Electro-hydraulic Actuator

Abstract

The invention relates to an electro-hydraulic actuator (1) comprising at least one bidirectionally operable hydraulic pump (2) for conveying hydraulic fluid, said hydraulic pump having two connection points (6a, 6b) designed for alternately supplying and / or removing hydraulic fluid, and a hydraulic actuator component (3) having two hydraulic fluid chambers (4a, 4b) into which hydraulic fluid can be supplied in order to operate the hydraulic actuator component (3), wherein filling one of the hydraulic fluid chambers (4a, 4b) with hydraulic fluid simultaneously causes displacement of hydraulic fluid from the other hydraulic fluid chamber (4b, 4a), and wherein a first connection point (6a) of the hydraulic pump (2) is connected to a first hydraulic fluid chamber of the hydraulic actuator component (3) by a first line (7a). a first connection point (6b) of the electro-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 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), the releasable hydraulic closing elements (8a, 8b) prevent undesired outflow of hydraulic fluid from the hydraulic fluid chambers (4a, 4b), and the releasable hydraulic closing elements (8a, 8b) are designed such that for release, both an electrical release signal and a hydraulic release signal must be present at the releasable hydraulic closing elements (8a, 8b).

Description

[Technical Field]

[0001] The present invention relates to electrohydraulic actuators, and more particularly to linear actuators capable of producing linear actuator movement. The electrohydraulic actuator includes a hydraulic actuator component and an electrically driven hydraulic pump that provides hydraulic fluid to drive the hydraulic actuator component.

[0002] Specifically, the electrohydraulic actuators described herein can be operated in up to four quadrants, i.e., the actuators are four-quadrant capable. Four-quadrant capability means that the electrohydraulic actuator can be driven in two directions of motion using electrical energy to produce actuator motion, and additionally, recovery is possible in which mechanical energy can be extracted from the actuator motion and converted to electrical energy in the two directions of motion.

[0003] Such electro-hydraulic actuators are particularly suited to electrifying and improving the energy efficiency of mobile machines that include hydraulic components. The four-quadrant capability of such linear actuators allows a significant amount of energy to be recovered as electrical energy during operation of the mobile machine. This is possible, for example, in situations where an excavator shovel driven by an electro-hydraulic actuator is being lowered. In that case, the potential energy of the excavator shovel can be dissipated into a hydraulic fluid flow using hydraulic actuator components. Energy can be extracted from this hydraulic fluid flow and converted into electrical energy using an electro-hydraulic pump in generator mode. [Background technology]

[0004] Hydraulic actuators are usually safety-relevant components. For example, in the case of hydraulic actuators on mobile machines, it must be ensured that in the event of a fault, no unwanted or uncontrolled movement of the mobile machine components occurs. For example, a crane arm or an excavator bucket must not fall uncontrolled in the event of a fault. Resilience to such scenarios is addressed in the field of "functional safety". Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to describe an electrohydraulic actuator which has particularly good behavior with regard to operational safety in the event of possible faults and at the same time has an advantageous design. [Means for solving the problem]

[0006] This object is achieved by the present invention according to the features of the independent claims. Further advantageous embodiments are also provided in the independently formulated claims and in the present description and in particular in the description of the drawings. It should be noted that a person skilled in the art can combine individual features with one another in a technically significant way, resulting in further embodiments of the invention.

[0007] The invention relates to an electro-hydraulic actuator having at least one bidirectionally operable electro-hydraulic pump for conveying hydraulic fluid, said pump having two connection points designed to alternately supply and / or remove hydraulic fluid, and a hydraulic actuator component having two hydraulic fluid chambers into which hydraulic fluid can be supplied to operate the hydraulic actuator component, the filling of one of the hydraulic fluid chambers with hydraulic fluid simultaneously causing the displacement of hydraulic fluid from the other hydraulic fluid chamber, the first connection point of the hydraulic pump being connected to the hydraulic actuator component by a first line. an electro-hydraulic actuator is described in which a first connection point of the hydraulic pump is connected to a first hydraulic fluid chamber of the hydraulic actuator component by a second line, and a second connection point of the hydraulic pump is connected to a second hydraulic fluid chamber of the hydraulic actuator component by a second line, a first releasable hydraulic closing element is disposed between the first hydraulic fluid chamber and the first line, and a second releasable hydraulic closing element is disposed between the second hydraulic fluid chamber and the second line, the releasable hydraulic closing elements prevent undesired outflow of hydraulic fluid from the hydraulic fluid chambers, and the releasable hydraulic closing elements are disposed such that for release, both an electrical release signal and a hydraulic release signal need to be applied to the releasable hydraulic closing element.

