US3813995A

US3813995A - Fluid pressure machines

Info

Publication number: US3813995A
Application number: US00370846A
Authority: US
Inventors: R Harris
Original assignee: Hydrostatic Transmissions Ltd
Current assignee: Hydrostatic Transmissions Ltd
Priority date: 1972-06-20
Filing date: 1973-06-18
Publication date: 1974-06-04
Anticipated expiration: 1991-06-04
Also published as: AU5706373A; DE2331273A1; ES416134A1; CA977211A; JPS4985604A; DE2331273C3; FR2190172A5; GB1378546A; AU474874B2; IT986490B; DE2331273B2; JPS5340963B2; BE801183A; SE389168B; CH564678A5

Abstract

In a radial, multi cylinder fluid pressure machine, adverse mechanical and/or fluid loads occurring during running are minimised by fluid pressure. The capacity of the machine is selectable by provision of a plunger sleeve and an inner plunger in each cylinder bore, and by valve means selectively controlling their operation so that they can work concurrently or the inner plunger works alone. The adverse loads are minimised by appropriate fluid pressure exerted at opposite ends of the working plungers.

Description

United States Patent 11 1 Harris June 4, 1974 [54] FLUID PRESSURE MACHINES 2,967,490 [/1961 Von Soden 417/487 3,030,932 4 1962 M 11 91 498 [75] Inventor: Bruce Hams Bremwmd, 3,199,469 8l1965 Bu sh et al. 91l494 England 3,777,624 12/1973 Dixon 91/488 [73] Assignee: Hydrostatic Transmission Limited,

[22] Filed: June 18, 1973 [2]] Appl. No.: 370,846

[57] ABSTRACT [30 Foreign Application p i i Data In a radial, multi cylinder fluid pressure machine, ad-

June 20 1972 Great Britain 28765/72 verse mechanical and/or fluid loads occurring during running are minimised by fluid pressure. The capacity [52 us. c1. 91/488 of the machine is Selectable by Pmvisio" of a Plungfir [51] Im- CL F) 13/06 sleeve and an inner plunger in each cylinder bore, and [58] Field of 'i; /486 488 by valve means selectively controlling their operation '4l7/2l4 so that they can work concurrently or the inner 3 plunger works alone. The adverse loads are minimised 56] References Cited by appropriate fluid pressure exerted at opposite ends UNITED STATES PATENTS of the wmkmg plungers' 2,650.543 9/1953 Pauget 417/214 8 Claims, 8 Drawing Figures 7 '82 Z2) /7 14 M II I9 22 1 /8 2 77 75 4139 Q 5 24 52 55 55 5 37 55 LE 4240 /0 6 I W W 78 England Primary Examiner-William L. Freeh Attorney, Agent, or FirmShapiro & Shapiro FLUID PRESSURE MACHINES This invention relates to fluid pressure machines by which I mean hydraulic or gas motors or pumps, the motors and pumps having stationary housings and rotary shafts or rotary housings and stationary shafts.

More particularly the present invention relates to a fluid pressure machine comprising a shaft, a block havin g a main bore by which it is supported on a cylindrical surface for rotation relative thereto about an axis eccentric to the shaft axis, a housing or ring coaxial with the shaft and surrounding the block, the shaft being formed or adapted to maintain a fixed angular relationship between itself and the cylindrical surface or the housing or ring, the block being formed with bores radially directed from its rotation axis and equispaced in a common plane normal to the rotation axis of the block and extending from main bore to the block periphery to provide cylinders containing plungers for driving the machine, thrust pads formed or secured to and the plunger sleeves when working concurrently, can be minimised by opposing fluid pressure.

