ian H l S ATTORNEY y 0, 1956 B. F. QUINTILIAN 2,753,810

' PUMP OR MOTOR Filed Jan. :50, 1953 3 Sheets-Sheet 2 IN VENTOR Eartha/omew F Ou/nf/l/an H [S ATTORNEY July 10, 1956 F. QUlNTlLlAN 2,753,810

PUMP OR MOTOR I Filed Jan. so} 195: I s Sheets-Sheet 5 FIG. 5

- I N VENTOR Barf/w/amew F Ou/n/i/ian HIS ATTORNEY United States Patent PUMP OR MOTOR Bartholomew Frank Quintilian, Baltimore, 'Md., assignor to Gerotor May Corporation of Maryland, a corporation of Maryland Application January 30, 1953, Serial 'No. 334,137

9 Claims. (Cl. 103l2'6) My application for patent is a companion to my copending applications Serial Nos. 535,083 and 578,418, respectively, of May 11, 1944 .and February 17, 1945, and both entitled Hydraulic Pump and Motor, now U. .8. Letters Patent 2,672,824 and 2,672,825 of March 23., 1954,

and the present invention relates generally to hydraulic pumps and motors of the type wherein rotatable elements cooperate to provide a plurality .of compressor compartments of continuously varying dimensions.

An object of my invention is to provide an improved rotary pump involving low relative rotational speeds between the component parts and characterized both in its basic simplicity and in its ease and rapidity in both construction and assembly while at the same time displaying high efficiency, the while it is rugged, compact and displays long useful life under the most arduous and demanding heavy duty requirements and adverse operating conditions, all with minimum demand of supervision and servicing.

Another object is to provide arotary hydraulic pump of the general type described wherein marked simplicity of constructional design, together with materially lessened requirement of constructional detail and refinement, is coupled with improved adherence to close dimensional tolerances, and yet with substantial reduction in cost of construction as compared to known pumps of generally similar construction.

A still further object is toprovide a hydraulicmachine of the foregoing general type which in operation is quiet, self-aligning and self-equalizing, with radially applied, constant bearing pressure, while eifectivelysuppressing all tendency towards diametral looseness and attendant inefliciencies, all with reduced tendency towards tooth scuff.

All of the foregoing, as well as many other highlypractical objects and advantages, attend .upon the practice of my invention, and these in part will The obvious and in ,part more fully pointed out hereinafter during the course of the following disclosure, particularly when taken in the light of the accompanying drawings.

Accordingly, my invention resides in the several parts, elements and combinations thereof, in the various constructional features, and in the relation of each of the same with one or more of the others, the scope of all of which is more fully set forth in the claims at the end of this specification.

In the accompanying drawings, wherein illustratively, .I have disclosed that embodiment of my invention which I presently prefer.

Fig. 1 discloses, in perspective, a .pump or motor according to my invention wherein part of the constructional features, for clarity, are disclosed in drop perspective;

Fig. 2 is an exploded perspective of the-device according to Fig. 1, the component elements 'of the assembly being disclosed in their proper relation to -'each other; While Figs. 3 and 4 are elevations disclosing a pump assemplace at a suitable outlet port.

ice

bly in different phases of its operating cycle, to aid in readily understanding the mode of operation, and

Figs. 5 and 6 disclose certain essential portions of two modified forms of my new pump or motor.

Throughout the several views of the drawings like reference characters denote like parts.

To enable ready understanding of the nature of my invention it is advantageous at this point to give brief consideration to the development of rotary hydraulic equipment of the general type to which my invention has application.

Considering for convenience a hydraulic pump, it is to be noted that one fundamental type of pump is comprised by rotating one within the other, two generally cylindrical members conveniently having the form of gears, these being disposed asymmetrically with respect to each other, and the two members in turn being disposed within a suitable casing. This operation comprises supplying a fluid between the two members by way of a suitable inletport, the supply of fluid coming from any convenient source, typically a suitable reservoir. At some convenient point along the casing, circumferentially remote from the fluid intake port thereon, discharge takes During the rotatingpassage from inlet to outlet ports the two rotating members bring about an increase in pressure exerted upon the fluid, and this within a progressively diminishing space between .the two cooperating rollingelements. Thence the fluid is discharged through the outlet port. Long wear and simplicity are but two of many important advantages of this type pump.

