CN116025535A

CN116025535A - Sliding shoe for axial plunger machine and axial plunger machine with sliding shoe

Info

Publication number: CN116025535A
Application number: CN202211317706.1A
Authority: CN
Inventors: T·纳夫兹
Original assignee: Robert Bosch GmbH
Current assignee: Robert Bosch GmbH
Priority date: 2021-10-27
Filing date: 2022-10-26
Publication date: 2023-04-28
Also published as: DE102021212098A1

Abstract

A shoe for slidably supporting a plunger on a swash plate of an axial piston machine has a recess with a concave, spherical band-shaped surface section for abutment against a ball head of the piston. In addition, an axial piston machine having such a shoe is disclosed.

Description

Sliding shoe for axial plunger machine and axial plunger machine with sliding shoe

Technical Field

The present invention relates to a shoe of an axial piston machine of a swash plate construction according to the preamble of claim 1 and to an axial piston machine of a swash plate construction according to claim 9 having such a shoe.

Background

Axial plungers in the form of swash plates are currently available with spherical shoe joints, which require the transmission of large forces. In this shoe joint, the piston ball is supported in a spherical recess of the shoe, wherein both the piston ball and the shoe are made of metal. In order to load such a joint hydraulically and to prevent metal-to-metal contact which can lead to increased wear, the piston ball is flattened at its end facing the shoe. The volume thus formed between the piston ball and the shoe forms a pressure space and is acted upon by the pressure medium under high pressure. The loading can be efficiently achieved by the rearward hydrostatic working space delimited by the piston by means of the through-opening. This pressurized medium under high pressure resists the piston force. The flattened portion of the piston ball may not be selected to be too large in order to mechanically transfer the residual face pressure between the piston ball and the shoe. In addition, there is a risk of the shoe cracking in this case, since as the flattening increases, the plunger force is increasingly introduced by its radial component (and thus splits).

From these boundary conditions, it can be seen that today's slipper-piston joints are far from adequately relieved. In particular in motor applications, high residual surface pressures can occur, which can lead to wear at the shoes and/or the piston balls up to a complete failure.

In another technical field, axial piston machines of entirely different design, which are constructed using a diagonal shaft, for example as disclosed in DE 10 2006 019 884 B4, have piston balls into which the discharge grooves are introduced. The disadvantage here is that the relief surface is small and the permissible pivot area of the ball head is very limited, since for efficiency reasons an uncontrolled excessive leakage of hydraulic fluid into the housing of the axial piston machine must be prevented in terms of construction.

Disclosure of Invention

The object of the present invention is therefore to provide a shoe for an axial piston machine of the swash plate type, which shoe eliminates or at least reduces the disadvantages of the prior art. In particular, the object of the present invention is to provide a shoe for an axial piston machine of the swash plate type, which is resistant to premature wear of the shoe and thus prevents complete failure of the axial piston machine. Another object is to provide an axial piston machine of the swash plate type that is better protected against premature wear.

The first task is solved by a slipper having the features of claim 1; the second object is achieved by an axial piston machine having the features of claim 9.

Advantageous modifications of the invention are specified in the dependent claims.

In particular, shoes for slidably supporting pistons, in particular working pistons, are provided at the swash plate of the axial piston machine. The shoe has a sliding surface which can face the swash plate, in particular the swash plate, and has a recess on the opposite side of the sliding surface for receiving the ball head of the piston at least in sections. The recess has a spherical surface section which is configured for abutment with a ball head. According to the invention, this face section comprises a first groove, which extends away from the relatively smaller diameter of the face section in a direction towards the larger diameter of the face section, or away from the smallest diameter of the face section towards the larger diameter.

In other words, the shoe, by means of which the piston can be supported by means of a sliding surface on a swash plate of an axial piston machine, is formed with a recess, in particular in the form of a spherical crown. The recess is configured and arranged to receive a ball head of the piston. The inner face of the recess comprises a concave, spherical surface section, against which the ball head of the piston rests at least in sections. A first groove is formed in the spherical band section, said first groove extending away from the spherical band section toward the edge of the sliding surface.

The pressurized medium under high pressure can reach between the ball head and the spherical band section via the first groove from the pressure space, which can preferably be formed by the flattened portion of the top side of the ball head and the bottom of the spherical crown-shaped recess, and form a hydrostatic relief zone there. In this way, load shedding can be increased and thus wear between the ball head and the shoe can be significantly reduced. Furthermore, the provision of the first groove makes it possible to keep the permissible pivot range of the ball head in the shoe relatively large, without leakage of hydraulic fluid into the housing of the axial piston machine being caused.

