Hydraulic drive and method for regenerative lowering of components of working machine

Abstract

The invention relates to a hydraulic drive for a working machine, comprising: a hydraulic linear load (30), which has a first chamber (38); and at least one further hydraulic load (32). The hydraulic drive has: a hydraulic machine (4) that can be pivoted through zero; and a hydraulic pump (6) mechanically coupled thereto; the invention relates to a valve unit, comprising a first hydraulic valve input connection (24), a second hydraulic valve input connection (25), a first hydraulic load connection (34), which is or can be hydraulically connected to a first chamber (38) of a linear load, and at least one further hydraulic load connection, which is or can be hydraulically connected to at least one further load, a first hydraulic valve input connection (24) is hydraulically connected in a controllable manner to the first hydraulic load connection and a second hydraulic valve input connection is hydraulically connected in a controllable manner to at least one further hydraulic load connection, and wherein the hydraulic pump working connection (22) is connected to the second valve input connection; and a switching valve (10) which is connected between the hydraulic machine working connection (16) and the first valve input connection and which can be switched into a through state and into a blocked state, the hydraulic machine working connection being connected to a return line which is designed to return the hydraulic machine working connection to the first valve input connection. A volumetric flow of pressurized fluid exiting the first chamber is received during the descending phase.

Description

Technical Field

[0001] The invention relates to a hydraulic drive and a method for regeneratively lowering an element of a working machine. Background Art

[0002] Mobile working machines, such as excavators, telescopic forklifts, reach stackers and other devices, have a boom with which heavy loads are lifted and which can lower the load again after transport or displacement. In this case, the lowering process can be very fast and not very precisely positioned, or else more slowly and precisely positioned, depending on the application. Usually, the lowering of the load is carried out in a consumption-based manner by regulating the volume flow through an adjustable valve, by means of which the speed can be very well controlled. Summary of the invention

[0003] According to the invention, a hydraulic drive for or in a working machine and a method for regeneratively lowering an element of a working machine are proposed, having the features of the independent claims. Advantageous embodiments are the subject matter of the dependent claims and the following description. The embodiments and advantages described below apply in the same manner to the drive and the method.

[0004] The proposed drive assembly and control assembly can expand the existing system in the following manner, so that an active (active) regenerative lowering of the weight can be achieved and potential energy can be recovered for the most part. The assembly can ensure that additional load members can also be controlled. The proposed solution can be constructed as a feasible platform in a modular manner and implemented in a manner that can be transferred to various applications. In order to achieve these advantages, a return line is provided between the linear load member (e.g., lifting cylinder) and the hydraulic machine in the hydraulic drive to guide the fluid (hydraulic fluid, such as hydraulic oil) used to drive the hydraulic machine back, and at the same time a switching valve is provided between the hydraulic machine and the valve unit (directional valve assembly) to block the connection of the hydraulic machine to the valve unit. When the switching valve is closed, that is, the switching valve is in a blocking state, the fluid returning from the first load member can be used to drive the hydraulic machine, which can also act as a hydraulic motor because it can pivot through zero (nulldurchschwenkbar). The hydraulic power is then converted into mechanical power, which is regenerated by coupling with a hydraulic pump. The excess power can be converted into electrical energy and stored. Overall, it is then possible to regenerate the potential energy of a heavy object, such as an element of a working machine (eg a boom), which during lowering causes a return flow of the fluid under pressure.

[0005] The hydraulic drive is provided for or in a working machine having a hydraulic linear load and at least one further hydraulic load, wherein the linear load has a first chamber and is arranged such that a volume flow of a fluid under pressure entering the first chamber causes an element of the working machine (e.g. an excavator) to move (raise or lower, depending on whether the fluid flows into or out of the first chamber). The element is, for example, a boom, a lifting platform or the like of the working machine. The linear load has, in particular, one or more fluid cylinders (hydraulic cylinders). In principle, it can be provided that the linear load has a plurality of fluid cylinders and thus a plurality of chambers, the pressure loading of which causes the same movement (e.g. a boom of an excavator, which is moved by two fluid cylinders). For the sake of simplicity, the plurality of chambers, if any, are collectively considered within the scope of the present description as a first chamber (e.g. as a first chamber comprising a plurality of subchambers, one of which is present in each fluid cylinder). Alternatively, the expression "at least one first chamber" can be used instead of "first chamber".

[0006] A hydraulic drive has an adjustable hydraulic machine and a hydraulic pump, which can be pivoted through zero (i.e., the pivot angle of the hydraulic machine can assume both positive and negative values), and whose drives are mechanically coupled (mechanical energy or power can then be transmitted between the hydraulic machine and the hydraulic pump). The mechanical coupling is realized in particular via shafts and / or transmissions. A hydraulic machine is a hydraulic machine which, depending on the set (positive / negative) pivot angle, can function both as a hydraulic pump and as a hydraulic motor. A hydraulic pump can only function as a hydraulic pump and therefore cannot be pivoted through zero if it is an adjustable pump.

