Electrohydraulic actuator

Abstract

The invention relates to an electrohydraulic actuator (1), comprising at least one bidirectionally operable hydraulic pump (2) for conveying hydraulic fluid, said hydraulic pump having two connection points (6a, 6b) which are designed to alternately provide and / or withdraw hydraulic fluid, and having a hydraulic actuator component (3) which has two hydraulic fluid chambers (4a, 4b) into which hydraulic fluid can be fed in order to actuate the hydraulic actuator component (3), wherein: filling one of the hydraulic fluid chambers (4a, 4b) with hydraulic fluid simultaneously causes hydraulic fluid to be displaced from the other hydraulic fluid chamber (4b, 4a); a first connection point (6a) of the hydraulic pump (2) is connected to a first hydraulic fluid chamber (4a) of the hydraulic actuator component (3) by a first line (7a) and a second connection point (6b) of the electric hydraulic pump is connected to a second hydraulic fluid chamber (4b) of the hydraulic actuator component (3) by a second line (7b); a first releasable hydraulic closure element (8a) is disposed between the first hydraulic fluid chamber (4a) and the first line (7a) and a second releasable hydraulic closure element (8b) is disposed between the second hydraulic fluid chamber (4b) and the second line (7b); the releasable hydraulic closure elements (8a, 8b) prevent undesired flow of hydraulic fluid out of the hydraulic fluid chambers (4a, 4b); and the releasable hydraulic closure elements (8a, 8b) are designed such that, for a release, both an electrical release signal and a hydraulic release signal must be present at the releasable hydraulic closure elements (8a, 8b).

Description

[0001] Electro-hydraulic actuator

[0002] The invention relates to an electro-hydraulic actuator, in particular a linear actuator capable of inducing a linear actuator movement. The electro-hydraulic actuator consists of a hydraulic actuator component and an electrically driven hydraulic pump that supplies hydraulic fluid to drive the hydraulic actuator component.

[0003] The electro-hydraulic actuator described here can be operated in up to four quadrants, meaning the actuator is four-quadrant capable. Four-quadrant capability means that the electro-hydraulic actuator can be driven with electrical energy in two directions of movement to generate actuator movement. Furthermore, recuperation is also possible in both directions of movement, whereby mechanical energy can be extracted from the actuator movement and converted into electrical energy.

[0004] Such electro-hydraulic actuators are particularly suitable for electrifying and increasing the energy efficiency of mobile machinery with hydraulic components. The four-quadrant capability of such linear actuators allows significant amounts of energy to be recovered into electrical energy during the operation of mobile machinery. This would be possible, for example, in a situation in which an excavator bucket driven by the electro-hydraulic actuator is lowered. The potential energy of the excavator bucket can then be dissipated into a hydraulic fluid flow using the hydraulic actuator component. Energy can be extracted from this hydraulic fluid flow using the electric hydraulic pump in generator mode and converted into electrical energy.

[0005] Hydraulic actuators are often safety-relevant components. For example, with hydraulic actuators in mobile machinery, it must be ensured that no unwanted or uncontrolled movements of the mobile machinery's components occur in the event of a fault. For example, a crane arm or excavator bucket must not descend uncontrollably in the event of a fault. Resilience to such scenarios is addressed in the area of ​​"functional safety."

[0006] The object of the present invention is to describe an electro-hydraulic actuator which, with regard to operational safety in the event of possible errors occurring, has a particularly good behavior and which, at the same time, has an advantageous design.

[0007] This object is achieved by the invention according to the features of the independent patent claim. Further advantageous embodiments are specified in the dependent claims as well as in the description and, in particular, in the description of the figures. It should be noted that the person skilled in the art can combine the individual features in a technologically expedient manner and thus arrive at further embodiments of the invention.

[0008] The invention relates to an electro-hydraulic actuator comprising at least one bidirectionally operable electric hydraulic pump for conveying hydraulic fluid with two connections, which is alternately configured for the provision and / or removal of hydraulic fluid, as well as a hydraulic actuator component with two hydraulic fluid chambers, which can be pressurised with hydraulic fluid to actuate the hydraulic actuator component, wherein filling one of the hydraulic fluid chambers with hydraulic fluid simultaneously causes a displacement of hydraulic fluid from the other hydraulic fluid chamber,wherein a first connection of the hydraulic pump is connected by a first line to a first hydraulic fluid chamber of the hydraulic actuator component and a second connection of the hydraulic pump is connected by a second line to a second hydraulic fluid chamber of the hydraulic actuator component, wherein a first releasable hydraulic closing element is arranged between the first hydraulic fluid chamber and the first line and a second releasable hydraulic closing element is arranged between the second hydraulic fluid chamber and the second line, wherein the releasable hydraulic closing elements prevent an unwanted outflow of hydraulic fluid from the hydraulic fluid chambers, wherein the releasable hydraulic closing elements are configured such thatthat for unlocking, both an electrical unlocking signal and a hydraulic unlocking signal must be present at the unlockable hydraulic locking elements.

[0009] Possible designs and configurations for the electro-hydraulic actuator, and in particular the design of the hydraulic actuator component and electric hydraulic pump, are described in detail below. It is generally preferred that both the hydraulic pump and the actuator component each have two connections for hydraulic fluid (each acting as an inlet and outlet), which are each connected to one another via a line, thus forming a hydraulic fluid delivery circuit. Otherwise, hydraulic pumps and actuator components of various designs can be used. It should also be noted that the hydraulic actuator component can also be a parallel circuit of several hydraulic (individual) actuator components.For example, the hydraulic actuator component can be a pair of adjacent (parallel-acting) hydraulic cylinders, which, together with an electric hydraulic pump, form an electro-hydraulic actuator and are referred to, for example, as tandem cylinders. Lines from the hydraulic pump to the hydraulic (individual) actuator components are then preferably branched, whereby the branches can possibly be understood as part of the actuator component. Dividing the hydraulic pump into (individual) hydraulic pumps is fundamentally just as possible as dividing the actuator component into (individual) actuator components.

