US3204572A

US3204572A - Multiple piston type pump or motor

Info

Publication number: US3204572A
Application number: US234386A
Authority: US
Inventors: Bruce H Mosbacher
Original assignee: Roper Hydraulics Inc
Current assignee: Roper Technologies Inc
Priority date: 1962-10-31
Filing date: 1962-10-31
Publication date: 1965-09-07
Anticipated expiration: 1982-09-07

Description

Sept. 7, 1965 B. H MOSBACHER MULTIPLE PISTON TYPE PUMP OR MOTOR 2 Sheets-Sheet 1 Filed Oct. 31, 1962 P 1965 B. H MOSBACHER 3,204,572

MULTIPLE PISTON TYPE PUMP OR MOTOR Filed Oct. 31, 1962 2 Sheets-Sheet 2 CD 404 [Q lo 7 i I 405 q: 1 )//8 United States Patent 3,204,572 MULTKPLE PISTUN TYPE PUMP 0R MOTOR Bruce H. Mosbacher, Rockford, lll., assignor to Roper Hydraulics, Inc., Commerce, Ga., a corporation of Georgia Filed Oct. 31, 1962, Ser. No. 234,386 9 (Ilairns. (Cl. 103174) This invention relates to a multiple piston type pump or motor device.

An important object of this invention is to provide a multiple piston type pump adapted to provide either plural separate discharges for supplying proportional flows to several outlets or to provide combined flows from several or all of the piston pumping units.

It is an important object of this invention to provide an improved multiple piston pumping apparatus adapted to provide plural segregated flows or combined flows from several or all of the pumping units, and which pumping apparatus is of simple and economical construction.

Another object of this invention is to provide an improved multiple piston type pump or motor wherein the pistons are mounted on the pump casing and the cylinders are formed in a member which is moved in orbital fashion relative to the casing and pistons to effect cyclic reciprocation of the pistons in the cylinders and to also valve the flows of fluid to and from the pump cylinders in proper timed relation to the reciprocation of the pistons.

A more particular object of this invention is to provide a multiple piston type pump or motor of the type wherein the pump cylinders are formed in a cylinder member which is moved in orbital fashion in a pump casing by an eccentric, and which pump or motor has an improved arrangement for mounting the piston members on the casing to hold the piston members against axial shifting while permitting limited crosswise oscillation of the piston members during rotation of the eccentric.

These, together with various ancillary objects and advantages of this invention will be more readily appreciated as the same becomes better understood by reference to the following detailed description when taken in connection with the accompanying drawings wherein:

FIG. 1 is a longitudinal sectional view through the pumping apparatus;

FIG. 2 is a transverse sectional view taken on the plane 22 of FIG. 1;

FIG. 3 is an enlarged fragmentary sectional view taken on the plane 2-2 of FIG. 1;

FIG. 4 is a transverse sectional view taken on the plane 44 of FIG. 1 and illustrating one of the port plates;

FIG. 5 is a transverse sectional view taken on the plane 5-5 of FIG. 1 and illustrating the other of the port plates; and

FIG. 6 is a fragmentary end view of the pumping apparatus illustrating a manifold arrangement for interconnecting several of the pump outlets.

The apparatus of the present invention is adapted for use as a pump or motor. For convenience, the apparatus is hereinafter described as a fiuid piunp, it being understood that it can also be operated as a motor if fluid under pressure is supplied thereto.

The pumping apparatus in general includes a casing 10 defining a cavity 11, a cylinder member 12 disposed in the cavity and connected to an eccentric 13 on a shaft 14, a plurality of piston members 15, and a means 16 for mounting the piston members on the pump casing. The cylinder member 12 is moved in orbital fashion in the pump cavity to effect cyclic reciprocation of the pistons 15, and the cylinder member 12 has valve ports therein which cooperate with inlet and discharge ports in the casing to valve the flows of fluid to and from the pump cylinders in proper timed relation with the reciprocation of the pistons.