[0008] The structure and design of the electrohydraulic actuator, in particular the structural options for the hydraulic actuator component and the electrohydraulic pump, are described in detail below. In principle, both the hydraulic pump and the actuator component each have two connection points for hydraulic fluid (each serving as an inlet or outlet), which are preferably connected to each other via a line, thereby forming a delivery circuit for the hydraulic fluid. Alternatively, hydraulic pumps and actuator components of various designs can be used. It should be noted here that a hydraulic actuator component can also be a parallel connection of several hydraulic (individual) actuator components. For example, a hydraulic actuator component can be a pair of hydraulic cylinders working side by side (in parallel), which, together with an electrohydraulic pump, form an electrohydraulic actuator, and the pair of hydraulic cylinders is called, for example, a tandem cylinder. In this case, the line from the hydraulic pump to the hydraulic (individual) actuator component is preferably branched, and the branch can be understood as part of the actuator component. In principle, it is possible to divide an actuator component into (individual) actuator components, just as it is possible to divide a hydraulic pump into (individual) hydraulic pumps.

[0009] In order to achieve particularly good protection in terms of functional safety by means of the releasable hydraulic closing elements, it is advantageous if the releasable hydraulic closing elements are arranged directly at the transition of the line to the hydraulic fluid chamber of the actuator component, in which case several releasable hydraulic closing elements arranged at corresponding connection points of (individual) actuator components of a hydraulic (overall) actuator component connected in parallel with one another can also be understood as a (common) releasable hydraulic closing element.

[0010] Therefore, the releasable hydraulic closing element is arranged between the line connecting the actuator component to the hydraulic pump and the hydraulic fluid chamber. The releasable hydraulic closing element is designed to hydraulically isolate the hydraulic fluid chamber of the actuator component from the line. When the releasable hydraulic closing element is locked or unlocked, leakage of hydraulic fluid from the hydraulic fluid chamber can be reliably prevented by means of the releasable hydraulic closing element. The releasable hydraulic closing elements are designed to be locked in the idle state (when no unlocking signal is acting on them).

[0011] The term "released" means that the releasable hydraulic closing element is open. In this situation, the releasable hydraulic closing element preferably has no or little effect on the hydraulic fluid flow in the line or into or out of the hydraulic fluid chamber. To release the releasable hydraulic closing element, both release signals (electrical release signal and hydraulic release signal) must be applied to the releasable hydraulic closing element. In normal operation, the hydraulic closing element is released and therefore both release signals (electrical release signal and hydraulic release signal) are applied to the releasable hydraulic closing element. At least one of the release signals can be applied indirectly, for example by configuring the releasable hydraulic closing element and the electro-hydraulic actuator such that the hydraulic release signal is only sent to the releasable hydraulic closing element if the electrical release signal is also present.

[0012] The arrangement of the releasable hydraulic closing element between the line connecting the actuator component to the hydraulic pump and the hydraulic fluid chamber satisfies all or some of the following characteristics: Advantageously, no further branches to other hydraulic components, such as expansion tanks, intermediate circuits, etc., are provided between the releasable hydraulic closing element and the hydraulic fluid chamber. However, compensation lines can be provided for other parallel cylinders which together form an actuator component. For example, such compensation lines are common between two individual cylinders in a tandem cylinder arrangement, such as those often used in the lowest stages of excavator arms. The hydraulic fluid retaining portion of the releasable hydraulic closing element facing the hydraulic fluid chamber preferably has a very high leakage resistance. Preferably, such a hydraulic fluid retaining portion is not made of a flexible material such as a hose, but may be entirely made of metal. In the absence of both the electrical release signal required for release and the hydraulic release signal required for release, the hydraulic closing element is advantageously configured to close regardless of other boundary conditions. Such a further boundary condition is, for example, the maximum allowable pressure in the actuator component, exceeding which could result in the actuator component's rupture. Another such boundary condition is, for example, the maximum allowable braking acceleration of the actuator component, which, due to mass inertia, could cause forces and / or torques on the moving machine that exceed allowable limits. Many other such boundary conditions typically exist. Such boundary conditions are not taken into account when closing the hydraulic closing element as a result of the loss of one of the release signals. The locking is performed to secure the electrohydraulic actuator regardless of the consequences that could result if such boundary conditions are exceeded or violated. However, the hydraulic closing element preferably has an additional function integrated into the valve that ensures that such boundary conditions are not actually exceeded. Such an additional function is, in particular, a bypass function that operates above a certain limit pressure and is described in more detail below.

[0013] It is particularly advantageous if the releasable hydraulic closing element is a releasable check valve.

[0014] Preferably, the releasable hydraulic closing element functions as a check valve, particularly within the operating pressure range, in the absence of the aforementioned release signal. This means that in the operating pressure range, hydraulic fluid is allowed to flow into the hydraulic fluid chamber but cannot flow out. Here, "operating pressure range" refers to the pressure range of hydraulic fluid in the lines and hydraulic fluid chambers that normally occurs during operation of the electrohydraulic actuator. Pressure peaks, for example, caused by sudden valve closure and / or acceleration of the hydraulic fluid volume in the lines, are preferably not due to the operating pressure range. Such pressure peaks are preferably outside the operating pressure range. Preferably, the releasable hydraulic closing element has an additional function in the form of a bypass flow path and / or bypass function, which opens at pressures above the operating pressure range and then, despite functioning as a check valve in the operating pressure range, allows a limited amount of hydraulic fluid to pass through in order to buffer such pressure peaks and prevent the operating pressure range from being permanently overwritten. Such a function is primarily used for component protection, for example to prevent hydraulic actuator components from bursting due to pressure peaks occurring in the hydraulic fluid chamber as a result of sudden deceleration due to closure of a releasable hydraulic closing element.

