US3793924A

US3793924A - Fluid-traversed flow piston unit

Info

Publication number: US3793924A
Application number: US00189598A
Authority: US
Inventors: K Eickmann
Original assignee: Individual
Current assignee: Individual
Priority date: 1970-03-03
Filing date: 1971-10-15
Publication date: 1974-02-26
Anticipated expiration: 1991-02-26

Abstract

Fluid-traversed flow piston unit, having a housing and pistons for moving in cylinders of an axially mounted rotor and having a control body for controlling the induction with fluid of the cylinders. A coupling body is mounted in a recess of the housing or of a housing part for axial movement. The coupling body is provided with shoulders and at least one eccentric extension so that at least one radial eccentrically extending fluid pressure chamber is formed between the shoulders and a wall of the recess of the housing. In this manner the fluid in the fluid pressure chamber presses the coupling body against the rotor.

Description

United States Patent Eickmann 1 Feb. 26, 1974 FLUID-TRAVERSED FLOW PISTON UNIT 2,932,256 4/1960 Orshansky 91/485 2,80 94 101957 h k [76] Inventor: Karl Elckmann, 2420Issh1k1 9 5 org ans y 92/485 Hayama-machi, Kanagawa-ken, Japan Primary Exammer-W1ll1am L. Freeh Assistant Examiner-Gregory P. LaPointe F1169: s 1971 Attorney, Agent, or FirmToren and McGeady [21] Appl. No.: 189,598

[57] ABSTRACT [30] Forelgn Apphcat lon Priority Data Fluid-traversed flow piston unit, having a housing and Oct. 22, 1970 Austria 1954/70 pistons for moving in Cylinders of an axially mounted rotor and having a control body for controlling the in- [52] US. Cl. 91/487 duction with fluid of the cylinders A Coupling body is [51] Int. Cl. F011) 13/04 mounted in a recess of the housing or of a housing [58] Field Of Search 91/484-489 part for axial movement The coupling body i vided with shoulders and at least one eccentric exten- [56] References C'ted sion so that at least one radial eccentrically extending UNITED STATES PATENTS fluid pressure chamber is formed between the shoul- 3,092,036 6/1963 Creighton 91/485 ders and a a f th r ess of the housing. in this 3,410,220 12/1968 Kratzenberg et a1. 91/485 manner the fluid in the fluid pressure chamber presses 2,861,552 11/1958 Creighton et al. 91/485 the coupling body against the rotor. 2,779,296 l/l957 Dudley 91/485 3,043,233 7/1962 Rumsey 91/485 3 Claims, 5 Drawing Figures 5 E 25 [0 5 9 H 6 1y l i 1 49 /5 VIII 6 26 I I 3 47- a\ I L 25 5/ /4 J l0 1 /3 /B 244 5 11 PAIENTEBFEBZBIQH 3.793.924

sum a *nr 3 I INVENTOR.

KA RL E/CKMANN A 770/? Mt):

PMENIED FEB2 61974

sum

3 or 3 FLUID-TRAVERSED FLOW PISTON UNIT FIELD OF INVENTION The invention relates to a fluid-traversed axial flow piston unit with pistons which move in cylinders of an axially mounted rotor and having a control body for controlling the admission or induction of fluid to the cylinders.

BACKGROUND INFORMATION Such axial flow piston units, particularly axial flow piston pumps, compressors, motors, transmissions and the like, have been used successfully for a long time with excellent results in the field of pneumatics and hydraulics. However, the manufacture of the rotors is extremely difficult and expensive in such units. Further, the control is complicated and a positioning angle of the rotor to the drive flange axis can be realized in highpressure units only up to about 25 to 30. This sets a limit for the output of the presently known axial flow piston units, while on the other hand a certain minimum expenditure can not be reduced.

SUMMARY OF lNVENTlON The object of the invention is to overcome or minimize these disadvantages of the present axial flow piston units and to provide an inexpensive, powerful, dependable and safe axial flow piston unit of high efficiency and improved output.

The invention resides, therefore, on the one hand, in mounting a coupling body in a housing or cover part of the unit for limited axial movement, to design the coupling body simply and expediently and to press it against the rotor unit of the axial flow piston machine by means of fluid chambers arranged on its rear shoulders. 1

According to another feature of the invention, the entire above mentioned coupling body is associated with an axial-cylinder-rotor with through-going cylinders of the same diameter over the entire cylinder length.

