EP3837446B1 - Electrohydrostatic actuator system with an expansion reservoir - Google Patents

Description

The present invention relates to an electrohydrostatic actuator system, and more particularly to an electrohydrostatic actuator system having a reservoir.

Electrohydrostatic actuator systems are known in the prior art and are mainly used for injection molding machines, presses and deep-drawing devices. Typically, prior art actuator systems have at least one cylinder with unequal area ratios. This inequality leads to a difference in volume in the flow of hydraulic fluid in the system, which is not advantageous either for the movement sequence or for the maintenance of the system.

The pressure accumulators commonly used in such systems maintain the pressure in the system, but their ability to compensate for a volume difference is at least partially limited by the usually small storage volume and usually lead to a pressure increase or pressure drop.

Furthermore, in conventional actuator systems, the hydraulic fluid is cooled and cleaned by leaks and flushing of the pump. The cooling is severely restricted due to the limited volume flow that is available at such locations, which is why both an increased expenditure of energy and an increased expenditure of time are necessary in order to provide an increase in the cooling capacity. Proceeding from this prior art, it is the object of the present invention to at least partially overcome or improve the disadvantages of the prior art.

The object is achieved with a device according to claim 1. Preferred embodiments and modifications are the subject matter of the dependent claims. A use according to the invention of the system according to the invention is specified in claim 13.

The electrohydrostatic actuator system according to the invention comprises: a hydraulic machine with variable volume and/or speed, driven by an electric motor, for providing a volume flow of a hydraulic fluid; a Differential cylinder with a piston side and a ring side, and at least one preload source.

The actuator system has a closed hydraulic circuit, with pressure being applied to the hydraulic fluid in the hydraulic circuit during operation by means of the hydraulic machine and/or the preload source. Furthermore, according to the invention, the differential cylinder provides the operating modes of a power gear and a rapid gear.

In order to equalize a volume of the hydraulic fluid in the closed hydraulic circuit, according to the invention a suction tank is connected to the piston side of the differential cylinder via a valve.

According to the invention, a second valve designed as a proportional valve is arranged at the connection between the preload source and the piston side of the differential cylinder or between the piston side of the differential cylinder and the replenishment tank.

The actuator system according to the invention is referred to as an electrohydrostatic actuator system because it has both an electric motor and a hydraulic machine for providing a volume flow of a hydraulic fluid, and the cylinder is coupled to the hydraulic machine via a hydrostatic transmission.

Electric motors are known in the prior art and are used to drive the hydraulic machine.

The hydraulic machine is variable in terms of volume and/or speed and can preferably provide two possible directions of flow of the hydraulic fluid in the closed hydraulic circuit during operation. The hydraulic machine can also have either a variable-speed electric motor and a constant pump, or a constant-speed electric motor and a variable-displacement pump, or a variable-speed electric motor and a variable-displacement pump. The selection of the hydraulic machine is determined by factors such as - e.g. - system costs, reliability or permitted noise emissions or efficiency.

The actuator system also has a differential cylinder, which includes a ring side and a piston side, as well as a ring surface and a piston surface. A differential cylinder is a hydraulic cylinder in which the cylinder surfaces on the front and rear of the piston differ. The side with the smaller cylinder surface is referred to as the rod side because a piston rod is arranged on this side. The cylindrical surface on the rod side is called the annular surface. The side with the larger cylinder surface of a differential cylinder is the so-called piston side. Either no piston rod is arranged on the piston side, or a piston rod with a smaller diameter than on the rod side. The cylinder surface on the piston side is called the piston surface.

According to the invention, the differential cylinder provides the operating modes of power gear and rapid gear.

The drive system provides movement of the cylinder, i.e. the differential cylinder, in a first direction, for example towards the workpiece to be machined. This is achieved by means of a volume flow from the hydraulic machine or into or out of the suction tank. The preload source ensures that the hydrostatic transmission is preloaded and provides the hydraulic machine with fluid for compressing the hydraulic fluid. A controller and additional components - e.g. valves - can coordinate the volume flow according to the required movement sequences.

The drive system also provides movement of the cylinder in a second direction, e.g., in the opposite direction to the first aforesaid direction. This is also achieved by means of a volume flow of the hydraulic machine and a volume flow into and out of the suction tank.