[0015] An additional or bypass function can, if necessary, be realized by a pressure relief valve working in parallel with the hydraulic closing element, which opens at pressures above the actuation pressure limit and thus allows a certain braking distance for the actuator component. At pressures within the actuation pressure range or below the actuation pressure limit, such a pressure relief valve is preferably inoperable. If the closing element closes as quickly as possible, so that the actuation pressure limit is exceeded, the parallel acting pressure relief valve opens, for example, in such a way as to achieve a compromise between the "braking distance" and the load on the actuator component (as far and / or as long as possible).

[0016] Another alternative to a pressure relief valve in the bypass is that the releasable hydraulic closing element can be set for damped closure, which can also reduce pressure peaks. Thus, if one of the release signals is omitted, the releasable hydraulic closing element preferably closes with a specific time delay, which can also depend on the applied / resulting pressure.

[0017] In principle, the hydraulic closing element is designed so that during normal operation (open state with release signal applied) the flow resistance and pressure drop of the hydraulic fluid entering and leaving the hydraulic fluid chamber are as small as possible, which is advantageous for the greatest possible energy efficiency of the electrohydraulic actuator.

[0018] It is also advantageous if the hydraulic actuator component has a displaceable element via which the hydraulic fluid chambers communicate with one another and which together with the line and the hydraulic pump at least partially form a delivery circuit, such that hydraulic fluid leaving one hydraulic fluid chamber can flow directly into the other hydraulic fluid chamber via the line and the hydraulic pump.

[0019] In this case, the concept of "directly" flowing into a chamber means in particular that the hydraulic fluid flowing out of the hydraulic fluid chamber does not first flow into a reservoir for hydraulic fluid to which several hydraulic actuator components are connected, but rather flows directly into another hydraulic fluid chamber of the same hydraulic actuator component via a hydraulic pump.

[0020] Therefore, when using an electrohydraulic actuator, there is preferably a circulating hydraulic fluid in the delivery circuit, which involves a displaceable element in the hydraulic actuator component. The term "communication" between the hydraulic fluid chambers means, in particular, that a change in the volume of one hydraulic fluid chamber always inevitably results in a change in the volume of the other hydraulic fluid chamber. On the one hand, the displaceable element is moved by the hydraulic fluid. On the other hand, the displaceable element transfers the movement of the hydraulic fluid in one hydraulic fluid chamber to the other hydraulic fluid chamber, and vice versa. By driving the hydraulic pumps in different delivery directions, the displaceable element can be moved by the hydraulic fluid. The movement of the actuator of the actuator component is the movement of the displaceable element and the components connected to it. Preferably, the delivery circuit is not completely self-contained, but is connected to an intermediate hydraulic circuit via other hydraulic components. However, this intermediate circuit is not directly involved in the circulating hydraulic fluid in the delivery circuit itself, but rather is configured to ensure appropriate operating conditions for the circulating hydraulic fluid in the delivery circuit. Further explanation is provided below, particularly in the description of the drawings.

[0021] Furthermore, it is advantageous if the hydraulic fluid chambers of the hydraulic actuator component have different hydraulic cross sections, whereby when the displaceable element is displaced a differential volume occurs as a change in the total volume of the hydraulic fluid chambers, and if the hydraulic pump has a two-part pump chamber, and a first partial pump chamber is connected with lines to form a delivery circuit, and a second partial pump chamber is connected with a line to a hydraulic fluid chamber with a larger hydraulic cross section and to a hydraulic fluid reservoir that can compensate for the differential volume.

[0022] Hydraulic actuator components are common, in which two corresponding hydraulic fluid chambers have different hydraulic cross sections. These are usually called differential components (e.g., differential cylinders). The different volumes result, for example, from the fact that one of the two hydraulic fluid chambers houses a feed rod that transmits the movement of a displaceable element to a movable machine component (e.g., to the arm of an excavator).

[0023] For this type of hydraulic actuator component, the principle of circulating delivery and delivery circuits is only possible for that portion of the hydraulic fluid that can be absorbed in the hydraulic fluid chamber with the smaller hydraulic cross section. The additional amount of hydraulic fluid that leaks from the hydraulic fluid chamber with the larger hydraulic cross section is referred to here as the "differential volume." The differential volume must not only be discharged when the displaceable element is moved towards the hydraulic fluid chamber with the larger hydraulic cross section, reducing its volume. The differential volume must also be supplied when the displaceable element is moved towards the hydraulic fluid chamber with the smaller hydraulic cross section, increasing the volume of the hydraulic fluid chamber with the larger hydraulic cross section.

[0024] To achieve this, a hydraulic pump having two pump chambers is proposed. The first pump chamber forms part of a delivery circuit. The first pump chamber is dimensioned so that the volume that can flow from one hydraulic fluid chamber to the other is conveyed therethrough. The second pump chamber is used to pump hydraulic fluid from a hydraulic fluid reservoir into the circuit or to pump hydraulic fluid from the circuit back into the hydraulic fluid reservoir. This serves to equalize the differential volume, i.e., supply or discharge, depending on the direction of movement of the displaceable element. Preferably, both pump chambers are connected to a common pump drive motor, possibly via a common shaft. Energy can be both supplied to and extracted from the hydraulic fluid flow via both pump chambers for conversion into electrical energy (recovery).