Another feature of the invention consists in dimensioning and placing the fluid chambers on the shoulders of the coupling body in such a way that the sealing web between the rotor unit and the control part on the coupling body or the control part of the coupling body requires insignificant radial extension or expansion whereby the friction surfaces between rotor and stator are thus reduced, which in turn results in a reduction of the friction and consequently in an increase of the efficiency of the unit.

An advantage of the invention is that it is possible, with a suitable design of the unit, to increase the positioning angle of the rotor to the drive shaft from the presently customary 25 to 28 to much larger angles, for example, up to 45 and thus considerably to increase the piston stroke and the output of the unit, in some cases up to almost 100 percent.

A further feature of the invention is the arrangement of fluid pressure fields in the piston walls, arranged tan gentially or in the direction of the thrust-piston, with automatic control of the induction or charging of the latter by means of bores provided in the piston and by means of connecting recesses in the piston rods. This arrangement also contributes to enlarging the positioning of the angle of the axial flow piston unit with simultaneous reduction of the friction between the pistons and cylinders of the unit.

The small positioning angles and the low output of the prior art axial flow chamber units, their extended supporting bearings and sealing surfaces between stator and rotor, as well as their friction between pistons and cylinders, and their construction costs and precision requirements, are successfully replaced according to the invention by improved structural and operating conditions.

The various features of novelty which characterize the invention are pointed out with particularity in the claims annexed to and forming a part of this sepcification. For a better understanding of the invention, its operating advantagesand specific objects attained by its use, reference should be had to the accompanying drawings and descriptive matter in which there is illustrated and described a preferred embodiment of the invention.

IN THE DRAWINGS FIG. 1 shows a longitudinal section through an embodiment of an axial flow piston unit designed according to the invention;

FIG. 2 shows a cross-section through FIG. 1 along line 11-";

FlG. 3 is a cross section through a part of the unit of FIG. 1 along line lIl-lll; and

FIGS. 4 and 5 are partial sectional views taken along the line lV--lV in FIG. 1.

In housing 11 the rotor 12 is rotatably mounted, in a known manner, for example, in bearings 15 and secured against axial displacement. in the rotor are arranged the cylinders 13 in which the pistons 14 slide axially outwardly and inwardly in order to admit fluid, such as a liquid or gas, into the cylinder or to eject the fluid from the cylinders. The pistons 14 are driven in known manner by means of the connecting rods or piston rods 18, the latter being arranged between the pistons 14 and the drive flange 19. The drive flange 19 has an inclined position to the rotor 12 relative to the axial movement; or the pistons drive the drive flange 19 when the unit works as a motor. The drive flange is likewise mounted rotatably in the unit housing 11 by means of the

bearings

21, 22 and of the holder 23, if necessary. Between rotor 12 and drive flange 19 there can be arranged, likewise in known manner, the

gearing

16 and 17 for synchronizing the rotation of the rotor and of the drive flange. In the housing 11 or on the latter can be arranged a cover 24 with the

feedand discharge connections

25 and 26, as it is likewise customary in the art.

According to the invention, a recess is provided in the housing part or rear cover 24, which has at least two different diameters at different areas and in which a coupling body 1 according to the invention is arranged for limited movement in axial direction. One part of the recess has a cylindrical outer surface, which is arranged eccentrically offset to the cylindrical outer surface of the other part of the recess. The coupling body 1 is in turn provided with at least two cylindrical outer surfaces of different diameter which are offset with the same eccentricity to each other and which are fitted into said two cylindrical inner surfaces of the recess in part or cover 24.

The form or configuration of the above mentioned recesses according to the invention in the coveror housing part 24 and of the coupling body according to the invention will be understood best by viewing FIG. 2 together with the corresponding part in FIG. 1. As can be seen from FIG. 2, the inner surface 9 of the recess, which is equal to the outer surface 9 of the respective part of the coupling body 1, is arranged eccentrically relative to the center and the outer diameter of housing 11 or cover part 24. The eccentricity between the axis of the coupling body 1, which may be equal to the axis of housing 11 or cover 24 and to the axis of the respective coupling body part with the outer flange 9, is designated with e in order to clearly identify this important prerequisite of the invention. As is seen from FIG. 1, the

cylindrical surfaces

9, 8 and are arranged in series in axial direction. They can be separated from each other by recesses or dividing cut-outs. In FIG. 2, it can clearly be seen from the dash lines representing the cylindrical surfaces 8 that the cylindrical surfaces 9 are arranged eccentrically to the cylindrical surfaces 8. The respective cylindrical

