Electrohydrostatic Actuator System with an Expansion Reservoir

Abstract

An electrohydrostatic actuator system comprising: a volume- and/or speed-variable hydraulic machine which is driven by an electric motor, for providing a volumetric flow of a hydraulic fluid; a differential cylinder with a piston side and a ring side; and at least one pretensioning source. The actuator system has a closed hydraulic circuit, wherein, during operation, the hydraulic fluid in the hydraulic circuit is pressurized by means of the hydraulic machine and/or the pretensioning source. Furthermore, according to the invention, the differential cylinder provides a power motion operating mode and a rapid motion operating mode. In order to balance a volume of the hydraulic fluid in the closed hydraulic circuit, according to the invention an expansion reservoir is connected to the piston side of the differential cylinder via a valve.

Claims

1. Electrohydrostatic actuator system comprising: a variable-volume and/or variable-speed hydraulic machine which is driven by an electric motor, for the provision of a volumetric flow of a hydraulic fluid; a differential cylinder having a piston side and a ring side; at least one pretensioning source; wherein the actuator system has a closed hydraulic circuit, and the hydraulic fluid in the hydraulic circuit is pressurized by means of the hydraulic machine and/or the pretensioning source during operation; wherein the actuator system has operating modes of a power motion and a rapid motion which are provided by the differential cylinder; and an expansion reservoir connected to the piston side of the differential cylinder via a valve for balancing a volume of the hydraulic fluid in the closed hydraulic circuit.

2. Electrohydrostatic actuator system according to claim 1, wherein the hydraulic fluid is pretensioned in the expansion reservoir at a pressure of less than 5 bar.

3. Electrohydrostatic actuator system according to claim 1, wherein the hydraulic fluid in the expansion reservoir has an ambient pressure and/or is arranged above the piston side of the differential cylinder.

4. Electrohydrostatic actuator system according to claim 1, wherein the expansion reservoir has a volume equal to or more than a volume difference of the closed system in a power end position and upper end position of the differential cylinder.

5. Electrohydrostatic actuator system according to claim 1, wherein the valve is a controlled check valve.

6. Electrohydrostatic actuator system according to claim 5, wherein the controlled check valve can be unlocked by means of one, 2-way valve.

7. Electrohydrostatic actuator system according to claim 1, wherein the valve is a controlled, 2-way valve with a flow position or an electrically-controlled, 3-way valve with a flow position, a locking position, and a check function.

8. Electrohydrostatic actuator system according to claim 1, wherein the hydraulic fluid of the pretensioning source has a pressure between 5 bar and 50 bar.

9. Electrohydrostatic actuator system according to claim 1, wherein the pretensioning source is hydraulically connected via a second valve to a line between a connection of the hydraulic machine and the ring side of the differential cylinder.

10. Electrohydrostatic actuator system according to claim 9, wherein the second valve is a check valve.

11. Electrohydrostatic actuator system according to claim 1, wherein the hydraulic machine comprises a first pump and the pretensioning source comprises an accumulator and/or a second pump.

12. Electrohydrostatic actuator system according to claim 11, wherein the pretensioning source comprises the second pump and the second pump has a pump inlet connected via a first line to the expansion reservoir and a pump outlet connected via a second line to a second valve.

13. Electrohydrostatic actuator system according to claim 1, wherein at least one valve with a flow position and a locking position is arranged in a line between the ring side of the differential cylinder and a connection of the hydraulic machine;

14. Electrohydrostatic actuator system according to claim 1, wherein the hydraulic machine comprises a pump having a first pump connection to the ring side of the differential cylinder and a second pump connection to the piston side of the differential cylinder and the hydraulic machine can be pressurized on both the pump connections.

15. Electrohydrostatic actuator system according to claim 1, wherein a valve connects the piston side of the differential cylinder to the pretensioning source or to the expansion reservoir.

16. Electrohydrostatic actuator system according to claim 1, wherein the pretensioning source has a pump, the closed system has a device for cleaning the hydraulic fluid, and the device is arranged between the expansion reservoir and a pump inlet of the pump or between a pump outlet of the pump and a second valve.

17. Electrohydrostatic actuator system according to claim 1, wherein the expansion reservoir has a device for venting the hydraulic fluid and/or a device for cooling the hydraulic fluid.

18. Electrohydrostatic actuator system according to claim 1, wherein the system has several differential cylinders.

19. Method for operating a hydrostatic actuator system according to claim 1 comprising the step of, when the actuator system is extended in rapid motion, the expansion reservoir conveying hydraulic fluid into the piston side of the differential cylinder in order to balance a volume of the hydraulic fluid in the closed system.

