Electrohydraulic pressing device and method

Abstract

The invention relates to an electrohydraulic pressing device (10), in particular for pressing a workpiece, comprising: a hydraulic pump (20) which is driven by an electric motor (24); a hydraulic piston arrangement (12) for actuating a pressing tool by supplying hydraulic fluid by means of the hydraulic pump from a reservoir (46) into a piston chamber (14) to move a hydraulic piston (16) of the hydraulic piston arrangement; a valve apparatus (30) which is arranged in a return line (32) between the piston chamber and the reservoir, the valve apparatus being designed as a directional seat valve.

Description

[0001] Electrohydraulic press device and process

[0002] The present invention relates to an electro-hydraulic pressing device, in particular for pressing a workpiece, and a method for operating such an electro-hydraulic pressing device.

[0003] Electro-hydraulic presses have a hydraulic pump driven by an electric motor. To generate a pressing force, the hydraulic pump pumps hydraulic fluid from a reservoir into a piston chamber. A hydraulic piston is arranged in the piston chamber, through which the pressing force is transferred to a pressing tool. For this purpose, the pressing tool is usually connected to the press device indirectly via a tool holder. A pressure relief valve is provided in a return line through which the hydraulic fluid can be returned from the piston chamber to the reservoir. When the desired pressing force is reached, the pressure relief valve opens and the hydraulic fluid flows back into the reservoir, allowing the hydraulic piston to return to its original position. Common pressure relief valves are spring-loaded valves that open when a limit pressure is exceeded.When the limit pressure is reached during a completed compression cycle, the mechanical pressure relief valve opens automatically. Since this causes a sudden drop in pressure in the piston chamber, an increase in the electric motor's speed can be detected, for example, and the electric motor can then be shut down.

[0004] In conventional pressure relief valves, the valve spring, which pushes the valve into the closed position and holds it there, must be designed in such a way that only the limit pressure overcomes the spring force and opens the pressure relief valve. The valve spring must be designed accordingly.

[0005] However, if the pressure relief valve is to be opened before a limit pressure is reached, for example due to an emergency stop of the pressing tool, the entire force required to overcome the spring force of the pressure relief valve must be applied by the user in the case of a mechanical emergency opening device.

[0006] In DE 10 2010 049 946 A1, the pressure relief valve also serves as a control valve, which opens when a predetermined pressing force is reached. DE 10 2010 049 946 A1 describes such a control valve as a solenoid valve. However, the electromagnet of the solenoid valve, which opens the control valve, must be sufficiently strong to also overcome the spring force of the valve spring. This prevents a compact design of the electro-hydraulic pressing tool.

[0007] The object of the present invention is to provide an electro-hydraulic pressing device which is compact and can be reliably controlled.

[0008] The object is achieved according to the invention by an electro-hydraulic pressing device according to claim 1 and a method for operating an electro-hydraulic pressing device according to claim 12.

[0009] The electro-hydraulic pressing device according to the invention, which is particularly suitable for connecting pipes by means of fittings to be pressed, has a hydraulic pump driven by an electric motor. To actuate the pressing tool or a tool holder for holding a pressing tool, a hydraulic piston arrangement is pressurized by the hydraulic pump. For this purpose, the hydraulic pump pumps hydraulic fluid from a reservoir into a piston chamber of the hydraulic piston arrangement to move the hydraulic piston. In order to be able to push the hydraulic piston back to its starting position, a return line is provided between the piston chamber and the reservoir, which is controlled by a valve device. By opening the valve device, hydraulic fluid can flow back from the piston chamber into the reservoir.This enables the hydraulic piston to be returned to its initial position, in particular by means of a return spring of the hydraulic arrangement, which pushes the hydraulic piston back to its initial position and thereby pumps the hydraulic fluid into the reservoir. According to the invention, the valve device comprises a directional seat valve. By using a directional seat valve, the valve device can be actuated with low force and, in particular, is independent of the pressure in the piston chamber. In particular, it is not necessary to overcome the spring force of a valve spring to open or close the valve device.

[0010] The valve device preferably has an actuator for opening the valve device and in particular the directional seat valve. Alternatively or additionally, an actuator is provided for closing the valve device, which can preferably be the same actuator by which the valve device is opened, so that only one actuator is provided for opening and closing the directional seat valve. Because the valve device is designed as a directional seat valve and only a small force is required to control the directional seat valve, the corresponding actuator can be compact and small. The actuator can thus be integrated into a hand-held electro-hydraulic pressing device, thus creating the possibility of controlling the valve device as needed.

