EP1248906A2

EP1248906A2 - Piston arrangement for a piston engine

Info

Publication number: EP1248906A2
Application number: EP00951318A
Authority: EP
Inventors: Josef Beck
Original assignee: Brueninghaus Hydromatik GmbH
Current assignee: Brueninghaus Hydromatik GmbH
Priority date: 1999-07-21
Filing date: 2000-06-29
Publication date: 2002-10-16
Anticipated expiration: 2020-06-29
Also published as: WO2001007757A3; EP1248906B1; DE50011468D1; DE19934217A1; WO2001007757A2

Abstract

The invention relates to a piston arrangement (1) for a piston engine, comprising a tubular piston (2) and a slipper (3) which are pivotably connected to each other by a ball-and-socket connection (1A). The latter consists of a ball (4) on the slipper (3) and a hemispherical socket (5) in the tubular piston (2). A recess edge of (7) of the joint recess (5) protrudes beyond the equator (6) of the joint recess (5) and grips the ball (4) from behind. The tubular piston (2) has a base section (11). The joint recess (5) and the recess edge (7) are located at one end of said base section (11). A peripheral wall (15) extends from the base section (11) in a single piece, in the opposite axial direction to the joint recess (5), and surrounds the cavity (9). The cavity (9) of the tubular piston (2) is closed by a lid (12) which is connected to the peripheral wall (15) and the tubular piston (2) has a middle part (13) that extends from the base section (11) to the lid (12). As a result, the length of the construction is reduced further.

Description

Piston arrangement for a piston engine

The invention relates to a piston arrangement according to the preamble of claim 1.

A piston arrangement is described in DE 197 34 217 AI. This known piston arrangement has a piston with a base section, from which an articulated part extends in one axial direction and a hollow cylindrical peripheral wall in the other axial direction up to the front free end of the hollow piston, which encloses a cylindrical cavity in the piston. The joint part which extends in the other axial direction is formed by a hemispherical joint recess in which the joint ball of a sliding block is pivotally mounted, a recess edge projecting beyond the equator of the joint recess being flanged to a position which engages behind the joint ball in a form-fitting manner. In this known piston arrangement, the piston, which is prefabricated with a cross-sectional oversize, is positively connected to the joint ball of the sliding block after it has been connected to the sliding block by cold flanging a recess edge projecting radially from the lateral surface of the piston. The piston is then hardened on its outer surface, after which the outer surface is finished, in particular by grinding. This known method requires a considerable amount of work, the machining step being the last step. In addition, a considerable widening of the flare is to be expected, which can be attributed to the fact that due to the considerable tensions occurring during cold deformation, the flare springs back and therefore the flare only engages behind the joint ball with a relatively large amount of play.

In this known piston arrangement, the jacket surface of the piston forming a guide surface can extend into the region of the recess edge, whereby on the one hand improved guidance for the piston is achieved and on the other hand, a shorter design for the piston arrangement and, as a result, also for the piston machine can be achieved.

The invention has for its object a

To design the piston arrangement of the type specified at the outset in such a way that the length of the sliding surface is increased and a dead volume which is also compressed is avoided.

This object is solved by the features of claim 1.

The arrangement of the joint ball on the slide shoe instead of the piston creates a longer sliding surface. By closing off the cavity, a dead volume that is also compressed when a piston is open toward the working volume is avoided.

In the piston arrangement according to the invention according to claim 1, the hollow piston has an annular cavity which is delimited on the inside by a central pin which extends from the base section of the hollow piston ^" to a cover which is in contact with the

Peripheral wall of the piston is connected and the

Ring cavity closes. In this embodiment, the central pin forms an axial support and stabilizing element which is able to be supported axially on the cover and thereby the

Base section significantly stabilized. As a result, the base portion can be formed with a smaller axial length. In addition to this shortening and stabilization, material and weight can also be saved, which is due to the reduced longitudinal dimension of the

Hollow piston is caused.

Advantageous developments of the invention are described in the subclaims.

The invention and further advantages which can be achieved by it are explained in more detail below with the aid of preferred configurations and drawings. Show it: Figure 1 shows a piston assembly according to the invention in axial section.

FIG. 2 shows the piston arrangement according to FIG. 1 in a modified configuration;

3 shows the piston arrangement in a further modified embodiment;

4 shows the piston arrangement in a further modified embodiment;

Fig. 5 shows the piston arrangement in a further modified embodiment.

