Regenerative hydraulic actuator

Abstract

The present invention relates to a hydraulic actuator (1), wherein the hydraulic actuator (1) comprises at least one bidirectionally operable hydraulic pump (2) for pumping hydraulic fluid and having two ports (6a, 6b), and a hydraulic actuator component (3) comprising two hydraulic fluid chambers (4a, 4b). Hydraulic fluid can be applied to hydraulic fluid chambers (4a, 4b) to operate a hydraulic actuator component (3), and hydraulic fluid chambers (4a, 4b) are each connected to ports (6a, 6b) of a hydraulic pump (2) through lines (7a, 7b), the first line (7a) connects the first chamber (4a) to the hydraulic pump (2), and the second line (7b) connects the second chamber (4b) to the hydraulic pump (2), and when one of the hydraulic fluid chambers (4a, 4b) is filled with hydraulic fluid, the hydraulic fluid is simultaneously pushed out from the other hydraulic fluid chambers (4b, 4a), and the volume of hydraulic fluid is moved through the hydraulic pump (2). The second chamber cross-section (8b) of the second chamber (4b) is different from the first chamber cross-section (8a) of the first chamber (4a), and the first line (7a) is connected to the pressure reservoir (5), and a differential volume (28) can be received and provided within the pressure reservoir (5), and the differential volume (28) is generated as a result of the different chamber cross-sections (8a, 8b) of the chambers (4a, 4b), and there is a compressible element (17) within the pressure reservoir (5), and the compressible element (17) can be compressed to receive the pressurized hydraulic fluid within the pressure reservoir (5) and expands when the hydraulic fluid is withdrawn from the pressure reservoir (5). The first line (7a) also includes a supply port (15), and hydraulic fluid is supplied to a hydraulic actuator (1) through the supply port (15), and a hydraulic fluid supply unit (16) is connected to the supply port (15), and the hydraulic fluid supply unit (16) maintains a minimum pressure within the first line (7a). A controllable shut-off valve (35) is positioned between the first line (7a) and the pressure reservoir (5), and the controllable shut-off valve (35) can be used to disconnect the pressure reservoir (5) from the first line (7a).

Description

Technology Field

[0001] The present invention relates to a regenerative hydraulic actuator, and more specifically, to a regenerative hydraulic actuator comprising at least one hydraulic actuator having a differential volume and a hydraulic pump unit. Background Technology

[0002] Hydraulic actuators with differential volume are specifically so-called differential cylinders. Hydraulic differential cylinders are used for work tasks, for example, to raise and / or lower loads. Typical applications of such hydraulic differential cylinders may be, for example, applications in excavator arms, telescopic loader arms, or tractor front attachments. In these applications, hydraulic differential cylinders are used to raise and lower, for example, the arms of a telescopic loader or the front attachment of a tractor. Regarding these hydraulic differential cylinders, there are numerous other applications, particularly in the fields of construction machinery, agricultural machinery, municipal machinery, and forestry machinery. In these applications, differential cylinders are frequently used due to their potential to provide large forces.

[0003] Basically, during the operation of construction and agricultural machinery, many tasks are performed by hydraulic differential cylinders. When excavating foundation pits, the excavator arm is raised and lowered very frequently. The same applies, for example, to the arm of a telescopic loader used for loading and / or unloading loads. Often, it is necessary to drive the hydraulic differential cylinder in only one direction of movement (upward). In other directions, energy must instead be dissipated from the movement process in a controlled manner. In the field of hydraulics, it is a desirable goal to enable regenerative recovery in such situations. In particular, for hydraulic differential cylinders, it is desirable to enable the regeneration of energy from movement.

[0004] In operations performed by a hydraulic differential cylinder, for example, when the lifting of a load (e.g., the arm of a telescopic loader) counteracts the action of gravity, potential energy is typically increased by the movement. Conversely, when the load is lowered again by the hydraulic differential cylinder, this potential energy must be dissipated.

[0005] Essentially, it is desirable that this potential energy be utilized or recovered and then made available again for further operation of the hydraulic actuator or for other applications. Energy recovery can be achieved by a hydraulic pump unit coupled to a hydraulic differential cylinder. The lowering of the load preferably generates a volumetric flow of hydraulic fluid, which flows into another chamber of the differential cylinder or into a tank along with a pressure gradient. This volumetric flow can be restricted to prevent uncontrolled lowering of the load. Alternatively, controlled lowering of the load can be performed with the assistance of a hydraulic pump unit. In this process, potential energy is recovered in the form of torque and rotational speed.

[0006] A hydraulic differential cylinder is a double-acting hydraulic cylinder. They typically consist of a piston guided within the cylinder, with a chamber on each of the two sides of the piston. Hydraulic fluid is injected into these chambers to move the piston in one direction or the other within the cylinder. As a double-acting hydraulic cylinder, the hydraulic differential cylinder is essentially suitable for both pushing and pulling.

[0007] The movement of the piston expands or contracts the size of each chamber of the hydraulic cylinder. In the case of a hydraulic differential cylinder, a rod connected to the piston extends from one side of the hydraulic differential cylinder through one of the two chambers. Through this rod, the force applied to the piston by the hydraulic fluid can be transmitted externally. The ends of the rod opposite the cylinder and the rod opposite the cylinder each form the ends of the differential cylinder, which are pushed against each other by the differential cylinder when the differential cylinder extends and pulled back in when the differential cylinder retracts.

[0008] The side of the piston through which the rod extends is commonly referred to as the ring side or rod side, because on this side, the chamber forms a ring around the rod. Therefore, the chamber through which the rod extends is referred to here as the ring chamber. The other side of the piston is commonly referred to as the head side or piston side. Therefore, the chamber on this other side of the piston is referred to here as the head chamber. The rod can be extended and retracted from the hydraulic differential cylinder depending on which of the two chambers hydraulic fluid flows into and then flows out of the other chamber. When hydraulic fluid is pumped into the ring chamber, the rod retracts. The differential cylinder then applies a pulling force. When hydraulic fluid is pumped into the head chamber, the rod extends. The differential cylinder then applies a pushing force.

[0009] By design, the cross-sectional areas of the two chambers differ due to this rod. The cross-sectional area of ​​the ring chamber is smaller than that of the head chamber by the amount of the rod's cross-sectional area.

[0010] Due to these differences in the cross-sectional areas of the hydraulic fluid chambers, there exists a difference in the volumetric flow entering and exiting the chambers during the movement of the piston. When hydraulic fluid is supplied to the head chamber, which has a larger cross-sectional area, the volumetric flow of hydraulic fluid exiting from the ring chamber is smaller than the volumetric flow of hydraulic fluid entering the head chamber. Conversely, when hydraulic fluid is supplied to the ring chamber, the volumetric flow of hydraulic fluid exiting from the head chamber is larger than the volumetric flow of hydraulic fluid entering the ring chamber. This difference in volumetric flow, or the total volumetric difference occurring during a specific movement of the piston, is referred to as differential volume, which is why such a hydraulic cylinder is called a “differential cylinder.” In the following text, the term “differential volume” is used comprehensively—that is, it is used for the difference between the volumetric flow entering and exiting the ring chamber and the head chamber, as well as for the actual differential volume that occurs when the piston moves a specific distance.

[0011] Differential cylinders should be distinguished from so-called “synchronized cylinders,” in which two chambers have the same cross-sectional area. In the case of a synchronized cylinder, neither a difference in volumetric flow nor a differential volume occurs. However, a special concept is required for the configuration of a synchronized cylinder. In the case of a synchronized cylinder, measures must be taken to ensure that the cross-sectional areas of the chambers match. One possible configuration for a synchronized cylinder is, for example, to have two rods, each extending through one of the two chambers of the synchronized cylinder. Another possible configuration for a synchronized cylinder is to connect two differential cylinders opposite each other with a single actuator. This configuration is not practical in many applications. For this reason, so-called “differential cylinders” are more widely used.

[0012] The differential volume of a differential cylinder presents a challenge in the design of regenerative hydraulic actuators. This applies particularly when the characteristics of the differential cylinder as a double-acting cylinder must be additionally utilized, along with the ability to exert both pulling and pushing actions.

[0013] The technical implementation of the regenerative capability of a hydraulic actuator is achieved, for example, by connecting the two chambers of a hydraulic cylinder to each other through a hydraulic pump unit. The hydraulic pump unit can then, on the one hand, preferably pump hydraulic fluid in both directions. That is, fluid can be pumped from the ring chamber into the head chamber to extend the hydraulic cylinder, or fluid can be pumped from the head chamber into the ring chamber to contract the hydraulic cylinder. Additionally, the hydraulic pump unit can preferably counteract the hydraulic fluid flow in both directions with torque to remove or recover energy from the hydraulic fluid and make it available to other components. The energy obtained from the flow of hydraulic fluid by the hydraulic pump unit can be stored, for example, in a hydraulic or electric energy storage device.

[0014] In the case of a differential cylinder, the connection of the two chambers by a hydraulic pump unit requires additional measures due to the differential volume. When the differential cylinder extends, additional differential volume must be provided because the head chamber is larger than the ring chamber and the volumetric flow of hydraulic fluid discharged from the ring chamber cannot completely fill the head chamber. When the differential cylinder retracts, differential volume must be released because the volumetric flow exiting from the head chamber is greater than the volumetric flow that can be absorbed by the ring chamber. To address this problem, a circuit is proposed in which the hydraulic pump used is a dual pump. Such a dual pump has two separate pump chambers. In this case, the first pump chamber serves to pump the volume of hydraulic fluid from the ring chamber between the ring chamber and the head chamber. At the same time, the second pump chamber serves to simultaneously pump the differential volume between the accumulator and the head chamber. Here, it is necessary to match the dual pumps very precisely to the respective connected differential cylinders. In particular, it is necessary for the ratio of the pump chamber to be precisely matched to the ratio of the differential volume to the chamber volumes of the head chamber and ring chamber. Especially due to the compressibility of the oil and the resulting movement of the cylinder during load fluctuations, this circuit also often requires a so-called “intermediate circuit.”

[0015] Such intermediate circuits are described, for example, in German Patent DE102011056894B4. The intermediate circuit ensures that the pressure within the lines leading to the ring chamber and the head chamber is maintained within a predetermined pressure range. When the pressure within each chamber and its associated line exceeds an upper limit, a volume of hydraulic fluid is released into the intermediate circuit. When the pressure falls below a lower limit, each line receives additional fluid. The intermediate circuit and its connection to the lines leading to the ring chamber and the head chamber require a number of additional hydraulic components.