[0007] A valve unit, which can also be referred to as a main valve, is provided, which has a first hydraulic valve input connection, a second hydraulic valve input connection, a first hydraulic load connection (or output connection) which is hydraulically connected or connectable to a first chamber of a linear load, and at least one further hydraulic load connection (or output connection) which is hydraulically connected or connectable to at least one further load. The first hydraulic valve input connection is hydraulically connected to the first hydraulic load connection in a controllable manner, and the second hydraulic valve input connection is hydraulically connected to the at least one further hydraulic load connection in a controllable manner. The expression "controllable manner" means that the valve unit can be actuated so that the hydraulic connection can be adjusted between a closed state and an open state. The valve unit can be, for example, a separate structural unit, for example regarded as a separate (main) valve, or can be constructed modularly from a plurality of structural elements, for example individual (sub)valves.

[0008] Preferably, the valve unit (main valve) comprises a directional valve assembly or a directional valve assembly, which has a first hydraulic valve input interface and a second hydraulic valve input interface, and the directional valve assembly has a first directional valve and at least one second directional valve, a first hydraulic load interface (or output interface) being arranged at the first directional valve, and at least one further hydraulic load interface being arranged at the second directional valve. The first directional valve is hydraulically connected to the first valve input interface, and the at least one second directional valve is hydraulically connected to the second valve input interface. The directional valves of the directional valve assembly can then be supplied with fluid independently of one another (i.e., a dual-circuit hydraulic system) via the valve input interfaces, which fluid can be transferred to different loads via the directional valves. The directional valve assembly is an example of a modular design for the valve unit.

[0009] In addition, it can be provided that the first load component interface, in particular the first directional valve, can be hydraulically connected to the second valve input interface. For this purpose, a sequence valve (for example a switching valve or a proportional valve) or a summing valve can be provided in the valve unit, in particular in the directional valve assembly. The second valve input interface is then hydraulically connected to the first load component interface, in particular the first directional valve, via a sequence valve or a summing valve. It is conceivable that this functionality is integrated into the first directional valve as necessary. The first directional valve is then directly hydraulically connected to the second valve input interface. Such a design can be advantageous in order to be able to temporarily provide the linear load with the combined hydraulic power of the hydraulic machine and the hydraulic pump. As an additional or alternative, it can be provided that at least one further load component interface, in particular at least one second directional valve, can be hydraulically connected to the first valve input interface. For this purpose, a sequence valve (for example a switching valve or a proportional valve) or a summing valve can be provided in the valve unit, in particular in the directional valve assembly, or this functionality can be integrated into at least one second directional valve as necessary.

[0010] The supply of fluid is achieved by means of a hydraulic machine and a hydraulic pump. Here, the hydraulic pump working interface is (directly) hydraulically connected to the second valve input interface. A switching valve is arranged in the connection between the hydraulic machine working interface and the first valve input interface, or the switching valve is hydraulically connected between the hydraulic machine working interface and the first valve input interface, and the switching valve can be switched to a through state and a blocked state, in which the first valve input interface is hydraulically connected to the hydraulic machine working interface and in which the first valve input interface is hydraulically separated from the hydraulic machine working interface. If no regenerative descent is performed or outside the descent phase, the switching valve is in particular in the through state, so that the hydraulic machine can supply the valve unit, in particular the directional valve assembly, with fluid, for example for lifting heavy objects by means of a linear load.

[0011] Furthermore, the hydraulic machine working interface is hydraulically connected to a return line which is designed to receive a volume flow of the pressurized fluid from the first chamber of the linear actuator during the lowering phase when the linear actuator is connected (that is to say when the first chamber is hydraulically connected to the hydraulic drive). Suitable means (e.g. a valve) can be provided at the linear actuator, which prevent a volume flow into the return line outside the lowering phase. In contrast, a return line directional valve is preferably provided as a component of the hydraulic drive for this purpose (see below).

[0012] Preferably, the hydraulic drive has a control unit which is designed to, during the lowering phase, actuate the switching valve so that it switches into a blocked state, actuate the valve unit (in particular the first directional valve) so that the hydraulic connection from the first valve input interface to the first load interface is closed, and actuate the hydraulic machine so that it changes the pivot angle so that the hydraulic machine is operated or can be operated as a hydraulic motor. These steps are carried out simultaneously or at least overlappingly. If the first load interface or the first directional valve can be hydraulically connected to the second valve input interface, the valve unit or the directional valve assembly (in particular the first directional valve and / or the sequence valve and / or the summing valve) is actuated by the control unit during the lowering phase so that this connection is closed.

[0013] Preferably, the hydraulic drive has an electric motor which is coupled to the hydraulic machine and the hydraulic pump (in order to drive them, or to be driven by them, or to be mechanically coupled to a drive of the hydraulic machine and the hydraulic pump, for example a drive shaft), wherein the control unit is further preferably configured to control the electric motor and / or an inverter of the electric motor, in particular, in such a way that the electric motor acts as a generator during the lowering phase. The use of an electric motor to drive the hydraulic machine and the hydraulic pump is advantageous because, when the power recovered by the hydraulic machine exceeds the power required by the hydraulic pump, the excess power can be converted into electrical power by the electric motor which can be operated as a generator. The electrical energy obtained can be stored, for example, in a battery.