The application of pressure medium under high pressure to the pressure space can be efficiently achieved by the hydrostatic working space delimited by the piston and directed toward the rear by means of a through-hole, which has a junction opening at the top section of the ball head, which is directed toward the recess of the shoe.

In a first aspect of the invention, the shoe can comprise a central axis, with respect to which the at least one first groove extends, in particular helically, at least in part circumferentially.

In other words, the shoe is substantially rotationally symmetrical with respect to an axis, which can then be referred to as the central axis of the shoe. Another expression is: the central axis extends through a midpoint of a smallest diameter of the spherical band-shaped surface section and is oriented perpendicular to the sliding surface. The first groove extends in the spherical segment and, with reference to the central axis, extends in the spherical segment in a spiral shape having a continuously increasing diameter.

By means of the first groove, which extends in particular in a spiral shape in the circumferential direction, a uniform distribution of the pressure medium between the ball head and the spherical band-shaped surface section can be achieved, and thus the relief between the ball head and the shoe is further increased.

In another aspect, the shoe can have a second groove in the spherical band shaped face section that extends in the entire circumferential direction between a smaller or minimum diameter and (relative to) a larger diameter. The second groove can be in particular a ring groove, which is closed in the entire circumferential direction. The second groove can be arranged in particular perpendicularly to the central axis.

In other words, a second groove can be formed in the spherical band section, which is arranged in parallel to the sliding surface with a constant diameter in the spherical band section. The second grooves serve here to distribute the pressure medium uniformly over the entire circumference of the spherical band-shaped surface section, which contributes to uniform relief.

In another aspect, the diameter of the second groove can be less than the equatorial diameter of the recess.

In other words, the diameter of the second groove can be smaller than the maximum diameter of the spherical band-shaped surface section. In this way, it can be ensured that the sealing surface formed between the ball head and the ball web section of the shoe is reliably sealed and thus leakage of the pressure medium to the housing of the axial piston machine is prevented and thereby a high pressure drop between the ball head and the ball web section is prevented.

In a further aspect, the pressure space, which is delimited/delimited at least in sections by the spherical band-shaped surface section and the spherical head, can be fluidically connected/connectable to the second groove by means of at least one first groove.

In other words, the first groove can transition into the second groove and thus form a free space or a hydraulic fluid line communicating with the pressure space. In this way, the hydraulic fluid can be reliably guided from the pressure space, independently of the position/oscillation of the piston relative to the shoe, via the first groove into the second groove, which distributes the pressure medium under high pressure uniformly over the circumference.

In a further aspect, the at least one first groove can merge into the second groove at a gentle angle, in particular an angle of less than 20 °.

In other words, the angle enclosed by the first and second grooves at the transition/merging position can be less than 20 °. By choosing such a gentle angle/acute angle, it is achieved that the pressure medium is flushed from the first groove into the second groove in a manner that is as uniform as possible and that no local backflow occurs, which contributes to a uniform distribution of the pressure medium in the circumferential direction.

In another aspect, the at least one first slot can have at most one turn.

In other words, the first groove can extend in the spherical segment, with reference to the central axis, around which the spiral with a continuously increasing diameter extends up to 360 °. However, embodiments can also be provided in which at least one first groove has more than one turn.

By definition of at most one turn it can be ensured that a pressure medium with a sufficiently high pressure can reach the end of the first groove or into the second groove and that the pressure loss over the stroke of the first groove can be kept low.

In another aspect, the shoe can have a plurality of first grooves in the spherical band shaped surface section. Preferably, the spherical band section has two first grooves, which are formed opposite one another at the spherical band section. It is further preferred that the spherical band section has more than two first grooves which extend at a reference of a circumferential angle relative to the central axis, preferably at equal angular intervals. Further preferably, at least two first grooves can intersect.

In other words, the plurality of first grooves can extend in the spherical band section away from its smallest diameter, wherein the plurality of first grooves preferably extend in a spiral shape in the spherical band section.

The provision of a plurality of first grooves ensures that the pressure medium under high pressure is introduced uniformly over the entire surface of the relief diameter, without the first grooves being excessively extended in this way, and thus no pressure loss occurs over the travel of the first grooves.

