Axial piston machine with partially spherical seal ring

Abstract

The invention relates to an axial piston machine, in which pistons perform a stroke movement in a cylinder block, and in which the pistons have a seal ring carrier for the seal rings. In order to improve the robustness, wear resistance, friction and stick-slip, according to the invention the seal rings are spherical, wherein the radius of curvature of the seal rings, which are configured in a spherical manner in the region, essentially corresponds to half the diameter of the inner wall of the cylinder block.

Description

[0001] The present invention relates to an axial piston machine in which a piston performs a stroke motion in a cylinder, the piston having a sealing ring bracket for a sealing ring.

[0002] What all axial piston presses have in common is that a cylinder body is arranged around the cylinder axis in a circle, with the cylinder axis parallel to the cylinder axis. Each cylinder body houses a piston with a piston head, wherein the end of the piston opposite the piston head is fixed to or rests against the plate around the plate axis. When the cylinder axis and the plate axis intersect at an angle, the piston is forced to perform a stroke motion during the rotation of the cylinder and / or the plate.

[0003] Axial piston presses are a type of hydraulic positive displacement press, which operates based on the positive displacement principle. Therefore, when the flow of the pressure medium is controlled accordingly, these hydraulic displacement presses can function as both pumps and motors. Pumps and motors typically share the same design. In the case of a motor, the pressure medium is supplied under pressure to approximately the first half of the cylinder, and the piston is pushed towards the plate by the pressure within the cylinder and / or by a mechanical connection to the plate. If the angle between the cylinder axis and the plate axis is not zero, a tangential force component is generated. Depending on the design, this tangential force component causes the cylinder or plate to rotate, thus generating drive.

[0004] In the case of a pump, the cylinder axis or plate rotates according to the pump's design. If the angle between the cylinder axis and the swashplate axis is not zero, the constantly changing distance between the piston and the swashplate forces the piston to perform a vibratory stroke, during which expansion and compression phases alternate. During the downward motion (i.e., the expansion phase), the piston allows each cylinder to fill with the pressurized medium, which is then ejected from the bottom of the piston during the subsequent upward motion (i.e., the compression phase), thus generating a volumetric flow rate of the pressurized medium.

[0005] A prototype of an axial piston machine with a piston plate mounted on a swashplate and floating pistons is known from the following conference paper: “A NOVEL AXIAL PISTON PUMP / MOTOR PRINCIPLE WITH FLOATING PISTONS DESIGNAND TESTING”, Liselott Ericson and Jonas Forsell, Proceedings of the Bath / ASME Fluid Power and Motion Control Symposium, 12-14 September 2018, Bath, UK. The sealing between the piston chamber and the low-pressure housing interior of the hydrostatic press is achieved by a sealing ring, which is introduced between the piston and the cylinder. This sealing ring is made of a relatively soft, deformable material. The conference paper discloses a hybrid material composed of polytetrafluoroethylene (PTFE) and bronze. This sealing ring has a spherical sealing surface, with its outer diameter chosen to be slightly larger than the inner diameter of the cylinder to ensure a sealing effect even during deformation. The curvature diameter of the spherical sealing surface is significantly smaller than the piston diameter. Due to the inclined piston plate, the sealing ring moves along the inner wall of the cylinder at the piston speed and additionally moves in a circular trajectory relative to the piston bore axis. The inclined position of the sealing ring creates a gap in the cylindrical piston bore. To compensate for this gap, the diameter of the sealing ring is chosen to be approximately 1% larger than the cylinder diameter. In the piston proposed in the conference report, the sealing ring is supported by a support ring on the side away from the cylinder. The outer diameter of the support ring is smaller than that of the sealing ring, and it is made of polyetheretherketone (PEEK), a material that is harder than the sealing ring.

[0006] However, tests show that during operation, especially under high pressure, with a large angle between the cylinder axis and the piston plate axis, and at high speeds, the sealing ring tends to be squeezed towards the unpressurized interior of the housing, i.e., into the gap between the piston and the piston bore. Due to the tilted position of the piston axis relative to the piston bore axis, an axial offset occurs kinematically between the piston and the sealing ring. This axial offset increases the risk of the sealing ring being squeezed on the side farther from the piston.

[0007] For example, with an 8° swing angle, the sealing ring is stretched and compressed twice during a complete round trip, by approximately 1% of its diameter, which can lead to material fatigue in the long run. This can potentially cause seal failure. However, studies have also shown that, especially at low speeds, the increased preload, fracture torque, and stick-slip effect of the sealing ring can cause uneven machine operation. These effects are particularly detrimental in speed control applications. In speed control applications, stable system pressure cannot be achieved by applying a specific speed (even very low speeds). These effects significantly increase the difficulty of control.

[0008] DE 199 06 690A1 also provides a sealing ring for sealing a gap between a generally cylindrical outer surface of a body and a coaxially surrounding generally cylindrical wall surface resisting the pressure of a medium, wherein the pressure on one side is higher than on the other side, particularly for piston seals of hydraulic pumps or hydraulic motors, wherein at least one sealing ring is received in a groove of the piston.

[0009] Therefore, the objective of this invention is to design an axial piston machine of the type described above to ensure low friction, low pulsation, and reliable operation at the sealing position of the piston bore throughout the entire operating range of the machine.