[0025] It is also advantageous if the first line and the second line are each connected to a reservoir of hydraulic fluid, the reservoir being set to compensate for function-related fluctuations in the minimum system pressure in the closed hydraulic system.

[0026] It is also advantageous if the reservoir is connected to the first line and the second line via further hydraulic shut-off elements, which prevent the operating pressure generated by the hydraulic pump in one of the two lines from being transmitted to the reservoir.

[0027] Such a reservoir is preferably part of the above-mentioned hydraulic intermediate circuit. Preferably, this reservoir is connected to the line via further hydraulic closing elements, in particular check valves, through which hydraulic fluid can enter the line if the minimum pressure is no longer maintained. However, this reservoir is designed so that leakage in the line cannot be compensated for via the reservoir, but only function-related fluctuations that may occur due to, for example, fluctuations in ambient pressure, the thermal expansion behavior of the hydraulic fluid and similar phenomena are compensated for.

[0028] Preferably, the reservoir is also connected to the delivery circuit so that any excessively high pressure can also be vented from the delivery circuit to the reservoir. The reservoir and the hydraulic intermediate circuit are preferably connected to a hydraulic fluid supply device which provides the reservoir and the intermediate circuit with the amount of hydraulic fluid required to support the pumping action.

[0029] It is also advantageous if the releasable hydraulic closing element has a hydraulic release signal input, to which a hydraulic signal line is connected, and via which the presence of hydraulic system pressure of the electrohydraulic actuator is monitored as a hydraulic release signal.

[0030] The hydraulic signal line is a functional connection realized with hydraulic and / or hydromechanical components. The signal transmission connection can be implemented using any technical means. The signal transmission connection represents a connection to a component in or on which a hydraulic system resides during normal operation of the electro-hydraulic actuator. The hydraulic system pressure is transmitted via the signal transmission connection to the hydraulic release signal, which then functions as a hydraulic release signal. If the hydraulic system pressure drops or falls below a threshold value, this is transmitted via the signal transmission connection to the hydraulic release signal. The hydraulic release signal then disappears and the releasable hydraulic closing element closes.

[0031] The hydraulic release signal input is preferably an active surface on the releasable hydraulic closure element that must have a minimum pressure applied to it for release to occur. If desired, the release signal input can be set to not exceed a maximum pressure. Thus, the hydraulic release signal is an applied pressure signal within a specified pressure range.

[0032] It is also advantageous if the hydraulic release signal input is connected via a hydraulic signal line to a reservoir for monitoring hydraulic system pressure.

[0033] Preferably, there is a pressure transmission line from the reservoir to the two releasable hydraulic closing elements. If necessary, the pressure transmission line can be made in several parts. If necessary, the pressure transmission line can also be interrupted by a pressure transmission element that prevents hydraulic fluid from overflowing but transmits pressure changes to the release signal input. The connection between the reservoir and the hydraulic release signal input is in particular also a purely functional connection that allows the pressure or pressure changes in the reservoir to be transmitted to the hydraulic release signal input.

[0034] Using the pressure in the reservoir of the intermediate circuit has proven to be a very effective parameter that can be used to determine whether a fault exists in the hydraulic components of the electrohydraulic actuator that justifies or requires the closure of a releasable hydraulic closing element. Operation-related pressure fluctuations in the delivery circuit are compensated for by the reservoir. The hydraulic fluid supply preferably contributes to maintaining the pressure in the reservoir insofar as the reservoir compensates (only) for operation fluctuations in the delivery circuit that are not the cause of a fault (such as a leak). When a fluctuation can no longer be compensated for by the reservoir, it can be assumed that the fluctuation is due to a fault (such as a leak). In this case, it is desirable to block the releasable hydraulic closing elements or to stop their release. This behavior can be achieved by connecting the reservoir to the hydraulic release signal input.

[0035] It is also advantageous if the releasable hydraulic closing element has at least one electrical release signal input, an electrical signal line is connected to the at least one electrical release signal input, and via the electrical signal line the presence of a function signal of the electrohydraulic pump and / or a function signal of the drive power supply and / or control device of the electrohydraulic pump is monitored as an electrical release signal.

[0036] Preferably, this electrical signal line is also a functional connection, which is preferably realized at least in part using electrical components.

[0037] The electrical release signal is preferably used to monitor whether there is a fault in the electrical components of the electro-hydraulic actuator, e.g., absence of supply voltage to the control unit, interruption of drive power supply, etc. In an embodiment, the presence or absence of other voltages and / or signals (in particular some voltages) may also be monitored and monitored at the electrical release signal input.

[0038] In particular, the electrical release signal is used to monitor whether overvoltages and / or undervoltages occur in the drive power supply of the control unit and / or in the power electronics of the drive power supply (e.g. on an inverter for powering an electrohydraulic pump).

