EP0697520B1 - Ball joint for supporting a piston of an hydrostatic axial or radial machine - Google Patents

Description

The invention relates to a ball head according to the preamble of claim 1.

Ball heads of this type are known for example from DE-PS 4 024 319, which describes a swash plate pump, the pistons of which are supported on the swash plate indirectly via piston rods. Each piston rod has at its opposite ends a spherical head, which in a hollow spherical section in the piston or in the lifting body, i.e. in the swashplate.

Furthermore, ball heads of the type mentioned at the outset are known from DE-OS 2 307 641, which describes a radial piston machine, the pistons of which are supported indirectly via sliding shoes on the lifting body designed in the form of an outer ring. The ball heads are formed on the slide shoes and are received in corresponding hollow ball sections in the piston.

The known ball heads described above each have a larger diameter than the circular openings of the associated hollow ball sections, in which they are rotatably mounted and in which they can only be used with the aid of the cylinder surfaces, provided that the corresponding inclination of the respective piston rod or the slide shoe Plane of the cylinder surface is brought into a position parallel to the plane of the circular opening.

The ball heads are hydrostatically relieved in the hollow ball sections in a known manner. For this purpose, a so-called pressure pocket in the form of a recess is formed in the spherical caps or in the bearing surfaces, to which pressure oil is supplied, which flows out through the bearing gap between the spherical cap and the bearing surface, forming a hydrostatic pressure field to the leakage oil chamber of the axial piston machine.

As in Fig. 5 using the piston rod and the swash plate in the DE-PS 4 024 319 swash plate pump is shown schematically, the swash plate 1 exerts a normal force F _N on the ball head K, which acts in the center of gravity S of the pressure field or the spherical cap KK and in the ball head K into a piston force F _K and a radial - or transverse force F _{R is} broken down. The radial force F _R is proportional to the distance x between said surface center of gravity S and the piston axis L _K and can move the ball head K in the hollow spherical section KA to the left in FIG. 5, so that an excessive amount of oil over the enlarged bearing gap h on the opposite side flows into the leakage oil chamber, as indicated by the arrow P. This reduces the effectiveness of the hydrostatic relief of the ball head K; this can lead so far that the pressure field completely collapses with the consequence of a metallic contact between ball head K and swash plate 1.

It is an object of the invention to further develop the ball head of the type mentioned in the introduction so that the radial force F _R acting on it under load is reduced.

This object is achieved by the characterizing features of claim 1 in conjunction with its generic features. The part of the pressure oil flowing into the bearing gap, which flows out in the direction of the relief groove, is collected by the latter and discharged to the leakage oil space via the cavity between the cylinder surface and the bearing surface. The pressure oil thus only wets the area of the bearing gap that is delimited by the relief groove and assigned to the counter bearing surface. Accordingly, the pressure field builds up only in this area of the bearing gap. The center of gravity of this pressure field or the counter bearing surface is at a smaller distance from the piston axis compared to the prior art. This fact is represented in claim 1 by the feature that the counter bearing surface is penetrated by the piston axis in the area of its center of gravity. The radial force is adjusted to such a value by appropriate selection of the size of this area or distance that there is no or only an insignificant displacement of the ball head and thus the largest possible pressure field is achieved.

When the relief groove is formed in the bearing surface, the changes Radial force with the position that the spherical piston occupies within the hollow spherical section, that is to say with the respectively set swivel angle of the radial or axial piston machine. In contrast to this, the swivel angle of the axial or radial piston machine has no influence on the magnitude of the radial force and thus the pressure field if the relief groove is formed in the spherical cap.

The relief groove preferably runs in a plane perpendicular to the piston axis. Other options for the course of the relief groove are also conceivable, for example in a plane perpendicular to the plane mentioned or to the plane of the equator line.

Fig. 1

eine Axialkolbenmaschine im Axialschnitt, deren Kolben an deren Hubkörper über Kugelköpfe gemäß dem bevorzugten Ausführungsbeispiel abgestützt sind,

Fig. 2

den in Fig. 1 mit A bezeichneten Ausschnitt im vergrößerten Maßstab,

Fig. 3

eine schematische Darstellung des Kolbens nach Fig. 2 mit den im Betrieb der Axialkolbenmaschine an ihn wirkenden Kräften, und

Fig. 4

einen Schnitt entlang der Linie IV-IV in Fig. 3.

The invention is described in more detail below on the basis of a preferred exemplary embodiment with reference to FIGS. 1 to 4. Show it:

Fig. 1

an axial piston machine in axial section, the pistons of which are supported on their lifting bodies via ball heads according to the preferred exemplary embodiment,

Fig. 2

1 on a larger scale,

Fig. 3

2 with the forces acting on it during operation of the axial piston machine, and

Fig. 4

a section along the line IV-IV in Fig. 3rd

The axial piston machine shown in FIG. 1 is designed in an inclined-axis design with an adjustable displacement volume and, in a known manner, comprises, as known components, a hollow cylindrical housing 10 with an open end on the front side, a housing end plate 11 closing this open end, a drive shaft 12 with a drive disk 13 formed in one piece , a control body 14 with an associated adjusting device 15 and a cylinder drum 16.