[0010] In the aforementioned type of axial piston press, this task is achieved by ensuring that the sealing ring is spherical in at least one region, providing a seal against the cylinder wall during the stroke, i.e., possessing a constant radius of curvature in at least that region. The radius of curvature of the spherical sealing ring in that region is substantially equivalent to half the cylinder diameter. In practice, the diameter of the sealing ring is slightly smaller than the cylinder diameter to ensure sufficient clearance between the cylinder wall and the sealing ring. For example, this clearance is approximately 10 μm.

[0011] Because the sealing ring has a spherical structure within the region, where the radius of curvature of the spherical sealing ring within the region is approximately half the cylinder diameter, the resulting sealing area is annular, forming a closed circumference. The frictional force generated by the closed circumference is far less than that of a seal comparable to a planar seal due to unfavorable dimensions and / or geometry. While the position of the circular sealing line on the surface of the at least partially spherical sealing ring changes during rotation or tilting of the spherical sealing ring, the diameter of this circular sealing line remains constant due to the spherical shape and the constant inner diameter of the cylinder. Therefore, regardless of the position of the spherical piston within the cylinder and its tilt angle, as long as the sealing ring bracket allows for balanced lateral movement of the sealing ring relative to the piston axis, the resulting clearance between the inner wall of the cylinder and the partially spherical sealing element is always identical. This balanced movement is necessary because, during cylinder rotation, the distance between the sealing ring and the cylinder axis cyclically changes based on the tilt position of the piston axis relative to the cylinder axis.

[0012] By using a sealing ring support that allows the sealing ring to move laterally across the piston's longitudinal axis, the sealing ring can avoid radial and tangential forces transverse to the piston axis, forces generated by the relative movement between the cylinder wall and the sealing ring. While this is possible in the prior art, because the radius of curvature of the resilient sealing ring is much smaller than the cylinder's inner diameter, if the cylinder's inner diameter and the sealing ring's diameter are chosen to be approximately the same, the sealing line of the sealing ring will only ideally correspond to the cylinder's inner diameter twice during rotation. Between these two ideal positions, the sealing circle will be much smaller than the cylinder's inner diameter, thus leading to leakage. Therefore, in the prior art, the diameter of the sealing ring is chosen to be slightly larger than the cylinder's inner diameter. Due to the excessive size of the resilient sealing ring, these dynamic differences are partially absorbed by the reversible deformation of the resilient sealing ring; however, this results in a planar sealing surface at some locations within the cylinder, while gaps appear between the sealing ring and the cylinder's inner wall at other locations. However, if the diameter of the sealing ring is larger than the cylinder's inner diameter, when a sealing ring made of a rigid material is chosen, the sealing ring will inevitably become stuck.

[0013] According to the design of the present invention, a sealing surface is now created at each position between the inner wall of the cylinder and the sealing ring during the rotation of the cylinder barrel. This sealing surface is approximately circumferential, wherein the gap between the sealing ring and the cylinder wall remains constant during the stroke. This allows for the selection of a non-deformable material for the sealing ring, preventing it from being extruded under high pressure and / or high-speed cylinder rotation. Simultaneously or alternatively, the sealing ring can be made of a particularly wear-resistant material. This results in a longer service life for the sealing ring, thus requiring fewer replacements or none at all during the service life of the piston press.

[0014] Because the diameter of the great circle remains constant regardless of the direction of rotation of the sphere, the piston elements will not get stuck in the cylinder during their stroke and simultaneous balancing motion, as the diameter of their respective sealing circumferences remains unchanged compared to the cylinder diameter. Therefore, the losses and wear of the axial piston machine are reduced.

[0015] In one embodiment, the sealing ring is made of ceramic. Suitable ceramics include oxide ceramics, such as alumina (Al₂O₃) or zirconium dioxide (ZrO₂), or non-oxide ceramics, such as silicon carbide (SiC) or silicon nitride (Si₃N₄).

[0016] In another embodiment, the sealing ring bracket includes a pin, and the sealing ring has a central inner opening corresponding to the pin, wherein the inner diameter of the sealing ring is selected to be larger than the pin diameter. Therefore, the difference between the pin diameter and the inner diameter of the sealing ring can be selected according to the desired horizontal clearance, i.e., a clearance transverse to the piston's longitudinal axis.

[0017] In another embodiment of the axial piston mechanism, the piston is designed to achieve pressure balance between the interior of the piston and the interior of the sealing ring. For example, this pressure balance can be achieved by fixing the sealing ring with a vertical clearance (i.e., a clearance in the direction of the piston's longitudinal axis) in a sealing bracket, such that the pressure within the sealing ring bracket dynamically adapts to the pressure within the piston chamber through the gap. In an alternative embodiment, pressure balance between the interior of the piston and the interior of the sealing ring can be achieved via one or more perforations on the cap. In another embodiment, alternatively or additionally, a pressure balancing hole is provided, extending from the top surface of the pin to the interior of the sealing ring. This allows for directional deformation of the sealing ring using different geometries on the outer and inner surfaces of the sealing ring, thereby improving the sealing effect of the sealing ring.

[0018] When the geometry of the outer surface of the sealing ring differs from that of the inner surface, the normal force exerted on the sealing ring by the pressure medium within the piston chamber differs from the normal force exerted on the inner side of the sealing ring within the sealing ring holder. This can lead to deformation of the sealing ring, especially under very high pressures of the pressure medium. In another embodiment, this deformation, initially considered undesirable, is even reinforced, wherein the central inner opening of the sealing ring has a circumferential flange-like groove.