inner surfaces

8, 9 and 10 in housing 11 or cover 24 and the cylindrical

outer surfaces

8, 9 and 10 on the coupling body 1 are represented in the figures only by a line, because the cylindrical inner surfaces of the coupling body are fitted tightly or strongly in part 1 1 or cover 24, so that no two surfaces are seen anymore with the naked eye after the assembly of the unit. The fitting of the outer surfaces into the inner surfaces is, however, effected with so much play, that the coupling body 1 can move easily in the part 11 or 24 in axial direction by the indicated amount. Frequently packing rings are inserted in the outer surfaces of the coupling body 1, which are crosshatched in the drawing. These serve to improve the scaling between the inner surfaces and outer surfaces. Finally, FIG. 1 and FIG. 2 also show that the additional cylindrical inner surface 10 can be provided in cover 24 or in a separate insert 244, which surface encloses a corresponding outer surface 10 on the coupling body 1. The purpose of this arrangement will be explained later.

The corresponding parts of the coupling body 1 are somewhat. shorter than the corresponding recesses in the cover or

housing

24, 244 or 11, so that the

fluidcontaining fluid chambers

3 and 2 or 3 and 50 can be designed according to the invention axially of the respective coupling body parts. Into the fluid chamber 3 opens the fluid line connection 25 and the fluid line 6 passing through the coupling body. Into the fluid chamber 2 opens the line connection 26 and the fluid line 5. These fluid lines are also frequently called cuts or channels. The fluid pressure chamber 50, which will be called hereafter counter-pressure chamber 50, is connected either to the fluid pressure chamber 2 or to the fluid pressure chamber 3. This connection can be effected by means of the ducts, or it is effected by corresponding ducts with non-return valves or reversal switches arranged in the latter. If the counter-pressure chamber 50 is provided, it is necessary that it is connected with the respective fluid-traversed

fluid chamber

2 or 3 of the respective higher pressure.

FIGS. 4 and 5 show the alternate arrangements for such connections.

In FIG. 4, one-way valves are demonstrated, while in FIG. 5, the alternate of a flow control valve is illustrated.

In FIG. 4 a fluid passage 331 extends from the chamber 3 to a one-way or check valve 332 which is loaded by a spring member 333. Pressure in the chamber 3 causes the check valve 332 to open and pass fluid through the passage 334 into the counter-pressure chamber 50, if however, the pressure is higher in the counterpressure chamber 50, then the higher pressure acting through line 334 will close the check valve 332. Further, in FIG. 4, a fluid passage 22] extends from the chamber 2 to a one-way valve means 222 retained in place by a spring member 223. The valve will open if higher pressure exists in chamber 2 and will pass fluid from the chamber 2 into the counter-pressure chamber 50. On the contrary, if chamber 50 contains the higher pressure, then the higher pressure fluid from chamber 50 will pass through line 224 and cause the valve 222 to close.

As an alternative, in FIG. 5, a fluid flow control chamber 444 contains a flow control piston 445 which is axially movable in the chamber. The middle of the control chamber 444 is in communication with a fluid passage 443 connected at its other end to the counterpressure chamber 50. At one end, the control chamber 444 communicates through a passage 441 to chamber 3 and at its other end through a passage 442 it communicates with the chamber 2. Accordingly, if a higher pressure fluid is contained within the chamber 3, the fluid control flow piston 445 is moved to the right, as shown in FIG. 5, to open the passage 443 to the chamber 50 and, if the higher pressure exists within the chamber 2, the piston 445 is moved in the opposite direction so that chamber 2 and counter-pressure chamber 50 communicate with one another and are at the same pressure.

The rotor 12 is secured against axial displacement in the bearings 15. The coupling body 1 or the associated control body bears with its end face 7 or control body arranged on the coupling body on the respective rotating end face of the rotor 12. The face 7 on the rotor 12 and the face 7 on the coupling body or control body 1, 111 form in known manner the control level (German: Steuerspiegel) of the unit. Since such control levels are known per se, reference is made with regard to their description to the literature. The control body 111, which may be associated with the coupling body, is shown in broken lines in FIG. 1. If the control body 11 l is not provided, then the respective end of the coupling body is designed as a control body. The axial length of the recesses and of the coupling body parts are so designed that the coupling body 1 can move axially to a limited extent toward the rotor 12 or away from it. This is necessary so that the proper control level distance is always adjusted between the rotating control surface 7 and the stationary control surface 7.

