US3613511A

US3613511A - Fluid-powered, positive-displacement engine

Info

Publication number: US3613511A
Application number: US818206A
Authority: US
Inventors: George D Eddington
Original assignee: Individual
Current assignee: Individual
Priority date: 1969-04-21
Filing date: 1969-04-21
Publication date: 1971-10-19
Anticipated expiration: 1988-10-19

Abstract

A fluid-powered, positive-displacement engine of the type wherein pistons, in annular series arrangement within respective cylinders, act successively on the circumferential margin of a positionally fixed shuttle plate to rotate a power-output shaft to which the plate is rigidly secured, concentrically therewith. There is disclosed a compact and efficient fluid-flow system for both the supply and exhaust of a pressure fluid, such as steam, that provides the power to operate the engine, and a rotary valve operated by the power-output shaft for timing supply and exhaust of pressure fluid progressively around the annular series of cylinders and for effecting reverse operation of the engine. Each piston is formed to straddle the shuttle plate and to, thus, be double acting at respectively opposite sides of such plate. Adjustable low-friction couplings connect the pistons with the shuttle plate.

Description

United States Patent [72] Inventor George D. Eddington 266 East 100 South, Logan, Utah 84321 [21] Appl. No. 818,206 [22] Filed Apr. 21, 1969 [45] Patented Oct. 19, 1971 [54] FLUID-POWERED,POSITIVE-DISPLACEMENT ENGINE 11 Claims, 12 Drawing Figs.

[52] US. Cl 91/502, 91/503, 92/138 [51] Int.Cl .L F01b3/02, F01b 13/04 [50] Field of Search 91/175, 501,502, 503; 92/138, 88, 57; 103/173; 308/234 [56] References Cited UNITED STATES PATENTS 1,781,068 11/1930 Michell 91/175 2,434,747 l/1948 Ruben 91/175 2,997,956 8/1961 Stewart 103/173 3,006,324 10/1961 Shaw 91/175 673,220 4/1901 Perkins 308/234 1,127,267 2/1915 McElwain 2/138 2,409,868 10/1946 Kahl 92/138 Primary Examiner-Paul E. Maslousky Attorney-Mallinckrodt & Mallinckrodt ABSTRACT: A fluid-powered, positive-displacement engine of the type wherein pistons, in annular series arrangement within respective cylinders, act successively on the circumferential margin of a positionally fixed shuttle plate to rotate a power-output shaft to which the plate is rigidly secured, concentrically therewith. There is disclosed a compact and efficient fluidflow system for both the supply and exhaust of a pressure fluid, such as steam, that provides the power to operate the engine, and a rotary valve operated by the poweroutput shaft for timing supply and exhaust of pressure fluid progressively around the annular series of cylinders and for effecting reverse operation of the engine. Each piston is formed to straddle the shuttle plate and t0, thus, be double acting at respectively opposite sides of such plate. Adjustable low-friction couplings connect the pistons with the shuttle plate.

PAIENIEnucr 19 I97! SHEET 2 OF 3 INVENTOR. GEORGE D. EDDINGTON II/ I AT TORNE YS PATENTEDUBT 19 I97! 3,613,511 SHEET 30F 3 PTMX INVENTOR. GEORGE D. EDDINGTON ATTORNEYS FLUID-POWERED, POSITIVE-DISPLACEMENT ENGINE BACKGROUND OF THE INVENTION 1. Field The invention is in the field of positive displacement engines adapted to be driven by a fluid under pressure, such as steam, and particularly those of the type equipped with pistons arranged in annular series about the circumferential margin of a wobble or other form of positionally fixed shuttle plate for rotating a drive shaft upon which the plate is mounted.

2. State of the Art Many different forms of the type of engine concerned have been proposed. Although prototypes of some of these have been built and operated successfully, so far as applicant is aware none have achieved any significant degree of commercial success. Examples of this type of engine are found in U.S.'

Pat. Nos. 3,383,930; 3,370,511; 3,274,897; 3,246,577; 3,120,816; 3,082,697; 3,080,854; 3,071,014; Re23,803; 2,157,692; and 1,837,724.