[0016] If regenerative capability and the use of hydraulic differential cylinders are established as boundary conditions for the design of the hydraulic actuator, another alternative to the use of intermediate circuits and two hydraulic pumps exists: namely, the use of a pressure reservoir that is fixedly and permanently connected to the ring chamber and capable of absorbing the differential volume flowing from the head chamber toward the ring chamber when the differential cylinder retracts. This pressure reservoir always maintains exactly the same pressure as the ring chamber in a static state, as an open connection exists therein and pressure equilibrium is always achieved. In this context, the term “static” state describes that pressure differences that occasionally occur within the line due to hydraulic flow are not taken into account here.

[0017] In such circuits, the hydraulic actuator or the differential cylinder within the hydraulic actuator loses the ability to act in both directions, namely, the ability to pull and push. In such circuits, only pushing is possible, and pulling is impossible. However, these circuits enable the recovery of energy from the pressure of the hydraulic fluid when the hydraulic cylinder contracts.

[0018] The reason why a hydraulic actuator connected in this manner is unsuitable for a pulling action lies in the influence of a pressure reservoir permanently connected to the ring chamber. This pressure reservoir is configured to absorb the differential volume of hydraulic fluid that is displaced from the head chamber and cannot be transferred to the ring chamber when the differential cylinder is retracted. The pressure reservoir is also configured to make this differential volume available again for transfer into the head chamber when the differential cylinder is extended again.

[0019] As previously explained, the pressure within the pressure reservoir and the pressure within the ring chamber always correspond to each other in a static state. The pressure within the pressure reservoir and the ring chamber increases due to the absorption of the differential volume of hydraulic fluid into the pressure reservoir. Conversely, when the differential volume becomes available for transfer into the head chamber, the pressure within the pressure reservoir and the ring chamber decreases.

[0020] In these pressure reservoirs, a base pressure is supplied prior to the initial commissioning of the hydraulic actuator, for example, by providing a gas bubble having a specified gas volume and a specified pressure within the pressure reservoir. During the contraction and extension of the differential cylinder, the gas bubble within the pressure reservoir is compressed or expanded by the inflow and outflow of the differential volume. The pressure within the pressure reservoir is determined by the amount and pressure of the gas, or by the remaining volume of the pressure reservoir available to the gas. The pressure within the pressure reservoir propagates to the ring chamber through the connecting hydraulic fluid line.

[0021] This pressure reservoir replaces a significant portion of the role previously performed by the aforementioned intermediate circuit and two parallel hydraulic pumps for the individual processing of fluid volume flow and differential volume exchanged between the two chambers. The intermediate circuit can be omitted by the pressure reservoir. On the other hand, a limitation arises in that the pressure within the ring chamber (and within the pressure reservoir itself) depends on the position of the piston and can no longer be controlled precisely, and therefore it is no longer possible to apply pressure to the ring chamber in a controlled manner to draw it into the differential cylinder or hydraulic actuator.

[0022] The limitation that hydraulic actuators can only push when extended and regenerate when retracted but cannot pull is acceptable in many applications. Hydraulic actuators equipped with differential cylinders that raise and lower arms operate primarily against gravity in their normal operation. Since many machines commonly move large masses and possess significant self-weight, regenerative capability (as previously explained) is very useful for these hydraulic actuators. A large amount of energy can be recovered.

[0023] However, there are sometimes situations where, even in applications where a hydraulic actuator can only push and is typically sufficient, it is desired to be able to pull temporarily for at least specific special purposes. For example, a telescopic loader can push against the ground with its arm to lift itself or the machine's axle, or to press a load against the ground. This is very advantageous for changing tires because it eliminates the need to lift the machine onto a block. Although such applications are rare, sacrificing this capability for regenerative braking would nevertheless limit the machine's general usability.

[0024] In such applications, where both the full capability (pulling and pushing) and regenerative capacity of the hydraulic actuator must be achieved, a hydraulic actuator with the described intermediate circuit must be used. Due to the much more complex circuit, this is generally undesirable. The problem to be solved

[0025] The objective of the invention presented herein is to propose a novel hydraulic actuator that is regenerative in most situations and is simultaneously suitable for both pulling and pushing. At the same time, its structure must be significantly simplified compared to a hydraulic actuator having an intermediate circuit and a dual pump, which is capable of pulling and pushing and is fully regenerative during both retraction and extension. means of solving the problem

[0026] A hydraulic actuator is described herein, the hydraulic actuator comprising at least one bidirectionally operable hydraulic pump having two ports for pumping hydraulic fluid, and a hydraulic actuator component having two hydraulic fluid chambers, wherein hydraulic fluid may be applied to the hydraulic fluid chambers to actuate the hydraulic actuator component, and the hydraulic fluid chambers are each connected to a port of the hydraulic pump through a line, wherein a first line connects the first chamber to the hydraulic pump and a second line connects the second chamber to the hydraulic pump, so that when one of the hydraulic fluid chambers is filled with hydraulic fluid, the hydraulic fluid is simultaneously pushed out from the other hydraulic fluid chamber and the volume of the hydraulic fluid is moved through the hydraulic pump.

[0027] - The second chamber cross-section of the second chamber is different from the first chamber cross-section of the first chamber, and the first line is connected to a pressure reservoir, within which a differential volume can be accommodated and provided, and this differential volume is generated as a result of the different chamber cross-sections of the chambers, and there is a compressible element within the pressure reservoir, and this compressible element can be compressed to accommodate the pressurized hydraulic fluid within the pressure reservoir and expands when the hydraulic fluid is withdrawn from the pressure reservoir,

[0028] - The first line also includes a supply port, through which hydraulic fluid is supplied to a hydraulic actuator, and a hydraulic fluid supply unit is connected to the supply port, and this hydraulic fluid supply unit maintains a minimum pressure within the first line,

[0029] - A controllable shut-off valve is placed between the first line and the pressure reservoir, and the pressure reservoir can be disconnected from the first line by this controllable shut-off valve.

[0030] It is particularly desirable that the hydraulic actuator component is at least one differential cylinder.

[0031] The basic configuration of a differential cylinder having a piston movable within the cylinder and a rod penetrating the first chamber of the differential cylinder has already been described in the introduction. This is adopted herein in its entirety. A differential cylinder is a particularly frequently used type of hydraulic actuator having different chamber cross-sections and differential volumes. In particular, differential cylinders are commonly employed when the lifting, pushing, and / or pulling of a load is critical. Differential cylinders are widely used, particularly in the fields of construction machinery, agricultural machinery, municipal machinery, and forestry machinery. In particular, for applications of differential cylinders, it is advantageous to have the possibility of generating force in both directions (pushing and pulling) by the differential cylinder while simultaneously enabling energy regeneration. At the same time, in such cases, it is common for one of the two directions of movement (pushing or pulling, especially pushing) to be used particularly frequently in the differential cylinder, whereas there are particularly many situations where regeneration is possible in the opposite direction (preferably during the contraction of the differential cylinder). For this reason, it is particularly advantageous to apply the hydraulic actuator described herein in conjunction with a differential cylinder. However, the principle of the hydraulic actuator described herein is not limited to differential cylinders and can be applied and adapted to other hydraulic actuators having differential volumes.

[0032] The hydraulic actuator preferably has at least one movable actuator element disposed between hydraulic fluid chambers and capable of moving into the hydraulic fluid chambers by the pressure or pressure difference of the hydraulic fluid. In the case of a differential cylinder, the movable actuator element is, in particular, a piston capable of moving within the cylinder. As previously described, in a differential cylinder, the first chamber is a ring chamber through which a rod connected to the piston extends, and the second chamber is a head chamber. The second chamber then has a second chamber cross-section larger than the first chamber cross-section of the first chamber.

[0033] The hydraulic actuator described herein includes the described pressure reservoir connected to the first line. During operation, the pressure reservoir serves to receive or release the differential volume described above when hydraulic fluid is pumped into one chamber of the hydraulic actuator component and, in the process, flows out from another chamber of the hydraulic actuator component. A compressible element is located within this pressure reservoir, and this compressible element compresses or expands to provide a variable volume within the pressure reservoir for receiving and / or providing the differential volume of hydraulic fluid. Due to the change in volume and the compression / decompression of the compressible element, the total volume of the lines and chambers of the hydraulic actuator also varies depending on the location of the hydraulic actuator component.

[0034] The pressure reservoir and compressible element also result in limitations on the possibility of pumping hydraulic fluid from the second line and second chamber into the first line and first chamber by a hydraulic pump to operate, for example, a hydraulic actuator component by pulling. By providing the pressure reservoir, the hydraulic fluid pumped from the second line or second chamber into the first line or first chamber is also pumped into the pressure reservoir. The pumped hydraulic fluid may not contribute at all or may contribute only partially to increasing the pressure and causing movement against the load.

[0035] For this reason, it is proposed herein to provide a controllable shut-off valve between the first line and the pressure reservoir. The pressure reservoir can be disconnected from the first line by this controllable shut-off valve. When the pressure reservoir is disconnected from the first line, the first line and the first chamber can be pressurized with hydraulic fluid by a hydraulic pump and / or through a supply port. The closed shut-off valve prevents the hydraulic fluid from flowing toward the pressure reservoir. Disconnection means that it is impossible for the hydraulic fluid to move from the first line to the pressure reservoir, or for the hydraulic fluid to move from the pressure reservoir to the first line. The controllable shut-off valve has a closed switching position in which a blocking action is caused in both flow directions. Thus, movement against the load can be generated. When this movement ends or is no longer needed, the shut-off valve can be reopened, and the pressure reservoir becomes available again for regeneration in normal operation involving regeneration.

[0036] Accordingly, the hydraulic actuator described herein can be operated in two different operating modes. In the first (normal) operating mode with an open shut-off valve, the hydraulic actuator cannot or can only implement force and movement requiring pressurization of the first chamber. Instead, regenerative capability is particularly excellent, and the driving of the hydraulic actuator is greatly simplified. In the second operating mode, the described limitations on the implementation of force and movement are eliminated. Instead, regenerative capability is limited or reduced, and the control of the hydraulic actuator in this operating mode is more complex.

[0037] A hydraulic fluid supply unit is connected to a supply port, which can be used to supply hydraulic fluid to a hydraulic actuator (particularly the line, chamber, and hydraulic pump of the hydraulic actuator). In the hydraulic actuator described, the hydraulic fluid supply unit is preferably used to maintain a minimum pressure in the hydraulic fluid within the first line by providing a target amount of hydraulic fluid at the supply port.

[0038] The hydraulic fluid supply unit is also specifically referred to as a charging circuit capable of charging hydraulic actuators.

[0039] The hydraulic supply unit includes, in particular, a supply port capable of supplying hydraulic fluid to a hydraulic actuator.

