US3915603A

US3915603A - Radial balancing means with sealing vanes for a hydraulic device

Info

Publication number: US3915603A
Application number: US530777A
Authority: US
Inventors: Nils Einar Swedberg
Original assignee: Eaton Corp
Current assignee: Eaton Corp
Priority date: 1973-05-03
Filing date: 1974-12-09
Publication date: 1975-10-28
Anticipated expiration: 1992-10-28

Abstract

An improved radial, pressure-balancing arrangement for fluidoperated devices of the geroter type wherein an internallytoothed ring member eccentrically receives an externally-toothed star member to form a plurality of expanding and contracting volume chambers by tooth interaction. The ring member has a plurality of pockets receiving a like number of rollers rotatable therein which serve as the teeth of the ring member. Particularly configured recesses are located at predetermined positions within each pocket and each recess loosely receives a sealing vane member therein. The recesses and vane members cooperate to provide a predetermined pressure pattern behind each roller when and as it is momentarily positioned between chambers at high and low pressure at various times during the operation cycle. The pressure pattern thus formed behind a selective roller biases it against a mating star tooth to seal volume chambers at high pressure from those at low pressure. The vanes are effective to trap fluid at high pressure behind the selective roller when the selective roller indexes to a position between chambers at low pressure during the operation cycle thus reducing frictional drag between the pocket and roller.

Description

United States Patent [191 Swedberg 1 Oct.28, 1975 RADIAL BALANCING MEANS WITH SEALING VANES FOR A HYDRAULIC DEVICE [75] Inventor: Nils Einar Swedberg, Chanhassen,

[21] Appl. No.: 530,777

Related US. Application Data [63] Continuation-impart of Ser. No. 356,867, May 3,

1973, abandoned.

[52] US. Cl. 418/61 B; 418/225 [51] Int. Cl. F04C 1/02 [58] Field of Search 418/61 B, 125, 129, 139, 418/171, 225, 229

[56] References Cited UNITED STATES PATENTS 1,997,184 4/1935 Ruehman 418/139 X 3,289,602 12/1966 l-ludgens 418/61 B 3,415,196 12/1968 Adler 418/139 X 3,614,274 10/1971 Ohrberg r 418/61 B 3,619,089 11/1971 Pierrat 418/171 X 3,692,439 9/1972 Woodling 418/61 B Primary Examiner-William L. Freeh Assistant ExaminerLeonard Smith Attorney, Agent, or FirmTeagno & Toddy [57] ABSTRACT An improved radial, pressure-balancing arrangement for fluid-operated devices of the geroter type wherein an internally-toothed ring member eccentrically receives an externally-toothed star member to form a plurality of expanding and contracting volume chambers by tooth interaction. The ring member has a plurality of pockets receiving a like number of rollers rotatable therein which serve as the teeth of the ring member. Particularly configured recesses are located at predetermined positions within each pocket and each recess loosely receives a sealing vane member therein.

The recesses and vane members cooperate to provide a predetermined pressure pattern behind each roller when and as it is momentarily positioned between chambers at high and low pressure at various times during the operation cycle. The pressure pattern thus formed behind a selective roller biases it against a mating star tooth to seal volume chambers at high pressure from those at low pressure. The vanes are effective to trap fluid at high pressure behind the selective roller when the selective roller indexes to a position between chambers at low pressure during the operation cycle thus reducing frictional drag between the pocket and roller.

12 Claims, 6 Drawing Figures RADIAL BALANCINGfMEANS WITH SEALING VANES For; A HYDRAULIC DEVICE CROSS-REFERENCETO RELATED APPLICATION This application is a continuation-in-part of my copending application S'er. No. 356,867, filed May- 3, 1973, now abandoned. a

BACKGROUND vOF THE DISCLOSURE This invention relates to hydraulic devices of the geroter type and more particularly to a pressure-balancing arrangement for geroter type devices employing rollers as teeth of one of the displacement members therein. f 1

Hydraulic devices of the type commonlyreferred to as geroters comprise an internally-toothed ring member eccentrically receiving an externally-toothed star member. The star member usually has one less tooth than the ring member to define a number of volume chambers which expand and contractupon one members hypocycloidal orbiting movement about the axis of the other. To maintain volumetric efficiency within such devices, leakage between volume chambers at high pressure and those at low pressure must be minimized. Thus the fit between mating teeth is critical and the teeth of one member must be precisely formed to provide an accurate fit with the teeth of the other member. When the teeth wear, clearance between the members becomes excessive and leakage with resultant inefficiency occurs.