It is well known that these pumps operate due to relative rotation taking place between the inner and outer rotors, and this as a result of having the teeth of the inner rotor one less in number than the corresponding .teeth of the outer rotor. This is typically shown in the United States Letters Patent to Hill No. 2,011,338. The onepiece, ring-like outer rotors in these devices are circular in outer periphery, possessing internally disposed teeth, thereby providing a plurality of inwardly projecting rounded teeth with inter-viewing valley or concave portions.

The operation of such a unit is well known as briefly suggested above. Given the foregoing construction of the outer rotor, and with the inner rotor axially off-set or eccentric with respect to the outer rotor to such extent that certain of the teeth of the two rotors are in full engagement, then upon rotation of one of the rotors (say the inner rotor) to drive the other, a constant but slow gain in revolutions occurs between the two rotors. The outer rotor rotates at an annular speed slightly less than that of the inner rotor, in proportion to the number of teethof the respective rotors.

At all times during this operation the teeth of the two rotors are intermeshed, thus defining a plurality of se arate compartments. And because of the eccentric relationship of the two rotors each such compartment is of continuously varying dimensions. Proper design, particularly as concerns the casing for the rotors, insures that these separate compartments are each sealed against the exterior. Therefore, when a fluid, such as air or liquid, is introduced through a suitable port into a compartment where this latter momentarily has approximately its greatest dimensions, then in subsequent phases of any particular revolution of the driving rotor, the several compartments conveying the fluid undergo a progressive, continuous and nearly constant decrease in dimensions to a minimum. A suitable port adjacent the region of minimum dimensions serves for the discharge of the fluid under maximum compression.

'It is apparent from the foregoing that this type of pump displays many practical advantages, particularly when contrasted to the old, single-compartment pump. Typical of these are its basic simplicity and, due largely to the small number of moving parts and relative low rotational speeds, its display of long wear with but little demand for maintenance, repair and supervision.

In practice, however, certain characteristic difficulties are encountered with the prior art pump. lllustratively, the contact between the cooperating parts of the inner and outer rotors is frictional and sliding in nature. Thus, where a non-lubricating substance is undergoing compression, illustratively a gas, undue wear experienced between the contacting parts of the unit. Readjustment and even replacement of parts more frequently than is desirable accordingly is required with this known unit. Moreover, definite limitations are thus placed upon the range and scope of utility of this type of pump.

Perhaps even more important than the foregoing, however, is the expensive broaching and other machining processes which are required in producing the one-piece outer rotors employed in the known units. For it is to be recalled that these ring-like outer rotors must be handled as a unit and subjected to manufacturing processes while surrounded by the ring of solid metal from which the teeth are shaped. To machine or grind the circular conjugate action on the internal face of the conventional one-piece outer rotor or ring gear interposes much difficulty because of the confinement necessarily interposed by the one-piece design. Of necessity, the broaching or shaping of the teeth in the conventional one-piece ring gear is largely across the tooth surface, rather than circumferentially thereof. This is attended by some maladjustment between the teeth of the two gear elements, and tooth scuff, together with tooth running friction, is observed between the inner and outer elements.

A still further difficulty is encountered when a noncompressible fluid is being handled by the pump. Where there is an appreciable arcuate distance between the inlet part and the outlet part it will be recognized that this fluid will be trapped in the cooperating teeth within this region and as the space between the teeth continued to decrease, high pressures will be established. Such high pressures perform no useful function; on the contrary they give rise to imbalance of parts and objectionable wear.