Mechanical loads on the thrust pads may thus be opposedwhen the inner plungers are working alone and when they are working concurrently with the plunger sleeves. So also may fluid pressure, which is exerted on the cylindrical surface by the reaction of the inner plungers when working alone, and of the inner plungers and the plunger sleeves when working concurrently, be

opposed by corresponding fluid pressure supplied to the cylindrical surface.

the housing or ring interior equispaced in a manner thrust directly or indirectly from the plungers and a fluid pressure supply passage and exhaust passageopening on opposite parts of the cylindrical surface which supports the block, whereby communication between each cylinder can be established cyclically with the supply and exhaust passages in sequence during relative rotation between the block and cylindrical surface supporting it, outward thrust on the plunger due to admission of fluid pressure thereto in sequence causing driving thrust on the cylindrical surface supporting the block, and eccentric motion of the rotation axis of the block relative to the shaft axis. Such a machine is hereinafter referred to as a fluid pressure machine as hereinbefore specified.

It is customary to supply working fluid at pressures of several tons per square inch to such'a motor. Adverse mechanical and/or fluidloads which such fluid can engender can be taken care of in thedesign stage of the motor by making load-bearing parts, such as shaft bearings, correspondingly massive.

An object of I the invention is to provide a dualvolume cylinder capacity machine in which the adverse loading mentioned above can be kept below an objectionable level at whichever capacity the machine is running. It will be appreciated that it would be possible to The present invention deals with the adverse loading in a different manner and resides in a fluid pressure machine as hereinbefore specified, in which the effective cylinder capacity is selectable, each cylinder bore containing a plunger in the form of a sleeve surrounding an inner plunger slidable relatively to the plunger sleeve, and a seal interposed capable of mutually isolating their effective areas, and in which valve means and openings are provided by which working fluid is admissible to each cylinder bore and which are so arranged that the working fluid can be admitted to one or to both of the areas in each cylinder bore, and that adverse mechanical and/or fluid loads attributable to the inner plungers when they are working alone, and attributable to them The following is a description, by way of example, of certain embodiment of the present invention, reference being made to the accompanying drawings, in which:

FIGS. 1 and 2 are axial sections at of one form of dual capacity, 5-cylinder, hydraulic motor, the inner plungers, however, being in different phases;

FIGS. 3 is an end view partly in section of FIG. 1 on line Ill-III of the latter Figure but showing the outer plungers in phase with the inner plungers;

FIG. 4 is a diagram of the hydraulic circuit for operating the motor;

FIGS. 5 and 6 are fragments of sections of modified constructions viewed as in FIG. 1;

FIGS. 7 and 8 show views of simplied axial section and end view, partly in section, of an alternative form of the motor.

Referring particularly to FIGS. 1 and 2, the motor 10 comprises a shaft 11 with an eccentric 12 formed between its ends, the shaft being supported on taper roller bearings 13 adjacent opposite faces of the eccentric 12 in a casing 14, which is also shown in FIG. 3. A block 15 formed with a central or main bore 16 is supported on the eccentric for rotation, a part of the housing or casing 14 in the form of a ring 17 being coaxial with the shaft 11 and surrounding the block 15. The arrangement described preferably includes an Oldham coupling 77 to maintain the angular relationship between the block 15 and the pads 20.

The block is formed with five bores 18 (only three of which are shown in FIG. 3) radially directed from the rotation axis of the block and extending from the main bore 16 to the block periphery 19 to provide the motor cylinders. These bores 18 or cylinders are equispaced in a common plane normal to the rotation axis of the block.

Secured to the interior of the ring 17 and equispaced in a manner corresponding to the bores 18 are thrust pads20, which, as can be seen in FIG. 3, each have a face normal to a radius of the ring 17.

Each of the bores 18 contains a plunger 21 in the form of a sleeve which surrounds and supports an inner plunger sleeve 21. Each

plunger

21, 22 is formed at its inner end with a groove 23 containing a piston ring 24 whereas its outer end is reduced externally at 25 to reduce the bearing length of the plunger and allow it to align itself with the pad and compensate for manufacturing errors. The plunger sleeve 21 is plain at its outer end face 81 for bearing directly and sealing on a film of the motive fluid on the associated thrust pad 20 or indirectly by a slipper pad, not shown. The inner plunger 22 on the other hand is slightly recessed centrally at 26 to provide a sealing land 82 for bearing directly or by the slipper on the flim of fluid on the pad 20.

