Piston and sliding shoe pair

Abstract

The present invention relates to a piston-sliding shoe pair for an axial piston machine, the pair comprising a piston (10) having a spherical joint head (14) at the end of a piston rod (12), the spherical joint head (14) being at least partially received by a spherical receiving portion (16) of a piston shoe (18) having two shoe portions (30, 32), the shoe portions together defining a receiving space (46) through which the spherical joint head (14) passes, the receiving space (46) communicating with the environment adjacent to the piston shoe (18) for medium transport by at least one discharge opening (70).

Description

Technical Field

[0001] The present invention relates to a piston and sliding shoe pair for an axial piston machine, the pair comprising a piston having a spherical joint head at an end of a piston rod, the spherical joint head being at least partially received by a spherical receiving portion of a piston shoe having two shoe portions, the two shoe portions together defining a receiving space through which the spherical joint head passes.

Background Art

[0002] Patent Document 1 (German Patent Application Publication No. 102011108960) discloses such a pair for an axial piston machine, wherein the pair has a concave recess in the piston shoe for receiving the piston head, a sliding surface for supporting the piston, and a lubricant flow passage through which the piston shoe penetrates from the concave recess to the sliding surface, the concave recess transitioning continuously tangentially to the transition portion of the continuously narrowing tapered portion of the lubricant flow passage, and the transition portion is convex. Correspondingly, the continuous tangential and convex transition portion is intended to reduce the notch effect at the transition between the concave recess and the lubricant flow passage, and tests have shown that such a geometry allows a higher piston support force to be introduced into the piston shoe.

[0003] Patent Document 2 (German Patent Application Publication No. 102007055167) discloses a further pair of piston and sliding shoe for axial piston machines, particularly swash plate machines, the pair comprising a piston and a piston shoe articulated on the piston, wherein the piston is connected to the piston shoe by a joint head formed of a ball and a substantially spherical recess, a hydrostatic relief is provided in the region of the ball joint, and a support surface for supporting the ball of the joint head is provided in the radially inward region of the joint head. The above arrangement of the support surface in the radially inward region of the ball joint results in a favorable angle with respect to the longitudinal axis of the piston or the longitudinal axis of the piston shoe, resulting in a reduced frictional force at the ball joint. This effectively prevents the piston shoe from clogging and, consequently, from tilting away from the swash plate of the axial piston machine, minimizing leakage between the piston shoe and the swash plate.

[0004] Patent Document 3 (German Patent Application Publication No. 102013008677) discloses a single piston in a piston arrangement for a hydraulic pump, wherein the piston has a pivot head, a piston base opposite the pivot head, and at least one hollow chamber, each essentially or completely enclosed by a piston housing that closes the hollow chambers to the outside. The hollow chambers within the piston reduce the overall mass of the hollow chambers, resulting in significantly less energy being required to accelerate and decelerate each piston during pump operation using a hydraulic pump, which would otherwise lead to considerable wear in the area of ​​the piston and sliding shoe assembly.

[0005] Patent Document 4 (U.S. Patent No. 2880042) discloses a pair of pistons and sliding shoes for an axial piston machine, the piston having a spherical joint head at the end of a piston rod, which is at least partially received by a spherical receiving portion in a piston shoe having two shoe portions, the two shoe portions together defining a receiving space through which the spherical joint head passes. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] German Patent Application Publication No. 102011108960 Specification [Patent Document 2] German Patent Application Publication No. 102007055167 Specification [Patent Document 3] German Patent Application Publication No. 102013008677 Specification [Patent Document 4] U.S. Patent No. 2880042 [Patent Document 5] German Patent Application Publication No. 102023004369.9 Specification [Overview of the project] [Problems that the invention aims to solve]

[0007] Based on this level of technology, the present invention aims to improve upon known solutions. [Means for solving the problem]

