EP3987183A1

EP3987183A1 - Radial reciprocating engine having a ball piston

Info

Publication number: EP3987183A1
Application number: EP20735095.0A
Authority: EP
Inventors: Dirk Becher; Daniel FLACH
Original assignee: Moog GmbH
Current assignee: Moog GmbH
Priority date: 2019-06-19
Filing date: 2020-06-18
Publication date: 2022-04-27
Also published as: US20220349394A1; WO2020254501A1; DE102019116680A1; CN113994091A

Abstract

The invention relates to a radial reciprocating engine (1) having cylinders (5) arranged in a cylinder carrier (16) and a piston element (21) arranged in every cylinder (6), which piston element is connected to a guide element (22), wherein the guide element (22) runs on a sliding surface (14), as a result of which a stroke movement is imposed on the piston element (21). Because the piston element (21) is spherical, at least in the region of the piston element (21) which effects a seal during the stroke movements on inner walls (51) of the cylinder (5), a linear seal is created which allows a more compact design compared to radial pumps having cylindrical piston elements.

Description

Radial piston machine with a spherical piston

The invention relates to a radial piston machine with pistons which perform a stroke movement in a cylinder. Such radial piston machines can either be used as

Work machines serve, for example, as a pump, or as a motor. Common to all radial piston machines is that cylinders are arranged in a rotor and a piston element is arranged in each cylinder, which is connected to a guide element, the guide element running on a sliding surface and thereby forcing the piston element to move.

In radial piston machines, cylinders are arranged with their longitudinal axes radially in a rotor. Hydraulic displacement machines, which include radial piston machines, work according to the displacement principle. They can therefore be operated both as pumps and as motors if the pressure medium flow is controlled accordingly. Pumps and motors usually have the same structural design.

In the case of radial piston machines, a distinction can then still be made between radial piston machines that are acted upon from the inside and those that are acted upon from the outside. In radial piston machines with internally applied pressure, the working spaces of the cylinders are filled with a pressure medium and emptied from the inside, for example via a radial hollow shaft. The cylinders rotate around the radial hollow shaft. In this case, pistons arranged in the cylinders are supported on an outer ring, which is why they are acted upon on the inside

Radial piston machines are also referred to as externally supported radial piston machines. The outer ring on which the working pistons are supported is in an eccentric position to the hollow shaft.

In contrast to this, in the case of radial piston machines acted on from the outside, the pressure medium is fed to the cylinders radially from the outside, the pistons arranged in the cylinders being supported on a centrally arranged eccentric shaft. Outside applied

Radial piston machines are therefore also referred to as internally supported radial piston machines. In a commercially available radial piston pump, a drive shaft has a

Transferring drive torque to a cylinder star in which a plurality of radially aligned cylinders are arranged in a star shape. The cylinder star is rotatably mounted on a control pin. Pistons arranged radially in the cylinders of the cylinder star are supported by hydrostatically relieved sliding shoes on a cam ring mounted eccentrically to the cylinder star. The piston and sliding shoe are connected to each other by a ball joint and tied with a snap ring. Alternatively, the ball joint can also be flanged. An oil flow is in fluid connection with the cylinders of the cylinder star via inlet and outlet channels in the housing. When the cylinder star rotates, the pistons perform a stroke movement due to the eccentric position of the cam ring, sucking in the oil from the supply ducts in an expansion phase and pushing the oil into the discharging ducts in a compression phase.

EP 0 011 145 B1 discloses in particular a slide shoe for hydrostatic

Ring piston machines in which a shaft with a ball head is mounted in a spherical surface of a piston. The spherical surface is formed in a stepped bore penetrating the piston in the longitudinal direction. The piston itself is arranged in a cylinder bore located in a cylinder body. A snap ring holds the piston and shoe together.

In radial piston machines, cylindrical pistons in particular are used. In order to reduce the friction of the pistons on the inner walls of the cylinder, the pistons must be designed to be long in relation to their diameter. This increases the volume of such a radial piston machine, since the cylinder star must be designed with a correspondingly sufficient diameter in order to provide the appropriate installation space for the cylinders.