[0010] To achieve particularly good protection in terms of functional safety through the releasable hydraulic closing elements, it is advantageous if the releasable hydraulic closing elements are arranged directly at the transitions between the lines and the hydraulic fluid chambers of the actuator components. Several releasable hydraulic closing elements arranged at corresponding connections of parallel-connected (individual) actuator components of a hydraulic (overall) actuator component can then also be understood as a (common) releasable hydraulic closing element.

[0011] The releasable hydraulic locking elements are arranged between the lines connecting the actuator component to the hydraulic pump and the hydraulic fluid chambers. The releasable hydraulic locking elements are designed to hydraulically separate the hydraulic fluid chambers of the actuator component from the lines. The releasable hydraulic locking elements can reliably prevent hydraulic fluid from escaping from the hydraulic fluid chambers when the releasable hydraulic locking elements are locked or not unlocked. The releasable hydraulic locking elements are designed to remain closed in the idle state (without any unlocking signals acting on them).

[0012] The term "unlocking" refers to the unlockable hydraulic closing elements being open. In this situation, the unlockable hydraulic closing elements preferably have little or no effect on the flow of hydraulic fluid in the lines or into or out of the hydraulic fluid chambers. To unlock the unlockable hydraulic closing elements, both unlocking signals (the electrical unlocking signal and the hydraulic unlocking signal) must be present at the unlockable hydraulic closing elements. During normal operation, the hydraulic closing elements are unlocked, and therefore both unlocking signals (the electrical unlocking signal and the hydraulic unlocking signal) are present at the unlockable hydraulic closing elements.At least one of the release signals can also be applied indirectly, for example, by arranging the releasable hydraulic locking elements and the electro-hydraulic actuator in such a way that a hydraulic release signal is only forwarded to the releasable hydraulic locking element if an electrical release signal is also present. An arrangement of the releasable hydraulic locking elements between the lines connecting the actuator component to the hydraulic pump and the hydraulic fluid chambers fully or partially fulfills the following properties:

[0013] - Advantageously, no further branches to other hydraulic components such as expansion tanks, intermediate circuits, etc. are provided between the releasable hydraulic closing elements and the hydraulic fluid chambers. However, compensating lines to additional parallel cylinders, which together form an actuator component, can be provided. Such compensating lines are common, for example, between the two individual cylinders of a tandem cylinder, which is often used on the lowest stage of an excavator arm.

[0014] - Hydraulic fluid-carrying sections on the side of the releasable hydraulic closing elements facing the hydraulic fluid chambers preferably have a very high degree of leak resistance. Such hydraulic fluid-carrying sections are preferably not made of flexible materials such as hoses or similar and, if appropriate, are constructed entirely of metal.

[0015] - The hydraulic closing elements are advantageously designed to close regardless of further boundary conditions if the electrical unlocking signal required for unlocking and the hydraulic unlocking signal required for unlocking are not present. One such further boundary condition is, for example, a maximum permissible pressure in the actuator component, which, if exceeded, could lead to the actuator component bursting. Another such further boundary condition is, for example, a maximum permissible braking acceleration of the actuator component, which, due to mass inertia, could trigger forces and / or moments on a mobile work machine that exceed permissible limits. Many other such boundary conditions usually exist. When the hydraulic closing elements close following the loss of one of the unlocking signals, such boundary conditions are not taken into account.The locking is performed to protect the electro-hydraulic actuator, regardless of any effects that may arise from exceeding or violating such boundary conditions. However, the hydraulic closing elements preferably have additional functions integrated into the valve that ensure that such boundary conditions are not actually exceeded. Such additional functions include, in particular, bypass functions that operate above certain limit pressures and are explained in more detail below.

[0016] It is particularly advantageous if the pilot-operated hydraulic closing elements are pilot-operated check valves.

[0017] The pilot-operated hydraulic closing elements preferably act as check valves, particularly in a working pressure range when the aforementioned release signals are not present. This means that, within the working pressure range, hydraulic fluid can flow into the hydraulic fluid chambers, but not out. The "working pressure range" here refers to a pressure range of the hydraulic fluid in the lines and hydraulic fluid chambers that regularly occurs during operation of the electro-hydraulic actuator. Pressure peaks that occur, for example, due to sudden valve closures and / or acceleration of hydraulic fluid volumes in the line are preferably not included in the working pressure range. Such pressure peaks are preferably located outside the working pressure range.The releasable hydraulic closing elements preferably have additional functions in the form of bypass channels and / or bypass functions that open at pressures above the working pressure range and then, despite functioning as a check valve in the working pressure range, allow a limited amount of hydraulic fluid to pass through in order to buffer such pressure peaks and prevent the working pressure range from being permanently exceeded. Such functions primarily serve to protect components, for example, to prevent a hydraulic actuator component from bursting due to pressure peaks that occur in the hydraulic fluid chambers due to sudden deceleration caused by the closing of the releasable hydraulic closing elements.