An important object of my invention, therefore, is to provide a new internal gear hydraulic unit which, while generally subscribing to the constructional features of conventional rotary pumping units, nevertheless avoids in substantial measure the many aforementioned disadvantages and defects, and which at the same time permits markedly easier, cheaper, more rapid and more accurate grinding of the tooth segments hereinafter to be defined, together with a greater freedom of tooth grinding in a circumferential direction, thereby permitting tooth contact in tooth areas where the action is along the grain of the surface finish rather than across the grain, that is, more complete running in of the intermeshing gear teeth, all with effective relief for the establishment of excessive non-functional fluid pressures.

With the known pumps not only is considerable noise observed, but as well, non-uniform tooth loading is encountered, accompanied by heating and frictional losses. All of this interposes frequent and constant demand for adjustment and even for replacement.

A further object of my invention, therefore, is to produce a unit of the general type described, which is characterized by its appreciably quieter operation, its better and more uniform load distribution over the surface of the intermeshed teeth with lower peak loading, with attendant longer, diminished and more uniform wear with reduced friction, smoother operation, lower developed heat and reduced tooth scuff, all with decreased cost of machining.

Referring now more particularly to the practice of my invention, attention is directed to the embodiment of my invention disclosed in the several views of the drawings. In these, especially Figs. 1 and 2, I disclose a rotary unit of the type described, here a pump, having an outer body portion 10. Cooperating with body portion 14 is a head portion 12, cylindrical in form, having an inner cylindrical recess or bore indicated generally at 11. A machined wall 11a, illustratively a plane surface perpendicular to the axis of the bore, terminates the latter at its inner end. In operation the head 12 may be retained in suitable position against the body portion 10 in any suitable manner. Here I disclose bolts 13 extending through washers 13a and holes 14 in the head 12 near the periphery of the latter. These bolts fit in corresponding threaded apertures 15 in the adjacent end of the body member 10. Preferably I shoulder the holes 14 for reception in inconspicuous manner of the washers 13a and so as to provide a smooth and generally continuous and uninterrupted outer surface on the head 12 near the periphery thereof, i. e., without external raised or projecting portions. As shown, I provide a dowel pin 12a at any suitable point along the inner face of head 12, preferably near the periphery thereof. A cooperating positioning opening 10a in the adjacent face of body 10 serves to receive this dowel pin. Automatic assurance is thus provided of ready and proper position of the head 12 relative to the body 10 during assembly of the unit. The body 10 and head 12 together comprise the casing of my new pump.

On diametrically opposite sides of the body 10 I provide ports 16 and 17, generally circular in cross-section. These ports respectively extend from the exterior through and into the elongated relatively shallow and arc-shaped manifolds 18 and 19. Each manifold extends for a substantially accurate distance in each direction away from the center line of the port. Illustratively, but not as a limitation, each manifold in the present embodiment extends approximately 60 degrees in each direction from its port, for a total angular reach of approximately degrees. The purpose of these manifolds will be'developed at a later point herein.

Particular novelty is resident in the outer rotor according to my construction. This rotor fits snugly within the casing defined by body 10 and head 12. It is made up of a plurality of tooth segments, each separate and apart from the other. This outer rotor, indicated generally at 20, is thus comprised of a plurality of like tooth segments 21, the design of which is such that the proper number of tooth segments of which it is comprised will, in assembly just complete an entire circle, forming a completed outer rotor. The width of these segments 21 is almost exactly that of the interior depth of bore 11, being at the most, only a few thousandths of an inch less than each depth. As will be seen, this permits adequate seal against lateral leakage, while permitting high rotational speed of the tooth segments. This composite outer rotor 20 is received in sealed relation within cooperating and mating surfaces of bore 11 and head 12.

An inner rotor indicated generally at 22 is disposed within the outer rotor 20 in manner enabling relative movement therebetween. The inner rotor 22, which is toothed, has generally the appearance of a fluted starwheel. Thus the inner rotor has a series of projecting teeth 22a, with depressions or valleys 22b between adjacent teeth. As shown, these valleys are ground on continuous curves. While these curves may be simple, i. e., struck on a single radius, preferably, and for a proper tooth contact, they are ground on compound curvature, according to equations either logically or empirically derived.