[0039] Preferably, there is a control unit for self-monitoring the inverter of the drive power supply. Preferably, such a control unit emits a so-called "enable signal", which can be used as a release signal connected via a line to the electrical release signal input.

[0040] Such a control unit within the drive power supply monitors internal signals and conditions to detect (with some degree of certainty) a "loss of control."

[0041] If desired, a setpoint / actual deviation provided by, for example, external (safety) electronics monitoring the movement of the actuator component may also be considered as an electrical disengagement signal. An external (safety) electronic system is particularly an electronic system that supervises the electro-hydraulic actuator component described herein and is preferably configured to monitor the effect of the electro-hydraulic actuator component on its intended function. If the electro-hydraulic actuator component is used, for example, to operate an excavator arm, the external (safety) electronics may be connected, for example, to sensors that monitor the movements of the excavator arm and determine whether these movements are occurring as expected and desired as a result of control signals to the electro-hydraulic actuator.

[0042] For example, travel and speed signals can be determined and monitored. Such signals can be transmitted, for example, from external (safety) electronics to the control unit of the electro-hydraulic pump, where they can be collected and evaluated as required. As long as the target value or target value range of such signals is maintained by the actual value of such signals, an electrical release signal is preferably output and an electrical release signal is applied to the electrical release signal input. As soon as the actual value exceeds or deviates from such target value and / or target value range, the electrical release signal is preferably no longer provided. In that case, the releasable hydraulic closing element is blocked.

[0043] External (safety) electronics can preferably also be used to evaluate measurements related to the operation of the electrohydraulic actuator itself. For example, pressure sensors, force sensors, acceleration sensors, etc. can be provided on the components of the electrohydraulic actuator to monitor their functioning. This makes it possible to maintain very high safety standards.

[0044] The electrohydraulic pump is preferably controlled by a controller. Preferably, the controller has at least one output stage that drives an electric drive force for the hydraulic pump in response to a control signal from a higher-level control component of the mobile work-performing machine so that the hydraulic actuator component performs the desired actuator movement. The supply voltage may be, for example, an input voltage of the output stage, which is used by the control system in response to the control signal to transmit the electric drive force to the hydraulic pump. Electrical parameters that can be determined by the output stage and are essential for operation of the electrohydraulic actuator may also be used as an electrical release signal.

[0045] In a preferred embodiment, the electrical release signal is a digital signal formed from various individual release signals, which are linked together in an appropriate manner, for example with AND links, such that several individual release signals must be present simultaneously to form the electrical release signal, or with OR links, such that several individual release signals must be present alternatively to form the electrical release signal. If desired, there can be more complex networks forming the electrical release signal from a large number of individual signals.

[0046] It is particularly advantageous if the hydraulic pump is configured so that it can also function as a generator for converting the mechanical energy of the hydraulic fluid flow from one of the connection points to the other of the connection points into electrical energy.

[0047] The electrohydraulic actuator is particularly preferably configured to transmit mechanical energy to the hydraulic actuator component through lines and via hydraulic fluid to the electrohydraulic pump and to recover the mechanical energy to electrical energy using the hydraulic pump.

[0048] The possibility of operating a hydraulic pump in generator mode has already been discussed above in conjunction with the four-quadrant capability of electro-hydraulic actuators. The electro-hydraulic actuator described herein is a four-quadrant actuator that is recoverable and at the same time has a high level of functional safety (due to the releasable hydraulic closing elements and their linkage with both electrical and hydraulic release signals).

[0049] It is also advantageous if the hydraulic actuator component is a linear actuator.

[0050] The described designs are particularly suitable for providing actuators that can be used to generate very large linear forces.

[0051] The electrohydraulic actuators described herein are preferably configured to produce mechanical power outputs in excess of 10 kW (kilowatts).

[0052] Also described herein is a mobile work-performing machine including at least one electro-hydraulic actuator as described.

[0053] The mobile work-performing machine may be, for example, an excavator or similar machine, although the electro-hydraulic actuators described herein may be used in other applications.

[0054] The invention and its technical context will be explained in more detail below with reference to the figures, which show preferred exemplary embodiments to which the invention is not limited, and it should be noted in particular that the figures, and in particular the scales shown in the figures, are merely schematic. [Brief explanation of the drawings]

[0055] [Figure 1] 1 shows a first variant of the electrohydraulic actuator described; [Figure 2] 1 shows a second variant of the electrohydraulic actuator described. DETAILED DESCRIPTION OF THE INVENTION

[0056] FIG. 1 shows a variant of the described electro-hydraulic actuator 1, in which the hydraulic actuator component 3 has hydraulic fluid chambers 4a, 4b with the same hydraulic cross-sections 20a, 20b. Here, 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 of the described electro-hydraulic actuator 1, in which the hydraulic actuator component 3 has hydraulic fluid chambers 4a, 4b with different hydraulic cross-sections 20, 20b. Here, the total actuator volume 5 is variable and depends on the position of the displaceable element between the two hydraulic fluid chambers 4a, 4b. Such a hydraulic actuator component 3 is also called, for example, a differential hydraulic actuator component 3, or (in the case of a hydraulic cylinder as the hydraulic actuator component 3) a "differential cylinder." Such differential hydraulic actuator components 3 are widely used. The invention described herein makes no fundamental difference whether the hydraulic actuator component 3 is a differential hydraulic actuator component 3 or not. However, some differences should be noted, since in Figures 1 and 2 the electro-hydraulic actuator 1 according to the invention is described with differential and with non-differential hydraulic actuator components 3. However, identical features in both variants will now be described together.