Since the piston machines described are designed to exert pressures of over 300 bar due to their design, the joints between the piston and the sliding block are exposed to high alternating loads. In particular, the joint can only withstand a certain maximum tensile force itself. If this force is exceeded, the joint is separated, which leads to a failure of the piston machine. The object of the invention is therefore to design a radial piston machine in such a way that the friction is reduced. Another object of the invention is to increase the permissible tensile force on the piston or to extend the service life of a piston before a defect occurs.

In a radial piston machine of the type mentioned at the outset, this object is achieved in that the piston element is spherical at least in the region of the piston element which seals the inner walls of the cylinder during the stroke movements. The spherical design of the piston element results in a sealing area which is ring-shaped, that is to say forms a closed circular line. A closed circular line causes far lower frictional forces than a flat seal with a cylindrical piston. With a rotation or tilting movement of the spherical piston element, the position of the circular sealing line changes on the surface of the at least partially spherical piston, but the diameter of the circular sealing line is constant due to the spherical shape and also the

Inside diameter of the cylinder is constant, there is always exactly the same play between the inner wall of the cylinder and the spherical piston element regardless of the position of the spherical piston element in the cylinder and regardless of the tilt angle of the spherical piston element. Cost-intensive friction-reducing

This means that coatings or tribological contours in the outer jacket of a piston can be dispensed with. Likewise, the technical effort is sufficiently perfect

Spherical shape to manufacture far less than a conventional longitudinal piston

to produce comparable performance with sufficient perfection; or in other words the manufacturing quality of a spherical piston element can be selected to be lower than that of a longitudinal piston according to the prior art in order to achieve the same purpose.

However, since the diameter of a great circle of a ball is constant regardless of the direction in which the ball is rotated, the piston element cannot get jammed in the cylinder during the stroke movement, because the diameter of the respective sealing circle remains unchanged compared to the diameter of the cylinder . At least that The partially spherical piston element is also center-centering independently due to the pressure applied over a large area. The losses of the piston machine and the wear within the piston guide in the cylinder are thus reduced.

Since the at least partially spherical shape of the spherical piston reduces the overall length of the piston in the piston axis, the rotor diameter can be selected to be smaller with the same output, so that this results in a more compact design of the

Radial piston machine results. At the same time, a higher working pressure can also be selected because the weak point of the radial piston machine is no longer determined by an articulated connection. The round bottom flask therefore eliminates the limitation of the internal pressure in the housing caused by the tensile, compressive and lateral forces acting on a joint. In piston machines with longitudinal pistons, there were limitations with regard to internal housing pressures or dynamic pressures in an external leakage oil line, which were caused, for example, by the elevated position of the hydraulic tank, filters or coolers in the leakage oil line. With the elimination of such a restriction, that expands

The range of applications for piston machines in such applications or makes certain applications possible in the first place.

From a mathematical point of view, the surface of the segmented spherical piston that comes into contact with the inner walls of the cylinder is a symmetrical spherical zone. A spherical zone is the curved outside of a spherical disk or a spherical ring, for example. A spherical disk, also known as a spherical layer, is obtained as the middle part of a solid sphere when the solid sphere is cut into three parts by two parallel planes. If the parallel planes are on different sides of the

The center of the sphere and at the same time have the same distance from the center of the sphere, then it is a symmetrical spherical disk, the outer surface of which results in a symmetrical spherical zone. A symmetrical spherical zone can also be obtained by a radial drilling through a sphere.

In a prototype of a radial piston pump according to the invention, a tilt angle α of the spherical zone on both sides of approximately 9 ° resulted on the basis of the selected geometric conditions. With an appropriate tolerance, a tilt angle would be advantageous a of about 10 °, better 12 ° should be selected. The ratio of the thickness of the spherical disk or the height H of the spherical disk to the diameter di <that of the spherical disk corresponds to twice the tangent function of the tilt angle a. At 12 ° on both sides, this results in a ratio of the thickness H of the spherical disk to the diameter di <of the spherical disk of approximately 0.4. It is of course clear to the person skilled in the art that this can only be a guide. Depending on the geometric dimensions of the radial piston machine, larger values for the tilt angle a may also be required in individual cases, or a small tilt angle a may also be sufficient. Tilt angles a of up to 20 ° seem to be technically sensible or achievable.