The motor has two possible capacities. As later described, both plungers 21, 22 in each bore 18 are employed when the motor is running at full capacity (FIG. 3) but only the inner plungers are employed for partial capacity running (FIGS. 1 and 2).

The inner plunger 22, as shown, has a shaped interior but provided it includes a through passage the interior could otherwise be solid. As shown,'the through passage includes a conical surface 27. The effective area of the inner plunger 22 therefore consists in the surface 27 and an annular face 28 at its inner end.

The effective area of the plunger sleeve 21 consists in an annular face 29 at its inner end.

Thus for the full capacity running, the effective area is contributed by the

faces

27, 28, 29; for the partial capacity running, the

faces

27, 28 only.

The plunger sleeve 21 has an internal lip 30 on which pressure liquid in the working space 31 below the inner plunger 22 can react as later described to retain the sleeve 21 in an inoperative position for the partial capacity running.

The inner end of each bore 18 contains an annular seal the precise form of which is not important. As shown, the seal is a formation conveniently in the form of a disc 32 inset in the block 15. The upper face of the disc 32 is formed with a central boss 33 providing in this case an external frusto-conical seating 34 against which the plunger sleeve 21 can seal by contact with a peripheral edge 35 of the lip 30 when the plunger sleeve 21 is inoperative.

The disc 32 is formed with a central opening 36 and openings 37 in its margin. The central opening 36 can admit pressure liquid directly to the working space 31. The openings 37 in the disc margin can vent or admit liquid to a space 38 below the face 28 of the plunger sleeve 21.

Pressure liquid for driving the

plungers

21, 22 can be circulated from a supply through the motor by screwthreaded ports 39, 40 (FIGS. 1 and 2) located towards one end of the casing 14, the direction of circulation determining the sense of rotation of the shaft 11, supposing the casing 14 is held stationary. These ports are in constant communication with respective

annular grooves

41, 42 inside the casing 14. The

grooves

41, 42 communicate with

respective passages

43, 44 extending longitudinally through part of the shaft 11 and eccentric 12. At one end the passages terminate in short

radial portions

45, 46 which are oppositely directed and open into

respective grooves

47, 48 in the surface of the eccentric 12, and thence by bores 49, S0 in the block to the central opening 36 of the respective discs 32. At the other end the

passages

43, 44 terminate at the left hand end of the shaft 11 in FIGS. 1 and 2 at a valve block 52 enclosed by an extension 52 of the casing 14 and rotating with the shaft 11.

The block 51 is formed with

waisted bores

53, 54 aligned with the

respective passages

43, 44. These

bores

53, 54 contain check valves, comprising waisted

spools

55, 56 respectively, operation of which controls venting and pressurising of the space 38 below each of the plunger sleeves 21 and thereby whether the motor is arranged for the full or partial capacity running. The

spools

55, 56 are normally spring-urged to the left in FIGS. 1 and 2 but are displaceable against the spring pressure by a plunger 57 which is slidable to the right in a recess 58 at the outer end of the block 51 by the admission of pressure fluid into the extension 52 through a screwthreaded port 59.

The

spools

55, 56 normally seal on

corresponding seatings

60, 61 under spring pressure and are held off the

seatings

62, 63. Inward movement of the plunger 57 reverses the condition, the

spools

55, 56 becoming held off the

seatings

60, 61 and sealed on the

seatings

62, 63.

The waisted part of the bore 53 communicates with a pair of grooves 64 extending in the eccentric 12 parallel with and on each side of the groove 47 at a position where, druing part of a 360 rotation of the shaft 11 relative to the casing 14, the grooves 64 communicate with the openings 37 in the margin of the disc 32 as in FIG. 1. The communication between the bore 53 and openings 37 is by bores 65 to 67, grooves 64, and bores 68 in the block 15, there being two bores 67, which are parallel branches of the bore 66.

Similarly during part of a 360 rotation of the shaft 11, the waisted part of the bore 54 communicates with a pair ofgrooves 69 in the eccentric 12 in planes parallel with and'on each side of a radial plane containing the groove 48 through bores 70 to 72. The grooves communicate with bores 73 in the block 15 and thence with the openings 37 in the disc 32.