The casing is advantageously arranged to enable stacking of two or more pumping units, if desired. For this purpose, the pump casing is formed with an annular casing member 21 having

port plates

22 and 23 attached to opposite sides and sealed thereto as by O-rings 24 to form a casing unit. One such casing unit can be employed, or several of such casing units can be stacked. End plates 26 and 27 are provided at opposite sides of the single or multiple casing unit assembly, and the several parts are retained in assembled relation as by fasteners 28. The

port plates

22 and 23 have generally fiat side faces 31 and 32 at opposite sides of the cavity and the cylinder member 12 has end faces 33 and 34 disposed in rubbing engagement with the side faces 31 and 32. The cylinder member has an axial bore 36 and a plurality of cylinder bores 37 extending generally radially of the annular cylinder member. As shown herein, twelve cylinder bores are provided, it being understood that a greater or lesser number of cylinder bores could be provided if desired. The cylinder bores 37 are conveniently arranged to intersect the axial bore 36 and the cylinder member is rotatably supported on the eccentric 13 by a steel backed bushing 39 which is pressed into the bore 36 in the cylinder member to also close the inner ends of the cylinder bores 37. Plugs such as 49 are preferably provided in the inner ends of the cylinder bores to limit the dead space in the cylinders and to avoid forming an air or gas trap in the cylinder bores. The shaft 14 is rotatably supported in bushings 41 and 42 in the port plates and has a keyed end which is connected through an Oldham type coupling 44 to a stub drive shaft 45. In the form shown, this drive shaft is rotatably supported in bearings 46 on the end member 26 and a shaft seal 47 is provided for sealing the interface between the stub shaft and the pump casing.

The piston members 15 are herein shown in the form of generally cylindrical pins which reciprocate in the cylinder bores 37 as the eccentric 13 rotates and moves the cylinder member in orbital fashion in the cavity. In accordance with the present invention, the piston members are mounted on the casing in such a manner as to constrain the piston members against axial reciprocation relative to the casing while permitting oscillation of the piston members in a direction circumferentially of the shaft during orbital movement of the cylinder member. For this purpose, the annular casing member 21 is formed with a plurality of notches 51 on the inner periphery thereof which define circumferentially spaced stop faces 51a and 51b. The cylinder member 12 will shift circumferentially of the shaft 14 a distance equal to twice the eccentricity of the eccentric 13, and designated E in FIG. 3. The stop faces 51a and 5111 are accordingly spaced apart a distance designated W in FIG. 3 and which is substantially equal to the circumferential width of the piston member 15 at the point of contact with the stop faces, plus twice the eccentricity E of the eccentric. The piston members can, accordingly, shift circumferentially from their mid position shown in FIG. 3, in either direction, a distance corresponding to the eccentricity of the cam to allow the cylinder member to oscillate during rotation of the eccentric cam. With this arrangement, one pair of diametrically opposed piston members will engage relatively opposite stop faces 51a and 51b at substantially all times to prevent rotation of the cylinder member and to control the oscillation of the cylinder member 12 during rotation of the eccentric. As best shown in FIG. 2, the piston members 15 which are disposed substantially perpendicular to the plane through the axes of the eccentric 14 and shaft 13, engage relatively opposite stop faces 51a and 51b. The other piston members are spaced varied distances from their respective stop faces. However, as the eccentric rotates, for example in a clockwise direction as viewed in FIG. 2, the next piston members in a clockwise direction from the aforementioned piston members move into engagement with the opposed stop faces 51a and 51b while the first mentioned piston members begin to move away from their respective stop faces. The piston members thus successively operate the control turning movement of the cylinder member as the eccentric rotates.

