US3865093A

US3865093A - Machine driven by rotary pistons

Info

Publication number: US3865093A
Application number: US302922A
Authority: US
Inventors: Rodriguez Miguel Ferragut
Original assignee: Individual
Current assignee: Individual
Priority date: 1971-11-04
Filing date: 1972-11-01
Publication date: 1975-02-11
Anticipated expiration: 1992-02-11
Also published as: FR2160014A5; JPS5819841B2; IT974816B; ES396667A1; JPS4853103A; GB1402593A; DD103030A5; DE2212020A1; SU466675A3

Abstract

A rotary piston machine has a stator, wherein an assembly functioning as a rotor turns. The rotor is joined to a shaft through which moving power is sent or received, depending on whether it is used as a generator or receiver of movement. The machine is characterized in that the rotor consists of at least a cylindrical block wherein a cylindrical chamber is radially housed, with the characteristic that a piston, whose crankshaft rests on bearings in the rotor and which support a pinion which engages with a ring gear fixed to the stator, reciprocates in the chamber.

Description

ilnited States Patent Ferragut Rodriguez MACHINE DRIVEN BY ROTARY PISTONS Miguel Ferragut Rodriguez, Paseo Santa Maria de la Cabeza, 85, Madrid, Spain Filed: Nov. 1, 1972 Appl. No.: 302,922

Inventor:

Foreign Application Priority Data Nov. 4, 1971 Spain 396667 US. Cl 123/44 D, 91/197, 92/117 A, 417/461 Int. Cl. F02b 57/02 Field of Search 123/44 R, 44 A, 44 D; 417/461; 91/196, 197; 92/117 R, 117 A References Cited UNITED STATES PATENTS 10/1912 Seibak 123/44 A 4/1919 Sheridan..... 123/44 R 3 1929 MCKlusky... 123 44 R 5/1933 Harper 123/44 R 1 1 Feb.l11,1975

2.990.820 7/1901 Saijo 123/43 R 3.431.894 3/1969 Allred 123/44 c 3.521.533 7/1970 Avermaete 123/44 C FOREIGN PATENTS OR APPLICATIONS 24.143 3 1901 Switzerland 123/44 0 1,378,232 10/1964 France 123/43 Primary ExaminerClarence R. Gordon Attorney, Agent, or FirmWenderoth, Lind & Ponack [57] ABSTRACT A rotary piston machine has a stator, wherein an assembly functioning as a rotor turns. The rotor is joined to a shaft through which moving power is sent or received, depending on whether it is used as a generator or receiver of movement. The machine is characterized in that the rotor consists of at least a cylindrical block wherein a cylindrical chamber is radially housed, with the characteristic that a piston. whose crankshaft rests on bearings in the rotor and which support a pinion which engages with a ring gear fixed to the stator, reciprocates in the chamber.

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saw D80? 15 i Pf-IEHTED FEB 1 1 I975 sum 11% 15 I FIG-TI FfJENTEUFEBI I 19. 5

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SHEET l aUF 15 Fls m PATENTEUFEBI H915 3,865,093

SHEET 1 5 OF 15 FiG-IB MACHINE DRIVEN BY ROTARY PISTONS BACKGROUND OF THE INVENTION The present invention relates to a rotary machine of the type which can be used as an engine, a pump or a compressor by merely modifying certain constructive details which do not in any way change the fundamental structure of the invention. Such machine is characterized in that a cylinder, wherein a piston moves, is housed within the rotor of the machine, functioning of same being achieved by the movement of the piston.

The machine in question may, of course, be simple or composite, in the latter case comprising an assembly of a plurality of simple units.

SUMMARY OF THE INVENTION When the machine in question deals with a more simple construction, it includes a stator having an inner cavity with a cylindrical surface. In the interior of the stator there is a tightly moving cylindrical rotor which adjusts to the walls of the entire stator. Such rotor has therein a radial cylindrical chamber, in which a reciprocating piston may move, the crankshaft of such piston is supported by bearings housed in the rotor. A very important characteristic of the machine of the present invention is that one of the ends of the crankshaft is extended to form the pivot support for a pinion which is permanently engaged with a ring gear fixed to the stator.

With a similar arrangement, it is perfectly understood that when the rotor turns within its stator, such rotation causes turning of the pinion along the ring gear which turning of the pinion is converted into rotation of the crankshaft, which, inturn and by means of its eccentric journal, converts the circular movement into a reciprocating movement of the piston.