I provide a central bore 220 for the inner rotor 22 and provide this with a key-way 22d for locking engagement with a drive shaft, to be described.

Thus, I mount the inner rotor 22 on a drive shaft 23, making the same fast on the shaft in any suitable manner as by key 23a on the drive shaft 23 cooperating with and engaging in the key-way 22d, heretofore described. I mount the shaft 23 for rotation in suitable anti-friction bearings 24, 24 provided in the casing body 10 and head 12. For the reception of these hearings, which illustratively may be of any suitable type but are shown here as roller-bearings, I provide holes 1012 and 12b in the body 10 and head 12, each such hole being bored eccentrically with respect to the bore 11 in head 12. One such bearing is shown in the casing body 10, but for convenience, is omitted in the disclosure of the head 12.

In my new construction the rotors are powered through shaft 23 to which the inner rotor 22 is made fast.

As has been suggested hereinbefore, the inner rotor 22 comprises a plurality of radially disposed teeth 22a between which are formed recesses or valleys 22b of epicycloidal or other suitable configuration. Preferably, the teeth are of uniform contour and shaping, and in number, comprise one less than the number of separate, tooth segments which make up the outer rotor 20. Bearing in mind that the inner rotor 22 is disposed eccentrically relative to the outer rotor 20, it follows that at any given time one tooth 22a of the inner rotor momentarily is substantially fully enmeshed and engaged with two adjacent teeth 21, 21 of the outer rotor. In this momentary situation, the remaining inner rotor teeth 22a are in various stages of mesh or contact with the remaining outer rotor toothed segments 21. Accordingly, when the drive shaft 23 is rotated, carrying with it the inner rotor 22, the driving impulse from this latter is transmitted to the outer rotor 20 through the intermesh- .ing teeth of the two rotors, these rotors are rotated at a high speed, i. e., the rotational speed of the drive shaft 23, relative to the composite casing comprised by parts 10 and 12. Despite this high rotational speed, however, the change in phase of the two rotors relative to each other is much slower, and is brought about due to the slightly lower speed with which the outer rotor 20 will rotate relative to the inner rotor 22. In the embodiment shown, wherein the outer rotor 20 is provided with nine separate tooth segments 21, while the inner rotor 22 has eight projecting teeth 22a, it will be seen that the outer rotor rotates at a speed that of the inner rotor and the difference between the two is ,4; of that of the inner rotor. Where desired, the number of teeth of outer rotor and cooperating inner rotor may differ by two or even three, the difference in every instance, however, must be at least one.

It is apparent from a consideration of the foregoing that forming the tooth segments 21 of the outer rotor 20 as separate elements greatly simplifies the manufacture of these elements. As has already been suggested, the expensive broaching operation necessary for the proper shaping of the internal teeth of the ring gear according to the known and conventional pump construction is replaced by a much simpler and far more rapid and accurate grinding of each separate tooth segment. Expressed in other words, the disconnected tooth principle according to my present invention, in manufacture, enables precision machining or grinding of the tooth surface in a circumferential direction. Not only is this more simple and rapid, but at the same time it enables the production of a surface finish pattern or grain effect that extends in the same direction as that of the direction of rotation or tooth action of the inner rotor or gear. I find that with this construction there is far less tooth scuff and running friction between the teeth than there is with the conventional one-piece outer rotor produced by broaching or shaping in a longitudinal direction and where, in operation, the teeth of the inner rotor slide across the grain of the teeth of the outer rotor.

When placing my new construction in use I first slip the inner rotor 22 on the drive shaft 23, properly aligning and engaging the key 2311 projecting from drive shaft 23 with key-way 22d of the inner rotor 22. Where desired, however, the shaft 23 may be slipped into the bearing in head 12, key 23a inserted in key-Way 23b of shaft 23, and then rotor 22 slid into place on the shaft in engagement with the key.