The at least partially spherical piston element can advantageously be connected to the guide element via a connecting element, the

Connecting element is rigidly connected to the piston and / or rigidly to the sliding element. Due to the spherical section of the piston element, the spherical

Piston element, as long as its movement is not restricted by a forced guidance, or the connecting element does not come into contact with the cylinder walls, all degrees of freedom to rotate in the cylinder, for example, to perform a pitch, yaw or roll movement. In general, the forced movement of the piston element is restricted to a nodding movement and a lifting movement. As a result, in most applications it is no longer necessary to connect the sliding element or the piston element movably to one another, since the required

Rotational movements through the at least partially spherical

Piston element can be run. The losses of the piston machine and the wear within the piston guide in the cylinder are reduced.

The person skilled in the art will select the length and diameter of the connecting element in accordance with the desired kinematics and the desired tilt angle α. In the case of radial piston machines in particular, the sliding shoe has a rounded contour that is matched to the pivot angle and the inside diameter of the cylinder. The contour of the sliding shoe only needs to be able to map the kinematic pivoting movement of the sliding shoe due to the design. The piston according to the invention with at least partially spherical piston element can be produced, for example, by means of turning, milling or grinding. Alternatively, production, also of individual parts, is the same

can be put together by means of casting, additive manufacturing, MIM technology, sintering or the use of formed parts.

In special applications, the piston element can of course also be connected to the connecting element by a joint and / or the connecting element can be connected to the guide element by a joint.

In the case of the radial piston machine, this can be an internally acted upon

Act radial piston machine or an externally loaded radial piston machine. In the case of an internally acted upon radial piston machine, the guide elements run on a cam ring which is arranged eccentrically to the radial axis of the cylinder carrier. In the case of the externally loaded radial piston machine, the guide elements run on an eccentric shaft rotating in the interior of the cylinder carrier eccentrically to the center of the cylinder carrier.

The invention will now be illustrated with reference to in the drawings

Embodiments described and explained in more detail. Show it:

1 shows a radial piston machine with the round piston according to the invention

2 shows a round bottom flask according to the invention

3A, 3B and 3C show a section from a radial piston machine

4 shows an externally supported rotary piston machine with one according to the invention

Round bottom flask

The invention relates to a novel piston for a radial piston machine, wherein the radial piston machine, apart from the novel piston, can be a radial piston machine according to the prior art. Due to the shape of the piston, it is referred to below as a round bottom flask, although the part of the round bottom flask which comes into contact with an inner wall of a hollow cylinder, strictly speaking, only a segment of a sphere must correspond. In this sense, when a spherical shape is spoken of in the following for linguistic simplification, it is intended to mean only a section

Spherical shape to be included.

FIG. 1 shows a simplified view of a radial piston machine 1 loaded on the inside and supported on the outside, partially in section. In general, if no special design features prevent this, this radial piston machine can be operated both as a pump and as a motor. The following is representative of both

Operating modes the operating mode is described as a pump. The principle of such

Radial piston pump is known to the person skilled in the art, so that only the essential parts are described here insofar as they are necessary for understanding the invention. The

Radial piston pump 1 has a housing 10 which is approximately cup-shaped and is closed by a housing cover, not shown. In the interior 11 of the housing 10 there is mounted a cam ring 12 which can be displaced in an adjustment direction 3 and which is mounted with its side faces between the shoulders of the housing bottom and the housing cover with appropriate play. Due to the sectional view, only the side surface 13 of the cam ring 12 facing the viewer is visible in FIG. 1, which when the housing 10 is closed comes to rest on the inside of the housing cover. The shoulders of the housing bottom are covered by the cam ring 12 in this illustration, or are omitted for the sake of clarity.

The inner circumference of the cam ring 12 forms a sliding surface 14 for sliding shoes 22, on which ball pistons 21 are supported and which are movably guided in radially extending bores 5 of a cylinder carrier. Since the cylinder carrier is set in rotary motion in this design, the cylinder carrier is referred to below as rotor 16. Due to the

When these bores interact with the spherical pistons 21, these bores are referred to below as piston bore 5.

