Hydraulic actuator with recuperation, method for operating the hydraulic actuator, and mobile work machine

Abstract

A hydraulic actuator (1) having a hydraulic actuator component (3) with a first chamber (4a) with a first cross section (20a) and a second chamber (4b) with a second cross section (20b) which is greater than the first cross section (20a), and having a bidirectionally operable hydraulic pump (2), by means of which, in order to actuate the actuator component (3), hydraulic fluid can be conveyed bidirectionally between the chambers (4a, 4b) and by way of which hydraulic energy from the chambers (4a, 4b) can be recuperated, wherein, owing to the greater second cross section (20b), a delta volume (22) occurs as a change in the overall volume of the chambers (4a, 4b) when hydraulic fluid is conveyed from one chamber (4a, 4b) into the other chamber (4b, 4a), wherein the hydraulic pump (2) is designed in two parts, comprising a first sub-pump (21a), which connects the chambers (4a, 4b), and comprising a second sub-pump (21b), which is connected to the second chamber (4b) having the greater hydraulic cross section (20b) and to a valve assembly (5), by way of which the second sub-pump (21b) can be selectively connected to a first hydraulic fluid supply (23a) or a second hydraulic fluid supply (23b), wherein the hydraulic fluid supplies (23a, 23b) are configured to be able to provide or receive hydraulic fluid in order to compensate for the delta volume (22).

Description

[0001] Hydraulic actuator with recuperation, method for operating the hydraulic actuator and mobile working machine

[0002] The invention relates to a hydraulic actuator, in particular an electro-hydraulic actuator, especially a linear actuator, which can produce a linear actuator movement. The hydraulic actuator comprises a hydraulic actuator component and a (preferably) electrically driven hydraulic pump that supplies hydraulic fluid to drive the hydraulic actuator component.

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

[0004] Such hydraulic actuators are particularly suitable for the electrification and increased energy efficiency of mobile machinery with hydraulic components. Thanks to the four-quadrant capability of these linear actuators, significant amounts of energy can be recuperated into electrical energy during the operation of mobile machinery. This would be possible, for example, in a situation where an excavator bucket driven by the electro-hydraulic actuator is lowered. The potential energy of the excavator bucket can then be transferred into a hydraulic fluid flow by the hydraulic actuator component. Energy can then be extracted from this hydraulic fluid flow by the electric hydraulic pump in generator mode and recovered, or (in the case of an electro-hydraulic actuator) converted into electrical energy.Designing such hydraulic actuators for a specific application presents a particular challenge – especially for variants where the hydraulic actuator component has a delta volume (also called differential volume). Hydraulic actuators with a delta volume are primarily differential cylinders. Hydraulic differential cylinders are used for many tasks – for example, lifting and / or lowering a load. A typical application for such hydraulic differential cylinders would be in an excavator arm, the arm of a telescopic handler, or the front attachment of a tractor. In such applications, hydraulic differential cylinders are used, for example, to raise and lower the arm of a telescopic handler or the front attachment of a tractor. There are many other applications for such hydraulic differential cylinders, particularly in the construction and agricultural machinery sectors.of municipal and forestry machinery. Differential cylinders are frequently used in such applications due to their ability to provide high forces.

[0005] Depending on the application, different operating points of the hydraulic actuator component occur with varying frequency. For example, a hydraulic actuator component used in an excavator arm is primarily driven to lift the excavator arm against gravity. When lowering the excavator arm, gravity typically provides assistance, and the potential energy of the excavator arm, and potentially also of the load on a bucket attached to the excavator arm, can be recuperated. Driving such an actuator component in the opposite direction occurs in this application when the excavator arm is used to push the excavator bucket into the ground. By adapting the hydraulic actuator to the specific application, a particularly high efficiency can be achieved for both driving the hydraulic actuator component and during energy recuperation.The object of the present invention is to at least partially solve the problems described with reference to the prior art. In particular, a hydraulic actuator is to be proposed which offers special degrees of freedom with regard to its design and can be designed in a particularly advantageous manner for specific operating points.

[0006] This problem is solved by the invention according to the features of the independent claims. Further advantageous embodiments are specified in the dependent claims, as well as in the description and, in particular, in the description of the figures. It should be noted that the person skilled in the art can combine the individual features in a technologically meaningful way and thereby arrive at further embodiments of the invention.

[0007] The invention relates to a hydraulic actuator with a hydraulic actuator component comprising a first chamber with a first cross-section and a second chamber with a second cross-section larger than the first, and a bidirectionally operable hydraulic pump with which hydraulic fluid can be conveyed bidirectionally between the chambers for actuating the actuator component and with which hydraulic energy can be recuperated from the chambers, wherein, due to the larger second cross-section, a delta volume occurs as a change in the total volume of the chambers when hydraulic fluid is conveyed from one chamber to the other, wherein the hydraulic pump is designed in two parts with a first sub-pump that connects the chambers and with a second sub-pump that is connected to the second chamber with the larger hydraulic cross-section and to a valve arrangement.with which the second sub-pump can be optionally connected to a first hydraulic fluid supply or a second hydraulic fluid supply, the hydraulic fluid supplies being designed to provide or receive hydraulic fluid to compensate for the delta volume. The hydraulic actuator component is, in particular, a so-called differential cylinder. Hydraulic differential cylinders are double-acting hydraulic cylinders. They are typically designed with a piston guided within a cylinder body, with a chamber on each side of the piston. Hydraulic fluid can be forced into this chamber to move the piston within the cylinder in one direction or the other. As double-acting hydraulic cylinders, hydraulic differential cylinders are fundamentally suitable for both pushing and pulling applications.

[0008] The movement of the piston causes the chambers of the hydraulic cylinder to enlarge or shrink. In hydraulic differential cylinders, a rod connected to the piston extends through one of the two chambers on one side of the cylinder. This rod transmits the force exerted on the piston by the hydraulic fluid. The end of the cylinder body opposite the rod and the opposite end of the rod form the ends of the differential cylinder. These ends are pushed apart by the differential cylinder when it extends and retracted when it retracts.

[0009] The side of the piston where the rod extends through the chamber is commonly referred to as the annular side or rod side because the chamber on this side is ring-shaped around the rod. Accordingly, the chamber through which the rod extends is called the annular chamber. The other side of the piston is commonly referred to as the bottom side or piston side. Accordingly, the chamber on this other side of the piston is called the bottom chamber. The rod can be extended from and retracted from the hydraulic differential cylinder depending on which of the two chambers receives hydraulic fluid and which chamber receives hydraulic fluid. When hydraulic fluid is pumped into the annular chamber, the rod retracts. The differential cylinder then exerts a pulling force. When hydraulic fluid is pumped into the bottom chamber, the rod extends.The differential cylinder then exerts a compressive force.

[0010] Due to the design, the cross-sectional areas of the two chambers differ because of this rod. The cross-sectional area of ​​the annular chamber is smaller than the cross-sectional area of ​​the bottom chamber by the cross-sectional area of ​​the rod. If the hydraulic actuator is a differential cylinder, the second chamber with the larger cross-section is the bottom chamber. The first chamber with the smaller cross-section is then the annular chamber.

[0011] Due to the difference in the cross-sectional areas of the hydraulic fluid chambers, there is a difference in the volume flow rates that enter and exit the chambers when the piston moves. If the bottom chamber, with its larger cross-sectional area, is filled with hydraulic fluid, the volume flow rate of hydraulic fluid exiting the annular chamber is smaller than the volume flow rate of hydraulic fluid entering the bottom chamber. Conversely, if the annular chamber is filled with hydraulic fluid, the volume flow rate of hydraulic fluid exiting the bottom chamber is larger than the volume flow rate entering the annular chamber. The difference in volume flow rates, or the total volume difference occurring at a given piston displacement, is called the delta volume and is one reason why such a hydraulic cylinder is called a "differential cylinder."The term "delta volume" is used in the following in a general sense - both for a difference in the volume flows entering and exiting the annular chamber and the bottom chamber, and for the actual delta volume that occurs when the piston is moved a certain distance.

[0012] Differential cylinders must be distinguished from so-called constant-velocity cylinders, in which the two chambers have the same cross-sectional area. In constant-velocity cylinders, there is no difference in volume flow rates or delta volume. However, special concepts are required for the design of constant-velocity cylinders. Measures must be implemented to equalize the cross-sectional areas of the chambers. One possible design for a constant-velocity cylinder, for example, has two rods, each extending through both chambers of the cylinder. Another possible design for constant-velocity cylinders is the counter-rotating connection of two differential cylinders to form an actuator. Such designs are impractical in many applications. This is one reason why so-called differential cylinders are more widespread.