[0040] The hydraulic actuators described herein are typically components of a more complex overall hydraulic system comprising multiple hydraulic actuators.

[0041] The hydraulic fluid supply unit preferably includes a central transfer pump having a main hydraulic drive, and the main hydraulic drive is preferably configured to operate the central transfer pump. By means of the central transfer pump, hydraulic fluid is made available to the hydraulic actuators described herein through supply ports. As described, the main hydraulic pump also supplies hydraulic fluid to other hydraulic actuators. The hydraulic actuators described herein are regenerative and, for this purpose, additionally include the hydraulic pump described above together with a pump drive, which can be supplied by the hydraulic fluid supply unit in addition to the other hydraulic actuators, and these other hydraulic actuators may be designed differently. In particular, these other hydraulic actuators do not need to include their own hydraulic pumps and pump drives. These additional hydraulic actuators may be operated directly by the hydraulic fluid pressure provided by the hydraulic fluid supply unit.

[0042] The hydraulic fluid supply unit preferably further comprises a main reservoir (also referred to as a central hydraulic tank), and a main hydraulic pump continuously pumps and supplies hydraulic fluid from this main reservoir. Preferably, a first pressure relief valve is present, and hydraulic fluid is released from the first line through this first pressure relief valve when the pressure in the first line exceeds a first limit pressure. Preferably, a second pressure relief valve is present, and hydraulic fluid is released from the second line through this second pressure relief valve when the pressure in the second line exceeds a second limit pressure. The first limit pressure and the second limit pressure may be different from each other. The supply port preferably also comprises a pressure release valve, and by this pressure release valve, the pressure in the hydraulic actuator, particularly in the first line, can be released in a desired manner, for example, at the end of the operating phase of the hydraulic actuator described herein or when the machine to which the hydraulic actuator described herein is provided is deactivated.

[0043] It is particularly desirable that the hydraulic fluid supply unit can optionally deliver hydraulic fluid to the supply port or receive hydraulic fluid from the supply port.

[0044] The hydraulic fluid supply unit preferably also includes a central hydraulic pump capable of providing pressurized hydraulic fluid. The pressure level and volumetric flow of the hydraulic fluid, preferably provided (released into a hydraulic actuator) or received at a supply port by the hydraulic fluid supply unit, can be accurately set.

[0045] This pressurized hydraulic fluid is preferably distributed to various consumers by a power distribution system (also referred to as power distribution for short). The hydraulic actuator described herein is preferably a consumer connected to the power distribution system. In the case of the hydraulic actuator described herein, the power distribution system is part of the hydraulic fluid supply unit, thereby supplying hydraulic fluid to the hydraulic actuator.

[0046] The principle of power distribution is a fundamental element of complex hydraulic systems equipped with various hydraulic actuators, widely used, for example, in tractors, excavators, and work machinery. Hydraulic power from a central hydraulic pump is supplied to a block, from which it is branched to multiple consumers via valves. In detail, several structures of power distribution are distinguished. The one basically suitable for the hydraulic actuators highlighted and described here is the so-called “open center system,” which uses, for example, valves with an open center position without individual pressure compensators. Unused oil, made available to the power distribution system by the central hydraulic pump, flows back into the tank through the block. Since there are no individual pressure compensators, the volumetric flow into a single consumer depends on load fluctuations in other consumers within the same circuit. A power distribution system configured as a “closed center system” uses valves with a closed center position and individual pressure compensators at each consumer.

[0047] Particularly suitable for supplying the hydraulic actuators described herein is a power distribution system configured to measure the pressure of each consumer (in this case, the pressure at the supply port) and to take this pressure into account when supplying hydraulic fluid.

[0048] When the hydraulic actuator described herein is operated with a closed shut-off valve, the differential volume cannot be accommodated by the pressure reservoir. For this reason, it is advantageous for the power distribution system or hydraulic fluid supply unit not to be suitable only for providing hydraulic fluid from the supply port. The power distribution system is preferably also suitable for receiving hydraulic fluid from the supply port and, in this process, maintaining or setting the pressure in the first line in a desired manner. In this operating situation, the hydraulic fluid supply unit or power distribution system preferably provides or accommodates the differential volume (depending on the pumping direction of the hydraulic pump) in place of the function of the pressure reservoir.

[0049] During the operation of the shut-off valve to disconnect the pressure reservoir from the first line and subsequently reconnect it to the first line, it is advantageous to avoid, as much as possible, a rapid pressure rise and sudden equilibrium flow of the hydraulic fluid between the first line and the pressure reservoir. This is more important when the shut-off valve is opened than when it is closed, because the disconnection when the shut-off valve is closed implies the blockage of hydraulic fluid flow in both flow directions, and thus, when the shut-off valve is closed, different pressures are typically formed within the pressure reservoir and the first line. The hydraulic actuator is preferably configured such that, before the shut-off valve is opened, the pressure within the first line is set to the actual value of the pressure within the accumulator by the hydraulic fluid supply unit.

[0050] The first line and the second line are connected to each other by a bypass line, and when the pressure in the second line drops to a critical value, bypass flow is formed from the first line into the second line through the bypass line, thereby preventing a shortage of hydraulic fluid supply in the hydraulic pump as a result of the bypass line.

[0051] - It is particularly desirable that a deactivation circuit be placed within the bypass line, and that the bypass line be blocked by this deactivation circuit when the pressure within the second line is above a threshold value.

[0052] In the hydraulic actuators described herein, two lines or two-line systems are distinguished. The first line system (referred to herein as the first line, or the ring chamber line in the case of a differential cylinder as a hydraulic actuator) connects the first chamber or ring chamber to the hydraulic pump. The second line system (referred to herein as the second line, or the head chamber line in the case of a differential cylinder as a hydraulic actuator) connects the second chamber or head chamber to the hydraulic pump. Wherever a line or line system is mentioned, it always refers to the first line or first line system (ring side / ring line) and the second line or second line system (head side / head line) together.

[0053] The first line and the second line are typically separated from each other and at different pressure levels. The exchange of hydraulic fluid between the first line and the second line (and accordingly between the first chamber or ring chamber and the second chamber or head chamber) is accomplished solely through a hydraulic pump.

[0054] The hydraulic actuator comprises exactly one hydraulic actuator component, which may, in some cases, be composed of multiple individual elements (e.g., multiple differential cylinders connected in parallel) and interacts with exactly one hydraulic pump. In principle, it is this interaction between the actuator component and the hydraulic pump that enables regeneration.

[0055] Here, there is a bypass line that connects the lines as needed to release the separation between them. Bypass flow is the fluid flow of hydraulic fluid through the bypass line.

[0056] The bypass line is a protective measure provided by the accumulator connected to the first chamber. It serves to prevent a possible shortage of hydraulic fluid supply to the hydraulic pump and, consequently, protect the hydraulic pump from cavitation. Cavitation can occur when there is a shortage of hydraulic fluid supply to the hydraulic pump at the port where the hydraulic pump draws in the fluid or where the fluid enters the hydraulic pump during pumping. This shortage of supply generates low pressure, resulting in the formation of gas bubbles. This phenomenon is called cavitation. Significant damage to the hydraulic pump can be caused by cavitation. During the contraction of the cylinder, hydraulic fluid is pumped from the second chamber into the first chamber. At this time, if mechanical resistance occurs in the cylinder or the retaining valve in the second line is closed, a shortage of supply occurs in the second line, and as a result, cavitation occurs immediately, which can damage or destroy the hydraulic pump. When the occurrence of cavitation is mentioned below, it also implies that a shortage of hydraulic fluid supply to the hydraulic pump occurs, and as a result, cavitation occurs.

[0057] This closeable retaining valve is preferably positioned between the second chamber and the second line, and by this retaining valve, the second chamber can be closed to maintain the hydraulic actuator component in a specified position.

[0058] This closeable retaining valve securely seals hydraulic fluid within the second chamber (or within the head chamber in the case of a differential cylinder), thereby allowing the hydraulic actuator to be maintained in a specific position even under very large external forces. This closeable retaining valve may be a valve that, for example, closes when power is off and opens when power is applied, and prevents uncontrolled movement of the hydraulic actuator (and consequently uncontrolled drop of components driven by the hydraulic actuator, for example, the arm of a telescopic loader) in the event of a system failure. This closeable retaining valve is typically a defined safety element. However, this closeable retaining valve increases the risk of cavitation in the hydraulic pump because the closure of this retaining valve immediately prevents the leakage of additional hydraulic fluid from the second chamber or the head chamber into the hydraulic pump.

[0059] To prevent cavitation in the pump, the described bypass line is provided, and within it, a check valve is provided that is typically opened toward the second line or head side and closed toward the first line or ring side. Through this bypass line, preferably, circulation transfer from the first line into the second line by the hydraulic pump occurs as soon as the pressure in the second line falls below the pressure in the first line. This circulation transfer reliably prevents cavitation within the pump. However, at the same time, it is impossible to lower the pressure in the second line below the pressure in the first line. In practice, it is impossible to generate a pulling force by the differential cylinder during the contraction of the hydraulic cylinder.

[0060] Additionally, hydraulic actuators fundamentally tend to move in one direction (toward the first chamber). In the case of a differential cylinder, this tends to extend the differential cylinder by moving the piston toward the ring chamber. Due to the larger cross-sectional area of ​​the second chamber or head chamber, a situation where the pressure in the first chamber or ring chamber is equal to the pressure in the second chamber or head chamber always results in pressure accumulation or pressure pushing the hydraulic actuator components of the hydraulic actuator. However, in typical applications, this does not play a significant role, as, for example, the weight of the arm of a telescopic loader or a similar load always acts on the differential cylinder.

[0061] Here, by the deactivation circuit proposed, the bypass line is selectively deactivated when the pressure in the second line is sufficiently high or above a threshold value.

[0062] The threshold value is a fixed pressure value based on the absolute pressure level and / or the ambient pressure level, and is not a relative pressure value that specifically refers to a comparative pressure obtained at another location within the hydraulic actuator.

[0063] It is particularly desirable that the threshold value of the pressure maintained within the second line be in the range of 2 bar to 20 bar.

[0064] This deactivation circuit represents an improved alternative to the check valve in the bypass line. The check valve in the bypass line prevents the pressure in the second line (head side) from dropping below the pressure in the first line (ring side). This provides good protection against cavitation. The check valve in the bypass line very fundamentally couples the minimum pressure in the second line to the pressure existing in the first line.