The prior art has attempted to overcome the'problems associated with the close fit between the ring member and star member by forming the teeth of the ring member from cylindrical rollers rotatably positionedin pockets formed in the ring member. Geroter gear sets utilizing rollers as the teeth of the ring member maybe classified, or distinguished, by the relationship,,for' each particular geroter set, between the roller diameter and pocket diameter, as well as by the relationship betweenthe tangent circle of the ring-roller assembly (i.e., a ci rcle tangent to the inner peripheries of the rollers centered within their respective pockets) and the average diameter of the star member (i.e.,

the average. of the major and minor diameters of the star member.)

Thus, a geroter set is referred to as having an interference fit when each of the rollers has substantially a bearing fit with its respective pocket (i.e., a diametral clearance between the roller and pocket of less than about 0.00 l5'inches (.038 mm)), and the average diameter of the star member interferes with the tangent circle of the ring-roller assembly (i.e., the average diameter is larger than the tangent circle by as much as about 0.0010 inches (.025 mm), or more). In such a geroter set, the interference fit precludes any biasing or inward radial movement of the rollers. A geroter set is referred to as having a non-interference fit when each roller has a bearing fit with its respective pocket, as in the case of the interference fit, but there is a clearance between the average diameter of the starmember and the tangent circle of the ringroller assembly [(i.e., the average diameter is dimensionally smaller than the tangent circle byabout 0.0010 inches (.025 mm), or more)]. in a geroter set having a non-interference fit, radial movement or biasing of the rollers is possible because of the clearance between the average diameter and the tangent circle.

A geroter set is referred to as having a loose fit when each roller and its respective pocket have more diamctral clearance than the running clearance attributable to a bearing fit relationship. Typically, with a loose fit geroter set there is a diametral clearance between each roller and its respective pocket of about 0.003 inches (.076 mm) to about 0.005 inches (.127 mm); With the rollers loosely received in the pockets, the relationship of the average diameter and the tangent circle is less critical'and there may be a nominal interference between the average diameter and the tangent circle, although, typically, a clearance is provided.

Therefore, because the present invention relates to biasing of the rollers, it will be understood by those skilled in the art that the invention would be advantageous only when utilized with a geroter set having a non-interference fit or with a geroter set having a loose fit, and. preferably, with a geroter set having a noninterference fit to minimize leakage problems.

Among the prior art methods of biasing the rollers inward into the sealing contact with the star member. one known balancing arrangement taps high pressure from a source, such as the valving or one of the volume chambers, and directs it constantly to the pocket behind the roller. With such an arrangement, volumetric efficiency is seriously reduced because of constant leakage which occurs when the rollers remain continuously biased by fluid at high pressure.

It is thus a principal object of the subject invention to provide a hydrostatic pressure-balancing arrangement for rollers used as chamber forming elements in a geroter type device which arrangement exerts a controlled radial-balancing force behind selective rollers sequentially positioned between adjacent chambers at differential pressure during the operation cycle while also maintaining proper geroter geometry and also providing pressure cushioning means behind rollers adjacent chambers at low pressure.-

In accordance with the invention, there is provided a geroter comprising a roller-type; internally-toothed ring member receiving an externally-toothed star member. The ring and star members are associated with a housing having commutator type valving supplying and exhausing fluid from the volume chambers formed by the star and ring member teeth. Each roller in the ring member. is. disposed within a pocket of the ring mem" ber. Each pocket has a plurality of recesses formed therein with two recesses loosely receiving a sealing vane member movable radially-inwardly or outwardly under pressure. The recesses are separated from one another by a roller support. surface or land and communicate with one another by grooves or depressed areas extending around or through the support surfaces.