The inner rotor 22 is slipped into the recessed portion 11 of head 12 against the machined wall 11a thereof, the latter being disposed at right angles to the shaft 23. The anti-friction bearing 24 is mounted in the hole 12b and the shaft 23 is thereupon fitted in this bearing. With the inner rotor 22 thus positioned on the shaft 23 relative to the head 12, I next position the tooth segments 21 about the inner rotor 22 and between it and the outer periphery of the recessed portion 11 of the head 12. Pins, where used as illustratively shown are then inserted. As a matter of preference, however, tooth segments 21 are fashioned for direct contact segment-to-segment without benefit of pins or other spacers as shown in Fig. 5.

When this has been done I fit body 10 having the manifolds 18, 19 onto the head 12. These manifolds are properly oriented with respect to the rotors by virtue of the dowel pin 12a engaging in opening 10a of body portion 10. The terminal end 230 of drive shaft 23 is received by the bearing 24 in body 10. The bolts 13 with washers are then inserted through holes 14 in head 12 and threaded into the apertures 15 in body 10. The pump is thereby assembled for ready use.

It will be noted from the foregoing that I achieve what may properly be called a free-floating effect so far as concerns the interplay of the separate tooth segments 21 comprising the outer rotor. When fluid, either gaseous or liquid, enters through the intake port, and the pump is placed in operation through rotation of the shaft 23, the tooth segments 21 immediately seek and achieve a selfalignment, the while they are meshing with the momentarily mating teeth of the inner rotor 22. This self-alignment gives rise to many highly advantageous effects, among which may "be noted that quieter operation attends, resulting in part from the effective suppression of the normal tooth noise which accompanies tooth interference. This tooth interference is characteristic of nor- "mal completeness of continuous tooth contact between cooperating teeth of the inner and outer rotors when the conventional one-piece outer rotor is employed. Expressed in other words, and perhaps more simply, the diminished tooth clash or interference attending my new construction is accompanied by quieter operation.

Moreover, it will be seen that the establishment of excessive fluid pressures is effectively averted, this particularly in the changing space between teeth throughout the are between inlet and outlet parts. Pressure relief is directly provided by the minute tooth segments. And some of the quietness of operation which is had in my new pump may be attributed to this feature.

Additionally, longer life and more uniform loading is achieved through my present construction. The disconnected teeth 21 of the outer rotor 20 provide more surface of support on the outer periphery of the intermeshed teeth than is true of the conventional ringer-gear.

And this increased support is not only highly desirable but may properly be considered to be even necessary because of the load resulting from the hydraulic pressure created by the displacement occurring with relative rotation of inner and outer rotors. So that this may be better understood, it may be noted that in a conventional one-piece outer rotor it is the full internal projected area of the teeth which "is acted upon by the hydraulic pressure, so that by consequence, the external peripheral support is limited to a small and confined area of the circular outer periphery. This in turn results in a detrimentally higher unit loading of the arc piece rotor.

A still further and highly important, advantageous result attendant upon the practice of my invention is that full lubrication of all moving parts is readily and effectively achieved thus contributing importantly to greatly diminished wear between the moving parts, together with appreciably improved life of the assembly, considered as a unit. And this results from the fact that with disconnected teeth 21 of the outer rotor 20, a pressurized thin curtain of oil under pressure, is discharged in the nice clearance between adjacent tooth segments 21 and effectively promotes lubrication from the forward end of the advanced tooth towards the rear end thereof as the latter bodily rotates during operation. Again, by strategically applying an inwardly-directed radial force on the group of separate tooth segments 21 through the aforesaid pressurized channel of oil around the periphery of the teeth, these teeth are thereby forced radially inwardly. The result attendant thereupon, when desired, is a constant tooth contact between the cooperating teeth of the inner and outer rotors throughout the life of the unit. This assures high volumetric efficiency. Through this lubrication metal-to-metal contact is effectively suppressed, lubrication being recurrent as each tooth passes and leaves the region of influence of the outlet port manifold, prior to entering the zone of influence of the inlet port manifold.

