Piston-piston shoe pairing

Abstract

The invention relates to a piston-piston shoe pairing for an axial piston machine, comprising a piston (10) which, at the end of a piston rod (12), has a spherical rod end (14) which is at least partially received by a spherical receptacle (16) in a piston shoe (18) comprising two shoe parts (30, 32) which together delimit a receiving space (46) through which the spherical rod end (14) extends, wherein the receiving space (46) is medium-conductingly connected to the environment adjoining the piston shoe (18) by means of at least one discharge opening (70).

Description

[0001] Piston-sliding shoe pairing

[0002] The invention relates to a piston-sliding shoe pairing for an axial piston machine, with a piston which has a spherical joint head at the end of a piston skirt, which is at least partially received by a spherical receptacle of a sliding shoe, which has two shoe parts which together delimit a receiving space through which the spherical joint head penetrates.

[0003] DE 10 201 1 108 960 A1 discloses such a pairing for an axial piston machine, comprising a concave recess in the sliding block for receiving a piston head, a sliding surface for supporting the piston, and a lubricant channel traversing the sliding block from the concave recess to the sliding surface. The concave recess transitions tangentially into a transition section of a continuously narrowing tapered section of the lubricant channel, and the transition section is convex. The convex and tangentially continuous transition section is intended to reduce a notch effect at the transition between the concave recess and the lubricant channel. Tests have shown that such a geometry enables the introduction of higher supporting forces from the piston into the sliding block.DE 10 2007 055 167 A1 discloses another piston-sliding-shoe pairing for an axial piston machine, in particular a swash-plate machine, comprising a piston and a sliding shoe articulated to the piston. The piston is connected to the sliding shoe by means of a ball joint formed by a ball and a substantially spherical recess. Hydrostatic relief is provided in the region of the ball joint, and a support surface is provided for supporting the ball of the ball joint, which support surface is arranged in the radially inner region of the ball joint. The aforementioned arrangement of the support surface in the radially inner region of the ball joint results in favorable angles with respect to the piston longitudinal axis and the sliding shoe longitudinal axis, respectively, resulting in lower frictional forces at the ball joint.This effectively prevents the sliding shoe from jamming and thus tipping off the swash plate of the axial piston machine, and also ensures minimal leakage between the sliding shoe and the swash plate.

[0004] DE 10 2013 008 677 AI discloses a single piston within a piston assembly for a hydraulic pump. The piston assembly has a pivot head and a piston head opposite the pivot head, as well as at least one hollow chamber, which is at least partially enclosed by a piston housing that essentially or completely seals off the respective hollow chamber from the outside. Due to the hollow chamber in the piston, its overall mass is reduced, so that significantly less energy is required to accelerate and decelerate each piston during pumping with the hydraulic pump, which could otherwise lead to significant wear in the area of ​​the piston-sliding shoe connection.

[0005] US 2,880,042 discloses a generic piston-sliding shoe pairing for an axial piston machine, comprising a piston which has a spherical joint head at the end of a piston skirt, which is at least partially received by a ball socket of a sliding shoe, which has two shoe parts which together delimit a receiving space through which the spherical joint head passes.

[0006] Based on this prior art, the invention seeks to improve upon the known solutions. This objective is achieved by a piston-sliding shoe pairing having the features of patent claim 1 in its entirety.

[0007] The fact that, according to the characterizing part of patent claim 1, the receiving chamber is in media-conducting communication with the environment adjacent to the sliding block by means of at least one relief opening reliably prevents the unwanted buildup of pressure in the receiving chamber to such an extent that the two shoe parts of the sliding block are moved away from each other, which could potentially lead to the sliding block falling apart and thus to the unusability of the axial piston machine, usually in the form of a hydraulic or hydro pump as a whole. A support of the rod end on one of the shoe parts in the form of a bearing cannot rule out the possibility of a leakage or very small amount of pressure medium reaching the receiving chamber from there. If this amount of pressure medium in the receiving chamber becomes too large, an unacceptably high pressure can build up there, leading to the disadvantages described above.This is definitely avoided with the piston-sliding shoe pairing according to the invention and its relief opening into the environment.