The invention further relates to an axial piston machine having a drive shaft and a cylinder-piston unit connected thereto in a rotationally fixed manner, each hydrostatic working space being delimited in sections by a piston thereof, said working spaces being able to be connected alternately with a low-pressure space and a high-pressure space of the axial piston machine with the rotating drive shaft, wherein a ball head of the piston is accommodated in a recess of a shoe, by means of which the piston is slidingly supported on a swash plate, wherein the recess has a spherical segment in which a first groove extends away from a smaller diameter of the spherical segment toward a larger diameter of the spherical segment.

Drawings

The invention will now be described in detail with reference to the drawings and according to advantageous embodiments. The drawings herein are merely schematic in nature and are intended to illustrate the present invention. Wherein:

FIG. 1 shows a diagram of a slipper according to the invention in a longitudinal section according to a first embodiment;

FIG. 2 shows a schematic representation of a slipper joint consisting of a slipper and a ball head of a piston in accordance with the present invention; and

fig. 3 shows an axial piston machine according to the invention in a longitudinal section in the form of a swash plate.

Detailed Description

Fig. 1 shows an embodiment of a slipper 2 according to the invention. The basic geometry of the skid shoe 2 is essentially multi-stage cylindrical, which in this embodiment has two consecutive cylinder sections of different diameters. Furthermore, the skid shoe 2 is rotationally symmetrical with respect to a first central or vertical axis M1.

The cylinder section having the larger diameter has an end face with a sliding surface 4 which is arranged and designed to be slidingly supported on the sliding surface of the swash plate 48 of the axial piston machine 36. At the cylinder section with the smaller diameter, the shoe 2 has a concave recess 6. Conventionally, this recess serves to accommodate a ball head of a piston 12 of the axial piston machine (see fig. 2) and has a concave, spherical band-shaped (kugelzonf-r) face section 8 which is provided and is designed for abutment against the ball head. The recess 6 merges at its bottom into a tapering section of a pressure medium channel 14, which merges toward the sliding surface 4. The sliding surface 4 is segmented by a parting bead 15.

In the spherical band-shaped surface section 8, a first groove 16 is formed, which extends away from the smallest diameter D1 of this surface section 8 in the direction of the larger diameter D2 of this surface section 8 and the largest diameter D of the recess 6. In the exemplary embodiment shown, the first groove 16 extends in the face section 8 in a spiral shape with a constant inclination about the central axis M1, wherein a different extension shape is of course possible.

For example, the first groove 16 can extend along an intersection line, which can be formed by a plane arranged with respect to the central axis M1 and the face section 8.

Irrespective of the extended shape (spiral shape, thread shape, intersection line or the like), the following is possible: the first groove 16 extends at a smaller angle relative to the central axis M1 than relative to the sliding surface 4; or conversely, extends more gently at a smaller angle relative to the sliding surface 4 than relative to the central axis M1; or a compound trend with varying tilt angles.

When interacting with the ball head of the piston, a pressure space 18 is formed in the region of the smallest diameter d1 (see fig. 2).

In the spherical band-shaped surface section 8, the second groove 20 is formed in the circumferential direction having a diameter d2 larger than the diameter d 1. In other words, the second groove 20 is oriented parallel to said sliding surface 4. In contrast, the second groove 20 can be oriented obliquely to the plane of the sliding surface 4, for example, in order to optimize the hydrostatic relief area between the ball head 10 and the shoe 2, which can be delimited thereby.

The first groove 16 connects the pressure space 18 with the second groove 20 by way of its converging opening into the pressure space 18 on one side and into the second groove 20 on the other side. According to fig. 2, when the ball head 10 is in contact with the surface section 8, the pressure space 18, the first groove 16 and the second groove 20 form a communicating pressure space. The junction 22 of the junction or the first groove 16 into the second groove 18 is configured in such a way that the angle α is relatively gentle. Said angle alpha is in particular smaller than 20 deg.. The sealing surface boundary 24 is formed parallel to the second groove 20 on the side of the second groove 20 facing away from the sliding surface 4, by means of which sealing off the relief zone is sealed off towards the interior of the axial piston machine 36.