The diameters of the parts of the coupling body with the

outer surfaces

9 and 8 and the eccentricity between them are so dimensioned that in units with reversible direction of rotation, the radial sections through the

fluid pressure chambers

2 and 3 are of equal size and that it is ensured by the eccentricity e between them that one fluid pressure chamber exerts its main pressure over about l of the control level, and the other exerts its main pressure over the other l80 of the con" trol level. The rear end of the fluid pressure chamber 3 is bounded and sealed by means of the pin or journal with the cylindrical surfaces 49 on the coupling body and on the cover 24 or housing 11. If D is the diameter of the cylindrical surfaces 8, d the diameter of the cylindrical surfaces 49, and R the radius of the cylindrical surfaces 9, then the equal size of the cross-sections through the

chambers

2 and 3 can be determined by means of the equation The eccentricity e can also be determined mathemati cally or fraphically.

1f pre sure fluid flows through the ducts and

chambers

3, 6, 25, the fluid chamber 3 presses the coupling body 1 against the rotor in order to seal the control level 7. If fluid pressure prevails in chamber 2, or fluid pressure flows through the

ducts

2, 5, 26, the fluid pressure in chamber 2 presses the coupling body 1 against the rotor 12 to seal the control level 7.

According to the invention, the dimensions of the

diameters

8, 9 or 10 and 49 can be so reduced so that no extended support bearings have to be arranged between rotor 12 and coupling body 1 or control body 111. Narrow packing strips or webs in control level 7 suffice, since the pressure of the coupling body 1 against the rotor 12 can be very accurately dosed by the invention.

Due to the possibility of accurately dosing the bearing or contact pressure of the coupling body according to the invention against the rotor and the resulting pos' sibility of reducing the sealing surfaces and/or bearing surfaces in the control level, friction is saved and the efficiency of the machine is thus considerably increased.

The exact adaptability of the diameter conditions of the coupling body according to the invention and thus of its contact pressure on the rotor has also made it possible to provide the rotor 12 in a simple manner with cylinders of the same kind, because the coupling body can be so dimensioned that it can just counteract the fluid force from the cylinder openings. The rotor 12 can thus be made shorter and the production of the rotor 12 with cylinder throughbores is much simpler than the designs with cylinder bores which do not traverse the entire rotor. The rotor manufacture thus becomes much simpler and less expensive by the control or coupling body arrangement according to the invention.

Since the rotor is no longer pressed against the control body according to the invention, but, in the reverse, the coupling body is pressed in a simple manner against the rotor, the rotor 12 can be fixedly mounted in the bearings 15 and the rotor 12 can thus be imparted with a large positioning angle without impairing the safety of the unit. This permits very long piston strokes and consequently a high output in the unit according to the invention.

Due to the wide positioning angle of the rotor to the drive flange axis, force components are produced by the piston rods 18 on the outer piston walls and the walls of the cylinders 13 which are greater than in axial flow piston machines with smaller angles and lower outputs. In order to compensate for these force components, pressure fluid fields (recesses) 31 and 311 to 315 can be provided in the walls of the pistons 14, which extend in the direction of the axis of the connecting rods or thrust pistons and in which a fluid force is built up which counteracts the force component of the connecting rods 18 on the pistons 14. This permits radial forcefree floating of the pistons 14 in the cylinders 18, which in turn reduces the friction between piston walls and cylinder walls. To this end a simple control of the induction of these pressure fluid chambers is provided.

As can be seen from HO. 3 and FIG. 1, at least one recess, but preferably a number of

recesses

31, 311, 321, 313, 314, 315 or the like are worked in the pistons 14 radially from the outside. Through the piston 14 extends the bore 34. In the head of connecting rod 18 is provided, inside the piston 14, a customary flattening or cut-out of the spherical head, as it is also possible in the known axial flow piston units. A small fluid pressure chamber is thus formed between the connecting rod head and the piston, which is filled with compressed fluid from the respective cylinder through bore 34. According to the invention, a bore or a duct 32, 321-325 extends from each fluid pressure cut-out 31 or 311 to 315 up to the seat of the connecting rod head in the respective piston 14 and opens into the latter. Tl-le radial distance of these bore openings from the piston axis and the diameter of the connecting rod head or recess in the piston head are so dimensioned that, with greater positioning angle of the connecting rod to the piston axis, the flattening or cut-out on the connecting rod head establishes a connection between the piston bore 34 and one or several of the