The eccentric 12 is also formed with a pair of circumferential grooves 164 in planes parallel with the planes containing the

grooves

68, 69 but further removed than them from the

grooves

47, 48.

When the

spools

55, 56, are being held off the

seatings

62, 63 by spring pressure the waisted parts of the

bores

53, 54 communicate with ducting or a recess 74 in the inner end of the plunger 57. The ducting or recess 74 is permanently open to a bore 75 extending from the left hand end (FIG. 1) of the shaft 11 along the rotation axis, and intersecting a bore 76 which vents past the tapered rollers 13 into the casing enclosure and out through a port or sump hole 78 in the casing 14.

Assuming that the parts of the motor are in the relative positions shown inFIG. 1, the

spools

55, 56 engage the seating 60, 61 (FIG. 4), rendering the motor set for the partial capacity running. The groove 47 will be communicating simultaneously with the central opening 36 of each disc 32 within the three cylinders 18 above the equivalent of the horizontal diameter of the ring 17 shown in FIG. 3, that Figure however relating to full capacity running, whereas the groove 48 will be communicating in a corresponding manner with the two cylinders 18 below that diameter. Thus, liquid forced in the motor from the port 39 and arriving by the groove 41 and

passages

43, 45 at the groove 47 will enter respective working spaces 31 below the inner plungers 22 in the first three cylinders .mentioned through the bores 49 and openings 36 whereas liquid in the other-two cylinders will exhaust through the openings 36 and bore 50 into the groove 48 and out through thepassage 44 groove 42 and port 40.

The ensuing displacement cycle of the plungers 22 corresponds to that indicated in FIG. 3 and later described. Whilst the

spools

55, 56 engage the

seatings

60, 61, however, the plunger sleeves 21 remain inoperative, the hydraulic pressure in the spaces 31 acting on the inner radial surfaces of the lips 30, thereby holding the edges 35 of the lips in sealing contact with the seatings 34 and isolating the spaces 38 below the plunger sleeves 21 from the spaces 31.

Whilst the spaces 31 are isolated from the spaces 38, the spaces 38 are vented to the sump hole 78 through the

bores

37, 68, grooves. 64, bores 67 to 65, past the seating 62 in the valve bore 53, through the recess 74 and bores 75, 76 to the hole 78, and correspondingly through the bores 37, 73 channels 69 bores 72 to 70, past the seating 63 in the valve bore 54, through the recess 74 and to the hole 78.

To set the motor for full capacity running, hydraulic or other pressure is applied to the plunger 57 to displace it inwardly (to the right in FIGS. 1 and 4) to cause the

spools

55, 56 to seal against the

seatings

62, 63, respectively, and unseal from

seatings

60, 61. The spaces 38 are thereby subjected to hydraulic pressure in the

passages

43, 44; from passage 43 bore 53, past seating 66, through bores 65 to 67, groove 64 and bores 68, 37 to the spaces 38, and correspondingly from passage 44, bore 54, past seating 61, through bores 70 to 72, grooves 69, bores 73, 37 to spaces 38.

The plunger sleeves 21 will then be displaced in phase with their companion inner plungers 22, engagement being maintained between the inner radial face of the lip 30 and the inner end face of the inner plunger 22 in each case.

The longitudinal dimensions of the plunger sleeves 21 and inner plungers 22 are such that in each case, whilst the engagement of the lip 30 is maintained, the outer end of plunger sleeve 21 bears on the film ofliquid on the corresponding pad 20. a

The land 82 of the inner plunger 22 presents an area such that, when the motor is running at partial capacity, the land 82 is supported on the film of liquid on the pad 20, which is replenished by outward radial flow from the crown recess 36 under hydraulic pressure from the inner end of the plunger 22. Similarly the end face 81 on the plunger sleeve 21 presents an area such that, when the motor is running at full capacity, the liquid film on the pad 20 supports the face 81. Thus, whether the motor is running at partial or full capacity, the outward mechanical loading imposed by the outer ends of the inner plungers 22, and of the inner plungers and plunger sleeves 21, respectively, is balanced by the opposing hydraulic pressure of the liquid film on the pads 20.