An electro-hydrostatic system according to the invention provides at least the operating modes of a power gear and a rapid gear. These modes of operation are provided by means of the differential cylinder. The differential cylinder can be implemented as one cylinder or as a plurality of cylinders working in parallel. These additional cylinders can possibly have a different sequence of movements than the differential cylinder (main cylinder); however, they are part of the electro-hydrostatic system according to the invention and part of the closed hydraulic circuit.

The large piston surface acts in the power gear, i.e. high power at comparatively low speed. The ring surface, which is smaller than the piston surface, acts in rapid traverse, i.e. low force at high speed.

Furthermore, the actuator system according to the invention has a preload source. This can additionally have a reservoir for buffering the preload pressure, this reservoir generally having a smaller volume than the replenishment tank. The hydraulic fluid provided from the preload source is pressurized at a pressure of between 5 bar and 50 bar, in particular between 10 bar and 40 bar, preferably between 15 bar and 35 bar, particularly preferably between 20 bar and 30 bar prestressed.

In the power gear mode in particular, an increased pressure of the hydraulic fluid is necessary; the hydraulic fluid being acted upon by means of the hydraulic machine. The preload source provides the necessary fluid for compression. According to a further embodiment of the invention, the hydraulic machine can be pressurized on both pump connections, ie on the connection in the direction of the piston side of the differential cylinder and on the connection in the direction of the ring side of the differential cylinder.

In the following description, the term "pressure in the pressure accumulator", "pressure in the piston side/ring side" or modifications thereof refers to the pressure of the hydraulic fluid in the respective devices. The same applies to the term "volume", so that, for example, "low volume in the pressure accumulator" means a low volume of hydraulic fluid in the pressure accumulator.

According to one embodiment of the present invention, the preload source is hydraulically connected via a valve to the hydraulic machine and the ring side of the differential cylinder.

In particular, according to a further embodiment of the invention, the valve can be a check valve which, at a threshold pressure, feeds preloaded hydraulic fluid from the preload source into the system.

By selecting a suitable check valve and, in particular, by selecting the spring of the check valve, it is possible to determine at what pressure difference between the inlet and outlet of the valve the valve opens. In a further preferred embodiment of the electro-hydrostatic system according to the invention, the preload source can in particular also include a pressure accumulator and/or an additional pump.

Since the cylinder in the actuator system according to the invention is a differential cylinder, the piston side and the ring side have different volumes or areas.

When the cylinder is pushed towards the tool, for example, the hydraulic fluid flows out of the ring side of the differential cylinder via the hydraulic machine into the piston side of the differential cylinder. Because the ring side has a smaller volume than the piston side, additional volume of hydraulic fluid is required to fill the piston side and provide pressure equalization. The biasing source generally has a small volume of hydraulic fluid; this is usually too small to compensate for the difference in volume between the piston side and the ring side, since the preload source is mainly used to prevent cavitations in the hydraulic machine and not for complete volume compensation.

According to the invention, a suction tank is integrated into the system. In particular, the suction reservoir is hydraulically connected directly to the piston side of the differential cylinder and preferably by means of a non-return valve. The non-return valve opens, for example, as soon as there is a vacuum on the piston side of the differential cylinder compared to the reservoir. In this way, a flow is provided from the suction reservoir into the piston side, which equalizes the difference in volume.

The suction reservoir is preloaded with a lower pressure, preferably and according to a further embodiment of the invention with a pressure of less than 5 bar, in particular less than 4 bar, preferably less than 3 bar, particularly preferably less than 2 bar, and particularly preferably less than 1 bar. This allows the check valve to open only when the pressure in the piston side is actually too low and the volume difference needs to be compensated.

In addition, the suction tank can be separated from false air or can be charged with a protective gas, which, among other things, reduces oxidation of the hydraulic fluid.

According to a further embodiment of the invention, the hydraulic fluid in the suction reservoir essentially has the ambient pressure and/or is arranged above the piston side of the differential cylinder. Alternatively and also according to the invention, the replenishment container can be arranged below the piston side of the differential cylinder, in which case a volume flow from the replenishment container into the piston side of the differential cylinder must be provided actively, such as by replenishment, and is not automatically guaranteed by gravity.

According to a further embodiment of the invention, the replenishment container has a volume that is equal to or greater than the difference in volume of the closed system in a force end position and an upper end position of the differential cylinder.

The suction tank is hydraulically connected to the piston side of the differential cylinder via a valve. According to the invention, the valve can be a controlled non-return valve, and in particular a pilot-operated non-return valve.

