US3598509A

US3598509A - Hydraulic device

Info

Publication number: US3598509A
Application number: US8349A
Authority: US
Inventors: Raymond L Goff; Fredrick D Venable
Original assignee: TRW Inc
Current assignee: Northrop Grumman Space and Mission Systems Corp
Priority date: 1970-02-03
Filing date: 1970-02-03
Publication date: 1971-08-10
Anticipated expiration: 1988-08-10
Also published as: CA929416A

Abstract

A hydraulic device having a pair of fluid displacement members including an internally toothed stator and an externally toothed rotor disposed in meshing relation within the stator for relative orbital and rotational movement therewith to provide a series of expanding and contracting fluid pockets between the teeth thereof. The rotor has one less tooth than does the stator, and a fluid commutator valve is provided for directing fluid into and out of the fluid pockets in timed relation with the expansion and contraction thereof. The commutator valve is connected to the rotor for joint orbital and rotational movement and includes a radial wall facing the fluid pockets and having a plurality of ports formed therein arranged in a circular pattern and equaling in number twice the number of teeth of the rotor.

Description

Unite States atet Filed Feb. 3, 1970 Patented Aug. 10, 1971 Assignee TRW Inc.

Cleveland, Ohio nvnnauuc DEVICE 14 Claims, 6 Drawing Figs.

U.S. Cl

Int. Cl

Field of Search References Cited UNITED STATES PATENTS Huber 3.277,833 10/1966 Hudgens 3,288,034 11/1966 White, Jr. et a1.. 3.289542 12/1966 Fikse FOlc 1/00 Primary Examiner-William L. Freeh Assistant Examiner-Wilbur .l. Goodlin Attorney-Hill, Sherman, Meroni, Gross & Simpson ABSTRACT: A hydraulic device having a pair of fluid displacement members including an internally toothed stator and an externally toothed rotor disposed in meshing relation within the stator for relative orbital and rotational movement therewith to provide a series of expanding and contracting fluid pockets between the teeth thereof. The rotor has one less tooth than does the stator, and a fluid commutator valve is provided for directing fluid into and out of the fluid pockets in timed relation with the expansion and contraction thereof. The commutator valve is connected to the rotor for joint orbital and rotational movement and includes a radial wall facing the fluid pockets and having a plurality of ports formed therein arranged in a circular pattern and equaling in number twice the number of teeth of the rotor.

HYDRAULIC DEVICE BACKGROUND OF THE INVENTION Hydraulic devices utilizing a pair of relatively movable fluid displacement members are known in the prior art. In some known devices the fluid displacement members comprise an externally toothed stator and an internally toothed rotor disposed within the stator and movable simultaneously orbitally and rotationally relative to the stator to provide a series of alternately expanding and contracting fluid pockets between the teeth thereof. The expansion and contraction of the fluid pockets serve to pressurize the fluid, where the device is being utilized as a pump. or serve to move thedisplacement members relative to one another in the aforementioned manner, where the device is being utilized as a fluid motor.

Generally the rotor of such a device has one lesstooth than the stator and one characteristic of such arrangement is that v the orbital speed of the rotor relative to the stator is greater than the relative rotational speed by a factor equal to the number of teeth of the rotor.

It is essential to the operation of such devices that the fluid be directed to the expanding fluid pockets and from the contracting fluid pockets in close timed relation to the relative movement of the fluid displacement gears. Generally a valve arrangement is utilized to perform this function and because of the bidirectional fluid flow characteristics through the valve and because of the timed operation of the valve relative to the movement of the fluid displacement members, such valves are commonly referred to as fluid commutator valves.

Commutator valves must generally move in order to perform their intended function, and such movement must be related to the formation of the alternately expanding and contracting fluid pockets and hence to the relative movement of the rotor and stator members. In some arrangements of the prior art, such as disclosed, for example, in Hudgens U.S. Pat. No. 3,277,833 the commutator valve is connected to the fluid displacement gears for movement at the relative speed of rotation of the gear members, whereas in other arrangements as disclosed, for example, in White, Jr. et al. U.S. Pat. No. 3,288,034, the commutator valve is connected for movement at a speed corresponding to the relative orbital speed of the gear members. Reference may be conveniently made to the commutator valve of the Hudgens patent as being of the cylinder type as a consequence of the longitudinal parts or grooves formed in the circumferential face of the valve. The commutator valve of the White, Jr. et al. patent may be referred to as a face-type valve because of the formation of valve parts in a radial face thereof.

