CH714838A1 - Piston shoe unit for an axial piston machine. - Google Patents

Abstract

The invention relates to a piston-shoe unit for a hydraulic or pneumatic device, in particular a hydraulic or axial piston machine, with at least one piston (10) by means of ball joint (11, 20, 21, 30) with at least one sliding shoe (25 ), wherein the spherical cap of the ball joint is partially formed by a dome-shaped recess (11) of the piston (10) or the sliding block (25) and by at least one separate, with the piston (10) or sliding shoe (25) connectable Closing part (30) is completed.

Description

The invention relates to a piston-slide shoe unit for a hydraulic or pneumatic device, in particular a hydraulic machine or axial piston machine, with at least one piston which is articulated by means of a ball joint with at least one slide shoe. The invention also relates to a pneumatic or hydraulic device, such as, for example, a hydraulic machine, an axial piston machine, with a corresponding piston / slide shoe unit.

Equipping pistons with slide shoes is known to serve for hydrostatic relief of engines and actuators in axial piston machines. The connection between a piston and its slide shoe is made by a ball joint connection. Piston-glide shoe units, in which the ball head is integrally connected to the glide shoe and the spherical cap on the piston is designed accordingly, require a higher production outlay, but allow higher oblique angles of the slide shoe tread, also called the angle of attack. Operating piston machines at higher helix angles leads to better efficiencies and an increase in their power density.

The piston slide shoe units used in the engines of piston machines are alternately stressed by high tensile and compressive forces which act in the axial and vertical directions. Without claiming to be complete, the reasons for this are: In engine operation, the piston slide shoe units are acted upon by the oil pressure on the high pressure side. In pump operation, the pressure on the oil is exerted on the high-pressure side starting from the pistons, while on the low-pressure side the pistons are pulled out of the cylinder via the retraction device in order to generate the negative pressure necessary for oil intake. As a result, the ball head connections of the engine pistons are subject to strong tensile forces.

The resulting axial and radial forces put a load on a piston and sliding block unit and the special focus on the ball joint connection not only due to high absolute values, but sometimes also due to particularly rapid changes in these forces, so-called transients. The latter arise among other things due to never completely avoidable pressure pulsations in the hydraulic oil circuit; likewise in the case of pump operation by transient changes in the mechanical power supplied and in the case of motor operation by transient changes in the mechanical load.

According to the prior art, the creation of the ball joint connection of piston-shoe units by plastic deformation of the prepared spherical cap. Fig. 1 shows the central longitudinal section of a piston 1, which for inserting the slide shoe 2, respectively. his ball head 3 is prepared. The recess into which the ball head 3 is inserted can be seen on its left side. The lower region 4 of this recess already has the spherical shape adapted to the spherical head 3. The wall area of the piston 1 on the left-hand side of the last-mentioned section forms the so-called forming area 5. At least the surface of the spherical cap must be e.g. before inserting the ball head 3. can be smoothed accordingly by polishing. Before such a smoothing of the surface, this must the piston 1 are hardened.

After assembling the ball joint connection, the protruding collar of the recess for receiving the ball head 3 is joined so that an inner surface is formed in the forming area 5, which represents a form-accurate continuation of the spherical cap for enclosing the joint head 3. This process, which is indicated in Fig. 1, is carried out by forming (e.g. rolling, rolling, etc.) using a tool and is usually supported by heating. On the one hand, increasing heating increases the ductility of the forming zone 5 and thus reduces the occurrence of microcracks, on the other hand, excessive heating leads to damage to the surface smoothing.

[0007] DE 199 342 18 A1 deals with ball joint connections of piston-slide shoe units for use in piston machines. As an improvement of the prior art at that time, local heating of the recess edge of the spherical cap is proposed so that the ball joint connection can be joined even when using materials with a higher material hardness and comparatively low deformation forces. As an alternative, the use of a starting material is already proposed, the ductility of which allows the recess edge of the spherical cap to be plastically deformed. Material hardening is proposed to achieve the required strength.

In DE 19 734 217 A1 it is proposed to first add the ball joint connection between the piston and the sliding block and then to harden the outer surface of the piston. The piston prepared for inserting the slide shoe contains two characteristic features in the region of its recess edge, namely an annular groove on its inside and an oversize on its outside. The latter serves to ensure that a cylindrical surface is present on the piston after the shaping due to the tool engagement points provided here.