Furthermore, according to a further embodiment of the invention, the valve can be a pilot operated check valve which can be piloted by means of a control circuit and a directional control valve.

It is also within the meaning of an embodiment of the invention that the valve is a controlled 2-way valve with a flow position and check function or an electrically controlled 3-way valve with a flow position, a blocking position and check function.

The use of a controlled non-return valve between the reservoir and the piston side of the differential cylinder is particularly advantageous during rapid traverse to keep the valve actively open, or during decompression.

The system is decompressed between the power mode and the rapid mode. After machining the workpiece with increased pressure, it must first be relieved before the cylinder can be moved in rapid traverse; this is done by decompressing the hydraulic fluid in the system.

If the non-return valve between the reservoir and the piston side of the cylinder can be controlled, or if the non-return valve is embedded in a 2-way valve that has a flow position, it can be opened during decompression so that the pressure in the system is relieved and a volume flow from the Piston side of the differential cylinder can be done back in the suction tank.

The pressure level of the reservoir is independent of the preload of the pump. The suction tank compensates for the lack of oil volume in the system, which is required in the event of fluctuating temperatures in the system and/or compression of the smaller cylinder surface and generally during the process. Furthermore, the formation of cavitation is thus at least partially prevented.

In an embodiment of the system according to the invention, a further valve is arranged in the line between the ring side of the differential cylinder and a connection of the hydraulic machine, which has a flow position and a blocking position.

This is preferably to be understood as a safety valve. If there is a problem in the system and it is necessary to stop the cylinder without causing the cylinder to drop, this valve can be set to the off position. In all other situations, this valve is set to flow.

If the preload source is configured as a pump, according to another embodiment of the invention, its pump inlet is connected to the replenishment tank via a line, while the pump outlet is integrated into the circuit via another line with a valve or check valve.

In this embodiment, the suction tank is hydraulically connected to two lines. One line connects the replenishment tank to the piston side of the differential cylinder, while the other line hydraulically connects the replenishment tank to a section between the hydraulic machine and the ring side of the differential cylinder.

According to this embodiment of the invention, another pump is arranged in this additional line, which at the same time assumes the function of the preload source, i.e. the pump applies sufficient pressure to the hydraulic fluid to preload the hydraulic machine. In this embodiment, the hydraulic fluid is taken directly from the suction reservoir.

According to a further embodiment according to the invention, the closed system has a device for cleaning the hydraulic fluid. Furthermore, according to one embodiment of the system, the device is preferably arranged between the suction tank and a pump inlet of the pump or between a pump outlet of the pump and a check valve.

Additionally or alternatively, according to a further embodiment according to the invention, the after-suction tank can have a device for venting the hydraulic fluid and/or a device for cooling the hydraulic fluid
The additional pump is thus a volume flow of hydraulic fluid provided to the replenishment tank through the additional line and, according to a further embodiment of the invention, through a cleaning device.

The arrangement of additional units in the container, such as filtering devices, cooling devices and venting devices for filtering, cooling or venting the hydraulic fluid contained in the container is also advantageous.

In order to clean hydraulic fluid, the hydraulic fluid must be in motion. The flow can, for example, be provided by a further circuit in the after-suction tank. The advantage of the embodiment described above is that both cleaning and pressurization take place through a further line, which results in energy, material and cost savings.

The contaminated hydraulic fluid is fed into the suction tank, for example during decompression, from where it can be cleaned through this additional line and fed back into the circuit.

Furthermore, in contrast to systems in which cleaning or ventilation takes place through leaks and flushing oil, in this case a larger volume flow is treated.

The valve, which is arranged between the piston side and the replenishment container, can be opened according to further embodiments of the invention. During decompression, for example, hydraulic fluid thus flows from the piston side of the differential cylinder into the replenishment tank. This hydraulic fluid contains dirt and is usually very hot due to friction, which is why filtering and cooling this fluid is also beneficial for the maintenance of the entire system.

The system according to the invention is not limited to a single differential cylinder and, in further embodiments according to the invention, can also have several differential cylinders which work together or independently of one another, but are arranged in the same system.

The system according to the invention in any of its arbitrary embodiments can be embedded in a method according to the invention in which, when the actuator system is extended in rapid traverse, the suction reservoir pumps hydraulic fluid into the piston side of the differential cylinder to compensate for a volume of hydraulic fluid in the closed system.

