DIGITAL PUMP AXIS CONTROL SYSTEM

Abstract

A digital pump axis control system having a circuit including an electric engine, powering first and second hydraulic machines connected in a rotationally locked manner to each other. At least one cylinder has a first chamber connected through a first pipeline to the first hydraulic machine and a second chamber of the cylinder is connected through a second pipeline to the second hydraulic machine. A first valve is arranged in the first pipeline; a second valve is arranged in the second pipeline; a third valve is arranged in a third pipeline, wherein the third pipeline connects a portion of the first pipeline between the first hydraulic machine and the first valve and a portion of the second pipeline between the second hydraulic machine and the second valve. An open tank provides hydraulic fluid to inlets of the first and second hydraulic machines. The first and second hydraulic machines are digital variable displacement pumps, each providing a positive and a negative displacement of hydraulic fluid.

Claims

1. Digital pump axis control system with an at least partially open circuit comprising: an electric engine connected to power a first hydraulic machine and a second hydraulic machine, wherein the first and second hydraulic machines are connected in a rotationally locked manner to each other; at least one cylinder having a first chamber and a second chamber, wherein the first chamber of the cylinder is connected through a first pipeline to the first hydraulic machine and the second chamber of the cylinder is connected through a second pipeline to the second hydraulic machine; a first valve arranged in the first pipeline; a second valve arranged in the second pipeline; a third valve arranged in a third pipeline, wherein the third pipeline connects a portion of the first pipeline between the first hydraulic machine and the first valve and connects a portion of the second pipeline between the second hydraulic machine and the second valve; and an open tank providing hydraulic fluid to inlets of the first and second hydraulic machines, wherein the first and second hydraulic machines are digital variable displacement pumps, each providing a positive and a negative displacement of hydraulic fluid, and wherein the third valve, when open, enables both of the hydraulic machines to work together on the same chamber of the cylinder.

2. The control system according to claim 1, wherein the digital variable displacement pumps provide coordinated displacement of hydraulic fluid when the third valve is open.

3. The control system according to claim 1, wherein the digital variable displacement pumps provide different volume of hydraulic fluid and/or hydraulic fluid with different pressure, into the first pipeline and the second pipeline, respectively.

4. The control system according to claim 1, wherein the digital variable displacement pumps are axial piston pumps, bent axis pumps, variable displacement vane pumps, or radial piston pumps.

5. The control system according to claim 1, wherein the cylinder is a differential cylinder having a rod chamber and a piston chamber.

6. The control system according to claim 1, wherein the cylinder is operable in rapid speed and/or in force speed.

7. The control system according to claim 1, wherein the first and the second valves are controlled 2/2-way valves having a closed state and an open state.

8. The control system according to claim 1, wherein the first and the second valves further comprise a position monitoring device.

9. The control system according to claim 1, wherein the third valve is a controlled 2/2-way valve having a closed state and an open state.

10. The control system according to claim 1, wherein a second tank is hydraulically connected with the second chamber of the cylinder through a fourth valve having an open state and a closed state.

11. The control system according to claim 10, wherein a controlled pilot valve to pilot open the fourth valve is connected through a further pipeline to the fourth valve.

12. The control system according to claim 11, wherein a pressure generator is connected to the controlled pilot valve in order to control the pilot valve through pressurized hydraulic fluid coming from a pressure source.

13. The control system according to claim 11, wherein the pilot valve is a controlled 2/3-way valves having a pressurizing state and a depressurizing state.

