Electro-hydraulic drive

Abstract

Electro-hydraulic drive for at least one hydraulic consumer (16), comprising an electrical machine (4); a first hydraulic constant-displacement machine (6) and a second hydraulic constant-displacement machine (8), which are mechanically coupled to one another and which are jointly driven by the electric machine (4), wherein the first constant-displacement machine (6) has a first pressure output (62) and the second constant-displacement machine (8) has a second pressure output (82), wherein the first and the second pressure output (62, 82) are hydraulically connected to a hydraulic summation point (30) which is connected to a hydraulic consumer connection (32) which is or can be hydraulically connected to the at least one hydraulic consumer (16); and a valve arrangement comprising a relief valve (10) which is hydraulically connected between the second pressure outlet (82) and a first tank connection (46) and which has a closed position (a) in which no flow of pressure medium from the second pressure outlet (82) through the relief valve is possible, and a relief position (b) in which a flow of pressure medium from the second pressure outlet (82) through the relief valve to the first tank connection (46) is possible; wherein the relief valve (10) is controllably adjustable selectively into the closed position (a) or the relief position (b); an electronic drive control (22) configured to control the relief valve (10); wherein the drive control (22) is configured to determine a pump pressure of the pressure medium at the summation point (30) and: to control the relief valve (10) so that it is moved to the relief position (b) when the pump pressure is above a relief pressure, and / or to control the relief valve (10) so that it is moved to the closed position (a) when the pump pressure is below the relief pressure wherein the drive controller (22) is configured to receive and / or determine a value indicating a maximum available torque of the electric machine (4) and to determine the relief pressure based on the maximum available torque.

Description

[0001] The present invention relates to an electro-hydraulic drive. Background of the invention

[0002] Work machines, e.g., mobile work machines such as excavators or wheel loaders, may have a hydraulic drive. One or more hydraulic pumps supply pressure fluid to hydraulic consumers (e.g., hydraulic cylinders and / or hydraulic motors) in the hydraulic system. Valves control the flow of pressure fluid to the individual hydraulic consumers. The one or more hydraulic pumps may be driven by an internal combustion engine (typically a diesel engine) or an electric motor.

[0003] The patent documents EP 3 094 782 B1 and DE 10 2021 130 272 A1 are known from the prior art. Disclosure of the invention

[0004] According to the invention, an electro-hydraulic drive with the features of the independent patent claim is proposed. Advantageous embodiments are the subject of the subclaims and the following description.

[0005] The invention makes use of the measure of providing, in a hydraulic drive in which a first and a second hydraulic fixed displacement machine, which are jointly driven by an electric machine and which can convey pressure medium to a consumer connection of the hydraulic drive via a summation point hydraulically connected to pressure outputs of the fixed displacement machines, a valve arrangement with a relief valve which can be adjusted to a relief position in which a flow of pressure medium is enabled from the pressure output of the second fixed displacement machine to a tank connection. The electric machine can thus be relieved by switching the relief valve to the relief position when a pump pressure at the summation point causes a torque on the fixed displacement pumps and thus on the electric machine which exceeds the torque that can be applied by the electric machine.

[0006] The relief valve, for example, can be adjusted or controlled electromagnetically and has the closed position as the normal position.

[0007] According to one embodiment, the valve arrangement further comprises a backflow limiting valve configured to prevent a flow of pressure medium from the summation point to the second pressure outlet, or configured to controllably prevent a flow of pressure medium from the summation point to the second pressure outlet; wherein the backflow limiting valve is, in particular, a check valve. A flow of pressure medium from the summation point through the relief valve to the tank connection can thus be prevented when the relief valve is switched to the relief position.

[0008] According to one embodiment, the electro-hydraulic drive comprises an electronic drive controller configured to control the relief valve. The drive controller is configured to determine a pump pressure of the pressure medium at the summation point and: to control the relief valve so that it is moved to the relief position when the pump pressure is above a relief pressure, and / or to control the relief valve so that it is moved to the closed position when the pump pressure is below the relief pressure. Furthermore, the drive controller can be configured to receive and / or determine a value indicating a maximum available torque of the electric machine and to determine the relief pressure based on the maximum available torque.In particular, the relief pressure can be determined such that the corresponding torque generated by the pump pressure of the pressure medium on the fixed-displacement machines exceeds the maximum available torque of the electric machine. This prevents a drop in speed (e.g., if the maximum torque achievable by the electric machine is exceeded, or due to so-called derating) or overheating of the electric machine.

[0009] According to one embodiment, the electro-hydraulic drive may comprise a pump pressure sensor arranged to measure the pump pressure of the pressure medium at the summation point; wherein the drive control is connected to the pump pressure sensor (e.g., via an electrical signal line) to receive measured values ​​for the pump pressure.