[0008] In a particularly preferred embodiment of the piston-sliding shoe pairing according to the invention, it is provided that the media-conducting receiving space is composed of a first space portion between the two mutually facing end faces of the shoe parts and a second space portion which is smaller in comparison and which is delimited on the one hand by a cross-sectionally conical penetration area in one shoe part which at least partially forms a receptacle for the joint head, and on the other hand by the joint head itself. The two space portions create an increase in the fluid receiving volume for the receiving space, which likewise counteracts an inadmissibly high pressure build-up in the receiving space, to which the conicity tapering towards the free piston end also contributes.At the narrowest point of the conical receptacle, a first circular central recess is created, which is delimited by wall parts of the first shoe part, which at this point enclose the joint head in this area in a tight fit in the manner of a constriction.

[0009] In a further preferred embodiment of the piston-sliding shoe pairing according to the invention, it is provided that the respective relief opening is guided as a bore or channel in one shoe part and / or in the other shoe part and / or between both shoe parts and / or within wall parts of the piston, preferably radially introduced into a side wall of one shoe part, which is left free from the other shoe part at least in this area.By using at least one relief bore or one relief channel, the respective relief opening can be introduced into the indicated pairing in a cost-effective manner. It is generally advantageous to provide several relief openings simultaneously, for example, at least two relief openings that are arranged in pairs diametrically opposite one another to the longitudinal axis of the piston in one shoe part, extend continuously in the radial transverse direction within the shoe part, and open into the receiving space with parts of the joint head. In a particularly preferred embodiment of the piston-sliding shoe pairing according to the invention, it is provided that the first spatial portion of the receiving space, viewed in the axial travel direction of the piston, is larger than the corresponding axial length of the second spatial portion.This arrangement according to the claim also leads to a significant increase in the space or volume share for the receiving space in the axial direction to the actuating axis of the piston, so that undesirable pressure increases or pressure peaks are avoided.

[0010] In a further preferred embodiment of the piston-sliding-shoe pairing according to the invention, the two shoe parts are in direct contact with one another without the interposition of additional components, such as additional sealing and guide shells. This results in a space-saving design in this area, since the two shoe parts of the sliding shoe are in direct operative connection with the piston rod end. Manufacturing costs can also be saved by reducing the number of parts. By using modern materials, such a direct operative connection or coupling between the components of the pairing can also be designed to be functionally reliable and long-lasting during operation.

[0011] In a further preferred embodiment of the piston-sliding shoe pairing according to the invention, the rod end has a diameter along its largest outer circumference that is larger than the diameter of the piston shaft along its largest outer circumference. This creates a solid, high-strength piston solution that can withstand even the highest stresses during pump operation with an axial piston machine, in particular in the form of a wobble shaft machine. Otherwise, the pairing can also be used in swash plate machines, which also fall under the technical category of axial piston machines. Since the piston shaft diameter is reduced compared to the rod end diameter, the result is a slender piston shaft with a reduced mass compared to known solutions in which the shaft diameter is larger than the rod end diameter; even if such a piston shaft is provided with a hollow chamber.

[0012] Due to the low input mass of the piston as a whole, significantly less energy is required to accelerate and decelerate the respective pistons during pump operation with a hydraulic pump. This also reduces wear in the area of ​​the piston-sliding block connection, which benefits the longevity of the axial piston machine or hydraulic pump. Furthermore, the diameter of the head is also larger than that of the shaft because, given the high forces generated during operation due to the high pressures, the contact surface at the support of the rod end with the sliding block would otherwise have to be enlarged. This is avoided by the measures described.

[0013] In a further preferred embodiment of the piston-sliding-block pairing according to the invention, a concave constriction is provided at the transition point between the rod end and the piston shaft, which constriction is smaller in diameter than the adjacent rod end and the piston shaft. This constriction results in particular from the manufacture of the piston as a whole, and in addition to strengthening the material, the constriction also serves to act as a stop, ensuring that the possible free pivoting movement of the sliding block on the rod end is limited. This prevents malfunctions during the piston-pump movement.

[0014] In a further preferred embodiment of the invention

[0015] The piston-sliding-shoe pairing is designed so that the piston has a longitudinal channel that opens out at each end of the piston. This longitudinal channel can function as a pressure equalization channel to eliminate any obstructions to piston movement. Furthermore, this allows for a lubricant supply via the interior of the piston and its rod end to the end or front side of the pairing facing the sliding-shoe connection.