[0013] The delta volume of differential cylinders presents a challenge in the design of hydraulic actuators capable of recuperation. This is especially true if the property of the differential cylinders as double-acting cylinders, capable of both pulling and pushing, is to be utilized as well.

[0014] The hydraulic actuator component can also have a different design than that of a differential cylinder. The essential point is that the second chamber has a larger second cross-section and the first chamber a smaller first cross-section, resulting in the described delta volume.

[0015] The hydraulic actuator is specifically capable of four quadrant operation. This four-quadrant capability is achieved primarily through the four-quadrant capability of the hydraulic pump, which is designed to allow the pump to deliver hydraulic fluid bidirectionally and to recuperate energy from the hydraulic fluid bidirectionally. The ability to operate the hydraulic pump bidirectionally means that it is configured to function in both directions (from a first port to a second port and vice versa), both as a motor and as a generator. In motor mode, the hydraulic pump delivers hydraulic fluid.In generator mode, the hydraulic pump extracts mechanical energy from a hydraulic fluid flow from one port to the other to supply this energy – in the case of an electric hydraulic pump, as electrical energy. The ability to operate the hydraulic pump both as a generator and as a motor is generally referred to as four-quadrant capability.

[0016] The hydraulic pump is, in particular, an electrically driven hydraulic pump.

[0017] The hydraulic pump is designed in two parts, consisting of a first sub-pump and a second sub-pump. These two sub-pumps can also be considered sub-pump chambers of a hydraulic pump. Preferably, each sub-pump or sub-pump chamber contains a pumping element that interacts with the hydraulic fluid flowing through it, either to drive the hydraulic fluid (motor operation) or to recuperate energy from the flowing hydraulic fluid (generator operation). Preferably, both hydraulic pumping elements are connected to a pump drive via a common shaft. The pump drive is preferably an electric motor that can also be operated as a generator.

[0018] The first sub-pump or the first sub-pump chamber forms part of a pumping circuit that connects the two chambers of the hydraulic actuator component. Preferably, a first line connects a first port of the first sub-pump to the first chamber of the hydraulic actuator component. Preferably, a second line connects a second port of the first sub-pump to the second chamber of the hydraulic actuator component.

[0019] The second sub-pump or sub-pump chamber preferably serves to receive or provide the delta volume (depending on the flow direction). Preferably, a second connection of the second sub-pump is also connected to the second chamber of the hydraulic actuator component via the second line. The first connection of the second sub-pump, however, is not connected to the first line or the first chamber of the hydraulic actuator component. Rather, this connection is connected to a hydraulic fluid supply capable of receiving or providing the delta volume. When it is stated below that a hydraulic fluid supply is connected to the second sub-pump, this always also means that the hydraulic fluid supply is connected to the first connection of the second sub-pump.

[0020] The dimensions of the first sub-pump or sub-pump chamber and the second sub-pump or sub-pump chamber are preferably matched to each other. Preferably, the sub-pumps and sub-pump chambers, or their respective delivery rates, are matched to each other, taking the delta volume into account. Minor deviations between the resulting volumes of flow through the pump chambers, which cannot be compensated for by precise matching of the sub-pumps and sub-pump chambers, may occur. Such deviations can also arise, for example, from imperfect matching of the sub-pumps to each other and / or from a slight, possibly unavoidable, compressibility of the hydraulic fluid at high pressures. To compensate for such deviations, additional circuits are preferably implemented, which can be connected to the first and second lines or to the first and second chambers.Such circuits are often also referred to as intermediate circuits. Such circuits are described, for example, in the documents DE 10 2011 056 894 B4 and DE 10 2022 121 962 A1.

[0021] A hydraulic fluid supply connected to the first port of the second sub-pump can be, in particular, a tank that can hold or supply any quantity of hydraulic fluid without pressure (without back pressure). However, it is advantageous if the hydraulic fluid supply is a pressure reservoir. A pressure reservoir, as described here, differs from a hydraulic tank in that it acts as a pressure accumulator, which assists the second sub-pump in pumping hydraulic fluid and is also suitable for absorbing energy from the hydraulic fluid during recuperation and storing it as pressure. The pre-charge pressure of a pressure reservoir is usually higher than that of a tank. A tank, for example, has atmospheric pressure or a pressure of a few bar. The pre-charge pressure of a pressure reservoir can be set to a value between 50 bar and 100 bar, depending on the application.A pressure reservoir is explicitly designed to maintain a certain pressure (higher pre-charge pressure). This allows hydraulic energy to be stored in the pressure reservoir. In preferred embodiments, a pressure increase occurs when hydraulic fluid is added to the pressure reservoir and a pressure decrease occurs when hydraulic fluid is withdrawn from the pressure reservoir. This is particularly true if the storage volume of the pressure reservoir for hydraulic fluid is not very large.

[0022] For many applications, it is advantageous to implement the hydraulic fluid supply using a pressure reservoir. One such application would be a hydraulic actuator designed to lift an excavator arm. Such a hydraulic actuator is primarily used to raise and lower the excavator arm. The (larger) second chamber typically maintains a higher pressure than the (smaller) first chamber. If a pressure reservoir connected to the first port of the second sub-pump is configured so that its pre-charge pressure approximately corresponds to the average operating pressure in the second chamber, this pressure reservoir significantly reduces the load on the second sub-pump. The pressure in the reservoir then assists the hydraulic pump when it is driven to lift the excavator arm. Preferably, the pressure in the pressure reservoir exerts a force on the hydraulic pump, or the second sub-pump, or...The pumping element in the second sub-pump transmits a torque to a shaft that connects the pump drive and the pumping elements. This torque preferentially assists the pump drive. A hydraulic pump drive can therefore be designed to be significantly smaller than if this assistance from the pressure reservoir were not present. However, the use of such a pressure reservoir shifts the operating range of the hydraulic actuator. The operating range of the hydraulic actuator is typically limited by the hydraulic pump drive. An electric hydraulic pump can usually generate certain maximum torques in motor operation. These maximum torques also limit the pressure differentials that can be generated between the first and second ports of the hydraulic pump.Similarly, in generator mode, only certain maximum torques can typically be recuperated with an electric hydraulic pump. This also limits the pressure differentials between the first and second connections that can be supplied for recuperation. Depending on the pressure differentials, the flow rates that the electric hydraulic pump can deliver, or from which it can recuperate energy, are also regularly limited. With particularly large pressure differentials, only smaller flow rates may be possible. These pump limitations define the operating range of the hydraulic actuator. This operating range is typically shifted by a pre-pressure provided by the pressure reservoir. For example, if the electric hydraulic pump...If the actuator is capable of generating a torque of 100 Nm [Newton meters] on a shaft in both directions of flow, and the pressure reservoir provides an additional torque of 25 Nm [Newton meters], the maximum torque is 125 Nm [Newton meters] in one direction and 75 Nm [Newton meters] in the other. This means, for example, that pressures of up to 250 bar can be generated in one chamber, while pressures of up to 150 bar can be generated in the other. Therefore, setting a pre-pressure that is favorable for most operating points of a particular application of a hydraulic actuator can, under certain circumstances, render the hydraulic actuator inoperable at other operating points. In other words, the hydraulic actuator component could potentially be pressurized to 200 bar. However, this is no longer possible due to the pre-pressure in the pressure reservoir.The limiting factor here is the resulting torque on the pump shaft. The described hydraulic actuator addresses this issue. It is proposed that the hydraulic fluid supply is not directly connected to the first port of the second sub-pump, but rather that a valve assembly is connected there, allowing the second sub-pump to be selectively connected to either a first or a second hydraulic fluid supply. Whenever it is stated below that a valve assembly is connected to the second sub-pump, this always also means that the valve assembly is connected to the first port of the second sub-pump.

[0023] The two hydraulic fluid supplies can have different properties. This makes it possible to shift the operating range of the hydraulic actuator as needed. For example, a first hydraulic fluid supply can be configured for typical, frequently occurring operating points of the hydraulic actuator, while a second hydraulic fluid supply can be configured for other, less frequent operating points. Many other configurations are conceivable.