3. Objectives Although the general concept of the engine was old at the time the invention was made, it was a primary purpose of the invention to achieve at least as great efficiency of operation as previously, but by a simpler and more compact construction that virtually eliminates external piping and the heat losses incidental thereto; that provides double power strokes and balanced operation in the powered reciprocation of each piston; that utilizes adjustable, low-friction couplings between the respective pistons and the shuttle plate, without springs and unaccompanied by backlash; that includes an exhaust system enabling the pressure fluid to be collected and reused; that incorporates a control valve as a part of a pressure fluid distribution system of the engine; that provides positive, accurate, and trouble-free timing for all aspects of engine operation; that achives such a timing of piston power strokes as neutralizes end-thrusts on the power output shaft of the engine; and that provides for reverse drive in a manner eliminating gears or other mechanical linkage andpermitting shifting by remote control from forward to reverse and vice versa with the engine stopped, idling or at an operating speed.

SUMMARY OF THE INVENTION The inventive construction comprises elongate, rectilinear pistons, each recessed centrally of its length to receive the peripheral margin of the shuttle plate intermediate its opposite ends, so that, in operating within opposed, rectilinearly aligned cylinders, each piston becomes double acting and receives power on each reciprocative stroke. The intermediate, confronting faces of each piston are advantageously coupled to respective opposite faces of the shuttle plate by adjustable antifriction means, which, in one form, may comprise combined radial and thrust type of antifriction bearings for respective opposite faces of a shuttle plate formed as a cam plate, and, in another form, may comprise respective ball and socket couplings and annular bearing race plates for respective opposite faces of a shuttle plate formed as a wobble plate.

The sockets of the balland socket couplings of the latter form of antifriction means advantageously comprise recessed pads that rest and slide freely on the respective bearing race plates, and recesses in corresponding ones of the confronting intermediate faces of the respective piston end portions. Each end portion of a piston is advantageously provided with a passage axially thereof, which is open at both ends-as by making such piston end portion tubular-to receive a rod formed with a ball, or with a ball-receiving socket recess, at the intermediate face that is coupled to the wobble plate. It is advantageously threaded at the other end for screwing into corresponding threading provided internally of the outer end of such piston end portion. This enables the seating pressure of the ball within its receiving socket to be adjusted as desired.

The control valve is positioned at one end of the power output shaft to which the shuttle plate is fixedly secured, and includes a rotary valve member coupled to the power output shaft for rotation therewith and for movement axially of such shaft to shift operation of the engine into reverse and back into forward drive when desired.

The pressure fluid distribution system and the exhaust system are formed internally of and closely about the cylinder block, which results in a very compact structure, virtually without outside piping.

THE DRAWINGS Specific constructions presently contemplated as the best mode of carrying out the invention in actual practice are illustrated in the accompanying drawings, in which:

FIG. 1 represents one fonn of the engine in longitudinal vertical secton taken on the line 1-1 of FIGS. 3, 4, and 8, with the control valve in forward-drive position;

FIG. 2, a fragmentary view corresponding to the control valve portion of FIG. 1, but taken on the line 2-2 of FIG. 9 and showing the valve in reverse-drive position;

FIG. 3, a transverse vertical section taken on the line 3-3 of FIG. 1;

FIG. 4, a similar section taken in the line 4-4 of FIG. 1;

FIG. 5, a similar section taken on the line 5-5 of FIG. 1;

FIG. 6, a fragmentary vertical section taken with respect to the line 6-6 of FIG. 4, but not limited axially of the engine;

FIG. 7, a diagrammatic representation of the several cylinders and pistons in operative conjunction with a transverse vertical section taken on the line 7-7 of FIG. 1 to reveal pressure fluid supply ports and passages of the valve in its forwarddrive position and to indicate the firing" order of the several cylinders;

FIG. 8, a view similar to the sectional portion of FIG. 7, but showing a corresponding transverse vertical section taken on line 8-8 of FIG. 1 with respect to the reversing portion of the valve in the forward-drive position of such valve;

FIG. 9, a view similar to FIG. 8, but taken on the line 9-9, FIG. 2, to show the positions of the several parts and flow passages of the valve in the reversing position thereof;

FIG. 10, a corresponding view taken on the line 10-10 of FIG. 2;

FIG. 11, an end elevation taken from the right in FIG. I; and

FIG. 12, a view corresponding to an intermediate portion of FIG. 1, but showing a simplified form of shuttle plate and antifriction couplings for the several pistons.