[0057] The electro-hydraulic actuator 1 comprises a hydraulic actuator component 3 and an electro-hydraulic pump 2 drivable by an electric pump drive motor 26. The hydraulic actuator component 3 generally has two hydraulic fluid chambers 4a, 4b between which there is a displaceable element 19 that can be moved by simultaneously filling one hydraulic fluid chamber 4a, 4b and emptying the other hydraulic fluid chamber 4b, 4a to produce actuator movement 24. In this way, large forces can be generated by the hydraulic actuator component 3, which can be used, for example, to drive an excavator arm or a crane arm.

[0058] In the electro-hydraulic actuator 1 described herein, both hydraulic fluid chambers 4a, 4b are connected to connection points 6a, 6b of the electro-hydraulic pump 2 via lines 7a, 7b, respectively. 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 electro-hydraulic pump 2 together form a delivery circuit 10. The electro-hydraulic pump 2 can be used to increase the pressure at one of its connection points 6a, 6b and provide hydraulic fluid under pressure at this connection point 6a, 6b so that the hydraulic fluid flows into the respective hydraulic fluid chambers 4a, 4b of the actuator components via the respective lines 7a, 7b. In this process, the hydraulic pump 2 delivers the hydraulic fluid provided to it at the respective other connection points 6b, 6a and thus removed from the respective other hydraulic fluid chambers 4b, 4a via the respective other lines 7b, 7a. The hydraulic pump 2 can optionally be operated in both delivery directions, i.e., providing hydraulic fluid under pressure at the first connection point 6a or the second connection point 6b, and thus generating actuator movements 24 in different directions using the hydraulic actuator component 3. In this way, the electro-hydraulic actuator 1 can be used to convert electrical energy into mechanical energy, which is provided by the hydraulic actuator component 3. The electrical energy is first converted into hydraulic energy by the electro-hydraulic pump 2, and then converted into mechanical energy by the hydraulic actuator component 3 using actuator movements 24. The actuator movements 24 can be used, for example, to move an excavator driven by the hydraulic actuator component 3. The electro-hydraulic pump 2 here operates in a so-called delivery mode. The pump drive motor 26 here is electrically driven. This is preferably possible in both conveying directions.

[0059] The electro-hydraulic actuator 1 can also be used to convert the mechanical energy of the actuator's movement 24 into electrical energy. First, the mechanical energy of the actuator's movement 24 is converted or recovered into hydraulic energy using the actuator component 3, and then converted or recovered into electrical energy using the electro-hydraulic pump 2 or the electric pump drive motor 26. This can be used, for example, to convert the potential energy of an excavator driven by the hydraulic actuator component 3 into electrical energy. The electro-hydraulic pump 2 then operates in so-called generator mode. This is also preferably possible in both conveying directions.

[0060] An electro-hydraulic pump 2 that can function in both delivery and generator modes is also said to be four-quadrant capable. Thus, the delivery circuit 10 formed by the lines 7a, 7b, the hydraulic pump 2 and the hydraulic actuator component 3 or its hydraulic fluid chambers 4a, 4b can be operated in both delivery and generator modes.

[0061] The electrohydraulic 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 from electrical energy in the hydraulic actuator component 3 and for the recovery of mechanical energy to electrical energy in the hydraulic actuator component 3, i.e. to ensure adequate hydraulic conditions in the delivery circuit 10 so that both delivery operation and generator operation are possible with the highest possible efficiency of the conversion of electrical energy into mechanical energy and vice versa.

[0062] The intermediate circuit 25 comprises several other hydraulic components 9, the most important of which will now be briefly described. The hydraulic intermediate circuit 25 is connected to the lines 7a, 7b by means of further 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 one of the two lines 7a, 7b in the delivery circuit 10 is too low. However, the hydraulic intermediate circuit 25 is set up in such a way that losses of hydraulic fluid in the delivery circuit 10 above a threshold value are not compensated for, but only permissible fluctuations during normal operation are compensated for.

[0063] Preferably, the hydraulic intermediate circuit 25 comprises a reservoir 11 which receives hydraulic fluid from the delivery circuit 10 by means of the closing elements 12a, 12b and pressure release and holds a reservoir of hydraulic fluid ready to release it into the delivery circuit 10 where it remains in suitable conditions for operation. The intermediate circuit 25 and in particular the reservoir 11 are themselves supplied with hydraulic fluid, for example by a hydraulic fluid supply device 18.

[0064] In the connection between the hydraulic fluid chambers 4a, 4b and the lines 7a, 7b, there are releasable hydraulic closing elements 8a, 8b, which are in particular check valves. When these releasable hydraulic closing elements 8a, 8b are closed, hydraulic fluid can no longer leave the hydraulic fluid chambers 4a, 4b. In this way, the hydraulic actuator component 3 is locked. The releasable hydraulic closing elements 8a, 8b therefore ensure that the hydraulic actuator component 3 or a component driven thereby (such as an excavator shovel) does not perform undesired (uncontrolled) movements in the event of a failure of the hydraulic actuator component 3 or another part of the mobile work-performing machine 15.

