Hydraulic piston machine, in particular water hydraulic machine

Abstract

The invention concerns a hydraulic piston machine, in particular a water hydraulic machine, with at least one cylinder, in which a piston (4) is arranged to reciprocate, the piston (4) comprising a hollow that is surrounded by an annular wall and has one open end. It is endeavored to keep cavitations small. For this purpose, a filling member (13) is arranged in the hollow (12), the filling member (13) having at least a radial projection (22) and the annular wall (16) having at least a radial depression (17) in the inside facing the hollow (12), or the annular wall (16) having a radial projection and the filing member (13) having a radial depression, the depression having a restraint (19), at least at the end adjacent to the open end (18) of the hollow (12), and the projection (22) and the depression (17) engaging each other.

Claims

1. A hydraulic piston machine comprising: at least one cylinder in which a piston is arranged to reciprocate; the piston comprising: an annular wall defining a hollow and one open end; and a filling member of a plastic material configured to be inserted into the hollow; wherein the filling member has at least a radial projection and the annular wall has at least a radial depression in the inside facing the hollow, the radial projection being larger than the radial depression in a radial direction when the filling member is not inserted into the hollow; wherein the depression has a restraint adjacent to the open end of the hollow; wherein the projection and the depression are configured to engage each other; wherein the projection is configured to compress in the radial direction when the filling member is inserted in the hollow of the piston and the projection contacts the annular wall; and wherein the projection is configured to expand in the radial direction into the depression when the filling member is inserted into hollow of the piston and the projection overlaps the depression.

2. The machine according to claim 1, wherein the depression is circumferential.

3. The machine according to claim 2, wherein the projection is uninterrupted in the circumferential direction.

4. The machine according to claim 1, wherein the restraint is made as a step.

5. The machine according to claim 4, wherein the step encloses an angle of at least 90 with the axis of the piston.

6. The machine according to claim 1, wherein the free end of the hollow forms a conical bulge.

7. The machine according to claim 1, wherein the projection, together with the end of the filling member adjacent to the free end of the hollow, forms a common front face.

8. The machine according to claim 1, wherein the radial extension of the projection amounts to maximum 5% of the filling member diameter.

9. The machine according to claim 1, wherein the radial projection is smaller than the radial depression in an axial direction when the filling member is not inserted into the hollow.

10. The machine according to claim 1, wherein the depression has a bottom that encloses an acute angle with a parallel to the axis of the piston, several depressions being arranged in series parallel to the axis of the piston.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) In the following, the invention is described on the basis of preferred embodiments in connection with the drawings, showing:

(2) FIG. 1 is a strictly schematic view of a hydraulic axial piston machine

(3) FIG. 2 is a first embodiment of a piston with a filling member, and

(4) FIG. 3 is a second embodiment of a piston with a filling member.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

(5) A hydraulic axial piston machine 1 comprises a cylinder drum 3 that is arranged to be rotatable in a housing 2. In the cylinder drum 3, pistons 4 are arranged to be movable in the axial direction. Only one piston 4 is visible. All other pistons are located outside the sectional plane. The pistons 4 are guided on a wobble plate 6 by means of a slide shoe 5. A pressure plate 7 holds the slide shoe 5 in a bearing position against the wobble plate 6. Via a ball 8, the pressure plate bears on one end of a pressure piston 9 that is accommodated in the cylinder drum. The pressure piston 9 is acted upon in the axial direction by a spring 10, meaning that it is pressed in the direction of the wobble plate 6.

(6) Preferably, the piston 4 is made of stainless steel. In dependence of the conditions, under which the machine will be used, in particular the pressures, media and designs, also other materials can be used, in particular plastic.

(7) As known per se, a rotation of the cylinder drum 3 causes a reciprocating movement of the pistons 4 in the axial direction. As the pressure plate 7 must always remain parallel to the wobble plate 6, it performs a continuous tilting movement in relation to the cylinder drum 3. In this connection, the ball 8 provides an articulated connection between the pressure plate 7 and the cylinder drum 3. Each slide shoe 5 tilts around a ball 11 that is arranged on the end of the piston 4 protruding from the cylinder drum 3.

(8) The machine 1 is operated with water as hydraulic fluid. It must also have a high output when working as a pump. Volumes of 30 m.sup.3/h and higher are considered to be high outputs. However, in such applications, problems may arise in that cavitations occur in the piston 4, which comprises a hollow 12 (FIG. 2b) with the purpose of saving weight, as the underpressure gets too large, because the fluid cannot move fast enough. For this reason, a filling member 13, also called filling piece, is arranged in the hollow 12 of the piston 4. The explanation below concerns the FIGS. 2 and 3. However, it must be noted that such problems do no only occur in connection with axial piston machines, but also with radial piston machines, and basically with all hydraulic machines, in which pistons are arranged to reciprocate in particular machines, in which water is used as hydraulic fluid.