While a variety of commutator valve arrangements are known in the prior art, improvements therein are continually being sought for the purpose of increasing the efficiency of the hydraulic devices, reducing space requirements, simplifying design and construction, reducing costs, reducing wear and increasing operating life. To the better attainment of these goals the present invention is primarily addressed.

SUMMARY OF THE INVENTION The present invention may be summarized as comprising a hydraulic device having fluid pocket-forming relatively orbitally and rotationally moving rotor and stator gear members and utilizing a radial face-type commutator valve which moves both orbitally and rotationally at the relative orbital and rotational speed of the gear members. The radial face of the valve has a series of ports formed therein which are arranged in a circular pattern in pairs which are spaced from one another in a manner corresponding to the spacing of the fluid pockets between the teeth ofthe rotor.

The commutator valve of the present invention, which may also be referred to as a fast-speed valve (since it moves at the orbital speed of the gear members) as contrasted with a slowspeed valve (which moves at the rotational speed of the gear members), opens and closes the ports rapidly as their respective fluid pockets alternately expand and contract. It also provides for a compact arrangement of the hydraulic device, produces relatively little pressure drop thereacross, is simple in design and lends itself to several inexpensive modes of manufacture.

In addition to the foregoing many other features, advantages and additional objects of the present invention will become manifest to those versed in the art upon making reference to the detailed description which follows and to the accompanying sheets of drawings in which a preferred structural embodiment incorporating the principles of the present invention is shown by way of illustrative example.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a longitudinal cross-sectional view of a hydraulic device incorporating the principles of the present invention.

FIGS. 2-4 are cross-sectional views of the device shown in FIG. 1 and are taken respectively substantially along lines lI-lI, III-Ill and lV-IV of FIG. 1.

FIG. 5 is a view showing in elevation a driving connection between a pair of relatively movable members of the device shown in FIG. 1 and is taken substantially along lines V-V of FIG. 1.

FIG. 6 is similar to FIG. 5 but discloses means for providing relative axial movement of the two relatively movable members and is taken substantially along lines Vl-Vl of FIG. 1.

DESCRIPTION OF THE PREFERRED EMBODIMENT The principles of the present invention and the structures in which they are embodied may be conveniently utilized in any hydraulic device incorporating a pair of fluid displacement members which move simultaneously relatively orbitally and rotationally to form a series of alternately expanding and contracting fluid pockets. Thus, the principles of the present invention may be embodied in a commutator valve employed in association with a simple fluid pump or motor or in a more complex version thereof utilized, for example, in a one-piece hydrostatic unit of a vehicular power steering system.

Accordingly, embodiment of the invention disclosed illustratively herein is employed in a one-piece hydrostatic unit, wherein it finds particular utility, but in principle the invention is sufficiently broad to find general utility in a variety of hydraulic devices of the rotor-stator type and in many or all applications thereof.

The hydraulic device disclosed herein, indicated generally in the drawings at reference numeral 10, may be employed in vehicular power steering systems but may also be utilized as a primary control mechanism in controlling the operation of numerous hydraulically operated servomotors.

The device 10 comprises a housing 11 consisting essentially of four sectionsindicated respectively at

reference numerals

12, 13, 14 and 15. The housing sections 12-15 are clamped together in fixed assembly by virtue of a plurality of assembly bolts as indicated in FIGS. 2-4 at reference numerals 16.

Section 12 closes off one end of the housing 11 and section 15 closes the other end but also serves to mount a work inputoutput shaft 16. The shaft 16 is supported in the housing section 15 by virtue of bearing assemblies 17 and I8 and the axis of rotation of the shaft 16 coincides with a longitudinal axis of the entire housing I l.

The housing section 13 is shaped substantially in the form of an annular ring and disposed within the axial confines thereof are a pair of fluid displacement gear members including a stator indicated at reference numeral 19 and a rotor indicated at reference numeral 20. The stator is keyed stationarily to the housing section I3 as indicated at reference numeral 21 and comprises a series of internal lobes or teeth 22 which engage in meshing relation with a series of external lobes or teeth 23 formed on the rotor 22. In the embodiment illustrated the stator 19 has a total of seven teeth 22, whereas the stator 20 has only six teeth 23. As a consequence of this differential as well as the construction and arrangement of the teeth, the gear members are movable simultaneously orbitally and rotationally relative to one another.