[0065] The deactivation circuit within the bypass line proposed herein is a novel approach to meet the requirements for protection against the aforementioned cavitation. The deactivation circuit preferably checks the pressure within the second line immediately before connection to the hydraulic pump. It has been found that if sufficient pressure to reliably prevent cavitation still exists at this location, the operation of the bypass line can be omitted. However, the deactivation circuit loses its effect or activates the bypass line as soon as this pressure is no longer present within the second line. Ideally, the deactivation circuit regulates the pressure at the second port of the hydraulic pump to a predetermined fixed value, regardless of the pump's rotational speed or the pressure at the first port of the hydraulic pump.

[0066] The deactivation circuit enables the pressure in the second line to be lowered below the pressure in the first line, as long as the pressure in the second line is at least above a threshold value. This creates, for the first time, the ability to generate a force (a pulling force in the case of a differential cylinder) toward the first chamber by the hydraulic actuator.

[0067] The deactivation circuit enables the hydraulic pump to lower the pressure in the second line and head chamber below the pressure in the first line and ring chamber. Only when the pressure in the second line drops to a critical value or falls below the critical value does the bypass line intervene and a connection is formed between the first line and the second line. By lowering the pressure in the head chamber below the pressure in the ring chamber, a pulling force can be generated by the hydraulic actuator component, which is impossible without the described deactivation circuit, because without the described deactivation circuit, it is, in principle, prevented from lowering the pressure in the ring chamber below the pressure in the head chamber.

[0068] The deactivation circuit within the bypass line forms the basis for the pressure within the first line to rise further beyond the pressure within the second line without generating bypass flow through the bypass line by disconnecting the pressure reservoir from the first line with the help of a shut-off valve. The bypass line is provided within the hydraulic actuator as a protective measure to protect the hydraulic pump from cavitation. The deactivation circuit for deactivating the bypass line, in principle, allows the pressure within the first line to rise above the pressure within the second line, thereby enabling pressurization of the first chamber by the hydraulic pump, which can generate a pulling force by the hydraulic actuator component. The disconnection of the pressure reservoir by the shut-off valve makes it possible to further increase the pressure within the first line and the first chamber, which can generate a pressure within the first line and the first chamber that exceeds the maximum allowable pressure of the pressure reservoir, and a particularly large pulling force can be generated by the hydraulic actuator or the hydraulic actuator component. Therefore, the shut-off valve prevents hydraulic fluid from moving from the first line to the pressure reservoir in the closed switching position that causes disconnection, in order to protect the pressure reservoir from excessive pressure.

[0069] In addition to the deactivation circuit within the bypass line, a check valve capable of opening from the first line toward the second line is provided, which is particularly advantageous to ensure that the pressure in the second line does not fall below the pressure in the first line even when the pressure in the second line is below a critical value.

[0070] The check valve and the deactivation circuit are preferably connected in series within the bypass line, thereby ensuring that, on the one hand, the pressure in the second line or at the second port of the hydraulic pump is always above the threshold value, and, if the pressure in the second line or at the second port nevertheless falls below the threshold value, it is also ensured that the pressure in the second line does not fall below the pressure in the first line.

[0071] In other words, as long as the pressure in the second line or at the second port of the hydraulic pump is above the threshold value, the pressure in the second line or at the second port of the hydraulic pump may be below the pressure in the first line. Below the threshold value, the pressure in the second line or at the second port of the hydraulic pump will rise to the pressure in the first line. However, in practice, the pressure in the second line or at the second port of the hydraulic pump does not fall below the threshold value, because this case is already reliably prevented by the deactivation circuit, and there is always sufficient hydraulic fluid pressure in the first line to maintain the pressure levels of both lines overall above the threshold value.

[0072] As previously stated, the deactivation circuit within the bypass line proposed herein is an alternative to the check valve within the bypass line. Cavitation in the hydraulic pump is prevented by a simple check valve within the bypass line, thereby ensuring that the pressure in the second line does not drop below the pressure in the first line. Since the pressure in the first line typically cannot drop abruptly due to the closure of the holding valve, and circulation from the first line to the second line through the bypass line occurs when the check valve opens, this ensures that no cavitation occurs.

[0073] The combination of a deactivation circuit and a check valve provides particularly excellent safety against cavitation in hydraulic pumps.

[0074] It is particularly advantageous to place a check valve first within the bypass line and then a deactivation circuit in the direction from the second line to the first line.

[0075] In most operating situations of a hydraulic actuator, the pressure in the second line is higher than the pressure in the first line. This is particularly because the hydraulic actuator is preferably used so that the pressure in the second line acts against gravity—for example, in the case of a differential cylinder used in the arm of a telescopic loader, pressure is supplied to the second line on the head side to raise the arm of the telescopic loader.

[0076] Accordingly, the pressure in the second line acts preferably on the check valve in the bypass line as long as the pressure in the second line is higher than the pressure in the first line. The pressure in the second line propagates to the deactivation circuit only when a hydraulic pump is used to pump hydraulic fluid from the second chamber (head chamber) to generate a pulling force with a hydraulic actuator, for example, and the pressure in the second line is lowered below the pressure in the first line.

[0077] The deactivation circuit may have structural (slight) leakage in some cases. By placing the deactivation circuit after the check valve, starting from the second line, the impact of this structural (slight) leakage can be reduced.

[0078] In addition, it is advantageous for the hydraulic pump to be suitable for operation in generator mode and motor mode.

[0079] Hydraulic pumps of various configurations are suitable for this purpose, such as vane pumps, gear pumps, and axial piston pumps. In principle, there are no restrictions on the types of pumps that can be used for hydraulic actuators. Pumps capable of operating in both generator mode and motor mode in both directions are also referred to as “quadruple-operable.” It is particularly desirable to use such quadruple-operable pumps as hydraulic pumps for the actuators described herein.

[0080] It is particularly desirable that a hydraulic pump is connected to a drive unit, and that energy from the pressure and volumetric flow of the hydraulic fluid is converted by the hydraulic pump and stored in an energy storage device by this drive unit.

[0081] The drive unit serves to drive the hydraulic pump and, accordingly, operate the hydraulic actuator components of the hydraulic actuator. In the case of a differential cylinder as a hydraulic actuator component, this differential cylinder can extend or retract by driving the hydraulic pump with its drive unit.

[0082] In a preferred modified embodiment, the drive unit is an electric drive unit. When the hydraulic pump is driven as a hydraulic motor in generator mode by the electric drive unit, electrical energy can be regenerated into an electric energy storage device (e.g., a battery or a capacitor).

[0083] The drive unit should preferably be designed as an electric drive unit that operates at variable speed and is supplied from a DC circuit via an inverter. In generator mode, the inverter feeds the converted energy back into the DC circuit, where this energy is absorbed by a battery or capacitor or immediately drawn out by a simultaneously operating consumer.

[0084] In another variant embodiment, the drive unit may include an additional hydraulic pump, and the energy regenerated by this additional hydraulic pump may be stored hydraulically or as pressure in an additional hydraulic accumulator.

[0085] It is particularly advantageous that the deactivation circuit includes a separation valve capable of blocking the bypass line, and that this separation valve closes proportionally according to the pressure in the second line so that a pressure above a threshold value is maintained in the second line.

[0086] The separation valve of the deactivation circuit preferably opens the flow passage cross-section of the line according to the pressure in the second line. Preferably, the flow passage cross-section of this line widens as the pressure drops further. Preferably, there exists a control pressure range of the separation valve, which is near a critical value, for example, starting at an upper control pressure value slightly above the critical value and ending at a lower control pressure value slightly below the critical value. As soon as the pressure in the second line drops and reaches the control pressure value, the separation valve begins to open. If the pressure in the second line drops further, the separation valve opens further, and when it reaches the lower control pressure value, the flow passage cross-section of the line of the separation valve is fully opened. Within the control pressure range, the separation valve behaves proportionally.

[0087] By this circuit, adjustment to a critical value of the pressure in the second line is achieved. If a check valve is placed in front of the deactivation circuit starting from the second line, this adjustment occurs only when the pressure in the second line is below the pressure in the first line.

[0088] It is particularly advantageous that the separation valve is clamped (directly or indirectly in a pilot manner) between the effective surface where pressure in the second line acts and the preload element, and that the preload element is configured to open the separation valve so that the pressure in the second line is maintained above a critical value.

[0089] The preload element is, for example, a spring, and this spring is preferably preloaded to maintain a control pressure range having an upper control pressure value and a lower control pressure value. However, the preload element may also be implemented electronically or by magnets and in any other possible configuration. The preload element is configured to provide a comparative force against the pressure from the second line acting on the effective surface.

[0090] In addition, it is advantageous for the threshold value of the pressure maintained within the second line to be in the range of 2 bar to 20 bar.

[0091] Depending on the application and configuration of the hydraulic actuator, the threshold value is determined to ensure that cavitation in the hydraulic pump is reliably prevented. The appropriate design of the threshold value can be determined by simulation and / or testing for each circuit and application. In principle, a relatively low threshold value is preferred so that the pressure in the second line can be lowered further, thereby enabling the hydraulic actuator to generate a stronger force toward the second chamber (or a force toward the head chamber or a pulling force in the case of a differential cylinder).

[0092] In modified embodiments, the deactivation circuit and the check valve may be integrated with each other and may be implemented in a common hydraulic component that is implemented as a reverse pressure limiting valve having a backflow prevention function to limit the pressure drop in the second line below a threshold value.

[0093] A possible configuration of the pressure reservoir previously described, which is connected to a first line and can be separated from the first line by a shut-off valve, is described in detail here. It is advantageous to have a compressible element within the pressure reservoir that can be compressed to accommodate the pressurized hydraulic fluid within the pressure reservoir and expands when the hydraulic fluid is withdrawn from the pressure reservoir.

[0094] The compressible element is typically implemented as a gas bubble formed within a pressure vessel. Alternatively, the compressible element may be implemented, for example, by a spring-loaded diaphragm or any other modified embodiment.

[0095] The minimum pressure provided by the hydraulic fluid supply unit represents the lower pressure level that may exist within the first line, the first chamber, and the pressure reservoir. In the case of a differential cylinder as a hydraulic actuator component, this pressure level appears, for example, when the differential cylinder is fully extended. This is because the chamber with the larger cross-section is large and the chamber with the smaller cross-section is small, so the total internal volume of the hydraulic actuator is at its maximum. If there is a gas bubble as an elastic element within the pressure reservoir, this gas bubble expands. The maximum pressure within the pressure reservoir appears when the differential cylinder is fully retracted. At this time, the total internal volume of the hydraulic actuator is at its minimum because the chamber with the smaller cross-section is large and the chamber with the larger cross-section is small. If there is a gas bubble as a compressible element within the pressure reservoir, this gas bubble within the pressure reservoir is compressed. In this situation, the maximum differential volume of the hydraulic actuator or differential cylinder is absorbed by the pressure reservoir.