While the foregoing disclosure has illustratively been directed to a new pump construction, and while this presently comprises the preferred embodiment of my invention, it is to be noted that this principle of disconnected ring-gear teath supported in a housing and driven by a cooperating inner gear, as disclosed herein, can be effectively employed in a motor where a quiet-running drive is sought. I obtain this motor action by supply ing a sheath of roller bearings 26 between head 12 and outer rotor 21, all as illustrated in Fig. 6. In addition, the coursing of fluid through the ports of the composite casing is reversed thereby permitting the fluid, under pressure, to enter into the compartments of minimum volume. Expansion of the compartment under this pressure causes a movement and change of the rotor position. Power take-off preferably is through the inner rotor shaft.

In my new motor it will be seen that the separating force exerted between adjacent teeth 21 as they pass from inlet to outlet manifolds tends to expand the outer periphery defined by the cooperating tooth segments thereby creating complete pre-loading of the rollers of the bearing 26 throughout the full complement of teeth. In this manner, all diametral looseness is effectively avoided, it being noted that diametral looseness is a detrimental phenomenon evidenced by a strong tendency towards skewing of the bearing. In roller and needle bearings, skewing creates heat, noise, increased drag and sometimes premature failure of bearings. The removal of this tendency is of considerable importance.

I find that my construction applying a sheath of roller bearings between outer segmented rotor and head is of advantage also in a pump, especially where the fluid being pumped is of non-lubricating quality.

Through the use of my new unit, therefore, it is to be noted that the separate tooth segments 21 of the outer rotor automatically are properly positioned under load conditions relative to the housing comprised by body portion and head 12. Easier, cheaper, more rapid and more accurate grinding of the tooth segments is made possible. Close intermeshing, with substantial reduction of drag or frictional loss, is achieved between cooperating tooth surfaces. And this is accompanied by what may be termed a full floating application of the exterior teeth against those of the inner rotor, with resultant effective and more uniform loading.

All of the foregoing, as well as many other highly practical advantages tend upon the practice of my invention.

It is apparent from the foregoing that once the broad aspects of my invention are known, many embodiments thereof will readily occur to those skilled in the art, and that, moreover, many modifications of the present embodiment will likewise be suggested, all falling within the scope of the present invention. Accordingly, I desire the foregoing disclosure to be considered as merely illustrative, and not as limitative.

I claim:

1. An hydraulic power unit comprising in combination, a ported casing with cylindrical bore and having fluid inlet and outlet; inner and outer tooth rotors Within said casing bore in eccentric meshing relation; and a power shaft within said casing to which said inner rotor is fast, said inner rotor comprising a gear and said outer rotor comprising a plurality of discrete tooth segments, at least one greater in the number than the teeth of said gear, in loose end-to-end assembly and having the effect of a ring-gear concentric with the casing bore and continuously enmeshed with the teeth of said inner rotor.

2. An hydraulic pump comprising in combination, a casing comprising a ported body portion having an interior cylindrical bore and a head portion secured to said body portion in fluid-tight manner; hearings in said body and head portions and in alignment with each other and eccentric with said bore; a drive shaft received in said bearings; a pinion gear in said casing and fast on said drive shaft; and discrete gear-tooth segments snugly received against the head portion of said casing and disposed around said gear in non-rigid end-to-end assembly, concentric with said casing bore and eccentric with respect to said pinion gear and in continuous contact therewith, said discrete gear-tooth segments being at least one greater in number than the teeth on said pinion gear.

3. An hydraulic power unit comprising in combination, a ported casing with cylindrical bore and having fluid inlet and outlet; inner and outer tooth rotors positioned within said casing eccentrically of each other and with the outer rotor concentrically of the bore; and a power shaft extending within said casing and to which said inner rotor is fast, said inner rotor comprising a gear and said outer rotor comprising a plurality of discrete tooth segments arranged about and enmeshed with said inner rotor and with adjacent segments abutting one another in non-rigid contact and in continuous contact with the teeth of said inner rotor, said discrete tooth segments being at least one greater in number than the teeth of said gear.