In the embodiment illustrated the stator 19 is fixed, and consequently the rotor 20 will move both orbitally and rotationally relative to the stator 19 upon operation of the device 10.

Between the teeth 22 of the stator 19 and the teeth 23 of the rotor 20 are formed a plurality of fluid pockets indicated at reference characters 24a24f. As the rotor 20 moves relative to the stator 19 the fluid pockets 24a24f alternately expand and contract. Thus, during any moment of operation some of the fluid pockets are expanding whilst others are contracting, as in understood by those skilled in the art. A radially outwardly biased vane 26 is mounted on each of the rotor teeth 23 to reduce leakage between the adjacent fluid pockets 24a-24f.

In addition to providing a housing for the

gear members

19 and 20 the housing section 13 also has formed therein a radial wall 27 and a circumferential wall 28 which, in part and together with a radial wall 29 formed at one end of the housing section 13, provide a chamber 30 in which is housed a fluid commutator valve indicated generally at reference numeral 31. The function of the commutator valve 31 is to direct fluid into and out of the expanding and contracting fluid pockets 24a24f in timed relation to the relative orbital and rotational movement of the

fluid displacement members

19 and 20.

A pair of

fluid connections

32 and 33 are formed in the housing section 14 and communicate through suitable fluid circuitry with the commutator valve 31. When the device is being utilized as a servomotor controller in a power steering system or the like, the fluid connection 32 may be connected to the discharge or high pressure side of a main power fluid pump, whereas the connection 33 may be coupled to the suction side of the pump or to the fluid reservoir located on the suction side of the pump Also formed in the housing section 14 are a pair of work cylinder fluid connections indicated respectively at reference numerals 34 and 36. These latter two connections may be coupled to the opposite ends of a servomotor such as, for example, the main hydraulic cylinder in a vehicular power steering system.

In addition to the commutator valve 31, the illustrated hydraulic device 10 also includes a directional control fluid valve indicated generally at reference numeral 37. The purpose of valve 37 is to control the direction of fluid flow between the fluid connections 33 and through the fluid displacement gear members 19 and and also to control the direction of flow into and out of the work-cylinder fluid connections 34 and 36,

The directional control valve 37 is tubularly shaped and resides within a cylindrical bore in the housing section 14 formed by a bore wall 38 which is aligned axially with the work input-output shaft 16 as well as the stator 19. The valve 37 is coupled to the rotor 20 for joint rotation by means of an intermediate shaft part of wobble shaft 39 which is splined at one end 40 to the directional control valve 37 and at an opposite end 41 to the rotor 20. The valve 37 is also connected to the work input-output shaft 16 for relative axial and rotational movement.

Referring to FIGS 1 and 5, a threaded stud 42 is threaded radially into the shaft 16 and an enlarged head 43 thereof is disposed in an oversized slot 44 formed in the control valve 37. In addition a ball 45 resides in a semispherical recess 45a formed in an inner wall 370 of the valve 37 and extends in a complementarily shaped helical groove 45!; formed in a circumferential wall 16:: ofthe shaft 16.

As the shaft I6 is rotated relative to the valve 37 the valve will shift axially, in a direction depending upon the direction of relative rotation, as a consequence of the ball 45 riding in the helical groove 45b. However, in the event that the shaft 16 rotates relative to the valve 37 beyond a given degree then the head 43 of the stud 42 will abut a sidewall 44a or 44b of the slot 44, whereupon further rotation of the shaft 16 will cause the valve 37 to be driven thereby.

In order to enable the control valve 37 to perform its directional control function the bore wall 38 is provided with a series of grooves indicated respectively at P, M, C, X, R, Y, C, P, R and P. The aforesaid grooves correspond with another series of grooves 46-50 formed in a peripheral wall 51 of the control valve 37 and a pair of radial passages or bores 52 and 52 which extend through the cylinder wall of the control valve 37. The function of the various grooves and passages identified above will be explained in detail hereinafter.