[0016] In a further preferred embodiment of the piston-sliding shoe pairing according to the invention, one shoe part, with a diameter reduction at the end in the region of the first circular central recess, encloses the joint head of the piston flush along a circumferential line in such a way that only rotational movements relative to each other are possible for the piston and / or the sliding shoe. The possible rotational movements in this respect occur in all directions, since the piston is longitudinally guided, but the sliding shoe is forced to move in a rotational manner with the control disc or swash plate. In this way, the sliding shoe with its shoe parts can directly and without delay follow the movements of a control disc of the hydraulic pump, usually in the form of a swash plate with an inclined control surface (DE 10 2023 004 369.9).

[0017] In a further preferred embodiment of the piston-sliding shoe pairing according to the invention, one shoe part partially radially surrounds the joint head with a support and preferably forms a linear contact point with the latter at its end. A fluid medium to be conveyed, such as hydraulic oil, can reach this linear contact point via the conical through-opening in one shoe part, in order to minimize the friction between the sliding shoe as a whole and the joint head. It is preferably further provided that the other shoe part delimits a further shell-shaped or spherical recess on its end face, which has a shell-shaped or dome-shaped bearing in the manner of a ring segment at its one free edge end for the axial support of the joint head, which projects in the direction of the joint head by a predeterminable projection relative to the further recess.Since the shell-shaped bearing mentioned can be dimensioned spatially small, little friction is generated in the bearing area mentioned, which enables long-lasting and trouble-free operation.

[0018] Preferably, it is further provided that the piston is guided to be movable back and forth in the longitudinal direction, and that pivoting of the sliding block with its two shoe parts is enabled via its joint head, with one shoe part driving the other shoe part along via a guide surface. By coupling the two shoe parts of the sliding block to one another in this way, a corresponding limitation of the degrees of freedom during the pivoting movement of the sliding block on the joint head is achieved, which increases functional reliability and improves power transmission during the piston-pump movement. Furthermore, due to the aforementioned coupling during operation, malfunctions are avoided during the movement sequence.

[0019] In a further preferred embodiment of the piston-sliding shoe pairing according to the invention, the other shoe part is penetrated, starting from its free end face, by a nozzle channel which opens into the further recess serving as a fluid chamber between the joint head and the other shoe part, which is fluidly connected to the longitudinal channel of the piston. In this way, the fluid delivered by the pump device or hydraulic pump can be directed via the longitudinal channel and the nozzle channel onto the front side of that shoe part of the sliding shoe which is in direct contact with the control disk, usually in the form of a wobble or swash plate, for improved lubricant application. Furthermore, the piston-sliding shoe pairing preferably has an annular, flange-like widening on one shoe part which projects at a right angle to the surroundings.The widening serves in particular to provide circumferential support for a preloading device which is a component of the axial piston machine and whose force flow acts perpendicularly on the widening, so that one shoe part of the sliding shoe arrangement is brought into contact with parts of the outer circumference of the rod end of the piston arrangement with a predeterminable contact force, which also increases the functional reliability of the pairing in question.

[0020] The piston-sliding shoe pairing according to the invention is explained in more detail below using an embodiment shown in the drawing. The sole figure shows a longitudinal section through the pairing in question.

[0021] The above figure shows a piston-sliding-shoe pairing for an axial piston machine, in particular a swash-wave machine in the style of a hydraulic pump, as is well known in the prior art. The pairing comprises a piston 10 having, at the end of a hollow-cylindrical piston shaft 12, a spherical joint head 14 which is at least partially received by a spherical receptacle in the style of a ball socket 16 of a sliding shoe 18. Such pistons 10 are accommodated in a plurality and in a series arrangement in a receiving cylinder with piston receptacles (not shown) as part of a pump arrangement, wherein the piston receptacles enable a longitudinal movement of the piston 10 with its piston shaft 12 as part of a pump movement.As already explained, the respective free, front piston end is guided in an associated sliding guide, which is also technically referred to as a sliding shoe 18. The respective sliding guide is usually supported by means of a preloading device with a predeterminable preload in each position of a control disc on the associated adjacent control surface of the same. This control disc, which is usually designed in the manner of a swash plate of an axial piston machine, has at least one obliquely inclined control surface. This arrangement of a control disc with a control surface and a preloading device operatively connected thereto is common practice, so it will not be discussed in further detail here, particularly in the drawings (DE 10 2023 004 369.9).

