Method for manufacturing a spherical-cap-shaped recess in a drive shaft, drive shaft comprising the recess, and hydrostatic axial piston machine comprising the drive shaft

Abstract

A method for manufacturing an at least sectionally spherical-cap-shaped recess on a drive shaft for a hydrostatic axial piston machine includes whirling of the recess and heat treatment of the recess to form a wear layer. A drive shaft for a hydrostatic axial piston machine includes at least one recess manufactured according to the method. A hydrostatic axial piston machine includes a drive shaft with at least one recess manufactured according to the method.

Claims

1. A method for manufacturing an at least sectionally spherical-cap-shaped recess on a drive shaft for a hydrostatic axial piston machine, the recess configured to receive a ball head of a guide piston or working piston of the axial piston machine, the method comprising: whirling of the recess; and heat treatment of the recess to form a wear layer, the heat treatment satisfying specifications of the recess with respect to dimensional tolerance and wear behavior.

2. The method according to claim 1, wherein the heat treatment satisfies specifications of the wear layer with respect to thickness, surface hardness, and ductility.

3. The method according to claim 1, wherein the whirling of the recess is effected with air cooling.

4. The method according to claim 1, wherein the heat treatment is effected in a plurality of stages of differing temperatures and durations.

5. The method according to claim 1, wherein a nitriding hardness depth is approximately 0.1 mm to 0.25 mm.

6. The method according to claim 1, further comprising cleaning the heat-treated recess.

7. The method according to claim 1, wherein a nitriding hardness depth is approximately 0.15 mm.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) An exemplary embodiment of an axial piston machine according to the disclosure and of a method according to the disclosure are shown in the drawings. The disclosure will now be explained in more detail with reference to the figures in these drawings, in which:

(2) FIG. 1 shows, in a longitudinal section, an axial piston machine according to the disclosure of oblique axis design, and

(3) FIG. 2 shows a block diagram of a method according to the disclosure.

DETAILED DESCRIPTION

(4) As shown in FIG. 1, an axial piston machine 1 configured with an oblique axis design has a two-part housing 2, in which a drive shaft 4 is mounted by way of two tapered-roller bearings 6 and 8, rotatable about an axis of rotation 10. The exemplary embodiment of the axial piston machine 1 as shown in FIG. 1 is configured as a constant-displacement machine, i.e. with a constant displacement volume, and can alternatively be configured with a variable displacement volume.

(5) The drive shaft 4 is received by way of the bearings 6, 8 in a first housing part 12 with a pot-like shape. A second housing part 16 angled in relation to the first housing part 12 is positioned at the opening 14 of said first housing part, by way of which the drive shaft 4 is mountable, with a cylinder drum 18 being mounted in said second housing part in a manner rotatable about an axis of rotation 20. In this case, the cylinder drum 18 has a plurality of cylinder bores 22, which are arranged on a pitch circle arranged concentrically with respect to the axis of rotation 20 and in each of which there is arranged a working piston 24 in an axially displaceable manner. Coaxially with respect to the axis of rotation 20, the cylinder drum 18 has a central cylinder bore 26, in which a guide or centering piston 28 of the cylinder drum 18 is received slidingly.

(6) The guide piston 28 and the working pistons 24 each have a ball head 30, which is formed in a respective spherical-cap-shaped recess 32 of a drive shaft flange 34 which is located on the end face of the drive shaft 4 and is arranged close to the opening 14. The non-rotatable connection between the drive shaft 4 and the cylinder drum 18 is realized via the ball heads 30 received in the recesses 32 and the working pistons 24.

(7) The second housing part 16 has a low-pressure connection and a high-pressure connection (neither shown), by way of which hydrostatic working spaces 36 delimited by the working pistons 24 and the cylinder bores 22 thereof are each alternatively fluidically connectable to low pressure and high pressure. The fluidic connection is reversed in this case by way of a control disk 38, arranged immovably in the second housing part 16, and kidney-shaped pressure ports formed therein (not shown).

(8) Each ball head 30 is hydrostatically relieved in the recess 32. This is achieved by virtue of the fact that the respective piston 24, 28 has a centric through-recess 40 (only shown for the centering piston 28), by way of which a gap formed in each case between the ball head 30 and the recess 32 is supplied with hydrostatic pressure medium from an inner space of the cylinder drum 18 assigned to the respective piston 24, 28for the working pistons 24, these are the working spaces 36.