[0024] It is preferred if the first hydraulic fluid supply comprises a pressure reservoir which enables the intake and supply of pressurized hydraulic fluid to the second sub-pump, wherein hydraulic energy is stored in the pressure reservoir when hydraulic fluid is taken in, which is released again when hydraulic fluid is discharged from the pressure reservoir.

[0025] The differences between a pressure reservoir and a tank were explained above. A tank can also be pressurized. However, the volume of a tank is usually large enough that the tank pressure at the second pump stage does not change depending on the current position of the hydraulic actuator component (i.e., depending on the volumes of the pump chambers). In contrast, the volume of a pressure reservoir is usually smaller and specifically tailored to the volume of the chambers or the resulting delta volume of the hydraulic actuator component. Therefore, the pressure in the pressure reservoir changes depending on the delta volume in the second chamber. In the case of a differential cylinder, for example, this means that the pressure in the pressure reservoir is low when the differential cylinder is fully extended and high when it is fully retracted.Particularly preferred is the size of a pressure reservoir such that it is matched to the delta volume in such a way that the difference between a maximum possible pressure in the pressure reservoir (depending on the state or position of a piston of the hydraulic actuator component) and a minimum possible pressure in the pressure reservoir corresponds to a predetermined value.

[0026] Using a pressure reservoir as the primary hydraulic fluid supply offers advantages in the design of the hydraulic actuator. The ability to deactivate the primary hydraulic fluid supply and activate a secondary one via the valve arrangement makes it possible to design the hydraulic actuator in such a way that infrequently occurring operating points of the hydraulic actuator component in the respective application are no longer accessible with the primary hydraulic fluid supply. If such operating points nevertheless need to be accessed, the primary hydraulic fluid supply can be deactivated and the secondary hydraulic fluid supply activated via the valve arrangement. Accessing these operating points is then possible with the secondary hydraulic fluid supply.In particular, it is possible that a first hydraulic fluid supply is configured to provide a specific assisting torque for the hydraulic pump. Preferably, the second hydraulic fluid supply is then configured such that this assisting torque is omitted, and the hydraulic actuator can also be operated at operating points that cannot be reached when the assisting torque is applied. It is also preferred that a compressible element is arranged at the pressure reservoir, which can be compressed by the pressure present in the pressure reservoir in order to store hydraulic energy in the pressure reservoir.

[0027] The compressible element can, for example, be a gas bubble present in the pressure reservoir. The amount of gas in the gas bubble, together with the volume of the pressure reservoir, defines the pre-charge pressure. Optionally, the compressible element can also be a spring that pre-tensions a section of the pressure reservoir wall. Optionally, a diaphragm can be provided that separates the hydraulic fluid from a gas bubble and thus forms a section of the pressure reservoir wall.

[0028] It is further preferred if the pressure reservoir is connected to a charging circuit with which a pressure level can be established in the pressure reservoir.

[0029] The charging circuit allows the amount of hydraulic fluid in the pressure reservoir to be adjusted. This also adjusts the pre-charge pressure in the pressure reservoir. Preferably, hydraulic fluid can be pumped into the pressure reservoir. Preferably, hydraulic fluid can also be drained from the pressure reservoir.

[0030] As long as the valve arrangement is configured such that the second sub-pump is connected to a first hydraulic fluid supply designed as a pressure reservoir, the hydraulic actuator component with its chambers, the lines, the hydraulic pump, and the pressure reservoir preferably form a closed system from which no significant quantities of hydraulic fluid escape during operation. If, to shift the operating range of the hydraulic actuator, the valve arrangement is reconfigured and the second sub-pump is connected to the second hydraulic fluid supply, then hydraulic fluid can be supplied to the second hydraulic fluid supply. The charging circuit is then particularly useful for restoring the pre-pressure level in the pressure reservoir.

[0031] The charging circuit can, for example, be a section of a hydraulic power branch system with which pressurized hydraulic fluid from a central hydraulic pump can be selectively supplied to individual consumers.

[0032] It is further preferred if the second hydraulic fluid supply includes a tank connection to a tank to which hydraulic fluid from the second sub-pump can be supplied to the tank.

[0033] Furthermore, it is preferred if the second hydraulic fluid supply has a pressure relief valve which maintains a minimum pressure of the hydraulic fluid in the second sub-pump when hydraulic fluid is discharged from the second sub-pump to the tank.

[0034] As described above, the second hydraulic fluid supply is a tank. The pressure level of the hydraulic fluid in a tank is typically lower than the minimum hydraulic fluid pressure that must be maintained in the second pump section and also in the entire hydraulic system of the hydraulic actuator (chambers of the hydraulic actuator component, hydraulic pump, lines, etc.). Such a minimum pressure in the hydraulic system is maintained, for example, to prevent cavitation in the hydraulic pump.

[0035] For this reason, it may be advantageous to include a pressure relief valve in the second hydraulic fluid supply between the tank and the second sub-pump. This valve limits the downward pressure and ensures that a minimum pressure is maintained. This pressure relief valve could, for example, be a spring-loaded valve where the pressure in the second sub-pump acts against the valve's spring. When the pressure is high enough to overcome the spring force, the valve opens. The minimum pressure could be approximately 20 bar, for example. When hydraulic fluid is discharged from the second sub-pump into the tank of the second hydraulic fluid supply, this second minimum pressure must be overcome or maintained.

[0036] Furthermore, it is preferred if the pressure relief valve has an electronic valve control with which the pressure relief valve can be actively controlled to allow adjustment of the opening pressure during operation.

[0037] Electronic valve control allows, in particular, the setting of the pressure threshold / opening pressure that must be exceeded for the pressure relief valve to open. Preferably, the opening pressure can be set to a very high value relative to the minimum pressure, for example, more than 300 bar. This very high pressure value corresponds, for example, to a maximum safety pressure that should preferably not be exceeded in the entire hydraulic system of the hydraulic actuator (chambers of the hydraulic actuator component, hydraulic pump, lines, etc.). The pressure relief valve can then also be used as an overpressure relief device for the entire hydraulic system of the hydraulic actuator.

[0038] When using a simple (non-adjustable) pressure relief valve designed to open at a certain opening pressure in the second pump section, this opening pressure must correspond to the minimum pressure. Pressures in the second pump section exceeding the minimum pressure are only possible if the pressure relief valve is isolated from the second pump section by another element (particularly the valve assembly).

[0039] By using a pressure relief valve with electronic control, which allows the opening pressure to be set, a pressure relief valve can be used as part of the valve assembly to selectively connect the first hydraulic fluid supply and / or the second hydraulic fluid supply to the second sub-pump. The pressure relief valve can also be connected in parallel to other components of the valve assembly to the second sub-pump or its first port. When the second hydraulic fluid supply is connected to the second sub-pump, the pressure relief valve is preferably set electronically to ensure the maintenance of the minimum pressure in the second sub-pump and, at higher pressures, discharge hydraulic fluid from the second sub-pump through the pressure relief valve into the tank.When the first hydraulic fluid supply is connected to the second sub-pump, the pressure relief valve is preferably set to a very high pressure value via electronic control. The pressure relief valve then preferably acts as a pure pressure relief valve, which generally prevents excessively high pressures in the entire hydraulic system of the hydraulic actuator.

[0040] The proposed use of a pressure relief valve with electronic control may eliminate the need for an additional pressure relief valve, which would otherwise prevent excessive pressure in the entire hydraulic system or passively open to prevent excessive pressure. Such a pressure relief valve can be integrated with the described pressure relief valve with electronic control. Preferably, the pressure relief valve with electronic control is designed to open at a very high pressure when de-energized, thus ensuring overload protection regardless of the electronic control's function. Furthermore, the pressure relief valve with electronic control is preferably designed so that an electrical control signal is required to reduce the opening pressure to the minimum pressure.Then it is possible to force hydraulic fluid from the second sub-pump into the second hydraulic fluid supply or into the tank via the pressure relief valve. Furthermore, it is preferred that the second hydraulic fluid supply has a safety valve which opens when hydraulic fluid is supplied to the second sub-pump in order to supply the second sub-pump with pressurized hydraulic fluid from another hydraulic fluid source.