The drive shaft 12 passes through a through hole formed in the housing end wall 17 opposite the housing end plate 11 and is rotatably mounted in the latter. The drive pulley 13 is in the interior of the housing arranged and rotatably supported on its inner surface on the inner surface of the housing end wall 17.

The control body 14 is a so-called control lens of biconvex shape, which can be displaced in a circular support and pivot bearing 18 in the housing end plate 11 and can be fixed within this bearing by means of the adjusting device 15 in any desired position. In the control body 14, two opposing control kidneys, not shown, are formed in a known manner, which are connected to the pressure port and the suction port (also not shown) of the inclined axis machine.

The adjusting device 15 is provided for changing the displacement volume of the inclined axis machine and comprises a pin 19 and an actuating rod 20 which is guided in a bore 21 perpendicular to the drive shaft 12 in the housing end plate 11. The pin 19 is fastened to the actuating rod 20 and engages in a bore 22 in the control body 14.

The cylinder drum 16 is arranged between the drive pulley 13 and the control body 14 and is supported for the purpose of self-centering mounting with a concave bearing surface on the convex control surface of the control body 14 facing it.

In the cylinder drum 16 axially extending and evenly distributed on a pitch circle cylindrical bores 23 are formed, which open out via outlet channels 24 on the concave bearing surface of the cylinder drum 16 and connect the cylinder bores 23 via the control kidneys with the pressure and suction nozzle when the latter rotates . In the cylinder bores 23, pistons 25 are arranged so that they can be moved back and forth. Their free ends are rotatably connected to the drive pulley 13 via ball joints. Each ball joint consists of a ball head K formed at the free end of the associated piston 25 and a hollow ball section KA formed in the drive disk 13 (see FIG. 2), in which the ball head K is accommodated in a rotatable manner. The hollow spherical sections KA are arranged on a pitch circle that is slightly smaller or larger than the pitch circle of the Cylinder rooms 23 is.

In a central stepped bore in the cylinder drum 16 there is a compression spring 26 which supports a central pin 27 on the cylinder drum 16, which is also supported by a ball and socket joint in the drive pulley 13, projects into the stepped bore and guides the cylinder drum 16, and thus supports it when no oil pressure forces occur , in contact with the control body 14.

The pistons 25 essentially correspond to the pistons described in DE-AS 2 358 870 and are therefore not described in more detail here. It should only be mentioned that each piston 25 has a piston ring 28 received in a groove, to which a section in the form of a spherical zone connects in the direction of the piston head. The piston sections between this spherical zone and the piston crown and above the piston ring 28 are frustoconical.

Each hollow spherical section KA is delimited by a circular opening 29 which lies in a plane E _{1 which} is parallel to the end face 30 of the drive pulley 13 and is set back to it by a small amount. A conical surface 31 connects the hollow spherical section KA at the level of the circular opening 29 with the end face 30 of the drive pulley 13. The diameter of the circular opening 29 is smaller than that of the hollow spherical section KA and the spherical head K accommodated therein.

In order to be able to be inserted into and removed from the hollow spherical section KA, the spherical head K is formed with a cylindrical surface 32 which runs symmetrically on both sides of a spherical head equatorial line Q which, with the piston axis L _K, includes an angle β deviating from 90 ° and one has a smaller diameter than the circular opening 29. The assembly and disassembly of the ball head K can only take place if the piston 25 is brought into such an inclined position that the cylinder surface 32 or the equator line Q is parallel to the plane E _{1 of} the circular opening 29. After inserting the ball head K, the piston 25 is pivoted clockwise by the angle γ into the inclined position shown in FIG it is no longer possible to remove the spherical head K from the hollow spherical section KA. This inclination corresponds to a swivel angle of 0 ° enclosed by the drive shaft axis L _T and the cylinder drum axis L _{Z of} the axial piston machine and thus a zero displacement volume. By further pivoting the piston 25 clockwise by the angle α, the axial piston machine is set to the maximum pivoting angle shown in FIG. 3, that is to say to the maximum displacement volume.

As can be clearly seen in FIG. 2, inside the hollow spherical sections KA, the cylinder surfaces 32 on the respective spherical head K each have a spherical cap KK, in which a relief groove 33 runs in a plane E ₂ perpendicular to the piston axis L _K and has two open ends, with which it opens into the cylindrical surface 32 or into the cavity 34 defined by this and the concave surface of the hollow spherical section KA. For the sake of simplicity, the bearing gap h is not shown in FIG. 2.