(9) During intended operation of the axial piston machine 1, which for example has a working pressure of up to 500 bar and a rotational speed of the drive shaft 4 of up to 5000 l/min, the frictional pairing of the ball head 30 with the spherical-cap-shaped recess 32 is exposed to high levels of loading. It is therefore necessary to observe narrow tolerances in relation to the shape of the ball head 30 and of the recess 32, in particular with respect to their respective circularity, and a correspondingly hard but nevertheless ductile surface of the two friction partners 30, 32.

(10) As shown in FIG. 1, the ball heads 30 each have an annular shoulder 31, which extends in a radially extensive manner with respect to a piston longitudinal axis and by way of which the pressure medium arranged in the gap between the ball head 30 and the recess 32 and provided for the hydrostatic relief of said frictional pairing is effectively retained in the gap.

(11) In the exemplary embodiment shown, this retention is improved yet further by virtue of the fact that the inner lateral surface of the respective recesses 32 additionally engages behind the respective ball head 30 beyond the equator thereof.

(12) The aforementioned specifications are achieved in relation to the recesses 32 by way of the manufacturing method 42 according to the disclosure which is shown in FIG. 2. As shown in FIG. 2, said method comprises a step of whirling 44 of the recesses 32 on the drive shaft flange 34.

(13) The accuracy of the whirling is achieved in this case to a deviation of the dimensional tolerance, in particular circularity, of less than or equal to 0.01 mm, in particular on account of the aforementioned aspects of pre-manufacturing by cutting and whirling on the same machine tool and 5-axis-synchronized machine with temperature compensation.

(14) With this improved circularity after whirling as compared with the prior art, a further method step 46 involves a heat treatment of the whirled recess 32 by means of 3-stage gas nitrocarburizing (GNC).

(15) The layers formed thereby are: right at the bottom, a comparatively thick base layer, also referred to as a diffusion layer. The actual wear layer has, following the latter in the direction of the inner lateral surface of the recess 32, a first layer, also referred to as a connecting layer. In the exemplary embodiment according to the disclosure, the latter has a thickness of approximately 6 to approximately 8 m on account of the optimized heat treatment.

(16) Compared with thicknesses of approximately 4 to approximately 15 m which are known from conventional manufacturing methods with whirling and heat treatment, it is therefore formed in a more uniform manner and on average to be thinner. In addition, a higher ductility and therefore a reduced inclination toward brittle fracture are achieved.

(17) In particular, the three properties of the connecting layer of the wear layer according to the disclosure which are mentioned last render said finishing to achieve the specifications of the wear layer superfluous.

(18) According to the method according to the disclosure, said specifications are therefore already achieved after the step of heat treatment, and therefore at least the aforementioned finishing is superfluous.

(19) In addition, to increase the quality of the wear layer, a step of grinding of the wear layer can be effected after the step of heat treatment (not shown).

(20) Finally, a step of cleaning 48 of the wear layer is effected in the exemplary embodiment shown.

(21) The method is then repeated for every further necessary recess 32 on the drive flange 34.

(22) What is disclosed is a method for manufacturing an at least sectionally spherical-cap-shaped recess on a drive shaft for a hydrostatic axial piston machine, said method comprising the steps of whirling of the recess and then heat treatment of the recess to form a wear layer. In this case, parameters of the two method steps are optimized in such a manner that specifications of the recess and of the wear layer in relation to dimensional tolerance and wear behavior are already satisfied after the heat treatmentin particular without additional grinding and finishing.

(23) What are furthermore disclosed are a drive shaft for the hydrostatic axial piston machine comprising recesses manufactured in such a manner, and a hydrostatic axial piston machine comprising said drive shaft.

LIST OF REFERENCE SIGNS

(24) 1 Axial piston machine

(25) 2 Housing

(26) 4 Drive shaft

(27) 6, 8 Tapered-roller bearing

(28) 10 Axis of rotation

(29) 12 First housing part

(30) 14 Opening

(31) 16 Second housing part

(32) 18 Cylinder drum

(33) 20 Axis of rotation

(34) 22 Cylinder bore

(35) 24 Working piston

(36) 26 Cylinder bore

(37) 28 Centering piston

(38) 30 Ball head

(39) 31 Annular shoulder

(40) 32 Recess

(41) 34 Drive flange

(42) 36 Hydrostatic working space

(43) 38 Control disk

(44) 40 Pressure medium duct

(45) 42 Method

(46) 44 Whirling

(47) 46 Heat treatment

(48) 48 Cleaning