[0008] A pair of pistons and sliding shoes having the features described in claim 1 solves the above problem as a whole. According to the feature portion of claim 1, the receiving space is connected to the environment adjacent to the piston shoe by a medium transport communication via at least one discharge opening, so that the two shoe portions of the piston shoe are moved away from each other, thereby ensuring that pressure does not unintentionally accumulate in the receiving space, which could cause the piston shoe to fall apart under certain circumstances, and thus render the entire axial piston machine, usually in the form of a hydraulic or fluid pressure pump, unusable. The pad of the joint head on one of the two shoe portions in the form of a bearing cannot eliminate the possibility of leakage or a very small amount of pressure medium entering the receiving space from there, and if this amount of pressure medium in the receiving space becomes excessively large, an unacceptably high pressure may accumulate therein, resulting in the above-mentioned drawback. This is ensured in the pair of pistons and sliding shoes according to the present invention by its discharge opening to the environment.

[0009] In a particularly preferred embodiment of the piston-sliding shoe pair according to the present invention, the receiving space is provided to consist of a first space between two opposing end faces of two shoe portions in a medium-transport communication, and a second, smaller space defined on the one hand by a conical through-region in the cross-section of one shoe portion that at least partially forms a receiving portion for the joint head, and on the other hand by the joint head itself. The two spatial components result in an increase in the fluid receiving product for the receiving space, which also counteracts the accumulation of unacceptably high pressure in the receiving space, and the tapering conicality toward the free end of the piston also contributes to this. At the narrowest point of the conical receiving portion, a first circular central recess is formed, and the first central recess is defined at this point by a wall portion of the closely fitting first shoe portion that encloses the joint head in the form of a constriction in this region.

[0010] In a more preferred embodiment of the present invention, the piston and sliding shoe pair has the following discharge openings: On one shoe portion, and / or, The other shoe portion, and / or Between the two shoe parts, and / or It is provided that a hole or flow path is provided within the piston wall, preferably radially incorporated within the side wall of one shoe portion where the other shoe portion is absent in at least this region. By using at least one discharge hole or flow path, each discharge opening can be introduced into the indicated pair in a cost-effective manner, thereby generally advantageous to provide several discharge openings, for example, at least two discharge openings simultaneously, these discharge openings extending radially opposite to each other in the radial transverse direction in one shoe portion and opening into the receiving space together with a portion of the joint head.

[0011] In a particularly preferred embodiment of the piston-sliding shoe pair according to the present invention, the first space of the receiving space, as viewed in the axial direction of the piston, is provided to be larger than the corresponding axial length of the second space. The arrangement according to the claim also results in a significant increase in space or volume for the axial receiving space with respect to the operating axis of the piston, thereby avoiding undesirable pressure increases or pressure peaks.

[0012] In a more preferred embodiment of the present invention, a pair of pistons and sliding shoes is provided in which the two shoe portions are in direct contact with each other without the interposition of further components such as additional sealing and guide shells between them. This results in a space-saving design in this area, as the two shoe portions of the piston shoe are directly and operably connected to the joint head of the piston. The reduction in the number of parts also leads to a reduction in manufacturing costs. By using modern materials, the direct functional connection or link between the components of this pair can be designed to be functionally reliable and long-lasting during operation.

[0013] In a more preferred embodiment of the present invention, the piston-sliding shoe pair has a diameter along its maximum circumference that is larger along its maximum circumference than the diameter of the piston rod. In this way, a huge, high-strength piston solution is produced that can withstand the highest loads, particularly in pump operation using axial piston machines in the form of wobble shaft machines. Alternatively, this pair can also be used in relation to swash plate machines, which are also covered by the technical category of axial piston machines. Since the diameter of the piston rod is smaller than the diameter of the joint head, a slim piston rod with less mass is obtained compared to known solutions in which the shaft diameter is larger than the diameter of the joint head, and such a piston rod may be provided with a hollow chamber.