[0014] Preferably, the hydraulic drive has a return line directional valve, which is hydraulically connected to the return line and is hydraulically connected or connectable to the first chamber of the linear load and is designed to (when connected to the linear load) selectively close or at least partially open the hydraulic passage between the return line and the first chamber in a controllable and / or adjustable manner. The return line directional valve is further preferably a proportional valve. It is also further preferred that the control unit is designed to control the return line directional valve during the lowering phase if necessary so that it partially or completely opens the hydraulic passage between the return line and the first chamber. Outside the lowering phase, the passage of the return line directional valve is preferably closed. Accordingly, no fluid can flow from the linear load to the hydraulic machine working interface outside the lowering phase. If the return line directional valve is a proportional valve (i.e. has an intermediate position), the volume flow from the linear load to the hydraulic machine working interface and thus the lowering speed can be controlled.

[0015] Preferably, the hydraulic drive has a circulation directional valve, which is hydraulically connected to the hydraulic pump-working interface and the tank interface of the hydraulic pump and is configured to selectively close or at least partially open the hydraulic channel between the hydraulic pump-working interface and the tank interface of the hydraulic pump in a controllable manner. The circulation directional valve is further preferably a proportional valve. It is also further preferred that the control unit is configured to control the circulation directional valve during the descending phase so that it partially or completely opens the hydraulic channel between the hydraulic pump-working interface and the tank interface. Thus, the neutral circulation loss of the hydraulic pressure can be avoided for the situation that at least one other load does not need or only needs less power during the descending phase. If the hydraulic pump is a fixed displacement pump, this design is particularly advantageous.

[0016] According to other preferred designs, the hydraulic pump is an adjustable hydraulic pump. In this case, even without a circulation directional valve, neutral circulation loss can be avoided.

[0017] Preferably, when the linear load has a second chamber, the hydraulic drive has a compensating directional valve, which is hydraulically connected or connectable to the first chamber and the second chamber and is designed to, when connected, selectively close or at least partially open the hydraulic passage between the first chamber and the second chamber in a controllable manner. The compensating directional valve is further preferably a proportional valve. It is also further preferred that the control unit is designed to control the compensating directional valve during the lowering phase so that it partially or completely opens the hydraulic passage between the first chamber and the second chamber. The second chamber is, for example, the second chamber of a double-acting fluid cylinder. The second chamber can be filled with fluid from the first chamber accordingly, so that no further supply of fluid is required. For example, when the linear load comprises a plurality of fluid cylinders that jointly cause a movement (lifting / lowering) of an element of the working machine, here (as in the first chamber) the second chamber can also again comprise a plurality of subchambers.

[0018] Preferably, the switching valve and / or the control unit, if applicable, is designed such that the switching valve switches to the through-state outside the lowering phase. The switching valve can be designed, for example, such that it automatically switches to the through-state by means of a spring or the like when no further control signal is applied. As an alternative or in addition, active control can be achieved by the control unit.

[0019] Preferably, the return line directional valve and / or the control unit, if necessary, is designed so that the hydraulic passage between the first chamber and the return line is closed outside the lowering phase, and / or the compensation directional valve and / or the control unit, if necessary, is designed so that the hydraulic passage between the first chamber and the second chamber is closed outside the lowering phase, and / or the circulation directional valve and / or the control unit, if necessary, is designed so that the hydraulic passage between the hydraulic pump working interface and the hydraulic pump tank interface is closed outside the lowering phase. It can also be provided here independently of one another that the closed position is automatically assumed, for example by means of a spring, by means of a corresponding prestressing, when no other actuation is present, or that, as an alternative or in addition, a corresponding actuation is effected by the control unit.

[0020] Further advantages and embodiments of the invention are apparent from the description and the drawings.

[0021] It goes without saying that the features mentioned above and those yet to be explained below can be used not only in the respectively specified combination but also in other combinations or alone, without departing from the scope of the present invention.

[0022] The invention is schematically illustrated in the drawings using exemplary embodiments and is described in more detail below with reference to the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1A hydraulic drive according to a preferred embodiment of the present invention is shown;

[0024] Figure 2 A hydraulic drive according to another preferred embodiment of the present invention is shown;

[0025] Figure 3 The sequence of a preferred embodiment of the method according to the present invention is shown. DETAILED DESCRIPTION

[0026] Figure 1 A hydraulic drive according to a preferred embodiment of the present invention is shown. The hydraulic drive forms an open dual-circuit hydraulic system. The hydraulic drive includes a hydraulic machine 4, a hydraulic pump 6, a valve unit (Ventilblock): that is, an exemplary directional valve assembly 8, and a switching valve 10. The hydraulic machine 4 and the hydraulic pump 6 or their drive shafts are mechanically coupled to each other, that is, they can be driven together. This coupling can be achieved, for example, by a drive shaft or a transmission mechanism. The rotational speeds of the hydraulic machine 4 and the hydraulic pump 6 are then the same or at least in a specific ratio relative to each other.