[0010] According to one embodiment, the valve arrangement comprises a pressure relief valve which is hydraulically connected between the second pressure outlet of the second fixed-displacement machine and a tank connection and which is configured to enable a flow of pressure medium from the second pressure outlet of the second fixed-displacement machine when the pump pressure or a pressure difference between the pump pressure and a pressure of the pressure medium at the tank connection exceeds a pressure limit; wherein the pressure limit of the pressure relief valve is preferably adjustable. Very high pressures at the second pressure outlet of the second fixed-displacement machine can thus be avoided, so that the second fixed-displacement machine can be designed as a simple (particularly suitable for lower pressures), cost-effective fixed-displacement machine.

[0011] According to one embodiment, the valve arrangement comprises a check valve arranged between a second tank port and a suction port of the second fixed-displacement machine. The valve arrangement is then configured, in particular, to controllably enable a flow of pressure medium from the summation point to the suction port of the second fixed-displacement machine. This allows for further relief. This functionality can also be referred to as a circulation functionality, which can be implemented in various ways.

[0012] According to one embodiment with which the circulation functionality can be implemented, for example, the valve arrangement has a circulation valve which is hydraulically connected between the summation point and the suction port of the second constant machine and can be controlled to be brought into an open position in order to allow pressure medium from the summation point to the suction port of the second constant machine.

[0013] According to a further embodiment, the drive control is further configured to switch the circulation valve to the open position when the pump pressure exceeds an overload pressure, which is in particular greater than the relief pressure. This embodiment allows relief to be achieved in two stages.

[0014] According to another embodiment, with which the circulation functionality can also be implemented, for example, the relief valve is hydraulically connected to the summation point, has a circulation position and can be controlled to be moved into the circulation position; wherein in the circulation position a flow of pressure medium is possible from the summation point to the suction port of the second fixed machine and a flow of pressure medium is possible from the second working port to the first tank port; and wherein in the closed position a flow of pressure medium is preferably possible from the first tank port to the suction port of the second fixed machine via the relief valve and / or wherein in the relief position a flow of pressure medium is preferably possible from the suction port of the second fixed machine via the relief valve to the first tank port. In this embodiment, the relief valve is designed, for example, as a 4 / 3 switching valve or4 / 3-way valve that can be adjusted electromagnetically.

[0015] According to one embodiment, the relief valve is further adjustable into a circulation position and hydraulically connected to the summation point and a suction port of the second constant machine; wherein in the closed position, a flow of pressure medium from the first tank port to the suction port of the second constant machine through the relief valve is possible and no flow of pressure medium from the summation point through the relief valve is possible; wherein in the relief position, a flow of pressure medium from the first tank port to the suction port of the second constant machine is possible and no flow of pressure medium from the summation point through the relief valve is possible; and wherein in the circulation position, a flow of pressure medium from the summation point to the suction port of the second constant machine and a flow of pressure medium from the second pressure outlet of the second constant machine to the first tank port are possible.This represents another possibility to implement a circulation functionality in which no check valve is used in the inlet to the suction connection of the second fixed machine.

[0016] According to a further embodiment, which relates to embodiments in which the relief valve has a bypass position, the relief valve is adjustable from the closed position through the relief position to the bypass position. The adjustment is particularly continuous. Accordingly, the relief valve can have intermediate positions with which the volume flow can be better controlled.

[0017] According to a further embodiment relating to embodiments in which the relief valve has a bypass position, the drive control is further configured to switch the relief valve to the bypass position when the pump pressure exceeds an overload pressure, which is in particular greater than the relief pressure. As in the embodiment with the bypass valve, a two-stage relief can thus be achieved.

[0018] The terms “hydraulically connected” or “hydraulic connection” (or also “connected” or “connection” unless otherwise stated) are to be understood in the sense of connections, passages, channels, lines, or similar, through which a volume flow of pressure medium can occur, whereby valves, throttle points, or similar can be provided in hydraulic connections.

[0019] Further advantages and embodiments of the invention will become apparent from the description and the accompanying drawings.

[0020] It is understood that the features mentioned above and those to be explained below can be used not only in the combination specified in each case, but also in other combinations or on their own, without departing from the scope of the present invention.

[0021] The invention is illustrated schematically in the drawing using exemplary embodiments and is described in detail below with reference to the drawing. Character description Fig. 1 shows a hydraulic system including an electro-hydraulic drive according to an embodiment of the invention. Fig. 2 shows a hydraulic system including an electro-hydraulic drive according to another embodiment of the invention. Fig. 3 shows a hydraulic system including an electro-hydraulic drive according to another embodiment of the invention. Fig. 4 shows a hydraulic system including an electro-hydraulic drive according to another embodiment of the invention. Fig. 5 shows a hydraulic system including an electro-hydraulic drive according to another embodiment of the invention. Fig. 6 shows a hydraulic system including an electro-hydraulic drive according to another embodiment of the invention. Detailed description of the drawing

[0022] Fig. 1 shows a hydraulic system including an electro-hydraulic actuator 101 according to an embodiment of the invention.