[0018] Additional functions or bypass functions can, if necessary, be implemented by a pressure relief valve acting parallel to the hydraulic closing element. This valve opens at a pressure above a working pressure limit, thus allowing a certain braking distance of the actuator component. At pressures within the working pressure range or below the working pressure limit, such a pressure relief valve is preferably inoperative. If the closing element closes as quickly as possible, thereby exceeding the working pressure limit, the parallel-acting pressure relief valve opens, for example, in a manner (as far and / or as long as necessary) to achieve a compromise between the "braking distance" and the load on the actuator component.

[0019] Another alternative to the pressure relief valve in the bypass is that the pilot-operated hydraulic closing elements can be configured for damped closing. This can also reduce pressure peaks. Thus, if one of the release signals is lost, the pilot-operated hydraulic closing elements preferably close with a certain time delay, which may also depend on the applied / occurring pressures.

[0020] In principle, the hydraulic closing elements are designed to minimize flow resistance and pressure drop during normal operation (in the open state with release signals present) when hydraulic fluid flows into and out of the hydraulic fluid chamber. This is beneficial for the best possible energy efficiency of the electro-hydraulic actuator.

[0021] It is also advantageous if the hydraulic actuator component has a displaceable element via which the hydraulic fluid chambers communicate with each other and wherein the hydraulic actuator component with the lines and the hydraulic pump at least partially form a delivery circuit, so that hydraulic fluid escaping from one hydraulic fluid chamber can flow directly into the other hydraulic fluid chamber via the lines and the hydraulic pump.

[0022] By "immediate" overflow, it is meant in particular that hydraulic fluid flowing out of a hydraulic fluid chamber does not first flow into a hydraulic fluid reservoir to which several hydraulic actuator components are connected, but rather via the hydraulic pump directly into the other hydraulic fluid chamber of the same hydraulic actuator component.

[0023] When using the electro-hydraulic actuator, hydraulic fluid is preferably conveyed in a circular manner in the delivery circuit, in which the movable element in the hydraulic actuator component participates. The term "communication" of the hydraulic fluid chambers specifically means that a change in the volume of one hydraulic fluid chamber always inevitably causes a change in the volume of the other hydraulic fluid chamber. On the one hand, the movable element is moved by the hydraulic fluid. On the other hand, the movable element also transfers the movement of the hydraulic fluid in one of the hydraulic fluid chambers to the other hydraulic fluid chamber, and vice versa. By driving the hydraulic pump in different delivery directions, the movable element can be displaced by the hydraulic fluid.Actuator movements of the actuator component are movements of the movable element and the components connected to it. Preferably, the delivery circuit is not completely self-contained, but rather connected to a hydraulic intermediate circuit via additional hydraulic components. However, this intermediate circuit does not directly participate in the circular delivery of hydraulic fluid in the delivery circuit; rather, it is designed to ensure suitable operating conditions for circular delivery in the delivery circuit. Further explanations of this are provided below, particularly in the description of the figures.Furthermore, it is advantageous if the hydraulic fluid chambers of the hydraulic actuator component have different hydraulic cross sections, so that when the displaceable element is displaced, a delta volume occurs as a change in the total volume of the hydraulic fluid chambers, wherein the hydraulic pump has a two-part pump chamber and a first partial pump chamber connects the lines to form the delivery circuit and wherein a second partial pump chamber is connected to the line to the hydraulic fluid chamber with the larger hydraulic cross section and to a hydraulic fluid container with which the delta volume can be compensated.

[0024] Hydraulic actuator components in which the two corresponding hydraulic fluid chambers have differing hydraulic cross-sections are widespread. They are often referred to as differential components (e.g., differential cylinders). The different volumes arise, for example, simply because one of the two hydraulic fluid chambers accommodates a push rod, which transmits the movement of the movable element to components of a mobile machine (e.g., the arm of an excavator).

[0025] With such hydraulic actuator components, the principle of circular delivery and the delivery circuit is only possible for the portion of the hydraulic fluid that can be accommodated in the hydraulic fluid chamber with the smaller hydraulic cross-section. Any excess fluid escaping from the hydraulic fluid chamber with the larger hydraulic cross-section is referred to here as the "delta volume." The delta volume must not only be discharged when the movable element is moved toward the hydraulic fluid chamber with the larger hydraulic cross-section, causing its volume to decrease. The delta volume must also be supplied when the movable element is moved toward the hydraulic fluid chamber with the smaller hydraulic cross-section, causing the volume of the hydraulic fluid chamber with the larger hydraulic cross-section to increase.

[0026] To achieve this, a hydraulic pump with a two-part pump chamber is proposed here. The first partial pump chamber forms part of the delivery circuit. The first partial pump chamber is dimensioned so that the volume that can flow from one hydraulic fluid chamber to the other hydraulic fluid chamber is pumped with it. The second partial pump chamber serves to pump hydraulic fluid from a hydraulic fluid reservoir into the circuit or to drain it from the circuit into the hydraulic fluid reservoir. This serves to compensate for the delta volume - i.e., to supply or discharge fluid, depending on the direction in which the movable element is moved. Preferably, both partial pump chambers are connected to a common pump drive motor, if necessary via a common shaft.Energy can be added to or removed from the hydraulic fluid flow via both partial pump chambers and then converted (recovered) into electrical energy.

[0027] It is also advantageous if the first line and the second line are each connected to a reservoir for hydraulic fluid which is designed to compensate for functional fluctuations in a minimum system pressure in the closed hydraulic system.