Fig. 2 shows an exemplary embodiment of a shoe joint 26, which is formed by a ball head 10 of a piston 12 and a variant of the shoe 2 according to the invention according to fig. 1. Unlike the sliding shoe 2 according to fig. 1, the sliding shoe 2 shown in fig. 2 has no parting bead 15 on the sliding surface 4, and the pressure medium channel 14 is configured less complex than the pressure medium channel 14 shown in fig. 1. More precisely, the pressure medium channel 14 of fig. 2 has a cone-column shape. Furthermore, the skid shoe 2 in fig. 2 has a circumferential groove 27 on the side of the cylindrical section with the larger diameter. The ball head 10 is inserted into a recess of the shoe 2 and is engaged from behind (hittergreifen) by the recess toward the flange 28 of the tapered neck section of the ball head 10. The ball head 10 is thereby pivotally mounted in the spherical crown-shaped recess 6 of the shoe 2 and is connected to this shoe in a tensile manner.

The piston 12 is configured as a hollow piston and has an interior 29 delimited by a piston skirt. In the case of a piston 12 which is provided as a working piston, this interior space 29 is alternately connected to high pressure and to low pressure in the normal operation of the axial piston machine 36. The following circulation section is particularly important here for the hydrostatic load shedding of the friction pair (i.e. the friction pair of the shoe 2 and the ball head 10, and also the friction pair of the shoe 2 and the swash plate 48): in the circulation section, the pressure medium with high pressure fills the inner space 29. In this case, the greatest piston and thus the greatest surface pressure acts on the shoe 2, not only between the ball head 10 and the surface section 8, but also between the sliding surface 4 and the swash plate 48.

The through-hole 30 passes from the inner space 29 along the central axis M2 of the piston 12 through the neck section of the piston 12 to a flattened portion 32 located at the top of the ball head 10. According to fig. 2, the pressure space 18, which has been described in advance in accordance with fig. 1, is delimited in sections by the flattening 32 and the spherical band-shaped surface section 8, to be precise by sections thereof. As can be seen best from fig. 1 and 2, the pressure space 18 is not defined in a geometrically fixed manner, but rather is associated with the angle enclosed by the axes M1, M2. As shown in fig. 3, in the axial piston machine 36 whose pressing volume is adjustable, if the axis M2 of the piston 12 is parallel to the rotation axis of the cylinder tube, the enclosed angle corresponds to the swing angle of the swash plate 48. This angle varies with the swashplate 48. As it increases, the pressure space 18 moves away from its concentric arrangement with respect to the central axis M1 (see fig. 2); conversely, the pressure space extends rotationally symmetrically with respect to the central axis M1 when the oscillation angle and the extrusion volume are zero (see fig. 1).

As already mentioned, the pressure medium is alternately under high pressure in the hydrostatic working space delimited towards the rear by the piston 12 and in the interior 29 of the piston 12. The inner space 29 is in fluid connection with the pressure space 18 via a through hole 30, and the pressure space 18 is in fluid connection with the second tank 20 via the first tank 16. The pressure medium is fed out both through the first groove 16 and through the second groove 20 into the gap surface between the ball head 10 and the spherical band-shaped surface section 8. The pressure medium there creates a hydrostatic relief zone between the friction pairs mentioned in such a way that the surface pressure caused by the piston forces effects less wear between the piston and the shoe by improved lubrication.

The sealing surface boundary 24 delimits a hydrostatic relief zone towards the interior 34 of the axial piston machine. At this boundary, the pressure drops from the high pressure (region of relief zone) to the housing internal pressure (ambient or the interior space 34 of the axial piston machine). Rather, the high pressure has fallen at the edges of the

grooves

16, 20, which should however be neglected here. A small leakage of the pressure medium then passes through the sealing surface boundary 24 into the interior 34 of the axial piston machine. By continuously passing the sealing surface boundary 24, it can be ensured that the pressure medium in the relief zone is not damaged by heat generation or the like. In addition, a small amount flows out through the pressure medium channel 14 via the sliding surface 4 and serves here to form a continuous fluid film between the sliding surface 4 and the swash plate 48.