The piston bores 5 are distributed rotationally symmetrically around the radial axis 17 of the rotor 16. The number of piston bores partly depends on the size of the rotor 16 or on the displacement or absorption volume of the radial piston pump 1. In the example shown here of a radial piston pump with a displacement or Displacement volume of 19 cm ³ / rev at a maximum operating pressure of 350 bar, seven piston bores 5 are provided in the rotor 16.

The rotor 16 is fixed in a control pin bore of the housing 10

arranged control pin 18 and is set in rotation by a drive shaft. In the operating mode as a motor, that generated by the spherical piston 21 is

Transferring torque to the drive shaft, which is now technically correctly referred to as the output shaft. The spherical piston 21 seals a working space of the

Radial piston machine 1 from the interior 11 of the radial piston machine 1, the working space within the piston bore 5 extending from the spherical piston 21 as an extension of the piston bore in the direction of the control pin 18 to the control pin 18. The control pin bore and the drive shaft are covered in FIG. 1 by the control pin 18, or on the cut-off side of the diagram, and are therefore not visible.

Ball piston 21 and slide shoe 22 are connected to one another by means of a piston rod 23. The piston rod 23 can also be designed as a connecting rod, that is to say the connecting rod can be movably connected to the spherical piston 21 via a joint arranged on the spherical piston 21. Alternatively or in addition, the piston rod 23 or the connecting rod can be movably connected to the sliding shoe 22 by a joint arranged on the sliding shoe 22. A synergetic effect results, however, in particular when the piston rod 23 is connected both rigidly to the spherical piston 21 and rigidly to the slide shoe 22. In this case, the spherical shape of the spherical piston 21 is used not only as a seal between the working space and the interior 11 of the radial piston machine 1, but also as the sole joint. This has the particular advantage that a weakening of the combination of ball piston 21, piston rod 23 and slide shoe 22 by joints is avoided. Particularly in the case of a rigid connection between the round bottom flask 21 and the slide shoe 22, the piston rod 23 can be designed as a taper of the round bottom flask 21 such that the piston rod achieves a high level of strength.

The spherical shape, or the spherical segment shape, allows the spherical piston 21 to move within the piston bore 5, positively guided by the slide shoe 22 in particular to execute a limited tilting movement in or against the direction of rotation of the rotor 16 in its plane of rotation. The tilting movement of the round piston 21 is limited by the piston rod 23, which can come to a stop on the piston bore walls, in particular the piston bore openings that point towards the stroke ring 12. As a result of the positive guidance of the sliding blocks 22 on both sides between ring strips (not shown) on the inside of the cam ring 12, the ball piston 21 is not subjected to any lateral movements.

The cam ring 12 can be displaced in the interior space 11 transversely to the control pin 18 for the purpose of changing the delivery rate by means of two actuating pistons 31, 32 in the adjustment direction 3. The two actuating pistons 31, 32 act at two diametrically opposite points on the

Outer circumference of the stroke ring 12 with two adjustable sliding blocks 33, 34.

In the control pin 18, an eccentric, parallel to the central axis of the control pin 18 longitudinally extending first low-pressure channel 41 and a second low-pressure channel 42, each of which opens into a first circumferential groove, hereinafter referred to as low-pressure slot 45, on the control pin 21 are formed for the supply of a pressure medium. Furthermore, an eccentric, parallel to the central axis of the control pin 21, a first high-pressure channel 43 and a second one are in each case for the discharge of the pressure medium

High-pressure channel 44 is formed, each of which opens into a second circumferential groove, hereinafter referred to as high-pressure slot 46, on the control pin 21. The low-pressure slot 45 and the high-pressure slot 46 are located in the mouth area of the piston bore 5 of the rotor 16 that accommodates the round pistons 21 a high pressure connection of the radial piston pump 1. low pressure connection and

The high pressure connection of the radial piston pump 1 are not visible in this drawing because they are located on the back of the housing base from the viewer. In this exemplary embodiment, two low-pressure channels 41, 42 and two high-pressure channels 43, 44 were selected because this, in conjunction with a known special geometric configuration of the control pin 18, offers advantages in terms of flow technology. To that To fulfill the basic principle of the radial piston machine 1, however, a single low-pressure channel 41 and a single high-pressure channel 43 would be sufficient.