Disadvantages of the known piston-shoe units result from the requirements for a high material hardness on the one hand and on the other hand for a high ductility for the plastic deformation used to produce the ball joint connection. Two demands that are commonly known to be incompatible. On the one hand, the ball head and the inside of the spherical cap must have smooth surfaces to reduce friction and prevent wear as much as possible. In addition, the ball head and the wall of the spherical cap must have sufficient strength so that the surfaces of the ball joint connection in the connection area do not change at all during use, and the connection is prevented from breaking.

CH 714 838 A1

The forming area of the projecting collar, the so-called recess edge of the recess for enclosing the ball head, however, represents a weak point area of the ball joint connection produced in this way.

The invention therefore has for its object to improve the strength of the ball joint connection of a piston-shoe unit, which is a weak point in conventional piston-shoe units of the prior art.

This object is achieved by a piston-shoe unit according to the features of claim 1. Advantageous embodiments of the invention are the subject of the dependent claims.

[0012] According to the invention, a piston / slide shoe unit is proposed for a pneumatic or hydraulic device. The focus here is on a piston / slide shoe unit for a hydraulic machine, in particular for an engine piston of an axial piston motor / axial piston pump, although the idea according to the invention should not be restricted to such a special application. Such a piston and slide shoe unit can also be used within an actuating device. Rather, the idea according to the invention can be advantageously used for any form of ball joint connection between any components or even for any type of form-fitting connection that exhibits a joint-like characteristic, for example, has at least one translational and / or at least one rotational degree of freedom. For the sake of simplicity, however, the invention is explained below with the aid of a ball and slide shoe unit for a pneumatic / hydraulic device, but the following embodiment also applies to the alternative applications mentioned above.

Starting from the generic piston-sliding block unit, it is proposed that the spherical cap of the ball and socket joint be formed only partially by a spherical recess either inside the piston or alternatively within the sliding block. The spherical cap is only completed by at least one separate closure part which is or is connected to the piston or alternatively to the sliding shoe.

Due to the modular structure of the spherical cap, the ball head can first be inserted into the recess in the piston or the sliding block. After insertion, the joint can be closed by installing the separate locking part. As a result, the conventional joining process by cold forming the protruding collar in the area of the spherical cap can be dispensed with and the resulting material strength reduction is effectively avoided. Instead, the invention creates an extremely stable ball joint connection without the known weak points.

Ideally, the separate closure part forms that radius section of the spherical joint of the spherical joint, which engages behind the inserted spherical head, consequently ensuring a positive joint connection and absorbing tensile forces acting on the spherical head.

According to a particularly preferred embodiment, the dome-shaped recess within the piston or alternatively within the slide shoe is dimensioned such that exactly one ball half of the ball head is received by the recess. As a result, the wall of the spherical recess extends to the equator of the spherical head, which ensures simple manufacture of the spherical recess and simple insertion of the spherical head is possible.

The piston itself can be made as a one-piece component or, alternatively, can be modularly composed of individual components. In addition, the piston can provide one or more cavities.

For the reception and attachment of the separate closure part on the component having the spherical recess, i.e. either the piston or the joint shoe can be done in different ways. If the dome-shaped recess is machined into the piston, the end section of the piston jacket surface can be tapered in the region of the dome-shaped recess in order to enable the separate closure part to be securely fastened. In this embodiment, the separate closure part, also referred to below as the holder, can be placed on the face of the piston on the face side and at least partially encompass the tapered jacket circumference of the piston, in particular come into play flush with it.

Preferably, the closure part or the holder comprises a plate which can be attached to the face of the piston and has an opening, the opening wall of which completes the spherical cap of the piston. The opening wall consequently forms the part of the calotte that engages behind the inserted ball head, the plate thickness of the closure part accordingly determining how far behind the inserted ball head is engaged, which ultimately has an influence on the maximum oblique angle of the slide shoe relative to the piston. The closure part preferably comprises a cylinder open on one side, the bottom side of which is closed by the plate. In the assembly position, the cylinder wall lies against the tapered jacket area of the piston, the plate covers the end of the piston.

For a precisely fitting assembly of the separate closure part, it is useful if this and the piston have complementary connecting elements that simplify the positioning of the closure part on the piston. A combination of a groove, in particular a radial groove on the outer surface of the piston, and a complementary bead, in particular a radial bead formed on the cylinder inner wall of the closure part, can be considered as complementary connecting elements.