[0022] As further shown in the figure, the aforementioned joint head 14 has a diameter along its largest outer circumference that is larger than the diameter of the piston shaft 12 along its largest outer circumference, with the respective diameter being determined transversely to the displacement movement of the piston 10, specifically along the longitudinal axis 20 of the piston-sliding shoe pairing. Preferably, the diameter of the piston shaft 12 is approximately 70 to 90%, particularly preferably approximately 80%, of the diameter of the joint head 14. Other sizes are possible if required.

[0023] At a transition point between the joint head 14 and the piston skirt 12, a concave constriction 22 is present, which is reduced in diameter compared to the adjacent joint head 14 and the piston skirt 12. This constriction 22 results, in particular, from the manufacture of the piston 10 from solid material, for example, in the form of steel. In addition to material hardening, the constriction 22 also serves, in the manner of a stop, to tangibly limit the free pivoting movement of the sliding block 18 on the spherical joint head 14 toward the upper side of the piston skirt 12.Coaxial to the longitudinal axis 20, the piston 10 further has a longitudinal channel 24 which extends continuously through the piston 10 essentially with a constant, identical inner diameter, the longitudinal channel 24 exiting outwards at the end of the piston 10 via funnel-shaped extensions 26, 28, the left funnel-shaped extension 26, as viewed in the direction of the figure, being larger than the right extension 28 and in particular having a larger free cross-section than the funnel-shaped extension 28. The inner diameter of the longitudinal channel 24 does not necessarily have to remain constant, but the geometry can also be changed if necessary. The funnel-shaped extensions 26, 28 can also be omitted or have a different geometry if required.In the example shown, a fluid flow from extension 26 to extension 28 creates a jet effect in the longitudinal channel 24, accelerating the lubricant toward the application point on the slide shoe 18. Depending on the manufacturing process, extension 28 can also be larger than extension 26 while achieving the same technical effect.

[0024] The sliding shoe 18 has two shoe parts 30, 32, which, in cooperation with the joint head 14, form the essential parts of the ball socket 16 as a whole. In particular, the other shoe part 32, viewed individually, has a bearing support 34 for the joint head 14 of the piston 10. In contrast, one shoe part 30, with a reduced diameter 36, encloses the joint head 14 of the piston 10 in the direction of the constriction 22 in such a way that, during an axial longitudinal movement of the piston 10 along the longitudinal axis 20 during a pumping process, only rotational movements are possible for the sliding shoe 18, specifically in directions transverse to the aforementioned longitudinal movement of the piston 10 during such a pumping movement. In this respect, one shoe part 30 forms with a contact surface 38 a kind of linear, circumferential contact point 40 for the outer circumference of the joint head 14.Due to the diameter reduction 36, one shoe part 30 is securely held on the joint head 14. The other shoe part 32, however, with its support 34, axially supports the joint head 14 in the direction of the longitudinal axis 20 and, in this respect, forms with it a shell-shaped bearing 42 in the manner of a ring segment, which is partially concavely curved in accordance with the convex shape of the joint head 14. One shoe part 30 is rotationally symmetrical and concentric to the longitudinal axis 20 and, on its inner side, delimits a first central recess 44 with a circular cross-section in the manner of a truncated cone 43. The diameter of this first central recess 44 is reduced on one side due to the diameter reduction 38. On the opposite side, the truncated cone 43, with its second end-side circular central recess 45, expands in diameter and merges into a receiving space 46.The other shoe part 32 forms a type of longitudinal guide 48 on the outer circumference side for a hollow cylindrical inner circumference 50 of one shoe part 30, which encompasses the other shoe part 32 in this area. The conicity of the truncated cone 43 is in any case selected such that it widens in the direction of the receiving space 46.