[0023] The electro-hydraulic drive has an electric machine 4, which is supplied with alternating voltages or phase voltage by an inverter 2, as well as a first hydraulic constant machine 6 and a second hydraulic constant machine 8, wherein in this application the simplified term “constant machine” is used instead of “hydraulic constant machine”. The first and the second constant machine are mechanically coupled to one another (e.g. their drive shafts are coupled to one another in a rotationally fixed manner) and mechanically coupled to the electric machine 4 (e.g. an output shaft of the electric machine) so that they are jointly driven by the electric machine 4. The term “constant machine” refers to a hydraulic machine (i.e. a hydraulic machine that can act as a hydraulic pump and / or as a hydraulic motor) with constant displacement or constant displacement. “Displacement” or“Displacement volume” refers to the volume of pressure medium (hydraulic fluid, typically hydraulic oil) delivered per revolution of the fixed displacement machine.

[0024] A first pressure outlet 62 of the first fixed-displacement machine 6 and a second pressure outlet 82 of the second fixed-displacement machine 8 are hydraulically connected to a hydraulic summation point 30. Suction ports of the first and second fixed-displacement machines 6, 8 are hydraulically connected to a pressure medium tank via respective tank ports.

[0025] The hydraulic summation point 30 is hydraulically connected to a hydraulic consumer connection 32 or forms such a connection. Hydraulic consumers 16 (e.g., hydraulic cylinders) can be or become hydraulically connected to the consumer connection 32 (or output connection) via a valve module 14, e.g., a directional control valve block or similar. The valve module 14 can comprise one or more valves with which the flow of pressure medium from the consumer connection 32 or from the hydraulic drive to the individual hydraulic consumers 16 can be controlled. This control is carried out, for example, by means of control signals from an electronic control system, referred to as electronic consumer control system 24, based on operating inputs from an operator of the machine in which the hydraulic system is installed, wherein the operating inputs are detected by a suitable operating device (e.g., joystick).

[0026] The hydraulic drive can have an electronic control system, referred to as an electronic drive control system 22, which controls and / or regulates elements (e.g., inverter and / or electric machine and / or valve arrangement, see below) of the hydraulic drive based on control specifications (e.g., pressure specification and / or volume flow specification) of the machine control system and recorded sensor measurements (e.g., by a pressure sensor). In particular, the drive control system 24 can be configured to control or regulate the inverter 2, for example in order to obtain a specific torque or a specific speed of the electric machine 4 (and thus of the constant speed machines 6, 8). This can also be done indirectly via an inverter control system, which, for example, regulates the electric machine 4 according to a speed specification from the drive control system.It is also conceivable that the electronic drive control 22 is implemented by an inverter control of the inverter 2 or by the machine control.

[0027] Control signals and sensor signals, or corresponding (electrical) signal lines, are shown in the figures as dashed lines with arrows. Hydraulic control lines are shown as dashed lines without arrows.

[0028] In particular, a pressure sensor referred to as pump pressure sensor 18 is provided, which measures the pump pressure, i.e. the pressure of the pressure medium at the summation point 30, and transmits corresponding pump pressure measured values ​​to the drive controller 22, which records the transmitted pump pressure measured values. The drive controller 22 can, for example, implement load pressure control of the electric machine 4. For this purpose, the drive controller 22 can detect a load pressure, which is measured, for example, by a load pressure sensor 20 and transmitted to the drive controller, and regulate the speed of the electric machine 4 (by appropriately controlling the inverter 2) so that a pump pressure determined based on the load pressure is achieved (e.g. pump pressure is equal to load pressure plus a pressure difference). The load pressure sensor 20 can be part of the electrohydraulic drive or provided independently of it.Demand flow control can also be implemented by the drive controller 22, wherein the drive controller receives a volume flow specification from the machine controller (which determines this, for example, based on operator inputs) and controls or regulates the speed of the electric machine so that, with a known displacement of the fixed-displacement machines, the delivered volume flow of pressure medium is equal to the volume flow specification. Of course, other control and / or regulation methods are also conceivable. Such control and / or regulation methods are known per se to those skilled in the art and, in their specific embodiment, are not relevant to the invention.

[0029] The torque generated in a hydraulic pump, particularly in a fixed displacement machine, due to the pressure of the pressure medium on its drive shaft is proportional to the product of displacement and output-side pressure or pressure difference across the hydraulic pump (between pressure output and suction port). In the hydraulic drive, the torque to be applied by the electric machine 4 is therefore also dependent on the pressure of the pressure medium, i.e., dependent on the pump pressure. The valve arrangement explained below, particularly the relief valve, makes it possible to reduce the torque acting on the fixed displacement machines, and thus also the torque to be applied by the electric machine 4, as required.

[0030] The hydraulic drive comprises a valve arrangement which includes a valve called relief valve 10 which is Fig. 1 is designed as a switching valve or 2 / 2-way valve.

[0031] The relief valve 10 has a closed position a and a relief position b. The relief valve 10 is hydraulically connected on the one hand to the second pressure outlet 82 and on the other hand hydraulically connected to a first tank connection 46 and can be controlled to selectively, i.e. according to a control, enable (or permit) or prevent (or not permit) a flow of pressure medium between the second pressure outlet 82 and the first tank connection 46. In the closed position a, no flow of pressure medium is possible from the second pressure outlet 82 through the relief valve 5 to the first tank connection 46. In the relief position b, a flow of pressure medium is possible from the second pressure outlet 82 through the relief valve to the first tank connection 46.