[0041] While the pressure relief valve described above ensures that hydraulic fluid can be discharged from the second sub-pump, provided a minimum pressure in the second sub-pump is exceeded, the safety valve serves the purpose of ensuring that the second sub-pump does not run dry, even when it is connected to the second hydraulic fluid supply. The safety valve is preferably configured to open a connection to another hydraulic fluid source when the minimum pressure is undershot. The safety valve is preferably a continuously opening valve that opens further depending on the degree to which the minimum pressure is undershot, thus ensuring that the minimum pressure is maintained.If a large amount of hydraulic fluid is required from the hydraulic fluid source to maintain the minimum pressure, the safety valve opens wider than if only a small amount is needed. The safety valve can also be described as an "inverse pressure relief valve." While the pressure relief valve limits pressure by allowing hydraulic fluid to be released when a certain pressure is exceeded, the safety valve allows additional hydraulic fluid to be drawn in from a hydraulic fluid source when the pressure in a given area threatens to drop below a minimum pressure.

[0042] The additional hydraulic fluid source preferably provides hydraulic fluid at a higher pressure than the minimum pressure. The opening pressure at which the safety valve opens is preferably below the minimum pressure at which the pressure relief valve opens. The safety valve is preferably configured to open only when the pressure relief valve described above is closed. This prevents a direct overflow of hydraulic fluid from the additional hydraulic fluid source into the second hydraulic fluid supply.

[0043] A small difference between the switching pressures of the pressure relief valve and the safety valve is preferred. The pressure relief valve serves to maintain the minimum pressure when hydraulic fluid is discharged into a tank. The safety valve serves to maintain the minimum pressure when hydraulic fluid is pumped from the second sub-pump into the second chamber. The difference is preferably selected such that even during pressure fluctuations and / or pressure pulses occurring in the system due to operational reasons, no hydraulic fluid overflows from the pressure reservoir through the safety valve and the pressure relief valve into the tank. The difference is, for example, between 0.5 bar and 5 bar and is determined according to the design of the hydraulic actuator. Both switching pressures of the pressure relief valve and the safety valve are referred to above as the minimum pressure.The difference between the two switching pressures is preferably as small as possible in order to minimize throttling losses occurring during the operation of the hydraulic actuator.

[0044] The second hydraulic fluid supply is preferably configured such that when it needs to receive hydraulic fluid from the second sub-pump (a delta volume), this hydraulic fluid is discharged via the pressure relief valve (particularly to a tank). Furthermore, the second hydraulic fluid supply is preferably configured such that when it needs to supply hydraulic fluid (the delta volume) to the second sub-pump, this hydraulic fluid is supplied from the additional hydraulic fluid source.

[0045] Situations in which hydraulic fluid needs to be absorbed here are those in which the second chamber of the hydraulic actuator component shrinks. In the case of a differential cylinder, these are situations in which the differential cylinder is retracted. Particularly when high forces are to be applied with the differential cylinder, it is helpful if the delta volume does not have to be forced into a pressure reservoir of the first hydraulic fluid supply, but only a minimum pressure needs to be overcome to discharge the delta volume via the pressure relief valve into a tank of the second hydraulic fluid supply.

[0046] Situations where the second hydraulic fluid supply provides hydraulic fluid but does not receive it are generally avoided by activating the first hydraulic fluid supply and deactivating the second hydraulic fluid supply via the valve arrangement when hydraulic fluid needs to be supplied to the second sub-pump. Nevertheless, such situations can occur, for example, because the valve arrangement cannot switch to the first hydraulic fluid supply due to a lack of a corresponding switching signal. In such situations, the second hydraulic fluid supply is then able to supply hydraulic fluid from the additional hydraulic fluid source via the safety valve.

[0047] It is also preferred if the additional hydraulic fluid source is connected to the first hydraulic fluid supply.

[0048] Preferably, the additional hydraulic fluid source is formed by a connecting line that links the safety valve to the first hydraulic fluid supply and, in particular, to a pressure reservoir of the first hydraulic fluid supply. The first hydraulic fluid supply and / or the pressure reservoir are capable of supplying pressurized hydraulic fluid. A simple safeguard can be achieved by connecting the safety valve to the first hydraulic fluid supply in the event that, for any reason, the valve arrangement fails to switch to the first hydraulic fluid supply. Dry running of the second pump is reliably prevented in all situations. The direction of movement and the load direction of the hydraulic actuator component can change independently of each other.When a hydraulic actuator component designed as a differential cylinder, or the hydraulic actuator itself, performs a pulling movement against an externally applied force, a high pressure is present in the first chamber. In this case, the second hydraulic fluid supply is preferably active, which in particular establishes a connection to the tank through which the delta volume from the second chamber can be discharged, whereby only the minimum pressure defined by the pressure relief valve needs to be overcome. However, if the direction of movement of the hydraulic actuator component designed as a differential cylinder then changes and it is extended again with the unchanged load, the high pressure remains in the first chamber.In certain operating situations, the second hydraulic fluid supply remains activated and the first hydraulic fluid supply deactivated – particularly if a switching signal to switch from the second to the first hydraulic fluid supply is not received quickly. The pressure reservoir of the first hydraulic fluid supply is therefore unavailable as a component of the first hydraulic fluid supply. In such situations, the safety valve can be opened. The pressure reservoir of the first hydraulic fluid supply can then act as an additional hydraulic fluid source to provide pressurized hydraulic fluid.

[0049] It is preferred if the valve arrangement has a signal input to which a switching signal can be applied, with which it can be specified whether the first hydraulic fluid supply or the second hydraulic fluid supply is connected to the second sub-pump.

[0050] Furthermore, it is preferred if the valve arrangement is configured to selectively connect the second sub-pump to either the first hydraulic fluid supply or the second hydraulic fluid supply, depending on a pressure in the first chamber.

[0051] The valve arrangement preferably includes a changeover valve that selectively connects or disconnects the second sub-pump from the pressure reservoir of the first hydraulic fluid supply. Preferably, the changeover valve has at least two inlets for hydraulic fluid, with a first inlet connected to the second sub-pump and a second inlet connected to the pressure reservoir. In a first position of the changeover valve, the second sub-pump and the pressure reservoir are connected. In a second position of the changeover valve, the second sub-pump and the pressure reservoir are disconnected. The changeover valve is preferably a discretely operated valve that is selectively in either a first or a second position.Intermediate states, in which the switching valve is partly in the first position and partly in the second position, preferably do not occur or only occur briefly during regular operation.

[0052] In further preferred embodiments, the changeover valve is designed such that the second sub-pump is selectively connected to either the first or the second hydraulic fluid supply. In preferred embodiments, the changeover valve also has a third inlet, which is connected to the second hydraulic fluid supply or to the tank (described above). The internal routing of the changeover valve is then preferably such that the third inlet is always connected to the first inlet when the second inlet is disconnected from the first inlet – i.e., in the second position.

[0053] The pressure in the first chamber is a good criterion for deciding whether it is more advantageous to connect the second pump to the first or second hydraulic fluid supply. The pressure in the second chamber is essentially determined by the loads acting on the hydraulic actuator component and the hydraulic fluid delivery by the first pump. If the hydraulic actuator component is used to generate large forces by compressing the first chamber, then it generally makes sense to use a valve arrangement to isolate the first hydraulic fluid supply from the second pump and connect the second pump to the second hydraulic fluid supply. In such a situation, the second hydraulic fluid supply would generate high back pressure, which would prevent the movement of the hydraulic actuator component.This is particularly relevant because the hydraulic fluid would have to be pumped into a pressure reservoir. In contrast, with the second hydraulic fluid supply, the hydraulic fluid can be discharged – especially into a tank – even after overcoming the relatively low minimum pressure.

[0054] It is particularly preferred if the valve arrangement includes a switching valve which has a signal input connected to a first line which connects the hydraulic pump to the first chamber.

[0055] In particular, the signal input is at least indirectly connected to the first chamber. This can be achieved, in particular, via the first line described above. The signal input is preferably a hydraulic signal input, at which pressure in the first line or the first chamber acts on the changeover valve. If the pressure exceeds a threshold value, the pressure preferably moves the changeover valve into a second position, in which the second sub-pump is connected to the second hydraulic fluid supply. If the pressure is less than a threshold value, the changeover valve is preferably in a first position, in which the second sub-pump is connected to the first hydraulic fluid supply.

[0056] The design of the valve assembly with a hydraulic signal input for applying a pressure signal to switch the valve assembly is only one possible embodiment. In other embodiments, the valve assembly can, of course, also be equipped with one (or more) electrical signal inputs to which an electrical signal can be applied to switch the valve assembly. For example, an electrical drive current from a pump drive can be used to generate an electrical switching signal. If the pump is driven in such a way that the first chamber of the hydraulic actuator component is pressurized, then the valve assembly can, if necessary, switch to the second hydraulic fluid supply.