[0028] It is also advantageous if the accumulator is connected to the first line and the second line via further hydraulic closing elements, wherein these further hydraulic closing elements prevent a transmission of an operating pressure generated by the hydraulic pump in one of the two lines to the accumulator.

[0029] Such an accumulator is preferably part of the hydraulic intermediate circuit described above. This accumulator is preferably connected to the lines via additional hydraulic closing elements, which are in particular check valves, through which hydraulic fluid can flow into the lines when a minimum pressure is no longer maintained. However, the accumulator is designed in such a way that leaks in the lines cannot be compensated for by the accumulator, but only functional fluctuations that can occur, for example, due to fluctuating ambient pressures, thermal expansion of the hydraulic fluid, and similar phenomena.

[0030] Preferably, the accumulator is also connected to the delivery circuit in such a way that excessive pressures from the delivery circuit can be released into the accumulator. The accumulator or the hydraulic intermediate circuit are preferably connected to a hydraulic fluid supply, which provides the accumulator and the intermediate circuit with the necessary hydraulic fluid to support the delivery operation.

[0031] Furthermore, it is advantageous if the unlockable hydraulic locking elements have a hydraulic unlocking signal input to which a hydraulic signal line is connected, via which the presence of a hydraulic system pressure of the electro-hydraulic actuator is monitored as a hydraulic unlocking signal.

[0032] The hydraulic signal line is a functional connection implemented with hydraulic and / or hydraulic-mechanical components. The signal-conducting connection can be implemented using any technical means. The signal-conducting connection represents a connection to components in or on which a hydraulic system is present during normal operation of the electro-hydraulic actuator. The hydraulic system pressure is transmitted via the signal-conducting connection to the hydraulic release signal, where it acts as a hydraulic release signal. If the hydraulic system pressure drops or falls below a threshold value, this is transmitted via the signal-conducting connection to the hydraulic release signal. There, the hydraulic release signal is canceled, and the releasable hydraulic locking elements close.

[0033] The hydraulic release signal input is preferably an active surface on the releasable hydraulic locking element, where a minimum pressure must be applied for release to occur. If necessary, the release signal input can also be configured so that a maximum pressure must not be exceeded. The hydraulic release signal would thus be an applied pressure signal within a specified pressure range.

[0034] It is also advantageous if the hydraulic release signal input is connected to the accumulator via the hydraulic signal line in order to monitor the hydraulic system pressure.

[0035] For this purpose, a pressure transmission line preferably exists from the accumulator to the two releasable hydraulic locking elements. If necessary, the pressure transmission line can be designed in several parts. If necessary, the pressure transmission line can also be interrupted by pressure transmission elements that prevent hydraulic fluid from overflowing but transmit pressure changes to the release signal input. A connection between the accumulator and the hydraulic release signal input is, in particular, also a purely functional connection that enables the pressure or pressure changes in the accumulator to be transmitted to the hydraulic release signal input.

[0036] It has been found that using the pressure in the intermediate circuit accumulator is a very efficient parameter that can be used to determine whether there is a fault in the hydraulic components of the electro-hydraulic actuator that justifies or requires the locking of the pilot-operated hydraulic closing elements. Operational pressure fluctuations in the delivery circuit are compensated for by the accumulator. The hydraulic fluid supply preferentially contributes to maintaining a pressure in the accumulator as long as the accumulator (only) compensates for operational fluctuations in the delivery circuit that are not the cause of a fault (leakage, etc.). If fluctuations can no longer be compensated for by the accumulator, it can be assumed that they are fluctuations due to a fault (leakage, etc.). In this case, the pilot-operated hydraulic closing elements must be blocked orTermination of the unlocking is desired. This behavior can be achieved by connecting the accumulator to the hydraulic unlocking signal input.

[0037] It is also advantageous if the unlockable hydraulic closing elements have at least one electrical unlocking signal input to which the electrical signal line is connected, via which the presence of a function signal of the electric hydraulic pump and / or a function signal of a drive power supply and / or a control of the electric hydraulic pump is monitored as an electrical unlocking signal.

[0038] This electrical signal line is preferably also a functional connection, which is preferably at least partially realized with electrical components.

[0039] The electrical release signal is preferably used to monitor whether there is a fault in the electrical components of the electro-hydraulic actuator, for example the absence of the supply voltage of a control system, an interruption of the drive power supply, etc. In design variants, the presence or absence of other voltages and / or signals (in particular multiple voltages) can also be monitored and monitored at the electrical release signal input.

[0040] The electrical release signal is used in particular to monitor whether an overvoltage and / or an undervoltage occurs in the drive power supply of the control system and / or the power electronics in the drive power supply (for example, in an inverter for supplying the electric hydraulic pump with electrical power).

[0041] Preferably, a control unit for self-monitoring of an inverter is present in the drive power supply. Such a control unit preferably outputs a so-called "enable signal," which can be used as an unlocking signal and is connected to the electrical unlocking signal input via a cable.

[0042] Such a control unit in the drive power supply monitors internal signals and states and detects (more or less reliably) a “loss of control”.

[0043] If necessary, setpoint / actual value deviations can also be taken into account as the electrical unlocking signal. These deviations are provided by external (safety) electronics that, for example, monitor the movement of the actuator component. External (safety) electronics are, in particular, electronics that are higher-level than the electro-hydraulic actuator component described here and that are preferably configured to monitor the effects of the electro-hydraulic actuator component in its intended function. If the electro-hydraulic actuator component is used, for example, to actuate an excavator arm, then external (safety) electronics can, for example, be connected to sensors that monitor the movement of the excavator arm and determine whether these movements are being moved as expected and desired following control signals to the electro-hydraulic actuator.