[0019] This flange-like groove allows the sealing ring to expand additionally within the piston chamber under high internal pressure conditions. It has been shown that even with robust cylinder construction, if the piston chamber is connected to the high-pressure side, this internal pressure causes expansion or deformation of the corresponding cylinder. This unilateral expansion leads to an increase in the gap between the cylinder's inner wall and the sealing ring. Therefore, it makes sense to design the sealing ring geometry such that it can also expand, thus keeping the gap between the piston bore and the sealing ring almost constant. Since the working pressure within the piston chamber acts on the internal geometry of the sealing ring at the same height, the sealing ring will expand accordingly. Now, the shape or wall thickness of the sealing ring's inner profile can be designed so that the degree of expansion of the sealing ring is exactly equivalent to the inner diameter of the piston bore in the cylinder. Thus, the gap remains constant. In the first approximation, this can be achieved through a flange-like groove in the sealing ring. At very high pressures, such as 350 bar and above, the cross-sectional shape of the sealing ring can be precisely determined through deformation analysis using the finite element method, thus allowing for an optimized design of the sealing ring's geometry.

[0020] In an alternative implementation, the central inner opening of the sealing ring has a stepped curve. A first stage has a first inner diameter, and a second stage has a second inner diameter, wherein the second inner diameter is chosen to be larger than the first inner diameter. The first inner diameter corresponds to the inner diameter of a non-stepped sealing ring. Therefore, the first inner diameter can be matched with the pin diameter of the sealing ring holder, allowing the first inner diameter to be optimized for torque transmission between the cylinder and piston / piston plate via the contact surface of the sealing ring and pin. However, since the second inner diameter does not participate in torque transmission, it can be optimized for optimal expansion to accommodate the continuously expanding piston bore under increasing high operating pressures.

[0021] In one embodiment, the sealing ring is made of a metal, such as iron, steel alloy, or other metal alloy. Hardened steels with a surface hardness greater than 48 Rockwell hardness (HRC), particularly quenched and tempered steels, such as 100Cr6 with a surface hardness of approximately 62 HRC, and surface-hardened steels, such as 16MnCr5 with a surface hardness of approximately 60 HRC, are particularly suitable for this purpose. Compared to many ceramics, sealing rings made of metal have the advantage that, with relatively thin walls, the sealing ring expands due to the internal pressure of the piston, thereby contributing to a better seal between the sealing ring and the piston chamber wall. However, this effect can also be achieved using ceramics with an elastic modulus similar to that of steel. For example, for ceramics made of zirconia (ZrO2), rings made of zirconia (ZrO2) and steel expand in most cases.

[0022] In another embodiment, the surface properties of the sealing ring made of metal are improved in terms of surface hardness, coefficient of friction and wear resistance through downstream processes such as nitriding, soft nitriding or hard material coating.

[0023] The sealing ring obtained by the spherical disc is not necessarily symmetrical in the axial direction. Due to the asymmetrical geometry of the spherical disc, the pressure-related clearance between the spherical ring and the cylinder wall can be kept small to achieve the lowest possible leakage. Through this design and the applied pump pressure, the spherical ring expands directionally.

[0024] In another embodiment, the sealing ring is secured in a sealing ring holder with a cap to prevent movement along the longitudinal axis of the piston. The cap forms the bottom of the piston and, during the piston's downward movement (i.e., during the expansion phase), restricts the sealing ring's movement toward the cap, except for a planned vertical clearance.

[0025] In another implementation, the cap is secured to the piston with screws or by clamping or pressing. These are methods of securing the cap so that it can be removed during maintenance, thus simplifying replacement when the sealing ring wears out.

[0026] Mathematically, the surface of a partially spherical sealing ring that contacts the inner wall of the cylinder is a symmetrical spherical region. This spherical region is, for example, the curved outer side of a spherical disc or ring. A spherical disc, or spherical layer, is obtained as the middle portion of a solid sphere when it is cut into three parts by two parallel planes. If the parallel planes are located on different sides of the sphere's midpoint and are at the same distance from the midpoint, then it is a symmetrical spherical disc, and its outer surface produces a symmetrical spherical region. If the two parallel cutting planes are at different distances from the center of the sphere, an asymmetrical spherical disc can also be easily manufactured in this way. Because the technical cost of manufacturing a sufficiently perfect sphere is relatively low, such sealing rings can be manufactured at a relatively low cost from solid spheres of a corresponding diameter by cutting off spherical portions from both sides of a selected great circle, for example by milling, to produce the desired symmetrical or asymmetrical spherical disc. Such solid spheres, for example, are supplied as standard components for spherical joints and rotary bearings with corresponding manufacturing precision, and are therefore generally available at low cost.

[0027] A central opening of the desired diameter can then be created in the spherical disk obtained in this way through a hole, allowing the sealing ring to be received in the pin. As set in the alternative implementation, the interior of the sealing disk can be milled, for example, to adapt the wall thickness of the sealing ring to the desired curve.

[0028] In another embodiment, one end of the piston is connected to a piston plate. Since the piston's positional variations within the cylinder are entirely compensated for by the clearance of the sealing rings and the spherical cross-sectional shape of the sealing rings, the piston does not require any joints or sliders at the end of the piston base away from the piston. Instead, the piston can be securely attached to the piston plate.

[0029] In another embodiment, the piston diameter decreases in the region between the sealing ring bracket and one end. This allows the piston to tilt within the cylinder, a tilting motion that prevents the piston from contacting the cylinder wall during operation.

[0030] In another embodiment, the piston has a truncated conical shape in the region between the sealing ring bracket and one end.