[0014] Due to the small overall mass of the pistons, the energy required to accelerate and decelerate each piston during pumping by the hydraulic pump is significantly reduced. This also reduces wear in the area of ​​the connection between the piston and the sliding shoe, thereby benefiting the lifespan of the axial piston machine or hydraulic pump. Furthermore, the diameter of the joint head is selected to be larger than the diameter of the rod, because, considering the large forces generated during operation due to high pressure, the contact surface at the contact pad between the joint head and the piston shoe must be enlarged, which is avoided by the means described.

[0015] In a more preferred embodiment of the present invention, a piston-sliding shoe pair has a concave constriction at the transition point between the joint head and the piston rod, the diameter of which is reduced compared to the adjacent joint head and adjacent piston rod. The corresponding constriction arises particularly from the manufacturing of the entire piston and, in addition to making the material more solid, the constriction also serves to act as a kind of stopper to ensure that the possible free rotational movement of the piston shoe on the joint head is restricted. This eliminates malfunctions in the operation of the piston pump.

[0016] In a further preferred embodiment of the present invention, the piston-sliding shoe pair is provided to have longitudinal passages that open at each end of the piston. The longitudinal passages can function as pressure equalizing passages to eliminate such obstructions to the piston's movement. Furthermore, this allows for the supply of lubricant from inside the piston and through its joint head to the pair of ends or front sides facing the connection with the piston shoe.

[0017] In a more preferred embodiment of the present invention, a piston-sliding shoe pair is provided in which one shoe portion having a reduced diameter portion at the end in the region of the first circular central recess surrounds the piston joint head flush along the circumference such that only rotational motion of the piston and / or piston shoe relative to each other is possible. As the piston is guided longitudinally, the piston shoe is forced to rotate together with the control plate or wobble plate, so that possible rotational motion occurs in all directions. In this way, the piston shoe having the shoe portion can follow the movement of the control plate of the hydraulic pump directly and without delay in the form of a wobble plate having an inclined control surface (see Patent Document 5 (German Patent Application Publication No. 102023004369.9)).

[0018] In a more preferred embodiment of the present invention, a pair of pistons and sliding shoes is provided in which one shoe portion having a pad partially surrounds the joint head radially, preferably in this process, forming a linear contact point with the end of the joint head. A conveyed fluid medium, such as hydraulic fluid, can reach this linear contact point through a conical passage opening in the one shoe portion to minimize friction between the entire piston shoe and the joint head. Preferably, the other shoe portion defines a further shell-shaped or spherical recess at its end face, the further recess having a shell-shaped or dome-shaped bearing in the form of an annular segment for axially supporting the joint head at one of its free ends, the bearing protruding forward by a predetermined distance toward the further recess. The above shell-shaped bearing can be configured to be dimensionally small in terms of space, so that friction is reduced in the bearing area, thereby enabling long-lasting and unhindered operation.

[0019] Preferably, the piston is guided to move back and forth in the longitudinal direction, and the piston shoe having two shoe portions is rotatable via a joint head, in which one shoe portion is provided to support the other shoe portion together with it via a guide surface. By connecting the two shoe portions of the piston shoe to each other, corresponding degrees of freedom are limited during the rotational movement of the piston shoe on the joint head, thereby increasing functional reliability and improving power transmission during piston pump motion. Furthermore, the above-described connection avoids obstacles during the movement stroke in operation.

[0020] In a pair of a piston and a sliding shoe according to a further preferred embodiment of the present invention, the nozzle flow path starts from its free end face, passes through the other shoe portion, the nozzle flow path opens into a further recess that functions as a fluid chamber between the joint head and the other shoe portion, and is fluidly communicatively connected to the longitudinal flow path of the piston. In this way, the fluid conveyed by the pump device or the hydraulic pump can be conveyed via the longitudinal flow path and the nozzle flow path to the front side of the shoe portion of the piston shoe that is in direct contact with the control plate, which is usually in the form of a swash plate or a wobble plate, to improve the application of the lubricant.