[0027] The hydraulic machine 4 and the hydraulic pump 6 are preferably driven by an electric motor 12, which is connected to an electric energy supply, for example a DC voltage system and / or a battery, via an inverter 14. The inverter 14 can, for example, convert a direct current of the electric energy supply into an alternating current for the electric motor when the electric motor functions as an electric motor, and vice versa, convert the alternating current into a direct current when the electric motor functions as a generator.

[0028] The hydraulic machine 4 is adjustable, that is to say the pivot angle of the hydraulic machine is adjustable. Furthermore, the hydraulic machine 4 can be pivoted through zero and can thus be operated both as a hydraulic pump (e.g. corresponding to a positive pivot angle) and as a hydraulic motor (e.g. corresponding to a negative pivot angle). Such a hydraulic machine is also referred to as "anchorable". The hydraulic machine 4 has a (hydraulic) hydraulic machine working connection 16 and a tank connection 18 which is connected here to a tank 20. In pump operation, the hydraulic machine generates a flow of fluid (from the tank) from the tank connection 18 to the hydraulic machine working connection 16, for example, driven by the electric motor 12. In motor operation, the volume flow of fluid from the hydraulic machine working connection 16 to the tank connection 18 generates a torque or mechanical power on the drive shaft of the hydraulic machine 4 which can be used to (at least partially) drive the hydraulic pump 6 and, if excess mechanical power is generated, can, for example, additionally drive the electric motor 12.

[0029] The hydraulic pump 6 is a fixed displacement pump and has a tank connection 23 (here hydraulically connected to the tank 20 ) and a hydraulic pump working connection 22 . The hydraulic pump 6 is designed to pump fluid from the tank connection 23 to the hydraulic pump working connection 22 when driven.

[0030] The directional valve assembly 8 has a first valve input interface 24 and a second valve input interface 25, through which the directional valve assembly can be supplied with fluid liquid. The directional valve assembly 8 includes a first directional valve 26 and at least one second directional valve 28, wherein the first directional valve 26 is hydraulically connected to the first valve input interface 24, and at least one second directional valve 28 is hydraulically connected to the second valve input interface 25 (each not shown in detail). Generally, the directional valve assembly can include more than two directional valves. The directional valve assembly shown is exemplarily implemented as a modular directional valve unit, which has a plurality of directional valve sections, and fluid liquid can be supplied to these directional valve sections through input sections in which valve input interfaces are provided. Each directional valve section corresponds to a directional valve with a corresponding load part interface. The directional valves of the individual directional valve sections can generally be operated or controlled independently of each other. The directional valves are Figure 1 In the example, there are two load connections in each case, in general, the directional valve can also have a different number of load connections independently of one another, that is to say the directional valve generally has at least one load connection. If the valve unit is not designed in a modular manner, but is designed as a (at least partially) unified structural unit, the valve unit is designed to realize the functionality described below in conjunction with the directional valve assembly.

[0031] In the illustrated embodiment, the first directional valve 26 and the at least one second directional valve 28 each have two load connections, i.e., hydraulic connections, to which hydraulic lines leading to the corresponding loads can be connected. The first directional valve 26 and the at least one second directional valve 28 are configured to completely or partially release or block the hydraulic passage or connection from the valve input connection to the load connection, depending on how they are actuated, so that the flow of fluid to each of the load connections or to the loads connected thereto can be controlled.

[0032] As already explained above, it can be provided that the first load component interface 34 can be hydraulically connected to the second valve input interface 25 and / or at least one further load component interface can be hydraulically connected to the first valve input interface (via corresponding functionality of at least one suitable sequential valve and / or at least one suitable summing valve and / or directional valve).

[0033] The hydraulic pump working port 22 is hydraulically connected to the second valve input port 25 .

[0034] The hydraulic machine working interface 16 is connected to the first valve input interface 24 via the switching valve 10. The switching valve 10 can be switched into a through state (the state shown in the figure) and a blocked state. In the through state, the switching valve 10 is open, that is, there is an (open) hydraulic connection between the hydraulic machine working interface 16 and the first valve input interface 24, so that the fluid can flow between these interfaces. In the blocked state, the switching valve 10 is closed, that is, there is no hydraulic connection between the hydraulic machine working interface 16 and the first valve input interface 24, so that the fluid cannot flow between these interfaces. The switching valve 10 can be actuated, for example, electrically or electromagnetically, wherein, in another advantageous embodiment, the switching valve 10 can also be controlled or actuated in an electrohydraulic manner, for example, by a so-called pressure regulating element.