[0031] In another embodiment, the piston bore axis of the cylinder is distributed on a first circumference (piston bore pitch circle) around the cylinder barrel axis, and the piston longitudinal axis is distributed on a second circumference (piston pitch circle) around the piston plate axis, wherein the diameter (D) of the second circumference is selected. K ) is greater than the diameter of the first circumference (D) Z The dimensional difference between the first and second circumferences can be compensated for through the ingenious design of the sealing ring and pin, thereby achieving a more compact axial piston machine structure.

[0032] In another implementation, this piston is designed for use in a so-called floating piston machine.

[0033] In another implementation, the axial piston mechanism creates a swashplate machine.

[0034] The invention will now be further described and illustrated with reference to the embodiments depicted in the accompanying drawings. The drawings show:

[0035] Figure 1 A schematic diagram of an axial piston machine with a piston in an intermediate position according to the present invention is shown;

[0036] Figure 2 A schematic diagram of an axial piston machine having a piston in a swinging position according to the present invention is shown;

[0037] Figure 3 The piston structure is shown as a truncated cone shape;

[0038] Figure 4 A cylindrical piston structure is shown;

[0039] Figure 5 A piston in the shape of a truncated cone with a sealing ring is shown;

[0040] Figure 6 An embodiment of a symmetrical sealing ring is shown;

[0041] Figure 7 An embodiment of an asymmetric sealing ring is shown;

[0042] Figure 8 An embodiment of a symmetrical sealing ring with an inner flange is shown;

[0043] Figure 9 An embodiment with a sealing ring having a stepped inner side is shown;

[0044] Figure 10 An embodiment of a sealing ring with an ever-increasing diameter in its upper region is shown;

[0045] Figure 11 A piston with a sealing ring is shown, which has a flange-shaped inner groove and a pressure balancing hole;

[0046] Figure 12 A piston with a sealing ring is shown, which has a stepped inner profile and a pressure balancing hole.

[0047] Figure 1 and Figure 2 A schematic diagram of a so-called floating piston machine is shown, representing the structure and function of an axial piston machine. Figure 1 and Figure 2 Different operating states of the same floating piston mechanism are shown. The structure and function of the floating piston mechanism are well known to technicians, therefore... Figure 1 and Figure 2 The text only describes the cooperation between the piston 2 with cylinder 7, piston plate 8, and swashplate 9. The piston plate 8 rests against the swashplate 9 and is rotatably positioned on the swashplate. Figure 1 The diagram shows an intermediate state of the floating piston machine 1, in which the pivot 9 and cylinder 7 are arranged parallel to each other. Figure 2 The state of the floating piston machine 1 is shown, in which the swashplate 9 and the cylinder are not arranged parallel to each other.

[0048] In this embodiment, multiple cylinders 3 are evenly distributed in a circle around the cylinder axis 70 of the cylinder barrel 7. In this embodiment, the cylinder 3 is implemented as piston bores 3, and is hereinafter referred to as piston bores. However, it will be apparent to those skilled in the art that the cylinder 3 can also be manufactured in a manner different from piston bores. To avoid resonance, an odd number of piston bores 3 is typically chosen. On the top surface 71 of the cylinder barrel 7, each piston bore 3 has a connecting hole 33 through which pressure medium can be supplied to or discharged from the so-called high-pressure side of the floating piston machine 1.

[0049] The cylinder 7 is arranged such that it can rotate about the cylinder axis 70. To transmit torque, a shaft 72 is provided on the cylinder 7; this shaft provides the drive shaft in the operation mode of the floating piston machine as a pump, and provides the driven shaft in the operation mode of the floating piston machine as a prime mover. In the described embodiment, the distance R from the piston bore axis 30 to the cylinder axis 70 is 45 mm, and the inner diameter D of each piston bore 3 is 15 mm. For better illustration of the invention, the accompanying drawings are not reproduced to scale, but rather some details are reproduced at a significantly enlarged scale.

[0050] Piston 2 is implemented as a rotationally symmetric piston. The axis of symmetry of piston 2 is also referred to below as the longitudinal axis 20 of piston 2. Figure 3 The basic structure of piston 2 is shown, with a piston head 21 at the upper end and a piston foot 22 at the lower end. In the case of piston 2, the direction indicator "upward" indicates that piston 2 moves towards piston head 21 within piston chamber 31, while the direction indicator "downward" indicates that piston 2 moves towards piston foot 22 within piston chamber 31. Typically, the diameter of piston head 21 is larger than that of piston foot 22. Therefore, as... Figure 2 As shown, the piston 2 can have a truncated conical shape in its central region 24. Importantly, the diameter of the piston head 21 is chosen such that the piston head 21 does not contact the inner wall 32 of the piston bore 3 at any time during piston machine operation. However, the piston 2 can also be implemented in a cylindrical shape in its central region 24, provided this is taken into account. Figure 4 As shown.

[0051] The piston plate 8 is implemented as a disk, with a piston plate axis 80 extending perpendicularly to the piston plate 8 through its center. The piston plate 8 is arranged to be rotatable, allowing it to rotate about its piston plate axis 80. The swashplate 9 is also implemented as a disk, with a swashplate axis 90 extending perpendicularly to the swashplate 9 through its center. In the intermediate state of the floating piston mechanism 1, the piston plate axis 80 and the swashplate axis 90 are aligned with the cylinder axis 70.