[0011] The actuator is preferably an electric actuator such as a linear servomotor. This has the advantage over the known solenoid valve that positions can be reached precisely and, in particular, the valve position can be held without energy. This means that the valve position is retained even if, for example, the pressing device is disconnected from the power supply. In particular, it is an electromechanical actuator such as an electric motor with a lever or cam, an electric motor with a spindle, a DC motor with a spindle and lifting nut, or a piezo actuator with a lever. Alternatively, the actuator is a shape memory alloy, in particular in the form of a wire that is stretched linearly as an arc, or in the form of a spring, whereby the position of the valve device can be controlled by means of the shape memory alloy.Alternatively, the directional seat valve is actuated hydraulically, in particular by redirecting the system pressure by means of another valve which is controllable.

[0012] Preferably, the force required to open the directional seat valve is independent or substantially independent of the pressure in the piston chamber and thus, in particular, independent of the pressure control of the pressing tool. Thus, the actuator can be designed to be compact, since only a small and consistently constant force is required to open the directional seat valve. Furthermore, the valve device of the present invention can be provided for different pressing tools by means of which a different pressing force is to be achieved. Thus, even with higher forces and thus higher pressures in the piston chamber, it is always ensured that the directional seat valve can be reliably opened by the actuator.

[0013] Preferably, the directional seat valve of the valve device is closed in the rest position. Alternatively, the directional seat valve of the valve device is open in the rest position.

[0014] Preferably, the directional seat valve is preloaded in a closed position. Alternatively, the directional seat valve is preloaded in an open position. This ensures that the directional seat valve is always in a defined position, which is predetermined by the preload of the directional seat valve. The preload can be achieved, for example, by a suitable spring element or the preload force is applied by the actuator. In particular, when the preload force is formed by a spring element, this spring element is significantly smaller than the valve springs in pressure relief valves from the prior art, since the directional seat valve is essentially force-free even at high pressures. In particular, the spring element has a spring force orA spring force of ION to 100N, and in particular between 20N and 60N, is generated, which is significantly lower than the corresponding required spring forces of the valve springs in the pressure relief valves of the prior art, which are usually between 400N and 1000N. Since the directional seat valve is essentially controllable without force, the actuator for controlling the directional seat valve only needs to be designed to overcome the force of the preload.

[0015] Preferably, the preload of the directional seat valve is independent of the opening pressure in the piston chamber at the end of a pressing cycle, at which the valve device is to be opened. Thus, the valve device of the present invention can be controlled to open at different pressures, thus providing variable control of the electro-hydraulic pressing device. The preload of the directional seat valve no longer determines the opening pressure of the valve device at the end of a pressing cycle, as is the case with pressure relief valves of the prior art.

[0016] The directional seat valve preferably has a valve body which is arranged in a valve housing of the valve device, wherein a valve element is connected to the valve body. The valve element is in particular designed as a valve disk and rests against a valve seat in a closed position of the valve device and is spaced from the valve seat in an open position of the valve device. For this purpose, the valve body is arranged in the valve housing so as to be displaceable from the closed position to an open position and vice versa. In particular, the valve element is displaced by the actuator from the closed position to the open position or vice versa. The displacement of the valve body can take place as a pulling actuation of the valve body or as a pushing actuation of the valve body.Thus, the actuator can be arranged on both sides of the valve device in the direction of movement of the valve body, which enables space-saving integration into the electro-hydraulic pressing device.

[0017] The directional seat valve preferably has a pressure chamber, in particular designed as an annular channel, which is in contact with the valve element or surrounds it. The pressure chamber is connected to the piston chamber. Thus, the same or essentially the same pressure prevails in the pressure chamber of the directional seat valve as in the piston chamber. In particular, the valve body has a first pressure surface which points in the direction of the closed position and an opposite second pressure surface which points in the direction of the open position. In particular, the pressure chamber of the directional seat valve is delimited in the axial direction of the valve body or in the direction of movement of the valve body by the first pressure surface and the second pressure surface. If the valve body is moved into the open position, the hydraulic fluid can flow from the pressure chamber of the directional seat valve through the gap between the valve element and the valve seat into the reservoir.