[0035] Shown is a hydraulic linear load 30 or a fluid cylinder (here a differential cylinder) which is hydraulically connected to a first directional valve 26. In this case, the load connection of the first directional valve 26 is hydraulically connected to a working connection or chamber of the linear load 30. In detail, the first load connection 34 is hydraulically connected to a first chamber 38 and the second load connection 36 is hydraulically connected to a second chamber 40. The linear load can also be referred to as a first hydraulic load or as a hydraulic main stage load.

[0036] Also shown is a further hydraulic load 32 (here also a differential cylinder by way of example) which is hydraulically connected to the at least one second directional valve 28. Generally, more further loads 32 than shown can be provided which are hydraulically connected to the respective second directional valve. At least one further hydraulic load is then provided, which can also be referred to as at least one second hydraulic load or as a hydraulic secondary load.

[0037] The linear load 30 is designed, in particular arranged, on a working machine in which a hydraulic drive is used, such that a weight is lifted (not shown) when a fluid is directed into the first chamber 38 of the linear load (and the fluid is directed out of the second chamber 40) by corresponding actuation of the first directional valve 26. This can be achieved, for example, by means of a boom of the working machine. The weight is lifted against the effect of gravity, with the normal working position of the working machine being the starting point. The fluid in the first chamber is under a corresponding pressure (caused by the weight).

[0038] A return line directional valve 42 is preferably arranged between the first chamber 38 of the linear load 30 and the hydraulic machine working connection 16 of the hydraulic machine 4, which return line directional valve is a 2 / 2 directional valve (proportional valve) with a center position. The connection of the return line directional valve is hydraulically connected to the first chamber, and the other connection of the return line directional valve is hydraulically connected to the hydraulic machine working connection 16 via a return line 46. The return line directional valve 42 can be adjusted between a closed end position and an open end position, wherein in the closed end position (position shown in the figure) there is no hydraulic connection between the first chamber and the return line or the hydraulic machine working connection, and when adjusting in the direction of the open end position, the passage opening is increasingly released or the return line directional valve 42 is increasingly opened, so that there is a hydraulic connection between the first chamber and the return line or the hydraulic machine working connection and it is released as the cross section increases. In the open end position, the passage opening is completely open. The return line directional valve 42 or its adjustment can be controlled, for example, electrically, that is to say the return line directional valve 42 can be actuated, for example, electrically or electromagnetically, wherein in a further advantageous embodiment the return line directional valve 42 can also be controlled or actuated electrohydraulically, for example, by a so-called pressure regulating element. The closed end position can be a position which is automatically assumed (particularly outside the lowering phase, when no further control signal is present, for example, as explained, by a preload element (for example a spring) which causes a movement into the closed end position).

[0039] When the control valve 10 is closed and the return line directional valve 42 is (at least partially) open, the fluid under pressure is conducted from the first chamber 38 of the linear load element 30 via the return line directional valve 42 and the return line 46 to the hydraulic machine working interface 16, so that the hydraulic machine 4 can be operated as a motor in order to convert hydraulic energy into mechanical energy (torque, speed). The weight is lowered accordingly, so that the potential energy is converted into mechanical energy. The mechanical energy is used to drive the hydraulic pump 6 or the electric motor 12 operated as a generator. Overall, a regenerative lowering of the weight lifted by the linear load element is thus achieved during the lowering phase.

[0040] During regenerative lowering, the first directional valve 26 is controlled in such a way that there is no hydraulic connection between the first valve input connection 24 and the first load connection 34. If the first load connection 34 can be hydraulically connected to the second valve input connection 25, this connection is closed during regenerative lowering, during which the directional valve arrangement is controlled in such a way that there is no hydraulic connection between the second valve input connection 25 and the first load connection 34. Preferably, the first directional valve 26 is additionally controlled during regenerative lowering in such a way that there is no hydraulic connection between the first valve input connection 24 and the second load connection 36 (if the directional valve arrangement is designed to enable such a connection to be established).

[0041] During regenerative lowering (control valve 10 closed), the hydraulic supply to the at least one further consumer 32 is ensured by the hydraulic pump 6 , which continues to supply the directional valve assembly with fluid via the second valve input connection 25 .

[0042] Furthermore, a compensating directional valve 44 is preferably provided, which here is a 2 / 2-way directional valve with a center position, which is arranged between the first chamber 38 and the second chamber 40. One port of the compensating directional valve is hydraulically connected to the first chamber (and therefore also to the first load interface), and the other port of the compensating directional valve is hydraulically connected to the second chamber (and therefore also to the second load interface). Like the return directional valve 42, the compensating directional valve 44 is adjustable between a closed end position (no hydraulic connection between the first chamber and the second chamber) and an open end position, wherein the channel is increasingly opened starting from the closed end position (in which the channel is closed) (hydraulic connection between the first chamber and the second chamber with increasing cross section). The compensating directional valve 44 can be actuated, for example, electrically or electromagnetically, wherein in a further advantageous embodiment the compensating directional valve 44 can also be controlled or actuated electrohydraulically, for example by a so-called pressure regulating element. The closing end position can be a position which is automatically assumed (particularly outside the lowering phase when no further control signal is present, for example, as explained, by a preload element (eg a spring) which effects a movement into the closing end position).