Fig. 3 shows an axial piston machine 36 according to the invention, which has a housing 38 in which a drive shaft 40 is rotatably mounted with reference to a rotation axis M3. Within the housing 38, the drive shaft is surrounded by a cylinder tube 42 in which a plurality of pistons 12 are accommodated movably in the direction of the rotation axis M3. The cylinder 42 is rotationally fixedly connected to the drive shaft 40, for example by means of a spline shaft toothing 44. The pistons 12 which are identical to one another are preferably distributed uniformly about the rotational axis M3 and are arranged at a distance from this rotational axis, wherein they are each supported by hydrostatic shoes 2 on a planar control surface 46 of a swash plate 48. The swash plate 48 is supported in the housing 38 so as to be pivotable about a pivot axis M4. The pivot axis M4 preferably extends perpendicular to the rotation axis M3. It can (as in this embodiment) be arranged at a distance from the rotation axis M3, wherein it can also intersect the rotation axis M3.

Furthermore, an adjusting cylinder 50 is provided, by means of which the swash plate 48 can be pivoted relative to the pivot axis M4 in order to adjust the pressing volume of the axial piston machine 36. The adjusting cylinder 50 likewise comprises a piston 12 with a shoe 2, which are coupled by means of a ball joint 50, wherein the shoe 2 is supported on the control surface 46. The immovable element of the adjusting cylinder 50 is fixedly connected with the housing 38.

In summary, the invention relates to a shoe 2 having a first groove 16 which extends in a spiral manner in the spherical surface section 8 of the shoe 2 in the direction of the longitudinal axis M1 of the shoe; and has a second groove 20 which extends in the spherical belt section 8 perpendicularly to the longitudinal axis M1 of the shoe at the end of the first groove 16; and to an axial piston machine having such a shoe.

List of reference numerals

2. Slipper

4. Sliding surface

6. Recess (es)

8. Spherical band shaped surface section

10. Ball head

12. Piston

14. Hydraulic fluid passage

15. Division bar

16. First groove

18. Pressure space

20. Second groove

22. Transition portion

24. Sealing surface boundary

26. Slipper joint

27. Circumferential groove

28. Neck section

29. Interior space

30. Through hole

32. Flattening part

34 Internal space (of axial piston machine)

36. Axial plunger machine

38. Shell body

40. Driving shaft

42. Cylinder barrel

44. Spline shaft tooth part

46. Control surface

48. Swash plate

50. Adjusting cylinder

d1 Minimum diameter (of spherical segment)

d2 Larger diameter (of spherical surface section)

Maximum diameter of D (spherical segment)

M1 central axis (of slipper)

M2 central axis (of plunger)

M3 (of drive shaft) rotation axis

M4 (swashplate) swing axis

Angle alpha.

Claims

1. A slipper having a sliding surface (4) for slidingly supporting a piston (12) at a swash plate of an axial piston machine; having a recess (6) with a concave, spherical surface section (8) for abutment with a ball head (10) of the piston (12), characterized by at least one first groove (16) which extends in the spherical surface section (8) away from a smaller diameter (d 1) of the spherical surface section (8) towards a larger diameter (d 2) of the spherical surface section (8).

2. Slipper according to claim 1, having a central axis (M1) with respect to which at least one first groove (16) extends at least in part circumferentially.

3. Slipper according to claim 2, wherein in the spherical band-shaped face section (8), the second groove (20) extends over the entire circumference between a smaller or minimum diameter (d 1) and a larger diameter (d).

4. A slipper as claimed in claim 3, wherein the diameter (d 2) of the second groove (20) is smaller than the equatorial diameter of the recess (6).

5. Slipper according to claim 3 or 4, wherein a pressure space (18) can be fluidly connected with the second groove (20) by means of at least one first groove (16), which pressure space can be delimited at least in sections by a spherical band-shaped surface section (8) and the ball head (10).

6. Slipper according to any of claims 3 to 5, wherein at least one first groove (16) merges into a second groove (20) at a gentle angle (α).

7. The skid shoe according to any one of claims 2 to 6, wherein at least one first groove (16) has at most one turn.

8. A slipper according to any preceding claim having a plurality of such first grooves.

9. Axial piston machine having a drive shaft and a cylinder-piston unit connected thereto in a rotationally fixed manner, each hydrostatic working space being delimited in sections by a piston (12) thereof, which working spaces can be connected alternately with the rotating drive shaft to a low-pressure space and to a high-pressure space of the axial piston machine, wherein a ball head (10) of the piston (12) is accommodated in a recess (6) of a shoe (2), by means of which the piston (12) is slidingly supported on a swash plate, characterized in that the recess (6) has a spherical band section (8) in which a first groove (16) extends away from a smaller diameter (d 1) of the spherical band section (8) toward a larger diameter (d 2) of the spherical band section (8).