[0018] Preferably, the first pressure surface is the same size as the second pressure surface. Thus, the forces generated by the hydraulic fluid pressure in the pressure chamber of the directional seat valve on the valve body in the direction of the closed position by the first pressure surface and in the direction of the open position by the second pressure surface are precisely balanced. This enables force-free movement of the valve body. The control of the directional seat valve is completely independent of the pressure in the piston chamber.

[0019] Alternatively, the second pressure area is larger than the first pressure area, so that a force is generated in the direction of the open position and the directional seat valve is opened when a maximum pressure is exceeded. In this case, the maximum pressure can correspond to the maximum permissible pressure in the hydraulic piston arrangement and / or hydraulic pump, so that the directional seat valve opens before damage to the hydraulic pump and / or hydraulic piston arrangement occurs. The present valve device thus has a pressure limitation. In this case, the second pressure area can be in particular 0.5%-20% larger than the first pressure area, preferably 2%-10% and particularly preferably 2%-5% larger than the first pressure area.

[0020] The directional seat valve can preferably be opened manually, in particular by manually moving the valve body into the open position. Instead of providing an actuator, manual opening of the valve device can be provided, so that manual return of the hydraulic piston is possible by manual actuation. However, it is preferred that, in addition to the actuator, manual opening of the directional seat valve is possible, in particular for emergency opening of the directional seat valve, so that the hydraulic piston can be pushed back to its initial position. Alternatively, manual closing of the directional seat valve may be possible. In particular, an actuating element can be connected to the valve body, which is accessible to the user from the outside, whereby the valve body is movable.In particular, the actuating element can be arranged on the side opposite the actuator, so that if the actuator pushes the valve body of the directional seat valve, pulling the actuating element opens the valve device.

[0021] Preferably, the valve device is connected to a control unit, and in particular, the actuator of the valve device is connected to the control unit for controlling the directional seat valve. Thus, the actuator can be electronically activated by the control unit, thereby moving the valve device from a closed position to an open position at the time of need, or vice versa.

[0022] The control unit is preferably connected to the hydraulic pump and in particular to the electric motor of the hydraulic pump for controlling the hydraulic pump. The control unit can electronically start and stop the electric motor for conveying hydraulic fluid through the hydraulic pump from a reservoir into the piston chamber to move the hydraulic piston. Thus, the control of the pressing process is independent of the control of the valve device, in particular the directional seat valve. Preferably, the electro-hydraulic pressing device has a sensor for detecting one or more operating variables of the pressing device. The sensor is connected to the control unit, wherein the control unit controls the valve device, in particular the actuator, depending on the one or more detected operating variables.Alternatively or additionally, the control unit controls the electric motor of the hydraulic pump depending on the one or more detected operating variables. Depending on the detected operating variable, the electric motor of the hydraulic pump can first be stopped and then the valve device can be opened or closed, in particular automatically or manually, by the actuator. The valve device thus regulates, in particular, exclusively the return flow of the hydraulic fluid, independently of the pressure control of the hydraulic piston. In particular, the operating variable can be, for example, a pressure which is detected in the hydraulic piston arrangement or the hydraulic pump. Alternatively or additionally, the operating variable is a force which is generated by the hydraulic piston arrangement. Alternatively or additionally, it is a current which is supplied to the hydraulic pump.Alternatively or additionally to this, it is a temperature and in particular a temperature of the hydraulic fluid, so that when a limit temperature is exceeded the valve device is opened or closed. In this case, the aforementioned operating variables are used in particular for controlling the electric motor of the hydraulic pump. The operating variables can alternatively or additionally also be used for controlling the valve device, in particular the actuator. In particular, a stop signal for the electric motor of the hydraulic pump can also be used as an operating variable for controlling the valve device, in particular the actuator. Alternatively or additionally to this, a control signal for activating the valve device can be used as a stop signal for the electric motor, so that when the valve device is opened during the pressing process the delivery of the hydraulic pump is also stopped.