Due to transmission and conversion of movement elements, it will be understood that movement initiated by the piston (specifically in the case of an engine) is converted by means of the crankshaft into rotary movement.

The machine functions in four different ways, depending on the application to which it is destined, and also on the way in which movement is obtained.

The machine may be used as a movement receiver (pump or compressor) or as a movement generator (engine), transmissions in each case being carried out in the manner briefly outlined above.

With respect to the way in which movement of the machine is obtained, such movement may be made in such a way that it is the rotor which turns, thus causing the rotation of the shaft connected thereto, or it may be made in such a way that the rotor is in a fixed position, thus permitting the stator to turn in order to effect the power output therethrough.

In the description which will shortly follow, the invention is explained as an engine, represented in various embodiments, presuming that the rotor turns while the power output is effected by a shaft connected to the rotor. However, it should be borne in mind that this case could be exactly the opposite without changing in any way the fundamental idea of the invention.

Brief reference will also be made to the use of the machine as a pump or compressor, taking for granted that the rotor turns while the stator remains stationary.

For a better understanding of the characteristics of the present invention, reference will be made to the following detailed description taken with the accompanying drawings. However, it should be understood that the specific details ofthe embodiment described do not constitute a fundamental part of the invention, inasmuch as the same may be modified as desired in order to adapt such details to the needs and requirements of a specific use or environment.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a longitudinal cross sectional view of an engine constructed in accordance with the invention and composed of a single working unit.

FIG. 2 is a cross section of said engine, taken on the line E-F in FIG. 1.

FIG. 3 is a section ofa working unit, taken on the line C-D indicated in FIG. 8, and corresponding to the moment in which the piston of the rotor is in one of its outermost neutral positions.

FIG. 4 is a section similar to that of FIG. 3, but taken at a different working moment, when the piston of the rotor is in one of its innermost neutral positions.

FIG. 5 is a longitudinal section of an engine constructed according to the invention, composed of two working units and taken along line A-B in FIG. 7.

FIG. 6 is a view similar to that of the preceding figure, but wherein the rotors have not been sectioned and taken along line G-I-I in FIG. 9.

FIG. 7 is a side elevational view of an engine constructed in accordance with FIGS. 5 and 6.

FIG. 8 is a side view of the same engine rotated from the view of FIG. 7.

FIG. 9 is an end elevational view of the engine of FIGS. 5 to 8, taken from one of its ends.

FIG. 10 is a second end elevational view taken from the end on which the inertia wheel is mounted.

FIG. 11 is a longitudinal section of an engine constructed according to the invention, composed of three working units.

FIG. 12 illustrates a rotor connecting element for a multiple engine, when three rotors are provided.

FIG. 13 illustrates the manner of carrying out the angular displacement of the pistons corresponding to the rotors of an engine, when three units are provided.

FIG. 14 is a longitudinal section of an engine constructed according to the invention, the engine being composed of four working units.

FIG. 15 is a cross-section of a machine according to the present invention, when said machine is intended to function as a pump or compressor.

DETAILED DESCRIPTION OF THE INVENTION As will be observed from the description below, a machine constructed according to the improvement of the present invention offers a series of practical advantages, whether it is used as a compressor, pump or engine.

It should be emphasized that in both cases there is no need to use valves nor all the accessory elements required for the functioning of such valves. Furthermore, a great reduction in the number of transmission and movement conversion elements necessary, whereby a reduction in weight is obtained, is made possible.

In the use of the invention as an engine, and as a result of the fact that the gear ratio between the ring gear of the stator and the pinion of the rotor is established at 2:], according to a preferred embodiment of the invention, the piston effecting a four-stroke cycle functions once for every revolution. This feature constitutes a considerable improvement in the efficiency of engines having four reciprocating cycles, the piston of which functions only once for every two complete revolutions.

In the embodiment represented in FIG. 1, wherein the invention used as an engine will be explained, it is seen that the stator casing comprises a body 1 which is hollow with a cylindrical internal surface. The stator has therein a cylindrical body 2 constituting the rotor which has a radial recess 3 constituting the chamber for a reciprocating piston 29 whose rod 30 is connected at its head to the journal 7 of a crankshaft, the supports of which are supported, by means of ball bearings 6, in the rotor body 2. On the other hand, it can be seen that one of the supports 5 of the crankshaft is concentrically extended to form a lug 33 which serves as a pivot support for a pinion 10, permanently engaged with a ring gear 12 which forms an integral part of the stator 1.