[0043] The compensating directional valve 44 enables the fluid to be guided between the chambers. In particular, it is possible to guide the fluid from the first chamber into the second chamber during regenerative lowering, thereby eliminating the need for a supply via the first directional valve or the directional valve assembly 8, which is hydraulically supplied only via the hydraulic pump due to the closed switching valve.

[0044] During regenerative lowering, the speed of the lowering can be controlled by correspondingly actuating the return line directional valve 42 and / or the compensating directional valve 44 , ie by controlling the cross sections of the corresponding channels.

[0045] The compensating directional valve 44 is designed here as a separate valve. Alternatively, the compensating directional valve or its functionality can also be integrated in the first directional valve 26.

[0046] Instead of the double-acting fluid cylinder shown as the linear load, a single-acting fluid cylinder can also be used (so that only the first chamber is loaded with fluid under pressure, wherein only a first load interface connected or connectable to the first chamber is provided on the first directional valve, and the second load interface can be omitted). In this case, the compensating directional valve 44 can be omitted.

[0047] Furthermore, a circulation directional valve 48 is preferably provided between the hydraulic pump working connection 22 of the hydraulic pump 6 and the tank connection 23, which circulation directional valve is a 2 / 2 directional valve with a center position. One connection of the circulation directional valve is hydraulically connected to the hydraulic pump working connection 22 (and therefore also to the valve input connection 24), and the other connection of the circulation directional valve is hydraulically connected to the tank connection 23 of the hydraulic pump 6 (and therefore also to the tank). Like the return line directional valve 42 and the compensation directional valve 44, the circulation directional valve 48 can be adjusted between a closed end position (no hydraulic connection between the hydraulic pump working connection 22 and the tank connection 23) and an open end position, wherein the channel is increasingly opened starting from the closed end position (in which the channel is closed) (hydraulic connection between the hydraulic pump working connection 22 and the tank connection 23 with an increasing cross section). The circulation directional valve 48 can be actuated, for example, electrically or electromagnetically, wherein, in a further advantageous embodiment, the circulation directional valve 48 can also be controlled or actuated electrohydraulically, for example, by a so-called pressure regulating element. If at least one further load part 32 does not require or only requires less hydraulic power during the regenerative descent, the circulation directional valve 48 can be actuated to at least partially occupy the open position. This is advantageous, since neutral circulation losses can be reduced in this way. The closed end position can be a position that is automatically occupied (particularly outside the descent phase, when no further control signal is present, for example, as explained, by a preload element (e.g. a spring) that causes a movement into the closed end position).

[0048] Furthermore, the hydraulic drive can include an (electronic) control unit 50, which is designed to control the hydraulic machine 4, the switching valve 10 and the directional valve assembly 8 or the first directional valve 26 and optionally at least one second directional valve 28. Furthermore, the control unit 50 can be designed to control the electric machine 12 or the inverter 14, if present, respectively, the return line directional valve 42, the compensation directional valve 44 and the circulation directional valve 48. In each case, the control can be carried out via corresponding control lines (not shown).

[0049] The control unit 50 is designed to control the switching valve 10 during the regenerative descent or during the descent phase so that the switching valve is switched to the blocked state and to control the adjustable hydraulic machine 4 or its pivot angle so that the hydraulic machine 4 acts as a hydraulic motor. In this case, the pivot angle is pivoted through zero so that the hydraulic machine generates a torque on the drive shaft in a given direction of rotation. In addition, the return line directional valve 42 is controlled by the control unit 50 to be switched to an at least partially open position. During the regenerative descent, the first directional valve 26 is also controlled by the control unit 50 to be switched to the following state in which there is no hydraulic connection between the first valve input interface 24 and the first load interface 34. Similarly, the compensation directional valve 44 is controlled if necessary to be switched to an at least partially open position. The descent speed can be controlled by appropriately selecting the open position of the return line directional valve 42 and, if necessary, the open position of the compensation directional valve 44.

[0050] If no or only little hydraulic power is required by the at least one second consumer 32 during the regenerative lowering, the control unit 50 can, if necessary, actuate the circulating valve 48 to switch it into an at least partially open position.

[0051] The control unit 50 can control the electric machine 12 or the inverter 14 when necessary during the regenerative lowering (that is, during the lowering phase) to reduce the power output or torque output of the electric machine 12. In particular, if the (regenerative) power output by the hydraulic machine 4 during the regenerative lowering exceeds the power absorbed by the hydraulic pump 6, the electric machine 12 can act as a generator.

[0052] Figure 2 A hydraulic drive according to another preferred embodiment of the present invention is shown. This embodiment corresponds essentially to Figure 1 , so only the differences are discussed below and see also Figure 1 Description.

[0053] and Figure 1 different, Figure 2 The hydraulic pump 6 of the embodiment is an adjustable hydraulic pump. In addition, no circulation direction valve is provided.

