Hydraulic pump and piston for such a hydraulic pump

Abstract

A hydraulic pump, in particular an adjustable axial piston pump, has at least one piston (22) movable in a reciprocating manner in a longitudinal direction within a pump housing during operation of the hydraulic pump. The piston (22) has a link head (24), a piston top (54) opposite the link head (24), and at least one hollow chamber (60) surrounded at least partially by a piston housing (62) that substantially or completely terminates each hollow chamber (60) towards the outside. A piston (22) for such hydraulic pump is also provided.

Claims

1. A hydraulic axial piston pump, comprising: a pump housing; at least one piston movable in opposite axial directions along a longitudinal axis of said piston inside said pump housing during operation of the pump, said piston having a link head, having a piston base opposite said link head, having a through-hole extending through said link head and said piston base and having at least one hollow chamber therein, said hollow chamber being at least partially encompassed by a piston housing substantially or entirely closing said hollow chamber to an outside of said piston, said hollow chamber being closed by a lid connected to said piston housing; and an equalizer in said piston housing or said lid connecting said hollow chamber to an environment outside of said piston chamber in a media conducting or fluid communication manner at said piston base to prevent excess pressure in said hollow chamber during joining of said lid to said piston housing.

2. A hydraulic axial piston pump according to claim 1 wherein said hollow chamber extends in a direction of or parallel to said longitudinal axis in said pump housing and extends through said piston from an axial spacing coupled to said link head to said piston base.

3. A hydraulic axial piston pump according to claim 1 wherein said equalizer comprises a spiral groove extending along an outer circumferential surface of said lid, said spiral groove being covered by said piston housing along an entire length thereof, except for a discharge end of said spiral path providing a fluid communication between an environment outside of said hollow chamber and inside of said hollow chamber.

4. A hydraulic axial piston pump according to claim 3 wherein said spiral groove opens into said hollow chamber at a bevel on said lid at an input end of said spiral groove opposite said discharge end.

5. A hydraulic axial piston pump according to claim 4 wherein said bevel has an outer diameter decreasing continuously toward said link head until reaching a final diameter.

6. A hydraulic axial piston pump according to claim 1 wherein said piston housing comprises a coupling part on said piston base coupling said lid to said piston base.

7. A hydraulic axial piston pump according to claim 6 wherein said lid is welded or brazed to said piston base.

8. A hydraulic axial piston pump according to claim 1 wherein said lid is permanently connected to said piston housing by a brazing or an electron beam weld.

9. A hydraulic axial piston pump according to claim 8 wherein, said piston is heat treated after welding.

10. A hydraulic axial piston pump according to claim 3 wherein an electron beam weld connects said lid to said piston base and closes said discharge end of said spiral groove.

11. A hydraulic axial piston pump according to claim 1 wherein said piston comprises plural hollow chambers arranged on a partial circle and circumferentially offset relative to one another in said piston housing.

12. A hydraulic axial piston pump according to claim 11 wherein each of said hollow chambers has an equal transverse diameter.

13. A hydraulic axial piston pump according to claim 1 wherein said lid closes and is inserted in said piston housing at said piston base, said equalizer extends between said housing base and said lid.

14. A hydraulic axial piston pump according to claim 1 wherein said lid closes and is inserted in said piston housing at said piston base, said equalizer extends in said lid.

15. A piston for a hydraulic axial piston pump, the piston comprising: a piston housing; a link head at one end of said piston housing; a piston base at an opposite end of said piston housing; a through-hole extending through said link head and said piston base; at least one hollow chamber in said piston housing, said hollow chamber being at least partially encompassed by a piston housing substantially or entirely closing said hollow chamber to an outside of said piston housing, said hollow chamber being closed by a lid connected to said piston housing; and an equalizer in said piston housing or said lid connecting said hollow chamber to an environment outside of said piston chamber in a media conducting or fluid communication manner at the piston base to prevent excess pressure in said hollow chamber during joining of said lid to said piston housing.

16. A piston according to claim 15 wherein said hollow chamber extends in a direction of or parallel to said longitudinal axis in said pump housing and extends through said piston housing from an axial spacing coupled to said link head to said piston base.

17. A piston according to claim 15 wherein said equalizer comprises a spiral groove extending along an outer circumferential surface of said lid, said spiral groove being covered by said piston housing along an entire length thereof, except for a discharge end of said spiral path providing a fluid communication between an environment outside of said hollow chamber and inside of said hollow chamber.

18. A piston according to claim 17 wherein said spiral groove opens into said hollow chamber at a bevel on said lid at an input end of said spiral groove opposite said discharge end.

19. A piston according to claim 18 wherein said bevel has an outer diameter decreasing continuously toward said link head until reaching a final diameter.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Referring to the drawings that form a part of this disclosure:

(2) FIG. 1 is a side view in section through an axial piston pump according to an exemplary embodiment of the invention;

(3) FIG. 2 is a side view in section of the piston of FIG. 1;

(4) FIG. 3 is a perspective view of the piston with a lid of FIG. 1;

(5) FIG. 4 is a side view in section of the piston of FIG. 2, wherein the production of the electron beam welding seam is shown;

(6) FIG. 5 is a perspective view of a piston according to the invention, having a lid affixed thereto; and

(7) FIGS. 6 to 8 are a top view, a side view, and a perspective view of the lid, respectively.