The piston arrangement, generally designated 1, comprises a hollow piston 2, preferably made of steel, and a sliding block 3, preferably made of bronze or brass, which are pivotally connected to one another by a ball joint connection 1A while ensuring unilateral limited pivoting movements between the hollow piston 2 and the sliding block 3. The central axes of the piston 2 and the sliding block 3 are designated 2a and 3a.

The hinge connection 1A has a dome-shaped or spherical segment-shaped joint recess 5 with a depth a that is greater than the spherical radius r of a joint ball 4 pivotally mounted therein, a recess edge 7 axially projecting beyond the equator 6 of the joint recess 5 engaging behind the joint ball 4 and thereby in this spherical ring zone convergent shape of the joint ball 4 can at least partially follow while maintaining a play of movement. As can be seen from Fig. 1, the axial length b of the recess edge 7 is dimensioned so long that in the maximum swivel position shown in Fig. 1 it extends into the corner region between the joint ball 4 and a ball neck or a base part 8 of the sliding block 3 extends. Tapered in the present embodiment the recess edge 7 towards its free end, the outer lateral surface preferably being a conical surface.

The cavity 9, which is designed as an annular space, extends from a rear base section 11, in which the joint recess 5 is arranged, to an end section, which is formed by a cover 12 and is preferably connected to the circumferential wall of the remaining piston part by a friction welding process. The gap between the welded parts before the friction welding process is illustrated by a dashed line. The annular cavity 9 surrounds a cylindrical central pin 13, which extends in one piece from the base section 11 to the front and is also connected by friction welding to the cover 12 or to a central pin extension 14 projecting therefrom. This also applies to the hollow cylindrical peripheral wall 15 of the piston 2 in the region of the cavity 9, which also extends forwards in one piece from the base section 11 and is connected by friction welding to the cover 12 or a peripheral wall attachment 16 arranged around it. On the inside of the welding point, generally designated 17, the central pin 13 is supported radially on the peripheral wall 15 by an annular disk 18, the annular disk 18 abutting an inner shoulder surface 13a which is preferably provided on the peripheral wall 15.

The closed design of the hollow piston 2 avoids an enlargement of the cross section of the hollow piston at high pressure and compression losses due to the relatively large volume of the piston chambers.

A channel 19a, 19b extends longitudinally through the hollow piston 2 and the slide shoe 3 and opens into a flat recess 22 arranged on the flat foot surface 21 of the slide shoe 3. Through the channels 19a, 19b, the working pressure in the hydraulic medium can extend up to the recess 22 in the functional operation of the hydrostatic machine reproduce where the hydraulic medium causes lubrication and the pressure relieves pressure in a manner known per se.

The hollow piston 2 preferably consists of hardenable steel, in particular of steel hardenable by nitriding. In order to increase the strength and hardness, its outer surface is preferably nitrided and hardened.

The present ball-and-socket joint 1A is suitable for the pivotable support of a piston 2 for piston machines, in particular axial piston machines, on a support surface S against which the slide shoe 3 rests with its foot surface 21. In the case of an axial piston machine, the support surface S can be the oblique surface of a so-called oblique writing.

The method steps of a preferred production method of the piston arrangement 1 comprising the hollow piston 2 and the sliding shoe 3, which are inseparably connected thereto, are described below.

The slide shoe 3 can be manufactured as a finally finished component in large numbers and provided for connection to the hollow piston 2.

The hollow piston 2 is preferably also prefabricated and made available in large numbers as a prefabricated piston blank. In this prefabrication form, the recess edge 7 extends axially with an inner diameter d, which can be adapted to the diameter of the joint ball 4 or the joint recess 5, taking into account a play of movement, so that the joint ball 4 can be inserted into the joint recess 5. The front cover 12 and the remaining piston part 2b are produced with a cross-sectional oversize x, which is hardened after welding, if necessary after prior nitriding, and finished by machining, for example by grinding. The order of the process steps can be before or after welding, namely the incorporation of the cavity 9 of the joint recess 5 and the channel 19a as desired. It is advantageous to carry out the positive connection of the joint ball 4 to the hollow piston 2 after the nitriding and / or hardening and finishing of the jacket surface 2c as the last step.