[0096] The compressible gas bubble is preferably formed of nitrogen, and this nitrogen is filled into the pressure reservoir during the initial commissioning of the hydraulic actuator. Particularly preferably, the gas bubble and the hydraulic fluid within the pressure reservoir are separated from each other by a separating element.

[0097] A diaphragm or a piston, in particular, may be used as the separating element. The pressure within the accumulator fluctuates within a pressure range, for example, between 20 bar and 45 bar, during the operation of the hydraulic actuator. When the cylinder is fully extended, the second chamber, having a (larger) second chamber cross-section, is large, and the pressure within the pressure reservoir is, for example, about 20 bar. When the cylinder is fully retracted, the second chamber, having a (larger) second chamber cross-section, is particularly small, and the differential volume to be absorbed by the pressure reservoir is particularly large. Then the pressure within the pressure reservoir is, for example, about 45 bar.

[0098] In principle, the pressure within a pressure reservoir is affected by various factors. In particular, temperature changes can cause changes in the pressure level due to thermal expansion.

[0099] The size of the gas bubble can be used to adjust the pressure characteristics of the pressure reservoir. During initial commissioning, the pressure reservoir is preferably (completely) filled with nitrogen (or other gas) so that the pressure within the gas bubble is below the minimum pressure at which the hydraulic actuator receives hydraulic fluid from the hydraulic fluid supply unit. The pressure reservoir must always be able to supply hydraulic fluid within the operating pressure range. The gas bubble within the pressure reservoir is compressed by the minimum pressure from the hydraulic fluid supply unit, and a certain amount of hydraulic fluid flows into the pressure reservoir. Before commissioning the hydraulic actuator, the initial filling pressure at which the gas bubble within the pressure reservoir is generated must always be lower than the lower limit operating pressure. In the previously described case where the operating pressure range is between 20 bar and 45 bar, the filling pressure may be, for example, 18 bar.

[0100] It is particularly desirable that at least one pressure sensor is placed in the first line and that the pressure within the first line can be measured by the pressure sensor, and that the hydraulic actuator includes a control unit and that the hydraulic fluid supply unit can be controlled in such a way that the pressure within the first line can be adjusted to a set value by the control unit.

[0101] The control unit may be configured independently for the described actuator, or it may be part of a higher-level control component in which special software components for the operation of the hydraulic actuator described herein are stored, for example.

[0102] The control unit uses the pressure signal of the pressure sensor in the first line, preferably in combination with a control signal received by the control unit to control the hydraulic actuator. The control unit includes, for example, a control lever that allows an operator to control the hydraulic actuator. In the operating conditions of the hydraulic actuator, where the first line or the first chamber is pressurized with hydraulic fluid and a shut-off valve is closed to disconnect the pressure reservoir from the first line, the pressure in the first line is preferably monitored.

[0103] In these situations, pressure within the first line and the first chamber is accumulated to pump hydraulic fluid from the second chamber into the first chamber, particularly with the help of a hydraulic pump. This is done, for example, when a pulling force is to be generated by a hydraulic actuator component. In these situations, the pressure within the first line and the first chamber is reduced, preferably by a hydraulic pump, as the hydraulic fluid is pumped back into the second line or the second chamber by the hydraulic pump.

[0104] If the desired pressure accumulation and / or desired pressure reduction in the first line or first chamber cannot be generated by the hydraulic pump alone, or if the pressure accumulation occurs faster than desired, the amount of hydraulic fluid in the first line and first chamber is preferably adjusted through the supply port. Additional hydraulic fluid may be supplied to the hydraulic actuator as needed through the supply port, and excess hydraulic fluid is discharged through the supply port.

[0105] When hydraulic fluid is pumped from the second chamber into the first chamber, a portion of the hydraulic fluid is typically discharged through the supply port because the volume of the second chamber is larger than the volume of the first chamber by a differential volume. If the shut-off valve is open, this differential volume will be contained within the pressure reservoir. Since the shut-off valve is closed, the differential volume must be discharged in a different manner. This is preferably done through the supply port. When hydraulic fluid is pumped back from the first chamber into the second chamber, additional hydraulic fluid is typically supplied to the hydraulic actuator through the supply port. The volume of the second chamber is larger than the volume of the first chamber by a differential volume. Due to the closed shut-off valve, the differential volume cannot be supplied from the pressure reservoir. The differential volume is preferably supplied through the supply port.

[0106] A hydraulic fluid supply unit connected to a supply port preferably includes a power distribution system (as previously described), through which pressurized hydraulic fluid can be supplied to a hydraulic actuator in a targeted manner by a central transfer pump. This power distribution system preferably has a valve actuator in which the supply or reception of hydraulic fluid can be controlled. The valve actuator can preferably be used by the power distribution system to regulate the pressure in a first line of the hydraulic actuator. The control unit of the described hydraulic actuator is preferably configured to actuate the valve actuator of the power distribution system to regulate the pressure in the first line of the hydraulic actuator.

[0107] The adjustment of the hydraulic actuator in the second operating mode with a closed shut-off valve is more complex than in the (typical) first operating mode with an open shut-off valve. Furthermore, in the second operating mode with a closed shut-off valve, regeneration by the hydraulic actuator is impossible at all or only possible to a limited extent. This is particularly because, as described, hydraulic fluid must typically be supplied or discharged through the supply port. This results in power loss that cannot be supplied for regeneration.

[0108] It is particularly desirable for the hydraulic actuator to have a switching switch. By means of this switching switch, when operation of the hydraulic actuator intended to apply a pressure that may be greater than the operating pressure of the accumulator to the first chamber of the hydraulic actuator component is provided, a controllable shut-off valve may be shut off.

[0109] The changeover switch may be configured, for example, as a switch for the operator. If a hydraulic actuator is installed on the working machine, the operator may operate this switch when, for example, intending to generate a particularly large pulling force with the hydraulic actuator that cannot be generated during normal operation (with the pressure reservoir connected to the first line). This may be the case, for example, in the situation described in the introduction, namely, when the operator intends to support the working machine with the hydraulic actuator to initiate a tire change.

[0110] The shut-off valve may be reopened, preferably via a switching switch, when the second operating mode in which the shut-off valve is closed needs to be terminated. Preferably, the switching switch does not act directly on the shut-off valve when the return switching to the open shut-off valve is performed. Preferably, when this return switching is performed, the pressure in the first line is first adjusted to the pressure in the pressure reservoir. Before the shut-off valve is reopened, the set pressure and actual pressure in the first line must again approach the actual pressure in the pressure reservoir. A signal from the switching switch for returning or opening the shut-off valve is preferably first transmitted to the control unit. The control unit preferably controls a hydraulic fluid supply unit (e.g., a valve drive unit of a power distribution system) to adjust the actual pressure in the first line to the actual pressure in the pressure reservoir. Only when it is identified using a pressure sensor in the first line that the actual pressure in the first line corresponds to the actual pressure in the pressure reservoir is a signal for returning or opening the shut-off valve, or the opening of the shut-off valve, implemented.

[0111] The value of the actual pressure within the pressure reservoir can preferably be stored in the control unit. Preferably, the actual pressure in the first line is measured by a pressure sensor before the shut-off valve is closed. When the shut-off valve is open, the pressure in the first line corresponds to the pressure within the pressure reservoir, so the pressure measured by the pressure sensor in the first line can be considered as the pressure within the pressure reservoir. As soon as the shut-off valve is closed, the pressure within the pressure reservoir can no longer change. Therefore, before the shut-off valve is opened again, the pressure in the first line is preferably adjusted to the pressure that appeared in the first line when the shut-off valve was closed and, for this reason, also appears within the pressure reservoir.

[0112] By adjusting the pressure in the first line to the pressure in the pressure reservoir before opening the shut-off valve, abrupt adjustment of the pressure in the pressure reservoir and the first line can be prevented. In particular, this can prevent noise, shock, or even damage to the hydraulic actuator.

[0113] The hydraulic actuator preferably has a control unit and a control section for operating a hydraulic actuator component. The control unit is designed to close a controllable shut-off valve when a control command is received through the control unit that a pressure, which may be greater than the maximum pressure of the accumulator, is intended to be applied to a first chamber of the hydraulic actuator component.

[0114] Particularly preferably, at least one pressure sensor is placed in the second line and connected to a control unit, and the pressure drop in the second line and at the second port can be monitored by the control unit, and the control unit is configured to close a controllable shut-off valve in response to the pressure drop in the second line.

[0115] Also preferably, a torque sensor is placed in the pump drive of the hydraulic pump and connected to a control unit, and the torque applied to the hydraulic pump by the pump drive can be monitored by the control unit, and the control unit is configured to close a controllable shut-off valve in response to an increase in torque when the hydraulic fluid is pumped out from the second line (7b).

[0116] The torque sensor can be configured in various ways here. The torque sensor may be a physical torque sensor that measures the torque of the pump drive unit, for example, through a strain gauge on the output shaft of the pump drive unit. The torque sensor may also be virtually configured here, for example, through current and voltage sensors on the electrical supply of the pump drive unit. Preferably, the torque within the pump drive unit can be estimated based on the operating voltage and / or operating current.

[0117] In this variant embodiment, it is preferable that a (manually operable) switching switch for closing the shut-off valve is not provided. Rather, the control unit is configured to identify a situation requiring the closing of the shut-off valve based on control commands, then first activate the shut-off valve in response to close the shut-off valve, thereby switching to a second operating mode in which the shut-off valve is closed, and then operate other components (hydraulic pump, hydraulic fluid supply unit, etc.) so that control commands predetermined by the control unit are implemented.

[0118] Particularly preferably, in this variant embodiment, the transition back to the first operating mode is also performed automatically. To this end, it must be identified that the operator no longer transmits control commands requiring the second operating mode. For this identification, for example, torque generated by the pump drive may also be used, in combination with consideration of the rotational direction signal.

[0119] In another variant embodiment, a pressure signal may be evaluated to identify a situation that allows a transition back to the first operating mode. Preferably, a pressure sensor is present in the second line. This pressure sensor is preferably connected to a control unit likewise to monitor the pressure within the second line.

[0120] If it is identified that a force requiring pumping hydraulic fluid into the second chamber by the hydraulic actuator is generated again based on the torque in the pump drive and / or the pressure in the second line, a transition to return to the first operating mode may be made or the shut-off valve may be opened again.

[0121] In another preferred variant embodiment of the hydraulic actuator, a retaining valve that can be closed is disposed between the first chamber and the first line, and by this retaining valve, the first chamber can be closed to maintain the hydraulic actuator component in a specified position.