The area of the concave surface of the hollow spherical section KA corresponding to the swivel angle range of the axial piston machine represents a bearing surface 35 on which the ball head K is supported with the bearing counter surface 36 delimited by the relief groove 33 on the spherical cap KK under hydrostatic relief by a pressure field.

For the purpose of building up this pressure field, each piston 25 is provided with a through bore 37, which is only shown in FIGS supplies the working space 39 of the cylinder bore 23. A portion of this pressure oil flows through through holes 40 in the drive pulley 13 to pressure pockets 41 in the drive pulley ring surface. With the help of these pressure pockets 41, a pressure field is also built up, which rotatably supports the drive pulley 13 on the housing end wall 17.

For the purposes of the invention, the term “hydrostatic relief” also includes the so-called “hydrostatic bearing”, in which the so-called inlet pressure in the pressure pocket 38 due to the use of a throttle in the through bore 37 is lower than the so-called supply pressure with which the pressure oil flows from the working space 39. In the case of hydrostatic relief, both pressures are essentially the same. The function of the relief groove is described below using the example of the hydrostatic bearing.

During operation of the inclined-axis machine, which is carried out in a known manner and is therefore not described further here, the pressure oil supplied to the pressure pocket 38 via the through bore 37 with a throttle, not shown, flows with the inlet pressure via the bearing gap h between the bearing counter surface 36 and the corresponding area of the bearing surface 35 directly on the one hand and on the other hand via the relief groove 33 into the cavity 34 between the cylinder surface 32 and the concave surface of the hollow ball section KA and from there to the leakage oil chamber. The oil film in the gap h forms a pressure field which absorbs the piston force F _K and thus prevents metallic contact between the ball head K and the concave surface of the hollow ball section KA. If the piston force F _K increases, the bearing gap h becomes smaller, the oil flow and the pressure drop at the throttle decrease, so that the inlet pressure increases and can take up the increased load. Conversely, when the pressure is relieved, the inlet pressure drops as the bearing gap increases.

As can be clearly seen in FIG. 3, the center of gravity S of the pressure field or the bearing counter surface 36 and thus the point of application of the piston force F _N on the ball head K is at a smaller distance x than in the prior art (cf. FIG. 5) from the piston axis L. _K , in the region of the point of penetration of the piston axis L _K through the bearing counter surface 36. In FIG. 4, the circular line with the radius x shows the position of the center of gravity S with the piston 25 rotating about its piston axis L _K. As in FIG. 3 shown, the radial force F _{R is} smaller compared to the prior art corresponding to the smaller distance x, namely by such a value that no displacement of the ball head K can take place.

The end face 30 of the drive pulley 13 is selected in the form of a conical surface with an inclination angle δ with respect to a plane E ₃ perpendicular to the drive shaft axis L _T. Passes through the apex of this conical surface 30 the drive shaft axis L _T. The angle δ corresponds to the deflection angle of the pistons, which arises due to the formation of ellipses during the rotation of the drive shaft with the cylinder drum running obliquely. This arrangement ensures optimal utilization of the retraction function of the hollow spherical sections as a result of their bearing surfaces enclosing the spherical heads at an angle greater than 180 °, since the piston offset during the revolution is almost symmetrical at the maximum swivel angle.

Claims (4)

1. Ball head (K) which directly or indirectly supports a piston of a hydrostatic axial or radial piston machine on its stroke body (13) with hydrostatic relief, whereby the ball head is provided in a hollow sphere section (KA) bounded by a circular opening (29) and is formed with a cylindrical surface (32) which develops to both sides of an equatorial line (Q) which includes with the piston axis (L_K) an angle (β) which differs from 90°, has a smaller diameter than the circular opening bounding the hollow sphere section and bounds spherical segment (KK) at the ball end for bearing in a bearing surface (35) of the hollow sphere section,
   characterized in that,
   in the spherical segment (KK) or in the bearing surface (35) there is formed a relief groove (33), open at both of its ends, which with these open ends always opens out into the chamber (34) bounded by the cylinder surface (32) and the bearing surface (35) and bounds in the spherical segment (KK) a counter-bearing surface (36) supported, with hydrostatic relief, on the bearing surface (35), the center of gravity of which counter-bearing surface (S) always lies in the vicinity of the piston axis (L_K).
2. Ball head according to claim 1,
   characterized in that,
   the relief groove (33) runs in a plane (E₂) perpendicular to the piston axis (L_K).
3. Ball head according to claim 1,
   characterized in that,
   the relief groove (33) runs in a plane perpendicular to the plane (E₂).
4. Ball head according to claim 1,
   characterized in that,
   the relief groove (33) runs in a plane which stands perpendicularly on the plane in which the equatorial line (Q) lies.

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