The piston members 15 are supported on the casing for oscillation between the stops 51a and 51b and are held against axial reciprocation by means of the piston mounting apparatus 16. This apparatus advantageously includes a roller 61 disposed in each of the notches 51, with its axis paralleling the axis of the shaft. The roller engages the radially outer end of the respective one of the pistons 15 and limits outward movement of the piston member while permitting free oscillation of the piston member in a direction crosswise of its axis. The roller has rolling contact with the base of the notch 51 and the end of the piston member and, when the piston member moves laterally a distance equal to twice the eccentricity E of the eccentric, the roller only has to move one-half this distance. Accordingly, the roller 61 is preferably formed with outer diameter that exceeds the width of the piston by an amount equal to the eccentricity E. Stated otherwise, if the notch 51 has a width equal to the circumferential width of the piston plus twice the eccentricity, then the roller has an outer diameter which is less than the width of the notch by an amount equal to the eccentricity. With this arrangement, the roller 61 will also engage the stop faces 51a and 51b at the time the respective piston engages the stop face.

In the embodiment illustrated, the pistons are small and displace only a small amount of fluid during each reciprocation. In accordance with the present invention, the pistons are magnetically held to the casing to inhibit axial reciprocation of the pistons during oscillation of the cylinder member. Either the casing member 21 or the piston 15 or both can be magnetized. If only one is magnetized, the other will, of course, have to be formed of a ferromagnetic material. However, when employing the rollers 61, it is preferable to at least magnetize the pistons to hold the pistons in contact with the rollers during lateral oscillation of the pistons with the cylinder member.

Since some of the pistons may tend to bind in the cylinder bores, particularly if the pump has not been in use for a while, a mechanical means is also provided for preventing radial shifting movement of the pistons. For this purpose, the piston members are formed with a notch 64 in the side thereof adjacent their outer ends and which notch defines inner and outer shoulders 64a and 641) (see FIG. 3). An annular ring 65 is disposed around the inner periphery of the annular casing member 21 and arranged to engage the outer shoulder 64a if the piston members tend to stick in the cylinder, to positively hold the piston members against inward movemnt. As will be noted from FIG. 1, the piston member is free to move circumferentially around the ring 65 between the stops 51a and 51b during oscillation of the piston members.

As shown in FIGS. 1 and 5, the ring 65 is disposed in a groove 66 in the port plate 23 and engages the inner periphery of the annular casing member 21. A similar ring 67 is disposed in a groove 68 in the port plate 22 and also engages the inner periphery of the casing member 21. The ring members 65 and 67 are thus radially supported on the

port plates

23 and 22 and engage the casing member 21 to radially center the same with respect to the port plates.

The cylinder member 12 is formed with a plurality of valve ports 81, each individual to one of the cylinders 37. In order to substantially balance the axial hydraulic forces on the cylinder, the valve ports 81 are advantageously arranged to extend completely through the cylinder member and open at opposite sides thereof, as is clearly shown in FIG. 1. Each valve port 81 in the rotor is cooperable with a respective pair of inlet and discharge ports in the casing to alternately communicate the cylinder 3'7 with the inlet and discharge ports. While the inlet and discharge ports could be located all in one or the other of the

port plates

22 and 23, it is preferable, when using a relatively large number of pump cylinders, to locate some of the ports in one of the plates and others of the ports in the other plate. As shown in FIG. 4, a plurality of pairs of inlet and

discharge ports

84 and 85, corresponding to one half the total number of inlet and discharge ports, are formed in the port plate 22 and alternate pairs of inlet and discharge ports designated 84' and 85' are formed in the other port plate 23. The

inlet ports

84 and 84 communicate through passages 86 and 86' with distributor grooves 87 and 87' in the

port plates

22 and 23 respectively. Fluid under pressure is supplied to the distributor grooves in any suitable manner.