[0122] By means of the shut-off retaining valve placed here, the pressure accumulated in the first chamber can be maintained without the continuous application of force by the hydraulic pump. The retaining valve for closing the first chamber is advantageous when used in conjunction with a shut-off valve for disconnecting the pressure reservoir, because a greater pressure can be generated in the first chamber by the shut-off valve and this pressure can be maintained by the retaining valve.

[0123] Additionally, a mobile work machine comprising a hydraulic actuator according to the present invention is described herein. The mobile work machine may be a construction machine, an agricultural machine, a municipal machine, or a forestry machine. The hydraulic actuator may be used, in particular, to raise and lower an excavator arm or an arm of a telescopic loader.

[0124] A method for generating force by pressurizing a first chamber of a hydraulic actuator component with a described hydraulic actuator is also described herein, comprising the following steps:

[0125] a) a step of disconnecting the pressure reservoir from the first line by closing a controllable shut-off valve;

[0126] b) adjusting the pressure in the first chamber to an increased pressure exceeding the designed operating pressure of the accumulator; and

[0127] c) A step of operating a hydraulic pump to pump hydraulic fluid from the second chamber and the second line into the first chamber and the first line.

[0128] It should be noted that the special advantages and design features described in relation to the hydraulic actuator components described above may also apply to the method. This method describes the operation of the described hydraulic actuator components. In step a), a transition is made from a first operating mode (where the pressure reservoir is connected) to a second operating mode in which the pressure reservoir is disconnected from the first line. Steps b) and c) are performed during the operation of the hydraulic actuator components in the second operating mode, whereby the hydraulic actuator is used to generate a force that requires a pressure in the first chamber above the design operating pressure of the accumulator. The design operating pressure is, in particular, the maximum pressure for which the accumulator is designed. This force is, in particular, a (relatively large) pulling force generated by the hydraulic actuator components.

[0129] The pressure adjustment according to step b) and the operation of the hydraulic pump according to step c) are preferably performed in a second operating mode with at least partial temporal overlap. Preferably, in step b) and / or step c), a hydraulic fluid supply unit is additionally used to adjust the pressure within the first line. At this time (depending on the operating conditions), hydraulic fluid is preferably supplied from the hydraulic fluid supply unit to the hydraulic actuator and / or received from the hydraulic actuator (from the first line).

[0130] The method of operation particularly preferably further comprises a transition to a first operating mode having a pressure reservoir connected to a first line, and comprises the following steps:

[0131] d) a step of adjusting the pressure in the first line to the pressure in the pressure reservoir; and

[0132] e) Step of opening the shut-off valve.

[0133] The method of operation for operating the described hydraulic actuator is preferably controlled by the control unit of the hydraulic actuator. In a modified embodiment, individual steps of the method (as previously described in relation to the hydraulic actuator) are initiated manually by an operator—for example, by operating a changeover switch to switch from a first operating mode to a second operating mode. In a modified embodiment, if a control command requiring a switch from the first operating mode to the second operating mode, and in some cases back to the first operating mode, is predetermined by the operator or by a higher-level control unit, it is also possible for the described method steps and the described switch to be performed in an automated manner with the assistance of the control unit. Brief explanation of the drawing

[0134] The present invention and the technical context of the present invention are described in more detail below with reference to the drawings. The drawings represent preferred embodiments, and the present invention is not limited thereto. In particular, it should be noted that the drawings and, in particular, the size ratios depicted in the drawings are merely schematic. FIGS. 1 through 6 illustrate circuit diagrams of the hydraulic actuators described herein in various operating states. First, the structure applicable to all drawings is described. Then, the operating states depicted in the drawings are examined in detail. FIGS. 1 to 4 show various modified embodiments of the hydraulic actuator (1) described. The operation method of the described hydraulic actuator (1) in various operating situations, having a differential cylinder as a hydraulic actuator component (3), is illustrated with reference to FIGS. 5 to 8. FIG. 9 shows another alternative variant embodiment of the hydraulic actuator (1) described. The basic configuration of the described hydraulic actuator (1) is similar according to all of FIGS. 1 through 9. FIGS. 1 through 4 particularly illustrate various concepts of driving the described hydraulic actuator (1). The operation method of the described hydraulic actuator (1) is generalized and described based on FIGS. 5 and FIGS. 8 (for all variant embodiments shown in FIGS. 1 through 4). FIG. 9 shows an alternative variant embodiment that differs from the variant embodiment according to FIGS. 1 through 8, particularly with respect to the hydraulic layout. The features of the variant embodiment according to FIG. 9 can be applied to all variant embodiments according to FIGS. 1 through 8. Specific details for implementing the invention

[0135] A hydraulic actuator (1) in the form of a differential cylinder according to all variant embodiments comprises a piston (26) guided within a cylinder body (25) and having a rod (27) coupled to one side. Within the cylinder body (25), there is a first chamber (4a), also referred to as a ring chamber, above the piston (26). Within the cylinder body (25), there is a second chamber (4b), also referred to as a head chamber, below the piston (26). The first chamber / ring chamber (4a) has a first chamber cross-section / ring chamber cross-section (8a). The second chamber / head chamber (4b) has a second chamber cross-section / head chamber cross-section (8b). The second chamber cross-section (8b) is larger than the first chamber cross-section (8a), thereby creating a differential volume (28) defined by the thickness or cross-section of the rod (27). The differential volume (28) is illustrated as an example in FIG. 1.

[0136] The hydraulic actuator (1) includes a hydraulic pump (2) having a first port (6a) and a second port (6b) and preferably capable of four quadrant operation, that is, capable of operating in both motor mode and generator mode in both directions from the first port (6a) to the second port (6b) and vice versa. A ring chamber (4a) is connected to the first port (6a) of the hydraulic pump (2) via a first line (7a). A head chamber (4b) is connected to the second port (6b) of the hydraulic pump (2).

[0137] A pressure reservoir (5) is connected to the first line (7a), and a compressible element (17) is present inside it, and this compressible element (17) is formed particularly by a gas bubble inside the pressure reservoir, and this gas bubble is initially filled with gas pressure (before the initial commissioning of the hydraulic actuator (1)).

[0138] A retaining valve (22) is present in the second line (7b), and this retaining valve (22) can be closed to block the second line (7b) and to maintain the pressure in the head chamber (4b) without needing to maintain the pressure difference between the second port (6b) and the first port (6a) in the hydraulic pump (2).

[0139] A supply port (15) connected to a hydraulic fluid supply unit (16) is provided in the first line (7a). The hydraulic fluid supply unit (16) includes a central transfer pump (21) capable of providing pressurized hydraulic fluid. The hydraulic fluid supply unit (16) preferably also includes a power distribution system (36), through which the pressurized hydraulic fluid provided by the central transfer pump (21) can be discharged to the supply port (15) in a desired manner. The drawings each illustrate a part of the power distribution system (36) responsible for supplying hydraulic fluid to the hydraulic actuator (1) described herein. A plurality of hydraulic consumers are preferably connected to the power distribution system (36). The power distribution system (36) preferably includes a plurality of valves or stages that may be arranged side by side, for example. The hydraulic actuator (1) described herein is preferably one of these consumers and is connected to one stage / one valve of the power distribution system (36). The power distribution system (36) preferably has its own valve assembly for each connected consumer, and the valve assembly of the power distribution system (36) responsible for the hydraulic actuator (1) described herein is schematically illustrated in this drawing. For each consumer, the power distribution system (36) has two ports A and B to which hydraulic fluid can be optionally supplied or received. The two ports A and B can be directly connected, for example, to the two chambers of a differential cylinder, and then the differential cylinder can be controlled by the power distribution system (36). In the circuit illustrated herein, only one of the two ports (here, for example, port B) is connected to the supply port (15) of the hydraulic actuator (1). Here, the pressure in particular within the first line (7a) and accordingly within the first chamber (4a) can be set by the power distribution system (36) in a desired manner.This is achieved by supplying or receiving hydraulic fluid from the supply port (15) in a targeted manner to control the pressure within the first line (7a) and the first chamber (4a).

[0140] The hydraulic fluid supply unit (16) or the central transfer pump (21) utilizes the main reservoir (24) to provide hydraulic fluid. Excess hydraulic fluid from all components of the entire system (particularly from all components of the hydraulic actuator (1)) is preferably recirculated to this main reservoir (24). The power distribution system (36) preferably has a port P that receives pressurized hydraulic fluid supplied by the transfer pump (21). The power distribution system (36) preferably has a port T that is connected to the main reservoir and from which excess hydraulic fluid can be discharged. Leakage flow (29) from components such as, for example, the hydraulic pump (2) is also preferably introduced into the main reservoir (24). The lines (7a, 7b) and chambers (4a, 4b) and the pressure reservoir (5) of the hydraulic actuator (1) are filled by the hydraulic fluid supply unit (16). After the initial charge for operation (e.g., when the hydraulic actuator (1) is activated on the working machine provided), no additional hydraulic fluid is typically delivered from the supply port (15) into the lines (7a, 7b) and chambers (4a, 4b) of the hydraulic actuator (1) (typically in the first operating mode of the hydraulic actuator). The hydraulic actuator (1) operates with the amount of hydraulic fluid present in the lines (7a, 7b), pressure reservoir (15), and chambers (4a, 4b). However, a minimum pressure is maintained in the first line (7a) through the supply port (15). When the pressure in the first line (7a) drops below a predetermined value, the line (7a) (and consequently other components, the second line (7b), chambers (4a, 4b), and pressure reservoir (5)) is recharged.

[0141] Preferably, a controllable pressure relief valve (18) is also disposed in the first line (7a), and hydraulic fluid can be discharged from the first line (7a) through this pressure relief valve (18) when the pressure in the first line (7a) is too high or the hydraulic actuator (1) is deactivated. The two lines (7a, 7b) each include a pressure relief valve (20a, 20b), and hydraulic fluid can be discharged to the main reservoir (24) through this pressure relief valve (20a, 20b) when there is overpressure in each line (7a, 7b). The pressure relief valve (20a, 20b) is preferably placed on a line (7a, 7b) immediately adjacent to the chamber (4a, 4b) so that no other part (especially a valve blocking the line (7a, 7b)) is placed between the pressure relief valve (20a, 20b) and the chamber (4a, 4b), and overpressure in the chamber (4a, 4b) is prevented by the pressure relief valve (20a, 20b).