[0057] In other embodiments, a pressure sensor could also be used to monitor the pressure in the first chamber or line in order to generate an electronic switching signal that can be used to switch the valve assembly. By using a valve assembly with an electrical signal input, various input variables can be used to detect situations in which switching the valve assembly is beneficial. Optionally, measurement signals from force sensors on the hydraulic actuator component or on the kinematics actuated by the hydraulic actuator component can also be used to generate a switching signal for changing the valve assembly. If necessary, a control unit can process multiple input variables to generate a switching signal.

[0058] In some embodiments, the valve arrangement may comprise several components that must be switched between the first and second hydraulic fluid supply. In such embodiments, one component of the valve arrangement is preferably a changeover valve with exactly two inlets, allowing the second pump to be selectively connected to the pressure reservoir or not. As described above, an electrically controlled pressure relief valve can be used, which, depending on the control configuration, can serve both as overload protection and to maintain a minimum pressure in the second pump. Preferably, such an electrically controlled pressure relief valve forms part of the valve arrangement.Preferably, such an electrically controlled pressure relief valve is also switched when other components of the valve assembly are switched to change between the hydraulic fluid supplies. When switching from the first to the second hydraulic fluid supply, the opening pressure of the pressure relief valve is preferably reduced from a maximum safety pressure to the minimum pressure. Conversely, the opening pressure is increased when switching back from the second hydraulic fluid supply to the first. In this embodiment, the pressure relief valve preferably forms another component of the valve assembly.

[0059] For the smooth switching of the valve assembly, it is essential that the overlap of the diverter valve's inlets is designed to minimize pressure spikes and drops at the second pump during the switchover. This is particularly important because the switchover regularly occurs under load. When using a three-inlet diverter valve, the overlap of the inlets must be minimal. When using a two-inlet diverter valve and an additional pressure relief valve with electrical actuation, undesirable pressure spikes and / or drops at the second pump can be avoided by coordinating the actuation of the diverter and pressure relief valves.

[0060] The hydraulic actuator described here preferably has two hydraulic fluid supplies. A first hydraulic fluid supply comprises a pressure reservoir which (as described above) supports a hydraulic pump in a main working range of the hydraulic actuator. In this preferred embodiment, the second hydraulic fluid supply allows hydraulic fluid to be discharged to a tank. This particularly enables the hydraulic actuator component to operate at operating points outside the usual working range, which would not be possible if the pressure reservoir were the only hydraulic fluid supply for providing and / or absorbing the delta volume. Such operating points regularly require particularly extreme pressures in one of the chambers of the hydraulic actuator component.The achievable pressure is typically limited by the maximum torque achievable by the hydraulic pump's drive. The pressure reservoir can provide additional support. The pressure generated by the pump's drive torque and the pressure in the reservoir add up in one direction of force. However, in the opposite direction, the pressure in the reservoir must be subtracted from the pressure achievable by the pump. The design of the hydraulic actuator described here is particularly advantageous when the hydraulic actuator component is intended to generate very large forces that are opposite to the direction of force supported by the pressure reservoir.

[0061] In principle, the concept described here can also be expanded. If necessary, additional (other) hydraulic fluid supplies can be connected to the valve arrangement, which, for example, have a pressure reservoir with a different pre-charge pressure, thus enabling particularly advantageous operation of the hydraulic actuator component in other operating ranges.

[0062] This document also describes a method for operating a described hydraulic actuator, comprising the following steps: a) Operation of the hydraulic actuator in a first operating mode, in which the first hydraulic fluid supply is connected to the second sub-pump and in which load requirements can be met with the support of a hydraulic pump of the hydraulic actuator with a pressure reservoir of the hydraulic fluid supply; b) Detection of a load requirement, the fulfillment of which is impaired by the pressure reservoir of the first hydraulic fluid supply; c) Switching the hydraulic actuator from the first operating mode to a second operating mode by actuating the valve arrangement to switch to the second hydraulic fluid supply;and d) operation of the hydraulic actuator in a second operating mode in which the second sub-pump is connected to the second hydraulic fluid supply, which facilitates the delivery of hydraulic fluid from the second sub-pump.;

[0063] It should be noted that the special advantages and design features described in connection with the hydraulic actuator described are transferable and applicable to the process.

[0064] This section describes the operation of the hydraulic actuator in two different operating modes: step a) with the first hydraulic fluid supply and step d) with the second hydraulic fluid supply. Steps b) and c) describe the switching process for changing between the two operating modes. The switching process can also be reversed, switching from the second operating mode (step d) back to the first operating mode (step a). This is preferred when it is detected that load requirements exist which can also be met with the pressure reservoir connected to the second sub-pump, or for which the pressure reservoir connected to the second sub-pump is advantageous.

[0065] In step b), a load requirement whose fulfillment is affected by the pressure reservoir of the first hydraulic fluid supply is identified, for example, by the fact that pressures above a limit pressure in the first chamber are required to fulfill this load requirement. Such a load requirement can also be identified in step b), for example, by the fact that the torques a pump drive must apply to fulfill this load requirement exceed a limit value. Conversely, to switch back to a first operating mode, it can be detected that such pressures or torques are no longer present in the first chamber. Then, a switch can be made from the second operating mode according to step d) back to the first operating mode according to step a).

[0066] The first operating mode according to step a) can be considered the "normal operating mode" of the hydraulic actuator. Preferably, the hydraulic actuator is designed such that, in regular operation, the vast majority of operating or load points occur that do not require pressures above the limit pressure.

[0067] Receiving the load request according to step b) and switching according to step c) preferably occur automatically, whereby the load request is detected by a pressure change in a hydraulic fluid line, and the valve arrangement switches immediately as a result of this pressure change. In some embodiments, this can also be achieved by first detecting the load request – for example, as an electronic signal (step b). The switching can then subsequently be initiated by a control unit based on this signal (step c)).

[0068] The switching process according to step c) may be carried out in two steps. In step c1), the first hydraulic fluid supply is disconnected from the second sub-pump. In step c2), the second hydraulic fluid supply is connected to the second sub-pump. The two steps c1 and c2) may, if necessary, be partially overlapping in time.

[0069] Furthermore, a mobile working machine comprising at least one hydraulic actuator is described here. The invention and its technical context are explained in more detail below with reference to the figures. The figures show preferred embodiments, to which the invention is not limited. It should be noted in particular that the figures, and especially the size relationships shown in the figures, are only schematic. They show:

[0070] Fig. 1 : a first embodiment of a described hydraulic actuator;

[0071] Fig. 2: a second embodiment of a described hydraulic actuator;

[0072] Fig. 3: a third embodiment of a described hydraulic actuator;

[0073] Fig. 4: a diagram of the operating points occurring for a described hydraulic actuator in a specific application; and

[0074] Fig. 5: a schematic flowchart of an operating procedure for a described hydraulic actuator.

[0075] Figures 1, 2, and 3 show different embodiments of a described hydraulic actuator 1. Figure 1 is a more general abstraction of the invention described herein. The embodiments shown in Figures 1 and 2 represent more concrete implementations of the invention described herein. The different embodiments shown in Figures 1, 2, and 3 are first described together insofar as they are similar. Then, the special features of the two different embodiments are discussed.

[0076] The hydraulic actuator 1 comprises a hydraulic actuator component 3 and a hydraulic pump 2. The hydraulic actuator component 3 can generate large forces. In the embodiments shown in Figures 1, 2, and 3, the hydraulic actuator component 3 is a differential cylinder. However, the hydraulic actuator component 3 can also be of a different type. The hydraulic actuator component 3 is driven by the hydraulic pump 2. The hydraulic pump 2 is connected to the hydraulic actuator component 3 via two lines 7a and 7b. The first ports 6a of the hydraulic pump 2 are connected via a first line 7a to a first chamber 4a of the hydraulic actuator component 3. The second ports 6b of the hydraulic pump 2 are connected via a second line 7b to a second chamber 4b of the hydraulic actuator component 3.

[0077] The hydraulic pump 2 can pump hydraulic fluid from the first chamber 4a to the second chamber 4b or vice versa to actuate the hydraulic actuator component 3. The chambers 4a and 4b are preferably both formed within a cylinder body 31 of the hydraulic actuator component 3 and separated from each other by a piston 25. Pumping hydraulic fluid from the first chamber 4a to the second chamber 4b or vice versa displaces the piston 25 within the cylinder body 31. Preferably, a rod 24 is connected to the piston 25, which can be extended or retracted by moving the piston 25 to change the length of the hydraulic actuator component 3.