[0032] The wording that a valve is controllable or adjustable to enable or prevent a flow of pressure medium between certain hydraulic components (or similar), or that the valve has different switching positions in which a flow of pressure medium between certain hydraulic components is possible or not possible (or is prevented), is to be understood in each case to mean that passages for pressure medium in the valve, which are formed between connections on the valve to the components, are opened or closed according to the switching positions. This opening / closing can occur discontinuously, i.e. a passage is either completely open or completely closed, or it can occur steadily or continuously, i.e. the cross-sectional area of ​​the passage can be continuously changed between completely open and completely closed (e.g. in the case of an electro-proportional valve).

[0033] The relief valve 10 is implemented, for example, as a switching valve or 2 / 2-way valve that is electromagnetically adjustable, with the closed position a being the normal position and which can be actuated by a control signal (electric current) to be adjusted to the relief position b. Furthermore, a design as an electro-proportional 2 / 2-way valve is possible, so that the relief valve can be continuously adjusted between the closed position a and the relief position b.

[0034] The valve arrangement may further include a valve referred to as a backflow limiting valve 12, which is provided in the hydraulic connection between the second pressure outlet 82 and the hydraulic summing point 30. The backflow limiting valve 12 is configured, optionally and selectively according to a control, to prevent a flow of pressure medium from the summing point 30 to the second pressure outlet 82 and to enable or permit a flow of pressure medium from the second pressure outlet 82 to the summing point 30. The backflow limiting valve 12 is, in particular, a check valve, as shown. A switching valve or directional control valve, which is controlled together with the relief valve 10, may also be used.

[0035] If the pump pressure becomes so great during operation of the machine in which the electro-hydraulic drive is used that the torque generated by it on the constant machines (ie the sum of the two torques of the constant machines 6, 8) is greater than the currently achievable drive torque of the electric machine 4 (e.g. in the case of derating due to excessive heating of the inverter, excessive heating of the electric machine or due to a limitation of the electrical power of the electric machine 4 specified by the machine control 24, if the battery is limited in its power output and other electrical consumers may have to be prioritized), a bypass from the second constant machine 8 to the tank can be realized by opening the relief valve 10.As a result, the pressure medium delivered by the second constant machine 8 can be delivered to the tank with almost no pressure and therefore does not generate any torque on the second constant machine 8. This means that the resulting load torque, which the electric machine 8 can still generate even in the derating state, decreases, and the speed does not drop to zero and can be maintained at its original value depending on the system and control status. Due to the now lower volume flow in the valve module 14, the consumers 16 do slow down (in so-called LUDV systems, LUDV: load pressure independent flow distribution) or the consumer with the highest load pressure does slow down (in LS systems, LS: load sensing), but this prevents the consumers from coming to a standstill and gives the inverter and the electric machine time to cool down until the full maximum torque of the drive can be realized again. The check valve orValve 12 prevents the volume flow delivered by the first fixed-displacement machine 6 from flowing into the tank when the relief valve 10 is open (although in this case, unintentionally). The drive control 22 also specifies the control of the relief valve 10. The drive control 22 can be a component of the inverter 2 or its inverter control.

[0036] Furthermore, this section describes an alternative application in which the present invention can be applied. If the volumetric flow (at any pressure) required by the valve module 7 becomes very small during operation of the machine in which the electro-hydraulic drive is used, an excess of volumetric flow is generated, which is provided by the fixed displacement machines. The reason for this is that there is a minimum speed of the electric machine 4, which is caused either directly by the minimum speed of the electric machines 4 or by the first fixed displacement machine 6 or by the second fixed displacement machine 8. The minimum speed can be 200 rpm, for example. Together with the constant displacement volume of the fixed displacement machines, this defines the minimum volumetric flow that must be delivered (minimum volumetric flow).The stated minimum volume flow causes significant power losses because more volume flow is provided than is necessary. By opening the relief valve 10, a bypass can be created from the second fixed displacement machine 8 to the tank. This allows the pressure medium delivered by the second fixed displacement machine 8 to be delivered to the tank with almost no pressure, and thus no volume flow for the valve module 14 is generated by the second fixed displacement machine 8. This reduces the volume flow that is fed to the valve module, so that the resulting load torque that the electric machine has to generate in order to provide the requested volume flow is reduced, and no unnecessary losses occur within the valve block 7 due to throttling orBypass elements, such as installed inlet pressure compensators, unloading valves or cut-off valves, must be generated if the volume flow required by the consumers is smaller than the minimum volume flow specified by the minimum speed of both pumps.

[0037] The drive controller 22 can be configured to receive measured values ​​for the pump pressure from the pump pressure sensor 18 and to compare them with a relief pressure. If the pump pressure is above the relief pressure, the drive controller can (by appropriately controlling it using a control signal) move the relief valve 10 to the relief position b. The drive controller 22 can, for example, be configured to determine the relief pressure based on a maximum available torque of the electric machine 4. The maximum available torque of the electric machine 4 or a corresponding value can be determined by the drive controller 22 itself and / or received from other controllers, in particular the machine controller 24 and / or the inverter controller of the inverter 2.As mentioned above, the maximum available torque of the electric machine 4 may depend, for example, on the temperature of the electric machine and / or the inverter (so-called derating). The maximum available torque of the electric machine 4 may also depend on a limitation of the available electrical current.

