HYDRAULIC MACHINE

Abstract

A hydraulic machine is described comprising a first part (1, 4) and a second part (7, 8), wherein the first part (1, 4) and the second part (7. 8) are movable relatively to each other in abutting relation, the first part (1, 4) comprises a pressure chamber (2) having a pressure chamber opening (6) in a contact face (5) contacting a sealing face (9) of the second part (7, 8), the second part (7, 8) comprises a low pressure area (10) connected to a low pressure opening (11) in the sealing face (9) and a high pressure area (12) connected to a high pressure opening (13) in the sealing face (9), wherein during a movement of the first part (1, 4) with respect to the second part (7, 8) in a moving direction (14) the pressure chamber opening (6) comes alternatingly in overlap with the low pressure opening (11) and the high pressure opening (13). Such a machine should be flexible in operation with low risk of damages caused by cavitation. To this end a throttling channel (15) in the second part (7. 8) connects the low pressure area (10) with an area in the sealing face (9) in moving direction in front of the low pressure opening (11).

Claims

1. A hydraulic machine comprising a first part and a second part, wherein the first part and the second part are movable relatively to each other in abutting relation, the first part comprises a pressure chamber having a pressure chamber opening in a contact face contacting a sealing face of the second part, the second part comprises a low pressure area connected to a low pressure opening in the sealing face and a high pressure area connected to a high pressure opening in the sealing face, wherein during a movement of the first part with respect to the second part in a moving direction the pressure chamber opening comes alternatingly in overlap with the low pressure opening and the high pressure opening, wherein a throttling channel in the second part connects the low pressure area with an area in the sealing face in moving direction in front of the low pressure opening.

2. The hydraulic machine according to claim 1, wherein a local throttling resistance of the throttling channel increases in a direction away from the sealing surface.

3. The hydraulic machine according to claim 2, wherein a cross section flow area of the throttling channel decreases in a direction away from the sealing surface.

4. The hydraulic machine according to claim 2, wherein the throttling channel has a conical or stepped form.

5. The hydraulic machine according to claim 1, wherein the throttling channel has a main flow direction which at least at an opening in the low pressure area is inclined or perpendicular with respect to the sealing surface.

6. The hydraulic machine according to claim 5, wherein the opening into the low pressure area has distance to the sealing surface which is at least as large as the smallest diameter of the throttling channel.

7. The hydraulic machine according to claim 1, wherein a second throttling channel in the second part connects the high pressure area with an area in the sealing face in moving direction in front of the high pressure opening.

8. The hydraulic machine according to claim 7, wherein a local throttling resistance of the second throttling channel increases in a direction towards the sealing surface.

9. The hydraulic machine according to claim 7, wherein a cross section flow area of the second throttling channel decreases in a direction towards the sealing surface.

10. The hydraulic machine according to claim 8, wherein the second throttling channel has a conical form.

11. The hydraulic machine according to claim 7, wherein the second throttling channel has a main flow direction which is at least at an opening in the sealing face inclined or perpendicular with respect to the sealing surface.

12. The hydraulic machine according to claim 11, wherein the opening of the second throttling channel into the sealing surface has distance to the high pressure opening which is at least as large as the smallest diameter of the second throttling channel.

13. The hydraulic machine according to claim 1, wherein the second part comprises a first element in contact with the first part and a second element on a side of the first element opposite to the first part, wherein the throttling channel passes through both elements.

14. The hydraulic machine according to claim 13, wherein in the first element the throttling channel runs at least partly perpendicular to the contact face.

15. The hydraulic machine according to claim 1, wherein a muffle chamber is arranged within the throttling channel.

16. The hydraulic machine according to claim 1, wherein the throttling channel passes through a nozzle element.

17. The hydraulic machine according to claim 3, wherein the throttling channel has a conical or stepped form.

18. The hydraulic machine according to claim 2, wherein the throttling channel has a main flow direction which at least at an opening in the low pressure area is inclined or perpendicular with respect to the sealing surface.

19. The hydraulic machine according to claim 3, wherein the throttling channel has a main flow direction which at least at an opening in the low pressure area is inclined or perpendicular with respect to the sealing surface.

20. The hydraulic machine according to claim 4, wherein the throttling channel has a main flow direction which at least at an opening in the low pressure area is inclined or perpendicular with respect to the sealing surface.

Description

BRIEF DESCRIPTION OF THE DRAWING

[0030] An embodiment of the invention will now be described in more detail with reference to the drawing, in which:

[0031] FIG. 1 shows a schematic sketch of a cut-view through a part of an axial piston pump in transition from high-pressure to low-pressure,

[0032] FIG. 2 shows a sketch of a cut-view through parts of an axial piston pump for transition between low-pressure and high-pressure,

[0033] FIG. 3 shows a schematic sketch of a cut-view through a part of a second embodiment of an axial piston pump in transition from high-pressure to low-pressure and

[0034] FIG. 4 shows a schematic sketch of a cut-view through a part of a third embodiment of an axial piston pump in transition from high-pressure to low-pressure.