CH 714 838 A1 [0021] According to an advantageous embodiment of the invention, the ball head can also be manufactured as a separate component and can be connected or connected to either the sliding block or alternatively the piston by means of suitable connecting methods. For this purpose, the ball head provides a cylindrical extension, which serves as a connecting element with the corresponding counterpart. If the ball head is to be a component of the slide shoe, the cylindrical extension serves to mount the ball head on the corresponding slide shoe foot, in particular within a bore provided there, particularly preferably a precisely fitting cylindrical bore into which the cylindrical extension is introduced.

It makes sense to dimension the diameter of the cylindrical extension smaller than the diameter of the ball head.

The cylindrical extension as well as the counterpart, i.e. the cylindrical bore within the slide shoe foot or alternatively the piston can be equipped with complementary connecting elements. Here, too, a combination of groove and bead, in particular radial groove and radial bead, has proven to be useful.

The slide shoe used, or the slide shoe foot can, according to an advantageous embodiment, have a coated running surface in order to improve sliding properties of the slide shoe foot, for example on a swash plate of an axial piston machine. Alternatively, in the two-part design of the slide shoe, the entire slide shoe foot could consist of the coating material.

According to a preferred embodiment, the piston and / or the holder and / or the ball head can be made of steel, preferably of a steel which has a relatively low carbon content, ideally with a carbon content of at most 0.5%, ideally of maximum 0.2%. The use of a nitriding steel simplifies the joining process, for example between the separate closure part and the piston or the ball head and slide shoe foot, since such steels, in particular nitriding steels, are easy to weld. In addition, these types of material are characterized by ideal strength values.

The slide shoe foot can also be made of steel, in particular nitriding steel, and be provided with a suitable slide coating in the area of the tread. Brass, for example, shows good sliding properties. Alternatively, the slide shoe foot can consist entirely of the slidable material, such as brass.

In addition to the piston-shoe unit according to the invention, the present invention also relates to a corresponding hydraulic or pneumatic device with at least one piston-shoe unit according to the present invention. Accordingly, the device, for example, axial piston motor / axial piston pump, has the same advantages and properties as have already been shown above with the aid of the piston / slide shoe unit according to the invention. For this reason, a repetitive description is omitted.

[0028] Furthermore, the present invention also relates to a method for producing a piston / slide shoe unit according to the present invention. The method according to the invention is characterized in that first of all the individual parts of the piston / slide shoe unit according to the invention, namely the piston, the slide shoe and the separate closure part, can be manufactured separately. In particular, these are already manufactured to the required final dimensions, which relates in particular to the dome-shaped recess within the piston or the sliding block or at least the corresponding radius of the separate closure part. The same applies to the ball head of the piston or the slide shoe.

After the manufacture of the individual components according to the invention takes place their hardening, which is finally followed by the assembly of the ball joint connection, by first mounting the ball head in the spherical cap and then the separate closure part in order to achieve an expected locking of the spherical head within the spherical cap.

It is conceivable that the separate closure part is attached to the piston or sliding block by welding, in particular by laser welding. This is particularly useful if both the piston and the separate closure part itself are made of suitable steel, in particular nitrided steel.

The attachment of the slide shoe foot to the slide shoe head can be carried out by welding or soldering, ideally by laser welding or laser soldering. The preferred method depends in particular on the material used for the shoe base. If this consists largely of a weldable material, such as steel, preferably nitriding steel, the ball head can be attached to the base of the shoe by welding, in particular laser welding. If instead a manufacture of the sliding shoe foot completely from sliding material, such as brass, is preferred, then a soldering method, in particular laser soldering, is used.

Further advantages and properties of the invention will be shown below with reference to the embodiment of the piston-shoe unit shown in the figures. It shows:

1: a piston-joint shoe unit according to the prior art,

2 shows a sectional illustration of the piston / slide shoe unit according to the invention, including a detailed illustration of the ball joint connection and

CH 714 838 A1

Fig. 3: representations of the piston-shoe unit according to the invention during assembly.

An embodiment of the piston-shoe unit according to the invention is shown in FIG. 2, which shows a sectional view of the piston-shoe unit and an enlarged detail view of the ball joint connection. The entire unit consists of four components, namely the piston 10, a holder 30, a slide shoe head 20 and a slide shoe foot 25. The order in which these four components are produced before the piston slide shoe unit according to the invention is assembled is irrelevant to the invention. With regard to its function-determining features, for example the design of the tread, the lubricating oil channel, etc., a piston and slide shoe unit according to the invention can be identical in all respects to the units corresponding to the prior art.