DETAILED DESCRIPTION OF THE INVENTION

(8) A detail of a hydraulic pump 10 in the form of an axial piston pump is shown in cross section in FIG. 1. Stationary cylinders 14 are disposed on a rotatable shaft 12 as part of the pump housing 16, such that the cylinders 14 rotate together with the shaft 12. An odd number of cylinders 14 are provided, which are disposed on a partial circle, circumferentially offset to one another. The longitudinal axes 18 of the cylinders 14 all have the same radius RZ to the longitudinal axis 20 of the shaft 12. A piston 22 that can be displaced longitudinally is disposed in each cylinder 14. A spherical surface 26 is provided on a link head 24 of each piston 22, which is retained in a corresponding receiving part 28 of a sliding shoe 30. Each sliding shoe 30 is provided with a longitudinal bore 32 for lubricating the receiving part 28. The sliding shoe 30 is supported on an adjustment mechanism such that it can slide, with an inclined plate 36 disposed therebetween. A fluid, in particular a hydraulic fluid, can be drawn into the cylinder 14 in a first stroke via a fluid inlet 38. The fluid can be subsequently discharged from the cylinder 14 in a second stroke via a fluid outlet 40. Thus, during a half rotation of the shaft 12, a cylinder 14 is filled, and during the other half of the rotation of the shaft 12, it is again emptied. A high and uniform pump performance can be obtained in this manner.

(9) Each piston 22 according to the invention is shown in detail in FIGS. 2 to 5. The piston 22 has a link head 24, which transitions via a neck 42 into a piston body 44. The link head 24 has the spherical surface 26. A through hole 46 extends through the piston 22, which is beveled at one end 48. A total of five axial bore holes 52 having the same diameter D are provided parallel to the through hole 46, and thus, to the longitudinal axis L of the piston 22. These extend from the piston base 54 toward the link head 24 and terminate at an axial spacing A to the link head 24. An annular recess 56 for a lid 58 is provided on the piston base 54. The bore holes 52 of the piston 22 form hollow chambers 60, which are disposed on a partial circle, circumferentially offset to one another. Thus, the hollow chambers 60 are provided in a piston housing 62. As a result of the annular recess 56, a protruding wall section 64 of the through bores 46 remains intact. This wall section 64 forms a coupling part 66 for the lid 58 that is to be coupled thereto, and centers this lid when it is inserted.

(10) As is shown more clearly in FIGS. 6 to 8, the lid 58 is a disk-shaped rotating part having a central bore hole 68 corresponding to the outer diameter of the protruding wall section 64. A spiral groove 72 is provided, as a part of an equalizing mechanism 74, on the outer circumferential surface 70 of the lid 58. Groove 72 connects the hollow chambers 60 to the environment U in a media conducting manner. When the lid 58 has been placed in the piston housing 62, the spiral groove 72 is covered by the piston housing 62, except for at a discharge point 76. The discharge point 76, as a part of the equalizing mechanism, establishes the media conducting connection between the environment U and the hollow chambers 60 in the piston 22 via the spiral groove 72. The discharge point 76 is disposed on a back surface 80 of the lid 58. The spiral groove 72 opens into an intake point 84 in a bevel 86 at the opposite, front surface 82. The outer diameter of the bevel 86 decreases toward the link head 24, up to a final diameter AD, when the lid 58 is in the inserted state EZ.

(11) As FIG. 4 shows in greater detail, after the lid 58 has been inserted into the piston housing 62, the lid 58 is welded, using an electron beam welding process, along the entire circumference of its internal diameter DI and its external diameter DA. As a result, the discharge point 76 is also closed. The electron beam 88 is oriented parallel to the longitudinal axis L of the piston 22 thereby, to enable the most efficient possible welding. For this welding, the lid 58 should be inserted and oriented in the piston housing 62 without gaps to prevent the formation of fissures during the welding. The electron beam welding is carried out in a vacuum, in accordance with DIN 4063. This welding involves an I-axial seam, in which the electron beam 88 is parallel to the longitudinal axis L. As a result of the welding, the hollow chambers 60 are entirely closed off to the environment U to the outside. After the welding, the piston 22 is finished and heat treated.

(12) The finished piston 22 is depicted in FIG. 5 in a perspective sectional view. It is distinguished by a reduced mass, due to the hollow chambers 60. The lid 58 prevents an increase in the dead volume in the cylinder 14. In this manner, no additional compression losses can occur through the hollow chambers 60. As a result, the efficiency of the hydraulic pump 10 is advantageously improved.

(13) While one embodiment has been chosen to illustrate the invention, it will be understood by those skilled in the art that various changes and modifications can be made therein without departing from the scope of the invention as defined in the claims.