Patent Application
20250207664
This application claims foreign priority benefits under 35 U.S.C. § 119 to European Patent Application No. 23218579.3 filed on Dec. 20, 2023, the content of which is hereby incorporated by reference in its entirety.
The present invention relates to a ball support arrangement for a piston shoe arrangement, wherein the piston shoe arrangement is configured to be provided in an axial piston machine, wherein the piston shoe arrangement comprises a piston body having a ball shaped end and a piston shoe, wherein the ball support arrangement is arranged between the piston shoe and the ball shaped end.
Furthermore, the present invention relates to a piston shoe arrangement configured to be provided in an axial piston machine, wherein the piston shoe arrangement comprises a piston body having a ball shaped end and a piston shoe, wherein the ball shaped end is provided in the piston shoe, wherein a ball support arrangement is provided between the piston shoe and the ball shaped end.
Further, the present invention relates to an axial piston machine.
An axial piston machine is for example a hydraulic (variable displacement) pump or motor. The axial piston machine comprises pistons, which reciprocate within respective cylinders, wherein the cylinders are provided in a drum. The drum rotates relatively to a swash plate or vice versa, wherein the swash plate and the drum are arranged at an angle to each other.
The pistons are in contact with the swash plate via piston shoes. To do so, the piston comprises a ball shaped end, which is accommodated within a respective cup-shaped recess of the piston shoe, wherein a ball support arrangement is provided between the ball shaped end and the piston shoe. The ball support arrangement also provides lubrication and damping. Usually, this ball support arrangement is a synthetic material layer, which is molded onto the piston shoe.
The piston shoe comprises a sliding element through which the piston shoe is in contact to the swash plate. In order to provide a low-wear interaction between the swash plate and the piston shoe, the sliding element is formed of ceramics, plastics, fiber reinforced plastics, non-ferrous metals or alike. The sliding element is connected to the piston shoe via a press-fit or similar connecting methods. Usually, the swash plate is made of steel and the piston shoe is made of fiber-reinforced plastic. For a more durable solution, ceramic is used against ceramic.
During operation of the axial piston machine, moving components, in particular the ball support arrangement, wear out. As soon as the ball support arrangement is worn out, it needs to be replaced. However, in the current design, the ball support arrangement is permanently molded onto the piston shoe, which locks the piston in place., That means the piston needs to be renewed as well. This requires a removal of the worn-out piston having a worn out ball support arrangement and an installation of a new piston having a new ball support arrangement. The replacement of the piston requires a high personal workload and maintenance effort. Furthermore, replacing the piston is cost intensive. It also means that still functional parts of the assembly are not reused as the whole assembly is exchanged.
Therefore, the objective of the present invention is to provide a ball support arrangement which requires a low maintenance effort and is cost effective.
This objective is solved by a ball support as described in the outset, wherein the ball support arrangement is separate and replaceable, wherein at least a ball holding portion of the ball support arrangement is configured to accommodate at least a part of the ball shaped end. The term “separate” means in the present application that the ball support arrangement is toolless mountable and dismountable to the piston shoe arrangement. There is no fastening means, adhesive or any other bonding means involved. By separating the ball support arrangement from the piston shoe, the ball support arrangement can be replaced by itself, without replacing the piston shoe as well. Thus, the piston does not need to be replaced, which results in a low maintenance effort. Further, solely the ball support arrangement can be replaced in a cost-effective manner and requires a low personal workload. Furthermore, the separation allows material pairings, which have a good friction characteristic, without being limited to certain materials which allow a molding connection. Furthermore, worn elements, e.g. ball support arrangements, can be replaced individually, resulting in less waste. Further, tolerances can be taken into account by using a separate ball support arrangements having respective dimensions. Moreover, wear compensation can be incorporated.
In one embodiment, the ball support arrangement is formed of at least one material of a group of materials comprising plastics, ceramics, metal and fibers, wherein plastics is preferably PEEK and the fibers are preferably carbon fiber and/or fiberglass. Furthermore, for example plastics material can comprise a filler, e.g. a ceramic powder. By using different materials for the piston, the piston shoe and/or the ball support arrangement, the lubrication and damping characteristics can be easily adapted to match a predetermined fluid transferred through the axial piston machine. For example, plastics, in particular thermoplastic materials, can be manufactured easily and cost effective by means of injection molding processes.