[0023] The present invention further relates to a method for operating an electro-hydraulic pressing device, which is designed in particular as described above. According to the method according to the invention, the hydraulic pump is activated to generate a pressure in the piston chamber, wherein hydraulic fluid is pumped from a reservoir into the piston chamber to move the hydraulic piston. The electric motor of the hydraulic pump is switched off when the required pressing force is reached or by an operator input, and the movement of the hydraulic piston is stopped. In this case, the force of the pressing tool is controlled in particular by measuring one or more operating variables with a sensor. Subsequently, the valve device is opened so that the hydraulic fluid can flow back from the piston chamber into the reservoir. The valve device regulates in particular exclusively the return flow of the hydraulic fluid, independently of the pressure control of the hydraulic piston.This allows the hydraulic piston to be pushed back to its original position, reducing the size of the piston chamber and thus allowing the hydraulic fluid to be pumped back from the piston chamber through the return line into the reservoir.

[0024] Preferably, a stop of the hydraulic pump and an opening of the valve device are triggered by an operator input. Thus, for example, the user can abort a pressing operation at any time, for example as an emergency stop. This is particularly possible before a maximum pressure is reached, since the valve device and in particular the directional seat valve of the present invention can be controlled independently of the pressure in the piston chamber and thus independently of the pressure or force control of the pressing tool. Preferably, the valve device is closed when an initial position of the hydraulic piston is reached. The initial position defined by the valve device does not have to coincide with the mechanical stop position of the hydraulic piston arrangement.Thus, pressing tools with a shorter travel path can also be used, with the starting position for these tools being located before the mechanical stop position of the pressing device, and this starting position being generated by closing the valve device. Thus, due to the provision of the valve device according to the invention, different pressing tools can be used with the pressing device, which in particular require a different travel path of the hydraulic piston.

[0025] Preferably, the valve device is only partially opened to reduce the backflow of the hydraulic fluid. This allows the speed of the backflow of the hydraulic fluid to be controlled, which simultaneously slows the return of the hydraulic piston. This makes it possible to move the press tool to precise positions by controlling the backflow using the valve device.

[0026] Preferably, the hydraulic pump is stopped and the valve device is opened depending on an operating variable of the electro-hydraulic pressing device. Alternatively or additionally, the electric motor of the hydraulic pump can be stopped depending on the one or more detected operating variables. This allows the pressing device to be used in a variety of ways, and in particular, the required pressing force can be adapted to the respective pressing tool. The pressing device can thus be used with a variety of different pressing tools, ensuring optimal pressing of the press fitting or workpiece at all times.

[0027] The method is preferably further developed based on the features of the electro-hydraulic pressing tool described above. The invention is explained in more detail below using preferred embodiments with reference to the accompanying figures.

[0028] The figures show:

[0029] Figure 1 is a schematic diagram of the essential part of an electro-hydraulic pressing device according to the present invention and

[0030] Figures 2A and 2B Detailed views of the directional seat valve.

[0031] In the embodiment of the figures, the electro-hydraulic pressing device 10 has a hydraulic piston arrangement 12. The hydraulic piston arrangement 12 defines a piston chamber 14. A hydraulic piston 16 is slidably arranged in the hydraulic piston arrangement 12 in order to apply a force to a pressing tool, which is directly or indirectly connected to the hydraulic piston 16. To move the hydraulic piston 16, a hydraulic pump 20, which is driven by an electric motor 24, pumps a hydraulic fluid from a reservoir 46 (the connecting line between the reservoir 46 and the hydraulic pump 20 has been omitted for reasons of clarity) via a supply line 22 into the piston chamber 14. As a result, the pressure in the piston chamber increases and the hydraulic piston 26 moves to the left in Figure 1. A valve device 30 is arranged in a return line 32, which is connected to the piston chamber 14.Here, the valve device 30 can be moved from a closed position, shown in Figures 1 and 2B, to an open position, shown in Figure 2A. When the valve device 30 is in an open position, the hydraulic fluid can flow back from the piston chamber 14 via the return line 32 and the valve device 30 into the reservoir 46. In the embodiment of Figure 1, the return line 32 and the inlet line 22 are shown as two separate channels connected to the piston chamber 14. Of course, the return line 32 can branch off directly from the inlet line 22.

[0032] The motor 24 is connected to a control unit 26 so that the motor 24 is controlled by means of the control unit 26. For this purpose, the control unit 26 is connected, for example, to a control element via which a user can initiate the activation of the electric motor 24.