[0021] Furthermore, the pair of piston and sliding shoe preferably has an annular flange-like widened portion protruding perpendicularly to the environment on one shoe portion. This widened portion functions in particular to provide circumferential support for a preloading device that is part of an axial piston machine and whose force flow acts perpendicularly on the widened portion, as a result of which one shoe portion of the piston shoe arrangement is pressed against a portion of the outer periphery of the joint head of the piston arrangement at a predetermined contact pressure, which in turn increases the functional reliability of the pair. The pair of piston and sliding shoe according to the present invention will be described in more detail below with reference to the embodiments shown in the drawings. Brief Description of the Drawings

[0022] [Figure 1] Figure 1 shows a longitudinal section through a pair of a piston and a sliding shoe according to the present invention. Mode for Carrying Out the Invention

[0023] Figure 1 shows a pair of pistons and sliding shoes for an axial piston machine, particularly a rocking shaft machine of the type of hydraulic pump, as is well known in the prior art. The pair has a piston 10 having a spherical joint head 14 at the end of a hollow cylindrical piston rod 12, the spherical joint head 14 being at least partially received by a spherical receiving portion in the form of a ball sket 16 of a piston shoe 18. Multiple pistons 10 are sequentially received in a receiving cylinder having a piston receiving portion (not shown) as part of a pumping device, the piston receiving portion enabling longitudinal movement of the pistons 10 together with the piston rod 12 as part of the pumping motion. As already described, in this process, the free front end of each piston is guided to an associated sliding guide (technically also called a piston shoe 18), each sliding guide is generally supported by a preloading device having a predetermined preload at any position on the associated adjacent control surfaces of a control plate, which in this case is generally configured in the form of a swash plate of an axial piston machine and has at least one inclined control surface. The arrangement of the control plate having a control surface, and consequently the preloading device in the operating connection, are common, and therefore will not be explained in more detail in the drawings (Patent Document 5 (German Patent Application Publication No. 102023004369.9)).

[0024] As can be further seen from the figure, the joint head 14 has a diameter along its maximum circumference that is larger than the diameter of the piston rod 12 along its maximum circumference, and each diameter is determined laterally with respect to the displacement motion of the piston 10 along the longitudinal axis 20 of the piston-sliding shoe pair. Preferably, the diameter of the piston rod 12 is about 70-90%, particularly preferably about 80%, of the diameter of the joint head 14. In this case, other size configurations are also possible as needed.

[0025] At the transition point between the joint head 14 and the piston rod 12, there is a concave constriction 22 that is reduced in diameter compared to the adjacent joint head 14 and piston rod 12, and the constriction 22 results in the manufacture of the piston 10 from a solid material, for example, in the form of steel. In addition to the material being solid, the constriction 22 also acts like a so-called stopper, significantly restricting the free rotational movement of the piston shoe 18 on the spherical joint head 14 in the upward direction of the piston rod 12. The piston 10 further has a longitudinal flow path 24 extending through the piston 10, which is coaxial with the longitudinal axis 20 and has a substantially constant inner diameter, and the longitudinal flow path 24 opens outward at the end of the piston 10 via funnel-shaped extensions 26, 28, and the funnel-shaped extension 26 on the left when viewed in the direction of the figure is larger than the extension 28 on the right, and in particular has a larger free cross-section than the funnel-shaped extension 28. However, the inner diameter of the longitudinal flow path 24 does not necessarily have to remain constant, and its geometric shape can be changed as needed. The funnel-shaped extensions 26 and 28 can be omitted or have different geometric shapes as needed. In the illustrated example, fluid flows from extension 26 to extension 28, and the nozzle effect has already occurred in the longitudinal flow path 24, accelerating the lubricant toward the additional point on the piston shoe 18. Depending on the manufacturing method, the extension 28 can be larger than the extension 26 while achieving the same technical effect.