FIG. 3 illustrates the displacement cycle of the

plungers

21, 22 laterally in relation to the thrust pads 20 during full capacity running. However, it will be appreciated that the inner plungers 22 will move in a corresponding cycle during partial capacity running. For convenience, only the inner plungers 22 have been marked A to E and will be referred to in the description of the cycle. Plunger A is at the beginning of its outward power stroke, plunger C almost at the end of its power stroke and plunger B is in an intermediate position. Plungers D and E are returning on their exhaust strokes. Correspondingly, the axes of the plungers A and C are displaced somewhat in the clockwise direction (FIG. 3) with respect to the centres of the corre-- sponding thrust pads 20 whereas the axis of the plunger B is at maximum displacement in this direction. The axes of the plungers D and E on the other hand are displaced in an anti-clockwise direction with respect to their thrust pad centres. 1

It will be observed that the lines of action through the plungers A to E all pass through the centre of the eccentric. This arrangement minimises torque on these plungers.

The motive liquid in driving the plungers A, B, C outwardly, reacts on the eccentric 12, thereby displacing its centre and the block 15 away from the corresponding thrust pads 20, the displacement due to the plunger C being the greatest of the three since it is almost at the end of its power stroke. The eccentric 12 thereby derives clockwise rotation (FIG. 3) about the shaft axis and imparts a corresponding eccentric motion to the rotation axis of the block 15.

The rotation of the eccentric 12 causes the motive liquid to be fed in sequence to all of the cylinders and exhausted in sequence in a repetitive cycle.

Fluid pressure is exerted on the eccentric by reaction of the innerplungers 22 when the motor is running at partial capacity. This pressure is opposed by corresponding pressure of motive fluid supplied to the surface of the eccentric 12 by the

grooves

47, 48. In this manner itis possible to balance hydraulically forces which would otherwise load the shaft and block 15. Similarly, when the motor is running at full capacity, fluid pressure'exerted on the eccentric 12 by reaction of the inner plungers 22 and the plungers sleeves 2] is opposed and hydraulically balanced by corresponding motive fluid pressure supplied to the surface of the eccentric 12 by the

grooves

47, 48, 64 and 69. In each mode of running, there is a degradation of fluid pressure from the

grooves

47, 48 outwards along the eccentric in both directions. In partial capacity running the degradation extends to the

grooves

64, 69; in full

capacity running grooves

47, 48, 64 and 90 are being supplied by motive fluid, and the degradation of the fluid pressure extends to the circumferential grooves 164.

It will be appreciated that if the casing 14 (inclusive of the ring 17) is held stationary, the shaft 11 provides the output, but if the shaft is held stationary the casing provides the output.

When the motor is put to use as a pump, input is by way of the shaft or the casing, and the casing or shaft is held stationary as appropriate.

. The modifications shown inFIGS. 5 and'6, respectively, involving plungers and the eccentric, and shown in FIGS. 7 and 8 involving a motor or pump arangement, also concern dual-volume cylinder capacity machines. Both such machines work in a manner analogous to the motor already described and involve oppos- I views inFIGS. 5 and 6 and the section in FIG. 2.

As to modifications, it will be noted that the plunger sleeve 21 in FIG. 5 is formed with a passage or bore 83 for pressure communication between the inner end 28 and the bottom of a recess 84 at a lipped outer end, which accommodates a lipped outer end of the inner plunger 22. Such communication ensures a faster, more positive response of the sleeve 21 between its operative position and its inoperative position when change is made either way between partial and full capacity running.

The seal formation 132 at the inner end of the sleeve 21 includes a cylindrical boss 85 incorporating a sealing member 86, for contact with the inner cylindrical surface of the lip 30 when the sleeve is inoperative.