However, in order to facilitate stacking of a plurality of pumping units each including a casing member 21,

port plates

22 and 23, and shaft 14, it is preferable to provide inlet passage such as 88 and 88' in both

port plates

22 and 23, with the inlet passages arranged to open at the outer side of the port plates to communicate with the inlet passage in an adjacent pumping unit, when more than one unit is stacked together. As shown, the inlet passage 38 in one port plate is closed by the end plate 26 and the inlet passage in the other end plate 23 communicates with an internally threaded opening an in the end member 27. When more than one pumping unit is stacked together, the inlet passage 88 in one unit will be positioned to communicate with the inlet passage 88' in the adjacent unit to enable supply of fluid to the several units from a common inlet. As shown in FIG. 1, the shaft 14 is keyed at both ends for connection. by a coupling such as 44 to the shaft of an adjacent unit. As will be seen from FIG. 5, fluid from one of the distributor grooves 87' can flow around the outer periphcry of the cylinder member 12 and through the pump cavity 11 into the other distributor groove 87, to supply fluid to the inlet ports 34 communicating with that groove. The several outlet passages 85 in the port plate 22 are connected to individual discharge passages 91a-9llf which passages open at end faces 94 and 95 on the port plate 22. The individual outlet passages 85' and the port plate 23 are similarly connected through individual outlet passages 92a-92f which open at opposite end face 94' and 95 on the port plate 23.

The inlet and discharge passages such as 84, 85; 84' and 85', of each pair are angularly spaced apart relative to the axis of the shaft 14 and, as best shown in FIG. 3, the valve ports 81 in the cylinder member are movable in an orbital path, alternately into communication with the inlet and discharge ports. Thus, the eccentric produces a radial shifting movement of the cylinder member to effect reciprocation of the cylinder member relative to the pistons and cyclically vary the volume of the displacement chambers in the cylinders. In addition, the eccentric produces an oscillation of the cylinder member in a direction circumferentially of the shaft and crosswise of the axis of the pistons, and which oscillation is substantially 90 out of phase with the reciprocation of the pistons. This crosswise oscillation of the cylinder member effects movement of the valve port between the inlet and discharge ports, and thus valves the flow of fluid to and from the pump cylinders in proper timed relation with the reciprocation of the pistons.

The outlets of the several pump cylinders are thus connected to individual discharge passages 91a91f and 9292f to provide separate proportional discharges, if desired. These individual discharges can be utilized separately, for example, in a fuel feed system for a multiple cylinder engine or in a lubrication system requiring multiple divided flows. Two or more of the independent discharges from the pump can also be combined, if desired, and, as shown in FIG. 6,

manifolds

101 and 102 are attached to end faces 95 and 95', as by fasteners 103. The manifold 101 has

openings

104, 105 and 106 which are adapted to communicate with the passages 91:1-91 and which openings are inter-connected by

passages

107 and 108 to combine the flows from the several passages. In the embodiment illustrated, the manifold 102 similarly has openings 111, 112 and 113 adapted to register with the passages 92d92f. These openings are also interconnected as by passages 115 and 116 to combine the flows from the several outlet passages 92d92f. Conveniently, the outlets from both manifolds can be combined by a cross pipe 118, which pipe is sealed to the

manifolds

101 and 102 as by O-rings 119 and intercommunicates the passages in the same to combine the flows from both manifolds. Obviously, by suitable arrangement of the manifolds, any desired combination of flows can be achieved. As previously described, a number of pumping units can be stacked to provide additional proportional flows, if desired.

From the foregoing, it is thought that the operation and construction of the device will be readily understood. As the eccentric 13 rotates, the cylinder member is moved in orbital fashion in the pump cavity to effect cyclic reciprocation of the pistons in the cylinders. The piston members are supported by the roller 61 and ring 65 on the casing in such a manner as to constrain the pistons against axial reciprocation while permitting oscillation of the pistons in a direction crosswise of the axis of the pistons during orbital movement of the cylinder member. The stop faces 51a and 51b are so arranged as to engage the ends of the pistons and control oscillation of the pistons. As the cylinder member oscillates in a direction circumferentially of the shaft, the valve port 81 moves alternately into communication with the inlet and discharge ports to valve the flow to and from the cylinders in proper timed relation with the reciprocation of the pistons therein,

I claim:

1. A fluid pump or motor comprising, a pump casing defining a cavity having end wall means, an annular cylinder member in said cavity, a shaft extending into said cavity and having eccentric means rotatably connected to said cylinder member for moving the same in an orbital path, said cylinder member having a plurality of generally radially extending displacement chambers therein, a plurality of piston members slidable in said displacement chambers and extending outwardly from said cylinder member, means for constraining said piston members and said cylinder member from turning with said eccentric means, said last mentioned means including pockets on said easing into which the piston members extend, each pocket defining a pair of stop faces to make contact with each individual piston member and spaced apart in a direction circumferentially of said shaft a distance substantially equal to the width of the piston member measured in a direction circumferentially of the shaft at the point of engagement with the stop faces plus twice the eccentricity of Said eccentric means to alloW the piston members and cylinder member to oscillate in a direction circumferentially of the shaft as the eccentric means rotates, and means for valving the flows of fluid to and from said displacement chambers in timed relation with the reciprocation of the pistons in the displacement chambers.

2. A fluid pump or motor comprising, a pump casing defining a cavity having end wall means, an annular cylinder member in said cavity, a shaft extending into said cavity and having eccentric means rotatably connected to said cylinder member for moving the same in an orbital path, said cylinder member having a plurality of generally radially extending displacement chambers therein, a plurality of piston members slidable in said displacement chambers and extending outwardly from said cylinder member, means for constraining said piston members and said cylinder member from turning with said eccentric means, said last mentioned means including means of said casing defining pairs of stop faces individual to each piston member and spaced apart in a direction circumferentially of said shaft a distance substantially equal to the width of the piston member measured in a direction circumferentially of the shaft at the point of engagement with the stop faces plus twice the eccentricity of said eccentric means to allow the piston members and cylinder member to oscillate in a direction circumferentially of the shaft as the eccentric means rotates, a roller disposed between each pair of stop faces and engaging the radially outer end of the piston member to radially support the piston members against outward movement, and means for valving the flows of fluid to and from said displacement chambers in timed relation with the reciprocation of the piston members in the displacement chambers, said rollers having a diameter which is less than the spacing between the respective pair of stop faces by an amount substantially equal to the eccentricity of said eccentric means.

3. A fluid pump or motor comprising, a pump casing including an annular casing member having an inner peripheral wall and end walls at opposite ends of the annular casing member defining a cavity, an annular cylinder member in said cavity, a shaft extending into said cavity and having eccentric means rotatably connected to said cylinder member for moving the same in an orbital path, said cylinder member having a plurality of generally radially extending displacement chambers therein, a plurality of piston members slidable in said. displacement chambers and extending outwardly from said cylinder member, said peripheral wall having a plurality of inwardly opening recesses into which the piston members extend to constrain said piston members and said cylinder member from turning with said eccentric means, said recesses each defining a pair of stop faces to make contact with each individual piston member and spaced apart in a direction circumferentially of said shaft a distance substantially equal to the width of said piston members plus twice the eccentricity of said eccentric means to allow the piston members and cylinder member to oscillate in a direction circumferentially of the shaft as the eccentric means rotates, means for limiting axial reciprocation of said piston members while permitting oscillating of said piston members in a direction circumferentially of said shaft, and means for valving the flows of fluid to and from said displacement chambers in timed relation with the reciprocation of said piston members in the displacement chambers.

4. A fluid pump or motor comprising, a pump casing defining a cavity having end wall means, an annular cylinder member in said cavity, a shaft extending into said cavity and having eccentric means rotatably connected to said cylinder member for moving the same in an orbital path, said cylinder member having a plurality of generally radially extending displacement chambers therein arranged in sets of four with the chambers of each set angularly spaced apart from each other, a plurality of piston members slidable in said displacement chambers and extending outwardly from said cylinder member, means for constraining said piston members and said cylinder member from turning with said eccentric means, said last mentioned means including pockets on said easing into which the piston members extend, each pocket defining a pair of stop faces to make contact with each individual piston member and spaced apart in a direction circumferentially of said shaft a distance substantially equal to the width of the piston member measured in a direction circumferentially 0f the shaft at the point of engagement with the stop faces plus twice the eccentricity of said eccentric means to allow the piston members and cylinder member to oscillate in a direction circumferentially of the shaft as the eccentric means rotates, said end wall means on said casing having a plurality of inlet and discharge ports arranged in pairs individual to each displacement chamber, said inlet and discharge ports of each pair being angularly spaced apart relative to the axis of said shaft a valve port in said cylinder member individual to each displacement chamber and communicating therewith, said valve ports being movable alternately into communication With the inlet and discharge ports of the respective pair as said cylinder member oscillates in a direction circumferentially of said shaft.