[0038] In the figure, the relief valve is designed as a 2 / 2-way valve, the normal position of which is the closed position, i.e. it is preloaded in the closed position, e.g. by means of a spring. The relief valve shown can be moved into the relief position by a control signal from the electronic control system. The adjustment is carried out, for example, electromagnetically, i.e. the control signal is an electric current. Alternatively, the reverse design is also conceivable (not shown), i.e. the relief valve is preloaded in the relief position and can be moved into the closed position by a control signal or an electric current. In order to obtain a summed volume flow of pressure medium at the summation point, the control signal or the electric current must be present in this design. If the control signal orIf the electrical power is not present, the relief valve automatically switches to the relief position. This design can be useful if the relief position is desired in the event of a malfunction of the electronic drive control.

[0039] Fig. Figure 2 shows a hydraulic system including an electro-hydraulic drive 102 according to another embodiment of the invention. The electro-hydraulic drive 102 of the Fig. 2 essentially corresponds to the electro-hydraulic drive 101 of the Fig. 1. The following points out differences to the electro-hydraulic drive 101 of the Fig. 1 and for similarities refer to the description of the Fig. 1.

[0040] In contrast to the electro-hydraulic drive 101 of the Fig. 1 shows the valve arrangement of the electro-hydraulic drive 102 of the Fig. 2 additionally has a pressure relief valve 34. The pressure relief valve 34 is hydraulically connected via working connections to the second pressure outlet 82 and a tank connection (which can be provided separately or can coincide with the first tank connection or second tank connection, see below) and is hydraulically connected via two control connections to the summation point 30 and the tank connection (via hydraulic control lines). The pressure relief valve 34 is adjusted in opposite directions by hydraulic pressures acting at the control connections. The normal position, preloaded by a spring, of the pressure relief valve 34 is a closed position in which no flow of pressure medium is possible from the second pressure outlet 82 to the tank connection.If the pressure difference between the pump pressure at the summation point 30 and the pressure at the tank connection exceeds a pressure limit given by the spring, the pressure relief valve 34 is moved to an open position in which a flow of pressure medium from the second pressure outlet 82 to the tank connection is possible.

[0041] At high system pressures, i.e., high pump pressures, the second fixed-displacement machine 8 is connected to the tank via the pressure relief valve 34 and delivers its volume flow into the tank with virtually no pressure. This allows the second fixed-displacement machine 8 to be designed more cost-effectively (than the first fixed-displacement machine 6), e.g., with a lower permissible maximum operating pressure. In general, however, pressure limitation can also be based purely on electronic evaluation, in that the signal determined by the pump pressure sensor 18 is evaluated accordingly and can be used to control the relief valve 10.

[0042] A pressure relief valve as in the design of the electro-hydraulic drive of the Fig. 2 can also be used in the design of the Fig. 3, Fig. 4, Fig. 5, Fig. 6 may be provided (not shown in each case).

[0043] Fig. Figure 3 shows a hydraulic system including an electro-hydraulic drive 103 according to another embodiment of the invention. The electro-hydraulic drive 103 of the Fig. 3 essentially corresponds to the electro-hydraulic drive 101 of the Fig. 1. The following points out differences to the electro-hydraulic drive 101 of the Fig. 1 and for similarities refer to the description of the Fig. 1.

[0044] In contrast to the electro-hydraulic drive 101 of the Fig. 1 shows the valve arrangement of the electro-hydraulic drive 103 of the Fig. 3 additionally has a check valve 36 and a switching valve or 2 / 2-way valve referred to as a circulation valve 38.

[0045] The check valve 36 is arranged in the hydraulic connection between the suction port 84 of the second fixed machine 8 and a second tank port 44, so that a flow of pressure medium from the suction port 84 of the second fixed machine 8 and to the second tank port 44 is not possible and a flow of pressure medium from the second tank port 44 to the suction port 84 is possible. The terms "first tank port" and, further below in the Fig. 4 and Fig. 5, "second tank connection" refers to tank connections associated with the second fixed displacement machine 8 and / or the valve assembly. A tank connection is also provided for the first fixed displacement machine 6.

[0046] Of course, the various tank connections can be brought together at a suitable location and connected to a common tank.

[0047] The circulation valve 38 is hydraulically connected on the one hand to the summation point 30 and on the other hand to the suction port 84 of the second constant displacement machine 8. The circulation valve 38 is preloaded into a closed position in which a flow of pressure medium through the circulation valve 38, i.e. from the summation point 30 to the suction port 84 of the second constant displacement machine 8, is not possible. The circulation valve 38 also has an open position in which a flow of pressure medium through the circulation valve 38, i.e. from the summation point 30 to the suction port 84 of the second constant displacement machine 8, is possible. The circulation valve 38 can be controlled to be adjusted between the two positions. The adjustment is carried out, for example, electromagnetically. The control can be carried out by the drive control 22, as shown.