The recesses and sealing vanes therein are particu larly configured and positioned to develop a controlled, essentially hydrostatic pressure biasing the roller toward the corresponding star tooth when the rolleris positioned between high and low pressure chambers. At this position, thesealing vane nearest the low pressure chamber is pressurized radially-inwardly into sealing engagement with the roller and the sealing vane nearest the high pressure'chamber is pressuraized' radially-outwardly. The pressure pattern developed is characterized by being symmetrically distributed over a portion of the pocket to produce a resultant forcehaving a controlled direction and suflicient magnitude to adequately seal high pressure chambers from low pressure chambers.

Still another feature of the invention resides in the vane position when the pressurized pocket indexes during the operation cycle to a position between volume chambers at low pressure. In this position, pressure in the pocket moves the outwardly disposed sealing vane inwardly into sealing engagement with the roller to provide a high pressure cushion of fluid film which reduces frictional drag between the pocket and roller.

Yet another feature of the subject invention residesin the roller support surfaces and depressed areas which permit the rollers to maintain their proper geometry within closefitting pockets even though the recesses provide an excessive clearance necessary to establish an adequate resultant hydrostatic balancing force.

It is thus an object of the subject invention to provide a p'ressurebalancing arrangement in a geroter type device, which also provides hydraulic cushioning of rollers disposed between chambers at low pressure.

It is still another object of the invention to provide a hydrostatic pressure-balancing arrangement in a geroter type device which develops a symmetrical pressure distribution about a portion of the pressurized pocket.

Yet another object of the invention is to provide a pressure-balancing arrangement for rollers used as chamber forming elements in a geroter type device which employs merely a running clearance between roller and pocket to maintain geroter geometry.

The invention may take physical form in certain parts and an arrangement of parts, a preferred embodiment of which will be described in detail herein and illustrated in the accompanying drawings which form a part hereof and wherein:

FIG. 1 is a sectional view ofa geroter device employ- .ing the subject invention;

FIG. 2 is an axial end view of the star and ring members taken along Line 22 of FIG. 1;

FIG. 3 is a developed view of a roller-pocket taken along-Line 33 of FIG. 2;

FIG. 4 is an enlarged end view of a roller applied within a pocket;

FIG. 5 is a perspective view of a sealing vane; and

FIG. 6 is a view similar to FIG. 4 showing an alternative roller-pocket construction.

DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic configuration of the geroter device shown in FIG. 1 to which this invention relates is well known in the fluid transmission art and may be appreciated in greater detail than will be described herein by reference to US. Pat. No. 3,572,983 to McDermott.

Referring now to the drawings wherein the showings are for the purpose of illustrating a preferred embodiment of the invention only and not for the purpose of limiting same, there is generally shown in FIG. 1 a housing 2 having inlet and

outlet ports

4, 6 communicating through ports 70 and 7b in a rotatable valve member 7 with fluid flow ports 80 and 8b in a port plate 8 t0 define a known commutator-type valving arrangement. The valve member 7 is connected by a splined shaft member 9 for driving rotation with an externallytoothed member 10. Housing 2 also includes a ring member 12 eccentrically receiving the star member to define a plurality of increasing and decreasing volume chambers 14 in communication at one axial end with ports 81! and 8b in port plate 8. Ring member 12 has a plurality of pockets l6 axially-extending therethrough, each of which receive a cylindrical roller 18 rotatably, disposed therein. Each pocket is semi-cylindrical and configured to=define axially-extending recesses 20 and each recess receives a sealing vane member 21 therein.

Referring now to HQ. 2 there is shown a ring member 12 having a plurality of N roller teeth 18 and a star member 10 having a plurality of N-l teeth 26. In the embodiment illustrated, the designation N refers to the number 7 and N-l correspondingly refers to the number 6. Ring member 12 eccentrically receives the star member 10 and the eccentricity of the arrangement is shown as the distance between the ring axis 32 and the 7 star axis 28. Circumferentially-spaced and opening to the internal periphery of the ring member 12, are N semi-cylindrical, axially-extending pockets 16. Each pocket 16 is adapted to receive a cylindrical roller 18, which are individually lettered A through G. Rollers l8 interact with the star teeth 26 to form variable volume chambers 14 which are individually identified by letters a through g.