For the manufacture of the piston-slide shoe unit according to the invention, it is necessary to manufacture a piston 10 which has a spherical cap-shaped recess 11 for receiving the spherical head 21 of the slide shoe head 20, such a configuration of the recess 11 that the spherical head 21 in the present installation position is enclosed up to its equator by the recess 11 of the piston 10. Furthermore, the outer surface of the piston has a taper in the end section of the side on which the spherical cap-shaped recess 11 is located. The piston 10 is preferably manufactured with respect to all details before it is hardened to its final mass. In any case, the spherical cap 11 must be manufactured to its final dimensions before curing.

In addition, it is necessary to manufacture a holder 30 which has a collar, so that the holder 30 can be placed flush on the tapered region of the piston 10. In addition, there is a recess 31 on the holder 30, which, when the holder 30 is placed on the piston 10 as intended, represents an exact continuation of the spherical cap. The holder 30 is preferably manufactured with respect to all details before it is hardened to its final mass. In any case, the part 31 of the surface that completes the spherical cap must be manufactured to its final dimensions before curing.

In a preferred embodiment, not only the tapered outer diameter of the piston 10 and the inner diameter of the collar present on the holder 30 are matched to one another, but the two adjoining surface areas of these two components 10, 30 are additionally provided with complementary surface elements, which a Force again more precisely defined positioning of the holder 30 on the piston 10. The exemplary embodiment shown shows a radial groove 12 introduced in the tapered area of the lateral surface of the piston 10 and a bead 32 applied on the holder 30 as a complementary element. For the sake of clarity, the surface elements in relation to the component dimensions are shown larger in these figures than would be the case in a preferred embodiment.

The slide shoe head 20 is manufactured as a further component. The diameter of the ball head 21 of the slide shoe head 20 and of the spherical cap formed by the piston 10 and holder 30 are coordinated with one another in such a way that a smooth and well-guided movement of the slide shoe relative to the piston 10 is possible. The width of the enclosure must ensure sufficient strength of the ball head connection on the one hand, but on the other hand must not restrict the range of movement unnecessarily.

The slide shoe head 20 has a cylindrical shape 22 at the end facing away from the spherical shape 21. The diameter of this cylindrical extension 22 must be smaller than that of the ball 21. The slide shoe head 20 is preferably made with regard to all details before it hardens to its final dimensions. In any case, the spherical area of its surface, which is located in the spherical cap or can move into it, must be made to its final dimensions before hardening.

A slide shoe foot 25 is produced as a further component, two variants exist for a piston slide shoe unit according to the invention:

Type A: The slide shoe foot 25 consists entirely of the coating material.

Type B: The slide shoe foot 25 consists of the same material or a material material that is similar to the other components of the piston / slide shoe unit. The sliding shoe foot 25 is preferably manufactured in all details before it is hardened to its final mass.

Applicable to type A and type B piston / slide shoe units The slide shoe foot 25 has a central bore 26 at the end facing away from the tread, the inner diameter of which is matched to the outer diameter of the cylindrical component section 22 of the slide shoe head 20. Preferably, the sections of the two components 20, 25 under consideration are additionally matched to one another in terms of their length or depth, so that a flush stacking - as can be seen in FIG. 2 - is possible.

In a particularly preferred embodiment, the adjoining surface areas of these two components 20, 25 are provided with further complementary surface elements, which force a further more precisely defined positioning of the slide shoe foot 25 on the slide shoe head 20. The exemplary embodiment shown shows a radial groove 23 and which is introduced on the lateral surface of the cylindrical extension 22 of the slide shoe head 20

CH 714 838 A1 a bead 27 applied to the inner wall of the slide shoe foot 25 as a complementary element. For the sake of clarity, the surface elements in relation to the component dimensions are shown larger in these figures than would be the case in a preferred embodiment.

Depending on the selected joining method between the slide shoe head 20 and the slide shoe foot 25, it may be necessary for the collar region of the slide shoe foot 25 to have two sections 28a, 28b with different outside diameters. The lower section 28b thereof has an outer diameter which is adapted to the guide circumference of the retraction plate. Clearly, the length of this section 28b is matched to the thickness of the retraction plate. The outer diameter of the upper collar section 28a must be sufficiently small that the jacket surface changed there after the joining process between the slide shoe head 20 and slide shoe foot 25 reaches the guide circumference of the retraction plate to a maximum.