[0048] The drive controller 22 can be configured to adjust the circulation valve 38 using control signals. In particular, the drive controller 22 can be configured to switch the circulation valve 38 to the open position when the pump pressure is above an overload pressure, which is preferably higher than the relief pressure.

[0049] The electro-hydraulic drive 103 of the figure and also the electro-hydraulic drives of the other Fig. 4, Fig. 5 and Fig. 6 implement a circulation functionality in which (e.g. in the case of very high pump pressure at the summation point 30 or very low torque available from the electric machine) a further relief can be achieved by directing pressure medium from the summation point to the suction side 84 of the second constant machine 8 and through the second constant machine 8 and through the relief valve 10 to the tank 46.

[0050] If, after the relief valve 10 has been moved to the relief position b, a further reduction in torque is necessary, e.g. the torque already reduced simply by controlling the relief valve 10 is not yet low enough to improve the thermal utilization, the bypass valve 38 can be opened. This now connects the pump line to the suction side of the second fixed displacement machine 8, which now operates as a motor and can therefore use the generated torque to relieve the first fixed displacement machine 6 and further reduce the drive torque to be generated by the electric machine. However, the second fixed displacement machine 8 takes a portion of the volume flow delivered by the first fixed displacement machine 6 in accordance with its selected displacement. In order to compensate for this, the electric machine 4 can be brought to a higher speed.In general, this allows for more energy-efficient operation, especially when the operator requires smaller volume flow rates, so the efficiency map of the second fixed-displacement machine 8 is optimized for this purpose, especially in its motor mode. The displacement of the first fixed-displacement machine 6 should be optimized for this functionality (the electro-hydraulic drives of the . Fig. 3, Fig. 4, Fig. 5, Fig. 6) must be dimensioned higher than the displacement of the second fixed-displacement machine 8. The check valve 36 prevents the pressure medium from flowing to the tank when the circulation valve 38 is open.

[0051] Fig. Figure 4 shows a hydraulic system including an electro-hydraulic drive 104 according to another embodiment of the invention. The electro-hydraulic drive 104 of the Fig. 4 essentially corresponds to the electro-hydraulic drive 103 of the Fig. 3. The following points out differences to the electro-hydraulic drive 103 of the Fig. 3 and for similarities refer to the description of the Fig. 3 and furthermore the Fig. 1 and Fig. 2.

[0052] In contrast to the electro-hydraulic drive 103 of the Fig. 3 the circulation functionality in the electro-hydraulic drive 104 of the Fig. 4 is not realized by a separate circulation valve, but is implemented as an additional switching position of the relief valve, referred to as circulation position c. In addition to the second tank connection 44, the first tank connection 46 is provided, which could also be connected to the second tank connection on the tank side of the check valve 36.

[0053] The relief valve 10 is designed in particular as an electromagnetically adjustable 4 / 3 valve and is additionally hydraulically connected to the summation point 30. In addition to the closed position a and the relief position b, it has a bypass position c. In the bypass position c, a flow of pressure medium from the summation point 30 to the suction port 84 of the second fixed displacement machine 8 and a flow of pressure medium from the second working port 82 to a first tank port 46 are possible. Furthermore, in the closed position a, a flow of pressure medium from the first tank port 46 to the suction port 84 of the second fixed displacement machine 8 via the relief valve 10 may be possible and / or in the relief position b, a flow of pressure medium from the suction port 84 of the second fixed displacement machine 8 via the relief valve 10 to the first tank port 46 may be possible.In the closed position a, both a flow of pressure medium from the pressure outlet 82 of the second constant machine 8 and a flow of pressure medium from the summation point 30 are prevented by the relief valve 10. In the relief position b, a flow of pressure medium from the summation point 30 is prevented by the relief valve 10 and, as with all embodiments, a flow of pressure medium from the second pressure outlet 82 of the second constant machine 8 to the first tank connection 46 is possible.

[0054] In the illustrated embodiment, the relief valve 10 is preloaded into the closed position a, i.e., the closed position a is the normal position. In this embodiment, the relief valve 10 is designed such that the closed position a is centrally located, i.e., it can be adjusted from the closed position a in one direction into the relief position b and in another direction into the circulation position c. The adjustment device comprises, for example, two electromagnetic actuators that can be controlled by control signals or electrical currents.

[0055] In the closed position a, normal operation of the two pumps can take place, in which the two pump volume flows can be summed via the backflow limiting valve 12. Via the relief position b, the second fixed displacement machine 8 can be relieved towards the tank, and in the overload position c, the pump pressure is connected to the suction side of the second fixed displacement machine 8, whereby a motor operation of the second fixed displacement machine 8 can be realized. This functionality therefore corresponds to the functionality of the electro-hydraulic drive 103 of the Fig. 3.