[0044] For example, travel and speed signals can be determined and monitored. Such signals can, for example, be transmitted from external (safety) electronics to the control system of the electric hydraulic pump, where they can be collected and evaluated if necessary. As long as target values ​​or target value ranges for such signals are maintained by actual values ​​of such signals, an electrical unlocking signal is preferably output, which is applied to the electrical unlocking signal input. As soon as such target values ​​and / or target value ranges are exceeded or exceeded by actual values, an electrical unlocking signal is preferably no longer provided. The unlockable hydraulic locking elements are then blocked.

[0045] External (safety) electronics can also be used to evaluate measured values ​​relating to the operation of the electro-hydraulic actuator itself. Pressure sensors, force sensors, acceleration sensors, etc. can be installed on components of the electro-hydraulic actuator to monitor its function. This allows very high safety standards to be maintained.

[0046] The electric hydraulic pump is preferably controlled by a controller. The controller preferably has at least one output stage that drives the electric drive power for the hydraulic pump in response to control signals from higher-level control components of a mobile work machine, so that the hydraulic actuator component performs the desired actuator movements. A supply voltage can, for example, be an input voltage of the output stage, which is used by the controller in response to the control signals to transmit the electric drive power to the hydraulic pump. Electrical parameters that can be determined in the output stage and that are essential for the operation of the electro-hydraulic actuator can also be used as an electrical release signal.

[0047] In preferred embodiments, the electrical unlocking signal is a digital signal formed from various individual unlocking signals, wherein the individual unlocking signals are linked to one another in a suitable manner—for example, with AND operations, so that several individual unlocking signals must be present simultaneously to form the electrical unlocking signal, or with OR operations, so that several individual unlocking signals must be present alternatively to one another to form the electrical unlocking signal. Optionally, a more complex network may exist that forms the electrical unlocking signal from a plurality of individual signals.

[0048] It is particularly advantageous if the hydraulic pump is designed in such a way that it can also act as a generator in order to convert mechanical energy of a hydraulic fluid flow from one port to the other port into electrical energy.

[0049] Particularly preferably, the electro-hydraulic actuator is configured to transmit mechanical energy at the hydraulic actuator component through the lines and via the hydraulic fluid to the electric hydraulic pump and to recuperate it into electrical energy with the hydraulic pump.

[0050] The possibility of operating the hydraulic pump in generator mode has already been explained above in connection with the four-quadrant capability of the electro-hydraulic actuator. The electro-hydraulic actuator described here presents a four-quadrant capable actuator that is capable of recuperation and, at the same time, offers a high level of functional safety (due to the unlockable hydraulic locking elements and their connection to both electrical and hydraulic unlocking signals).

[0051] It is also advantageous if the hydraulic actuator component is a linear actuator.

[0052] The described structure is particularly suitable for providing actuators with which very large linear forces can be generated.

[0053] The electro-hydraulic actuator described here is preferably designed to generate a mechanical power of more than 10 kW [kilowatts].

[0054] Also described here is a mobile work machine comprising at least one described electro-hydraulic actuator. The mobile work machine can be, for example, an excavator or a similar machine. However, the electro-hydraulic actuators described here can also be used in other applications.

[0055] The invention and the technical context of the invention are explained in more detail below with reference to the figures. The figures show preferred embodiments to which the invention is not limited. It should be noted in particular that the figures, and in particular the proportions depicted in the figures, are only schematic. They show:

[0056] Fig. 1 : a first embodiment of a described electro-hydraulic actuator, and

[0057] Fig. 2: a second embodiment of a described electro-hydraulic actuator.

[0058] Fig. 1 shows a variant embodiment of a described electro-hydraulic actuator 1, in which a hydraulic actuator component 3 has hydraulic fluid chambers 4a, 4b with identical hydraulic cross-sections 20a, 20b. The total actuator volume 5 is independent of the position of the displaceable element between the two hydraulic fluid chambers 4a, 4b. Fig. 2 shows a variant embodiment of a described electro-hydraulic actuator 1, in which a hydraulic actuator component 3 has hydraulic fluid chambers 4a, 4b with different hydraulic cross-sections 20a, 20b. The total actuator volume 5 is dependent on the position of the displaceable element between the two hydraulic fluid chambers 4a, 4b and is variable.Such hydraulic actuator components 3 are also called, for example, differential hydraulic actuator components 3 or (in the case of hydraulic cylinders as hydraulic actuator components 3) also "differential cylinders." Such differential hydraulic actuator components 3 are widespread. The invention described here does not fundamentally differ depending on whether the hydraulic actuator component 3 is a differential hydraulic actuator component 3 or not. However, some differences should be noted, so that in Figs. 1 and 2, the electro-hydraulic actuator 1 according to the invention will be described once with a differential hydraulic actuator component 3 and once with a non-differential hydraulic actuator component 3. However, features identical in both embodiments are described together here.

[0059] The electro-hydraulic actuator 1 comprises the hydraulic actuator component 3 and the electric hydraulic pump 2, which is driven by an electric pump drive motor 26. The hydraulic actuator component 3 typically has two hydraulic fluid chambers 4a, 4b, between which a displaceable element 19 is located, which can be moved by filling one hydraulic fluid chamber 4a, 4b and simultaneously emptying the other hydraulic fluid chamber 4b, 4a to generate an actuator movement 24. Thus, large forces can be generated in the hydraulic actuator component 3, which can be used, for example, to drive an excavator arm or a crane arm.