After the hardening of the components that need one, that is in a type A piston-shoe unit the piston 10, the holder 30 and the shoe head 20 and in a type B unit the shoe base 25th , the surfaces of its components sliding against each other in relation to an assembled piston / slide shoe unit must be smoothed accordingly. Prior to the assembly of the piston / slide shoe unit, all surfaces of these components are preferably smoothed, which must be smoothed due to other sliding partners in relation to the later use in the axial piston machine.

In a preferred sequence of manufacture, those component dimensions are produced to their final dimensions before component hardening, such that only a material removal, which serves for smoothing, has to be carried out on the surfaces to be smoothed after hardening, but not for Compliance with component dimensions. In a particularly preferred sequence of manufacture, all dimensions of all components of the piston / slide shoe unit are produced before their hardening to their final dimensions, including the lubricating oil hole in its final silhouette.

The individual steps for the assembly of the piston / slide shoe unit are outlined in FIG. 3. First, the holder 30, starting from the cylindrical end 22 of the ball head 21, is slipped over it until the spherical cap-shaped region 31 of the holder 30 rests on the ball 21 of the slide shoe head 20 (FIG. 3a). The ball head 21 is inserted into the recess 11 of the piston 10 provided for this purpose. The latter two steps can be carried out in reverse order or with a time overlap.

Next, as shown in step b), the connection between the holder 30 and the piston 10 is fixed, for example by means of laser welding. The fixing is preferably carried out in the area of the tapered lateral surface and the collar, away from smoothed surfaces.

Finally, the assembly of the slide shoe foot 25 takes place. This assembly step depends on the type of material selected for the slide shoe foot 25. In the case of the previously described type A piston and slide shoe unit, the slide shoe foot 25 is placed on and a fixation can be carried out by means of laser soldering (Fig. 3c)). If (at least) one exposed surface of the coating of the tread has a special configuration with respect to the finished piston / slide shoe unit, such as a possible labyrinth structure on the tread, the configurations of these surfaces are in a preferred sequence of manufacture Assembled the piston-shoe unit.

In the case of the piston-slide shoe unit type B, the coating is first applied to the slide shoe foot 25, which is subsequently placed on the slide shoe head 20 and fixed accordingly, for example by laser welding. Likewise, the coating can be applied after the slide shoe foot 25 has been put on or after it has been fixed.

The slide shoe foot 25 of a piston / slide shoe unit according to the invention does not necessarily have to consist entirely of the coating material. As an alternative to the embodiment described above, the slide shoe foot 25 can consist of a comparatively hard or very hard base body, which in turn has a coated running surface. With such a construction, the base body of the slide shoe foot 25 is connected to the slide shoe head 20 in accordance with the explanations shown, preferably by means of a material connection and particularly preferably by a welding process, e.g. Laser welding.

For the selection of the coating material or the coating concept, i.e. By means of material application or attachment of at least one component carrying the coating material, and the selection of the method with which the coating is applied, there are no restrictions for a piston / slide shoe unit according to the invention.

The piston-slide shoe unit according to the invention can be based on a piston 10 which has no or more cavities. In addition, a piston / slide shoe unit according to the invention can be based on a piston which is not made from solid material, but instead, for example, starting from one or more tubular basic elements.

Overall, the following advantages of the invention can be emphasized:

- Significant increase in process reliability during production

- Extension of durability

- Increased resistance to high peak loads

- Increase the maximum possible helix angle

CH 714 838 A1 The inventive manufacture of the piston and slide shoe units avoids all the disadvantages that exist in a state-of-the-art manufacture that requires the joint to be joined by plastic deformation. This is made possible by the design of components, the piston 10, the holder 30, the slide shoe head 20 and the slide shoe foot 25, from which the piston / slide shoe unit is assembled. The necessary hardening of the components can take place before assembly.

With regard to the finished components, the material hardness and the depth of penetration can therefore be completely geared towards an optimal cost-benefit ratio with regard to the hardening effort and the requirements of the application. The same applies to the selection of the starting material and the starting state of the material from which the components are made. The components can be fully shaped before they are hardened. After hardening, only the smoothing of surfaces and the application of necessary coatings, for example on the tread, are required.