The commutator valve 31 is essentially disc shaped and comprises a flat radial wall 53 which is aligned and in abutting engagement with the adjacent end walls of the stator 19 and the rotor 20. Formed in the radial wall 53 are a plurality of ports. The ports are grouped in pairs, one port of each pair being identified at reference numeral 54 and'the other port of each pair being identified at 56. The pairs of ports are spaced radially angularly about the central axis of the commutator valve 31 and furthermore the

ports

54 and 56 of each pair are also mutually angularly spaced. There are six pairs of ports, and thus the number of pairs corresponds to the number of teeth of the rotor 20. With respect to the rotor teeth, and as viewed in FIG. 2, the port 54 is on one radial side ofits respective rotor tooth whereas the port 56 is on the opposite side. The circular pattern in which the

ports

54 and 56 are arranged has a diameter which corresponds substantially to the pitch diameter of the stator teeth 22 and is such that the ports are closed or sealed as they move into axial alignment with thestator teeth 22 and are unsealed or opened for fluid communication and move into axial alignment with the fluid pockets 24a24f between the teeth of the stator 19.

The commutator valve 31 also comprises an outer peripheral wall 57 having a diameter which is less than the diameter of the adjacent cylindrical wall 28, and an inner peripheral wall 58. The ports 54 communicate with the inner peripheral wall 58 through a series of axial passages 59 and radial passages 60 whereas the ports 56 communicate with the outer peripheral wall 57 through axial passages 61 and radial passages 62. As a consequence the chamber 30 in which the commutator valve 31 resides is partitioned into two sub chambers, one of which surrounds the commutator valve 31 and the other of which is formed within the commutator valve 31.

In order to more clearly explain the operation of commutator valve 31 and its relation to the other components the operation of the device 10 may be described as follows.

Assuming that the device 10 is being used in a vehicular power-steering system, the outboard end of the shaft 16 may be splined as at 63 to receive a conventional vehicular steering wheel. Assuming that no torque is being applied to the shaft 16 the control valve 37 is axially disposed in a center or neutral position, the position thereof shown in FIG. 1. In that position the pressurized fluid from the discharge side of the main power fluid pump is connected to the fluid connection 32 but is blocked off at groove P by the valve 37. Consequently, there is no turning effect whatsoever on the dirigible wheels of the vehicle when the shaft 16 is in a static condition.

Assume, however, that the shaft 16 is turned in a clockwise direction. The rotor 20, and thus the control valve 37, is hydraulically locked against rotation and thus, as a consequence of the relative rotation of the shaft 16 and the valve 37, the valve is shifted axially leftwardly as viewed in FIG. 1.

When the valve 37 shifts axially, the groove P communicates through groove 46 with the groove M, and then communicates through a passage 64 formed in the housing section 14 with the chamber 30 in which the commutator valve 31 is housed. Pressurized fluid then flows through passages 62 and 6] to the ports 56.

Certain of the ports 56 (not covered by stator teeth 22) communicate with corresponding ones of the fluid pockets 2411-24)". Pressurization of these fluid pockets causes movement of the rotor both orbitally and rotationally relative to the stator 19.

The commutator valve is connected for joint movement to the rotor 20 by means of a tubular coupling 66 which is splined at 67 to the stator 20 and splined at 68 to the commutator valve 31. As the rotor 20 simultaneously orbits and rotates, the fluid pockets 24a-24f which are then contracting open to the ports 54 which correspond thereto. The fluid being delivered from the fluid pockets passes through the ports 54 and thence through the passages 59 and 60 and into an aperture 69 formed within the inner peripheral wall 58 of the commutator valve 31.

The fluid then flows through passages 70 formed in the wobble shaft 39 and thence through a longitudinal passage 71 into a hollow portion 72 of the directional control valve 37.

' From the hollow 72 the fluid flows through radial passages 52 and 52' into the groove C, and thence to the fluid connection 36 which may be connected to one end of a hydraulic work cylinder to urge the piston member thereof in one direction. The fluid being expelled from the opposite end of the work cylinder is directed to fluid connection 36, from which it flows into groove C and thence through groove 47 into groove X. From groove X, the fluid flows through groove 48 and into groove R, which communicates with groove R via an internal passage 73 formed in the housing section 14. From groove R the fluid flows out the fluid connection 33 and back to the main power fluid pump.