The entire system according to the invention and the method according to the invention for operating the system are provided according to the invention for use in a hydraulic press, a deep-drawing device, an injection molding device or the like.

The invention is explained below using various exemplary embodiments, it being pointed out that these examples also include modifications or additions as are immediately apparent to a person skilled in the art.

• Fig. 1a:eine schematische Darstellung einer Ausführungsform eines Systems, die nicht durch die beanspruchte Erfindung abgedeckt ist;
• Fig. 2a :eine schematische Darstellung der Konfiguration der nicht durch die beanspruchte Erfindung abgedeckten Ausführungsform eines Systems aus Figur 1 beim Ausfahren im Eilgang;
• Fig. 2b : eine schematische Darstellung der Konfiguration der nicht durch die beanspruchte Erfindung abgedeckten Ausführungsform eines Systems aus Figur 1 beim Ausfahren im Kraftgang;
• Fig. 2c :eine schematische Darstellung der Konfiguration der nicht durch die beanspruchte Erfindung abgedeckten Ausführungsform eines Systems aus Figur 1 bei der Dekompression;
• Fig. 2d : eine schematische Darstellung der Konfiguration einer weiteren Ausführungsform eines Systems, die nicht durch die beanspruchte Erfindung abgedeckt ist, bei einer alternativen Art von Dekompression;
• Fig. 2e :eine schematische Darstellung der Konfiguration der nicht durch die beanspruchte Erfindung abgedeckten Ausführungsform eines Systems aus Figur 1 beim Einfahren im Eilgang;
• Fig. 3 : eine schematische Darstellung einer Ausführungsform eines Systems, die nicht durch die beanspruchte Erfindung abgedeckt ist;
• Fig. 4 : eine schematische Darstellung einer weiteren Ausführungsform eines Systems, die nicht durch die beanspruchte Erfindung abgedeckt ist, mit einer Reinigungsvorrichtung;
• Fig. 5 : eine schematische Darstellung einer erfindungsgemäßen Ausführungsform des Systems.

show:

• Fig. 1a: a schematic representation of an embodiment of a system not covered by the claimed invention;
• Figure 2a : a schematic representation of the configuration of the embodiment of a system not covered by the claimed invention figure 1 when moving out in rapid traverse;
• Figure 2b : a schematic representation of the configuration of the embodiment of a system not covered by the claimed invention figure 1 when extending in power gear;
• Figure 2c : a schematic representation of the configuration of the embodiment of a system not covered by the claimed invention figure 1 at decompression;
• Fig. 2d Fig . 1 is a schematic representation of the configuration of a further embodiment of a system, not covered by the claimed invention, in an alternative type of decompression;
• Figure 2e : a schematic representation of the configuration of the embodiment of a system not covered by the claimed invention figure 1 when entering in rapid traverse;
• 3 Fig. 1 : a schematic representation of an embodiment of a system not covered by the claimed invention;
• 4 : a schematic representation of another embodiment of a system not covered by the claimed invention, with a cleaning device;
• figure 5 : a schematic representation of an embodiment of the system according to the invention.

figure 1 Figure 1 shows an exemplary embodiment of an actuator system 1 not covered by the claimed invention. The system includes a differential cylinder 20, which has a piston side 22a and a ring side 22b.

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 . Between the lines 71 and 72 there is a hydraulic machine 11 which is driven by an electric motor 10 and is variable in volume and/or speed, with the hydraulic machine being a pump 11 in this exemplary embodiment.

The line 71 thus connects the piston chamber 22a of the differential cylinder 20 to a 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. A 2-way valve 80 is also connected in the line 72 which has a flow position and has a locked position. This valve 80 serves as a safety valve and prevents, among other things, the piston from falling out in the event of a defect in the actuator system 1 or in the course of operation. Except in such emergency situations, the valve 80 is switched to flow.

The pump 11 can rotate in both directions of rotation according to the arrow shown and thus provide either a volume 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 . A bias source 60 , which may include an accumulator 30 and a source 65 , is also connected to line 72 via a check valve 70 . The hydraulic fluid in the pressure accumulator 30 has a pressure which is preferably higher than the ambient pressure. In the event of a pressure loss in the system 1, the necessary pressure is fed from the pressure accumulator 30 or from the preload source 60 via the check valve 70 into the actuator system 1.