[0052] In the following text, the plane extending perpendicularly around the cylinder axis 70 is referred to as the cylinder plane 75, and the plane extending perpendicularly to the piston plate axis is referred to as the piston plate plane 85. In the intermediate state, the cylinder plane 75 and the piston plate plane 85 are parallel to each other. When the cylinder 7 rotates, the distance between the bottom surface 72 of the cylinder 7 and the top surface 81 of the piston plate 8 remains constant in the intermediate position. Because the distance is constant, the piston 2 does not perform any stroke motion. Therefore, this distance between the bottom surface 72 of the cylinder and the top surface 81 of the piston plate 8 is referred to as the intermediate distance S0 in the following text.

[0053] In this embodiment, the piston plate 8 is configured to rotatably relative to the cylinder plane 85. When the swashplate 9 rotates, it must be ensured that the cylinder axis 70 intersects the swashplate axis 90 at the rotation point X at an angle α. Since the piston plate 8 slides on the swashplate 9, the piston plate 8 and the swashplate 9 always remain parallel to each other. By geometric laws, the angle α at which the cylinder plane 75 intersects the piston plate plane 85 corresponds to the swing angle α. The swing angle α also corresponds to the angle at which the piston axis 20 is tilted relative to the cylinder bore axis 30. When the swing angle α = 0°, i.e., in the intermediate position, the piston axis 20 is parallel to the piston bore axis 30.

[0054] When the swing angle α is not equal to 0°, half of the piston plate 8 tilts away from the cylinder 7, and the other half tilts towards the cylinder 7. Therefore, the distance between the bottom surface 72 of the cylinder and the top surface 81 of the piston plate changes continuously during rotation. Here, the piston plate 8 passes through the maximum distance S during the rotation from the middle distance to a quarter of a full circle. 最大 After rotating a quarter of a full circle, the top surface 81 of the piston plate 8 returns to the middle distance; after rotating another quarter of a full circle, the top surface 81 of the piston plate 8 passes through the minimum distance S. 最小 Upon reaching the bottom of cylinder 7, and then rotating a quarter of a circle, piston plate 8 returns to the starting point. (For illustration...) Figure 2 These positions show the distances between the piston chambers and the two pistons or an even number of n piston holes.

[0055] Because the piston foot 22 of piston 2 is firmly connected to piston plate 8, piston 2 is forced to perform these up-and-down movements when cylinder 7 and piston plate 8 rotate. During the upward movement, the piston chamber 31, sealed by the sealing ring 5 on the inner side of the housing, contracts until piston 2 reaches top dead center OT, at which point piston changes its stroke direction. The top dead center OT of piston 2 reaches its minimum distance S from piston plate 8. 最小 The positions are the same. During the subsequent downward movement, the piston chamber expands until piston 2 reaches the bottom dead center UT. At this bottom dead center, the downward stroke becomes an upward stroke. The bottom dead center UT and the top surface 81 of piston plate 8 reach the maximum distance S between the bottom surface 72 of cylinder 7 and the bottom surface 72 of cylinder 7. 最大 The positions are the same.

[0056] Advantageously, the piston foot 22 is cylindrical in shape, as this allows it to be accommodated by the through-hole in the piston plate 8. Since the piston either expands into a truncated cone or forms a step towards the larger cylindrical middle portion 24 at the connection of the piston foot 22, the piston 2 rests against the top surface 81 of the piston plate to transfer the force acting on the piston head 21 in the piston chamber 31 to the piston plate 8.

[0057] If the central portion 24 is not enlarged relative to the piston foot 22, this support can be alternatively achieved by making the receiving portion of the piston foot 22 a blind hole and supporting each piston foot 22 in its respective blind hole. The piston foot 22 is fixed, for example, by press-fitting through holes or blind holes to prevent any form of movement. Alternatively, the connection can be made by another form-fitting or force-fitting method, such as by press-fitting, shrink-fitting, threading, or welding.

[0058] Figure 5 A piston 4 is shown, which has a sealing ring 5 mounted in a sealing ring holder 4. In this case, the sealing ring holder 4 has a pin 23 centered on the piston head 21, which receives a central opening 51 of the sealing ring 5. Here, the inner diameter d of the central opening 51 is selected. i The diameter d is significantly larger than that of pin 23. Z The movement of the sealing ring 5 in the direction of the longitudinal axis 20 of the piston 2 is restricted by the cover 6 mounted on the pin 23.

[0059] Figure 6 The sealing ring 5 is shown in an embodiment of a very simple manufacturing technique. Figure 6 The sealing ring 5 is a spherical disk, wherein the spherical disk has equal height h / 2 upwards and downwards from the equatorial plane 58 of the sealing ring. The equatorial plane 58 comprises a great circle on the outer surface 52 of the sealing ring, and the sealing ring is perpendicular to the sealing ring axis 50. With the height h / 2 of the sealing ring being equal on both sides of the equatorial plane, this is a symmetrical design of the sealing ring 5. The diameter d of the sealing ring is derived from the radius of curvature r. aIdeally, the diameter of the sealing ring should be slightly smaller than the piston diameter d.

[0060] We first observe that the piston plate plane 85 is parallel to the cylinder plane 75, with the cylinder axis 70 coinciding with the piston plate axis 80 and the swashplate axis 90, i.e., in the intermediate position. When the cylinder 7 and piston plate 8 rotate in this intermediate position, the piston 2 does not perform any stroke because there is no relative movement in the direction of the piston bore axis 30. Therefore, no perpendicular force, i.e., no force parallel to the cylinder axis 70, acts on the sealing ring 5.