[0025] As already explained, the piston 10 is guided in a longitudinal direction so as to be movable back and forth in a correspondingly assignable piston receptacle in a cylinder or device housing (not shown) and its joint head 14 enables pivoting of the sliding shoe 18 with its two shoe parts 30, 32, wherein the other shoe part 32 takes along one shoe part 30 via its guide surface in the form of the longitudinal guide 48 and vice versa.Furthermore, the other shoe part 32, starting from its free end face 52, is penetrated by a type of nozzle channel 54, which opens into a fluid chamber in the form of the further recess or receptacle 56, which is lens-shaped in cross-section, between the joint head 14 and the other shoe part 32. This recess 56 is part of a dome-shaped receptacle 58 in the other shoe part 32, into which the free end face of the spherical joint head 14 engages at least partially, maintaining a distance in this area from the other shoe part 32. In this way, the joint head 14 bears against the other shoe part 32 in an axially supporting manner exclusively via the shell-shaped bearing 42. The nozzle channel 54 is part of a hollow cylindrical insert 60, which, starting from the further receptacle 56, is permanently inserted with a widened flange surface into an associated bore in the other shoe part 32.In the form of an aperture-shaped extension 62, the nozzle channel 54 opens via the further receiving or fluid chamber 56 into the funnel-shaped extension 28 of the longitudinal channel 24 within the piston shaft 12. In this way, a fluid to be pumped by the pump device can be conveyed as lubricant via the longitudinal channel 24 with the funnel-shaped extensions 26, 28 into the further receiving chamber 56, and from there, a supply to the front free end face 52 of the further other shoe part 32 is ensured via the nozzle channel 54. For improved lubricant application between the free end face 52 of the further shoe part 32 and an adjacent control surface of a control disk (not shown), a circular cylindrical recess 64 is introduced into the free end face 52 of the further shoe part 32, which is in direct media-conducting connection with the fluid supply via the nozzle channel 54.This lubricant supply ensures smooth, low-wear operation with the fluid or medium to be pumped. For improved lubricant delivery, the free diameter of the nozzle channel 54 is reduced, starting from the extension 62, toward the free end face 52 of the slide shoe 18.

[0026] As can also be seen from the figure, one shoe part 30 has an annular, flange-like widening 66, which, in every travel state of the piston 10, is supported circumferentially on a pretensioning device (not shown), the force flow of which is symbolically represented by the two arrows. The corresponding force direction of the pretensioning device is usually generated by an energy accumulator in the form of a compression spring, which is supported stationary with one free end on parts of a device housing of the hydraulic pump and, with its other free end, is in movable contact with a system part on which the flange-like widening 66 is supported with a support surface 68.In this way, the respective preloading device with its compression spring ensures that one shoe part 30, with its flange-like widened portion 66, can be tilted or pivoted around the joint head 14 in such a way that the free end face 52 of the other shoe part 32, which is thus carried along in the movement, remains in contact with the adjacent control surface of a control disc. In this way, the control disc can directly transmit the resulting force to the respective piston 10 for a pump delivery movement during its rotating movement.

[0027] At least one relief opening 70 can be provided in one shoe part 30, which connects the receiving space 46 with the adjoining environment. The respective relief opening 70 preferably runs radially through an annular side wall 71 of the one shoe part 30. During a lifting or pumping movement of the piston 10, viewed from right to left in the direction of the figure, the fluid to be pumped, which is located in the longitudinal channel 24 and in a further receiving space or fluid space 56, is pressurized. During a suction stroke, however, the piston 10 moves in the opposite direction, from left to right. The insert 60 with the nozzle channel 54 forms a throttle with a predeterminable cross-section, which can release a certain amount of fluid into the circular-cylindrical recess 64. The pressurized fluid in the recess 64 leads to the slight lifting of the sliding shoe 18 from the control disk, i.e.to a hydrostatic bearing of the sliding shoe 18. Furthermore, a very small amount of fluid can leak into the receiving chamber 46 outside the additional, bowl-shaped receiving or fluid chamber 56 via the support 34 of the piston W arn other shoe part 32. If the amount of fluid in one receiving chamber 46 becomes too large, an unwanted pressure builds up there which, without relief opening(s) 70, can lead to the two shoe parts 30, 32 being pushed away from each other. The sliding shoe 18 can then fall apart, causing the pump to fail as a whole. The respective relief opening 70 thus advantageously prevents this harmful pressure buildup in the receiving chamber 46.