[0056] Fig. Figure 5 shows a hydraulic system including an electro-hydraulic drive 105 according to another embodiment of the invention. The electro-hydraulic drive 105 of the Fig. 5 essentially corresponds to the electro-hydraulic drive 104 of the Fig. 4. The following points out differences to the electro-hydraulic drive 104 of the Fig. 4 and for similarities refer to the description of the Fig. 4 and furthermore the Fig. 1, Fig. 2 and Fig. 3.

[0057] In contrast to the electro-hydraulic drive 104 of the Fig. 4, the relief valve 10 is designed in such a way that it can be adjusted or switched from the closed position a via the relief position b to the overload position c. The relief valve 10 of the Fig. 5 has the same switching positions as the relief valve of the Fig. 4, which are arranged in a different order. The relief valve 10 of the Fig. 5 is preloaded in the closed position a and can be electromagnetically adjusted via the relief position b to the overload position c.

[0058] The relief valve 10 can, in particular, be a proportional valve, i.e., be designed such that the adjustment is continuous, or at least that the adjustment between the relief position b and the overload position c is continuous. "Continuous" means that when the valve is adjusted, the passage cross-sections are continuously increased or decreased, so that continuous transitions occur between fully closed and fully open.

[0059] Fig. Figure 6 shows a hydraulic system including an electro-hydraulic drive 106 according to another embodiment of the invention. The electro-hydraulic drive 106 of the Fig. 6 implemented like the electro-hydraulic drives of the Fig. 3 to 5 have a circulation functionality. The following discusses differences to the electro-hydraulic drives in Figures 1 to 5, and for similarities, reference is made to the description of the previous figures.

[0060] In the valve arrangement of the electro-hydraulic drive 106 of the Fig. 6, the relief valve 10 is arranged or configured such that the pressure medium supply from the first tank connection 46 to the suction connection 84 can take place via the relief valve 10 (with a suitable switching position, see below). Unlike in the embodiments of Fig. 3-5, no check valve is provided between the tank connection and the suction connection 84 of the second fixed-displacement machine 8. The backflow limiting valve 12 is still provided.

[0061] The relief valve 10 is designed as a 4 / 3 valve. It has four connections, one connection being hydraulically connected to the first tank connection 46, one connection being hydraulically connected to the suction connection 84 of the second constant machine 8, one connection being hydraulically connected to the pressure connection 82 of the second constant machine 8, and one connection being hydraulically connected to the summation point 30. The relief valve 10 has a closed position a, a relief position b, and a circulation position c. The functionality of these switching positions corresponds, apart from the pressure medium supply from the first tank connection through the relief valve, to that of the corresponding switching positions of the embodiments of the Fig. 4 and Fig. 5.

[0062] In the closed position a, a flow of pressure medium from the first tank connection 46 to the suction connection 84 is possible through the relief valve 10. In the closed position a, both a flow of pressure medium from the second pressure outlet 82 of the second constant machine 8 and a flow of pressure medium from the summation point 30 are prevented by the relief valve 10.

[0063] In the relief position b, a flow of pressure medium from the second pressure outlet 82 of the second constant-displacement machine 8 to the first tank connection 46 and a flow of pressure medium from the first tank connection 46 to the suction connection 84 of the second constant-displacement machine 8 are possible. Also, in the relief position b, in particular, a flow of pressure medium between the second pressure outlet 82 of the second constant-displacement machine 8 and the suction connection 84 of the second constant-displacement machine 8 is possible through the relief valve 10. In the relief position b, a flow of pressure medium from the summation point 30 is prevented by the relief valve 10.

[0064] In the circulation position c, a flow of pressure medium from the summation point 30 to the suction port 84 of the second constant-displacement machine 8 and a flow of pressure medium from the second pressure outlet 82 of the second constant-displacement machine 8 to the first tank port 46 are possible. A flow of pressure medium from the first tank port 46 to the suction port 84 of the second constant-displacement machine 8 is not possible.

[0065] The relief valve 10 is preloaded, for example, into the closed position a, thus forming the normal position. Starting from the closed position a, the relief valve 10 can be adjusted, for example, via the relief position b to the circulation position c, particularly electromagnetically.

[0066] For all designs ( Fig.1 to 6), some or all components, ie, in particular the first fixed-displacement machine 6, the second fixed-displacement machine 8, and the components or valves of the valve arrangement, can be integrated into a common housing. The hydraulic system does not have to be designed as an LS system (as shown). The invention can also be used in other hydraulic systems (e.g., LUDV, EHpQ, OC systems, etc.).