[0035] Same elements are denoted with the same reference numerals in all figures.

DETAILED DESCRIPTION

[0036] The figures show schematically parts of an axial piston pump, in particular a cylinder block 1 in which at least one cylinder 2 forms a pressure chamber having a variable volume. The variable volume is caused by a piston 3 which is moved in the cylinder 2 when the cylinder block 1 rotates. In an axial piston pump the movement of the cylinder is caused by a swash-plate which is not shown.

[0037] A valve plate 4 is secured to the cylinder block 1. The valve plate 4 comprises a contact face 5 on a side opposite to the cylinder block 1. For the purpose of the following illustration the cylinder block 1 and the valve plate 4 are considered as a first part since both elements 1, 4 are secured to each other and move together.

[0038] The cylinder 2 has a pressure chamber opening 6 which is arranged in the valve plate 4.

[0039] The valve plate 4 is in contact with a port plate 7 which is secured to a housing 8. Port plate 7 and housing 8 are for the purpose of the following illustration considered as a second part since these two elements 7, 8 are fixed to each other. The port plate comprises a sealing face 9 at the side facing the cylinder block 1. The sealing face 9 contacts the contact face 5.

[0040] The housing 8 comprises a low pressure area 10 which is connected to a low pressure opening 11 in the port plate 7 and accordingly in the sealing face 9.

[0041] As shown in FIG. 2, the housing 8 comprises a high-pressure area 12 which is connected to a high-pressure opening 13 in the port plate 7 and accordingly in the sealing face 9.

[0042] FIG. 1 shows a transition between high-pressure and low-pressure. The cylinder block 1 moves in a moving direction 14 which is symbolized by an arrow with respect to the second part formed by the port plate 7 and the housing 8. This movement is a rotational movement around an axis which is not shown. While the cylinder volume is in contact with a high pressure kidney (not shown), the piston 3 moves in a direction towards the second part formed by port plate 7 and the housing 8 to decrease the volume of the pressure chamber in the cylinder 2 to arrive at the bottom dead center. After reaching the bottom dead center the piston 3 will reverse its movement. Since the movement to increase the volume of the pressure chamber in the cylinder 2 takes place during a time in which the pressure chamber opening 6 is sealed by the port plate 7, the pressure in the cylinder 2 decreases but is still higher than the pressure in the low-pressure area 10.

[0043] In order to enable a pressure equalization before the pressure chamber opening 6 comes in overlapping relation with the low-pressure opening 11, a first throttling channel 15 is provided in the port plate 7, i.e. in the second part. The throttling channel 15 connects the low-pressure area 10 with an area in the sealing face 9 which is in moving direction 15 in front of low-pressure opening 11.

[0044] The first throttling channel 15 has a local throttling resistance which increases in a direction away from the sealing surface 9. The local throttling resistance is the resistance of small sections of first throttling channel 15 in lengthwise direction. A simple way to realize such increase of the local throttling resistance is to decrease a cross-section flow area of the first throttling channel 15 in a direction away from the sealing surface 9. The first throttling channel 15 can have a conical form to realize this increasing local throttling resistance.

[0045] The first throttling channel 15 is inclined with respect to the sealing surface 9. It can be at least partly be perpendicular to the sealing surface. An opening 16 of the first throttling channel 15 into the low pressure area 10 has a distance from the sealing surface 9 which is at least as large as the smallest diameter of the throttling channel to achieve a sufficient distance between the opening 16 and the sealing surface 9, for example five times the smallest diameter.

[0046] As soon as the pressure chamber opening 6 connects to the first throttling channel 15 a jet 17 of hydraulic fluid forms which is directed into the low-pressure area 10. Since the first throttling channel 15 is inclined with respect to the sealing surface 9 the jet 17 is directed away from the sealing surface 9 and from the contact surface 5. Due to the increasing throttling resistance the velocity of the fluid during travel through the first throttling channel 15 increases and accordingly the pressure of the fluid in the jet 17 decreases so that the risk of implosion of bubbles is minimized. Even if cavitation bubbles form near the jet, they will collapse far away from any surface. When cavitation bubbles collapse far from surfaces they cannot cause cavitation erosion damage.

[0047] The first throttling channel 15 has the advantage that the flow rate through the first throttling channel 15 depends on the pressure difference between the pressure chamber in the cylinder 2 and the low-pressure area 10. If this pressure difference is high then the flow rate will be high and vice versa. That means that the approach of the pressure in the cylinder 2 to the pressure in the low-pressure area 10 by means of the first throttling channel 15 becomes somewhat self-regulating.