In the specific embodiment contemplated, the ring gear 12 is mounted on a casing or housing 21, constituting an extention of the stator 1. Housing 21 is independent from stator body 1 in order to facilitate the mounting of the assembly, although it is fastened thereto in such a way that, functionally speaking, the two units may be considered as a single unit.

It can also be seen from FIG. 1 that the stator body 1 and the casing 21, wherein the ring gear is mounted, extend to

fixed bodies

18 and 20, respectively, which form the remainder of the casing of the machine, and which provide supports for two axle shafts 17 which are connected to opposite sides of the rotor by means of elements 19, one of which has a shape designed to house the portion of the pinion 10.

It can be seen that the joining of the different bodies constituting the external casing, which is of course mounted with the help of suitable joints, is carried out by means of through bolts 15 and with the help oflocating pins 16 which guide the connection or coupling.

An inertia wheel 23 is mounted on one of the axle shafts and is provided, internally and on its external face, with a crown gear 42 by means of which starting of the machine may be effected with the aid of any conventional device suitable for this purpose.

Cooling may be effected by air, in which case, the stator and the remaining parts of the fixed casing should include fins which would permit a better diffusion of heat outwardly; or by water, as in the embodiment shown, wherein all the mentioned elements composing the fixed casing, form a chamber 14 enclosing the assembly and through which a stream of cooling water is circulated.

Various manners of providing mounting and greasing of the above arrangement will be discussed below.

Referring specifically to the mounting of the head of the rod on the journal of the crankshaft, the general construction of the engine requires the crankshaft to be split, having, in the conventional manner, a journal which extends into a conical part, which part may be housed in a cavity similar to that provided in one of the supports kept from turning by means of keys, and an outer part projects a given length to secure the mounting by means ofa nut or the like. In the figure, the extended conical portion of the journal is indicated as 8 and the nut effecting the fixing as 9.

With regard to the greasing of the head of the rod and crankshaft bearings housed in the cylindrical body 2 which constitutes the rotor, a radially orientated bore 25 may be made in the pinion 10. Such bore stretches from the crest of one of its teeth to an axial duct 26 formed in the corresponding support 5 of the crankshaft.

Branches

27 and 28 may be provided from such bore or duct for greasing the roller bearings and the head of the rod. Greasing of the bottom of the rod, as well as of the bolt in which same is fastened, may take place for example by means of radial bores 31 provided in the piston wall in accordance with the lubricating segment. The inlet of oil may be effected by ducts 22 in the casing, said ducts communicating with the crank case.

FIG. 2 shows a section of the engine having a single cylinder, with which we shall now deal, taken on the line E-F indicated in FIG. 1. This figure better illustrates the way in which the pinion 10 is connected to the ring gear 12, as well as the way in which one element 19, whereby the rotor is joined to one shaft 17, has a grooved or notched interior 50, to house the portion of the pinion 10 situated below element 19 when element 19 is applied to the end of the machine on which said pinion is mounted.

This figure also shows the screws 24 in section by means of which and through the rotor 2 the axle shafts 17 are connected to each other. Movement is effected by these two axle shafts, as can be seen from the arrangement of the keys 13. By means of such arrangement the ring gear 12 is fastened to its supporting casing 21. As can be seen, these keys are distributed along the circumference of the assembly in such a way that they are equidistant from each other.

As shown in FIG. 2 the shape of element 19, by means of which the connection between the engine and the axle shafts is effected, is substantially elliptical, having perforations or holes near the ends thereof which are in a face to face relationship with corresponding perforations or holes in the rotors.

FIGS. 3 and 4 aid understanding of the way in which the engine functions. FIG. 3 specifically shows the piston 29 situated in one of its outermost neutral positions, on the point of starting to function, while FIG. 4 shows the same piston in one of its innermost neutral positions, when suction has terminated and the compression phase is about to start.

By observing these drawings it is deduced that the reciprocating movements of the piston is accompanied by a turn ofthe crankshaft, which during movement drives pinion 10, which engages fixed ring gear 12, thus causing rotor 2, including chamber 3 which constitutes the cylinder within which piston 29 reciprocates, to rotate.