[0078] The hydraulic pump 2 can also be used to extract and thus recuperate energy from a hydraulic fluid flow caused by external forces from the first chamber 4a to the second chamber 4b or vice versa. Such a hydraulic fluid flow occurs, for example, when the hydraulic actuator component, implemented here as a differential cylinder, is extended or retracted by an external load.

[0079] The first cross-section 20a of the first chamber 4a is smaller than the second cross-section 20b of the second chamber 4b. This is a characteristic of many common hydraulic actuator components 3. In the hydraulic actuator components 3 shown here, which are designed as differential cylinders, this is due to the rod 24, which is connected to the piston 25 and extends through the first chamber 4a. This rod 24 reduces the first cross-section 20a and thus also the volume of the first chamber 4a. Because of these different cross-sections 20a, 20b, the total volume of the two chambers 4a, 4b changes when hydraulic fluid is pumped from one chamber 4a, 4b to the other. When hydraulic fluid is pumped into the second chamber 4b, this total volume increases because the volume of the second chamber 4b increases more than the volume of the first chamber 4a decreases.When hydraulic fluid is pumped into the first chamber 4a, the total volume decreases because the volume of the first chamber 4a increases less than the volume of the second chamber 4b decreases. This change in the total volume is referred to here as the delta volume 22. For hydraulic actuator components 3 designed as differential cylinders, the delta volume 22 corresponds to the volume of the section of rod 24 that extends through the first chamber 4a. This delta volume 22 must be absorbed from the second chamber 4b when the second chamber 4b decreases in size. Conversely, this delta volume 22 must be additionally supplied to the second chamber 4b when the second chamber 4b increases in size.

[0080] To provide and absorb the delta volume 22, the hydraulic pump 2 of the described hydraulic actuator 1 is designed in two parts, comprising a first sub-pump 21a and a second sub-pump 21b. The two sub-pumps 21a and 21b each constitute independent pump chambers. In preferred embodiments (shown here), the two sub-pumps 21a and 21b are connected by a common pump drive 18, in particular via a common shaft 33, which connects the conveying elements 32 of both sub-pumps 21a and 21b to the common pump drive 18.

[0081] Both sub-pumps 21a and 21b each have a first port 6a and a second port 6b. During operation, hydraulic fluid flows from the first port 6a to the second port 6b, or vice versa. In motorized operation, the hydraulic fluid is driven by the pump drive 18 or the conveying elements 32 of the sub-pumps 21a and 21b. In regenerative operation (for recuperation), a pressure difference exists between the ports 6a and 6b, which drives a flow of hydraulic fluid. Energy can be recuperated from this hydraulic fluid flow using the sub-pumps 21a and 21b.

[0082] In the first sub-pump 21a, the first port 6a is connected to the first chamber 4a via the first line 7a, while the second port 6b is connected to the second chamber 4b via the second line 7b. The hydraulic fluid from the first chamber 4a is completely pumped into the second chamber 4b by hydraulic pump 2, i.e., the first sub-pump 21a. The first chamber 4a is not connected to the second sub-pump 21b.

[0083] The second port 6b of the second sub-pump 21b is connected to the second chamber 4b via the second line 7b. However, the first port 6a of the second sub-pump 21a is not connected to the first chamber 4a or the first line 7a. Instead, the first port 6a of the second sub-pump 21a is connected to the hydraulic fluid supplies 23a and 23b, which are configured to receive or supply the delta volume 22 from the second chamber 4b, depending on whether the second chamber 4b is reduced or enlarged.

[0084] In both embodiments shown in Figures 1, 2, and 3, a special configuration of the hydraulic fluid supplies 23a, 23b for receiving or supplying the delta volume 22 is presented. Two different circuits for supplying and / or receiving the delta volume 22 are provided, which are designated as the first hydraulic fluid supply 23a and the second hydraulic fluid supply 23b. A valve arrangement 5 allows switching between the two hydraulic fluid supplies 23a, 23b. Depending on the operating mode of the hydraulic actuator 1, one of the two hydraulic fluid supplies 23a, 23b is used. Figure 1 illustrates this as a general principle.Both hydraulic fluid supplies 23a and 23b are available, and as needed (depending on the operating mode and / or requirements), one of the two hydraulic fluid supplies 23a or 23b is connected to the first port 6a of the second sub-pump 21b by means of the valve arrangement 5. The valve arrangement 5 preferably has a signal input 17 to which a switching signal 40 is applied for selectively activating either the first hydraulic fluid supply 23a or the second hydraulic fluid supply 23b. Preferably, the first hydraulic fluid supply 23a is predominantly active during operation of the hydraulic actuator 1, while the second hydraulic fluid supply 23b is used for more specific, less frequent operating situations. Figures 2 and 3 now show specific embodiments of how this approach can be implemented, for example, with components.

[0085] The first hydraulic fluid supply 23a, according to the two embodiments shown in Figures 2 and 3, has a pressure reservoir 8. A compressible element 9 is arranged in the pressure reservoir 8 and is pre-tensioned within the reservoir. When hydraulic fluid is pumped into the pressure reservoir 8, the pressure present in the reservoir 8 must be applied, and the compressible element 9 is compressed. Conversely, when hydraulic fluid is drawn from the pressure reservoir 8, the compressible element 9 expands, and the pressure present in the reservoir assists in pumping the hydraulic fluid. The pressure reservoir 8 thus provides hydraulic support to the hydraulic pump 2 during operation of the hydraulic actuator 1.In the case of a differential cylinder as the hydraulic actuator component 3, the hydraulic cylinder can be extended against a force acting on the hydraulic actuator component 3, whereby the torque of the pump drive 18 required for the pressure of the hydraulic fluid in the second chamber 4b is provided at least partially from the pressure reservoir 8 of the first hydraulic fluid supply 23a via the first pump 21b. This design of the first hydraulic fluid supply 23a may, if necessary, allow for a smaller pump drive 18 in the hydraulic actuator 1. Preferably, the pressure reservoir 8 is designed to particularly effectively support or counteract the forces typically acting on the hydraulic actuator component 3 during average operation.

[0086] In certain operating situations, the pressure supplied by the pressure reservoir 8 of the first hydraulic fluid supply 23a to the second sub-pump 21b (or the first port 6a of the second sub-pump 21b) can be problematic. This is particularly true when large forces are to be generated with the hydraulic actuator component 3 by forcing hydraulic fluid into the first chamber 4a. For example, this is the case with a differential cylinder when large pulling forces are to be generated during retraction of the differential cylinder. In this case, the hydraulic pump 2 must also overcome the pressure in the pressure reservoir 8. The pressure that can be generated by the hydraulic pump 2 is usually limited by the maximum torque that can be generated by the pump drive 18.This may even prevent certain operating points (which could easily be reached by the basic design of the hydraulic actuator 1 without pressure reservoir 8) from being reached at all, because the hydraulic pump 2 can no longer build up the necessary pressures.

[0087] For this reason, the hydraulic actuators 1, according to the embodiments shown in Figures 1, 2, and 3, each have a valve arrangement 5 with which switching from the first hydraulic fluid supply 23a to a second hydraulic fluid supply 23b is possible. When the hydraulic actuator 1 is operating with the second hydraulic fluid supply 23b, the pressure reservoir 8 is preferably separated from the first port 6a of the second sub-pump 21b. The pressure present in the pressure reservoir 8 does not act on the first port 6a or the second sub-pump 21b. In particular, the pressure present in the pressure reservoir 8 then does not exert any torque on the conveying element 32 of the second sub-pump 21b or on the shaft 32 and the pump drive 18. The valve arrangement 5 has a switching valve 16 for this purpose, which can disconnect a connection between the pressure reservoir 8 and the second sub-pump 21 or the first connection 6a.

[0088] When switching to the second hydraulic fluid supply 23b, a tank connection 11 is preferably provided on a tank 12, through which hydraulic fluid from the second chamber 4b can be discharged directly into the tank 12. Between the tank connection 11 and the first connection 6a of the second sub-pump 21b, there is a pressure relief valve 13, which maintains a minimum pressure as a differential pressure between the tank and the second sub-pump 21b. This ensures that the pressure in the second sub-pump 21b, and in the entire hydraulic system of the hydraulic actuator (chambers 4a, 4b of the hydraulic actuator component 3, hydraulic pump 2, lines 7a, 7b, etc.), cannot fall below a predetermined minimum pressure.The minimum pressure is preferably significantly lower than the pressure provided by the pressure reservoir 8, so that with the hydraulic actuator 1, when switching to the second hydraulic fluid supply 23b, load points can be approached that would not be approachable with the first hydraulic fluid supply 23a.