During operation of the radial piston pump 1, that is to say when the rotor 16 is set in rotation, the ball pistons 21 are entrained in the piston bores 5 in the direction of the rotational movement. Due to the rotary movement of the rotor 16, a centrifugal force acts on the spherical pistons 21 guided in the piston bores 5, whereby the respective spherical piston 21 is pressed radially outward in the piston bores 5 until the sliding shoes 22 of the spherical piston 21 with their ends facing away from the control pin 18 come to rest on the stroke ring 12. In the following, the term "outward" denotes a direction starting from the axis of rotation 17 of the rotor 16 from the

The axis of rotation 17 of the rotor 16 points away, while the expression “inward” denotes a direction which points in the direction of the axis of rotation 17 of the rotor 16.

Equally, the term “outside” denotes a relative position of an object with a greater radial distance from the axis of rotation 17 of the rotor 16 than an object which has a radially smaller distance from the axis of rotation 17 of the rotor 16.

In the event that the position of the cam ring 12 is set such that the imaginary axis of the cam ring 12 is arranged identically to the axis of rotation 17 of the rotor 16, the distance D between the outside of the rotor 16 and the inside of the cam ring 12 is in each position of the Rotor 16 the same. In this case, the radial distance between the spherical pistons 21 with respect to the axis of rotation 17 does not change during a rotary movement of the rotor 16, so that the spherical pistons 21 do not perform a stroke within the respective piston bore 5.

If the cam ring 12 is adjusted so that the imaginary axis 19 of the cam ring 12 is no longer identical to the axis of rotation 17 of the rotor 16, the distance D between the rotor 16 and the cam ring 12 is changed cyclically when the rotor 16 rotates within the cam ring 12 . This change in distance has the effect that when the distance D between the cam ring 12 and the rotor 16 decreases, the sliding surface 14 of the cam ring 12 exerts a counterforce on the sliding shoes 22, which presses the spherical pistons 21 inward against the centrifugal force. In contrast, when the distance D between the cam ring 12 and the rotor 16 increases the cam ring 12, the sliding shoe 22 of the respective spherical piston 21 and the spherical piston 21 are pressed radially outward by the centrifugal force as well as by a compressive force, so that the sliding shoe 22 in question does not lose contact with the sliding surface 14 of the cam ring 12. Accordingly, the ball piston 21 during a

Full rotation of the rotor 16 imposes two periodic stroke movements, a first stroke movement radially outward, in which the volume of the working space increases steadily and which is therefore referred to below as the expansion phase, and a second stroke movement radially inward, in the direction of the control pin 18, at which the volume of the working space is steadily decreasing, and which is therefore referred to below as

Compression phase is called.

The low-pressure slot 45 is arranged on the control pin 18 such that the low-pressure slot 45 and thus also the first and second low-pressure channels 41, 42 are in fluid connection with the respective spherical piston 21 in the expansion phase. The lifting movement of the spherical piston 21 radially outward therefore generates a suction effect which sucks in the pressure medium applied to the low-pressure connection and fills the working space of the piston bore 5 with pressure medium. Furthermore, the high-pressure slot 46 is arranged on the control pin 21 in such a way that during the compression phase the

High pressure slot 46 and thus also the first and second high pressure channels 43, 44 are in fluid connection with the respective spherical piston 21. The lifting movement of the

Ball piston 21 radially inward therefore produces a pressure effect which the im

Working chamber of the relevant piston bore 5 pushes accumulated pressure medium through the high-pressure slot 46 into the high-pressure channels 43, 44.