[0033] According to the invention, the valve device 30 comprises a directional seat valve. The directional seat valve has a valve body 34, which is displaceable in a valve housing 35 from a closed position to an open position according to arrow 38 and vice versa (opposite arrow 38). Via the return line 32, which is connected to the piston chamber 14, the hydraulic fluid reaches an annular pressure chamber 42 of the directional seat valve. The pressure chamber 42 is delimited by pressure surfaces 50, 52. A first pressure surface 50 points in the direction of the closed position, i.e., opposite arrow 38, whereas the second pressure surface 52 points in the open position, i.e., in the direction of arrow 38. In particular, the first pressure surface 50 and the second pressure surface 52 are of the same size.Here, "equal size" refers in particular to the projection of the respective pressure surface in the axial direction, so that the effect of the pressure in the pressure chamber 42 on the first pressure surface 50 and the second pressure surface 52 is equal and thus the valve body 34 remains in its position without force. In particular, no force is applied to the valve body 34 by the pressure of the hydraulic fluid.

[0034] In particular, the valve body is preloaded into the closed position, shown in Figures 1 and 2B, by a spring element 36. Thus, the directional seat valve is always held in a defined position. An actuator 40 can then move the valve body 34 from the closed position to the open position, as indicated by arrow 38. Since the movement of the valve body 34 can be essentially force-free and only the actuator 40 needs to overcome the preload force of the spring element 36, the actuator 40 can be small and compact and can thus also be integrated into a hand-held electro-hydraulic pressing device. The actuator 40 is particularly designed as an electric motor with a linear drive, an electric motor with a spindle, an electric motor with a spindle and lifting nut, or the like. Thus, the position of the valve body 34 of the directional seat valve can be precisely controlled by the actuator 40.In particular, a current-free maintenance of the position of the valve body 34 is ensured. To control the actuator 40, the actuator 40 is connected to the control unit 26, and thus the actuator 40 can open or close the valve device 30 at a predetermined time using the control unit.

[0035] Furthermore, the valve body 34 can be connected to a manual operating element (not shown), allowing manual movement of the valve body 34 to move the valve device 30 from the closed position to the open position, or vice versa, independently of the actuator 40. Thus, even when the power supply is disconnected, the hydraulic piston can be returned by manually opening the valve device 30.

[0036] In Figures 2A and 2B, the directional seat valve is shown in an open position (Figure 2A) and a closed position (Figure 2B). In the open position, the valve element 44 or the valve plate does not rest against the valve seat 48. This creates a channel between the valve element 44 and the valve seat 48, so that hydraulic fluid can flow from the pressure chamber 42 towards the reservoir 46 as indicated by arrow 47. In the closed position, the valve element 44 rests against the valve seat 48 and a backflow of the hydraulic fluid towards the reservoir 46 is prevented. In an alternative embodiment, the second pressure surface 52 is larger than the first pressure surface 50. As a result, the pressure of the hydraulic fluid in the pressure chamber 42 exerts a greater force on the valve element 34 towards the open position.As soon as this force overcomes the restoring force of the spring element 36, the valve device 30 opens regardless of the position of the actuator 40. This makes it possible to provide a safety function which, regardless of the pressing tool actually used, opens the valve device 30 before damage occurs, for example, to the hydraulic arrangement and / or the hydraulic pump and / or another component of the pressing tool.

[0037] Furthermore, a pressure sensor 28 is connected to the piston chamber 14 so that the pressure in the piston chamber 14 can be detected by the pressure sensor 28. In the embodiment of Figure 1, the pressure sensor 28 is arranged in the return line 32. Other arrangements, such as in the supply line 22 or directly on or in the piston chamber 14, are also possible. In this case, the pressure is detected by the pressure sensor 28 as an operating variable by the control unit 26. Control of the electric motor 24 of the hydraulic pump 20 as a function of the detected pressure is thus possible. Alternatively or additionally, the control unit controls the valve device, in particular the actuator, as a function of the one or more detected operating variables.If a desired and, in particular, preset pressing pressure is thus achieved by the electro-hydraulic pressing device and, in particular, the hydraulic piston assembly 12, this is detected by the pressure sensor 28 and transmitted to the control unit 26. The control unit 26 stops the electric motor 24 and, by activating the actuator 40, opens the valve device 30 so that the hydraulic fluid can flow back from the piston chamber 14 into the reservoir 46 and the hydraulic piston 16 can be returned to its initial position. The hydraulic piston can be returned manually by pushing it back, or, as schematically shown in Figure 1, a return spring 18 is provided, which returns the hydraulic piston 16 to its initial position.