As a result of this, and should the piston be in a position adjacent the inlet port 40 (such position has not been shown), turning of the crankshaft causes the piston to start to be withdrawn from the outer end of chamber 3. Simultaneously, rotor 2 turns and the piston 29 reaches its innermost position within chamber 3 shown in FIG. 4, thus completing the intake phase. Thereafter, the progressive turning of rotor 2 causes piston 29 to raise, producing resulting compression, until the piston is opposite an ignition plug 32, or, in front of an injector, if the engine is of the diesel type. Once backfiring occurs, the piston 29 once more descends, effecting an expansion phase, and thereafter is forced by the constant turning of the rotor 2 to ascend in order to effect a progressive expulsion of burnt gases through the port 39. Therefore, the phases are repeated in the same way.

As can be seen from any one of FIGS. 3 and 4, and particularly from FIG. 3, a baffie 34 has been provided in the head of the piston 29. The shape of such baffle is complemented with that ofthe compression chamber 35 housed in the stator, in order to obtain a resultant of force in the expansion of the compressed gases which aids in obtaining the turning of the rotor.

FIG. 3 also shows that compression rings 36 and 37 have been placed on both sides of the recess, radially housed in the rotor 2, which forms the cylinder 3, in which the piston 29 moves. Such compression rings help to avoid the expansion ofthe gases from escaping in any way other than into cylinder 3 to lower the piston. A third compression ring 38 is provided in a forward position with regard to the direction of rotation of the rotor, so that just before the piston 29 reaches its uppermost position, when the compression phase is initiated, ring 38 prevents the compression from being destroyed before ring 37 has passed compression chamber 35 and come in contact with the stator.

Having sufficiently explained the general aspects of the engine, reference will now be made to specific embodiments which include more than one working unit.

FIGS. 5, 6, 7, 8, 9 and specifically show an engine whose general features are identical to those which have been previously described, but which is composed of two working units, joined together by a connection element 19 identical to those joining the axle shafts 17 to the rotor assembly.

It will be observed from FIG. 5 that the constructive solution that the stator body 1 is independent from the casing 21 wherein the fixed ring gears 12 are positioned, makes a,very simplified mounting possible, in which any damaged part may be substituted, irrespective of those parts which are not damaged.

FIG. 5 represents the assembly with one of the rotary units in section, the other rotary unit being only partly sectioned, so that the external part of the piston may be seen. The bearings 6 of the crankshaft, as can be seen, completely encircle the supports 5 and are mounted under pressure in a housing 4 formed in the part of rotor 2 diametrically opposite to that occupied by chamber 3 which constitutes the engine cylinder.

FIG. 6, wherein the rotors have not been shown in section, shows that the cylindrical shape of the periphery of the rotors insures a perfect air tightness with the inner surface of the stator and simultaneously with a support which cooperates with the bearing supports of the outlet axle shafts.

FIGS. 7 to 10 represent outside views of an engine made in accordance with the embodiment shown in FIGS. 5 and 6, from which the modification to screws 15, which join the various parts composing the outer casing, and to guide pins 16 which cooperate in guiding during coupling of the various parts, can be seen. There is also shown the arrangement of the inlet and

outlet ports

40 and 39, respectively, and the position of the inertia wheel 23 which includes a crown wheel 42 by means of which movement of the engine may be initiated.

In the specific embodiment of FIGS. 5-10 where the machine has two working units, the cylinders 3, housed in the rotors 2 acting as working chambers for the respective pistons 29, should be set at an angle of 180 from each other so that the expansion phase will not take place in both units simultaneously, thus producing smooth operation of the machine without imbalanced impact.

In the embodiment shown in FIG. 11, where the engine consists ofthree working units, the cylinders 3 acting as working chambers for the respective pistons 29 should be set at an angle of from each other, as indicated in FIG. 13.

To overcome the fact that the rotors 2 have openings for their connection by means of screws 24, which rotors cannot be joined by means ofelements such as elements 19 shown in FIGS. 1, 2, 5 and 6 because element 19 cannot be set at an angle of more than since they have only two perforations or holes, the use of elements such as those shown in FIG. 12 and indicated as 43 is necessary. As can be seen, besides having a groove or notch 49 to house the pinion 10 during mounting and which corresponds to the groove or notch 50 provided for in element 19, these elements have a plurality of orifices 44 whereby same may be connected to two adjacent rotors using different pairs of orifices. Such rotors, therefore, have the angular displacement necessary in each case.