When the steering shaft 16 is rotated in an opposite direction the directional control valve 37 is shifted rightwardly as viewed in FIG. 1 to close off groove P. Groove P, however, communicates with groove P via an internal passage 74 formed in the housing section 14. Thus, groove P is always under the same pressure as groove P. As the valve 37 shifts rightwardly groove P communicates through radial passages 52 and 52' into the hollow 72 of the control valve 37 from which it flows through the bore 71 of the wobble shaft 39 and into the aperture 69 of the commutator valve 31.

The pressurized fluid thus flows out of ports 54 and into the expanding pockets and the fluid from the contracting pockets is expelled through the ports 56 and thence into the chamber 30 surrounding the commutator valve 31.

Continuing with the flow path, the fluid flows through the passage 64 and into the groove M, from which it flows via groove 46 into the adjacent groove C. From groove C the pressurized fluid flows from the fluid connection 34 to said opposite end of the hydraulic work cylinder. The fluid expelled from the opposite end flows to fluid connection 36 and the groove C, from which it flows through the groove 49 and into groove Y, and then through groove 48 into the groove R. From groove R the fluid flows through passageway 73, thence into groove R and to the fluid outlet connection 33 back to the suction side of the main power fluid pump.

Upon termination of the turning torque on the shaft 16 the control valve 37 is biased to its neutral or shutof position (the position shown in FIG. 1 )by virtue of a spring arrangement indicated generally at reference numeral 76. The spring arrangement 76 provides a neutral bias to the valve 37 regardless of the direction of axial shifting of the valve and the direction of rotation of the shaft 16.

As shown in the drawing, the commutator valve 31 is disposed axiallybetween the

gear members

19 and 20 and the shaft 16 and also between the

gear members

19 and 20 and the directional control valve 37. Furthermore, it is centrally aper' tured in order to enable the wobble shaft 39 interconnecting the control valve 37 and the rotor 20 to extend therethrough. This relative disposition of the parts has the effect of providing a compact arrangementv it is also noted that the commutator valve 31 is moved through its operational path of travel by virtue of a direct connection to the rotor 20 for joint movement therewith. Thus, a most direct means is utilized for driving the commutator valve and the inefficiencies and wear problems which may be inherent in indirect driving connections are entirely eliminated.

The radial wall 53 of the commutator valve 31, while in abutting engagement with the ends of both the stator l9'and the rotor 21, moves in sliding relation only with respect to the stator 19. This arrangement reduces the wear potential of the valve 31 to increase the operational life thereof.

Although minor modifications might be suggested by those versed in the art, it should be understood that we wish to embody within the scope of the patent warranted hereon all such modifications as reasonably come within the scope of our contribution to the art.

We claim:

1. Ina hydraulic device having fluid displacement means including an internally toothed stator and an externally toothed rotor having less teeth than said stator and being in meshing engagement therewith for relative orbital and rotational movement with respect thereto to form alternately expanding and contracting fluid pockets between the teeth thereof, a work input-output shaft connected to said fluid displacement means for joint rotation therewith and a pair of fluid connections in communication with said fluid pockets, the improvement of commutation means for directing fluid between said fluid connections and said fluid pockets in timed relation to the relative movement of said fluid displacement means comprising a commutator valve connected to said fluid displacement means for orbital and rotational movement therewith and having a radial wall facing said fluid pockets,

means forming a series of ports in said radial wall in a circular pattern having a diameter related to the pitch diameter of said stator, each of said pairs and each of said ports in said pairs being mutually angularly spaced and the number of said pairs being equal to the'number of teeth of said rotor, and

means for communicating one of said ports in each of said pairs of ports with one of said fluid connections and the other of said ports in each of said pairs with the other of said fluid connections.

2. The invention as defined in claim 1 wherein said commutator valve further comprises means forming an inner peripheral wall, an outer peripheral wall and passages communicating one of said ports of each of said pairs with one of said peripheral walls and the other of said ports of each of said pairs with the other said peripheral wall.

3. The invention as defined in claim 2 wherein said outer peripheral wall communicates with one of said fluid connections and said inner peripheral wall forms a central opening communicating with the other of said fluid connections.

4. The invention as defined in claim 1 wherein said commutator valve is connected in fixed assembly to said rotor for joint movement therewith.