[0026] The piston shoe 18 has two shoe portions 30, 32 that interact with the joint head 14 to form an essential part of the ball socket 16 as a whole. In particular, the other shoe portion 32 has a support pad 34 for the joint head 14 of the piston 10 to its right. In contrast, one shoe portion 30 having a reduced diameter portion 36 surrounds the joint head 14 of the piston 10 in the direction of the constriction portion 22, and as a result, when the piston 10 moves longitudinally along the longitudinal axis 20 during the pumping process, only rotational motion is possible for the piston shoe 18, i.e., in a direction that crosses the longitudinal movement of the piston 10 during the pumping movement. In this regard, one shoe portion 30 having an attachment 38 forms a kind of linear circumferential contact point 40 for the outer circumference of the joint head 14. The reduced diameter portion 36 firmly holds one shoe portion 30 to the joint head 14. The other shoe portion 32, viewed in the direction of the longitudinal axis 20, supports the joint head 14 axially with its support pad 34, and thus, together with the joint head, forms a shell-shaped bearing 42 in the form of annular segments, which is configured to be partially concave in accordance with the convex shape of the joint head 14. The one shoe portion 30 is rotationally symmetric and concentric with the longitudinal axis 20, and inside it defines a first central recess 44 with a circular cross-section in the form of a frustocone 43, whose diameter is reduced on one side due to a reduced diameter portion 38, and on the opposite side, the frustocone 43, with its second end and circular central recess 45, transitions into a receiving space 46 with a wider diameter. The other shoe portion 32 forms a kind of longitudinal guide 48 for the hollow cylindrical inner circumference 50 of the one shoe portion 30, surrounding the other shoe portion 32 in this region. The conicity of the frustocone 43 is selected to widen in the direction of the receiving space 46 in any case.

[0027] As already described, the piston 10 is guided to move back and forth in a longitudinal view within a corresponding piston receiving portion in a cylinder or device housing (not shown), and a piston shoe 18 having two shoe portions 30, 32 is made rotatable via a joint head 14, so that the other shoe portion 32 supports the one shoe portion 30 together with it via its guide surface in the form of a longitudinal guide 48, and vice versa. Furthermore, a kind of nozzle passage 54 passes from its free end face 52 through the other shoe portion 32, and this nozzle passage opens between the joint head 14 and the other shoe portion 32 into a fluid chamber in the form of a further lens-shaped recess or receiving portion 56 in cross-section, the recess 56 forming part of a dome-shaped receiving portion 58 in the other shoe portion 32, and the free end face of the spherical joint head 14 engages at least partially with its receiving portion 58, while maintaining a distance from the other shoe portion 32 in this region. In this way, the joint head 14 contacts the other shoe portion 32 via only the shell-shaped bearing 42 so as to support it in the axial direction.

[0028] The nozzle channel 54 is part of a hollow cylindrical insert 60, which starts from a further receiving portion 56 having a widened flange surface and is permanently inserted into a corresponding hole in the other shoe portion 32. In the form of a diaphragm-shaped extension 62, the nozzle channel 54 opens into a funnel-shaped extension 28 of the longitudinal channel 24 in the piston rod 12 via a further receiving or fluid chamber 56. In this way, the fluid as a lubricant, which is transported by the pumping device, can be transported into the further receiving space 56 via the longitudinal channel 24 having funnel-shaped extensions 26, 28, and from this further receiving space 56, supply is ensured to the free front end face 52 of the other shoe portion 32 via the nozzle channel 54. To improve the addition of lubricant between the free end face 52 of the further shoe portion 32 and the adjacent control surface of a control plate (not shown), a cylindrical recess 64 is provided on the free end face 52 of the further shoe portion 32, which is directly connected to the fluid supply source via the nozzle channel 54. By supplying lubricant in this manner, unimpeded, low-wear operation is ensured with respect to the fluid or medium being conveyed. To improve lubricant supply, the free diameter of the nozzle passage 54, which begins at the extension 62 in the direction of the free end face 52 of the piston shoe 18, is reduced.