[0060] In the electro-hydraulic actuator 1 described here, both hydraulic fluid chambers 4a, 4b are each connected via a line 7a, 7b to connections 6a, 6b of the electric hydraulic pump 2. The hydraulic actuator component 3 or the two hydraulic fluid chambers 4a, 4b of the hydraulic actuator component 3, the lines 7a, 7b and the electric hydraulic pump 2 together form a delivery circuit 10. The electric hydraulic pump 2 can be used to build up pressure at one of its connections 6a, 6b and to provide hydraulic fluid under pressure at this connection 6a, 6b, so that the hydraulic fluid flows via the respective line 7a, 7b into the respective hydraulic fluid chamber 4a, 4b of the actuator component.The hydraulic pump 2 delivers hydraulic fluid that is made available to it at the other connection 6b, 6a and is therefore drawn from the other hydraulic fluid chamber 4b, 4a via the other line 7b, 7a. The hydraulic pump 2 can be operated optionally in both delivery directions, i.e. it can supply hydraulic fluid under pressure to the first connection 6a or to the second connection 6b and thus generate actuator movements 24 in different directions with the hydraulic actuator component 3. In this way, the electro-hydraulic actuator 1 can convert electrical energy into mechanical energy, which is made available to the hydraulic actuator component 3. The electrical energy is first converted into hydraulic energy by the electric hydraulic pump 2 and then into mechanical energy by the hydraulic actuator component 3 with the actuator movement 24.The actuator movement 24 can be used, for example, to move an excavator bucket driven by the hydraulic actuator component 3. The electric hydraulic pump 2 operates in a so-called conveying mode. The pump drive motor 26 is electrically driven. This is preferably possible in both conveying directions.

[0061] With the aid of the electro-hydraulic actuator 1, it is preferably also possible to convert mechanical energy of the actuator movement 24 into electrical energy. First, the mechanical energy of the actuator movement 24 is converted into hydraulic energy by the actuator component 3 and then converted or recuperated into electrical energy by the electric hydraulic pump 2 or the electric pump drive motor 26. This can be used, for example, to convert the potential energy of an excavator bucket driven by the hydraulic actuator component 3 into electrical energy. The electric hydraulic pump 2 is then operated in what is known as a generator mode. This is preferably also possible in both conveying directions.

[0062] An electric hydraulic pump 2 that can operate in both delivery mode and generator mode is also referred to as 4-quadrant capable. The delivery circuit 10 formed by the lines 7a, 7b, the hydraulic pump 2, and the hydraulic actuator component 3, or their hydraulic fluid chambers 4a, 4b, can thus be operated in both directions, delivery mode or generator mode. The electro-hydraulic actuator 1 or the delivery circuit, and in particular the lines 7a, 7b, are connected to a hydraulic intermediate circuit 25.The hydraulic intermediate circuit 25 has only an indirect function for the generation of mechanical energy at the hydraulic actuator component 3 from electrical energy and the recuperation of mechanical energy at the hydraulic actuator component 3 into electrical energy, namely to ensure suitable hydraulic conditions in the conveying circuit 10 so that the conveying operation and the generator operation are both possible with the highest possible efficiency of the conversion of electrical energy into mechanical energy and vice versa.

[0063] The intermediate circuit 25 comprises a plurality of additional hydraulic components 9, the most important of which will be briefly explained here. The hydraulic intermediate circuit 25 is connected to the lines 7a, 7b via additional hydraulic closing elements 12a, 12b. The additional closing elements 12a, 12b allow hydraulic fluid to flow into the delivery circuit 10 if the pressure in the delivery circuit 10 in one of the two lines 7a, 7b is too low. However, the hydraulic intermediate circuit 25 is configured such that hydraulic fluid losses above threshold values ​​in the delivery circuit 10 are not compensated, but only fluctuations acceptable during normal operation.

[0064] The hydraulic intermediate circuit 25 preferably has an accumulator 11, which holds a reservoir of hydraulic fluid in order to receive hydraulic fluid from the delivery circuit 10 via the closing elements 12a, 12b and the pressure relief, or to release it to the delivery circuit 10, and to maintain the conditions suitable for operation there. The intermediate circuit 25 and in particular the accumulator 11 are supplied with hydraulic fluid, for example, by a hydraulic fluid supply 18. At the connection between the hydraulic fluid chambers 4a, 4b and the lines 7a, 7b, there is a releasable hydraulic closing element 8a, 8b, which is in particular a check valve. When this releasable hydraulic closing element 8a, 8b is closed, hydraulic fluid can no longer escape from the hydraulic fluid chambers 4a, 4b. In this way, the hydraulic actuator component 3 is fixed.The unlockable hydraulic closing elements 8a, 8b thus ensure that the hydraulic actuator component 3 or components driven thereby (such as an excavator bucket) do not carry out any undesired (uncontrolled) movements in the event of malfunctions of the hydraulic actuator component 3 or other parts of a mobile work machine 15.

[0065] The releasable hydraulic locking elements 8a, 8b are configured such that they are closed unless two independent unlocking signals are present, namely an electrical unlocking signal and a hydraulic unlocking signal. The electrical unlocking signal and the hydraulic unlocking signal are thus linked to each other at the releasable hydraulic locking elements 8a, 8b, or preferably by the design of the releasable hydraulic locking elements 8a, 8b, in the manner of a logical AND operation. The releasable hydraulic locking elements 8a, 8b preferably have a hydraulic unlocking signal input 13 for the hydraulic unlocking signal and an electrical unlocking signal input 14 for the electrical unlocking signal.