[0089] The second hydraulic fluid supply 23b also features a safety valve 14, which ensures the safe operation of the hydraulic actuator 1 even in operating situations where hydraulic fluid must be supplied by the second hydraulic fluid supply 23b. A further hydraulic fluid source 15 can be connected to the first port 6a or the second sub-pump 21b via the safety valve if the pressure of the first sub-pump 21b drops too low due to the delivery of hydraulic fluid into the second chamber 4b. The safety valve 14 opens at a pressure below the minimum pressure at which the pressure relief valve 13 opens, in order to release hydraulic fluid to the tank 12. The further hydraulic fluid source 15 is preferably implemented by a connection to the pressure reservoir 8 of the first hydraulic fluid supply 23a.The pressure reservoir 8 can therefore be used as a source of pressurized hydraulic fluid in the second hydraulic fluid supply 23b.

[0090] The pressure reservoir 8 is preferably connected to a charging circuit 10 by which the pressure reservoir 8 can be refilled when hydraulic fluid is discharged from the pressure reservoir 8. This can occur, for example, in the situation described above, in which the pressure reservoir 8 acts as a further hydraulic fluid source 15 for a second hydraulic fluid supply 23b.

[0091] According to both embodiments shown in Figures 2 and 3, the valve arrangement 5 switches from the first hydraulic fluid supply 23a to the second hydraulic fluid supply 23b, or vice versa, by applying a switching signal to a signal input 17 of a changeover valve 16 of the valve arrangement 5. In both embodiments shown in Figures 2 and 3, the switching signal is a pressure signal, which is tapped from the first line 7a to the first chamber 4a (and thus indirectly from the first chamber 4a). When high pressure is present in the first chamber 4a and in the first line 7a, a switchover from the first hydraulic fluid supply 23a to the second hydraulic fluid supply 23b should occur. The signal input 17 of the changeover valve 16 of the valve arrangement 5 is preferably designed with an effective surface onto which the pressure in the first line 7a or the first line 7a is applied.The first chamber 4a acts against a spring. The spring holds the changeover valve 16 in a first position, in which the first hydraulic fluid supply 23a is active or connected to the second sub-pump 21b. When the pressure at the signal input 17 exceeds the force of the spring, the changeover valve 16 switches to the second position, in which the second hydraulic fluid supply 23b is active or connected to the second sub-pump 21b. Other principles are also possible for controlling the changeover valve 16. For example, the changeover valve 16 can be hydraulically piloted, electrically piloted, or fully electrically controlled. It is generally preferred that the changeover valve 16 be configured such that, when a threshold value (e.g., the limit pressure and / or a specific force requirement) is exceeded, the transition from one switching state to the other is as sharply defined as possible.In one switching state, the first hydraulic fluid supply 23a is connected to the second sub-pump 21b, and in the other switching state, the second hydraulic fluid supply 23b is connected. Preferably, the changeover valve is designed such that damping and / or hysteresis prevent dynamic switching states that could cause uncontrolled switching back and forth. The changeover valve 16 is also preferably designed to prevent shocks or noise during switching.

[0092] The valve arrangement 5 for switching between the first hydraulic fluid supply 23a and the second hydraulic fluid supply 23b is designed differently according to the embodiment variants in Figs. 2 and 3.

[0093] In the embodiment shown in Fig. 2, a changeover valve 16 of the valve arrangement 5 is a changeover valve 16 with three inlets, which selectively connects the second sub-pump 21b or the first port 6a of the second sub-pump 21b either to the pressure reservoir 8 of the first hydraulic fluid supply 23a or to the tank 12 associated with the second hydraulic fluid supply 23b. A first inlet of the changeover valve 16 is connected to the second sub-pump 21b. A second inlet can be connected to the pressure reservoir 8. A third inlet is connected to the tank 12. The first inlet is selectively connected to either the second or the third inlet. The other third or second inlet is then closed. In Fig. 2, the changeover valve 16 is shown in the second position, in which the first inlet is connected to the third inlet.

[0094] In the embodiment shown in Fig. 3, the changeover valve 16 of the valve arrangement 5 is a changeover valve 16 with two inlets, one inlet being connected to the first port 6a of the second sub-pump 21b and the other inlet to the pressure reservoir 8. The connection between the first and second inlets is established in a first position and disconnected in a second position. This changeover valve 16 therefore only controls the connection of the second sub-pump 21b to the first hydraulic fluid supply 23a or the associated pressure reservoir 8. The pressure relief valve 13, which has an electronic valve control 19, is used to connect the second sub-pump 21b to the second hydraulic fluid supply 23b. The opening pressure of the pressure relief valve 13 can be adjusted via the electronic valve control 19.When the pressure reservoir 8 is connected to the second sub-pump 21b via the changeover valve 16, thus activating the first hydraulic fluid supply 23a, the opening pressure of the pressure relief valve 13 is preferably set to a safety pressure that should preferably not be exceeded in the entire hydraulic system of the hydraulic actuator (chambers of the hydraulic actuator component, hydraulic pump, lines, etc.). The pressure relief valve 13 then preferably acts purely as overpressure protection and is closed during the regular operation of the hydraulic actuator 1. When the pressure reservoir 8 is disconnected from the second sub-pump 21b by the changeover valve 16, the opening pressure of the pressure relief valve 13 is preferably reduced to a minimum pressure that should be maintained in the entire hydraulic system of the hydraulic actuator (chambers of the hydraulic actuator component, hydraulic pump, lines, etc.).This is preferably achieved by applying a corresponding control signal to the electronic valve control 19 of the pressure relief valve 13. If the minimum pressure in the second sub-pump 21b is exceeded, hydraulic fluid can then be discharged to the tank 12 via the pressure relief valve. The controllable pressure relief valve 13 of the circuit according to Fig. 3 thus interacts with the changeover valve 16 and, together with the changeover valve 16, forms the valve arrangement 5 for switching between the hydraulic fluid supplies 23a and 23b. The control of the electronic valve control 19 of the pressure relief valve 13 can be carried out in various ways.An example shown here is a pressure sensor 34 with which the pressure in the first line 7a can be monitored, and a control unit 35 which processes a sensor signal from the pressure sensor 34 to generate a control signal for the electronic valve control 19. Preferably, the generated control signal is synchronized with the switching of the changeover valve 16. The embodiment according to Fig. 3 allows for separate monitoring of the connection of the first hydraulic fluid supply 23a to the second sub-pump 21b and the second hydraulic fluid supply 23b to the second sub-pump 21b. This enables very precise monitoring of any overlap of the connections of the two hydraulic fluid supplies 23a and 23b to the second sub-pump 21b.

[0095] Figure 4 shows a diagram of load points 29 that typically occur during the operation of a described hydraulic actuator in a specific application. Load points 29 are plotted on a velocity axis 27 (or flow rate axis), and the respective pressure or torque acting on a shaft of the hydraulic pump is plotted on the vertical pressure axis 26 (or torque axis). A load point 29 describes a specific flow rate that must be supplied by the hydraulic pump at a specific pressure to move the hydraulic actuator component according to a requirement. The load points 29 show a distribution as shown in Figure 4. The hydraulic pump used cannot deliver arbitrarily large flow rates at arbitrarily high pressures. Rather, the deliverable flow rate is limited depending on the required pressure level.This limitation is primarily due to the fact that the torque that can be generated by the pump drive is limited. The hydraulic actuator preferably has a design range 30 within which the hydraulic pump can supply flow rates and pressures, or corresponding torques, to drive the hydraulic actuator component.

[0096] Various design ranges 30 of the hydraulic actuator 1 are shown in Fig. 4, each represented by a dashed line. It can be seen that the design ranges each have a symmetrical basic shape, which is symmetrical with respect to a zero flow line 36. Around the zero flow line 36, there exists a region in which the generable pressure is independent of the requested flow rate. This is manifested in the fact that the depicted design ranges 30 each have a constant range 38 around the zero flow line 36, in which the generable pressure is largely independent of the requested flow rate. From a certain point, the deliverable pressure decreases depending on the requested flow rate. This is evident from the decreasing range 39, which all the depicted design ranges 30 exhibit.