20. The hydrostatic actuator system according to claim 1, wherein the system is in a hydraulic press, a deep-drawing device, or an injection-molding device.

Description

[0059] Shown are:

[0060] FIG. 1a: a schematic representation of a system according to the invention;

[0061] FIG. 2a: a schematic representation of the configuration of the system according to the invention from FIG. 1 when extended in rapid motion;

[0062] FIG. 2b: a schematic representation of the configuration of the system according to the invention from FIG. 1 when extended in power motion;

[0063] FIG. 2c: a schematic representation of the configuration of the system according to the invention from FIG. 1 in decompression;

[0064] FIG. 2d: a schematic representation of the configuration of a further system according to the invention in an alternative type of decompression;

[0065] FIG. 2e: a schematic representation of the configuration of the system according to the invention from FIG. 1 when entering the rapid motion;

[0066] FIG. 3: a schematic representation of another embodiment of the system according to the invention;

[0067] FIG. 4: a schematic illustration of another embodiment of the system according to the invention, with a cleaning device;

[0068] FIG. 5: a schematic representation of another embodiment of the system according to the invention.

[0069] FIG. 1 shows an exemplary embodiment of an actuator system 1 according to the invention. The system comprises a differential cylinder 20 which has a piston side 22a and a ring side 22b.

[0070] The piston side 22a is hydraulically connected to the ring side 22b of the differential cylinder 20 by means of a line 71 and a line 72. A volume- and/or speed-variable hydraulic machine 11 driven by an electric motor 10 is arranged between the lines 71 and 72, wherein the hydraulic machine is a pump 11 in this exemplary embodiment according to the invention.

[0071] The line 71 thus connects the piston space 22a of the differential cylinder 20 to one connection of the pump 11, and the line 72 connects the ring side 22b of the differential cylinder to the other connection of the pump 11. Furthermore, a 2-way valve 80 which has a flow position and a locking position is connected in the line 72. This valve 80 serves as a safety valve and prevents, inter alia, the piston from falling off in the event of a defect in the actuator system 1 or in the operating sequence. Except in such emergency situations, the valve 80 is switched to flow.

[0072] The pump 11 can rotate in both directions of rotation according to the illustrated arrow and thus provide either a volumetric flow of hydraulic fluid in the direction of the piston side 22a or in the direction of the ring side 22b of the differential cylinder 20.

[0073] Further, a pretensioning source 60, which may include a pressure accumulator 30 and a source 65, is connected to the line 72 via a check valve 70. The hydraulic fluid in the pressure accumulator 30 is at a pressure which is preferably higher than the ambient pressure. In the event of a pressure loss in the system 1, the necessary pressure from the pressure accumulator 30 or from the pretensioning source 60 is fed into the actuator system 1 via the check valve 70.

[0074] The source 65 provides the actual pressure in the accumulator 30, while the pressure accumulator generally functions as a reservoir for volume balancing.

[0075] The arrangement of the expansion reservoir 50 is significant in this exemplary embodiment according to the invention. This is hydraulically connected above the differential cylinder 20 via the line 42 to the piston side 22a of the differential cylinder 20. Connected to the line 42 is a controlled directional valve 48 which has a flow position and a position with a check valve 40. The valve is electrically controllable.

[0076] The position of the valves in the description of FIG. 1 is to be understood only as an example, since this figure serves to describe the individual devices and their connection, and not to determine operating modes or the position of the valves in different operating situations; this takes place in the following FIG. 2.

[0077] FIG. 2a shows the exemplary embodiment of the system according to the invention from FIG. 1 in the rapid motion “downwards” operating state. Most of the elements used and the reference symbols are here the same as in FIG. 1.

[0078] This operating state is brought about when the piston of the differential cylinder is to be quickly moved downwards in the direction of the tool. The pump 11 operates to provide a flow of hydraulic fluid from the ring side 22a of the differential cylinder 20 towards the piston side 22a of the differential cylinder.

[0079] The safety valve 80 is set to flow, as in each operating state. The volume of the ring side 22a of the differential cylinder 20 is smaller than the volume of the piston side 22a of the differential cylinder 20.

[0080] As a result of the flow of the hydraulic fluid from the ring side 22b into the piston side 22a of the differential cylinder 20, further hydraulic fluid is therefore necessary in order to fill the piston side 22a and to achieve pressure balancing. The difference in volume is balanced by the expansion reservoir 50. For this purpose, the directional valve 48 is set such that the check valve 40 between the expansion reservoir 50 and the piston side 22a is opened, and hydraulic fluid flows from the expansion reservoir into the piston side.