14-21. (canceled)

22. A method for controlling operation of an electro-hydrostatic system, comprising: selecting an electro-hydrostatic system including an electric engine; powering a first hydraulic machine and a second hydraulic machine with the electric engine, the first and second hydraulic machines being digital variable displacement pumps, each pump providing a positive and a negative displacement of hydraulic fluid, and the pumps being connected in a rotationally locked manner to each other; wherein the system is selected to include at least a first cylinder having a first chamber and a second chamber, the first chamber being connected through a first pipeline to the first digital variable displacement pump and the second chamber being connected through a second pipeline to the second digital variable displacement pump; wherein the system is selected to further include a first valve arranged in the first pipeline, a second valve arranged in the second pipeline, and a third valve arranged in a third pipeline, wherein the third pipeline connects a portion of the first pipeline between the first digital variable displacement pump and the first valve and connects a portion of the second pipeline between the second digital variable displacement pump and the second valve; providing hydraulic fluid from an open tank to inlets of the first and second digital variable displacement pumps; and operating the third valve, when open, to enable both of the first and second digital variable displacement pumps to work together on the same chamber of the cylinder.

23. The method according to claim 22, wherein: the third valve is switched to close, and the first and second valves are switched to open; the first digital variable displacement pump is switched to provide a positive displacement of hydraulic fluid, and the second digital variable displacement pump is switched to provide a negative displacement of hydraulic fluid, such that an upwards movement of the cylinder is achieved.

24. The method according to claim 22, wherein: the third valve is switched to close; the first digital variable displacement pump is switched to provide a negative displacement of hydraulic fluid; and the second digital variable displacement pump is switched to provide a positive displacement of hydraulic fluid, such that a downwards movement of the cylinder is achieved.

25. The method according to claim 22, wherein: the first, second and third valves are switched open; and the first and second digital variable displacement pumps are switched to provide the same displacement of hydraulic fluid towards the second chamber of the first cylinder, such that a low force downwards movement of the first cylinder is achieved.

26. The method according to claim 22, wherein: a second tank is hydraulically connected with the second chamber of the cylinder through a fourth valve having an open state and a closed state; a controlled pilot valve to pilot open the fourth valve is connected through a further pipeline to the fourth valve; and a pressure generator is connected to the controlled pilot valve in order to control the pilot valve through pressurized hydraulic fluid coming from a pressure source.

27. The method according to claim 26, wherein: the second valve is switched to closed and the pilot valve is switched to the depressurizing state; the first and third valve are switched open; and the first and second digital variable displacement pumps are switched to provide the same displacement of hydraulic fluid from the first chamber of the cylinder to the open tank, such that the tank causes a displacement of hydraulic fluid into the second chamber to compensate the volume of hydraulic fluid in the system.

28. The method according to claim 26, wherein the third valve is switched to closed and the pilot valve is, switched to depressurized state such that the fourth valve is closed; the first and second valve are switched open; such that a decompression phase of the cylinder occurs and a displacement of hydraulic fluid from the second chamber to the open tank causes a torque movement of the second digital variable displacement pump through which the engine acts as an energy generator.

29. The method according to claim 26, wherein: the pilot valve is switched to pressurized state, whereby the fourth valve is opened; the first and third valves are switched open and the second valve is switched closed; and the first and second digital variable displacement pumps are switched to provide the same displacement of hydraulic fluid towards the first chamber of the cylinder, such that the cylinder has a rapid speed upwards movement and the hydraulic fluids in the second chamber of the cylinder is displaced into the tank through the open fourth valve.

Description

[0053] The accompanying drawings incorporated herein and forming part of the specification, illustrate several aspects of the present invention and together with the description serve to explain certain principles of the invention. In the drawings:

[0054] FIG. 1 shows a pump axis control system according to a first embodiment of the current invention;

[0055] FIG. 2a shows a switch arrangement of the valves for a downwards movement of the system of FIG. 1;

[0056] FIG. 2b shows a switch arrangement of the valves for an upwards movement of the system of FIG. 1;

[0057] FIG. 3 shows a pump axis control system according to a second embodiment of the current invention, in which a further tank is arranged;

[0058] FIG. 4a shows a switching arrangement of the valves for a downwards movement of the system of FIG. 3;

[0059] FIG. 4b shows a switching arrangement of the valves for a decompression phase of the system of FIG. 3;

[0060] FIG. 4c shows a switching arrangement of the valves for an upwards movement of the system of FIG. 3.