Furthermore, the grooves 64 are subdivided into two short pairs, the members of which are fed or vented by suitably branched bores 67. The counterparts of the grooves 69 and bores 72 (not shown in FIG. 5) are modified in a manner analogous to the grooves 64 and bores 67 in FIG. 5. Such subdivision of the

grooves

64 and 69 is to provide a structural difference which influences the fluid pressure available at the surface of the eccentric 12 for opposing adverse reaction pressure exerted by the plunger sleeve 21 whenoperative.

In FIG. 6 a thinner annular disc 231 set in a corresponding recess in the block replaces the disc 32 of the earlier Figures. The disc 231 surrounds and holds the inner end of a tube 232 which is open at both ends. The passage by which fluid pressure is communicated between opposite ends of the inner plunger 22 is of larger radial dimensions at its inner end than at its outer end.

The inner end of the plunger 22 throughout the plunger stroke surrounds the tube 232 which serves to deliver working fluid to the inside of the inner plunger 22. The tube 232 and plunger 22 are mutually spaced to form between them a passage which maintains communication between the mouth of the tube 232 and an inner radial face of the lip 30 of the plunger sleeve 21.

The purpose of the tube 232 is to ensure that, when the passages 68 are vented, the fluid pressure supplied by the passage 36 acts on the inner radial face of the lip 30 and the plunger sleeve 21 to seal, by means of the lip 30, against the disc 231.

FIG. 6 also shows sealing rings 233 arranged in circumferential grooves 234 formed in the eccentric 12 on each side of the grooves 47 and between the grooves 64 and the end faces of the eccentric.

The five cylinder dual-capacity hydraulic motor shown diagrammatically in FIGS. 7 and 8 corresponds in some degree with the motor described withreference to FIGS. 1 to 4, and corresponding reference numerals are used on corresponding parts. Thus, the counterpart of the shaft 11 is supported on bearings 13 at one end ofa casing 90 which is coaxial with the shaft 11 and encloses the motor. The counterpart of the eccentric 12 is provided by a stub shaft 91 secured to the other end of the casing 90, the longitudinal axis of the stub shaft 91 being eccentric to the axis of shaft 11.

The shaft 11 is adapted by means of a housing 92 to provide the counterpart of the ring 17. The ring 17 surrounds a cylinder block 15 which is mounted for rotation by means ofa central bore 16 on the stub shaft 91.

The lines of action of plunger sleeves 21 and inner plungers 22 supported by the block 15 pass through the longitudinal axis of the stub shaft.

The motor includes an hydraulic circuit corresponding to FIG. 4 but for simplicity only the

passages

43, 44, groove 47 and discs 32 have been shown in FIGS. 7 and 8.

When pressure liquid is circulated through supply and

exhaust passages

43, 44 in the stub shaft 91, the action of the

plungers

22 or 21 and 22, depending on whether the hydraulic circuit is set for partial or full capacity running of the motor, corresponds to that of the plungers in the motor in FIGS. 1 and 2 or FIG. 3. The pressure driving the plungers 22 (or 21, 22) outwardly in FIG. 8 reacts on the stub shaft 91, displacing its centre and the block 15 away from the thrust. The rotation axis of the block 15 is moved eccentrically relative to the axis of the shaft 11 whereas the casing 90 is rotated on that axis.

The

spools

55, 56 could be operated pneumatically, mechanically or electrically instead or hydraulically. They could also be cylindrical spool valves or any other type of hydraulic control valve. They could also be arranged to operate automatically depending upon the operating pressure of the motor (or pump), such that if the pressure increases to a pre-set level during partial capacity running, the running would automatically change to full capacity. Similarly, when the operating pressure falls to a pre-set minimum during full capacity running, it would automatically change to partial capacity running.