5. A fluid pump or motor comprising, a pump casing including an annular casing member having an inner peripheral wall and end walls at opposite ends of the annular casing member defining a cavity, an annular cylinder member in said cavity, a shaft extending into said cavity and having eccentric means rotatably connected to said cylinder member for moving the same in an orbital path, said cylinder member having a plurality of generally radially extending displacement chambers therein, a plurality of piston members slidable in said displacement chambers and extending outwardly from said cylinder member, said peripheral wall having a plurality of inwardly opening recesses each for receiving the ends of a respective one of the piston members to constrain said piston members and said cylinder member from turning with said eccentric means, said recesses defining pairs of stop faces individual to each piston member and spaced apart in a direction circumferentially of said shaft a distance substantially equal to the width of said piston members plus twice the eccentricity of said eccentric means to allow the piston members and cylinder member to oscillate in a direction circumferentially of the shaft as the eccentric means rotates, means for limiting axial reciprocation of said piston members while permitting oscillating of said piston members in a direction circumferentially of said shaft, and means for valving the flows of fluid to and from said displacement chambers in timed relation with the reciprocation of said piston members in the displacement chambers and a roller disposed between each pair of stop faces and engaging the radially outer end of the piston member to radially support the piston member against outward movement, said rollers having a diameter less than the width of said recesses by an amount substantially equal to the eccentricity of said eccentric means.

6. A fluid pump or motor comprising, a pump casing defining a cavity having end Wall means, an annular cylinder member in said cavity, a shaft extending into said cavity and having eccentric means rotatably connected to said cylinder member for moving the same in an orbital path, said cylinder member having a plurality of generally radially extending displacement chambers therein arranged in sets of four with the chambers of each set angularly spaced apart 90 from each other, a plurality of piston members slidable in said displacement chambers and extending outwardly from said cylinder member, means for constraining said piston members and said cylinder member from turning with said eccentric means, said last mentioned means including means on said casing defining pairs of stop faces individual to each piston member and spaced apart in a direction circumferentially of said shaft a distance substantially equal to the width of the piston member measured in a direction circumferentially of the shaft at the point of engagement with the stop faces plus twice the eccentricity of said eccentric means to allow the piston members and cylinder member to oscillate in a direction circumferentially of the shaft as the eccentric means rotates, said end wall means on said casing having a plurality of inlet and discharge ports arranged in pairs individual to each displacement chamber, said inlet and discharge ports of each pair being angularly spaced apart 8 relative to the axis of said shaft, a valve port in said cylinder member individual to each displacement chamber and communicating therewith, said valve ports being movable alternately into communication with the inlet and diS- charge ports of the respective pair as said cylinder member oscillates in a direction circumferentially of said shaft, and a roller disposed between each pair of stop faces and engaging the radially outer end of each piston member, said rollers having an outer diameter less than the spacing between said stop faces by an amount substantially equal to the eccentricity of said eccentric means.

7. The combination of claim 6 wherein at least one, the pump casing or the piston members, are magnetized to magnetically hold the piston members against the rollers and the rollers against the casing to constrain the piston members against axial reciprocation.

8. The combination of claim 6 wherein said piston members have a notch in the side thereof, and means on said casing extending into said notch and engaging the piston members to limit movement of the piston members in a direction axially thereof while permitting limited oscillation of the piston members in a direction crosswise of their axes.