[0061] Now let's take a look. Figure 2 Let's see what happens when the swashplate 9 is tilted relative to the cylinder 7 by a swing angle α <> 0°. As the cylinder 7 rotates within the piston bore 3, the rigid piston head runs on an elliptical track, where the vertices of the principal axis of this elliptical track are passed through the top dead center OT and the bottom dead center UT. In... Figure 2 In the scenario shown, when piston 2 reaches top dead center OT, it will protrude from the inner wall 32 of the piston bore, where the distance between the piston bore and the cylinder axis 70 is minimal, i.e., closer to the cylinder axis 70. Conversely, when piston 2 reaches its bottom dead center UT, it will protrude from the inner wall 32 of the piston bore 3, where the distance between the piston bore and the cylinder axis 70 is maximum. Therefore, in Figure 2 In the diagram, the two pistons 2 will press against their respective right cylinder walls 31. In the case of a rigid piston head 21 and a rigid cylinder 7, this will inevitably cause the piston head 21 to be jammed in the piston bore 3.

[0062] In the floating piston mechanism 1 according to the invention, the clamping is counteracted in two ways. Firstly, the piston plate 8 is slidably arranged on the swashplate 9. Pressure from the piston chamber 31 is transmitted to the piston plate 8 via the rigid piston 2, causing the piston plate 8 to move on the swashplate 9. This... Figure 2 As can be seen, the piston plate axis 80 is now located to the left of the swashplate axis 90. On the other hand, since the sealing ring 5 is slidably accommodated within the sealing bracket 4, it can avoid the force acting on the sealing ring 5 from the inner wall 32 of the piston bore 3, which is transverse to the piston longitudinal axis. The inner diameter d of the sealing ring 5... i The diameter d of the pin Z It is an ideal match, thus creating a gap δ Q It is large enough that the sealing ring 5, when interacting with the moving piston plate 8 on the swashplate 9, can run along an elliptical track without getting stuck. If this clearance is set correctly, torque can be transmitted from the cylinder 7 through the sealing ring 5 to the piston plate 8, thereby driving the piston plate by the cylinder 7. However, alternatively, the piston plate 8 can be synchronized with the cylinder 7, for example, via a transmission mechanism, which provides greater freedom for the geometry of the inner sealing ring and the pin 23.

[0063] Because the radius of curvature r of the spherical outer surface 52 of the sealing ring 5 is approximately half the piston bore diameter D / 2, regardless of the inclination of the piston longitudinal axis 20 relative to the piston bore axis 30, and regardless of the depth to which the piston 2 enters the piston bore 3 during its stroke, the inner wall 32 of the piston bore and the sealing ring 5 are tangent to each other in a circle, i.e., the sealing circle 59. Therefore, the plane containing the sealing circle 59 is always perpendicular to the piston bore axis 30. This reduces wear between the sealing ring and the piston bore, making the axial piston mechanism more efficient and stable. Consequently, the service life of the metal sealing ring 5 is significantly longer than that of a sealing ring designed with elasticity according to existing technology.

[0064] In the following text, the circumference around which the piston bore axis 30 is distributed around the cylinder axis is called the piston bore pitch circle, and the diameter of the piston bore pitch circle is called the piston bore pitch circle diameter D. Z The piston feet 22, and especially the piston longitudinal axis 20 of each piston 2, intersect perpendicularly with the piston plate 8 and are evenly distributed around the piston plate axis 80 on a circumference, which is referred to below as the piston pitch circle. The diameter of the piston pitch circle is referred to below as the piston pitch circle diameter D. K .

[0065] In a variation of one implementation, the piston 2 is arranged on the piston plate 8 in such a way that, in the middle position, the longitudinal axis 20 of the piston 2 coincides with the longitudinal axis 30 of each piston bore 3. Therefore, the piston pitch circle diameter D... K and piston bore pitch circle diameter D Z They are the same. If the distance R between the piston bore axis 20 and the cylinder bore axis 70 is 45mm as described above, then the piston bore pitch circle diameter D... Z It is D Z =2R=90mm, piston pitch circle diameter D K It's also 90mm.

[0066] However, it has been shown that the piston pitch circle diameter D can be selected. K Also greater than the piston bore pitch circle diameter D Z Large. In a variation of the second implementation scheme, the piston pitch circle diameter D is selected. K Equals 90.4mm. Piston pitch circle diameter D K Larger than the piston bore pitch circle diameter D Z The advantage is that floating piston engines can be constructed more compactly because, for the same clearance δ Q A larger swing angle α can be obtained by adjusting the piston bore pitch circle diameter D. Z Compared to a relatively large piston pitch circle diameter D K This is achieved through a sealing ring 5, which is movably arranged transversely to the piston axis 20, and the large piston axis distance D is compensated by the displacement of the sealing ring 5 in the sealing ring bracket 4. K .