[0054] Since the hydraulic pump 6 is adjustable, the delivery volume flow of the hydraulic pump can be adjusted, for example, as a function of the pivot angle of the hydraulic pump 6 (at a given rotational speed). In particular, if at least one further load 32 requires no or only little hydraulic power during regenerative lowering, the pivot angle of the hydraulic pump 6 can be adjusted to zero or close to zero, so that no or only little delivery volume flow is generated. Accordingly, even without a recirculation directional valve, it is possible to Figure 2 Reducing neutral cycle losses in hydraulic drives.

[0055] exist Figure 2 In the embodiment of the invention, the control unit 50 is preferably configured to control the hydraulic pump 6 or its pivot angle. If no or only little hydraulic power is required by the at least one second load element 32 during the regenerative lowering, then Figure 1 In contrast to the at least partially opening of the mid-circulation directional valve, the control unit 50 can adjust the pivot angle of the adjustable hydraulic pump to zero or close to zero, ie, can control the adjustable hydraulic pump accordingly.

[0056] Figure 3 The flow chart of a preferred embodiment of the method according to the invention is shown. The steps performed during the lowering phase are shown here. A method for regeneratively lowering an element of a working machine is provided, which element is lowered by a hydraulic drive according to the invention (e.g. according to Figure 1 to Figure 2 Here, the element is lifted or lowered by supplying or draining fluid to or from the linear load.

[0057] In step 100, the switching valve is switched to a blocked state. In step 110, a volume flow of the fluid is directed from the first chamber to the working interface of the hydraulic machine, and in step 120, the hydraulic connection from the first valve input interface to the first load interface is closed. In step 130, the pivot angle of the hydraulic machine is changed so that the hydraulic machine functions as a hydraulic motor. These steps are performed substantially simultaneously or overlappingly. For a description of the effects of these steps, see Figure 1 to Figure 2 As already explained, the steps mentioned can be executed or brought about, in particular, by controlling a hydraulic drive.

Claims

1. A hydraulic drive for a working machine, the working machine having a hydraulic linear load (30) and at least one further hydraulic load (32), wherein: The linear load has a first chamber (38) and is arranged in such a way that a volume flow of a fluid under pressure into or out of the first chamber causes a lifting or lowering of an element of the working machine, The hydraulic drive has: an adjustable hydraulic machine (4) which can be pivoted through zero, and a hydraulic pump (6), whose drives are mechanically coupled, wherein the hydraulic machine has a hydraulic machine working interface (16) and the hydraulic pump has a hydraulic pump working interface (22); a valve unit having a first hydraulic valve input interface (24), a second hydraulic valve input interface (25), a first hydraulic load interface (34) hydraulically connected or connectable to a first chamber (38) of the linear load, and at least one further hydraulic load interface hydraulically connected or connectable to at least one further load, wherein the first hydraulic valve input interface (24) is hydraulically connected to the first hydraulic load interface (34) in a controllable manner, and the second hydraulic valve input interface (25) is hydraulically connected to the at least one further hydraulic load interface in a controllable manner, and wherein the hydraulic pump working interface (22) is hydraulically connected to the second valve input interface (25); a switching valve (10), which is hydraulically connected between the hydraulic machine working interface (16) and the first valve input interface (24), and the switching valve can be switched into a through state and a blocked state, in which the first valve input interface and the hydraulic machine working interface are hydraulically connected, and in which the first valve input interface and the hydraulic machine working interface are hydraulically separated; The hydraulic machine working interface is hydraulically connected to a return line (46) which is designed to receive a volume flow of pressurized fluid from a first chamber (38) of the linear actuator during a lowering phase when the linear actuator is connected.

2. The hydraulic drive according to claim 1, wherein the valve unit comprises a directional valve assembly (8), the directional valve assembly having a first hydraulic valve input interface (24) and a second hydraulic valve input interface (25); wherein, The directional valve assembly (8) comprises a first directional valve (26) and at least one second directional valve (28), a first hydraulic load component interface (34) being arranged at the first directional valve, and at least one other hydraulic load component interface being arranged at the second directional valve; wherein the first directional valve (26) is hydraulically connected to the first valve input interface (24), and wherein the at least one second directional valve (28) is hydraulically connected to the second valve input interface (25).

3. The hydraulic drive according to claim 1 or 2, comprising a control unit (50) which is designed to, during the lowering phase, Controlling the switching valve (10) to switch it to the blocking state; The valve unit, in particular the first directional valve (26), is actuated such that the hydraulic connection from the first valve input interface (24) to the first load interface (24) is closed; and The hydraulic machine (4) is controlled to change the pivot angle so that the hydraulic machine operates or can operate as a hydraulic motor.

4. The hydraulic drive according to claim 1 , further comprising an electric motor ( 12 ) which is coupled to the hydraulic machine ( 4 ) and the hydraulic pump ( 6 ); wherein: According to claim 3, the control unit (50) is preferably designed to control the electric machine (12) and / or an inverter (14) of the electric machine, in particular in such a way that the electric machine functions as a generator during the lowering phase.