Claims

[1] Electro-hydraulic drive for at least one hydraulic consumer (16), comprising an electrical machine (4); a first hydraulic constant-displacement machine (6) and a second hydraulic constant-displacement machine (8), which are mechanically coupled to one another and which are jointly driven by the electric machine (4), wherein the first constant-displacement machine (6) has a first pressure output (62) and the second constant-displacement machine (8) has a second pressure output (82), wherein the first and the second pressure output (62, 82) are hydraulically connected to a hydraulic summation point (30) which is connected to a hydraulic consumer connection (32) which is or can be hydraulically connected to the at least one hydraulic consumer (16); and a valve arrangement comprising a relief valve (10) which is hydraulically connected between the second pressure outlet (82) and a first tank connection (46) and which has a closed position (a) in which no flow of pressure medium from the second pressure outlet (82) through the relief valve is possible, and a relief position (b) in which a flow of pressure medium from the second pressure outlet (82) through the relief valve to the first tank connection (46) is possible; wherein the relief valve (10) is controllably adjustable selectively into the closed position (a) or the relief position (b); an electronic drive control (22) configured to control the relief valve (10); wherein the drive control (22) is configured to determine a pump pressure of the pressure medium at the summation point (30) and: to control the relief valve (10) so that it is moved to the relief position (b) when the pump pressure is above a relief pressure, and / or to control the relief valve (10) so that it is moved to the closed position (a) when the pump pressure is below the relief pressure wherein the drive controller (22) is configured to receive and / or determine a value indicating a maximum available torque of the electric machine (4) and to determine the relief pressure based on the maximum available torque. [2] Electro-hydraulic drive according to claim 1, wherein the valve arrangement further comprises a backflow limiting valve (12) which is configured to prevent a flow of pressure medium from the summation point (30) to the second pressure outlet (82), or which is configured to prevent a flow of pressure medium from the summation point (30) to the second pressure outlet (32) in a controllable manner; wherein the backflow limiting valve (12) is in particular a check valve. [3] Electro-hydraulic drive according to claim 1 or 2, comprising a pump pressure sensor (18) arranged to measure the pump pressure of the pressure medium at the summation point (30); wherein the drive controller (22) is connected to the pump pressure sensor (18) to receive measured values ​​for the pump pressure. [4] Electro-hydraulic drive according to one of the preceding claims, wherein the valve arrangement comprises a pressure relief valve (34) which is hydraulically connected between the second pressure outlet (82) of the second constant machine (8) and a tank connection and which is designed to enable a flow of pressure medium from the second pressure outlet (82) of the second constant machine (8) when the pump pressure or a pressure difference between the pump pressure and a pressure of the pressure medium at the tank connection exceeds a pressure limit; wherein the pressure limit of the pressure relief valve (34) is preferably adjustable. [5] Electro-hydraulic drive according to one of the preceding claims, wherein the valve arrangement comprises a check valve (36) arranged between a second tank connection (44) and a suction connection (84) of the second constant machine (8); and wherein the valve arrangement is configured to controllably enable a flow of pressure medium from the summation point (30) to the suction connection of the second constant machine. [6] Electro-hydraulic drive according to claim 5, wherein the valve arrangement comprises a circulation valve (38) which is hydraulically connected between the summation point (30) and the suction port (84) of the second constant machine (8) and is controllable to be brought into an open position to allow pressure medium from the summation point (30) to the suction port (84) of the second constant machine (8). [7] Electro-hydraulic drive according to claim 6, wherein the drive control (22) is further configured to switch the circulation valve (38) to the open position when the pump pressure exceeds an overload pressure, which is in particular greater than the relief pressure. [8] Electro-hydraulic drive according to claim 5, wherein the relief valve (10) is hydraulically connected to the summation point (30), has a circulation position (c) and can be controlled to be adjusted to the circulation position (c); wherein in the circulation position (c) a flow of pressure medium from the summation point (30) to the suction port (84) of the second constant machine (8) is possible and a flow of pressure medium from the second working port (82) to the first tank port (46) is possible; and wherein in the closed position (a) a flow of pressure medium from the first tank port (46) to the suction port (84) of the second constant machine (8) via the relief valve (10) is preferably possible and / or wherein in the relief position (b) a flow of pressure medium from the suction port (84) of the second constant machine (8) via the relief valve (10) to the first tank port (46) is preferably possible. [9] Electro-hydraulic drive according to one of claims 1 to 4, wherein the relief valve (10) is further adjustable into a circulation position (c) and is hydraulically connected to the summation point (30) and a suction connection (84) of the second constant machine (8); wherein in the closed position (a) a flow of pressure medium from the first tank connection (46) to the suction connection (84) of the second constant machine (8) through the relief valve (10) is possible and no flow of pressure medium from the summation point (30) through the relief valve (10) is possible; wherein in the relief position (b) a flow of pressure medium from the first tank connection (46) to the suction connection (84) of the second constant machine (8) is possible and no flow of pressure medium from the summation point (30) through the relief valve (10) is possible; and wherein in the circulation position (c) a flow of pressure medium from the summation point (309) to the suction connection (84) of the second constant machine (8) and a flow of pressure medium from the second pressure outlet (82) of the second constant machine (8) to the first tank connection (46) are possible. [10] Electro-hydraulic drive according to claim 8 or 9, wherein the relief valve (10) is adjustable from the closed position (a) via the relief position (b) to the circulation position (c); wherein the adjustment is carried out in particular continuously. [11] Electro-hydraulic drive according to one of the preceding claims 6 to 10, wherein the drive control (22) is further configured to switch the relief valve (10) into the circulation position (c) when the pump pressure exceeds an overload pressure, which is in particular greater than the relief pressure.

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