To connect the joint ball 4 and the joint recess 5 are plugged together and, if necessary, the slide shoe is held 3 m in its middle position, which can be done by supporting. Then the recess edge 7 is removed by means of a suitable heating device, e.g. In the form of a heating ring 23 shown in the drawing, approximately in the width of the axial length b, heated to a temperature at which the hardness of the material is reduced, so that even after the material has cooled, the recess edge 7 can be crimped with lower deformation forces or to a Temperature can be heated, at which the strength of the material is reduced and the recess edge 7 can be hot flanged. In both cases, the recess edge 7 can be crimped plastically with relatively low forces into the shape shown in FIG. 1, which engages the articulated ball 4 in a form-fitting manner.

The relatively low deformation forces ensure that the recess edge 7 without mechanical overloading of the e.g. made of softer material is deformed shoe 3. The heating can be done by direct heating e.g. by means of a flame or inductively by an inductive electrical heating device. Due to the local heating of the recess edge 7, the hardened material becomes soft again in this area and it can therefore be easily deformed without the remaining area of the piston 2 suffering significant losses in hardness.

A major advantage of the above-described method is that the hollow piston 2 can be completely finished before being joined and connected to the sliding block 3, without the above-described one Special measures with regard to the flaring would be necessary, such as covering the recess edge 7 to be deformed during nitriding, in particular gas nitriding, turning off already nitrided areas prior to flanging, etc. By fine-tuning the heating, flanging and cooling processes, the optimal play of the ball joint connection 1 set very easily and can also be reliably reproduced in series production.

The configuration according to the invention leads on the one hand to a substantial stabilization of the hollow piston 2 and not only with regard to bending stresses but also with regard to axial compressive stresses to which the hollow piston 2 is exposed in particular during a pressure stroke, in which a pressure force, indicated by arrow 25, against its working surface 26 on its surface acts free end, which is received by the sliding block 3 in the articulation 1A. In this case, the equally large and opposite directional resistance force, indicated by arrow 27, is introduced into the hollow piston 2, specifically against the base section 3. The base section 3 is thus the part of the hollow piston 2 that is directly exposed to the compressive stresses.

In the embodiment according to the invention, the central pin 13 forms an axially effective support or

Connection part that is effective in the pressure forces

25, 27 the compressive stress on the base section 3 and

Cover 12 distributed so that these parts with a lower

Compressive stress are applied. Therefore, the base section 3 and / or the lid 12 can have a smaller axial dimension, i.e. be made thinner. Consequently, the hollow piston 2 or a piston machine having this hollow piston 2, in particular

Execute axial piston machine with a correspondingly shorter overall length.

A comparable support and stabilizing effect is exerted by the center pin 13 even during a suction stroke of the hollow piston 2, in the case of which the pressure forces 25, 27 are directed Tensile forces are effective on it. These tensile forces are tapped by the means 13 distributed both on the cover 12 and on the base portion 13 and thereby reduced in their impact.

The supporting and stabilizing function of the center pin 13 is already fulfilled when the center pin 13 extends between the base section 3 and the cover 12, which may be a separate component which is held between the base section 3 and the cover 12. In such an embodiment, the support and stabilization function of the central pin 13 is limited to a compressive stress, since it is only able to transmit compressive stresses due to the lack of connection to the base section 3 and the cover 12. Such a center pin 13 would be ineffective in the presence of tensile stresses. However, since the tensile forces occurring during the suction stroke in the functional operation of the piston engine are significantly lower than during the pressure stroke, such a center pin 13 in the form of an additional component can also ensure the functionality of the piston engine, since the risk of overloading exists mainly only during a pressure stroke.

A preferred manufacturing measure for the central pin 13 and the peripheral wall 15 is to produce these parts by cold or hot extrusion. In such a manufacturing process, not only is a higher strength achieved in the material structure of these parts, but 9 U-shaped fiber structures are also created in the material by the extrusion with respect to the bottom of the ring hollow part, whereby the strength of the stability is further increased. Within the scope of the invention, however, it is also possible to manufacture the annular cavity 9 not by cutting but by cutting by deep drilling.

The embodiment according to FIG. 2, in which the same or comparable parts are provided with the same reference numerals, differs from the above-described exemplary embodiment in that instead of one, it is in one piece trained center pin 13 a two-piece center pin 13 is provided, which is formed by a pin or a sleeve, which is or in axial holes 12a corresponding cross-sectional size in the base portion 3 and in the cover 12 and is fixed therein, for example by welding, soldering or Glue.