DETAILED DESCRIPTION OF ILLUSTRATED EMBODIMENTS In the form illustrated in FIGS. 1-10, the engine of the invention comprises a cylinder block 15 of cylindrical formation provided with an annular series of individual cylinders [6 surrounding an axially extending bore 17 that receives and rotatably mounts a power shaft 18 to be driven by the engine. Mounted on the shaft 18, as by being formed integrally therewith, is a positionally fixed shuttle in the form of a wobble plate 19. The cylinder block 15 is annularly recessed internally thereof and intennediate its ends, transversely of the several cylinders 16, as at 20, to accommodate the circumferential margin of the wobble plate 19; antifriction bearings 21 serve to journal the shaft 18 for rotation relative to the cylinder block.

Slidably mounted for reciprocation in the cylinders 16 are respective, elongate pistons 22, each recessed intermediate its length, as at 23, for receiving and straddling the circumferential margin of the wobble plate 19. As shown, such pistons'are tubular, for adjustably receiving rods 24. They are shown provided with respective piston rings 25, but may, if desired, be provided with elongate sleeve bushings (not 1 shown) externally of their opposite end portions.

posite faces of wobble plate 19 by antifriction bearings 27 and 28 of ring formation. As so mounted, the wobble plate is free to rotate relatively to the pistons and the couplings with a minimum amount of frictional resistance.

In the form illustrated, the ball and socket couplings each comprise ball means at the intermediate face of the corresponding piston end portion 22a and a free-sliding pad 29 on the corresponding race plate 26, the pad having a socket recess formed therein for receiving the ball means. Although the ball means may be formed in various ways, as by making the appropriate end of the rod 24 hemispherical, it is preferred to recess such end of rod 24 as a ball-receiving socket and to provide a freely rotatable ball 30 fitted between the mutually opposing socket recesses.

The rods 24 are preferably adjustably mounted in their respective piston end portions 22a by screw-threading 31 at the opposite ends of such rods and at the outer ends of the piston end portions. This permits the position of each rod 24 to be adjusted axially along the corresponding piston end portion to regulate the degree of tightness of the ball 30 within its socket recesses and to take up any wear that might occur. The same arrangement could be used, of course, in instances of the rod end being made hemispherical as the ball member of the ball and socket coupling.

Cylinder heads are provided at opposite ends of cylinder block by sets of

annular disks

32 and 33, at one end, and 34 and 35 at the other. These serve to close, and, by means of respective sets of interposed

gaskets

36, 37, 38, and 39 to seal the cylinders 16 against fluid leakage. They also serve to supply pressure fluid to the several cylinders by way of passages formed in such cylinder heads and constituting part of the pressure fluid distribution system.

The pressure fluid distribution system includes a rotary valve, indicated generally at 40, that comprises a stationary valve body 41 of annular formation and an axially shiftable, rotary valve member 42 operable within the valve body. Pressure fluid, such as steam supplied form any suitable source under the control for a quantity control valve (not shown) to govern engine speed, is introduced by piping (not shown) to a forward-drive inlet passage 43, FIG. 1, that is formed through a nipple fitting 44 in stationary valve body 41.

For forward drive, such pressure fluid flows through axial passage 45, FIGS. 1 and 7, radial passage 46, and arcuate distribution port 460 (all in rotary valve member 42) and, progressively, into radial portions 47a of individual passages 47 of a circular series of such passages in the stationary valve body 41 as such valve member rotates. The passages 47 have longitudinal portions 47b that connect, by way of respective passages 48, FIG. 5, in cylinder head disk 35, with

distribution passages

49, 50, 51, 52, 53, and 54, respectively, also in such disk 35. Each distribution passage provides for simultaneous supply of the pressure fluid to opposite ends, respectively, of a pair of diametrically opposite cylinders 16, whereby wobble plate 19 is driven by equal and opposite forces applied, respectively, at diametrically opposite points on its circumferential margin, progressively therearound. For this purpose, cylinder head disk 34 is provided with a series of passages 55, FIG. 1, leading into the corresponding ends of respective cylinders 16, cylinder head disk 32 at the opposite end of the cylinder block is provided with

distribution passages

56, 57, 58, 59, 60, and 61, FIG. 4, its companion cylinder head disk 33 is provided with a series of passages 62, FIG. 1, leading into the corresponding ends of respective cylinders 16, and a circumferential series of longitudinal distribution passages 63, FIG. 3, are provided from end to end of cylinder block 15.