[0142] The first line (7a) and the second line (7b) are connected to each other through the bypass line (9). The connection between the bypass line (9) and the first line (7a) and the second line (7b) is preferably installed at connection points A and B, which enables a rapid and stable flow of additional hydraulic fluid from the first line (7a) toward the hydraulic pump (2) through the bypass line (9) and the second line (7b) when the bypass line (9) is opened to prevent cavitation within the hydraulic pump (2). Within the bypass line (9) there is a deactivation circuit (11), which includes a separation valve (12), which blocks the bypass line (9) until the pressure extracted from the second line (7b) becomes higher than a threshold value. Preferably, pressure extraction X is performed in the second line (7b) near the second port (6b) of the hydraulic pump (2). As soon as the pressure at the second port (6b) of the hydraulic pump (2) drops below the threshold value, the deactivation of the bypass line (9) by the deactivation circuit (11) is terminated and the bypass line (9) is activated. To maintain the pressure in the second line (7b) above the threshold value, additional hydraulic fluid is introduced from the first line (7a) through the bypass line (9). The pressure in the second line (7b) preferably acts on the effective surface (13) of the separation valve (12) and acts thereaga against the preload element (14). The opening and closing of the separation valve (12) is determined by the interaction between the pressure acting on the effective surface (13) and the force of the preload element (14) acting against this pressure. As soon as the pressure drops below the upper limit value, the separation valve (12) begins to open. When the lower limit value is reached, the separation valve (12) is fully opened. Between the upper and lower limits, the separation valve (12) is preferably opened proportionally so that the flow passage cross-section of the separation valve (12) is increasingly expanded.The limit value and proportional opening behavior are tuned, together with the structure of the lines (7a, 7b, 9), so that the critical value of the pressure in the second line (7b) is maintained as intended. The interaction between the effective surface (13) and the preload element (14) for controlling the separation valve (12) of the deactivation circuit (11) can be implemented directly in the valve element itself for closing and opening the flow passage cross-section, or in a pilot, where the pilot again controls the valve element of the separation valve (12). This control is called “pilot control.” In principle, a wide variety of approaches are possible for implementing the deactivation circuit (11).

[0143] In addition to the deactivation circuit (11), a check valve (10) is preferably also provided in the bypass line (9). The check valve (10) is basically closed when the pressure in the second line (7b) is greater than the pressure in the first line (7a). In the direction from the second line (7b) toward the first line (7a), the check valve (10) is preferably positioned in front of the deactivation circuit (11). Thus, the deactivation circuit (11) is subjected to pressure only when the pressure in the second line (7b) is lowered below the pressure in the first line (7a) by the hydraulic pump (2), that is, when hydraulic fluid is pumped out from the ring chamber (4a) and pumped into the head chamber (4b) to generate a pulling force (33) to the hydraulic actuator (1) of the hydraulic actuator component (3) configured as a differential cylinder. By design, the deactivation circuit (11) also typically has a leakage flow (29).

[0144] For cases where a particularly large pulling force needs to be generated by the described hydraulic actuator (1), a shut-off valve (35) is additionally provided to disconnect the pressure reservoir (5) from the first line (7a). The shut-off valve (35) is configured as a 2 / 2-way valve. In the first open switching position of the shut-off valve (35), the first line (7a) is connected to the pressure reservoir (5) to enable the flow of hydraulic fluid from the first line (7a) toward the pressure reservoir (5) and the flow of hydraulic fluid from the pressure reservoir (5) toward the first line (7a). In the second closed switching position of the shut-off valve (35), the first line (7a) is disconnected from the pressure reservoir (5) so that the hydraulic fluid cannot move from the first line (7a) toward the pressure reservoir (5) or from the pressure reservoir (5) toward the first line (7a), i.e., so that the flow of hydraulic fluid is blocked in both flow directions. By disconnecting the pressure reservoir (5) from the first line (7a), the hydraulic actuator (1) can be switched to a second operating mode and operated as described above.

[0145] In a modified embodiment according to FIG. 1, a switching switch (37) is provided that can close and reopen the shut-off valve (35). When an operator intends to generate movement and force requiring pressurization of the first chamber (4a) with the hydraulic actuator (1), the switching switch (37) must first be operated. Then, the control unit (38) can be operated to generate the corresponding movement and force with the hydraulic actuator (1). The control command from the control unit (38) is preferably converted by the control unit (39) into a driving signal to the pump driving unit (19) and the valve driving unit (41) of the power distribution system (36). To generate the driving signal, the control unit (39) preferably also considers the pressure in the first line (7a) monitored by the pressure sensor (40) in the first line (7a), whereby the pressure sensor (40) outputs a sensor signal to the control unit (38). Control commands, sensor signals, and driving signals are indicated by dashed arrows in the drawing.

[0146] In the modified embodiment according to FIG. 2, the switching switch (37) is omitted. In this modified embodiment, the control unit (39) is configured to identify when the control unit (38) generates a control command requiring pressurization of the first chamber (4a). This pressurization again requires the pressure reservoir (5) to be disconnected from the first line (7a). In this case, the control unit (39) is configured to transmit a driving signal to the controllable shut-off valve (35) that enables the closing of the shut-off valve (35). According to the modified embodiment according to FIG. 2, additional information regarding the state of the hydraulic actuator (1) helps in the automatic driving of the controllable shut-off valve (35). In particular, for the proper driving of the hydraulic pump (2) and the valve driving unit (41) of the power distribution system (36), it is helpful to monitor the pressure acting in the lines (7a, 7b) and on the hydraulic pump (2). Based on this pressure, the external load acting on the hydraulic actuator component (3) can be identified. Preferably, when it is determined that closing the shut-off valve (35) is necessary for the execution of a control command based on the control command present from the control unit (38) and the pressure in the lines (7a, 7b), the shut-off valve (35) is closed. To monitor the pressure in the second line (7b), an additional pressure sensor (40) is provided in the second line (7b).

[0147] In a modified embodiment according to FIG. 3, a torque sensor (23) is placed in the pump drive unit (19) instead of the pressure sensor (40) of the second line (7b). This torque sensor (23) is configured to transmit a sensor signal to the control unit (39). By monitoring the torque of the pump drive unit (19), resistance to the hydraulic pump (2) transporting hydraulic fluid can be identified. The torque sensor (23) of the pump drive unit (19) is an alternative to the pressure sensor (40) of the second line (7b) according to FIG. 2.

[0148] In a modified embodiment according to FIG. 4, a retaining valve (22) is disposed within the first line (7a). The first chamber (4a) can be separated from the first line (7a) by this retaining valve (22). This can be done particularly when pressure accumulates within the first chamber (4a) and the hydraulic actuator component (3) or hydraulic actuator (1) thereby needs to maintain force.

[0149] FIGS. 1 through 4 each illustrate an operating situation in which a hydraulic actuator (1) is charged by a hydraulic fluid supply unit (16). In each case, the direction of transfer of hydraulic fluid from the supply port (15) into the hydraulic actuator (1) or, in particular, into the first line (7a) is illustrated. Additional operating situations of the hydraulic actuator (1) are now illustrated in FIGS. 5 through 8, which are generalized with respect to specific features for controlling the shut-off valve (35), the power distribution system (36), and the hydraulic pump (2). The operating situations illustrated based on FIGS. 5 through 8 may be applied to all hydraulic actuators (1) according to FIGS. 1 through 4 and FIG. 9. Arrows indicate the transfer direction (30) and the flow (32) driven by the pressure gradient, respectively. Pressurized lines (7a, 7b) and chambers (4a, 4b) are each indicated.

[0150] According to the situation illustrated in FIGS. 1 to 4, the initial filling of the line (7a, 7b), chamber (4a, 4b), and pressure reservoir (5) is performed particularly through the supply port (15). Hydraulic fluid is pumped into the system in the transfer direction (30) from the supply port (15). A compressible element (17), preferably composed of a gas bubble within the pressure reservoir (5), is compressed so that the pressure reservoir (5) is filled and a predetermined initial pressure is formed within the line (7a). The magnitude of the predetermined initial pressure preferably depends on the respective position of the hydraulic actuator component (3). When the hydraulic actuator component (3) is fully retracted, the initial pressure is high because the total volume of the ring chamber (4a) and head chamber (4b) is particularly small and the differential volume (28) must be fully introduced into the pressure reservoir (5). When the hydraulic actuator component (3) is fully extended, the total volume of the ring chamber (4a) and the head chamber (4b) is particularly large, and the differential volume (28) is entirely within the head chamber (4b). Since there is no need to introduce a large amount of hydraulic fluid into the pressure reservoir (5), the initial pressure is low.

[0151] FIG. 5 illustrates a situation in which a hydraulic pump (2) is driven in motor mode by a pump drive unit (19), and hydraulic fluid is pumped from a ring chamber (4a) into a head chamber (4b) to extend a hydraulic actuator component (3). The hydraulic pump (2) operates as a pump. The pressure in the head chamber (4b) or the second line (7b) is higher than the pressure in the first ring chamber (4a) or the first line (7a). A check valve (10) blocks the bypass line (9). The deactivation circuit (11) is not loaded. Flow through the bypass line (9) is prevented.

[0152] FIG. 6 illustrates a situation in which a hydraulic actuator component (3) is maintained in a specific position. To achieve this, the holding valve (22) is closed. Now, the pressure in the segment (31) of the second line (7b) between the holding valve (22) and the hydraulic pump (2) can drop below the pressure in the first line (7a). In the situation illustrated in FIG. 6, no significant flow or transfer of hydraulic fluid occurs. In this state, if the pump is accidentally driven to pump hydraulic fluid from 7a to 6a, the pump will be protected from cavitation.

[0153] FIG. 7 now illustrates a situation in which a hydraulic pump (2) is driven in generator mode by the flow (32) of hydraulic fluid from the head chamber (4b) into the ring chamber (4a). An external load (34) pushes the hydraulic actuator component (3), which is configured as a differential cylinder. Thus, pressure is generated within the head chamber (4b), and this pressure drives the flow (32) into the ring chamber (4a). Energy from the pressure of the hydraulic fluid is converted in generator mode by the hydraulic pump (2) and the pump drive unit (19) and stored in an energy storage device (not shown here).

[0154] According to FIG. 8, to generate a pulling force (33) to the hydraulic actuator component (3) configured as a differential cylinder, the deactivation circuit (11) and the controllable shut-off valve (35) in the bypass line (9) are actuated. Hydraulic fluid is actively pumped by the hydraulic pump (2) from the head chamber (4b) and the second line (7b) into the first line (7a) and the ring chamber (4a). The pressure in the head chamber (4b) and the second line (7b) is lowered significantly below the pressure in the ring chamber (4a) and the first line (7a). Thus, a pulling force (33) is generated in the hydraulic actuator component (3). The check valve (10) in the bypass line (9) is not actuated. However, since the pressure in the second line (7b) is still above the threshold, the deactivation circuit (11) keeps the bypass line (9) closed. The pressure in the first line (7a) and the first chamber (4a) can be increased beyond the maximum allowable pressure for the pressure reservoir (5) due to the closed shut-off valve (35). The driving of the pump drive (19) of the hydraulic pump (2) and the valve drive (41) of the power distribution system (36) is performed as previously described, particularly in relation to FIGS. 1 to 4.