In one embodiment the ball support arrangement comprises a mounting arrangement configured to releasable mount the ball support arrangement to the ball shaped end and/or to the piston shoe. Using such a mounting arrangement allows that the ball support arrangement can be easily mounted and removed from the ball shaped end and/or from the piston shoe without requiring further fastening elements such as bolts, pins or alike, which results in a low maintenance and installation effort. For example, the mounting arrangement comprises protrusions, which are configured to interact with recesses of the piston shoe, and/or the mounting arrangement comprises a recess, which is configured to interact with a protrusion of the piston shoe. This allows a positioning having a high repeat accuracy.
In one embodiment at least the ball holding portion is configured to be retained to the piston shoe by a retainer cup. The retainer cup provides additional stability to the ball support arrangement, in particular if the ball support arrangement is formed of a soft material, such as plastics.
In one embodiment the ball support arrangement, preferably at least the ball holding portion, is configured to be attached via a snap-on connection to the ball shaped end. In the present embodiment, at least the ball holding portion comprises at least one element that returns to its intended state after deformation. During a mounting process, the ball holding portion is deformed to be slipped over the ball shaped end. After the deformation, the ball support element, in particular at least the ball holding portion, returns to its intended shape such that the ball support arrangement is retained to the ball shaped end, e.g. by friction fit and/or press fit. In order to remove the ball support arrangement, at least the ball holding portion is deformed again to slip over the ball shaped end. This is an easy process which can be performed without any tools.
In one embodiment, the ball holding portion comprises multiple ball holding elements. For example, a first ball holding element is bowl-shaped, while a second ball holding element is annular. The first ball holding element is configured to be close to the swash plate compared to the second ball holding element, in an assembled state. Further, an inner diameter of the second ball holding element can be smaller than a diameter of the ball shaped end. If the first and second ball holding elements are provided on both sides of a diameter of the ball of the ball shaped end, a degree of movement of the ball shaped end in the piston shoe can be adjusted. As a result, the ball support arrangement can be adjusted to desired characteristics and tolerances can be taken into account.
In one embodiment, the ball support arrangement comprises a retainer portion which is configured to separate a retainer plate from the piston shoe and/or the retainer cup. As described above, the piston shoe interacts with the swash plate, wherein the piston shoe is coupled to the swash plate by the retainer plate, depending on a design of the axial piston machine. In operation, the piston shoe and the swash plate move relatively to each other. The wear affected area is provided on the retainer portion, such that the retainer portion wears out instead of the piston shoe respectively the retainer plate and/or the retainer plate. Furthermore, the ball support arrangement, in particular the retainer portion, can be easily replaced, which is cost-effective and a low workload.
In one embodiment, the ball holding portion and the retainer portion are formed in one piece or separate from each other. In one piece design, the positioning of the ball holding portion and retainer portion is always correct, which simplifies the assembly.
In one embodiment, the ball holding portion and the retainer portion are formed separate from each other. The ball holding portion and retainer portion are separated from each other, such that the ball holding portion and retainer portion can be arranged individually which provides good adjustment options.
In one embodiment, the ball support arrangement comprises an axis, wherein the ball support arrangement is symmetrical about the axis. In the present case, the term “symmetrical” means that at least one of the following symmetries is present: Rotational symmetry about the axis and/or mirror geometry wherein a mirror plane comprises the axis. Symmetrical elements are easy to design and easy to manufacture. Furthermore, the assembly is easy, since there is no limitation regarding an orientation about the axis. In one embodiment, the ball holding portion
retainer portion comprises at least one second recess in at least partly a direction perpendicular to the axis. The recess can accommodate for example debris, dust or other particles. This prevents a premature failure of the ball support arrangement. Furthermore, the at least one recess allow a certain flexibility, which can be adjusted by the design of the at least one recess. More recesses lead to a higher flexibility. Here, a compromise must be found between flexibility and stability. This depends on the size, number and shape of the recesses.
Further, the above objective is solved by a piston shoe arrangement as described in the outset, wherein the ball support arrangement is formed as described above.
By providing the above described ball support arrangement to the piston shoe arrangement, the piston shoe arrangement can be easily maintained, by replacing solely the ball support arrangement. This is cost effective and easily to do, since neither the piston nor the piston shoe as a whole need to be replaced. Only the worn parts, in particular the ball support arrangement, are replaced.
In one embodiment, the ball support arrangement comprises a ball holding portion which is releasably connected to the piston shoe in a fixed manner. Thus, there is no relative movement between the piston shoe and the ball support arrangement, which leads to a low wear.