As thus described, the star and

ring members

10, 12 will interact with one another in the well-known manner. More particularly with the ring member 12 fixed to prevent rotation thereof, the star membenlflwill orbit hypocycloidally within the ring member'- 12,- whereby the star center defines a circle 34 about ring center 57 of a radius equal to the eccentricity of the device. This movement of the star member opens and closes volume chambers a through g while the star member rotates a peripheral distance equal to one tooth spacing.

More particularly the commutator valving will supply high pressure to three chambers and low pressure to three chambers with the seventh or odd chamber operating as a changeover chamber and being at a pressure between high and low. Thus in the chamber position illustrated in FIG. 2, the axis of eccentricity defined as a line extending between the ring and star members axes 32, 28; and shown as the Y-Y axis, separates high pressure chambers b, c and d from the low pressure chambers e, f and g with pressure chamber a being a changeover chamber at that instant. Furthermore, it will be appreciated that the YY axis of eccentricity will rotate at an angular speed equal to the orbiting speed of the star member 10. Thus when the star member has orbited one tooth position in the direction of orbiting arrow 36, which represents a motor application of the geroter, the YY axis will also have rotated and now will bisect roller C and pressure chamber g; chambers c, b and a being at high pressure and chambers (I, e and f at low pressure. Thus all volume chambers l4 lying on one side of the YY axis are either expanding or contracting and all expanding and contracting volume chambers are connected by the valving to either inlet or'

outlet ports

4, 6, respectively.

Now referring to FIGS. 3 and 4, it will be seen that the circular pockets 16 in ring member 12 are defined by a radius R nominally larger than the radius R of the rollers 18. Each pocket s configured surface includes a pair of axially-extending recesses 20 symmetrically spaced from the pocket centerline 39 and shown as having a rectangular configuration defined by inner, outer and rearward edge surfaces 3!, 33, 35.. Recesses 20 are separated from one another between their inner edge surfaces 31 by an arcuate roller support surface or land 22 (see FIG. 3), and communicate with one another by means of grooves or depressed areas 24 shown extending around the roller support surface 22. Extending from the outer edge surface 33 of each recess and opening to the internal periphery of ring member 12 is a pocket leading edge support surface 38 which is in radial alignment with roller support surface 22. Depressed areas or channels in leading edge support surfaces 38 provide communication from adjacent volume chambers 14 to the recesses 20. In the imbodiment shown, tests have indicated that an included angle X of at least 90 between inner edges 31 of recesses 20 which have effective peripheral widths intercepting Y of at least results in an efficient balancing arrangement. It will be appreciated that the position and configuration of lands 22 and channels 25 can be varied to provide geometric configurations other than that shown whereby recesses 20 can be communicated with one another and with volume chambers 14.

Positioned within each recess 20 is a sealing vane member 21 preferably constructed of material having wear and sealing characteristics such as that possessed by aluminum or brass. As shown in FIG. 5 each vane is wedge-shaped and includes an arcuate surface 49, an inner surface 51, an outer surface 53 and a rearward surface 55. Each

surface

49, 51, 53, 55 is adapted to move into and out of contact with the roller 18 and recess surfaces 31, 33, respectively. Additionally, the axial length of the sealing vane is slightly shorter than the depth of the ring member 12 to allow for radial vane movement and yet prevent leakage of fluid in recess 20 to a volume chamber 14 via the channels 25 in leading support surface 38 when a vane is in its sealing position.

The position of roller D in its pocket 16 is determined partly as a result of the biasing force from its mating star tooth 26. A force analysisof the pocket and roller Dindicates that the roller position is initially determined by the direction of the star tooth force on the roller which varies when the star moves relative to the ring as roller D, is between chambers at high and low pressure. More particularly the star tooth force estab- Iishes a sealing or tengency line which determines that peripheral portion of the rollerover which a hydrostatic gradient pressure is exerted; the pressure itself displacing the tangency line from a position it would otherwise assume. In the prior art, the hydrostatic gradient pressure within such clearance is insufficient to bias the roller into a most favored balanced position and maintain the roller in such a position, especially under nonnal operating conditions where the speed of rotation of the star member does not provide sufficient time for fluid to effectively fill the clearance.