Exhaust from opposite end portions of each of the cylinders 16 is accomplished primarily through respective ports 64, FIG. 1. Escape of fluid from each cylinder during the return stroke of the piston therein to avoid needless compression of such fluid and reduced efficiency of engine operation is accomplished primarily through the same passages that supply the pressure fluid. Thus, the pressure stroke of each piston 22 serves to exhaust residual fluid from the opposite end potion of the cylinder 16 concerned. For this purpose, valve body 41 is provided within exhaust passage 65, FIGS. 1 and 10, and rotary valve member 42 is provided with an arcuate distribution port 66, FIGS. 1 and 10, that establishes exhaust communication of the several distribution passages previously described with passage 65 by reason of the fact that valve member 42 is in the axially forward position of FIG. 1.

Cylinder head disks

32 and 33 and their interposed gaskets 36 and 37 are held tightly over the open cylinder ends at the one end of cylinder block 15 by a series of bolts 67, FIGS. 3, 4, and 6.

Cylinder head disks

34 and 35 with their interposed gaskets 38 and 39, together with valve 40 and an interposed gasket 68, are held tightly over the open cylinder ends at the other end of cylinder block 15 by a series of bolts 69, FIGS. 5 and 11. It is convenient to make cylinder block 15 in two cylindrical sections 15a and 1512, as shown in FIG. I, with an interposed gasket 70. Bolts 67 are long enough to pass entirely through the one section 1511 and to screw into the other section 15b, so as to hold the entire assembly securely together. Bolts 69 need only be long enough to screw into the adjacent cylinder block section 15b.

The assembly, as so secured, is advantageously enclosed by a cylindrical jacket 71, FIG. 1, that is recessed circumferentially internally to provide an elongate, annular exhaust manifold 72 into which the exhaust ports 64 open. Such manifold intersects exhaust passage 65, FIG. 10, in valve body 41, see FIG. 10, and both manifold and passage discharge to atmosphere through a port 74 in jacket 71. For sealing against escape of exhaust otherwise than through port 74, O-ring gaskets 75, FIG. I, are interposed between jacket 71 and the cylindrical assembly, an end plate 76 being provided at the power-output end 18a of shaft 18 and secured in place by screws 77, and a retainer ring 78 being secured in place at the opposite end of the assembly by screws 79.

Rotary valve member 42 is coupled to power shaft 18 to be driven thereby. For this purpose it is provided with a stem 42a that is polygonal in cross section and is received by a correspondingly elongate and polygonal recess in the adjacent end of shaft 18 for back and forth sliding movement axially of the shaft, thereby permitting the valve member to be shifted axially without uncoupling it from the shaft.

Reverse drive is achieved by axially shifting rotary valve member 42 from the forward-drive position of FIG. 1 to the reverse-drive position of FIG. 2. This is accomplished by introducing a reversing pressure fluid, preferably from the same source as the drive pressure fluid, under the control of a reversing valve (not shown) and through suitable piping connected to port 80, FIGS. 1 and 11. A passage 81, FIG. 1, conducts such pressure fluid to the forward face of rotary valve member 42 and shifts such valve member backwardly along the axis of the engine against the force of the incoming drive pressure fluid and of a compression spring 82.

In the shifted position of FIG. 2, see also FIG. 9, pressure fluid entering passage 45 of rotary valve member 42 through inlet port 43 of bushing 44 flows through radial passage 83 and arcuate distribution port 84 into the corresponding flow passages (47a, 47b, 48, etc.) of the distribution system. It should be noted that the arcuate port 84 extends circumferentially of rotary valve member 42 in a direction opposite to that in which arcuate distribution port 46a extends, thereby supplying the pressure fluid in a manner to rotate wobble plate 19 and power shaft 18 in reverse.

During this reverse operation of the engine, the residual fluid escapes from the several cylinders 16 by way of the distribution passages aforedescribed, arcuate distribution port 66, FIGS. 2 and 10, a port 85, and an annular bypass groove 86 that is in open communication with exhaust passage 65.

FOr fluid-sealing purposes O-rings 87, FIG. 2, are interposed between rotary valve member 42 and the stationary structure against which it both rotates and slides axially.