[0028] As the longitudinal section of the figure further shows, one receiving chamber 46 is connected to the environment by means of two fully shown and two partially shown relief openings 70, which can also be enclosed by parts of an axial piston machine, such as its housing parts (not shown). A total of eight relief openings 70 are used. It is understood that just one relief opening 70 can be sufficient to ensure the media-carrying connection from one receiving chamber 46 to the aforementioned environment, preventing an unacceptably high pressure buildup. The two relief openings 70 shown entirely in longitudinal section are each designed as a bore or fluid channel and, with their free opening cross-sections, are located within the plane of the drawing.Furthermore, the relief openings 70 are arranged in pairs diametrically opposite each other to the longitudinal axis 20 and are perpendicular to the aforementioned longitudinal axis 20 with their bore or opening axes, which also represents the actuation axis for the piston 10. All further relief openings 70 (not shown) can extend out of and into the plane of the drawing, preferably at equidistant radial distances from the other two relief openings 70.

[0029] The receiving chamber 46 has a first space portion 72 and a smaller second space portion 74. The two space portions 72, 74 of the receiving chamber 46 are permanently connected to one another by means of fluid or media. Furthermore, the first space portion 72 is arranged between the two mutually facing end faces 76, 78 of the shoe parts 30 and 32, respectively. In the shown initial or operating position of the piston-sliding shoe pairing, the end faces 76, 78 are arranged parallel to one another and are perpendicular to the longitudinal axis 20 of the piston 10. The second space portion 74 of the receiving chamber 46, which is smaller in terms of volume, is designed as a truncated cone 43, which is circumferentially delimited on both of its outlet sides by a circular central recess 44, 45.Furthermore, the other shoe part 32 is provided with an annular recess 80, which is part of the receiving space 46 and which delimits the shell-shaped bearing 42 in the direction of the receiving space 46.

[0030] The respective relief opening 70 is formed as a bore radially extending into the hollow cylindrical circumferential side wall 71 of one shoe part 30, transverse to the longitudinal axis 20, in one shoe part 30, wherein the side wall 71 is left free of the other shoe part 32 at least in this penetration area. In principle, it is also possible to establish the media connection from the outside to the receiving space 46 via at least one relief opening in the other shoe part 32, which runs parallel or obliquely to the longitudinal axis 20. Such a media-carrying connection can also be achieved via a channel guide (not shown) within the solid wall parts of the piston shaft 12.A preferred alternative, however, is to introduce the respective relief opening 70 in the manner of at least one groove-shaped channel between one shoe part 30 and the other shoe part 32, for example along the cylindrical outer circumference of the other shoe part 32, which serves as a longitudinal guide 48. In principle, the channel-like relief opening 70 can also be delimited on one side by one shoe part 30 and on the other side by the other shoe part 32.

[0031] The first space portion 72, in the form of a hollow cylindrical disc, viewed in the axial direction of travel of the piston 10 parallel to the longitudinal axis 20, is larger than the corresponding axial length of the truncated cone 43 in one shoe part 30, which is also related to the orientation of the longitudinal axis 20. The respective relief bore 70 has a bore diameter that is equal to or substantially equal to the axial height of the first space portion 72 of the receiving space 46 between the two end faces 76, 78.

[0032] The function of the respective relief opening 70 is described in more detail below. During a lifting or pumping movement of the piston 10, viewed from right to left in the figure, to build up pressure, the pressure medium located in the longitudinal channel 24 and in the further receiving chamber 56 is pressurized accordingly. Through the hollow cylindrical insert 60 with nozzle 54 in the manner of a throttle, a certain amount of this pressure medium is delivered to the circular cylindrical recess 64 in the free end face of the other shoe part 32. This pressure in the fluid chamber in the form of the recess 64 leads to a slight lifting of the other shoe part 32 relative to the control or swash plate, which is to be regarded as rigid, so that a hydrostatic bearing for the other shoe part 32 of the sliding shoe 18 is created.In any case, a relatively small amount of pressure medium can, in principle, enter the receiving chamber 46 with its two chamber sections 72, 74 as a leakage flow via the shell-shaped bearing 42 between the outer circumference of the joint head 14 and the adjacent inner circumference of the other shoe part 32. However, if the amount of pressure medium in this receiving chamber 46 becomes too large, a correspondingly high fluid pressure builds up therein, which leads to the two sliding shoes 30, 32 being pushed away from each other by a corresponding fluid pressure acting in opposite directions on their end faces 76 and 78, respectively. This could cause the sliding shoe 18 to fall apart, thus causing the hydraulic pump to suffer permanent failure.Thanks to the respective relief opening 70, any resulting pressure build-up in the receiving space 46 can now be prevented from the outset, so that the two sliding shoes 30, 32 always remain functionally positioned relative to one another as a ball joint receptacle for the joint head 14. Furthermore, a certain amount of leakage passes through the wedge-shaped gap, viewed in cross-section, between the first shoe part 30 and the outer peripheral side of the joint head 14 in this area in the direction of the circular diameter reduction 36 or the first central recess 44, which is penetrated by the joint head 14 at this point and is part of the truncated cone 43.