[0067] exist Figure 8 In another embodiment shown, the inner wall of the sealing ring 5 is provided with an inner flange 54, such that the sealing ring 5 has, for example, a uniform material thickness at its vertical height h. The geometry of the sealing ring deviates from a purely annular shape as follows:

[0068] When the piston chamber 31 of the cylinder 7 is connected to the high-pressure side through the connecting hole 33, the high pressure (up to 350 bar or higher) acts on the inner wall 32 of the bore of the cylinder 7 forming the piston chamber 31. It has been shown that, despite the robust design of the cylinder 7, this internal pressure can cause expansion or deformation of the corresponding piston bore 3. This unilateral expansion leads to an increase in the gap 34 between the piston bore 3 and the sealing ring 5. To overcome this drawback, the present invention proposes a geometric design for the sealing ring 5 such that when radial pressure is applied to the inner side of the sealing ring 5, the sealing ring can expand accordingly, thereby ideally keeping the gap 34 between the piston bore 3 and the sealing ring 5 constant throughout the entire operating pressure range. Due to the gap δ Q and δ H Pressure will enter the area behind the sealing ring or the space between the pin 23 and the inner diameter of the sealing ring 5. Since the working pressure in the piston chamber 31 acts on the internal geometry of the sealing ring 5 at the same height, the sealing ring 5 will also expand accordingly with the corresponding wall thickness or cross-sectional profile of the fit.

[0069] In the first variation, this can be achieved by having a flange-like groove 54 on the inner side 53 of the sealing ring 5. For example, the flange-like groove 54 can be implemented such that the sealing ring 5 has an approximately uniform horizontal thickness z in its vertical direction. With this uniform horizontal thickness z, the sealing ring can be intentionally weakened in order to enlarge the sealing ring, i.e., increase its outer diameter d. a This is to adapt to the pressure acting on the inside of the sealing ring.

[0070] In another embodiment of the sealing ring, such as Figure 7 As shown, the reduction in the sealing ring wall thickness is achieved by making the sealing ring 5 asymmetrical. That is, the height h2 of the sealing ring measured upwards from its equatorial plane 58 is greater than the height h1 measured downwards from its equatorial plane 58. In this way, a smaller wall thickness z2 at the upper end of the sealing ring 5 compared to the wall thickness z1 at the lower end is intentionally accepted to accommodate the high pressure of the pressure medium inside the piston. In this way, the required expansion of the sealing ring can be set by the upper height h2.

[0071] exist Figure 9 In another embodiment shown, the inner diameter of the sealing ring is stepped. At its upper part, i.e., the portion facing the piston 2 cap, the inner diameter d2 is chosen to be larger than the inner diameter d at its lower part. i Therefore, as a basis Figure 6 An alternative to the approximately constant sealing ring cross-sectional thickness z of the illustrated embodiment is that the sealing ring 5 adapts to higher operating pressures due to the lower material thickness z2 in its upper region, while the sealing ring 5 essentially maintains its shape in its lower region due to the higher material thickness z1. Therefore, the inner diameter d of the sealing ring... i With pin diameter d z The fit between them remains unchanged. The required expansion of the sealing ring in its upper region can be adjusted, in particular, by the upper diameter d2 and the height of the step between the upper and lower regions.

[0072] In an alternative implementation, such as Figure 10 As shown, the inner diameter of the sealing ring continuously increases in height. Therefore, the wall thickness of the sealing ring 5 decreases with increasing height, making it easier to accommodate the pressure of the inner sealing ring 57. In its lower region, the sealing ring 5 extends downward at a first height h1 from the equatorial plane, and in its upper region, it extends upward at a second height h2. Depending on the required degree of expansion, the expansion of the inner space 57 of the sealing ring 5 can begin from the equatorial plane 58 as shown, but it can also begin above or below the equatorial plane 58. For this purpose, a symmetrically designed sealing ring 5 can be used, where the first height h1 is equal to the second height h2, or a design such as... Figure 10 The sealing ring 5 is shown in an asymmetric design, where the first height h1 and the second height h2 are different. If necessary, the finite element method can be used to perform the corresponding deformation analysis to determine the optimal design of the ring geometry, which is a function z(h) of the height of the sealing ring 5.

[0073] Since the expansion of the piston inner wall 32 depends on many factors, such as the material used in the cylinder 7, the piston bore diameter d, and the wall thickness between two adjacent piston bores 3, these are the most important factors, so a general formula cannot be given here. However, laboratory tests show that at a working pressure of 350 bar, with the dimensions selected in the embodiment, the expansion of the piston bore 3 is between 10 μm and 30 μm, and may be greater or less than this value in specific individual cases. Therefore, one method to determine the sealing ring cross-sectional thickness z is to first determine the deformation of the piston bore 3 at the highest preset working pressure. In a series of tests, sealing rings 5 ​​with different cross-sectional thicknesses z are exposed to the highest preset working pressure, and the resulting increase in the diameter of the sealing ring 5, Δd, is determined. Then, the geometry of the sealing ring is selected, i.e., with the sealing ring 5 cross-sectional thickness z, the piston inner wall diameter d + Δd measured at the highest working pressure and the sealing ring diameter d at the highest working pressure are selected. i +Δd i The difference Δd corresponds to the gap between the selected piston inner wall 32 and the sealing ring 5.

[0074] Pressure balance is achieved through the vertical and horizontal gaps of the sealing ring 5 in the sealing ring bracket 4. Alternatively or additionally, pressure balance between the piston interior 31 and the sealing ring 5 interior 57 can also be achieved through one or more perforations on the cover 6. Figure 11 An embodiment of a piston 2 with a sealing ring 5 is shown, the inner wall 54 of which has a flange-like groove. In this embodiment, pressure balance between the piston interior 31 and the sealing ring 5 interior 57 is provided by one or more pressure balancing holes 9 extending downward from the top surface of the cap 6 through the pin 23 and then radially towards the pin 23. This pressure balance is suitable for sealing rings 5 ​​with a continuous thickness z-distribution, as well as for pistons with a sealing ring 5 with a sealing ring 5 having a continuous thickness z-distribution. Figure 12 The sealing ring shown has a stepped inner profile. In this embodiment, the pressure balance between the piston interior 31 and the sealing ring interior 57 is also provided by one or more pressure balancing holes 9 that extend downward from the top surface of the cover 6 through the pin 23 and then in the radial direction of the pin 23.