[0029] As can be further seen from the figure, one shoe portion 30 is circumferentially supported on a preloading device (not shown) at all displacement positions of the piston 10, and its force flow has an annular, flanged widening portion 66, symbolically represented by two arrows. The force direction of the preloading device is generally generated by an energy storage device in the form of a compression spring, which is stationary at one free end supported on a part of the hydraulic pump's device housing, and at the other free end, is in movable contact with an attachment portion supported by a support surface 68 where the flanged widening portion 66 is supported. In this way, each preloading device with a compression spring ensures that one shoe portion 30 with the flanged widening portion 66 can rotate or tilt around the joint head 14, and as a result, the free end surface 52 of the other shoe portion 32, which is transported along the movement, remains in contact with the aforementioned adjacent control surface of the control plate. In this way, the control plate can directly transmit the resulting force to each piston 10 for the pump delivery motion during its circumferential rotational motion.

[0030] One shoe portion 30 may be provided with at least one discharge opening 70 that connects the receiving space 46 to the adjacent environment. Each discharge opening 70 preferably extends radially through the annular side wall 71 of one shoe portion 30. During the lifting or pumping motion of the piston 10, viewed from right to left in the direction of the figure, the fluid to be pumped, located in the longitudinal flow path 24 and the further receiving space or fluid chamber 56, is pressurized. However, during the suction stroke, the piston 10 moves in the opposite direction, from left to right. A constriction with a predetermined cross-section is formed by the insert 60 having a nozzle flow path 54, which can supply a predetermined volume of fluid into the cylindrical recess 64. The pressurized fluid in the recess 64 slightly lifts the piston shoe 18 from the control plate, i.e., statically supports the piston shoe 18. In addition, a very small amount of fluid may leak through the support pad 34 of the piston 10 and the other shoe portion 32 into the receiving space 46 outside the shell-shaped receiving space or fluid chamber 56. If the amount of fluid in one of the receiving spaces 46 becomes too large, an unintended pressure increase can occur, and without a discharge opening 70, the two shoe sections 30 and 32 may be pushed apart from each other. Subsequently, the piston shoe 18 may fall apart, potentially causing the entire pump to fail. Therefore, each discharge opening 70 advantageously prevents this harmful pressure buildup in the receiving space 46.

[0031] As further shown in the longitudinal section of the figure, one receiving space 46 is connected to the environment by two fully shown discharge openings 70 and two partially shown discharge openings 70, which may be surrounded by a part of an axial piston machine, for example, its housing (not shown). A total of eight discharge openings 70 are used. It is understood that a single discharge opening 70 may be sufficient to ensure a medium transport connection from one receiving space 46 to the aforementioned environment in order to prevent the accumulation of unacceptable high pressure. The two discharge openings 70 shown in the longitudinal section are each configured as holes or fluid passages, and their free-opening sections lie in the plane of the drawing. Furthermore, the discharge openings 70 are paired facing each other diametrically with respect to the longitudinal axis 20, and their hole or opening axes are perpendicular to the aforementioned longitudinal axis 20, which also represents the operating axis of the piston 10. All further discharge openings 70 (not shown) can enter and exit the plane of the drawing at preferably equidistant radial distances from the two other discharge openings 70.

[0032] The receiving space 46 has a first space 72 and a correspondingly smaller second space 74. The two spaces 72 and 74 of the receiving space 46 are permanently connected to each other via a fluid or medium. Furthermore, the first space 72 is located between two opposing end faces 76 and 78 of the shoe portions 30 and 32, respectively, and the end faces 76 and 78 extend parallel to each other in the initial or operating position shown of the piston-sliding shoe pair and extend perpendicular to the longitudinal axis 20 of the piston 10. On the other hand, the smaller second space 74 of the receiving space 46 is configured as a frustocone 43, which is circumferentially defined by circular central recesses 44 and 45 on its two outlet sides. The other shoe portion 32 is provided with an annular recess 80 that defines a portion of the receiving space 46 and defines a shell-shaped bearing 42 in the direction of the receiving space 46.