[0155] FIG. 9 illustrates an alternative modified embodiment of the hydraulic actuator (1) described. All details regarding the mode of operation described in relation to FIG. 1 through 8 may be applied to the modified embodiment of the hydraulic actuator (1) according to FIG. 9. In the modified embodiment according to FIG. 9, the ring side and the head side are reversed. The first chamber (4a) is the head chamber and the second chamber (4b) is the ring chamber. The cross-section of the first chamber (8a) is larger than the cross-section of the second chamber (8b). As in the modified embodiment according to FIG. 1 through 6, the pressure reservoir (5) is connected to the first line (7a), where the first line (7a) forms the head chamber line.

[0156] In this modified embodiment, the differential volume (28) that is generated due to the difference between the first chamber cross-section (8a) and the second chamber cross-section (8b) and flows out of the first chamber (4a) when the rod (27) of the differential cylinder is extended does not flow into the pressure reservoir (5) at all through the hydraulic pump (2). Instead, the differential volume (28) moves directly from the first chamber (4a) into the pressure reservoir (5) through the segment of the first line (7a). In the case of such a hydraulic actuator (1), the hydraulic actuator component (3) within the differential cylinder can be used to generate pulling forces (33), particularly when the hydraulic actuator component (3) or the rod (27) of the differential cylinder is retracted. Conversely, regeneration is possible when an external load pulls the hydraulic actuator component (3), that is, when the rod (27) of the differential cylinder is pulled out. Then, energy from the pressure of the hydraulic fluid can be converted by a hydraulic pump (2) and a pump drive unit (19) operating in generator mode.

[0157] In the modified embodiment of the actuator (1) described here, when the pressure in the second line (7b) drops too much and reaches a critical value, a bypass flow is formed from the first line (7a) into the second line (7b), so that a shortage of supply to the hydraulic pump (2) and the resulting cavitation are prevented by the bypass line (9).

[0158] The deactivation circuit (11) and the controllable shut-off valve (35) enable the hydraulic actuator (1) according to FIG. 9, despite the bypass line (9), for the pressure in the second line (7b) to also be lower than the pressure in the first line (7a), and for the pressure in the first line (7a) to also be increased beyond the maximum pressure of the pressure reservoir (5). For this reason, the hydraulic actuator (1) according to FIG. 9 can also be used to generate pushing forces. Explanation of the symbols

[0159] 1: Hydraulic actuator 2: Hydraulic pump 3: Hydraulic Actuator Components 4a: First chamber, ring chamber 4b: Second chamber, head chamber 5: Pressure reservoir 6a: 1st port 6b: Port 2 7a: 1st line, ring chamber line 7b: 2nd line, head chamber line 8a: First chamber cross-section, ring chamber cross-section 8b: Second chamber cross-section, head chamber cross-section 9: Bypass line 10: Check valve 11: Deactivation circuit 12: Separation valve 13: Effective surface 14: Preload element 15: Supply port 16: Hydraulic fluid supply unit 17: Compressible elements 18: Pressure relief valve 19: Pump drive unit 20a: First pressure relief valve 20b: Second pressure relief valve 21: Central transfer pump 22: Retention valve 23: Torque sensor 24: Main Reservoir 25: Cylinder body 26: (Guided) Piston 27: Road 28: Differential volume 29: Leakage flow 30: Transfer direction 31: Segment 32: Yudong 33: Pulling force 34: External load 35: Controllable shut-off valve 36: Power distribution system 37: Changeover switch 38: Control unit 39: Control Unit 40: Pressure sensor 41: Valve actuator A: Second connection point B: 1st connection point X: Pressure extraction

Claims

Claim 1 As a hydraulic actuator (1), at least one bidirectionally operable hydraulic pump (2) for pumping hydraulic fluid, comprising two ports (6a, 6b); and a hydraulic actuator component (3) comprising two hydraulic fluid chambers (4a, 4b);The hydraulic fluid chambers (4a, 4b) may be supplied with hydraulic fluid to operate the hydraulic actuator component (3), and the hydraulic fluid chambers (4a, 4b) are each connected to the ports (6a, 6b) of the hydraulic pump (2) through lines (7a, 7b), the first line (7a) connects the first chamber (4a) to the hydraulic pump (2), and the second line (7b) connects the second chamber (4b) to the hydraulic pump (2), so that when one of the hydraulic fluid chambers (4a, 4b) is filled with hydraulic fluid, the hydraulic fluid is simultaneously pushed out from the other hydraulic fluid chambers (4b, 4a), and the volume of the hydraulic fluid is moved through the hydraulic pump (2), and the second chamber cross-section (8b) of the second chamber (4b) is different from the first chamber cross-section (8a) of the first chamber (4a), and the A first line (7a) is connected to a pressure reservoir (5), and a differential volume (28) may be accommodated and provided within the pressure reservoir (5), the differential volume (28) is generated as a result of different chamber cross-sections (8a, 8b) of the chambers (4a, 4b), and there is a compressible element (17) within the pressure reservoir (5), the compressible element (17) may be compressed to accommodate pressurized hydraulic fluid within the pressure reservoir (5) and expands when hydraulic fluid is withdrawn from the pressure reservoir (5), - the first line (7a) also includes a supply port (15), hydraulic fluid is supplied to the hydraulic actuator (1) through the supply port (15), a hydraulic fluid supply unit (16) is connected to the supply port (15), and the hydraulic fluid supply unit (16) maintains a minimum pressure within the first line (7a), - controllable shut-off A hydraulic actuator (1) wherein a valve (35) is positioned between the first line (7a) and the pressure reservoir (5), and the controllable shut-off valve (35) can be used to disconnect the pressure reservoir (5) from the first line (7a). Claim 2 In claim 1, the hydraulic actuator component (3) is a hydraulic actuator (1) which is at least one differential cylinder. Claim 3 In claim 1 or 2, the hydraulic fluid supply unit (16) is optionally capable of delivering hydraulic fluid to the supply port (15) or receiving hydraulic fluid from the supply port (15), a hydraulic actuator (1). Claim 4 A hydraulic actuator (1), wherein, in any one of claims 1 to 3, the first line (7a) and the second line (7b) are additionally connected to each other by a bypass line (9), and as a result of the bypass line (9), when the pressure in the second line (7b) drops and reaches a critical value, a bypass flow is formed from the first line (7a) into the second line (7b) through the bypass line (9), thereby preventing a shortage of hydraulic fluid supply in the hydraulic pump (2), and a deactivation circuit (11) is disposed within the bypass line (9), and by the deactivation circuit (11), the bypass line (9) can be interrupted when the pressure in the second line (7b) is above a critical value. Claim 5 A hydraulic actuator (1) wherein, in any one of claims 1 to 4, a retaining valve (22) capable of closing is disposed between the second chamber (4b) and the second line (7b), and the second chamber (4b) can be closed by the retaining valve (22) to maintain the hydraulic actuator component (3) in a specified position. Claim 6 A hydraulic actuator (1), wherein in any one of claims 1 to 5, the bypass line (9) is provided with a check valve (10) in addition to the deactivation circuit (11), and the check valve (10) can be opened in the direction from the first line (7a) to the second line (7b), thereby ensuring that the pressure in the second line (7b) does not fall below the pressure in the first line (7a) even when the pressure in the second line (7b) is below a threshold value. Claim 7 In any one of claims 1 to 6, the hydraulic pump (2) is a hydraulic actuator (1) suitable for operation in generator mode and motor mode. Claim 8 A hydraulic actuator (1) in any one of claims 1 to 7, wherein the hydraulic pump (2) is connected to a pump drive unit (19), and energy from the pressure and volume flow of the hydraulic fluid is converted by the hydraulic pump (2) and stored in an energy storage device by the pump drive unit (19). Claim 9 In any one of claims 1 to 8, at least one pressure sensor (40) is disposed on the first line (7a) and can be used to measure the pressure within the first line (7a), and the hydraulic actuator (1) includes a control unit (39), and by the control unit (39), the hydraulic fluid supply unit (16) can be controlled in such a way that the pressure within the first line (7a) can be adjusted to a set value. Claim 10 A hydraulic actuator (1) comprising a switching switch (37) in any one of claims 1 to 9, wherein when operation of the hydraulic actuator (1) is provided such that a pressure greater than the operating pressure of the pressure reservoir (5) is applied to the first chamber (4a) of the hydraulic actuator component (3) by means of the switching switch (37), the controllable shut-off valve (35) can be shut off. Claim 11 A hydraulic actuator (1) comprising, in any one of claims 1 to 10, a control unit (38) for operating the hydraulic actuator component (3) and a control unit (39), wherein the control unit (39) is designed to close the controllable shut-off valve (35) when a control command is received through the control unit (38) that a pressure which may be greater than the maximum pressure of the pressure reservoir (5) is intended to be applied to the first chamber (4a) of the hydraulic actuator component (3). Claim 12 A hydraulic actuator (1), wherein, in any one of claims 1 to 11, at least one pressure sensor (40) is positioned on the second line (7b) and connected to a control unit (38), and the pressure drop in the second line (7b) and in the second port (6b) can be monitored by the control unit (38), and the control unit (38) is designed to close the controllable shut-off valve (35) in response to the pressure drop in the second line (7b). Claim 13 A hydraulic actuator (1), wherein, in any one of claims 1 to 12, a torque sensor (43) is positioned on the pump drive unit (19) of the hydraulic pump (2) and connected to a control unit (38), and the torque applied to the hydraulic pump (2) by the pump drive unit (19) can be monitored by the control unit (38), and the control unit (38) is designed to close the controllable shut-off valve (35) in response to an increase in torque when hydraulic fluid is pumped out from the second line (7b). Claim 14 A mobile work machine comprising a hydraulic actuator (1) according to any one of claims 1 to 13. Claim 15 A method for generating force by pressurizing the first chamber (4a) of the hydraulic actuator component (3) with a hydraulic actuator (1) according to any one of claims 1 to 13, comprising: a) separating the pressure reservoir (5) from the first line (7a) by closing the controllable shut-off valve (35); b) adjusting the pressure in the first chamber (4a) to an increased pressure exceeding the designed operating pressure of the pressure reservoir (5); and c) operating the hydraulic pump (2) to pump hydraulic fluid (2) from the second chamber (4b) and the second line (7b) into the first chamber (4a) and the first line (7a).

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