[0033] With the piston-sliding shoe pairing shown in the figure, fluid flow rates can be achieved under very high pressure, whereby the pairing in question is designed to be largely force-balanced so that the forces occurring during the pump movement are compensated, which ensures long-lasting, wear-free operation, which has no equivalent in the state of the art.

Claims

Patent claims 1 . Piston-sliding shoe pairing for an axial piston machine, with a piston (10) which has a spherical joint head (14) at the end of a piston skirt (12), which is at least partially received by a spherical receptacle (16) of a sliding shoe (18) which has two shoe parts (30, 32) which together delimit a receiving space (46) through which the spherical joint head (14) passes, characterized in that the receiving space (46) is in media-conducting connection with the environment adjacent to the sliding shoe (18) by means of at least one relief opening (70).

2. Piston-sliding shoe pairing according to claim 1, characterized in that the receiving space (46) is made up of a first space portion (72) between the two mutually facing end faces (76, 78) of the shoe parts (30, 32) and a second space portion (74) which is smaller than the first space portion and which is delimited on the one hand by a truncated cone (43) in one shoe part (30) and on the other hand by the joint head (14) itself.

3. Piston-sliding shoe pairing according to claim 1 or 2, characterized in that the respective relief opening (70) is guided as a bore or channel in one shoe part (30) and / or in the other shoe part (32) and / or between the two shoe parts (30, 32) and / or within wall parts of the piston (10), preferably radially introduced into a side wall (71) of one shoe part (30), which is left free at least in this area from the other shoe part (32).

4. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the first space portion (72) of the receiving space (46) is larger in the axial direction of travel of the piston (10) than the corresponding axial length of the truncated cone (43) in one shoe part (30).

5. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the two shoe parts (30, 32) are in direct contact with one another without the interposition of additional components, such as additional sealing and guide shells.

6. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the joint head (14) has a diameter along its largest outer circumference which is larger than the diameter of the piston skirt (12) along its largest outer circumference.

7. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that at the transition point between the joint head (14) and the piston shaft (12) there is a constriction (22) which is reduced in diameter compared to the respectively adjacent joint head (14) and the piston shaft (12).

8. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the piston (10) has a longitudinal channel (24) which opens out at the end of the piston (10).

9. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the one shoe part (30) with a diameter reduction (38) the joint head (14) of the piston (10) partially flush in such a way that only rotational movements relative to one another are possible for the piston (10) and / or the sliding shoe (18).

10. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the one shoe part (30) with a linear contact point (40) radially surrounds the joint head (14).

11. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the other shoe part (32) defines on the end face a shell-shaped further receiving space (56) which has at its one free edge-side end for the axial support of the joint head (14) a shell-shaped or dome-shaped bearing (42) in the manner of a ring segment, which projects by a predeterminable projection relative to the further receiving space (56) in the direction of the joint head (14).

12. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the further receiving space (56) is delimited by a concave wall part of the other shoe part (32) and partially overlaps the convex joint head (14) on the edge side in such a way that the further receiving space (56) tapers in the direction of the bearing (42) in a slit-like manner and preferably forms a type of lens shape when viewed in cross-section.

13. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the piston (10) is guided to be movable back and forth in the longitudinal direction (20) and its joint head (14) enables pivoting of the sliding shoe (18) with its two shoe parts (30, 32) and that one shoe part (30) takes the other shoe part (32) along with it via a guide surface.

14. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the other shoe part (32) is penetrated from its free end face (52) by a nozzle channel (54) which leads into the further receiving space (56) serving as a fluid space between the joint head (14) and the other Shoe part (32) opens out and which is fluid-conductingly connected to the longitudinal channel (24) of the piston (10).

15. Piston-sliding shoe pairing according to one of the preceding claims, characterized in that the one shoe part (30) has an annular, flange-like widening (66) which in the right angle towards the surroundings.

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