[0038] In one embodiment, the control unit 26 can reactivate the actuator 40 during the return movement of the hydraulic piston 16, so that the valve device 30 closes. Thus, no further hydraulic fluid flows from the piston chamber 14 via the valve device 30 into the reservoir 46, thus defining a starting position for a new pressing operation. This is particularly helpful for pressing tools that require a shortened pressing path. Thus, it is not necessary for the hydraulic piston 16 to begin pressing from its mechanical stop position.

[0039] Further operating variables that can be taken into account for the activation of the actuator 40 by the control unit are the force applied by the hydraulic piston 16, which is detected, for example, by a force sensor. Alternatively, the current consumed by the electric motor 24 can be detected as an operating variable for controlling the actuator 40. Alternatively, the temperature of the hydraulic fluid can be detected as an operating variable, and thus the valve device 30 can be controlled by the control unit 26 via the actuator 40 depending on the temperature detected in this way. Alternatively, a stop signal for the electric motor 24 can be used as an operating variable. If the electric motor is switched off when a preset pressing force is reached, this switch-off signal is used to subsequently activate the actuator 40.Alternatively or additionally, the control unit can control the electric motor 24 of the hydraulic pump 20 depending on the one or more detected operating variables. Alternatively, other operating variables can be used. In particular, a combination of several of these operating variables can be used to control the actuator 40 and / or the electric motor 24. The design of the valve device as an actively controlled valve device 30 by means of the actuator 40 and a directional seat valve enables the pressing device to be used variably for different applications. Thus, the valve device provides a safety function that can electronically trigger the device's shutdown and the return travel of the hydraulic piston 16 at any time, for example, in the event of an emergency stop.In this case, the electric motor 24 is stopped and the valve device 30 is opened by the control unit 26 and in particular by an operator input from the user.

[0040] In another mode for operating the electro-hydraulic pressing device, the electric motor 24 is started by the user actuating the control element. This activates the electric motor 24 and the user can then release the control element. When the maximum pressing pressure is reached, the pressure sensor 28 signals this to the control unit 26, so that the electric motor 24 is stopped. The user can then check whether the pressing tool is completely closed and the workpiece has been fully pressed. After checking, the valve device 30 can be opened by manually actuating the valve device 30 and the pressing piston 30 can be moved back to its starting position. Alternatively, in another operating mode, when the maximum pressing force is reached, the valve device is automatically opened by the control unit 26 by activating the actuator 40 and the hydraulic piston is moved back.

[0041] In another operating mode of the electro-hydraulic pressing device, the load is initially approached. The pressure sensor 28 detects a predefined starting load and switches off the electric motor 24 upon detection of the starting load. The user can now check whether the workpiece is correctly gripped by the pressing tool and is correctly seated. If this is ensured, the pressing process is automatically carried out and terminated by the user pressing the control element again. Once the maximum pressing pressure has been reached, the valve device 30 opens automatically by activating the actuator 40, and the hydraulic piston 16 thus returns to its starting position. If a problem is detected upon reaching the starting load, the device can be returned to the starting position of the hydraulic piston 16 by manually opening the valve device 30.In particular, this allows the pressing tool to be opened and the pressing tool to be reattached to the workpiece.

[0042] In another operating mode, the user can be given the opportunity to check that the pressing is complete before the valve device 30 automatically opens upon reaching the maximum pressing force. For this purpose, the electric motor 24 is stopped. Pressing the control element again then opens the valve device, and the hydraulic piston 16 can be returned to its original position. Alternatively, the valve device 30 can be opened manually.

[0043] In another operating mode of the electro-hydraulic pressing device, automatic pressing occurs without approaching the load and without closure control. Pressing the control element by the user starts the pressing process. The pressure sensor 28 detects a predefined minimum pressure and then starts the automatic pressing sequence. The control element can now be released by the user. The pressing device automatically performs the full pressing process, and as soon as the maximum pressing pressure is reached, the electric motor 24 is automatically stopped and the valve device 30 is opened by the actuator 40, allowing the hydraulic piston 16 to return to its initial position.