In order to adjust the axial position of rotary valve member 42 relative to its stationary valve body 4I, a screw 88 may be threaded in the end of valve stem 42a and adjusted in position from time to time as may be found desirable.

A body of lubricant, such as motoroil, is introduced into the engine through an externally available port, such as is provided by an ordinary oil fitting 89, FIG. 1, and serves to lubricate all working parts during operation. Fitting 89 extends through jacket 71 and the adjacent wall of cylinder block to a discharge termination at an oil passage 90 provided by a circumferential recess in the uppermost piston 22. The lubricant makes its way to valve 40 through a passage 91 in power shaft 18, through a registering passage in adjustment screw 88, and through a passage 92 along the stem and in the body of rotary valve member 42.

The firing" order, i.e. the power strokes of the several pistons 22, are indicated in FIG. 7, along with the exhaust strikes. The several cylinders and pistons are designated by the numbers 1-6 respectively. The designation Pr indicates pressure, while the designation Ex" indicates exhaust. The directions of the respective piston strokes and fluid flows are indicated by appended arrows. Similar cylinder and piston designations, numbers 1-6 as applied to FIGS. 4 and 5, indicate fluid flow through the distribution and exhaust system in correspondence with the showing of FIG. 7.

The embodiment of FIG. 12 is similar in all respects to that of FIGS. 1-11, except for the nature of the positionally fixed shuttle and the antifriction coupling means. In FlG. 12, such shuttle takes the form of a cam plate 93 presenting circular tracks 94, respectively, that are mutually parallel but eccentric within the planes of their respective circles. The antifriction coupling means between the respective pistons 95 and cam plate 93 are antifriction bearings 96 of a type known commercially as combined radial and thrust needle bearings and readily obtainable on the open market, as, for example, those manufactured by Garlock-Nadella, lnc., Cherry Hill, New Jersey, as Type RAX. The only alteration required is to replace the outer race ring thereof with a race ring 96a having an appropriately sloping face 97, as illustrated.

The bearings 96 are mounted on respective pins 98, headed at one end, as at 98a, to insure retention in countersunk bore holes 99 that are provided in each of the opposite end portions of the respective pistons 95.

In order to provide for the takeup of slack caused by wear, it is desirable that each piston 95 be divided at its midpoint to make each of the opposite end portions thereof a separate and independent unit, and that these units be adjustably joined together, as by means of a bolt 100 passing freely through one of the parts and threaded into the other part. Other means of adjustably interconnecting the component piston units could, of course, be employed.

Whereas presently preferred embodiments of the invention are illustrated and described in detail, it should be understood that the invention concepts permit of various changes in construction.

lclaim:

1. ln fluid-powered, positive-displacement engine of the type wherein pistons, within respective cylinders and in annular series arrangement, act successively on a circumferential margin of a positionally fixed shuttle plate to rotate a poweroutput shaft to which the shuttle plate is rigidly secured, axially thereof, a pressure fluid distribution system including a control valve, having a stationary valve body and having a rotary valve member coupled to the power-output shaft for rotation therewith and for movement axially thereof to shift operation of the engine between forward and reverse drives; and wherein means are provided for moving said rotary valve member back and forth axially to shift operation of the engine.

2. ln a fluid-powered, positive-displacement engine of the type wherein pistons, within respective cylinders and in annular series arrangement, act successively on a circumferential margin of a positionally fixed wobble plate to rotate a poweroutput shaft to which said wobble plate is rigidly-secured, axially thereof, the improvement according to claim 14 comprisingrace plates at respectively opposite faces of said wobble plate; ball and socket couplings between said pistons and said race plates, said couplings each comprising ball means at the piston face that confronts the correspondin race plate and a rec-sliding pad on said race plate, said pa having a socket recess formed therein and said ball means being received by said socket recess.

3. The improvement set forth in claim 2 wherein the ball portion of each coupling is a freely rotatable ball; wherein each piston end portion is tubular and is adjustably fitted with an axially movable rod in the hollow interior thereof, one end of which is recessed to provide a socket for said ball; and wherein means are provided for adjustably securing the other end of said rod to said piston end portion.