The source 65 provides the actual pressure in the accumulator 30, while the accumulator generally functions as an accumulator to compensate for volume.

What is essential in this exemplary embodiment is the arrangement of the replenishment container 50. This is hydraulically connected above the differential cylinder 20 through the line 42 to the piston side 22a of the differential cylinder 20. A controlled directional control valve 48 is connected to the line 42, which has a flow position and a position with a check valve 40. The valve is electrically controllable.

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

Figure 2a Figure 12 shows the exemplary embodiment of the system figure 1 , which is not covered by the claimed invention, in the "down" rapid traverse mode. Most of the elements used and the reference numbers are the same as in FIG 1 This operating condition is caused when the piston of the differential cylinder needs to be brought down quickly towards 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.

As in every operating state, the safety valve 80 is set to flow. The volume of ring side 22a of differential cylinder 20 is smaller than the volume of piston side 22a of differential cylinder 20.

Due to the flow of hydraulic fluid from the ring side 22b into the piston side 22a of the differential cylinder 20, further hydraulic fluid is therefore required in order to fill the piston side 22a and to achieve pressure equalization. The difference in volume is compensated for by the after-suction container 50 . For this purpose, the directional control valve 48 is set in such a way that the check valve 40 between the replenishment tank 50 and the piston side 22a is opened and hydraulic fluid flows from the replenishment tank into the piston side.

Due to the increased volume in the piston side 22a, the pressure is reduced to such an extent that the pressure of the hydraulic fluid in the replenishment tank 50 is higher and the check valve 40 opens. Hydraulic fluid thus flows from the replenishment tank 50 into the piston space 22a of the differential cylinder, thereby compensating for the difference in volume.

The differential cylinder 20 is moved in the direction of the broken arrow.

Figure 2b Figure 12 shows the exemplary embodiment of the system figure 1 , which is not covered by the claimed invention, in the power gear "down" operating state. Most of the elements used and the reference numbers are the same as in FIG 1 .

Lower speed is usually required for the power gear down mode, but more pressure or force is required to actually close the workpiece to edit. In the power cycle (also referred to as the press cycle), the tool is pressed against the workpiece to be deformed, which means that an increased force is required and therefore an increased pressure of the hydraulic fluid must be provided.

As is evident from the exemplary embodiment Figure 2b As can be seen, the required increased pressure in the hydraulic fluid is provided by the hydraulic machine. The pump 11 works as in the Figure 2a , in which it provides a flow of hydraulic fluid from the ring side 22b of the differential cylinder 20 into the piston side 22a of the differential cylinder 20 . The missing volume flow is supplemented from the pressure accumulator 30 or preload source 60.

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 suction tank 50.

In this mode of operation, the piston of the differential cylinder 20 moves downwards in accordance with the dashed arrow.

When the pressing process is finished, there is a very high overpressure in system 1, which was required for pressing but is superfluous after pressing. Accordingly, in order to reduce the pressure, a decompression must take place, in which the system 1 is relieved, but without causing a movement of the piston. The decompression can take place according to two different exemplary embodiments, among others.

Figure 2c Figure 12 shows an exemplary embodiment of the system, not covered by the claimed invention, during decompression. The directional control valve 48 is switched from the check valve position to the flow position; thus, a volume flow into the after-suction container 50, according to the arrows shown, is made possible.

The pressure of the hydraulic fluid in the ring side 22b and the piston chamber 22a relaxes, as a result of which the suction reservoir fills.

An alternative type of decompression is described in Figure 2d shown. The system off Figure 2b has, instead of a single check valve 70, a controlled 2-way valve 75, which is arranged between the pressure accumulator 30 and the line 72.

In the operating states described above, the 2-way valve 75 is switched as a check valve; on decompression it becomes - as in Figure 2d evident - switched to flow. Since the pressure of the hydraulic fluid in the cylinder chambers and the lines 71 and 72 is higher than in the accumulator 30, two events take place when the valve 75 switches to flow.

First, the pressure in the entire system 1 relaxes so that decompression occurs; secondly, there is a volume flow from the line 71 through the pump 11 into the pressure accumulator 30, as a result of which the volume of the pressure accumulator 30 is refilled and the pressure of the hydraulic fluid in the pressure accumulator 30 is increased again.