[0033] Each discharge opening 70 is provided as a radially continuous through-hole within the hollow cylindrical circumferential side wall 71 of one shoe portion 30, transversely to the longitudinal axis 20 of one shoe portion 30, and the side wall 71 remains free from the other shoe portion 32, at least in this through-region. In principle, it is also possible to establish a medium connection from the outside to the receiving space 46 through at least one discharge opening of the other shoe portion 32, which extends parallel or obliquely to the longitudinal axis 20. Such a medium transport connection can also be realized via a flow channel duct (not shown) within the solid wall portion of the piston rod 12. However, a preferred alternative embodiment is that each discharge opening 70 may be provided between one shoe portion 30 and the other shoe portion 32 in the form of at least a groove-shaped flow channel along the cylindrical outer circumference of the other shoe portion 32, which functions as a longitudinal guide 48, for example. In this process, the flow-type discharge opening 70 can, in principle, be defined by one shoe portion 30 on one side and by the other shoe portion 32 on the other side.

[0034] The first space 72 in the form of a hollow cylindrical disc, viewed in the direction of the movement axis of the piston 10 parallel to the longitudinal axis 20, is greater than the corresponding axial length of the frustocone 43 in one of the shoe portions 30, also relating to the orientation of the longitudinal axis 20. Each discharge opening 70 has a bore diameter equal to or substantially equal to the axial height of the first space 72 in the receiving space 46 between the two end faces 76, 78.

[0035] The function of each discharge opening 70 is described in more detail below. During the upward or downward movement of the piston 10, viewed from right to left in the direction of the figure, the pressure medium located in the longitudinal flow path 24 and the further receiving space 56 is therefore subjected to fluid pressure due to the pressure rise. This defined volume of pressure medium is supplied to the cylindrical recess 64 on the free end face of the other shoe portion 32 via the hollow cylindrical insert 60 having a nozzle 54 in the form of a throttling. The pressure in the fluid chamber in the form of this recess 64 leads to a slight lift of the other shoe portion 32 relative to the control unit or swash plate, which should be considered rigid, and as a result, the other shoe portion 32 of the piston shoe 18 is supported by static pressure in this respect. A relatively small volume of pressure medium can enter the receiving space 46 as leakage flow through its two spaces 72, 74 via the shell-shaped bearing 42 between the outer circumference of the joint head 14 and the adjacent inner circumference of the other shoe portion 32. However, if the volume of the pressure medium in this receiving space 46 becomes excessively large, a correspondingly high fluid pressure will accumulate therein, thereby pushing the two piston shoes 30, 32 apart from each other by the corresponding fluid pressure acting in opposite directions on their end faces 76 or 78, respectively. This could cause the piston shoe 18 to fall apart, potentially leading to a permanent failure of the hydraulic pump. Thanks to the respective discharge openings 70, the pressure rise in the receiving space 46 can be prevented from the outset in either case, so that the two piston shoes 30, 32 remain in a functional position relative to each other as joint head mounts for the joint head 14. Furthermore, some volume leakage passes through a wedge-shaped gap in the cross section between the first shoe portion 30 and the outer circumference of the joint head 14 in this region, towards the reduced diameter portion 36 or the first central recess 44, through which the joint head 14 penetrates and is part of the frustocone 43.

[0036] The piston-sliding shoe pair shown in the diagram allows the fluid supply flow to be achieved under very high pressure, and this pair is designed to be highly force-balanced so as to compensate for the forces generated during the movement of the pump, which ensures a long-lasting, wear-free operation that is not comparable to conventional technology.

Claims

1. A pair of piston and sliding shoe for an axial piston machine, The piston-sliding shoe pair comprises a piston (10) having a spherical joint head (14) at the end of a piston rod (12), the spherical joint head (14) being at least partially received by a spherical receiving portion (16) of a piston shoe (18) having two shoe portions (30, 32), and these two shoe portions together define a receiving space (46) through which the spherical joint head (14) passes. The piston and sliding shoe pair is characterized in that the receiving space (46) is in communication with the environment adjacent to the piston shoe (18) for media transport by at least one discharge opening (70).