(9) FIG. 2a shows the piston 4 with the filling member 14 inserted into the hollow 12 and the ball 11. A channel 14 passes through the ball 11 and ends in the hollow 12. Through this channel fluid is supplied to the contact face between the slide shoe 5 and the ball 11. In order to maintain this fluid supply that serves for lubrication, also with inserted filling member 13, the filling member 13 has a through channel 15. However, the channel 15 must not necessarily be arranged centrally, as shown. It can also be arranged outside of an axis 20 of the piston 4 or be formed by a free space that is formed between the filling member 13 and the inner wall 16. Such a free space can, for example, be formed by an axial groove in the filling member 13 and/or in the inner wall 16.

(10) The filling member 13 is made of a plastic material, for example of polypropylene. Also another plastic material can be used for the filling member 13, in particular a plastic material that is volume constant.

(11) In the inner wall 16 of the hollow 12, the piston 4 has a preferably circumferential depression 17 in the form of a groove that has a restraint 19 in the form of a step at the end adjacent to the open end 18 of the hollow. For example, the step extends at right angles to the axis 20 of the piston 4. However, it can also enclose an acute angle with the axis in such a manner that an undercut appears.

(12) At its open end 18, the hollow 12 opens with a cone face 21. Together with the axis 20, the cone face 21 encloses an angle of, for example, 10 to 20, in particular 10 to 15. The difference between the smallest diameter and the largest diameter of the cone face 21 is larger than the radial extension of the depression 17.

(13) The filling member 13, shown in enlarged form in FIG. 2c, comprises a radial projection 22 with a front face 23 adjacent to the open end 18 of the hollow 12. The front face 23 ends in alignment with the projection 22. Preferably, the projection 22 is circumferential. When the channel 15 is made as a groove in the filling member 13, the projection 22 is interrupted here. The axial extension of the projection 22 is somewhat smaller than the axial extension of the depression 17, that is, in the axial direction the projection 22 has an undersize in relation to the depression 17.

(14) In the radial direction, the projection 22 has an extension that is somewhat larger than the radial extension of the depression 17. In other words, in the radial direction the projection 22 has an oversize in relation to the depression 17. However, this only applies for as long as the filling member 13 is separated from the piston 4. Otherwise, the filling member 13 has an outer diameter, which practically corresponds to the inner diameter of the hollow 12, so that the filling member 13 can be inserted into the hollow 12 of the piston 4 without problems. A small clearance is permissible, so that the filling member 13 can be moved into the piston 4.

(15) When the filling member 13 has been inserted so far into the piston 4 that the projection 22 bears on the cone face 21, a further pressing force will cause a compression of the projection in the radial direction. When the filling member 13 is pushed further and the projection 22 overlaps the depression 17, the projection 22 can expand again. However, it cannot expand to its original radial size, as the somewhat smaller radial extension of the depression 17 does not permit this. The material that is somehow in excess will then expand in the axial direction, meaning that the projection 22 fills the depression 17 completely in the axial direction. In the area of the depression 17, the filling member 13 is then held by means of form-fit in the piston 4, both in the axial direction and in the radial direction. Thus, there is no risk that the filling member 13 is detached from the piston 4.

(16) In a manner not shown in detail, the location of the depression 17 and the projection 22 can be exchanged, so that the depression 17 is arranged in the circumferential wall of the filling member 13 and the projection 22 is arranged in the radial inside of the circumferential wall 16. The effect is practically the same.

(17) FIG. 3 shows a modified embodiment. Here, several depressions 17 are provided parallel to the axis 20 in a series one after the other. Each depression 17 has a bottom 24 that encloses an acute angle with the axis 20. At the end facing away from their open end 18, each depression 17 has practically the inner diameter of the hollow 12.

(18) The filling member 13 comprises a projection 22 that is also circumferential and having on its end facing away from the open end 18 a cone section 25. The cone angle of the cone section 25 can be exactly as large as the cone angle of the cone face 21. However, it can also be smaller.

(19) In the embodiment of the piston 4 according to FIG. 3a, the depressions 17 form a fir-like structure. When the filling member 13 is pressed into the hollow 12, a number of zigzag-like depressions appear in the projection 22, so that also here the filling member 13 is held in the piston 4 by means of form-fit. Each depression 17 also has a restraint 19 in the form of a step, the height of the step being relatively small, also here.

(20) In all cases, the projection 17 has a radial extension that is maximum 5%, preferably even less, namely, for example, maximum 3% or even maximum 2.5%, of the diameter of the filling member 13. A larger radial extension gives practically no additional advantages.

(21) While the present invention has been illustrated and described with respect to a particular embodiment thereof, it should be appreciated by those of ordinary skill in the art that various modifications to this invention may be made without departing from the spirit and scope of the present.