I claim:

1. A fluid pressure machine comprising a structure carrying a housing, and a shaft providing a surface eccentric with respect to the housing and surrounded thereby, bearings arranged on the structure to permit relative rotation between the housing and the shaft, a block'having a main bore by which the block is borne by the eccentric surface for relative rotation thereto,

1 the block being surrounded by the housing and having.

a circular array of radially-directed cylinder bores provided therein, a plunger in the form of a sleeve in each cylinder bore and an inner plunger surrounded and slidably supported by the plunger sleeve,-the plunger sleeve and inner plunger by their arrangement in the radially-directed cylinder bore in the block being intermediate the housing and the eccentric surface for transmitting relative motion therebetween, the plunger sleeve and inner plunger each having a respective effective area for drivingly interacting with motive fluid, a seal interposed between the plunger sleeve and the inner plunger capable of mutually isolating their respective effective areas in the cylinder bore, each cylinder bore and the block being formed with openings for passage of the motive fluid to and from the respective areas, the shaft having inlet and outlet passages communicating with corresponding openings in the eccentric surface, and cyclically communicable with the respective openings in the block and each cylinder bore in each relative rotation between the eccentric surface and the block, a supply of motive fluid connected to the shaft inlet passage, and valve means arranged to select the effective cylinder capacity of the machine by controlling passage of the motive fluid to and from the openings in each cylinder and thereby operation of the seal, transfer of the motive fluid to one and to both of the effective areas in each cylinder corresponding respectively to partial capacity and full capacity running of the machine, there being fluid pressure existing between the eccentric surface and the block, and between the housing and the inner plungers and plunger sleeves during the partial and full capacity running respectively, acting in opposition to and minimising mechanical and fluid loads attributable, respectively, to the inner plungers when working alone, and when working concurrently with the plunger sleeves.

2. A fluid pressure machine according to claim 1, in which each inner plunger and plunger sleeve has an inner end adjacent the eccentric surface and an outer end adjacent the housing, and a formation is provided having a central opening arranged in each cylinder bore between the inner end of the plunger sleeve and the opening in the block, the opening in the formation communicating with the opening in the block and with the inner end of the inner plunger, and the formation having a periphery against which the inner end of the plunger sleeve can seal and thereby mutually isolate the respective effective areas of the plunger sleeve and inner plunger; and in which the plunger sleeve has at its inner end an internal lip with an internal radial face on which pressure fluid can act and urge the plunger sleeve into sealing contact with the periphery of the formation when the valve means is operating to admit the fluid to the inner plunger to the exclusion of the plunger sleeve, and furthermore is formed with a passage of larger radial dimension at the inner end of the inner plunger than itsouter end, a tube having an inner end carried in the opening in the block to each cylinder bore and having an outer end extending into the larger radial dimensioned portion of the passage in the inner plunger throughout the stroke of the inner plunger but being radially spaced therefrom, thereby maintaining communication between the outer end of the tube and the inner radial face of the plunger sleeve lip.

3. A fluid pressure machine according to claim 1, in which each inner plunger and plunger sleeve has an inner end adjacent the eccentric and an outer end adjacent the housing, and a formation is provided having a central opening arranged in each cylinder bore between the inner end of the plunger sleeve and the opening in the block, the opening in the formation communicating with the opening in the block and with the inner end of the inner plunger, and the formation having a periphery against which the inner end of the plunger sleeve can seal and thereby mutually isolate the respective effective areas of the plunger sleeve and inner plunger.

4. A fluid pressure machine according to claim 3, in which the plunger sleeve has at its inner end an internal lip with an internal radial face on which pressure fluid can act and urge the plunger sleeve into sealing contact with the periphery of the formation when the valve means is operating to admit the fluid to the inner plunger to the exclusion of the plunger sleeve.

5. A fluid pressure machine according to claim 1, in which each inner plunger is of a form permitting communication of fluid pressure between opposite ends of the inner plunger.

6. A fluid pressure machine according to claim 5, in which each inner plunger has an inner end adjacent the eccentric surface and an outer end adjacent the housing, and the outer end has a central recess surrounded by a peripheral land.

7. A fluid pressure machine according to claim 5, in which each plunger sleeve has at its inner end an internallip with an internal radial face, each inner plunger is formed with a passage of larger radial dimension at the inner end of the plunger than at its outer end, and a tube is provided having an inner end carried in the opening in the block to each cylinder bore and having an outer end extending into the larger radial dimensioned portion of the passage in the inner plunger and surrounded thereby throughout the stroke of the inner plunger but being radially spaced therefrom, thereby maintaining communication between the outer end of the tube and the plunger sleeve lip.