[0097] By setting a pressure at the first port of the second sub-pump, the design range 30 can be shifted relative to the pressure zero line 37. The various design ranges 30 shown in Fig. 4 are each set by a corresponding pressure at the first port of the second sub-pump. Preferably, the design range 30 is shifted by the pressure at the first port of the second sub-pump caused by the pressure reservoir such that as many load points 29 of the hydraulic actuator 1 as possible lie within the design range 30 or in a central area of ​​the design range.

[0098] Preferably, the pressure in the pressure reservoir is set such that the majority of the load points 29 lie within a central area of ​​the design range 30. However, by setting a corresponding pre-pressure in the pressure reservoir, it is possible that some (possibly particularly rare) load points 29 no longer lie within the working range 30. This is where the described possibility of switching from a first hydraulic fluid supply to a second hydraulic fluid supply comes into play. Figure 4 schematically illustrates, for example, a first working range 28a and a second working range 28b. The different hydraulic fluid supplies are specifically designed for different working ranges 28a and 28b of the hydraulic actuator.A first working area 28a is a main working area in which, using the pressure reservoir, a design area 30 is positioned to enable particularly energy-efficient operation of the hydraulic actuator 1. This first working area 28a is active, for example, when the second sub-pump is connected to the first hydraulic fluid supply. A second working area can be activated by switching to the second hydraulic fluid supply. Load points that lie outside the first working area can then also be accessed. Figure 5 shows a schematic flowchart of an operating procedure for a described hydraulic actuator. The described process steps a), b), c), and d) are shown, which schematically illustrate the operation of the hydraulic actuator in the two described operating modes and the switching between the two described operating modes.

[0099] Reference symbol list

[0100] 1 Hydraulic actuator

[0101] 2 Hydraulic pump

[0102] 3 hydraulic actuator components

[0103] 4a first chamber

[0104] 4b second chamber

[0105] 5 Valve arrangement

[0106] 6a first connection

[0107] 6b second connection

[0108] 7a first line

[0109] 7b second line

[0110] 8 Pressure reservoir

[0111] 9 compressible element

[0112] 10 Charging circuit

[0113] 11 Tank connection

[0114] 12 Tank

[0115] 13 Pressure relief valve

[0116] 14 Safety valve

[0117] 15 additional hydraulic fluid sources

[0118] 16 Diverter valve

[0119] 17 Signal input

[0120] 18 Pump drive

[0121] 19 electronic valve control

[0122] 20a first cross-section

[0123] 20b second cross section

[0124] 21a first sub-pump

[0125] 21b second sub-pump

[0126] 22 Delta volume

[0127] 23a First hydraulic fluid supply

[0128] 23b second hydraulic fluid supply 24 rod

[0129] 25 pistons

[0130] 26 Pressure axis

[0131] 27 Speed ​​axis

[0132] 28a first work area

[0133] 28b second work area

[0134] 29 load points

[0135] 30 Design area

[0136] 31 cylinder bodies

[0137] 32 Conveyor element

[0138] 33 wave

[0139] 34 Pressure sensor

[0140] 35 Control unit

[0141] 36 Volume flow zero line

[0142] 37 Pressure zero line

[0143] 38 Constant range

[0144] 39 sloping area

[0145] 40 Switching signal

Claims

Claims 1. Hydraulic actuator (1) with a hydraulic actuator component (3) having a first chamber (4a) with a first cross-section (20a) and a second chamber (4b) with a second cross-section (20b) that is larger than the first cross-section (20a), and with a bidirectionally operable hydraulic pump (2) with which hydraulic fluid can be conveyed bidirectionally between the chambers (4a, 4b) for actuating the actuator component (3) and with which hydraulic energy can be recuperated from the chambers (4a, 4b), wherein, due to the larger second cross-section (20b), a delta volume (22) occurs as a change in the total volume of the chambers (4a, 4b) when hydraulic fluid is conveyed from one chamber (4a, 4b) to the other chamber (4b, 4a), wherein the hydraulic pump (2) is designed in two parts with a first sub-pump (21a) that connects the chambers (4a, 4b) and with a second sub-pump (21b),which is connected to the second chamber (4b) with the larger hydraulic cross-section (20b) and to a valve arrangement (5), with which the second sub-pump (21b) can be selectively connected to a first hydraulic fluid supply (23a) or a second hydraulic fluid supply (23b), wherein the hydraulic fluid supplies (23a, 23b) are configured to be able to supply or receive hydraulic fluid to compensate for the delta volume (22).

2. Hydraulic actuator (1) according to claim 1, wherein the bidirectionally operable hydraulic pump (2) is an electrically driven hydraulic pump.

3. Hydraulic actuator (1) according to one of the preceding claims, wherein the first hydraulic fluid supply (23a) comprises a pressure reservoir (8) which enables the intake and supply of pressurized hydraulic fluid to the second partial pump (21b), wherein hydraulic energy is transferred during the intake of hydraulic fluid. The pressure reservoir (8) is stored and is released again when hydraulic fluid is released from the pressure reservoir (8).

4. Hydraulic actuator (1) according to claim 3, wherein a compressible element (9) is arranged on the pressure reservoir (8), which is compressible by pressure present in the pressure reservoir in order to store hydraulic energy in the pressure reservoir (8).

5. Hydraulic actuator (1) according to claim 3 or 4, wherein the pressure reservoir (8) is connected to a charging circuit (10) with which a pressure level in the pressure reservoir (8) can be established.

6. Hydraulic actuator (1) wherein the second hydraulic fluid supply (23b) comprises a tank connection (11) to a tank (12) at which hydraulic fluid from the second sub-pump (21b) can be supplied to the tank.

7. Hydraulic actuator (1) according to claim 6, wherein the second hydraulic fluid supply (23b) has a pressure relief valve (13) which maintains a minimum pressure of the hydraulic fluid in the second sub-pump (21b) when hydraulic fluid is discharged from the second sub-pump (21b) to the tank (12).

8. Hydraulic actuator (1) according to claim 7, wherein the pressure relief valve (13) has an electronic valve control (19) with which the pressure relief valve (13) can be controlled to enable an adjustment of the opening pressure during operation.

9. Hydraulic actuator (1) according to any one of claims 6 to 8, wherein the second hydraulic fluid supply (23b) has a safety valve (14) which opens when hydraulic fluid is supplied to the second sub-pump (21b) in order to prevent the second sub-pump (21b) from being pressurized. to provide hydraulic fluid from another hydraulic fluid source (15).

10. Hydraulic actuator (1) according to claim 9, wherein the further hydraulic fluid source (15) is connected to the first hydraulic fluid supply (23a).

11. Hydraulic actuator (1) according to one of the preceding claims, wherein the valve arrangement (5) has at least one signal input (17) to which a switching signal can be applied, with which it can be specified whether the first hydraulic fluid supply (23a) or the second hydraulic fluid supply (23b) is connected to the second sub-pump (21b).

12. Hydraulic actuator (1) according to one of the preceding claims, wherein the valve arrangement (5) is configured to selectively connect the second partial pump (21 b) to either the first hydraulic fluid supply (23a) or the second hydraulic fluid supply (23b) depending on a pressure in the first chamber (4a).

13. Hydraulic actuator (1) according to claim 12, wherein the valve arrangement (5) has a switching valve (16) which has a signal input (17) which is connected to a first line (7a) which connects the hydraulic pump (2) to the first chamber (4a).

14. Method for operating a hydraulic actuator (1) according to any one of claims 1 to 13, comprising the following steps: a) Operation of the hydraulic actuator (1) in a first operating mode in which the second partial pump (21b) is connected to the first hydraulic fluid supply (23a) and in which occurring load requirements can be met with the support of a hydraulic pump (2) of the hydraulic actuator with a pressure reservoir (8) of the hydraulic fluid supply (23a); b) Detecting a load requirement whose fulfillment is affected by the pressure reservoir (8) of the first hydraulic fluid supply (23); c) Switching the hydraulic actuator (1) from the first operating mode to a second operating mode by actuating the valve arrangement (5) to switch to the second hydraulic fluid supply (23b); and d) Operating the hydraulic actuator (1) in a second operating mode in which the second sub-pump (21b) is connected to the second hydraulic fluid supply (23b), which facilitates the delivery of hydraulic fluid from the second sub-pump.

15. Mobile working machine (15) comprising at least one hydraulic actuator (1) according to any one of claims 1 to 13.

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