In accordance with the present invention, roller D, as shown .in FIG. 4, bears against the pockets leading edge support surface 38 at low pressure volume chamber e and is displaced a distance Z (approximately 0.005 inches (.0l27 mm) to .0010 inches (.0254 mm) in the embodiment shown) from the leading edge support surface 38 at the high pressure volume chamber d and such roller position is maintained so long as roller D is between chambers at high and low pressure. This position results because the high pressure from volume chamber d forces the vane 21 adjacent chamber d rearwardly into its recess 20. The opposite vane 21 which is adjacent low pressure volume chamber 6 is forced into sealing engagement with roller D because outer vane surface 53 is exposed to low pressure while inner vane surface 51 is at high pressure. If the tangency line tends to be positioned between recesses 20 because of the star tooth loading, the hydrostatic pressure in that recess 20 and that portion of land 24 adjacent the peripheral portion of roller D which otherwise would be sealed is sufficient to bias roller D inwardly to establish hydrostatic pressure between the roller and pocket surfaces. This is more clearly shown by the vectorial peripheral force distribution shown in FIG. 4 which represents a summation of the pressures acting axially along the depth of roller D. The force distribution shown is essentially a uniform radial load extending around the periphery of roller D from the recess 20 closest low pressure volume chamber 2 and resolves itself into a constant resultant force 42 of greater magnitude and much better orientation than the resultant force of the prior art. It should be noted that FIG. 4 does not show any force acting along leading edge support surface 38 adjacent low pressure chamber e even though a bearing film is present because the sealing vane 21 adjacent chamber e prevents communication of high pressure to this area. The bearing film may develop a hydrodynamic force upon rotation of roller D, although such force if developed is considered insignificant when compared to the hydrostatic forces.

While FIG. 4 shows the pressure distribution behind roller D when it is positioned between high and low pressure zones, roller D will be disposed entirely in a low pressure zone when star member 10 orbits one tooth. The sudden pressure reversal will cause the high pressure behind the roller in FIG. 4 to move the retracted vane 21 radially-inwardly to trap a portion of the high pressure fluid behind the roller. The pressure behind roller D in this position at least: momentarily will be similar to that shown in FIG. 4 except that the pressure along the leading edge adjacent chamber d will not occur. Thus there is a relatively high component force which will be directed radially-inwardly toward the center of ring member 12 because of the symmetry of the pressure distribution.

The resultant force 42 in the present invention thus sufficiently biases the star member 10 downwardly forcing tooth contact to occur at

points

44, 46 on rollers G and A respectively. High pressure chambers b, c and d are sealed from low pressure chambers e, f and g and the geroter is balanced at this instant. Additionally rollers E, F and perhaps G have a hydraulic cushion of fluid at high pressure entrapped behind them which reduce frictional drag between rollers and pocket and improve the efficiency of the device. In this connection it will be appreciated that leakage occurring through the sealing vane 21 and at the pocket axial ends will dissipate the pressure as a function of time. However the geroter orbits rapidly when compared to the rotation of the output shaft and the fluid behind the low pressure rollers remains substantially at high pressure although the pressure behind roller E is greater than the pressure behind G in the geroter portion shown in FIG. 2.

An alternative pocket construction is shown in FIG. 6 which is similar to FIG. 4 wherein like numbers identify like parts where applicable. In'this embodiment a third recess 43 which does not contain a sealing vane 21 is positioned at the pocket center to obtain a quicker porting of pressure behind the roller. The remaining pressure distribution is identical to that of FIG. 4. Additionally each sealing vane 21 may be constructed of a wear-resistant, yieldable material such as polytetrafluoroethylene, is V-shaped to permit deflection, under pressure, of the sealing vane itself into the roller 18 to thus improve its sealing effect.