4. An hydraulic power unit comprising in combination, a ported casing with cylindrical bore and having fluid inlet and outlet; inner and outer tooth rotors within said casing eccentrically of each other; and a power shaft extending within said casing bore and to which said inner rotor is fast, said inner rotor comprising a gear and said outer rotor comprising a plurality of discrete tooth segments, at least one greater in number than the teeth of said gear, and a corresponding plurality of discrete separators between said tooth segments, said segments and separators being disposed about said inner rotor as a loose assembly concentric of said casing bore with the tooth segments enmeshed with the inner rotor and in uninterrupted contact therewith.

5. An hydraulic power unit comprising in combination, a ported casing with cylindrical bore and having fluid inlet and outlet; inner and outer tooth rotors within said casing; a power shaft eccentrically positioned within said casing and to which said inner rotor is fast; and a multiplicity of roller bearings between outer rotor and casing, said inner rotor comprising a gear and said outer rotor comprising a plurality of discrete tooth segments innon-rigid end-to-end contact which, in assembly, have the effect of a ring-gear maintained concentric with said casing bore and eccentrically enmeshed With said inner rotor in uninterrupted contact.

6. In an hydraulic power unit which comprises a casing including a ported body portion having interior cylindrical bore and a head portion secured to said body portion in fluid-tight manner, bearings on said body and head portions, a drive shaft received in said bearings, and a pinion gear in said casing and fast of said drive shaft, the combination of a plurality of discrete geartooth segments, at least one greater in number than the teeth on said pinion gear, and disposed around said pinion gear in uninterrupted contact with the teeth thereof and concentric with the bore of said casing and eccentric of said pinion gear, said discrete gear-tooth segments forming a complete ring, with just sufiicient space between segments to accommodate a film of fluid therebetween when in position and placed in operation.

7. In an hydraulic power unit which comprises a casing including a ported body portion having an interior cylindrieal bore and a head portion secured to said body portion in fluid-tight manner, bearings on said body and head portions, a drive shaft received in said bearings eccentrically of the bore of the casing, and a pinion gear in said casing and fast on said drive shaft, the combination which comprises a plurality of discrete gear-tooth segments, at least one greater in number than the teeth of said pinion gear, disposed within said casing in loose assembly contact between adjacent segments and eccentrically around said pinion gear in uninterrupted contact with the teeth thereof, said discrete gear-tooth segments forming a complete ring within said casing bore and concentric therewith.

8. In an hydraulic power unit which comprises a casing with cylindrical bore, a head portion secured thereto, and bearings in said head portion and easing eccentrically of ti e bore, the combination of a shaft received in said bearings, a gear fast to the shaft, and a plurality of individual gear-tooth segments, at least one greater in number than the teeth on said gear, disposed around said gear in uninterrupted contact therewith and in non-rigid abutting relation between adjacent segments so as to form a complete ring eccentric with said gear and concentric within said casing bore.

9. In an hydraulic power unit comprising a casing with cylindrical bore, a head portion secured thereto, and hearings in said head portion and easing, the combination of a shaft received in said bearings eccentrically of the casing bore, a gear fast to the shaft, and a plurality of individual gear-tooth segments, at least one greater number than the teeth on said gear, and a corresponding plurality of separators between said segments to effect separation of the same, said segments with intervening separators forming a complete ring about said inner gear eccentric therewith and concentric with said casing bore and with said segments enmeshing the teeth of said gear in continuous contact.

References Cited in the file of this patent UNITED STATES PATENTS 1,341,846 Gollings June 1, 1920 1,361,046 Gollings Dec. 7, 1920 1,926,692 Tarbox Sept. 12, 1933 1,994,397 Loveridge et al. Mar. 12, 1935 2,601,397 Hill et a1. -2 June 24, 1952 2,621,603 Thomas Dec. 16, 1952 FOREIGN PATENTS 270,000 Great Britain May 2, 1927 284,411 Great Britain Ian. 30, 1928

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