[0061] As can be taken from FIG. 1, this embodiment of the system 1 of the current invention has two digital variable displacement pumps, more precisely, a first digital variable displacement pump 12 and a second digital variable displacement pump 14. The first and second pumps 12, 14 are connected in a rotationally locked manner to each other as well as to an electric engine 10. The inlets of the two pumps 12 and 14 are hydraulically connected to an open tank 50 in which relaxed hydraulic fluid is available.

[0062] Further, a cylinder 20, which in this embodiment is a differential cylinder 20 having a first chamber 22a which is the rod chamber, and a second chamber 22b, which is the piston chamber, is arranged into the system 1.

[0063] The first chamber 22a is hydraulically connected to the first digital variable displacement pump 12 through a first pipeline 32 passing over a controlled 2-way valve 42, having a position monitoring device.

[0064] The second chamber 22b is hydraulically connected to the second digital variable displacement pump 14 through a second pipeline 34 passing over a controlled 2-way valve 44, having a position monitoring device.

[0065] Between the first valve 42 and the first pump 12 and between the second valve 44 and the second pump 14 a third pipeline 36 connects the first pipeline 32 with the second pipeline 34, passing over a third controlled 2-way valve 46.

[0066] In the figure all valves are switched to a closed position. This is a state which nearly never occurs, but has been used here in order to solely describe the arrangement of the various components. In the next figures the various switch position of the valves and the consequence of this switch arrangements are being described more in detail.

[0067] FIG. 2a shows the setting of the valves of system 1 of FIG. 1 required to achieve a downwards movement of the cylinder 20. Same referencing numbers are used for the same object as in FIG. 1.

[0068] As can be seen the third valve 46 is switched to close, such that the first digital variable displacement pump 12 only works on the first chamber 22a of the cylinder 20, while the second digital variable displacement pump 14 only works on the second chamber 22b of the differential cylinder 20.

[0069] In this embodiment, even though the two pumps are connected in a rotationally locked manner with each other, the displacement of hydraulic fluid caused by the pumps is different. The first pump 12 provides a negative displacement drawing hydraulic fluid from the first chamber 22a of the differential cylinder 20 and releasing it into the open tank 50.

[0070] The second digital variable displacement pump 14 instead draws hydraulic fluid from the open tank 50, and with a positive displacement pushes it into the second chamber 22b of the differential cylinder 20, providing hence a downwards movement of the piston, as can be taken from the dashed arrow in the figure.

[0071] FIG. 2b shows the setting of the valves of system 1 of FIG. 1 required to achieve an upwards movement of the cylinder 20. Same referencing numbers are used for the same object as in FIG. 1.

[0072] The embodiment is similar to the one of FIG. 2a and the valves have the same settings as before. The difference is that the first digital variable displacement pump 12 provides a positive displacement of hydraulic fluid from the open tank 50 into the first chamber 22a of the differential cylinder 20, while the second digital variable displacement pump 14 provides a negative displacement of hydraulic fluid from the second chamber 22b of the differential cylinder 20 into the open tank 50. As such, an upwards movement of the cylinder 20 is achieved.

[0073] FIG. 3 shows a second embodiment of the system 1 in which the first embodiment depicted in FIG. 1 has been implemented with a further tank 50b. Same referencing numbers are used for the same object as in FIG. 1.

[0074] More specifically a tank 50b is hydraulically connected to the second chamber 22b of the differential cylinder 20 trough a fourth valve 51, more precisely a pressure controlled non-return valve 51.

[0075] A further pipeline 53 connects the fourth valve 51 with a pressure generator through a pilot valve 52 having a pressurized and a depressurized setting. When the pilot valve is pressurized, pressurized fluid is pushed toward the fourth valve 51 opening it.