While the embodiment has been explained as operating as a motor with the star member orbiting in the direction of arrow 36, it should be apparent from the symmetry of the pocket construction that the radial balancing means disclosed herein will operate satisfactorily if the orbiting motion of the star member 10 is reversed resulting in reversed motor rotation of the output shaft. Similarly, the radial pressure balancing means, while described above in a motor application, will likewise function in a pump application.

It is also appreciated that the magnitude and direction of resultant force 42 is achieved by the particular force distribution established behind the roller 18 which is characterized by being substantially symmetrically distributed about the pocket periphery between recesses 20. Thus the symmetrical pressure distribution would be adversely affected if additional recesses were placed equidistantly from the pocket center.

Additionally the sealing vane-recess combination disclosed herein would adequately function if high pressure from a source were constantly communicated behind the rollers and into the recesses. The sealing vanes 21 would then move inwardly to their sealing position and prevent communication between pressure behind the rollers and pressure in the volume chambers 14.

The invention has been described with reference to a preferred embodiment. Obviously, other modifications and alterations will occur to others upon reading and understanding of the specification. It is my intention to include all such modifications and alterations insofar as they come within the scope of the present invention.

It is thus the essence of my invention to provide a radial, pressure-balancing arrangement in a fluidoperated device of the geroter type which utilizes a predetermined roller-pocket configuration comprising recesses and sealing vanes therein to port pressure behind the roller teeth resulting in a predetermined force distribution which effectively biases a ring-roller tooth to produce sealing engagement between the star and ringroller assembly while also providing a hydraulic cushion behind other roller teeth to improve the efficiency of the device.

' Having thus defined my invention, I claim:

1. An internally-toothed member for use in a rotary fluid pressure device of the geroter type, said internally-toothed member comprising a ring member having a plurality of substantially semi-cylindrical pockets therein, a substantially cylindrical roller received in each of said pockets, said pockets having a configured surface including recessed seal receiving portions and a roller support surface portion intermediate said seal receiving portions, and a seal member movably disposed in each of said seal receiving portions and operable to engage said roller upon movement thereof.

2. The device of claim 1 wherein said recessed seal receiving portions are symmetrically spaced about the centerline of said pockets.

3. The device of claim 1 wherein said configured surface includes groove portions communicating said seal receiving portions with one another.

4. The device of claim 1 wherein the recessed seal receiving portions are substantially rectangular in crosssection and said seal member is wedge-shaped in crosssection.

5. Pressure-balancing means in a hydraulic device of the geroter type having an internally-toothed ring member with a plurality of spaced, axially-extending pockets formed along its internal periphery and a roller rotatably disposed in each pocket to define the teeth thereof, an externally-toothed star member having less teeth than said ring member and eccentrically disposed with said ring member, said ring and said star members cooperating with one another to define increasing and decreasing volume chambers, the improvement comprising:

each of said pockets having a plurality of axiallyextending recesses therein spaced symmetrically about the centerline of said pocket, a sealing vane member disposed within said recesses and means for communicating pressure between said recesses.

6. The improvement of claim 5 wherein sealing vanes are disposed in the two recesses which are furthest removed from the pockets centerline.

7. The improvement of claim 6 wherein said vanes have a retracted position and a sealing position, and a vane is in said sealing position when its recess is adjacent a chamber at low pressure.

8. The improvement of claim 7 wherein the pocket configuration is further defined by arcuate roller sup port surfaces separating said recesses from one another and opposed arcuate leading support surfaces, each leading surface extending from said furthest-removed recess to the internal periphery of said ring member. and said edge surfaces and said support surfaces being radially aligned.

9. The improvement of claim 8 wherein said c0mmu-' nicating means comprise first depressed areas in said leading support surfaces communicating a chamber with a furthest-removed recess and second depressed areas in said support surfaces communicating said recesses with one another.