In the operating mode as a pump, the cyclical stroke movement of the ball piston 21 thus forces a pressure medium flow from the low-pressure to the high-pressure channel. In the operating mode as a motor, however, there is a pressure medium flow from the high pressure to the low pressure channel.Depending on the operating mode of the radial piston machine 1 as a pump or as a motor, the radial piston machine is given a pressure energy in pumping mode by a drive torque, or pressure energy is withdrawn and converted into a motor mode

Output torque converted. FIG. 2 shows a piston element 2 which comprises the spherical piston 21 and the sliding shoe 22, which are rigidly connected to one another by means of the piston rod 23. A bore 29 runs through a longitudinal axis of the spherical piston 21, the piston axis 20, through which during operation of the piston machine 1 pressure medium, which is located in the piston bore 5, is pressed onto a shoe sole 26. The sliding shoe sole 26 is thereby forced into a hydrostatic equilibrium, in which a friction-reducing film of pressure medium is formed between the sliding sole and sliding surface 14. At a

Radial piston machine 1, the sliding shoe sole 26 is adapted to the geometry of the sliding surface 14, that is to say it is curved outward. Furthermore, as shown in FIG. 3, the sliding shoe 22 has a front sliding shoe end 27 relative to its piston axis 20, viewed in the direction of rotation, and a rear sliding shoe end 28 opposite to this.

In principle, apart from the piston rod 23, the spherical piston 21 could assume a completely spherical shape. An ideally perfect spherical shape is required, however, only at the points of the spherical piston 21 which come into contact with the piston bore wall 51 in order to seal the piston bore space, or, to be more precise, almost come into contact. The great circle of the spherical piston 21, which is perpendicular to the piston axis 20, is referred to below as the center circle 24. If the piston axis 20 coincides with the piston bore axis 50, then the extension of the plane spanned by the central circle 24 cuts the piston bore beyond the central circle 24 in a cutting circle, which is referred to below as the sealing circle because it defines the working space of the piston bore 5 with respect to the interior space 11 of the piston engine 1 actually closes. The sum of all sealing circles that can form during one full revolution defines a spherical zone 250, that is, the outer circumference of a spherical disk in which the at least partially spherical piston element 71 must correspond to an ideal spherical shape.

In order to prevent the spherical piston 21 from jamming in the piston bore 5, the diameter di <of the center circle 24 is selected to be slightly smaller than the diameter of the piston bore 5. With a center circle 24 that is 10 μm smaller, for example, results in a central position of the center circle 24 and piston bore wall 51 all around a clearance of 5pm between working circle and center circle. This results from the viscosity of the pressure medium A sufficient seal between the working space and the interior 11 of the piston machine 1. The person skilled in the art will of course select the clearance between the spherical piston 21 and the piston bore wall 51 so that it is ideally suited for the given dimensions and the particular application.

3A shows the spherical piston 21 at its outer dead point, that is to say during the transition from the expansion phase to the compression phase. At the outer dead center is through the

Eccentric position of the cam ring 12, the distance between the rotor 16 and the sliding surface 14 of the cam ring 12 at a maximum distance D _m ax. By centrifugal force, respectively

The spherical piston 21 is generally aligned at its outer dead center in such a way that the piston axis 20 with the

Piston bore axis 50 more or less coincides. The geometry of the individual elements of the annular piston machine 1 are selected so that the center circle 24 of the spherical piston 21 is close to the outer piston bore opening 52, but still sufficiently deep in the piston bore wall 51 to ensure that the piston 2 is safely guided within the piston bore 5 and a To ensure sealing between piston bore wall 51 and center circle 24.

From the outer dead center, the piston 2 is then rotated further by the forces acting from the piston bore wall 51 on the center circle 24 of the spherical piston 21

Direction of rotation 15 of rotor 16 taken along. Since the distance between the stroke ring 12 and the rotor 16 decreases increasingly in the compression phase, the piston 2 is guided deeper inward into the relevant piston bore 5. Due to the eccentricity between cam ring 12 and rotor 16, the distance between cam ring 12 and rotor 16 at the position of the front shoe end 27 is different from the distance between cam ring 12 and rotor 16 at the position of the rear shoe end 27. This creates a force, which acts in the compression phase from the front shoe end 27 to the rear shoe end 28. As a result, the piston 2 of the spherical piston 21 in the

The compression phase is tilted about its center point Z opposite to the direction of rotation 15 of the rotor 16. As a result of this tilting movement, the center circle 24 rotates on the piston bore wall 51 facing away from the direction of rotation in the direction of the outer one