[0066] The hydraulic release signal is present when the hydraulic components of the electro-hydraulic actuator 1 are functioning properly. The hydraulic release signal is canceled, for example, if there is a leak in the first line 7a and / or the second line 7b. The hydraulic release signal is preferably derived from the previously described accumulator 11 of the hydraulic intermediate circuit 25. If the pressure in the accumulator 11 is above a predetermined threshold pressure, the hydraulic release signal is present. The pressure in the accumulator 11 can be used to monitor the tightness of the entire system consisting of the delivery circuit 10 and the intermediate circuit 25. If the pressure in the accumulator 11 is above a threshold pressure, it can be determined that there is no leak in the delivery circuit 10 and / or the intermediate circuit 25.Preferably, the accumulator 11 is connected directly to hydraulic unlocking signal inputs 13 of the unlockable hydraulic closing elements 8a, 8b via a hydraulic signal line 27.

[0067] The electrical unlocking signal is present when the electrical components of the electro-hydraulic actuator 1 and, if applicable, the higher-level components of the mobile work machine 15 are functioning properly. The electrical unlocking signal can be obtained, for example, from an electrical controller 17 of the electric hydraulic pump 2, which controls a pump drive motor 26 of the electric hydraulic pump 2. Preferably, the electrical controller 17 is configured to generate the electrical unlocking signal from internal electrical variables of the electrical controller 17, a drive power supply 16, and, if applicable, from further variables that the electrical controller receives from external safety electronics.The electrical unlocking signal can preferably be formed from individual unlocking signals that are interconnected with suitable operations ("AND" operations or "OR" operations) to form an electrical unlocking signal that reflects the full functionality of the electrical components of the electro-hydraulic actuator 1. When the electrical unlocking signal is applied to the unlockable hydraulic closing elements 8a, 8b, it can be assumed that the electrical components of the electro-hydraulic actuator 1 (in particular, the pump drive motor 26, the controller 17, and the drive power supply 16) are fully functional. The electrical unlocking signal is preferably forwarded directly to electrical unlocking signal inputs 14 of the unlockable hydraulic closing elements 8a, 8b via an electrical signal line 28.The controller 17 is preferably configured to supply electrical energy to the electro-hydraulic actuator 1 by a drive power supply 16, which provides a supply current or a supply voltage. Preferably, the controller 17 and the drive power supply 16 are also capable of recuperation. This means that energy recuperated by the electro-hydraulic actuator 1 can be fed back into the drive power supply 16.

[0068] The above explanations describe the functioning of the electro-hydraulic actuator 1, initially based on the embodiment shown in Fig. 1. The electro-hydraulic actuator 1 shown in Fig. 2 with a differential cylinder as actuator component 3 has further (sometimes slightly different) properties, which will be briefly discussed here.

[0069] In the embodiment shown in Fig. 2, the electric hydraulic pump 2 preferably has a first partial pump chamber 21a and a second partial pump chamber 21b. The different hydraulic cross-sections 20a, 20b result in a delta volume 22, which is shown here at the inlet of the second partial pump chamber 21b because it is pumped through the second partial pump chamber 21b during operation of the electric-hydraulic actuator 1. Preferably, both partial pump chambers 21a, 21b are driven by a common pump drive motor 26. The first partial pump chamber 21a essentially corresponds to the pump chamber (not shown separately) of the electric hydraulic pump 2 according to the embodiment shown in Fig. 1. This partial pump chamber 21a is connected to the two lines 7a, 7b and, together with the lines 7a, 7b and the hydraulic fluid chambers 4a, 4b of the hydraulic actuator component 3, forms the delivery circuit 10.

[0070] The second partial pump chamber 21b is connected only to the first line 7a to the first hydraulic fluid chamber 4a, which has the larger first hydraulic cross-section 20a. The second partial pump chamber 21b is also connected to a hydraulic fluid reservoir 23, into which hydraulic fluid is drained or from which hydraulic fluid is taken up during operation of the electro-hydraulic actuator 1, depending on the flow direction. The hydraulic fluid reservoir 23 can also be pressurized if necessary in order to store hydraulic energy in the hydraulic fluid. In this case, the recuperation of mechanical energy from the actuator movement 24 into electrical energy is preferably also possible.

[0071] List of reference symbols

[0072] 1 electric-hydraulic actuator

[0073] 2 electric hydraulic pumps

[0074] 3 hydraulic actuator components

[0075] 4a first hydraulic fluid chamber

[0076] 4b second hydraulic fluid chamber

[0077] 5 Total actuator volume

[0078] 6a first connection

[0079] 6b second connection

[0080] 7a first line

[0081] 7b second line

[0082] 8a first unlockable hydraulic locking element

[0083] 8b second unlockable hydraulic locking element

[0084] 9 additional hydraulic components

[0085] 10 Support group

[0086] 11 storage

[0087] 12a first additional hydraulic closing element

[0088] 12b second additional hydraulic closing element

[0089] 13 hydraulic release signal input

[0090] 14 electrical unlocking signal input

[0091] 15 mobile work machines

[0092] 16 Drive power supply

[0093] 17 Control

[0094] 18 Hydraulic fluid supply

[0095] 19 movable element

[0096] 20a first hydraulic cross-section

[0097] 20b second hydraulic cross-section

[0098] 21a first partial pump chamber

[0099] 21 b second partial pump chamber

[0100] 22 Delta volume

[0101] 23 Hydraulic fluid reservoir Actuator movement Hydraulic intermediate circuit Pump drive motor Hydraulic signal line Electrical signal line