5. The invention as defined in claim 1 wherein said device further comprises wall means forming a chamber adjacent said fluid displacement means and wherein said commutator valve is disposed within said chamber and comprises an inner peripheral wall forming a central opening through said valve, and outer peripheral wall disposed in spaced relation to said chamber wall and passages communicating one of said ports of each of said pairs of ports with one of said peripheral walls and the other of said ports of each of said pairs with the other of said peripheral walls,

said chamber between said chamber wall and said outer peripheral wall communicating with one of said fluid connections and said central opening of said valve communicating with the other of said fluid connections.

6. The invention as defined in claim I wherein said stator and said rotor comprise radial walls in sliding and in fixed relation respectively with said radial wall of said commutator valve.

7. A hydraulic device comprising a housing,

a rotor-stator gearset in said housing, the rotor member of which has one tooth less than the stator member and is movable orbitally and rotationally relative to the stator member to provide expanding and contracting fluid pockets between the teeth thereof,

a work input-output shaft connected forjoint rotation to the rotational member of said gearset,

a pair of fluid connections formed in said housing, and

fluid commutation means comprising means forming a valve chamber in said housing,

a commutator valve member disposed within said chamber and having a radial wall facing said fluid pockets,

means connecting said commutator valve and said gearset for rotational and orbital movement in mutually timed relation, means forming a series of angularly spaced ports in said radial wall numbering at least twice the number of rotor teeth, and

means communicating some of said ports with one of said fluid connections and other of said ports with the other of said fluid connections for directing fluid into the expanding fluid pockets and out of the contracting fluid pockets.

8. The invention as defined in claim 7 wherein said ports are arranged on said radial wall in a circular pattern about the axis of rotation of said commutator valve.

9. The invention as defined in claim 8 wherein said ports are arranged on said radial wall in a circular pattern with alternate ones of said ports communicating with one of said fluid connections and the other ports communicating with the other of said fluid connections.

10. The invention as defined in claim 7 wherein said ports are arranged in pairs disposed in radially angularly spaced relation corresponding to the radially angular spacing of the teeth of said rotor.

11. A hydraulic device comprising an axial housing having a pair of gear members disposed therewith including an internally toothed stator and an externally toothed rotor within the stator and movable orbitally and rotationally relative thereto to provide alternately expanding and contracting fluid pockets therebetween,

a work input-output shaft mounted for rotation on said housing, intermediate shaft means interconnecting said rotor and said work input-output shaft for joint rotation,

means in said housing including a cylindrical wall and a radial wall forming a chamber adjacent said gear members,

a disc-shaped commutator valve in said chamber having a pair of radial walls one of which abuts said gear members and the other of which abuts said chamber radial wall, an outer peripheral wall and an inner peripheral wall forming a central aperture extending axially therethrough,

a plurality of ports formed in said one radial wall of said valve and arranged in a circular pattern in radially angularly spaced pairs equal in number to the number of teeth of said rotor,

means interconnecting said rotor and said commutator valve for joint orbital and rotational movement,

passage means communicating one port of each of said pairs to said inner peripheral wall and the other port of each said pair to said outer peripheral wall,

a pair of fluid connections formed in said housing, and

means communicating one of said fluid connections with said valve aperture and the other fluid connection to said chamber radially outwardly of said outer peripheral wall of said commutator valve.

12. The invention as defined in claim 11 wherein said commutator valve is disposed between said work input-output shaft and said rotor and said intermediate shaft means comprises a shaft part extending through said commutator valve aperture.

13. The invention as defined in claim 11 and including means forming a pair of work-cylinder fluid connections in said housing, and means forming cylindrical bore in said housing in axial alignment with said work input-output shaft and said stator and in fluid communication with said fluid-connections, said intermediate shaft means comprising a tubularly shaped fluid directional control valve in said bore and an intermediate shaft part, said shaft part being connected to said rotor and to said control valve for joint rotation and said control valve being connected to said work input-output shaft for limited relative axial and rotational movement therewith, and means formed in said cylindrical bore and in said fluid directional control valve for controlling the direction of fluid flow between said fluid connections and said gear members, said commutator valve being disposed between said control valve and said gear members. 14. The invention as defined in claim 13 wherein said shaft part extends through the aperture formed in said commutator valve.