[0065] The releasable hydraulic closing elements 8a, 8b are set to be closed unless two independent release signals, i.e. an electrical release signal and a hydraulic release signal, are present. The electrical release signal and the hydraulic release signal are therefore linked to each other in the manner of a logical AND operation in the releasable hydraulic closing elements 8a, 8b or preferably by the structure of the releasable hydraulic closing elements 8a, 8b. Preferably, the releasable hydraulic closing elements 8a, 8b have a hydraulic release signal input 13 for the hydraulic release signal and an electrical release signal input 14 for the electrical release signal.

[0066] The hydraulic release signal is present when the hydraulic components of the electrohydraulic actuator 1 are functioning properly. The hydraulic release signal is omitted, for example, when there is a leak in the first line 7a and / or the second line 7b. The hydraulic release signal is preferably obtained in the aforementioned reservoir 11 of the hydraulic intermediate circuit 25. The hydraulic release signal is present when the pressure in the reservoir 11 exceeds a predetermined threshold pressure. The pressure in the reservoir 11 can be used to monitor the tightness of the entire system consisting of the delivery circuit 10 and the intermediate circuit 25. When the pressure in the reservoir 11 exceeds the threshold pressure, it can be recognized that there is no leak in the delivery circuit 10 and / or the intermediate circuit 25. Preferably, the reservoir 11 is directly connected to the hydraulic release signal input 13 of the releasable hydraulic closing elements 8a, 8b via a hydraulic signal line 27.

[0067] The electrical release signal is present when the electrical components of the electrohydraulic actuator 1 and, optionally, higher-level components of the mobile work-performing machine 15 are functioning properly. The electrical release signal may be obtained, for example, by the electrical control unit 17 of the electrohydraulic pump 2, which controls the pump drive motor 26 of the electrohydraulic pump 2. Preferably, the electrical control unit 17 is configured to generate the electrical release signal from internal electrical variables of the electrical control unit 17, the drive power supply 16, and possibly other variables that the electrical control unit receives from external safety electronics. The electrical release signal may preferably be formed from individual release signals connected to each other by appropriate links ("AND" links or "OR" links) to form an electrical release signal that represents the full functionality of the electrical components of the electrohydraulic actuator 1. When the electrical release signal is applied to the releasable hydraulic closing elements 8a, 8b, the electrical components of the electrohydraulic actuator 1 (particularly the pump drive motor 26, the control unit 17, and the drive power supply 16) may be assumed to be fully functional. Preferably, the electrical release signal is sent directly to the electrical release signal input 14 of the releasable hydraulic closing elements 8 a, 8 b via an electrical signal line 28. The control unit 17 is preferably supplied with electrical energy for supplying the electrohydraulic actuator 1 by a drive power supply 16 which provides a supply current or a supply voltage. Preferably, the control unit 17 and the drive power supply 16 are also regenerative, which means that energy recovered from the electrohydraulic actuator 1 can be fed back to the drive power supply 16.

[0068] In the above description, the operating mode of the electrohydraulic actuator 1 was first described using the variant shown in Figure 1. The electrohydraulic actuator 1 shown in Figure 2, which includes a differential cylinder as the actuator component 3, has further (possibly slightly different) characteristics which will now be briefly described.

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

[0070] The second partial pumping chamber 21b is connected only to the first line 7a to the first hydraulic fluid chamber 4a, which has a larger first hydraulic cross section 20a. The second partial pumping chamber 21b is also connected to a hydraulic fluid reservoir 23, into which hydraulic fluid is either discharged or from which hydraulic fluid is taken, depending on the delivery direction, during operation of the electrohydraulic actuator 1. The hydraulic fluid reservoir 23 can also be pressurized to store hydraulic energy in the hydraulic fluid. Preferably, recovery of mechanical energy from actuator movement 24 into electrical energy is also possible. [Explanation of symbols]

[0071] List of Reference Numbers 1 Electro-hydraulic Actuator 2 Electric Hydraulic Pumps 3 Hydraulic Actuator Components 4a First hydraulic fluid chamber 4b Second hydraulic fluid chamber 5 Total Actuator Volume 6a First connection point 6b Second connection point 7a First Line 7b Second Line 8a First releasable hydraulic closing element 8b Second releasable hydraulic closing element 9 Other Hydraulic Components 10 Sending circuit 11 Reservoir 12a first further hydraulic closing element 12b second further hydraulic closing element 13 Hydraulic release signal input 14 Electric release signal input 15 Mobile work-performing machines 16 Drive power supply 17 Controller 18 Hydraulic fluid supply device 19 Displaceable Elements 20a First hydraulic section 20b Second hydraulic section 21a First partial pump chamber 21b Second partial pump chamber 22 Differential Volume 23 Hydraulic fluid reservoir 24 Actuator Movement 25 Hydraulic intermediate circuit 26 Pump drive motor 27 Hydraulic signal line 28 Electrical signal line

