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Hydraulic axial piston machineRelated Patent Categories: Expansible Chamber Devices, Displacement Control Of Plural Cylinders Arranged In Parallel, Radial, Or Conical Relationship With Rotary Transmission Axis, Parallel CylindersHydraulic axial piston machine description/claimsThe Patent Description & Claims data below is from USPTO Patent Application 20070186764, Hydraulic axial piston machine. Brief Patent Description - Full Patent Description - Patent Application Claims
CROSS-REFERENCE TO RELATED APPLICATIONS: [0001] Applicant hereby claims foreign priority benefits under U.S.C. .sctn. 119 from German Patent Application No. 10 2004 043 745.9 filed on Sep. 10, 2004, the contents of which are incorporated by reference herein. FIELD OF THE INVENTION [0002] The invention concerns a hydraulic axial piston machine with a cylinder body, at least one piston to be axially displaceable in the cylinder body, said piston resting on a swash plate by way of a slide shoe, with a pressure plate loading the slide shoe in the direction of the swash plate, and a hold-down part, which bears with a contact surface on a counter surface of the pressure plate facing away from the swash plate. BACKGROUND OF THE INVENTION [0003] Such an axial piston machine is known from DE 43 01 120 C2. Here, the hold-down part has the form of a piston, which is supported in the cylinder body by way of a spring. The piston has a front side, which is perpendicular to the axis of the cylinder body. On this plane front side, the pressure plate bears, said pressure plate having in this area a cone shape. [0004] Such axial piston machines usually work satisfactorily. However, with a number of operating conditions wear problems occur, particularly when such a machine is used in connection with demineralised water. [0005] In principle, wear occurs everywhere, where parts are moving in relation to and rubbing on each other. When water is used as hydraulic fluid, the lubricating effect of the hydraulic fluid is missing. In many areas, a suitable material pairing will ensure that a relatively thin layer of fluid is sufficient, also when the fluid has no lubricating effect. However, it is relatively difficult to provide such a fluid layer in the contact zone between the contact surface and the counter surface. Accordingly, a wear particularly occurs in the contact area between the hold-down part and the pressure plate. BRIEF SUMMARY OF THE INVENTION [0006] The invention is based on the task of operating a machine with as little wear as possible. [0007] With a hydraulic axial piston machine as mentioned in the introduction, this task is solved in that the contact surface is formed by a circumferential surface section of a cone, whose peak is directed towards the swash plate. [0008] This embodiment provides a reduction of the friction between the hold-down part and the pressure plate. The pressure plate rolls off from the contact surface of the hold-down part, so that the share of rolling friction increases and the share of sliding friction decreases. The smaller the share of sliding friction, the smaller the wear. [0009] Preferably, the counter surface is formed by a circumferential surface section of a counter cone, whose peak is directed towards the cylinder body. With this embodiment, two cone circumferential surfaces roll off from each other. With such an embodiment, the share of sliding friction can be kept very small. The wear is correspondingly small. [0010] Preferably, the cone has a cone angle, which is 1/3 to 2/3 of the cone angle of the counter cone. The more alike the cone angles, the smaller the share of sliding friction. [0011] It is particularly preferred that both cone angles are equally large. This does not mean that they are equal in the mathematical sense of the word. Certain tolerances are permissible. The equality of the cone angles makes it possible that the contact occurs over a relatively large area (seen in the radial direction). In the circumferential direction, however, the contact remains an approximate line contact. With this embodiment, a contact between the hold-down part and the pressure plate is achieved, which is practically exclusively based on rolling friction. [0012] Preferably, the cone angle amounts to 25 to 75 percent of the angle, under which the swash plate is inclined in relation to a plane, to which the axis of the cylinder body is perpendicular. With this embodiment it is achieved that the slide shoe can be held on the swash plate in a substantially tilt-free manner. [0013] In a particularly preferred embodiment, it is ensured that the cone angle is half as large as the angle. Thus, the angle of the swash plate (swash plate angle) is divided between the contact surface and the counter surface. In this case the smallest wear occurs with a reliable bearing of the slide shoe on the swash plate. [0014] Preferably, the counter surface is located in a central recess of the pressure plate. This involves several advantages. Firstly, this permits some kind of self-centering of the pressure plate in relation to the hold-down part. Secondly, a sufficiently thick pressure plate is available in the area of the slide shoe, so that the slide shoe can be held on the swash plate with sufficient force. Finally, the weight of the pressure plate is kept small, so that the dynamic properties of the machine are improved. [0015] Preferably, the hold-down part has the form of a ring, which surrounds the bearing shaft of the cylinder body. Thus, the hold-down part is fixed and cantered at the cylinder body. [0016] Preferably, the contact surface of the hold-down part is made of plastic or ceramic. Particularly, when the machine is to be driven with water or even demineralised water as hydraulic medium, the use of a contact surface of plastic or ceramic permits low-friction interaction of the hold-down part and the pressure plate. [0017] It is preferred that the hold-down part is made of plastic or ceramic. This reduces the risk that the friction-reducing layer peels off from the hold-down part. [0018] It is also advantageous when the contact surface and/or the counter surface have a coating. This coating can also be chosen so that it contributes to the friction reduction of the relative movement between the hold-down part and the pressure plate. Such a coating can, for example, contain carbon, DLC (Diamond Like Coating). [0019] Preferably, the slide shoe is connected with the piston via a ball, a line through the centre of the ball in parallel with the swash plate and the peaks of cone and counter-cone intersect each other in a point. This ensures that no tilting movements occur during operation. [0020] In the following, the invention is described on the basis of a preferred embodiment in connection with the drawing, showing: Continue reading about Hydraulic axial piston machine... 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