Claims

1. An axial piston machine (1) wherein a piston (2) performs a stroke motion in a cylinder (3), the piston (2) having a sealing ring bracket (4) for a sealing ring (5), the sealing ring bracket (4) being designed to allow the sealing ring (5) to move transversely to the longitudinal axis (20) of the piston (2), Its features are, The sealing ring (5) is spherically shaped in at least one region, which provides a sealing effect against the inner wall (32) of the cylinder (3) during the stroke. The radius of curvature of the spherically shaped sealing ring (5) in the region is approximately half the diameter (d) of the cylinder (3). The cross-section of the sealing ring (5) is designed such that, under high working pressure, the deformation of the sealing ring (5) due to the working pressure largely compensates for the expansion of the inner wall (32) of the cylinder due to the working pressure. The cross-section of the central inner opening of the sealing ring (5) has a stepped curve (55, 56). The central inner opening of the sealing ring (5) has a first inner diameter and a second inner diameter that is larger than the first inner diameter. The first inner diameter is used to match the pin diameter of the sealing ring bracket (4), and the second inner diameter does not participate in torque transmission.

2. The axial piston machine (1) according to claim 1. Its features are, The sealing ring (5) is made of a rigid material.

3. The axial piston machine (1) according to claim 1. Its features are, The sealing ring (5) is made of metal.

4. The axial piston machine (1) according to claim 1. Its features are, The sealing ring (5) is made of ceramic.

5. The axial piston machine (1) according to claim 1. Its features are, The sealing ring bracket (4) includes a pin (23), and the sealing ring (5) has a central inner opening (51) corresponding to the pin (23), wherein the inner diameter (d) of the sealing ring (5) is selected. i The diameter (d2) of the pin is greater than that of the pin.

6. The axial piston machine (1) according to claim 1, characterized in that, The piston (2) is designed to achieve pressure balance between the inside of the piston (31) and the inside of the sealing ring (57).

7. The axial piston machine (1) according to claim 5, characterized in that, The horizontal gap (δ) between the inner diameter of the sealing ring (5) and the pin (23) Q The vertical gap (δ) between the sealing ring (5) and the sealing ring bracket (4) within the sealing ring bracket (4) H The size is selected to be at least large enough to enable pressure balance between the inside of the piston (31) and the inside of the sealing ring (5) (57).

8. The axial piston machine (1) according to claim 5, characterized in that, Pressure balance between the interior of the piston (31) and the interior of the sealing ring (5) can be achieved by one or more perforations and / or one or more pressure balance holes on the cover (6), which extend from the top surface of the pin (23) to the interior of the sealing ring (5).

9. The axial piston machine according to claim 5, characterized in that, If the sealing ring (5) is made of ceramic, then choose a ceramic with an elastic modulus similar to that of steel.

10. The axial piston machine (1) according to any one of claims 1 to 9. Its features are, The sealing ring (5) is fixed in the sealing ring bracket (4) by a cover (6) to prevent movement along the longitudinal axis (20) of the piston (2).

11. The axial piston machine (1) according to claim 10. Its features are, The cover (6) is mounted on the piston (2) by screws or by clamping or pressing.

12. The axial piston machine (1) according to any one of claims 1 to 9. Its features are, One end (22) of the piston (2) is fixed to the piston plate (8).

13. The axial piston machine (1) according to claim 12. Its features are, In the region between the sealing ring bracket (4) and one end (22), the piston diameter gradually decreases.

14. The axial piston machine (1) according to claim 13. Its features are, The piston (2) has a truncated cone shape in the region between the sealing ring bracket (4) and one end (22).

15. The axial piston machine (1) according to any one of claims 1 to 9, wherein the cylinder (3) is distributed on the cylinder (7) about a cylinder axis (70), and the piston (20) is distributed on the piston plate (8) about a piston plate axis (80). Its features are, The rotation of the cylinder (7) around the cylinder axis (70) is synchronized with the rotation of the piston plate (8) around the piston plate axis (80) by a synchronization device, wherein the synchronization is not achieved by the torque transmission of the piston (2).

16. The axial piston machine (1) according to claim 15, wherein the piston bore axis (30) of the cylinder (3) is distributed on a first circumference around the cylinder barrel axis (70), and the longitudinal axis of the piston (20) is distributed on a second circumference around the piston plate axis (80). Its features are, Choose the diameter (D) of the second circumference. K The diameter of the first circumference is greater than that of the first circle (D). Z ).

17. The axial piston machine (1) according to any one of claims 1 to 9. Its features are, The axial piston machine (1) is a so-called floating piston machine.

18. The axial piston machine (1) according to any one of claims 1 to 9. Its features are, The axial piston machine (1) is a swashplate machine.

19. A method for manufacturing a sealing ring for an axial piston machine (1) as described in any one of claims 1 to 18, Its features are, A solid sphere is selected as the initial product, and two spherical portions are cut off parallel to the great circle of the solid sphere to obtain a spherical disk.

20. The method according to claim 19, Its features are, A central hole is provided on the rotating axis of the spherical disk.

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