Claims

1. An electro-hydraulic actuator (1) comprising at least one bidirectionally operable hydraulic pump (2) for conveying hydraulic fluid, said pump having two connection points (6a, 6b) designed for alternately supplying and / or removing hydraulic fluid, and a hydraulic actuator component (3) having two hydraulic fluid chambers (4a, 4b) into which hydraulic fluid can be supplied for actuating said hydraulic actuator component (3), wherein filling one of said hydraulic fluid chambers (4a, 4b) with hydraulic fluid simultaneously causes displacement of hydraulic fluid from the other hydraulic fluid chamber (4b, 4a), a first connection point (6a) of said electro-hydraulic pump (2) being connected to a first hydraulic fluid chamber (4a) of said hydraulic actuator component (3) by a first line (7a). and a second connection point (6b) of the hydraulic pump (2) is connected to a second hydraulic fluid chamber (4b) of the hydraulic actuator component (3) by a second line (7b), 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), the releasable hydraulic closing elements (8a, 8b) prevent undesired outflow of hydraulic fluid from the hydraulic fluid chambers (4a, 4b), and the releasable hydraulic closing elements (8a, 8b) are designed such that for release, both an electrical release signal and a hydraulic release signal need to be applied to the releasable hydraulic closing elements (8a, 8b).

2. 2. The electrohydraulic actuator (1) according to claim 1, wherein the releasable hydraulic closing elements (8a, 8b) are releasable check valves.

3. 3. The electro-hydraulic actuator (1) according to claim 1 or 2, wherein the hydraulic actuator component (3) has a displaceable element (19) through which the hydraulic fluid chambers (4a, 4b) communicate with each other, and wherein the hydraulic actuator component (3) at least partially forms a delivery circuit (10) together with the lines (7a, 7b) and the electro-hydraulic pump (2) such that hydraulic fluid leaving one hydraulic fluid chamber (4a, 4b) can directly flow into the other hydraulic fluid chamber (4b, 4a) via the lines (7a, 7b) and the electro-hydraulic pump (2).

4. 4. The electro-hydraulic actuator (1) according to claim 3, wherein the hydraulic fluid chambers (4a, 4b) of the hydraulic actuator component (3) have different hydraulic cross sections (20a, 20b), whereby a differential volume (22) results as a change in the total volume of the hydraulic fluid chambers (4a, 4b) when the displaceable element (19) is displaced, and wherein the electro-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 a second partial pump chamber (21b) is connected to the lines (7a, 7b) to the hydraulic fluid chambers (4a, 4b) with the larger hydraulic cross sections (20a, 20b) and to a hydraulic fluid reservoir (23) by means of which the differential volume (22) can be compensated.

5. 5. The electrohydraulic 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) of hydraulic fluid, the reservoir (11) being configured to compensate for function-related fluctuations in the lowest system pressure in a closed hydraulic system.

6. 6. The electrohydraulic actuator (1) according to claim 5, wherein the reservoir (11) is connected to the first line (7a) and the second line (7b) via further hydraulic shut-off elements (12a, 12b), which prevent the operating pressure generated by the electrohydraulic pump (2) in one of the two lines (7a, 7b) from being transmitted to the reservoir (11).

7. 7. The electrohydraulic actuator (1) according to claim 1, wherein the releasable hydraulic closing element (8a, 8b) has a hydraulic release signal input (13), to which a hydraulic signal line (27) is connected, via which the presence of hydraulic system pressure of the electrohydraulic actuator (1) is monitored as a hydraulic release signal.

8. 8. The electrohydraulic actuator (1) of claim 7, wherein the hydraulic release signal input (13) is connected to the reservoir (11) via a hydraulic signal line (27) for monitoring the hydraulic system pressure.

9. 9. The electro-hydraulic actuator (1) according to claim 1, wherein the releasable hydraulic closing element (8a, 8b) has an electric release signal input (14), and an electric signal line (28) is connected to the electric release signal input (14), and via the electric signal line (28), the presence of a function signal of the electro-hydraulic pump (2) and / or a function signal of a drive power source (16) and / or a controller (17) of the electro-hydraulic pump (2) is monitored as an electric release signal.

10. 10. The electro-hydraulic actuator (1) according to any one of claims 1 to 9, wherein the electro-hydraulic pump (2) is arranged so that it can also function as a generator for converting mechanical energy of the hydraulic fluid flow from one of the connection points (6a, 6b) to the other of the connection points (6b, 6a) into electrical energy.

11. 11. The electro-hydraulic actuator (1) according to any one of claims 1 to 10, configured to transmit mechanical energy in the hydraulic actuator component (3) through the lines (7a, 7b) and via the hydraulic fluid to the electro-hydraulic pump (2) and to recover the mechanical energy into electrical energy by means of the electro-hydraulic pump (2).

12. The electro-hydraulic actuator (1) according to any one of claims 1 to 11, wherein the hydraulic actuator component (3) is a linear actuator.

13. A mobile work-performing machine (15) comprising at least one electro-hydraulic actuator (1) according to any one of claims 1 to 12.

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