[0081] Due to the increased volume in the piston side 22a, the pressure decreases to such an extent that the pressure of the hydraulic fluid in the expansion reservoir 50 is higher, and the check valve 40 opens. Thus, hydraulic fluid flows from the expansion reservoir 50 into the piston chamber 22a of the differential cylinder, thereby balancing the volume difference.

[0082] The differential cylinder 20 is moved according to the direction of the dashed arrow.

[0083] FIG. 2b shows the exemplary embodiment of the system according to the invention from FIG. 1 in the power motion “downwards” operating state. Most of the elements used and the reference symbols are here the same as in FIG. 1.

[0084] For the power motion downwards operating mode, less speed, but increased pressure or force, is usually required to actually machine the workpiece. In the power motion (also referred to as the pressing motion), the tool is pressed against the workpiece to be deformed, as a result of which an increased force is required, and thus an increased pressure of the hydraulic fluid has to be provided.

[0085] As can be seen from the exemplary embodiment according to the invention from FIG. 2b, the required increased pressure in the hydraulic fluid is to provided by the hydraulic machine. Here, as in FIG. 2a, the pump 11 operates by providing a hydraulic fluid flow from the ring side 22b of the differential cylinder 20 into the piston side 22a of the differential cylinder 20. The missing volumetric flow is supplemented by the pressure accumulators 30 or pretensioning source 60.

[0086] Since the pressure of the hydraulic fluid in the actuator system 1 is high—in this example, up to 400 bar—the check valve 48 remains closed, and there is no flow from or into the expansion reservoir 50.

[0087] In this operating mode, the piston of the differential cylinder 20 moves downwards according to the dashed arrow.

[0088] When the pressing operation is complete, a very high positive pressure prevails in the system 1, which is required for pressing, but which is superfluous after pressing. Accordingly, in order to reduce the pressure, decompression has to take place, in which the system 1 is relieved, but without causing a movement of the piston.

[0089] Decompression can occur according to, among others, two different exemplary embodiments.

[0090] FIG. 2c shows an exemplary embodiment of the system according to the invention during decompression. The directional valve 48 is switched from the position of the check valve to the flow position; thus, a volumetric flow into the expansion reservoir 50 according to the illustrated arrows is made possible.

[0091] The pressure of the hydraulic fluid in the ring side 22b and the piston chamber 22a relaxes, thereby filling the expansion reservoir.

[0092] An alternative type of decompression is illustrated in FIG. 2d. The system from FIG. 2b, instead of a single check valve 70, has a controlled, 2-way valve 75 disposed between the pressure accumulator 30 and the line 72.

[0093] In the previously described operating states, the 2-way valve 75 is switched as a check valve; in the case of decompression, it is switched to flow—as can be seen in FIG. 2d. Since the pressure of the hydraulic fluid in the cylinder spaces and the lines 71 and 72 is higher than in the pressure accumulator 30, two events occur when the valve 75 is switched to flow.

[0094] Firstly, the pressure in the entire system 1 relaxes, so that decompression takes place; secondly, a volumetric flow from the line 71 through the pump 11 into the pressure accumulator 30 takes place, as a result of which the volume of the pressure accumulator 30 is replenished, and the pressure of the hydraulic fluid in the pressure accumulator 30 is increased again.

[0095] This embodiment is advantageous, since energy is recovered in the pressure accumulator. Furthermore, by means of the volumetric flow from the piston chamber 22a through the pump 11 into the pressure accumulator 30, a movement of the pump 11 is brought about. The drive machine 10 thus operates as an energy generator and, furthermore, improves the energy recovery or reduces the energy loss.

[0096] The recovered energy can, according to the needs of the system 1, be reused, e.g., for the hydraulic machine.

[0097] When the pressing operation and the decompression are finished, the piston of the differential cylinder must be moved upwards again. The position of the valves and the volumetric flow of hydraulic fluid are shown in more detail in FIG. 2e. Most of the elements used and the reference symbols are here the same as in the previous figures.

[0098] As can be seen in FIG. 2e, the pump 11 operates in the reverse direction as in the rapid motion downwards, so that a volumetric flow is provided from the piston side 22a of the differential cylinder into the ring side 22b of the differential cylinder 20.

[0099] Since the volume of the piston side of the differential cylinder is greater than the volume of the ring side, a possibility must be provided for removing the superfluous hydraulic fluid from the circuit. For this purpose, the directional valve 48 is switched to flow, whereby the volume difference of the hydraulic fluid flows in the direction of the arrow from the piston side 22a of the differential cylinder 20 into the expansion reservoir 50. The piston of the differential cylinder is pushed upwards by the increased pressure in the ring side 22b and the low pressure in the piston side 22a.

[0100] FIG. 3 shows another exemplary embodiment of the system 1 according to the invention. Most of the elements used and the reference symbols are here the same as in FIG. 1.

