Hydraulic system with cooling circulation path, and machine tool

Abstract

To provide a hydraulic system that satisfies requirements in use, and is simple in design and high in cost effectiveness.SOLUTION: In a hydraulic system 10 for supplying at least one supply pump 12, a consumer connection part 14, a return connection part 16, a cooling circulation path 18, and a tank T to at least one hydraulic consumer 110, the cooling circulation path comprises a cooling pump 20, a cooling line 22 for circulation connected to the tank, and a heat exchanger 24. A branch line 26 connected to the consumer connection part 14 branches off from the cooling line for circulation downstream from the cooling pump and upstream from the heat exchanger, and the cooling circulation path comprises a changeover valve 28. The changeover valve can change over between a closed position 28.1 and an open position 28.2, The cooling line for circulation is closed at the closed position and the cooling pump is connected to only the branch line. At the open position, the cooling pump is connected to the heat exchanger.SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present invention relates to a hydraulic system with at least one cooling circuit and to a machine tool equipped with such a hydraulic system.

[0002] Such hydraulic systems with cooling circuits are known in the prior art. They typically comprise at least one supply pump, a tank, a consumer connection, and a return connection. The hydraulic consumer is connected to the consumer connection and the return connection and can therefore be pressurized via the supply pump.

[0003] Hydraulic systems, especially when used in machine tools, must meet a wide range of requirements. On the one hand, a constant volumetric flow rate at a nearly constant system pressure is required on a regular basis, for example, to maintain the clamping pressure of hydraulically actuated clamping devices used to secure a workpiece. For example, a volumetric flow rate of approximately 2 to 6 liters per minute at a constant system pressure of 100 bar must be guaranteed. Another requirement is that the temperature of the hydraulic fluid must be maintained within a specified range, e.g., between 20 and 40°C. For this purpose, hydraulic systems typically have a separate cooling circuit for offline cooling, complete with a cooling pump, a circulation cooling line, and a heat exchanger.

[0004] Furthermore, during operation of the machine tool, different peak volumetric flows may be required for additional functions, for example during hydraulically controlled tool changes. These dynamic additional volumetric flows must not cause a critical pressure drop in the pressure supply of other components of the machine tool, in particular in the pressure supply of the clamping device.

[0005] It is known from the prior art to provide these dynamic additional volume flows via hydraulic accumulators and corresponding accumulator charging circuits. The drawback of such hydraulic accumulators is that they require regular maintenance, thus increasing the operating costs of the machine tool, especially if the hydraulic accumulator is completely emptied during operation. Furthermore, the accumulator charging circuit also increases the complexity and thus the cost of the hydraulic system. An alternative solution is to drive the supply pump via an asynchronous motor with a frequency converter. However, this also increases the cost of the hydraulic system, and depending on the application, it is still necessary to use a hydraulic accumulator, even if it is a somewhat small one. Summary of the Invention

[0006] It is therefore an object of the present invention to provide a hydraulic system for supplying at least one hydraulic consumer, which meets the requirements of use, is simple in design and is cost-effective.

[0007] The solution to this problem is achieved by a hydraulic system according to claim 1 and a machine tool according to claim 13. Preferred embodiments are set out in the dependent claims.

[0008] A hydraulic system according to the present invention for supplying at least one hydraulic consumer comprises at least one supply pump, a consumer connection, a return connection, at least one cooling circuit, and a tank. The at least one supply pump is connected to the tank and the consumer connection, and the consumer connection or the hydraulic consumer connected to the consumer connection can be pressurized via the at least one supply pump. The return connection is connected to the tank. The at least one cooling circuit comprises a cooling pump, a circulation cooling line connected to the tank, and a heat exchanger. The hydraulic system according to the present invention is characterized in that a branch line connected to the consumer connection branches off from the circulation cooling line downstream of the cooling pump and upstream of the heat exchanger. Also according to the present invention, the cooling circuit has a first switching valve switchable between a closed position and an open position. When the first switching valve is in the closed position, the circulation cooling line is closed, so that when the first switching valve is in the closed position, the cooling pump is only connected to the branch line. In the open position of the first switching valve, the cooling pump is also connected to the heat exchanger.

[0009] In other words, the cooling circuit can be deactivated by switching the first switching valve so that the cooling pump is no longer connected to the heat exchanger but only to the branch line branching off from the circulation cooling line and therefore to the consumer connection. Since the cooling circuit is deactivated via the first switching valve only for a short time, and only to cover dynamic additional volumetric flows, the temperature rise of the hydraulic fluid caused by deactivation of the cooling circuit is negligible. This means that the cooling pump can be temporarily used to prevent a drop in system pressure due to required peak volumetric flows without excessively increasing the temperature of the hydraulic fluid. This provides a particularly cost-effective hydraulic system.