This embodiment is advantageous because energy is recovered into the accumulator. Furthermore, a movement of the pump 11 is caused by the volume flow from the piston chamber 22a through the pump 11 into the pressure accumulator 30 . Thus, the prime mover 10 operates as an energy generator and further improves energy recovery or reduces energy loss.

The energy recovered can be reused according to the needs of the system 1, for example for the hydraulic machine.

When the pressing process and the decompression are finished, the piston of the differential cylinder must be moved upwards again. The position of the valves and the volume flow of hydraulic fluid is explained in more detail in Figure 2e shown. Most of the elements used and the reference numbers are the same as in the previous figures.

Like in the Figure 2e As can be seen, the pump 11 works in the opposite direction than in the case of rapid traverse downwards, so that a volume flow is provided from the piston side 22a of the differential cylinder into the ring side 22b of the differential cylinder 20.

Since the volume of the piston side of the differential cylinder is greater than the volume of the ring side, a way must be provided to remove the excess hydraulic fluid from the circuit. For this purpose, the directional control valve 48 is switched to flow, as a result of which the difference in volume of the hydraulic fluid flows in the direction of the arrow from the piston side 22a of the differential cylinder 20 into the replenishment tank 50 . The piston of the differential cylinder is pushed up by the increased pressure in ring side 22b and the low pressure in piston side 22a.

In figure 3 a further example embodiment of the system 1 not covered by the claimed invention is presented. Most of the elements used and the reference numbers are the same as in FIG 1 .

The arrangement and control of the check valve 40 between the suction tank 50 and the piston side 22a of the differential cylinder 20 is in contrast to that figure 1 differing.

How from the figure 3 visible, the check valve 40 by means of a control circuit - comprising a 2-way valve 45 - controlled. A line 44 connects the piston side 22a of the differential cylinder 20 to the check valve 40 via the 2-way valve.

The directional valve 45 has a flow position and a position in which the overpressure from the upper part of the line 44 is decompressed and deviates into a container. The check valve 40 is thus opened depending on the pressure in the piston side 22a. If 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 due to the pressure on the piston side 22a. Since the valve 40 is open, the remaining hydraulic fluid can flow back into the replenishment tank.

figure 4 Figure 12 shows another exemplary embodiment of the system not covered by the claimed invention figure 3 . As in figure 3 the check valve 40 is controlled by means of the control circuit or the 2-way valve 45 .

In the bias source 60, the accumulator 30 of the previous figures has been replaced by a pump 65 in this exemplary embodiment. The pump 65 only works in one direction and accordingly has a pump inlet and a pump outlet. The pump inlet is connected to the after-suction tank 50 by means of a line 62 , while the pump outlet is connected to the line 72 by means of a line 63 via the check valve 70 .

On the line 63 side, the pump 65 works like the pressure accumulator 30 from the previous figures, in that it generates an overpressure which is used to preload the system.

The hydraulic fluid used in the pump 65 is shown in this example

Embodiment taken from the suction tank via line 62.

As in figure 4 A cleaning device 90 for cleaning the hydraulic fluid is shown in this exemplary embodiment of the system 1, arranged between the suction tank 50 and the pump 65. The hydraulic fluid that is sucked in by the pump 60 and accordingly fed into the line 72 is thus cleaned beforehand and preferably also vented.

This embodiment is advantageous because a closed circuit is provided in which the after-suction tank 50 is used as a static device, for example 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 promotes and cleans the fluid in the suction tank, but cannot be reused immediately.

the figure 5 1 shows a system 1 corresponding to the system described above, but with a different arrangement according to the invention.

How from the figure 5 As can be seen, the connection between the suction 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 .

Furthermore, a line 72 connects the replenishment tank 50 via a check valve 73 to the node 100, through which the hydraulic fluid can be directed both into the ring side 22b of the differential cylinder 20 and through the pump 11 into the line 71. Furthermore, the replenishment tank 50 is hydraulically connected to the preload source 60 and in particular to the input of the pump 65 by means of the line 72 and the line 62 .

The pump 11 is connected to both the line 71 and the line 72 . The hydraulic fluid is preloaded by means of the preload source 60, with the pump 65 providing the preload of the hydraulic fluid, similar to the embodiment in FIG figure 4 . This is a pump which can only work on one side. In the present exemplary embodiment according to the invention, an additional controlled proportional valve, in particular a controlled proportional pressure relief valve 85 on the line 71, is arranged between the preload source 60 or the pump 65 and the piston side 22a. The proportional valve 85 is preferably used for decompression of the system 1, as in previous

Embodiments has been explained.