[0101] The arrangement and control of the check valve 40 between the expansion reservoir 50 and the piston side 22a of the differential cylinder 20 is different, in contrast to FIG. 1.

[0102] As can be seen from FIG. 3, the check valve 40 is controlled by means of a control circuit comprising a 2-way valve 45. A line 44 connects the piston side 22a of the differential cylinder 20 to the check valve 40 via the 2-way valve.

[0103] The directional valve 45 has a flow position and a position in which the excess pressure is decompressed from the upper part of the line 44 and escapes into a reservoir. The check valve 40 is thus opened as a function of the pressure in the piston side 22a. Thus, when the pressure in the piston side 22a of the differential cylinder 20 is high enough and the valve 45 is switched to flow, the check valve 40 opens by the pressure of the piston side 22a. Since the valve 40 is open, the remaining hydraulic fluid can flow back into the expansion reservoir.

[0104] FIG. 4 shows another exemplary, non-limiting embodiment of the system from FIG. 3. As in FIG. 3, the check valve 40 is controlled by means of the control circuit or the 2-way valve 45.

[0105] In the pretensioning source 60, the pressure accumulator 30 of the previous figures has been replaced with a pump 65 in this exemplary embodiment according to the invention. The pump 65 operates in only one direction and accordingly has a pump inlet and a pump outlet. The pump inlet is connected to the expansion reservoir 50 by means of a line 62, while the pump outlet is connected to the line 72 via a line 63 above the check valve 70.

[0106] On the side of the line 63, the pump 65 operates like the pressure accumulator 30 from the previous figures, in which it generates an overpressure which is used for pretensioning the system.

[0107] In this exemplary embodiment, the hydraulic fluid used by the pump 65 is withdrawn from the expansion reservoir via the line 62.

[0108] As shown in FIG. 4, in this exemplary embodiment of the system 1 according to the invention, a cleaning device 90 for cleaning the hydraulic fluid is arranged between the expansion reservoir 50 and the pump 65. Thus, the hydraulic fluid drawn in by the pump 60 and accordingly fed into the line 72 is cleaned beforehand, and preferably also vented.

[0109] This embodiment is advantageous in that a closed circuit is provided in which the expansion reservoir 50 is used as a static means, e.g., for cooling the hydraulic fluid, and the hydraulic fluid can be cleaned by the cleaning device 90 and fed back into the system, instead of providing a further circuit which conveys and cleans the fluid in the expansion reservoir, but cannot be reused immediately.

[0110] FIG. 5 shows a system 1 corresponding to the system described above, but with a different arrangement.

[0111] As can be seen from FIG. 5, the connection between the expansion reservoir 50 and the piston side 22a of the differential cylinder 20 is ensured by means of a check valve 40 controlled by a control valve 45.

[0112] Furthermore, a line 72 via a check valve 73 connects the expansion reservoir 50 to the nodal point 100, through which the hydraulic fluid can be conducted both into the ring side 22b of the differential cylinder 20 and through the pump 11 into the line 71. Furthermore, the expansion reservoir 50 is hydraulically connected to the pretensioning source 60 and, in particular, to the inlet of the pump 65 by means of the line 72 and the line 62.

[0113] The pump 11 is connected to both the line 71 and the line 72.

[0114] The pretensioning of the hydraulic fluid is effected by means of the pretensioning source 60, wherein the pump 65 provides the pretensioning of the hydraulic fluid, similar to the embodiment of FIG. 4. This is a pump which can operate only on one side.

[0115] In the present exemplary embodiment according to the invention, an associated, controlled, proportional valve—especially, a controlled, proportional, pressure-limiting valve 85—is disposed on line 71 between pretensioning source 60 or pump 65 and piston side 22a. The proportional valve 85 preferably serves to decompress system 1, as explained in previous embodiments.

[0116] Further, a pretensioning valve 68 is hydraulically connected to the line 71 and hydraulically connected via the line 75 and a check valve 69 to the line 63, as well as to a connection of the hydraulic machine 11. [0117] 1 Electrohydrostatic actuator system 62 Line [0118] 10 Electric motor 63 Line [0119] 11 Hydraulic machine 65 Pump [0120] 20 Differential cylinder 66 Check valve [0121] 22a Piston side 68 Pretensioning valve [0122] 22b Ring side 69 Check valve [0123] 30 Pressure accumulator 70 Check valve [0124] 40 Check valve 72 Line [0125] 41, 42 Line 75 Line [0126] 45 2-way control valve 80 Valve [0127] 48 Controlled 2-way valve 85 Proportional valve [0128] 50 Expansion reservoir 90 Cleaning device [0129] 60 Pretensioning source