[0076] In the figure all valves are switched to a closed position. This is a state which nearly never occurs, but has been used here in order to solely describe the arrangement of the various components. In the next figures the various switch position of the valves and the consequence of this switch arrangements are being described more in detail.

[0077] FIG. 4a shows a valve switch arrangement in which the cylinder 20 can be moved downwards. As can be taken from the figure, the first and the third valve 42 and 46 are switched to open, while the second valve 44 is switched closed and the pilot valve 52 is depressurized.

[0078] Both the first and the second digital variable displacement pump 12 and 14 work in parallel and provide a negative displacement of hydraulic fluid. In this arrangement, the second digital variable displacement pump 14, which usually works on the second chamber 22b of the cylinder 20, works together with the first digital variable displacement pump 12 on the first chamber 22a of the differential cylinder 20.

[0079] Therefore, hydraulic fluid is drawn quickly and strongly from the first chamber 22a through the pipeline 32 and the pipeline 36 and through the two pumps 12, 14 into the open tank 50.

[0080] In order to have a pressure equilibrium, hydraulic fluid needs to enter chamber 22b contemporaneously. In fact, the pressure of chamber 22b diminishes with the consequence that the fourth valve 51 opens, and hydraulic fluid from the tank 50b flows into the second chamber 22b of the differential cylinder 20.

[0081] FIG. 4b shows the embodiment of system 1, according to FIG. 3 in a decompression phase.

[0082] This phase starts after the system was running in force speed and the tool was processed. Before decompression the pressure of the hydraulic fluid in the second chamber 22b of the cylinder 20 is very high. Before the cylinder 20 can be, pushed upwards again, a decompression of the hydraulic fluid needs to occur in the second chamber 22b of the cylinder 20.

[0083] The decompression is achieved by closing both the third and the fourth valves 46 and 51 while opening both the first and the second valves 42 and 44, without activating the second pump 14.

[0084] Due to the high pressure in the second chamber 22b of the cylinder 20, opening the second valve causes a displacement of hydraulic fluid from the second chamber 22b through the second pipeline 34 and through the pump 14 into the open tank 50. This causes a torque movement of the pump 14, which generates energy which can be used contemporaneously as an aid for running the first pump 12, which actively provides a positive displacement into the first chamber 22a. Alternatively the energy can also be saved and reused for further processes.

[0085] This embodiment is extremely advantageous as the energy generated by the torque movement of the inactive pump 14, is not lost, but reused for the movement of the first pump 12.

[0086] After the decompression a movement of the cylinder in the upwards direction as shown in FIG. 4c can be achieved.

[0087] In this embodiment the second valve 44 is closed. The first and third valve 42, 46 are open such that both the first 12 and the second 14 digital variable displacement pump can jointly and parallel work together on the first chamber 22a for the cylinder 20.

[0088] The two pumps draw hydraulic fluid from the open tank 50 and displace it into the first chamber 22a of the cylinder 20. The piston is pushed upwards and consequently the hydraulic fluid in the second chamber 22b of the cylinder needs to be released or it over pressurized and can cause a failure of the system as well as severe damages. To achieve this, the valve 52 is pressurized, such that the pressurized fluid runs through the pipeline 53 and causes the fourth valve 51 to open.

[0089] In this way, while the piston is being pushed up, the hydraulic fluid from the second chamber 22b of the cylinder 20 can escape into the tank 50b. In this way the tank 50b is refilled and the contained hydraulic fluid can be reused in a further phase.

TABLE-US-00001  1 digital pump axis control system 10 electric engine 12 first digital variable displacement pump 14 second digital variable displacement pump 20 cylinder 22a first chamber of the cylinder 22b second chamber of the cylinder 32 first pipeline 34 second pipeline 36 third pipeline 42 controlled first 2-way valve 44 second controlled 2-way valve 46 third controlled 2-way valve 50 open tank 50b tank 51 one-way pressure controlled valve 52 controlled 3-way valve 53 pipeline 60 pressure source