The exemplary embodiments according to FIGS. 3 to 5 include configurations that improve the sliding bearing of the sliding block 3. These measures make it possible, among other things, to manufacture the body 24 of the sliding shoe 3 from a less slippery material, e.g. from a metal of greater strength, e.g. from steel. On the other hand, it is common to make the slide shoe 3 from copper and zinc alloys, such as e.g. Form brass or bronze. Although these materials have good sliding properties, their strength is relatively low and lower than steel. 3, the hemispherical surface of the joint recess 5 is covered by a sliding material layer 25, e.g. Brass or bronze, lined. This layer 25 extends to the equator 6 of the joint recess 5. If the sliding material layer 25 is thicker than a film, the radial dimension of the recess 5 needs to be increased by the layer thickness.

In the exemplary embodiment according to FIG. 4, in which the same or comparable parts are also provided with the same reference numerals, the slide bearing layer 25 also extends into the region of the recess edge 7. As a result, there is relatively little wear even when tensile forces occur on the piston arrangement 1 ensures the annular zone-shaped sliding surface of the recess edge 7. With this configuration, it is also possible within the scope of the invention to form the recess edge 7 by means of the sliding layer material, and this makes it easier to flare the recess edge 7 due to the lower strength of the sliding bearing material compared to steel. In the embodiment according to FIG. 5, in which the same or comparable parts are provided with the same reference symbols, a corresponding slide bearing layer 26 is arranged on the preferably flat foot surface 21 of the slide shoe body 24. This sliding material layer 25 can extend over the entire surface of the foot surface 21 or only over partial surfaces, for example in the form of preferably concentric rings. 3 and / or 4 can also be formed in this embodiment.

The sliding material layer 25, 26 can be a prefabricated material layer which e.g. is attached to the surface carrying it by soldering, welding and gluing, or it can also be a layer application which is applied in a liquid or pasty state and then hardens.

As a result, both the base portion 11 and the end portion or lid 12 can be made with a smaller axial dimension, i.e. thinner, are formed, which both reduces the axial length and saves material and weight.

Claims

Expectations

1. Piston assembly (1) for a piston machine, with a hollow piston (2) and a slide shoe (3) which are pivotally connected to one another by a ball joint connection (1A), which is connected to the slide shoe by a joint ball (4)

(3) and a hemispherical joint recess (5) in

Hollow piston (2) is formed, wherein a recess edge (7) of the joint recess (5) projects beyond the equator (6) of the joint recess (5) and engages behind the joint ball (4) in a form-fitting manner, the hollow piston (2) having a base section (11) , at one end of which the joint recess (5) and the recess edge (7) are arranged, and a circumferential wall (15) extending in one piece from the base section (11) in the axial direction opposite the joint recess (5), which extends the cavity (9) Surrounds, characterized in that the cavity (9) of the hollow piston (2) is closed by a cover (12) which is connected to the peripheral wall (15), and the hollow piston (2) has a central pin (13) which is extends from the base section (11) to the cover (12).

2nd Piston arrangement according to claim 1, characterized in that the central pin (13) is formed in one piece on the base section (11).

3. Piston arrangement according to claim 2, characterized in that the central pin (13) is formed without cutting on the base portion (11).

4. Piston arrangement according to one of the preceding claims, characterized in that that the peripheral wall (15) is formed without cutting on the base section (11).

5. Piston arrangement according to claim 3 or 4, characterized in that the central pin (13) and / or the peripheral wall (15) by extrusion, in particular cold extrusion, preferably at the same time on the base portion (11) are integrally formed.

6. Piston arrangement according to one of the preceding claims, characterized in that the cover (12) with the means pin (13) is connected.

7. Piston arrangement according to one of the preceding claims, characterized in that the cover (12) by welding, in particular friction welding, is connected to the peripheral wall (15) and preferably also to the central pin (13).

8. Piston arrangement according to one of the preceding claims, characterized in that the recess edge (7) is cold or hot-beaded.

9. Piston arrangement, according to one of the preceding claims, characterized in that the hollow piston (2) and / or the sliding block (3) consists of steel.

10. Piston arrangement according to claim 9, characterized in that the joint recess (5) is lined with a sliding material layer (25).

11. Piston arrangement according to claim 10, characterized in that the sliding material layer (25) extends into the region of the recess edge (7).

12. Piston arrangement according to claim 11, characterized in that the recess edge (7) is formed by the sliding material layer (25).

13. Piston arrangement according to one of claims 9 to 12, characterized in that the foot surface (21) of the sliding block (3) is made of sliding material.

14. Piston arrangement according to claim 13, characterized in that the foot surface (21) is arranged on a sliding material layer (26).