2. The piston and sliding shoe pair according to claim 1, characterized in that the receiving space (46) is configured in media transport communication between a first space (72) between two mutually opposing end faces (76, 78) of the two shoe portions (30, 32) and a relatively smaller second space (74) which is defined on one side by the frustocone (43) of one shoe portion (30) and on the other side by the spherical joint head (14) itself.

3. Each of the aforementioned at least one discharge opening (70) One of the shoe portions (30) is, The other shoe portion (32) and / or Between the two shoe portions (30, 32), and / or The piston-sliding shoe pair according to claim 1 or 2, characterized in that the piston (10) is guided as a hole or flow path within the wall portion of the piston (10), preferably radially incorporated within the side wall (71) of the one shoe portion (30) where the other shoe portion (32) is absent in at least this region.

4. The piston and sliding shoe pair according to any one of claims 1 to 3, characterized in that the first space portion (72) of the receiving space (46), as viewed in the axial direction of the piston (10), is larger than the corresponding axial length of the frustocone (43) in one of the shoe portions (30).

5. The piston-sliding shoe pair according to any one of claims 1 to 4, characterized in that the two shoe portions (30, 32) are in direct contact with each other without the interposition of further components such as further sealing and guide shells between them.

6. The piston and sliding shoe pair according to any one of claims 1 to 5, characterized in that the spherical joint head (14) has a diameter along its maximum outer circumference that is larger than the diameter of the piston rod (12) along its maximum outer circumference.

7. The piston and sliding shoe pair according to any one of claims 1 to 6, characterized in that a constricted portion (22) exists at the transition point between the spherical joint head (14) and the piston rod (12), and the diameter of this constricted portion is reduced compared to both the adjacent spherical joint head (14) and the piston rod (12).

8. The piston-sliding shoe pair according to any one of claims 1 to 7, characterized in that the piston (10) has longitudinal passages (24) that open at each end of the piston (10).

9. The piston-sliding shoe pair according to any one of claims 1 to 8, characterized in that one shoe portion (30) having a reduced diameter portion (38) partially surrounds the spherical joint head (14) of the piston (10) so that only rotational movement of the piston (10) and / or the piston shoe (18) relative to each other is possible.

10. The piston-sliding shoe pair according to any one of claims 1 to 9, characterized in that one shoe portion (30) having a linear contact point (40) radially surrounds the spherical joint head (14).

11. The piston-sliding shoe pair according to any one of claims 1 to 10, wherein the other shoe portion (32) further defines a shell-shaped receiving space (56) at its end face, and the further receiving space has a shell-shaped or dome-shaped bearing (42) in the form of an annular segment at one free end thereof for supporting the spherical joint head (14) in the axial direction, and the bearing protrudes forward by a predetermined distance toward the further receiving space (56) in the direction of the spherical joint head (14).

12. The piston and sliding shoe pair according to any one of claims 1 to 11, characterized in that the further receiving space (56) is defined by the concave wall portion of the other shoe portion (32), the further receiving space (56) tapers in a slit shape toward the bearing (42), and preferably the further receiving space (56) partially overlaps with the convex joint head (14) at its edge such that the cross section forms a kind of lens shape.

13. The piston-sliding shoe pair according to any one of claims 1 to 12, characterized in that the piston (10) is guided to move back and forth when viewed in the longitudinal direction (20), the rotation of the piston shoe (18) having the two shoe portions (30, 32) is enabled via the spherical joint head (14), and one shoe portion (30) together supports the other shoe portion (32) via a guide surface.

14. The piston-sliding shoe pair according to any one of claims 1 to 13, characterized in that the nozzle passage (54) starts from its free end face (52), passes through the other shoe portion (32), the nozzle passage opens in the further receiving space (56) which functions as a fluid chamber between the spherical joint head (14) and the other shoe portion (32), and is fluid-transportable to the longitudinal passage (24) of the piston (10).

15. The piston and sliding shoe pair according to any one of claims 1 to 14, characterized in that one of the shoe portions (30) has an annular, flange-shaped widened portion (66) that protrudes perpendicularly to the environment.

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