CYLINDER DRUM OF A HYDROSTATIC AXIAL PISTON MACHINE HAVING A WEAR-RESISTANT LAYER

Abstract

A method is provided for forming wear-resistant layer on the surface of cylinder bores a cylinder drum of a hydrostatic axial piston machine within which a respective piston is moved in a manner subject to intensive wear. The cylinder bores are gas nitrocarburized in two stages to minimize the wear and include a thin uniform connecting layer that has a thickness of 4 to 16 μm and a comparatively thick underlying diffusion layer.

Claims

1. A method of forming a wear-resistant layer on the surface of a cylinder bore within a cylinder drum of a hydrostatic axial piston machine, the method comprising gas nitrocarburizing the surface of the cylinder bore in two stages: the first stage forming an oxide layer and a diffusion layer at the surface separated by a ductile connecting layer that is comparatively thin relative to the diffusion layer, the first stage comprising gas nitrocarburizing at a comparatively low treatment temperature and a comparatively long treatment duration; and the second stage comprising further gas nitrocarburizing while increasing the carbon content of the connecting layer by the addition of carbon donors at a comparatively high treatment temperature relative to the first stage.

2. The method according to claim 1, wherein the connecting layer is formed with a thickness of 4 to 16 μm.

3. The method according to claim 2, wherein the connecting layer is formed with a thickness of 5 to 12 μm.

4. The method according to claim 1, wherein the diffusion layer is formed with a thickness of at least 50 μm.

5. The method according to claim 1, wherein the comparatively low temperature of the first stage is 500 to 510° C.

6. The method according to claim 5, wherein the comparatively high treatment temperature of the second stage is greater than 500° C.

7. The method according to claim 1, further comprising adding during the gas nitrocarburizing stages more nitrogen than in an undersaturated furnace atmosphere.

8. The method according to claim 7, wherein the step of adding nitrogen includes adding during the gas nitrocarburizing stages less nitrogen than in a supersaturated furnace atmosphere.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0020] An exemplary embodiment according to the disclosure of a cylinder drum is shown in the drawings. The disclosure will now be explained in more detail with reference to the figures in the drawings, in which:

[0021] FIG. 1 shows a longitudinal section through the cylinder drum according to the disclosure, and

[0022] FIG. 2 shows the cylinder drum as shown in FIG. 1 in an elevated view.

DETAILED DESCRIPTION

[0023] FIG. 1 shows a cylinder drum 1 of the exemplary embodiment of the axial piston machine according to the disclosure in an oblique-axis construction in a sectional illustration. It has an approximately circular cylindrical shape and, during operation of the axial piston machine, rotates about its longitudinal axis 2. The cylinder drum 1 has a spherical shape on one end face 4 and is pressed with this end face 4 against a distributor disk. The other end face 6 faces towards a flange of a drive shaft, the cylinder drum 1 being set opposite said flange in the case of a constant-displacement machine and being settable at various angles in relation to said flange in the case of a variable-displacement machine.

[0024] FIG. 2 shows an elevated view of the end face 6 of the cylinder drum 1 which faces towards the flange or the shaft. A plurality of cylinder bores 8 are introduced on the circumference thereof in a uniformly distributed manner and extend over a large part of the length of the cylinder drum 1.

[0025] With reference to FIG. 1, in the region of the spherically shaped end face 4 each cylinder bore has a through bore 10, via which the cylinder bore 8 is alternately connected to a high-pressure kidney and a low-pressure kidney of the distributor disk as it revolves about the longitudinal axis 2. A piston is guided in each cylinder bore 8 and is hinged on its side remote from the cylinder drum 1 to the flange, the lifting movement of the piston in the cylinder bore being produced during a joint revolution owing to the oblique position of the flange. Therefore, each piston forms a sliding pairing with the cylinder drum 1—more precisely with the cylinder bore 8.

[0026] According to the disclosure, the cylinder drum 1 shown in FIGS. 1 and 2 was nitrocarburized in a furnace with gas or in a salt bath after its manufacture. An oxide layer OS, an underlying connecting layer VS and an underlying diffusion layer DS were thereby produced in particular in the region of the lateral surface of the cylinder bore 8, these layers serving as a wear-resistant layer for the cylinder bore 8. In the variant in which gas nitrocarburizing is carried out, the connecting layer VS has a thickness of 5 to 12 μm, while the underlying diffusion layer DS has a thickness of at least 50 μm. In this case, it is possible to employ a two-stage method, in the first stage of which the treatment was carried out with a comparatively long duration and at a comparatively low temperature of 500 to 510° C. In the second stage, the carbon content of the connecting layer (VS) was increased by the addition of carbon donors at a comparatively high treatment temperature.

[0027] The disclosure discloses a cylinder drum of a hydrostatic axial piston machine, wherein a plurality of cylinder bores, in each of which a piston is moved in a manner subject to intensive wear, are introduced into the cylinder drum. The cylinder bores of the cylinder drum are nitrocarburized in a salt bath or in gas to minimize the wear, a thin uniform connecting layer having a thickness of 4 to 16 μm and a comparatively thick underlying diffusion layer being provided.

LIST OF REFERENCE SIGNS

[0028] 1 Cylinder drum

[0029] 2 Longitudinal axis

[0030] 4 End face

[0031] 6 End face

[0032] 8 Cylinder bore

[0033] 10 Through bore

[0034] DS Diffusion layer

[0035] OS Oxide layer

[0036] VS Connecting layer