ducts

32, 321, 322, 323, 324, 325, while the connection to the other of these ducts remains closed by the connecting rod head. According to the invention it is thus made sure in this way that the fluid pressure fields 31 in piston 14 are charged with fluid pressure which are just in the extension of the connecting rod axis of the respective connecting rod or rods 18. lt is then no longer the piston surface that presses against the cylinder wall in the direction of the connecting rod axis, but the fluid in the respective

fluid pressure chamber

31 or 311 to 315. Actually a fluid film is, of course, also formed between the remainders of the surface of the respective pistons and the cylinder walls in which the pressure decreases with a certain pressure gradient with increasing distance from the pressure fluid chamber. The conditions in this film must be taken into account in the calculation of the size and position of the pressure fluid pockets 31, 311, 312, 313, 314 and 315. In this way the friction between the walls of the pistons 14 and the inner walls of the cylinders 13 is substantially reduced according to the invention and a larger positioning angle may be used between the piston axis and the drive flange axis, and thus a long piston stroke even for high fluid pressures, and a high output in the axial flow piston unit are achieved. The present measures with similar aims, as they are known from the literature, demonstrate the importance of realizing this aim for high pressures and positioning angles, but the prior art has not disclosed sufficiently simple and exact means for realizing this aim rationally, safely and simply.

From FIG. 2 and the corresponding part of FIG. 1 it can also be seen that the respective

fluid pressure chambers

2 and 3 extend with a larger surface over one half of the control level and with a smaller surface over the other half of the control level 7. This is realized, on the one hand by the eccentricity e between the center line of the

surfaces

49, 8, 10 and the center line of the surfaces 9, on the other hand. In FIG. 2, the fluid pressure chamber 2 is arranged between the cylinder surfaces 8 and 9, and the fluid pressure chamber 3 between the cylinder surfaces 9 and 49. The larger surface cross-sections of the fluid-

pressure chambers

2 and 3 press in the range of the high-pressure half of the control level against the rotor while the smaller surface cross-sections press against the low-pressure half of the control level 7. With lower and medium pressures, this said coupling body having an outer cylindrical surface type is suitable, because the coupling body 1 must also extending in the axial direction of said rotor from said be pressed against the rotor 12 in the respective lowend face and said cylindrical surface comprising a first pressure half of the control level 7 and in the reversing cylindrical surface extending from said end face, a seczones Of the lat r. 5 nd cylindrical surface extending from the transverse At high or very high fluid pressures and/0 rotor plane containing the end of said first cylindrical surface speeds it is advisable, however, to ensure that the couspaced f id d f d S id second lind ic l pling y 1 is not Pressed too much against the rotorsufiace disposed concentricallyof "S56E81 cylindri- A too great pressure represents a risk for the safety of ca] Surface, and a third cyhndrical Surface extending the unit, particularly in the respective low-pressure half 10 outwardly from the transverse plane containing the of the control level 7, because the control surfaces may end of said second cylindrical Surface Spaced run "1 here, m he welded or hused each other wardly from said first cylindrical surface and said under cxcesswe h For i rehsoh the Counter third cylindrical surface being eccentric to said first pressure chamber 50 arranged m hlgh'pressure and second surfaces and having a diameter less than els according to the invention on a shoulder of the couthe diameter of Said Second cylindrical surface pling body on the rotor i and is connected the so that said third cylindrical surface is disposed inabove igh z h $3 erkof the h'gher wardly from said second cylindricai su rface, said 5011s pressure "L e ac g i irlg having surfaces in closely contacting relationship pressure c am er g t e Cy er with said first second and third cylindrical surfaces of surfaces 8 and represmed m 2 m i i said coupling body, a first shoulder formed on said cou- The CmSs'.Secuon of this chambefr ls so dlmensloned pling body in the transverse plane between said first that the fluid pressure from the fluid pressure chambers and second cylindrical Surface; a Second Shoulder 2 and 3 or 2 or 3, so that the resulting contact pressure formed on said couplin bod the transverse lane of the coupling body 1 against the rotor just correg y p sponds to the desired optimum conditions. By the posibetween Said Second and thud .cylmdngal Surfaces and tion and dimension of the backor counter-pressure a thud shoulder formed on sand Couplmg body on an chamber 50 it is also possible to arrange the center of Outer end of said third cylindrical Surface said Second the pressure of the Coupling body 1 so that it is just shoulder and said third shoulder each combining with close to the fluid pressure center in the control gap or Said h h and each forming a radially elxtehdihg f' level 7. The counter-pressure chamber according to the cehmc h E r chamber arranged h h" invention permits thus a very simple, very accurate and Canon t e fluld passages through couphhg sensitive adaption of the contact pressure of the control body so that pressurized fluid enters said eccentric fluid body or coupling body 1 to the respective conditions in phessure chamhers and Presses the end face the comm] level 7. pling body against the uxtaposed end face of said ro- The invention is not limited to the embodiment tor, and said first shoulder and said housing combining shown in the figures, it is merely limited by the followto form. cohmer'pressure chamber, and {11621115 for m claims connecting said counter-pressure chamber with at least I claim: one of said pressure chambers so that the fluid pressure I. Fluid-traversed axial flow piston unit comprising a afjmltted to Said 'pf Chamber affords a housing, a rotor rotatably mounted within said housing 40 blasfng effect said coupling y in the pp d secured against i l displacement, a p|ura|ity f rection to said biasing effect within said pressure chamcylinders arranged within said rotor and extending in bersthe axial direction thereof, pistons positioned within Fluid-tfavafsed aXial W pi ton unit, as set forth said cylinders for displacement in the axial direction, in claim 1, wherein said housing Combining with Said said housing forming a recess extending outwardly p g to form Said Pressme chambers and Said from one end of said rotor, a coupling body positioned counter-pressure chamber includes a cover laterally within the recess in said housing and having fluid pasenclosing aid c upling body and retaining said cousages therethrough for controlling the flow of fluid to pling body within the recess in said housing.