8. A fluid pressure machine according to claim 5, in which the outer end of the inner plunger has a peripheral lip, the outer end of the plunger sleeve is formed with a recess having a bottom corresponding to the lip on the inner plunger for receiving the same, and with a passage permitting communication of fluid pressure between opposite ends of the plunger sleeve, such communication with the outer end of the plunger sleeve being made with the bottom of the recess.

. l l= =l

Claims

1. A fluid pressure machine comprising a structure carrying a housing, and a shaft providing a surface eccentric with respect to the housing and surrounded thereby, bearings arranged on the structure to permit relative rotation between the housing and the shaft, a block having a main bore by which the block is borne by the eccentric surface for relative rotation thereto, the block being surrounded by the housing and having a circular array of radially-directed cylinder bores provided therein, a plunger in the form of a sleeve in each cylinder bore and an inner plunger surrounded and slidably supported by the plunger sleeve, the plunger sleeve and inner plunger by their arrangement in the radially-directed cylinder bore in the block being intermediate the housing and the eccentric surface for transmitting relative motion therebetween, the plunger sleeve and inner plunger each having a respective effective area for drivingly interacting with motive fluid, a seal interposed between the plunger sleeve and the inner plunger capable of mutually isolating their respective effective areas in the cylinder bore, each cylinder bore and the block being formed with openings for passage of the motive fluid to and from the respective areas, the shaft having inlet and outlet passages communicating with corresponding openings in the eccentric surface, and cyclically communicable with the respective openings in the block and each cylinder bore in each relative rotation between the eccentric surface and the block, a supply of motive fluid connected to the shaft inlet passage, and valve means arranged to select the effective cylinder capacity of the machine by controlling passage of the motive fluid to and from the openings in each cylinder and thereby operation of the seal, transfer of the motive fluid to one and to both of the effective areas in each cylinder corresponding respectively to partial capacity and full capacity running of the machine, there being fluid pressure existing between the eccentric surface and the block, and between the housing and the inner plungers and plunger sleeves during the partial and full capacity running respectively, acting in opposition to and minimising mechanical and fluid loads attributable, respectively, to the inner plungers when working alone, and when working concurrently with the plunger sleeves.

2. A fluid pressure machine according to claim 1, in which each inner plunger and plunger sleeve has an inner end adjacenT the eccentric surface and an outer end adjacent the housing, and a formation is provided having a central opening arranged in each cylinder bore between the inner end of the plunger sleeve and the opening in the block, the opening in the formation communicating with the opening in the block and with the inner end of the inner plunger, and the formation having a periphery against which the inner end of the plunger sleeve can seal and thereby mutually isolate the respective effective areas of the plunger sleeve and inner plunger; and in which the plunger sleeve has at its inner end an internal lip with an internal radial face on which pressure fluid can act and urge the plunger sleeve into sealing contact with the periphery of the formation when the valve means is operating to admit the fluid to the inner plunger to the exclusion of the plunger sleeve, and furthermore is formed with a passage of larger radial dimension at the inner end of the inner plunger than its outer end, a tube having an inner end carried in the opening in the block to each cylinder bore and having an outer end extending into the larger radial dimensioned portion of the passage in the inner plunger throughout the stroke of the inner plunger but being radially spaced therefrom, thereby maintaining communication between the outer end of the tube and the inner radial face of the plunger sleeve lip.

7. A fluid pressure machine according to claim 5, in which each plunger sleeve has at its inner end an internal lip with an internal radial face, each inner plunger is formed with a passage of larger radial dimension at the inner end of the plunger than at its outer end, and a tube is provided having an inner end carried in the opening in the block to each cylinder bore and having an outer end extending into the larger radial dimensioned portion of the passage in the inner plunger and surrounded thereby throughout the stroke of the inner plunger but being radially spaced therefrom, thereby maintaining communication between the outer end of the tube and the plunger sleeve lip.