[0048] A similar solution is realized on the other side of the machine, i.e. at the transition between low-pressure and high-pressure. This is shown in FIG. 2. A second throttling channel 18 connects the high pressure area 12 and the sealing face 9 in an area in front of the high-pressure opening 13 in moving direction 14.

[0049] The second throttling channel 18 has a local throttling resistance which increases in a direction towards the sealing surface 9. This can be realized by decreasing the cross-section flow area which can in a simple way be realized by forming the second throttling channel 18 in a conical form.

[0050] The second throttling channel 18 as well is inclined or at least partly perpendicular with respect to the sealing surface 9. An opening 19 of the second throttling channel 18 into the sealing surface 9 has a distance to the high-pressure opening 13 which is at least as large as the smallest diameter of the second throttling channel 18, for example five times the smallest diameter.

[0051] When the pressure chamber opening 6 connects to the opening 19 of the second throttling channel 18, a jet 20 of hydraulic fluid forms which is directed into the pressure chamber opening 6 and into the cylinder 2.

[0052] Due to the decreasing cross-section flow area of the second throttling channel 18 the fluid continuously accelerates along the length of the second throttling channel 18. Therefore, the pressure keeps decreasing along the length of the second throttling channel 18, so that any cavitation bubbles that may form inside the second throttling channel 18 cannot collapse until they are clear of the opening 19 or muzzle of the second throttling channel 18.

[0053] The cross-section of the throttling channel 15, 18 can be quite small compared to the diameter of the piston 3 they will have a maximum cross-section of 4% or less of the diameter of the piston 3.

[0054] The invention has been described using an axial piston machine as example.

[0055] The invention can also be applied to other hydraulic machines such as an isobaric pressure exchanger.

[0056] When the invention is used in a pressure exchanger which has no piston, there is no variable volume of the pressure chamber. However, the transition between low pressure and high pressure and vice versa causes similar problems.

[0057] FIG. 3 shows a second embodiment of the axial piston pump in transition from high-pressure to low-pressure.

[0058] As mentioned above, the second part comprises the port plate 7 as first element and the housing 8 as second element.

[0059] In this embodiment the throttling channel 15 comprises a first channel part 18 in the port plate 7 and a second channel part 19 in the housing 8. The first channel part 18 runs perpendicular to the contact face 5. This simplifies the production of the port plate 7. The first channel part 18 has a flow resistance less than the second channel part 19. The relation of the flow resistances ensures that the pressure in the connection channel 15, in particular in the first channel part 18, does not get so low that cavitation bubbles can form in the throttling channel. This embodiment reduces the cost and complexity of the port plate 7, because it does not need to contain an accurately manufactured throttling channel with a defined flow resistance. This is an advantage because the port plate 7 is a wear part that will need to be replaced at regular intervals whereas the housing or port flange does not need to be replaced regularly.

[0060] FIG. 4 shows a third embodiment of an axial piston pump in transition from high-pressure to low-pressure.

[0061] In this embodiment the throttling channel comprises the first section 18, a muffler chamber 20 and a nozzle 21 which is provided in a separate nozzle element 22. It should be noted that such a nozzle element 22 can be provided in the embodiments according to FIGS. 1 to 3 as well.

[0062] The muffler chamber 20 has the effect that a fast pressure equalization occurs between the volume of the cylinder 2 and the muffler chamber 20, when the connection between the cylinder volume and the muffler chamber 20 forms, so that the combined volume quickly reaches an intermediate pressure between the high-pressure and the low-pressure. A slower equalization between the intermediate pressure in the muffler chamber 20 and the pressure in the low-pressure area 10 then follows through the nozzle 21.

[0063] The advantages of having the muffler chamber 20 are reduced formation of cavitation bubbles, reduced pulsations on the low pressure side, and reduced noise for the pump.

[0064] When the additional nozzle element 22 is used, the nozzle function can be realized in a way which is easier to manufacture.

[0065] Having the nozzle 21 in a separate nozzle element 22 also enables tuning of the pumps to specific operation conditions by changing only the nozzle element 22. This possibility can also be used to reduce the number of variants of port plates 7 needed to cover a wide range of applications, because the differences in functionality of the port plate variants can, to some extent, be replaced by combining a single port plate 7 with different nozzle elements 22.

[0066] It should be noted that in the embodiments shown in FIGS. 3 and 4 the jet 17 is located so far from the valve plate 4 that it would be acceptable to direct it parallel to the valve plate 4 without risking that the cavitation bubbles ejected from the throttling channel 15 will damage the valve plate 4.

[0067] While the present disclosure 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 disclosure may be made without departing from the spirit and scope of the present disclosure.