and from said cylinders, wherein the improvement 3. Fluid-traversed axial flow piston unit, as set forth comprises that said coupling body is arranged within in claim 1, wherein said coupling body includes a conthe recess in said housing for movement in the axial ditrol body positioned between the transverse end face of rection of said rotor, said coupling body having an end said rotor and the adjacent transverse end face of said face transverse to the axial direction of said rotor and coupling body.

juxtaposed to the adjacent transverse face of said rotor, a

Mm V ,7

Claims

1. Fluid-traversed axial flow piston unit comprising a housing, a rotor rotatably mounted within said housing and secured against axial displacement, a plurality of cylinders arranged within said rotor and extending in the axial direction thereof, pistoNs positioned within said cylinders for displacement in the axial direction, said housing forming a recess extending outwardly from one end of said rotor, a coupling body positioned within the recess in said housing and having fluid passages therethrough for controlling the flow of fluid to and from said cylinders, wherein the improvement comprises that said coupling body is arranged within the recess in said housing for movement in the axial direction of said rotor, said coupling body having an end face transverse to the axial direction of said rotor and juxtaposed to the adjacent transverse face of said rotor, said coupling body having an outer cylindrical surface extending in the axial direction of said rotor from said end face and said cylindrical surface comprising a first cylindrical surface extending from said end face, a second cylindrical surface extending from the transverse plane containing the end of said first cylindrical surface spaced from said end face and said second cylindrical surface having a greater diameter and disposed concentrically of said first cylindrical surface, and a third cylindrical surface extending outwardly from the transverse plane containing the end of said second cylindrical surface spaced outwardly from said first cylindrical surface and said third cylindrical surface being eccentric to said first and second surfaces and having a diameter less than the diameter of said first cylindrical surface so that said third cylindrical surface is disposed inwardly from said second cylindrical surface, said housing having surfaces in closely contacting relationship with said first second and third cylindrical surfaces of said coupling body, a first shoulder formed on said coupling body in the transverse plane between said first and second cylindrical surfaces, a second shoulder formed on said coupling body at the transverse plane between said second and third cylindrical surfaces and a third shoulder formed on said coupling body on an outer end of said third cylindrical surface, said second shoulder and said third shoulder each combining with said housing and each forming a radially extending eccentric fluid pressure chamber arranged in communication with the fluid passages through said coupling body so that pressurized fluid enters said eccentric fluid pressure chambers and presses the end face of said coupling body against the juxtaposed end face of said rotor, and said first shoulder and said housing combining to form a counter-pressure chamber, and means for connecting said counter-pressure chamber with at least one of said pressure chambers so that the fluid pressure admitted to said counter-pressure chamber affords a biasing effect on said coupling body in the opposite direction to said biasing effect within said pressure chambers.

2. Fluid-traversed axial flow piston unit, as set forth in claim 1, wherein said housing combining with said coupling body to form said pressure chambers and said counter-pressure chamber includes a cover laterally enclosing said coupling body and retaining said coupling body within the recess in said housing.

3. Fluid-traversed axial flow piston unit, as set forth in claim 1, wherein said coupling body includes a control body positioned between the transverse end face of said rotor and the adjacent transverse end face of said coupling body.