Further, the above objective is solved by an axial piston machine comprising the above described piston shoe arrangement having the above described ball support arrangement. By being able to replace solely worn-out parts, maintaining the axial piston machine is easy, cost effective and requires low maintenance effort, respectively a low personal workload.
In the following, preferred embodiments of the invention are described in conjunction with the drawing. Herein shown:
Identical components/elements are given the same reference numbers throughout the description.
In the first embodiment, the ball support arrangement is formed of the ball holding portion 5 and the retainer portion 7.
The piston shoe 4, the retainer cup 6, and the ball holding portion 5 share a not depicted axis, wherein the piston shoe 4, the retainer cup 6, and the ball holding portion 5 are at symmetrical about this axis, rotational symmetrical about the axis or mirror symmetric about a plane, wherein the plane comprises the axis.
The retainer cup 6 comprises an annular projection 11, which interacts with a top region of the ball holding portion 5 to retain the ball holding portion 5 to the piston shoe 4. In the present case, the ball holding portion 5 comprises protrusions 12 which protrude radially outward with regard to the axis and form ribs on the outer surface of the ball holding portion 5. These protrusions 12 interact with the annular projection 11.
As provided in
Further, the ball holding portion 5 is formed of plastics, in particular or PEEK. The ball holding portion 5 deforms elastically during an installation process to the ball shaped end 3, wherein the fingers 16 are pushed apart to accommodate the ball shaped end 3. As soon as the ball holding portion 5 is in its final position, the ball holding portion 5 returns to its original, respectively intended, shape. The deformation during assembly is a so called snap-on connection. The mounting assembly may comprise the snap-on connection for example.
The first ball support element 5a is cup shaped having a rim provided on its widest opening diameter. The first ball support element 5 interacts with the piston shoe 4 and is arranged between the piston shoe 4 and the ball shaped end 3. The second ball support element 5b is an annular ring and is provided distanced to the first ball support element 5a in a direction of the axis pointing away from the piston shoe 4. The retainer cup 6 retains the second ball support element 5b, wherein the second ball support element 5b is in touching contact with the retainer cup 6 and the ball shaped end 3.
A retainer portion 7 is provide on the outside of the retainer cup 6. The retainer cup 6 is radially and axially held to the compression ring 10. The retainer portion 7 is annular comprising a U-shape cross-section, wherein the opening of the U-shape points in a radial direction outwardly. In this embodiment, the ball support arrangement is formed of the first and second ball support elements 5a,5b and the retainer portion 7.
Each of the first and second ball support elements 5a, 5b may comprise at least one recess. This design allows an easy installation, while debris, dirt and/or dust is collected in the respective recess.
Depending on the required characteristics, a not depicted axial piston machine can be equipped with any of the above described ball support arrangements, respectively the piston shoe arrangements 1. The piston shoe arrangement 1 is coupled to a swash plate of the axial piston machine.
Each of the above described piston bodies 2, ball shaped ends 3, piston shoes 4 and ball holding portions 5, 5a, 5b is symmetrical, in terms of rotational symmetrical or mirror symmetrical, about an axis. The axis is arranged concentrically to an outer circumferential surface of the piston shoe 4.
Each of the above described piston bodies 2, ball shaped ends 3, piston shoes 4 and ball holding portions 5, 5a, 5b comprises an axial hole. Wherein the hole is a through hole in the ball shaped ends 3, piston shoes 4 and ball holding portions 5, 5, 5b.
In each embodiment, the piston body 2 and the ball shaped end 3 are formed in one piece. Therefore, the piston body 2 and the ball shaped end 3 are formed of the same material.
The ball support arrangement, in particular the ball holding portion 5, is formed to provide a friction fit, or a press fitted fit to the piston shoe 4, the retainer cup 6 and or the compression ring 10, which reassembles a mounting arrangement. This allows an easy mounting and disassembly.
A flexibility of the ball holding portion 5 is increased by the recesses 15, such that its diameter can be extended during a mounting operation to the ball shaped end 3. As soon as the ball holding portion 5 is provided in its position on the ball shaped end 3, the ball holding portion 5 returns to its intended respective original form. This reassembles a preferred version of the above described mounting arrangement in terms of a snap-on connection.
While the present disclosure has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this disclosure may be made without departing from the spirit and scope of the present disclosure.
| Number | Date | Country | Kind |
|---|---|---|---|
| 23218579.3 | Dec 2023 | EP | regional |