The following procedures are not conclusively conceivable for hardening

- Process selection of the heat treatment (e.g. nitriding, gas nitriding, gas nitrocarbonating, plasma nitriding etc.)

- process design

Simple: curing temperature & curing time

More complex: temperature control (temperature-time profile) during hardening. In the ball-and-socket joint of the piston / slide shoe unit according to the invention, the entire spherical cap exists and in particular the section having the thickness d which extends beyond the equator of the partial ball contained in the ball head 21 Part encloses, made of hardened material.

Due to this fact, a substantially higher tensile strength is achieved while maintaining the thickness d with a ball-and-socket joint of a piston-sliding shoe unit according to the invention. Or, with a significant reduction in the thickness d, a tensile strength can be achieved with a ball and socket connection of a piston / slide shoe unit according to the invention as in the case of a piston / slide shoe unit which corresponds to the prior art.

As is emphasized in FIG. 2 by the clearly exaggerated size of the thickness d, a reduction in the thickness d enables the freedom of movement of the ball joint connection to be increased. With regard to the use of an engine in an axial piston machine, a reduction in the thickness enables larger inclined angles to be set and thereby creates the advantages already explained.

Thus, the improvement of a piston-shoe unit according to the invention is not limited to an increase in strength, but offers a more far-reaching balance between strength and maximum adjustable helix angle. Up to certain limits, an increase in strength can be agreed with a simultaneous increase in the maximum adjustable helix angle.

claims

Claims (13)

1. piston-slide shoe unit for a hydraulic or pneumatic device, in particular a hydraulic machine or axial piston machine, with at least one piston which is articulated by means of a ball joint with at least one slide shoe, characterized in that the spherical cap of the ball joint is partially through a spherical recess of the piston or of the sliding block is formed and is completed by at least one separate closure part which can be connected to the piston or sliding block. 2. Piston-shoe unit according to claim 1, characterized in that the separate closure part forms the radius section of the cap, which engages behind the ball head used, preferably the spherical recess within the piston or shoe is dimensioned so that exactly one half of the ball Ball head is added. 3. Piston-shoe unit according to one of the preceding claims, characterized in that the piston comprises the spherical recess and the end portion of the lateral surface is tapered in the region of the spherical cap in order to accommodate the separate closure part. 4. Piston-shoe unit according to claim 3, characterized in that the separate closure part encloses the tapered end portion of the piston jacket surface, in particular the closure part forms a collar, whereby this is placed flush on the tapered area of the piston. 5. Piston-shoe unit according to one of the preceding claims, characterized in that the separate closure part and the piston or shoe comprise complementary connecting elements, preferably a groove, in particular a radial groove, and a complementary bead, in particular a radial bead. 6. Piston-shoe unit according to one of the preceding claims, characterized in that the ball head is made as a separate component and comprises at least one cylindrical extension for connecting the ball head to the piston or shoe, in particular a shoe foot, the diameter the cylindrical extension is preferably smaller than the diameter of the ball head. CH 714 838 A1 7. piston-slide shoe unit according to claim 6, characterized in that the slide shoe foot or the piston comprises a precisely fitting recess, in particular a central bore, for receiving the cylindrical extension, ideally for the flush final reception of the extension, optionally complementary connecting elements are provided on the slide shoe foot / piston and the cylindrical extension, in particular in the form of a radial groove and complementary radial bead. 8. Piston-shoe unit according to one of claims 6 or 7, characterized in that the shoe foot has a coated tread or is made entirely of a lubricious material. 9. Hydraulic or pneumatic device, in particular axial piston machine or hydraulic actuating device, with at least one piston-sliding shoe unit according to one of the preceding claims. 10. A method for producing a piston-slide shoe unit according to one of claims 1 to 8 with the method steps: a. Manufacture of the piston, the slide shoe and the separate closure part, b. Hardening of the piston, the slide shoe and the separate closure part, c. Connect the piston to the slide shoe by inserting the ball head into the calotte and then assembling the separate closure part. 11. The method according to claim 10, characterized in that the dome-shaped recess within the piston / sliding block and / or the separate closure part and / or the ball head are made to final size before curing. 12. The method according to any one of claims 10 or 11, characterized in that the separate closure part is attached to the piston or sliding block by welding, in particular by laser welding. 13. The method according to any one of claims 10 to 12, characterized in that the slide shoe foot is connected to the ball head by welding or soldering, preferably by laser welding or laser soldering.