Furthermore, a preload 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 and also to a connection of the hydraulic machine 11 . 1 Electrohydrostatic actuator system 60 bias source 62 Management 10 electric motor 63 Management 11 hydro machine 65 pump 20 differential cylinder 66 check valve 22a piston side 68 preload valve 22b ring side 69 check valve 30 accumulator 70 check valve 40 check valve 72 Management 41, 42 Management 75 Management 45 2-way valve 80 Valve 48 controlled 2-way valve 85 proportional valve 50 suction tank 90 cleaning device

Claims (13)

1. Electrohydrostatic actuator system (1) comprising:

   a variable-volume and/or variable-speed hydraulic machine (11) driven by an electric motor (10), for providing a volumetric flow of a hydraulic fluid;

   a differential cylinder (20) with a piston end (22a) and a ring end (22b);

   at least one pre-pressurizing source (60);

   wherein the actuator system (1) has a closed hydraulic circuit and, during operation, the hydraulic fluid in the hydraulic circuit is pressurized by means of the hydraulic machine (11) and/or the pre-pressurizing source (60), and

   wherein the differential cylinder (20) provides the operating modes of a power traverse and a rapid traverse, and

   wherein an expansion reservoir (50) is connected to the piston end (22a) of the differential cylinder (20) via a first valve (40) to compensate for a volume of the hydraulic fluid in the closed hydraulic circuit (1), wherein a second valve (85) connects the piston end (22a) to the pre-pressurizing source (60) or to the expansion reservoir (50),

   characterized in that

   the second valve is designed as a proportional valve (85).
2. Electrohydrostatic actuator system (1) according to Claim 1, wherein the hydraulic fluid is pre-pressurized in the expansion reservoir (50) at a pressure of less than 5 bar, preferably less than 4 bar, preferably less than 3 bar, particularly preferably less than 2 bar, and particularly preferably less than 1 bar.
3. Electrohydrostatic actuator system (1) according to any one of the preceding claims, wherein the expansion reservoir (50) has a volume which is equal to or greater than the volume difference of the closed system (1) in a power end position and upper end position of the differential cylinder (20).
4. Electrohydrostatic actuator system (1) according to any one of the preceding claims, wherein the first valve (40) is a controlled check valve (40), in particular a piloted check valve.
5. Electrohydrostatic actuator system (1) according to any one of the preceding claims, wherein the hydraulic fluid of the pre-pressurizing source (60) has a pressure between 5 bar and 50 bar, preferably between 10 bar and 40 bar, particularly preferably between 15 bar and 35 bar, particularly preferably between 20 bar and 30 bar.
6. Electrohydrostatic actuator system (1) according to any one of the preceding claims, wherein the pre-pressurizing source (60) is hydraulically connected via a third valve (70) to the line (72) between the connection of the hydraulic machine (11) to the ring end (22b) and the ring end (22b) of the differential cylinder (20).
7. Electrohydrostatic actuator system (1) according to Claim 6, wherein the third valve (70) is a check valve.
8. Electrohydrostatic actuator system (1) according to any one of Claims 6 or 7, wherein the pre-pressurizing source (60) comprises a pump (65) whose pump inlet is connected via a line (62) to the expansion reservoir (50) and a pump outlet of the pump (65) is connected to the third valve (70) via a line (63).
9. Electrohydrostatic actuator system (1) according to any one of the preceding claims, wherein at least a fourth valve (80) with a throughflow position and a blocking position is arranged, said valve being arranged in a line (72) between the ring end (22b) of the differential cylinder (20) and a connection of the hydraulic machine (11);
10. Electrohydrostatic actuator system (1) according to any one of the preceding claims, wherein the hydraulic machine (11) can be pressurized at both pump connections.
11. Electrohydrostatic actuator system (1) according to any one of the preceding claims, wherein the expansion reservoir (50) comprises a device for venting the hydraulic fluid and/or a device for cooling the hydraulic fluid.
12. Electrohydrostatic actuator system (1) according to any one of the preceding claims, wherein the system (1) has a plurality of differential cylinders.
13. Use of the electrohydrostatic actuator system (1) according to any one of Claims 1 to 12, in a hydraulic press, a thermoforming device, or an injection-molding device.

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