Piston bore opening 52 and at the one facing the direction of rotation Piston bore wall 51 in the direction of the inner piston bore opening 53. The

The center circle 24 of the spherical piston 21 thus loses contact with the piston bore wall 51. The spherical shape of the spherical piston 21 now creates a new great circle of the

Ball piston 21 to the sealing circle 25, specifically that great circle which comes to lie in a respective position of the ball piston 21 in the piston bore 5 perpendicular to the piston bore axis 50. As a geometric consequence, the center point of each sealing circle is identical to the center point Z of the spherical piston 21.

In the transition from inner dead center to exterior IT AT dead center of the piston 2, that is in the expansion phase, the distance between the outer side of the rotor 16 and the inner side of the cam ring 12 is increased steadily from D to D _m in _m ax. In the expansion phase, the distance D at the front shoe end 27 is therefore always greater than at the rear

Sliding shoe end 28. As a result, the counterforce component exerted by the stroke ring 12 on the piston 2 is lower at the front sliding shoe end 27 than at the rear

Slide shoe end 28. Consequently, the piston 2 deviates in the direction of the front slide shoe end 27 than in the direction of the direction of rotation 15 of the rotor 16. Seen in this way, the

Expansion phase of the tilt angle a of the rotational movement 15 ahead. In the

Compression phase, i.e. at the transition from outer dead center AT to inner

Dead center IT reverses these relationships and the tilt angle a hurries

Rotational movement 15 of the rotor 16 after. As a result of this tilting movement, the piston axis 20 is tilted by an angle α with respect to the piston bore axis 50. These

Tilting movement has its greatest extent on the one hand, as shown in FIG. 3B, in approximately half of the movement between inner dead center IT and outer dead center AT of piston 2, or in approximately half of the movement of piston 2 between the outer ones

Dead center AT and inner dead center IT.

Finally, FIG. 3C shows the spherical piston 2 at its inner dead center when the distance between the cam ring 12 and the rotor 16 has reached a minimum distance D _min . As can be seen, a piston head 210, which adjoins the partially spherical piston 21 on the side facing away from the piston rod 23, is essentially frusto-spherical, so that the piston head 210 at the inner dead center IT largely adjoins a funnel-shaped transition from the piston bore 5 can adapt to the control pin 18. This advantageously minimizes the dead volume in the inner dead center IT.

According to geometric laws, this angle a is also equal to the angle a between the plane of the sealing circle and the plane of the center circle. For manufacturing reasons, but also because of a possible change in the direction of rotation, the spherical surface of the

The spherical piston 21 is designed symmetrically so that the spherical section or the spherical zone 250, as shown in FIG. 2, comprises at least an angle between -a and + a. Furthermore, depending on the selected geometry of the round piston machine 1 and the piston 2, the tapering at the position of the piston rod 23 is to be selected so that the piston rod does not come into contact with the piston bore walls 51 or the rotor 16 during operation to prevent damage to the piston bore rod 23 , or rotor 16 and piston bore walls 51 to avoid.

The invention is also suitable for internally supported radial piston machines. Fig. 4 shows the basic structure of an internally supported radial piston machine 6, in which

Low-pressure channels and high-pressure channels are arranged on the outside 66 of a piston carrier 61, which in this case is stationary. The formation of the low pressure channels and high pressure channels in an internally supported radial piston machine 6 are the

Known to those skilled in the art, so that, for the sake of clarity, they are not explicitly shown in FIG. 4.

The piston carrier 61 forms a receptacle for a plurality of piston bores 5, which are arranged radially around a center point 60 of the piston carrier 61 at the same distance from one another, so that the extensions of the longitudinal axes 50 of the piston bores 5 intersect at the center point 60 of the piston carrier 61. The

For the sake of clarity, only three piston bores 5 are shown in the drawing FIG. An odd number between three and nine is common, but the person skilled in the art will select a suitable number of piston bores depending on the size and performance of the radial piston pump. The interior of the piston carrier 61 is designed as a cavity in which an eccentric shaft 63 rotates about the piston carrier center point 60. The eccentric center point E is located at a distance D from the piston carrier center point 60, as a result of which the eccentric center point E rotates on a circular path 64 around the piston carrier center point 60.