The engine may also be made to include four working units, including necessary rotors and corresponding stators and ring gear supporting casings (FIG. 14), and also including the rotor connecting elements 43 shown in FIG. 12, with the purpose of conferring to the rotors the required relative angular displacement.

FIGS. 1, 5, 11, and 14 illustrate screws 24 which fasten the different elements constituting the rotating part of each unit to each other, joining :such elements firmly together in such a way that the formation of a single driving machine takes place.

For the specific case shown in FIG. 1, the connecting screws 24 can pass through the rotor assembly from one side to the other, since they enter the perforations or holes in the elements 19 and the perforations provided for in the single rotor which are in perfect alignment.

The same is true in the case shown in FIG. 5 where, since the elements 19 and the rotors 2 are set at an angle of l 80 from each other, their respective perforations are also coincident, thus allowing the screws to pass from one end of the machine to the other.

However, for the embodiments illustrated in FIGS. 11 and 14, it is necessary to resort to the use of different screws, first to join each of the exterior connecting elements 19 to the respective nearest interior element of the other type 43, and then to subsequently join these interior elements 43 to each other through the rotor or the rotors situated thereb etween.

However, in one way or the other, it is possible to form an integral working assembly, wherein the role played by each cylinder is transmitted to all the rotors.

The functioning of the machine when it is used as a compressor or pump, which is illustrated in FIG. 15, will now be described.

As can be seen, the fundamental arrangement is exactly the same as discussed above, although those parts of course, those parts which are only inherent to engines have been eliminated.

As can be seen, in accordance with this embodiment and suited to the role which the machine plays, four

ports

45, 40, 47 and 48 have been provided,- such ports being arranged in pairs set at an angle of 180 from each other, each port forming a pair being situated a few degrees ahead and a few degrees behind respectively, with regards the two outermost neutral positions of the piston.

Of course, a pump or a compressor made according to the invention, may comprise, as in the case of engines, as many working units as necessary, the joining of the different rotors being effected in exactly the same way.

If port 48 is a suction port and if the rotor turns in a clockwise manner, in this case operation would be effected as follows: 7

In the first place and as a result of the turning of the rotor 2, the piston 29 would effect suction until reaching its lowermost position. Thereafter, with ascending of the piston, discharge of the fluid taken in would occur through port 40. Subsequently, a further suction from port 45 will occur which, later on, and following the turn of the rotor will be converted into a discharge through port 47.

I claim:

1. A rotary machine for use as either a generator or a receiver of movement, said machine comprising:

A. a stator casing having therein at least one cylindrical inner surface;

B. at least one rotor unit mounted within said casing adjacent a respective at least one inner surface thereof, each of said at least one rotor units comprising:

a cylindrical rotor body having an outer peripheral surface in contiguous contact with said respective inner surface of said stator casing, a single dead-end radial recess formed in said outer peripheral surface;

a piston-rod mechanism mounted to reciprocate within said recess;

a cylindrical opening extending transversely completely through said rotor body in communication with the inner end of said radial recess, said cylindrical opening having an axis parallel to but offset from the longitudinal axis of said rotor body;

a two-piece crankshaft having an outer diameter less than the diameter of said cylindrical opening and having the opposite ends thereof pivotally supported in said cylindrical opening about said axis thereof, said piston-rod mechanism being connected to an eccentric journal of said crankshaft, said eccentric journal being within said outer diameter of said crankshaft, said crankshaft at one end thereof having an extension;

a pinion rotatably supported on said extension; and

a ring gear rigidly fixed to said stator casing and meshing with said pinion; and

C. shaft means connected to the outermost of said at least one rotor unit at the rotor body thereof in alignment with said longitudinal axis thereof.

2. A machine as claimed in claim 1, wherein the gear ratio between said ring gear and said pinion is 2:1.

3. A machine as claimed in claim 1, wherein said at least one cylindrical inner surface comprises a single inner surface; said at least one rotor unit comprises a single rotor unit; and said shaft means comprises a pair of shafts, one each connected to opposite ends of the rotor body of said single rotor unit, and connection means extending completely through said rotor body for connecting said pair of shafts thereto, the one of said shafts connected to said rotor body adjacent the end thereof with said ring gear and pinion having recess means therein to accommodate a portion of said pinion.