10. A rotary fluid pressure device comprising:

a housing having inlet and outlet ports;

an internally-toothed ring member disposed within said housing, and an externally-toothed star member having less teeth than said ring member and eccentrically disposed within said ring member to define a line of eccentricity passing through the axes of said members;

one of said members having a plurality of generally semi-cylindrical pockets and a generally cylindrical roller disposed within each pocket to define the teeth thereof; said teeth of said members intermeshing as one member orbits about the axis of the other to define expanding volume chambers on one side of said line andcontracting volume chambers on the other side of said line;

commutator valving means communicating with said inlet and outlet ports to supply high pressure to those chambers on one side of said line'and low pressure to those chambers on the other side of said line;

balancing means biasing a roller momentarily positioned between a volume chamber at high pressure and a volume chamber at low pressure by exerting fluid pressure about the pocket centerline in a symmetrical distribution which extends over a portion of the pocket periphery to bias said roller toward said low pressure volume chamber, said balancing means comprising a plurality of axially extending recesses within said pocket, said recesses symmetrically spaced about the pocket periphery in relation to the centerline of the pocket and a sealing vane disposed within the two recesses furthest removed from the pocket centerline; and

said ring member and second depressed areas within each leading support surface communicating an adjacent volume chamber with a furthest-removed recess.

12. The rotary device of claim 11 wherein said depressed areas in each leading edge define channels in the axial ends of said ring member and said sealing vane members extend substantially the axial depth of said ring member.

Claims

4. The device of claim 1 wherein the recessed seal receiving portions are substantially rectangular in cross-section and said seal member is wedge-shaped in cross-section.

5. Pressure-balancing means in a hydraulic device of the geroter type having an internally-toothed ring member with a plurality of spaced, axially-extending pockets formed along its internal periphery and a roller rotatably disposed in each pocket to define the teeth thereof, an externally-toothed star member having less teeth than said ring member and eccentrically disposed with said ring member, said ring and said star members cooperating with one another to define increasing and decreasing volume chambers, the improvement comprising: each of said pockets having a plurality of axially-extending recesses therein spaced symmetrically about the centerline of said pocket, a sealing vane member disposed within said recesses and means for communicating pressure between said recesses.

6. The improvement of claim 5 wherein sealing vanes are disposed in the two recesses which are furthest removed from the pocket''s centerline.

8. The improvement of claim 7 wherein the pocket configuration is further defined by arcuate roller support surfaces separating said recesses from one another and opposed arcuate leading support surfaces, each leading surface extending from said furthest-removed recess to the internal periphery of said ring member, and said edge surfaces and said support surfaces being radially aligned.

9. The improvement of claim 8 wherein said communicating means comprise first depressed areas in said leading support surfaces communicating a chamber with a furthest-removed recess and second depressed areas in said support surfaces communicating said recesses with one another.

10. A rotary fluid pressure device comprising: a housing having inlet and outlet ports; an internally-toothed ring member disposed within said housing, and an externally-toothed star member having less teeth than said ring member and eccentrically disposed within said ring member to define a line of eccentricity passing through the axes of said members; one of said members having a plurality of generally semi-cylindrical pockets and a generally cylindrical roller disposed within each pocket to define the teeth thereof; said teeth of said members intermeshing as one member orbits about the axis of the other to define expanding volume chambers on one side of said line and contracting volume chambers on the other side of said line; commutator valving means communicating with said inlet and outlet ports to supply high pressure to those chambers on one side of said line and low pressure to those chambers on the other side of said line; balancing means biasing a roller momentarily positioned between a volume chamber at high pressure and a volume chamber at low pressure by exerting fluid pressure about the pocket centerline in a symmetrical distribution which extends over a portion of the pocket periphery to bias said roller toward said low pressure volume chamber, said balancing means comprising a plurality of axially extending recesses within said pocket, said recesses symmetrically spaced about the pocket periphery in relation to the centerline of the pocket and a sealing vane disposed within the two recesses furthest removed from the pocket centerline; and said balancing means also exerting pressure in a symmetrical distribution behind rollers adjacent chambers at low pressure on one side of said line.

11. The rotary device of claim 10 wherein the spacing between adjacent recesses defines roller support surfaces and first depressed areas in said roller support surfaces communicate adjacent recesses with one another, said pocket further defined by diametrically-opposed leading support surfaces extending from said furthest-removed recesses to the internal periphery of said ring member and second depressed areas within each leading support surface communicating an adjacent volume chamber with a furthest-removed recess.