Claims

Claims Electro-hydraulic actuator (1) comprising at least one bidirectionally operable hydraulic pump (2) for conveying hydraulic fluid with two connections (6a, 6b), which is alternately designed for the provision and / or removal of hydraulic fluid, and with a hydraulic actuator component (3) with two hydraulic fluid chambers (4a, 4b) which can be pressurised with hydraulic fluid to actuate the hydraulic actuator component (3), wherein filling one of the hydraulic fluid chambers (4a, 4b) with hydraulic fluid simultaneously causes a displacement of hydraulic fluid from the other hydraulic fluid chamber (4b, 4a),wherein a first connection (6a) of the electric hydraulic pump (2) is connected by a first line (7a) to a first hydraulic fluid chamber (4a) of the hydraulic actuator component (3), and a second connection (6b) of the hydraulic pump (2) is connected by a second line (7b) to a second hydraulic fluid chamber (4b) of the hydraulic actuator component (3), wherein a first releasable hydraulic closing element (8a) is arranged between the first hydraulic fluid chamber (4a) and the first line (7a), and a second releasable hydraulic closing element (8b) is arranged between the second hydraulic fluid chamber (4b) and the second line (7b), wherein the releasable hydraulic closing elements (8a, 8b) prevent an unwanted outflow of hydraulic fluid from the hydraulic fluid chambers (4a, 4b), wherein the releasable hydraulic closing elements (8a, 8b) are configured in such a way thatthat for unlocking, both an electrical unlocking signal and a hydraulic unlocking signal must be applied to the unlockable hydraulic closing elements (8a, 8b). The electro-hydraulic actuator (1) according to claim 1, wherein the unlockable hydraulic closing elements (8a, 8b) are unlockable check valves. Electro-hydraulic actuator (1) according to claim 1 or 2, wherein the hydraulic actuator component (3) has a displaceable element (19) via which the hydraulic fluid chambers (4a, 4b) communicate with one another and wherein the hydraulic actuator component (3) with the lines (7a, 7b) and the electric hydraulic pump (2) at least partially form a delivery circuit (10) so that hydraulic fluid emerging from one hydraulic fluid chamber (4a, 4b) can flow directly into the other hydraulic fluid chamber (4b, 4a) via the lines (7a, 7b) and the electric hydraulic pump (2).Electro-hydraulic actuator (1) according to claim 3, wherein the hydraulic fluid chambers (4a, 4b) of the hydraulic actuator component (3) have mutually differing hydraulic cross-sections (20a, 20b), so that upon displacement of the displaceable element (19), a delta volume (22) occurs as a change in the total volume of the hydraulic fluid chambers (4a, 4b), wherein the electric hydraulic pump (2) has a two-part pump chamber and a first partial pump chamber (21a) connects the lines (7a, 7b) to form the delivery circuit (10), and wherein a second partial pump chamber (21b) is connected to the line (7a, 7b) to the hydraulic fluid chambers (4a, 4b) with the larger hydraulic cross-section (20a, 20b) and to a hydraulic fluid container (23) with which the delta volume (22) can be compensated.The electro-hydraulic actuator (1) according to claim 3 or 4, wherein the first line (7a) and the second line (7b) are each connected to a reservoir (11) for hydraulic fluid, which reservoir is configured to compensate for functional fluctuations in a minimum system pressure in the closed hydraulic system. The electro-hydraulic actuator (1) according to claim 5, wherein the reservoir (11) is connected to the first line via further hydraulic closing elements (12a, 12b). (7a) and the second line (7b), wherein these further hydraulic closing elements (12a, 12b) prevent a transmission of an operating pressure generated by the electric hydraulic pump (2) in one of the two lines (7a, 7b) to the accumulator (11). The electro-hydraulic actuator (1) according to any one of the preceding claims, wherein the releasable hydraulic closing elements (8a, 8b) have a hydraulic release signal input (13) to which a hydraulic signal line (27) is connected, via which the presence of a hydraulic system pressure of the electro-hydraulic actuator (1) is monitored as a hydraulic release signal. The electro-hydraulic actuator (1) according to claim 7, wherein the hydraulic release signal input (13) is connected to the accumulator (11) via a hydraulic signal line (27) in order to monitor the hydraulic system pressure.An electro-hydraulic actuator (1) according to one of the preceding claims, wherein the releasable hydraulic closing elements (8a, 8b) have an electrical release signal input (14) to which an electrical signal line (28) is connected, via which the presence of a function signal from the electric hydraulic pump (2) and / or a function signal from a drive power supply (16) and / or a controller (17) of the electric hydraulic pump (2) is monitored as an electrical release signal. An electro-hydraulic actuator (1) according to one of the preceding claims, wherein the electric hydraulic pump (2) is configured such that it can also act as a generator in order to convert mechanical energy of a hydraulic fluid flow from one connection (6a, 6b) to the other connection (6b, 6a) into electrical energy. Electro-hydraulic actuator (1) according to one of the preceding claims, configured to transmit mechanical energy to the hydraulic actuator component (3) through the lines (7a, 7b) and via the hydraulic fluid to the electric hydraulic pump (2) and to recuperate it into electrical energy with the electric hydraulic pump (2). Electro-hydraulic actuator (1) according to one of the preceding claims, wherein the hydraulic actuator component (3) is a linear actuator. Mobile work machine (15) comprising at least one electro-hydraulic actuator (1) according to one of the preceding claims. - so

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