Claims

1. In a hydraulic device having fluid displacement means including an internally toothed stator and an externally toothed rotor having less teeth than said stator and being in meshing engagement therewith for relative orbital and rotational movement with respect thereto to form alternately expanding and contracting fluid pockets between the teeth thereof, a work input-output shaft connected to said fluid displacement means for joint rotation therewith and a pair of fluid connections in communication with said fluid pockets, the improvement of commutation means for directing fluid between said fluid connections and said fluid pockets in timed relation to the relative movement of said fluid displacement means comprising a commutator valve connected to said fluid displacement means for orbital and rotational movement therewith and having a radial wall facing said fluid pockets, means forming a series of ports in said radial wall in a circular pattern having a diameter related to the pitch diameter of said stator, each of said pairs anD each of said ports in said pairs being mutually angularly spaced and the number of said pairs being equal to the number of teeth of said rotor, and means for communicating one of said ports in each of said pairs of ports with one of said fluid connections and the other of said ports in each of said pairs with the other of said fluid connections.

5. The invention as defined in claim 1 wherein said device further comprises wall means forming a chamber adjacent said fluid displacement means and wherein said commutator valve is disposed within said chamber and comprises an inner peripheral wall forming a central opening through said valve, and outer peripheral wall disposed in spaced relation to said chamber wall and passages communicating one of said ports of each of said pairs of ports with one of said peripheral walls and the other of said ports of each of said pairs with the other of said peripheral walls, said chamber between said chamber wall and said outer peripheral wall communicating with one of said fluid connections and said central opening of said valve communicating with the other of said fluid connections.

6. The invention as defined in claim 1 wherein said stator and said rotor comprise radial walls in sliding and in fixed relation respectively with said radial wall of said commutator valve.

7. A hydraulic device comprising a housing, a rotor-stator gearset in said housing, the rotor member of which has one tooth less than the stator member and is movable orbitally and rotationally relative to the stator member to provide expanding and contracting fluid pockets between the teeth thereof, a work input-output shaft connected for joint rotation to the rotational member of said gearset, a pair of fluid connections formed in said housing, and fluid commutation means comprising means forming a valve chamber in said housing, a commutator valve member disposed within said chamber and having a radial wall facing said fluid pockets, means connecting said commutator valve and said gearset for rotational and orbital movement in mutually timed relation, means forming a series of angularly spaced ports in said radial wall numbering at least twice the number of rotor teeth, and means communicating some of said ports with one of said fluid connections and other of said ports with the other of said fluid connections for directing fluid into the expanding fluid pockets and out of the contracting fluid pockets.

11. A hydraulic device comprising an axial housing having a pair of gear members disposed therewith including an internally toothed statoR and an externally toothed rotor within the stator and movable orbitally and rotationally relative thereto to provide alternately expanding and contracting fluid pockets therebetween, a work input-output shaft mounted for rotation on said housing, intermediate shaft means interconnecting said rotor and said work input-output shaft for joint rotation, means in said housing including a cylindrical wall and a radial wall forming a chamber adjacent said gear members, a disc-shaped commutator valve in said chamber having a pair of radial walls one of which abuts said gear members and the other of which abuts said chamber radial wall, an outer peripheral wall and an inner peripheral wall forming a central aperture extending axially therethrough, a plurality of ports formed in said one radial wall of said valve and arranged in a circular pattern in radially angularly spaced pairs equal in number to the number of teeth of said rotor, means interconnecting said rotor and said commutator valve for joint orbital and rotational movement, passage means communicating one port of each of said pairs to said inner peripheral wall and the other port of each said pair to said outer peripheral wall, a pair of fluid connections formed in said housing, and means communicating one of said fluid connections with said valve aperture and the other fluid connection to said chamber radially outwardly of said outer peripheral wall of said commutator valve.

13. The invention as defined in claim 11 and including means forming a pair of work-cylinder fluid connections in said housing, and means forming a cylindrical bore in said housing in axial alignment with said work input-output shaft and said stator and in fluid communication with said fluid-connections, said intermediate shaft means comprising a tubularly shaped fluid directional control valve in said bore and an intermediate shaft part, said shaft part being connected to said rotor and to said control valve for joint rotation and said control valve being connected to said work input-output shaft for limited relative axial and rotational movement therewith, and means formed in said cylindrical bore and in said fluid directional control valve for controlling the direction of fluid flow between said fluid connections and said gear members, said commutator valve being disposed between said control valve and said gear members.

14. The invention as defined in claim 13 wherein said shaft part extends through the aperture formed in said commutator valve.