In each of the piston bores 5, a round piston according to the invention is arranged, which is essentially formed from a spherical piston element 71, a piston rod 73 and a sliding shoe 72. Each round bottom flask is served by one each

The restoring element, which in this exemplary embodiment are designed as helical springs 74, is pressed in the direction of the eccentric shaft 63 or the eccentric center point E, that is to say into the interior of the radial piston machine. With the internally supported

Radial piston machine 6 seals the at least partially spherical

Piston element 71 from the working space of the radial piston machine 6 inwards. The working space in which the pressure medium is supplied or discharged is thus the part of the piston bore 5 that extends between the outer periphery 66 of the

Piston carrier 61 and the at least partially spherical piston element 71 extends.

The outer circumference of the eccentric shaft 63 forms a sliding surface 65 on which the sliding shoes 72 of the round pistons 7 are supported with sliding soles 76. Since the sliding surface 65 of the eccentric shaft is convex in this embodiment, the

Shoe soles 76 correspondingly concave. During one full revolution of the eccentric shaft 63, two periodic stroke movements are forced on the ball piston 7 by the sliding shoes 72 sliding on the eccentric shaft 63, a first one

Lifting movement radially outwards, in which the volume of the working space is steadily reduced and which is therefore referred to below as the compression phase, and a second lifting movement radially inwards, in the direction of the piston carrier center point 60, in which the volume of the working space steadily increases, and the therefore it is referred to as the expansion phase in the following. The distance D between the eccentric center point E and the piston carrier center point 60 determines the amplitude of the piston stroke.

As with the externally supported radial piston machine 1 described in the first embodiment, the round pistons 7 lead in the expansion and Compression phases from a tilting movement. Due to the piston element 71, which is at least partially spherical, a circular sealing circle between an inner wall 51 of the piston bore 5 and a spherical zone 75 of the round piston 7 is maintained at all times. In this exemplary embodiment, too, a play between the ball piston 7 and the piston bore wall 51 prevents the ball piston 7 from jamming.

Claims

1. Radial piston machine (1) with cylinders (5) arranged in a cylinder carrier (16) and a piston element (21) arranged in each cylinder (5) which is connected to a guide element (22), the guide element (22) on a sliding surface (14) expires, whereby the piston element (21) is forced into a stroke movement, characterized in that

the piston element (21) is spherical at least in the area of the piston element (21) which seals the inner walls (51) of the cylinder (5) during the stroke movements.

2. Radial piston machine (1) according to claim 1,

characterized in that

the piston element (21) is connected to the guide element (22) via a connecting element (23), the connecting element (22) being rigidly connected to the piston element (21).

3. Radial piston machine (1) according to claim 1,

characterized in that

the piston element (21) is connected to the guide element (22) via a connecting element (23), the connecting element (23) being rigidly connected to the guide element (22).

4. Radial piston machine (1) according to one of claims 1, 2 or 3

characterized in that

the guide element is a sliding shoe (22) which runs on a sliding surface (14).

5. Radial piston machine according to one of claims 1 - 4,

characterized in that

the radial piston rail is an externally supported radial piston machine.

6. Radial piston machine (1) according to claim 5 characterized in that

the radial piston machine is a radial piston machine in which the guide elements (22) run on a cam ring (12).

7. Radial piston machine according to one of claims 1 - 4,

characterized in that

the radial piston rail is an internally supported radial piston machine.

8. Radial piston machine (1) according to claim 7

characterized in that

in the internally supported radial piston machine, the guide elements (22) run on an eccentric shaft (63).

9. Radial piston machine according to one of claims 1 - 8,

characterized in that

the area of the piston element (21), which at least in the area of the

Piston element (21), which during the stroke movements on the inner walls (51) of the cylinder (5) causes a seal, is a symmetrical spherical zone (250).

10. Radial piston machine according to claim 9,

characterized in that the symmetrical spherical zone comprises at least a tilting range of 20 ° to both sides.