9. A fluid pump or motor comprising, a pump casing including an annular casing member having an inner peripheral wall and end walls at opposite ends of the annular casing member defining a cavity, an annular cylinder member in said cavity, a shaft extending into said cavity and having eccentric means r-otatably connected to said cylinder member for moving the same in an orbital path, said cylinder member having a plurality of generally radially extending displacement chambers therein, a plurality of piston members slidable in said displacement chambers and extending outwardly from said cylinder member, said peripheral wall having a plurality of inwardly opening recesses into which the end of a respective one of the piston members extends to constrain said piston members and said cylinder member from turning with said eccentric means, each recess defining a pair of stop faces to make contact with each individual piston member and spaced apart in a direction circumferentially of said shaft a distance substantially equal to the width of said piston members plus twice the eccentricity of said eccentric means to allow the piston members and cylinder member to oscillate in a direction circumferentially of the shaft as the eccentric means rotates, means for limiting axial reciprocation of said piston members while permitting oscillating of said piston members in a direction circumferentially of said shaft, and means for valving the flows of fluid to and from said displacement chambers in timed relation with the reciprocation of said piston members in the displacement chambers, said means for limiting axial reciprocation of said piston members comprising a shoulder on each piston member and an annular ring on the casing concentric with said shaft and engaging said shoulders on each of the piston members, said ring being radially anchored in one of said end walls and engaging said peripheral wall of said casing member to radially locate the casing member.

References Cited by the Examiner UNITED STATES PATENTS 2,173,432 9/39 Benedek 103-161 3,016,019 1/62 Rineer 103-121 FOREIGN PATENTS 869,154 3/53 Germany. 321,313 11/29 Great Britain.

LAURENCE V. EFNER, Primary Examiner.

Claims

1. A FLUID PUMP OR MOTOR COMPRISING, A PUMP CASING DEFINING A CAVITY HAVING END WALL MEANS, AN ANNULAR CYLINDER MEMBER IN SAID CAVITY, A SHAFT EXTENDING INTO SAID CAVITY AND HAVING ECCENTRIC MEANS ROTATABLY CONNECTED TO SAID CYLINDER MEMBER FOR MOVING THE SAME IN AN ORBITAL PATH, SAID CYLINDER MEMBER HAVING A PLURALITY OF GENERALLY RADIALLY EXTENDING DISPLACEMENT CHAMBERS THEREIN, A PLURALITY OF PISTON MEMBERS SLIDABLE IN SAID DISPLACEMENT CHAMBERS AND EXTENDING OUTWARDLY FROM SAID CYLINDER MEMBER, MEANS FOR CONSTRAINING SAID PISTON MEMBERS AND SAID CYLINDER MEMBER FROM TURNING WITH SAID ECCENTRIC MEANS, SAID LAST MENTIONED MEANS INCLUDING POCKETS ON SAID CASING INTO WHICH THE PISTON MEMBERS EXTEND, EACH POCKET DEFINING A PAIR OF STOP FACES TO MAKE CONTACT WITH EACH INDIVIDUAL PISTON MEMBER AND SPACED APART IN A DIRECTION CIRCUMFERENTIALLY OF SAID SHAFT A DISTANCE SUBSTANTIALLY EQUAL TO THE WIDTH OF THE PISTON MEMBER MEASURED IN A DIRECTION CIRCUMFERENTIALLY OF THE SHAFT AT THE POINT OF ENGAGEMENT WITH THE STOP FACES PLUS TWICE THE ECCENTRICITY OF SAID ECCENTRIC MEANS TO ALLOW THE PISTON MEMBERS AND CYLINDER MEMBER TO OSCILLATE IN A DIRECTION CIRCUMFERENTIALLY OF THE SHAFT AS THE ECCENTRIC MEANS ROTATES, AND MEANS FOR VALVING THE FLOWS OF FLUID TO AND FROM SAID DISPLACEMENT CHAMBERS IN TIMED RELATION WITH THE RECIPROCATION OF THE PISTON IN THE DISPLACEMENT CHAMBERS.