4. A machine as claimed in claim 1, wherein said at least one cylindrical inner surface comprises at least two inner surfaces; said at least one rotor unit comprises at least two rotor units; the longitudinal axes of said rotor bodies of said rotor units being aligned; and the direction of reciprocation of said piston-rod mechanisms of said rotor units being equi-angularly spaced from each other.

5. A machine as claimed in claim 4, comprising two inner surfaces and respective rotor units, a first of said rotor units having an exterior ring gear and pinion, and a second of said rotor units having a ring gear and pinion positioned between said rotor units; and wherein said shaft means comprises a pair of shafts, one each connected to an opposite outer end of said of the two rotor bodies of said two rotor units, and connection means extending through said two rotor bodies for connecting said pair of shafts thereto, the one of said shafts connected to said rotor body of said first rotor unit having a recess means therein to accommodate a portion of said pinion of said first rotor unit, said connection means further comprising an element positioned between the rotor bodies of said first and second rotor units and having recess means to accommodate a portion of said pinion of said second rotor unit.

6. A machine as claimed in claim 4, comprising more than two inner surfaces and respective rotor units; and wherein said shaft means comprises a pair of shafts, one each connected to an outer end of the two outermost of the rotor bodies of said more than two rotor units, first type connection means extending through each of said two outermost rotor bodies to connect the respective of said shafts thereto, and second type connection means extending through adjacent interior of said rotor bodies for rigid positioning thereof; a first of said outermost rotor units having an exterior ring gear and pinion, and the remainder of said rotor units each having a ring gear and pinion positioned between adjacent rotor units; the one of said shafts connected to said rotor body of said first outermost rotor unit having a recess means therein to accommodate a portion of said pinion of said first outermost rotor unit; said second type connection means further comprising a plurality of elements, one each positioned between the rotor bodies of adjacent of said rotor units and each having recess means to accommodate a portion of the respective pinion positioned between said adjacent rotor units.

7. A machine as claimed in claim 1 for use as an engine, further comprising, for each of said at least one rotor units, an inlet port and an exhaust port extending through the respective of said at least one inner surface of said stator casing at a first position thereof adjacent a first outermost position of said piston-rod mechanism with respect to said recess; and a compression chamber formed in said respective inner surface of said stator casing at a second position thereof adjacent a second outermost position of said piston-rod mechanism with respect to said recess.

8. A machine as claimed in claim 1 for use as a compressor or pump, further comprising, for each of said at least one rotor units, a first pair of suction and discharge ports extending through the respective of said

Claims

1. A rotary machine for use as either a generator or a receiver of movement, said machine comprising: A. a stator casing having therein at least one cylindrical inner surface; B. at least one rotor unit mounted within said casing adjacent a respective at least one inner surface thereof, each of said at least one rotor units comprising: a cylindrical rotor body having an outer peripheral surface in contiguous contact with said respective inner surface of said stator casing, a single dead-end radial recess formed in said outer peripheral surface; a piston-rod mechanism mounted to reciprocate within said recess; a cylindrical opening extending transversely completely through said rotor body in communication with the inner end of said radial recess, said cylindrical opening having an axis parallel to but offset from the longitudinal axis of said rotor body; a two-piece crankshaft having an outer diameter less than the diameter of said cylindrical opening and having the opposite ends thereof pivotally supported in said cylindrical opening about said axis thereof, said piston-rod mechanism being connected to an eccentric journal of said crankshaft, said eccentric journal being within said outer diameter of said crankshaft, said crankshaft at one end thereof having an extension; a pinion rotatably supported on said extension; and a ring gear rigidly fixed to said stator casing and meshing With said pinion; and C. shaft means connected to the outermost of said at least one rotor unit at the rotor body thereof in alignment with said longitudinal axis thereof.

8. A machine as claimed in claim 1 for use as a comprEssor or pump, further comprising, for each of said at least one rotor units, a first pair of suction and discharge ports extending through the respective of said at least one inner surface of said stator casing at a first position thereof adjacent a first outermost position of said piston-rod mechanism with respect to said recess; and a second pair of suction and discharge ports extending through the respective of said at least one inner surface of said stator casing at a second position thereof adjacent a second outermost position of said piston-rod mechanism with respect to said recess.