[0044] The operating modes of the electro-hydraulic pressing device described above can be provided by the control unit 26. If appropriate, the individual pressing modes can be combined with one another. The pressing modes as described above are controlled based on the operating variable of the pressure detected by the pressure sensor 28. Of course, these operating modes can also be implemented based on other operating variables, such as the achieved pressing force or a combination of several of these operating variables. The provision of a directional seat valve as the valve device of the electro-hydraulic pressing device, which is controllable in particular via an actuator, represents a compact control of the return flow of the electro-hydraulic pressing device.In particular, an individually adjusted maximum pressing force can be provided for the respective pressing tool. Upon reaching this maximum force, the electric motor of the hydraulic pump can be stopped and the valve device can be opened for the return flow. At the same time, the valve device can implement a safety function, preventing damage to the electro-hydraulic pressing device due to excess pressure. This creates a versatile electro-hydraulic pressing device with a compact design.

Claims

Patent claims 1. Electro-hydraulic pressing device, in particular for pressing a workpiece, with a hydraulic pump driven by an electric motor, a hydraulic piston arrangement for actuating a pressing tool by supplying hydraulic fluid by means of the hydraulic pump from a reservoir into a piston chamber for moving a hydraulic piston of the hydraulic piston arrangement, a valve device arranged in a return line between the piston chamber and the reservoir, wherein the valve device has a directional seat valve.

2. Electro-hydraulic pressing device according to claim 1, characterized in that the valve device has an actuator for opening or closing the valve device.

3. Electro-hydraulic pressing device according to claim 1 or 2, characterized in that the force required to open or close the directional seat valve is independent of the pressure in the piston chamber.

4. Electro-hydraulic pressing device according to one of claims 1 to 3, characterized in that the directional seat valve is preloaded into a closed position or an open position.

5. Electro-hydraulic pressing device according to claim 4, characterized in that the preload of the directional seat valve is independent of a Opening pressure in the piston chamber at which the valve device is to be opened.

6. Electro-hydraulic pressing device according to one of claims 1 to 5, characterized in that the directional seat valve has a valve body which is arranged in a valve housing of the valve device, wherein a valve element is connected to the valve body, wherein the valve body is displaceable in the valve housing from a closed position to an open position of the valve device and vice versa.

7. Electro-hydraulic pressing device according to claim 6, characterized in that the valve body has a first pressure surface which points in the direction of the closed position and an opposite second pressure surface which points in the direction of the open position, wherein the first pressure surface and the second pressure surface are arranged in a pressure chamber of the directional seat valve which is connected to the piston chamber via the return line.

8. Electro-hydraulic pressing device according to claim 7, characterized in that the first pressure surface has a size identical to the second pressure surface or wherein the second pressure surface is larger than the first pressure surface, so that a force effect is generated in the direction of the open position and the directional seat valve is opened when a maximum pressure is exceeded.

9. Electro-hydraulic pressing device according to one of claims 1 to 8, characterized in that the directional seat valve can be opened or closed manually, in particular by a manual movement of the valve body into the open position or closed position.

10. Electro-hydraulic pressing device according to one of claims 1 to 9, characterized by a control unit which is connected to the valve device and in particular to the actuator for controlling the directional seat valve.

11. Electro-hydraulic pressing device according to one of claims 1 to 10, characterized by a control unit which is connected to the electric motor of the hydraulic pump for controlling the electric motor.

12. Electro-hydraulic pressing device according to claim 11, characterized by a sensor for detecting one or more operating variables of the electro-hydraulic pressing device, wherein the sensor is connected to the control unit, wherein the control unit controls the valve device and in particular the actuator as a function of the one or more detected operating variables.

13. A method for operating an electro-hydraulic pressing device according to one of claims 1 to 12, wherein the hydraulic pump is activated to generate a pressure in the piston chamber, the hydraulic pump is stopped to terminate the pressing process and subsequently the valve device opens so that the hydraulic fluid can flow back from the piston chamber into the reservoir.

14. The method according to claim 13, wherein a stop of the hydraulic pump and an opening of the valve device are triggered by an operator input.

15. The method according to claim 13 or 14, wherein the valve device is closed when the hydraulic piston reaches an initial position.

16. The method according to any one of claims 13 to 15, wherein the valve device is partially opened to reduce the backflow of the hydraulic fluid.

17. Method according to one of claims 13 to 16, wherein the valve device is opened depending on an operating variable of the electro-hydraulic pressing device.

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