4. In a fluid-powered, positive-displacement engine of the type wherein pistons, within respective cylinders and in annular series arrangement, act successively on the circumferential margin of a positionally fixed shuttle plate to rotate a poweroutput shaft to which the shuttle plate is rigidly secured, axially thereof, the improvement according to claim 14 characterized by the shuttle plate being of cam formation and the provision of combined radial and thrust-type antifriction bearings carried by the respective pistons and being interposed between said cam formation and the confronting faces of said pistons, the said bearings each including a mounting pin mounted in the corresponding piston, a race ring, and antifriction means mounting the race ring concentrically on said pin so its outer circumferential face rides against said cam formation.

5. An improvement in accordance with claim 4, wherein each mounting pin is headed at one end and fitted freely through a receiving aperture in the piston so as to be retained by said headed end, the race ring and antifriction means being freely mounted on the opposite end of said pin so as to be retained in position by the shuttle plate.

6. An improvement in accordance with claim 5, wherein the pistons are each one part of a double-acting piston that straddles the shuttle plate, each of the double-acting pistons comprising two piston parts adjustably secured together in end-toend relationship.

7. The improvement set forth in claim 1, wherein the cylinders are formed in a cylindrical cylinder block and are closed by cylinder heads at respective opposite ends of the block, and the pressure fluid distribution system is formed in said cylinder block and cylinder heads.

8. The improvement set forth in claim 7, wherein the cylinder heads are provided by respective sets of end disks of substantially the same diameter as the cylinder block, and wherein fluid flow passages are formed between the disks of each set.

9. The improvement set forth in claim 7, wherein the valve body of the control valve is formed as an end disk of substantially the same diameter as the cylinder block and cylinder heads.

10. The improvement set forth in claim 9, wherein a cylindrical jacket closely encompasses the cylinder block, the cylinder heads, and the valve, and provides an elongate annular fluid-flow passage for conducting exhaust from the cylinders, said cylinders being provided with exhaust ports leading into said exhaust passage.

11. The improvement set forth in claim 1, wherein the means for moving the rotary valve member axially comprise fluid-flow passage means extending from a location of pressure fluid access to the end of said valve member that is opposite the pressure fluid input end of the control valve.

mg UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent 3,613,511 Dated October 19, 1971 Inventor (1:) George D. Eddington It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

r- Column 6, Line 2, change "14" to --1-.

Column 6, Line 22, change "14" to 1-.

Signed and sealed this 21st day of Mar-ch 1972.

(SEAL) Attest:

EDWARD M.FLETCHER,JR. ROBERT GOTI'SCHALK Attesting Officer- Commissionerof Patents

Claims

1. In fluid-powered, positive-displacement engine of the type wherein pistons, within respective cylinders and in annular series arrangement, act successively on a circumferential margin of a positionally fixed shuttle plate to rotate a power-output shaft to which the shuttle plate is rigidly secured, axially thereof, a pressure fluid distribution system including a control valve, having a stationary valve body and having a rotary valve member coupled to the power-output shaft for rotation therewith and for movement axially thereof to shift operation of the engine between forward and reverse drives; and wherein means are provided for moving said rotary valve member back and forth axially to shift operation of the engine.

2. In a fluid-powered, positive-displacement engine of the type wherein pistons, within respective cylinders and in annular series arrangement, act successively on a circumferential margin of a positionally fixed wobble plate to rotate a power-output shaft to which said wobble plate is rigidly secured, axially thereof, the improvement according to claim 14 comprising race plates at respectively opposite faces of said wobble plate; ball and socket couplings between said pistons and said race plates, said couplings each comprising ball means at the piston face that confronts the corresponding race plate and a free-sliding pad on said race plate, said pad having a socket recess formed therein and said ball means being received by said socket recess.

4. In a fluid-powered, positive-displacement engine of the type wherein pistons, within respective cylinders and in annular series arrangement, act successively on the circumferential margin of a positionally fixed shuttle plate to rotate a power-output shaft to which the shuttle plate is rigidly secured, axially thereof, the improvement according to claim 14 characterized by the shuttle plate being of cam formation and the provision of combined radial and thrust-type antifriction bearings carried by the respective pistons and being interposed between said cam formation and the confronting faces of said pistons, the said bearings each including a mounting pin mounted in the corresponding piston, a race ring, and antifriction means mounting the race ring concentrically on said pin so its outer circumferential face rides against said cam formation.

6. An improvement in accordance with claim 5, wherein the pistons are each one part of a double-acting piston that straddles the shuttle plate, each of the double-acting pistons comprising two piston parts adjustably secured together in end-to-end relationship.