5. The hydraulic drive according to claim 1 , comprising a return line directional valve (42) which is hydraulically connected to the return line (46) and is hydraulically connected or connectable to the first chamber (38) of the linear load and is designed to selectively close or at least partially open a hydraulic passage between the return line (46) and the first chamber (38) in a controllable manner; in, The return line directional valve (42) is preferably a proportional valve; and / or wherein, according to claim 3, the control unit (50) is preferably configured to control the return line directional valve (42) during the lowering phase so that it partially or completely opens the hydraulic channel between the return line (46) and the first chamber (38).

6. The hydraulic drive according to claim 1 , comprising a circulation directional valve (48) which is hydraulically connected to the hydraulic pump working interface (22) and the tank interface (23) of the hydraulic pump and is designed to selectively close or at least partially open a hydraulic channel between the hydraulic pump working interface (22) of the hydraulic pump and the tank interface (23) in a controllable manner; in, The circulation directional valve (48) is preferably a proportional valve; and / or wherein, according to claim 3, the control unit (50) is preferably configured to control the circulation directional valve (48) during the lowering phase so that it partially or completely opens the hydraulic channel between the hydraulic pump-working interface (22) of the hydraulic pump and the tank interface (23).

7. A hydraulic drive according to any one of the preceding claims, wherein: The linear load (30) has a second chamber (40); wherein the hydraulic drive has a compensating directional valve (44) which is hydraulically connected or connectable to the first chamber (38) and the second chamber (40) and is configured to selectively close or at least partially open a hydraulic passage between the first chamber and the second chamber in a controllable manner when connected; wherein the compensating directional valve (44) is preferably a proportional valve; and / or wherein, according to claim 3, the control unit (50) is preferably configured to control the compensating directional valve (44) during the lowering phase so as to partially or completely open the hydraulic channel between the first chamber (38) and the second chamber (40).

8. A hydraulic drive according to any one of the preceding claims, wherein: The switching valve (10) and / or the control (50) according to claim 3 is designed in such a way that the switching valve is switched into the through-state outside the lowering phase.

9. A hydraulic drive according to any one of the preceding claims, wherein: The return line directional valve (42) and / or the control unit (50) according to claim 3 are set up in such a way that the hydraulic channel between the first chamber (38) and the return line (46) is closed outside the lowering phase, and / or the compensation directional valve (44) and / or the control unit (50) according to claim 3 are set up in such a way that the hydraulic channel between the first chamber (38) and the second chamber (40) is closed outside the lowering phase, and / or the circulation directional valve (48) and / or the control unit (50) according to claim 3 are set up in such a way that the hydraulic channel between the hydraulic pump working interface (22) of the hydraulic pump and the tank interface (23) is closed outside the lowering phase.

10. A hydraulic drive according to any one of the preceding claims, wherein: The first load-carrying part interface (34), in particular the first directional valve, can be hydraulically connected to the second valve input interface (25); wherein, according to claim 3, the control unit (50) is preferably configured to control the directional valve assembly during the lowering phase so that there is no hydraulic connection between the first load-carrying part interface (34) and the second valve input interface (25).

11. Method for regeneratively lowering an element of a working machine, the working machine having a hydraulic linear load element (30) and at least one further hydraulic load element (32), wherein: The linear load has a first chamber (38) and is arranged in such a way that a volume flow of a fluid under pressure entering or exiting the first chamber causes a lifting or lowering of an element of the working machine, wherein the working machine has a hydraulic drive according to any of the preceding claims; During the descending phase Switching (100) the switching valve to a blocking state; directing (110) a volume flow of fluid from the first chamber to a working interface of the hydraulic press; closing (120) the hydraulic connection from the first valve input interface (24) to the first load interface (34); and The pivot angle of the hydraulic machine (4) is changed (130) so that the hydraulic machine functions as a hydraulic motor.

12. The method according to claim 10, wherein: During the lowering phase, in particular when using a return line directional valve (42), the hydraulic passage between the first chamber (38) and the return line (46) is partially or completely opened.

13. The method according to any one of claims 10 or 11, wherein: The linear load (30) has a second chamber (40), wherein during the lowering phase, in particular using a compensating directional valve (44), a hydraulic passage between the first chamber (38) and the second chamber (40) is partially or completely opened.

14. The method according to any one of claims 10 to 12, wherein: During the lowering phase, in particular using a directional control valve (48), a hydraulic channel between a hydraulic pump working connection (22) and a tank connection (23) of the hydraulic pump is partially or completely opened.

15. The method according to any one of claims 10 to 13, wherein: Outside the lowering phase, the switching valve (10) is switched to a through state, and preferably the hydraulic passage between the first chamber (38) and the return line (46) is closed, and / or the hydraulic passage between the first chamber (38) and the second chamber (40) is closed, and / or the hydraulic passage between the hydraulic pump-working interface (22) and the hydraulic pump-tank interface (23) is closed.

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