[0010] Preferably, a check valve opening in the direction of flow to the consumer connection is arranged in the branch line, thereby preventing hydraulic fluid pumped by the supply pump from entering the circulating cooling line. Alternatively or additionally, it is also conceivable that the first switching valve is configured as a 3 / 2-way valve and that no check valve is provided in the branch line, but that the cooling pump is connected either to the heat exchanger or to the branch line depending on the switching position of the first switching valve.

[0011] Preferably, the first switching valve is preloaded to the closed position, for example, via a spring. The hydraulic system preferably includes a first control line connected to the consumer connection, whereby the pressure in the first control line is applied to the open side of the first switching valve. Thus, the system pressure present at the consumer connection is transmitted via the first control line to the first switching valve, and when the pressure exceeds the preload, the first switching valve is switched to the open position. In the event of a pressure drop in the system pressure, the first switching valve is preloaded and switches to the closed position, so that the cooling pump is connected only to the consumer connection via a branch line, thus ensuring a constant system pressure.

[0012] Alternatively, the hydraulic system may include a control unit, whereby the first switching valve is an electromagnetically controlled switching valve. The control unit controls the first switching valve using at least one determined parameter of the hydraulic system. The parameter may be, for example, a pressure or a volumetric flow rate determined via a sensor. For this purpose, the hydraulic system preferably includes at least one sensor, particularly a pressure sensor and / or a volumetric flow rate sensor, connected to the control unit. The first switching valve may be preloaded in the closed position, for example, via a spring. Alternatively, the first switching valve may be a switching valve that can be electromagnetically actuated on both sides, and this switching valve is appropriately actuated via the control system using at least one determined parameter of the hydraulic system.

[0013] Preferably, at least one of the supply pumps is a variable displacement pump. From an energy standpoint, a variable displacement pump is preferred.

[0014] Preferably, at least one supply pump includes a displacement device, a displacement line connected to the displacement device branching off from the circulating cooling line between the first switching valve and the heat exchanger, and a bypass line connecting the displacement device to the tank. A hydraulic resistor, such as an orifice or nozzle, is preferably disposed in the bypass line. The displacement device is preferably configured as a displacement cylinder.

[0015] In this case, a second switching valve is preferably disposed in the displacement line. The second switching valve is switchable between an open position and a closed position, so that the displacement line opens when the second switching valve is in the open position and closes when the second switching valve is in the closed position. The second switching valve can be designed as a proportional switching valve or a binary action switching valve. The second switching valve can be used for highly dynamic pressure control.

[0016] Preferably, the second switching valve is preloaded to the closed position, for example via a spring. The hydraulic system preferably has a second control line connected to the consumer connection, whereby the pressure in the second control line is applied to the open side of the second switching valve. This allows for particularly simple yet efficient pressure control of the supply pump. In the event of a pressure drop in the system pressure, the second switching valve is switched to the closed position, the pressure in the displacement device is reduced via the bypass line, and the supply pump is controlled to maximum power. At the same time, by switching the first switching valve, only the cooling pump is connected to the branch line, restoring a stable system pressure.

[0017] Alternatively, the second switching valve may be an electromagnetically controlled switching valve that is controlled via a control system of the hydraulic system using at least one determined parameter of the hydraulic system. As already mentioned above, the at least one parameter of the hydraulic system may be, for example, pressure or volume flow rate and may be transmitted to the control system via at least one sensor in the hydraulic system. The second switching valve may be, for example, a spring-loaded switching valve in the closed position or may be an electromagnetically controlled switching valve on both sides.

[0018] In an alternative embodiment, at least one supply pump can be configured as a direct electrical variable displacement pump. This has the advantage that the second switching valve and displacement device can be omitted. In this case, the direct electrical variable displacement pump is preferably controlled via the control system of the hydraulic system using the determined parameters of the hydraulic system. As already mentioned above, in this context, it is useful for the hydraulic system to have at least one corresponding sensor, such as a pressure sensor, a volumetric flow sensor, or a combined pressure and volumetric flow sensor.

[0019] Preferably, the cooling pump is a gear pump, which is inexpensive, easy to maintain, and robust. It is also preferred that at least one supply pump is a radial piston pump, which is particularly useful when the radial piston pump is made up of multiple pump elements, each of which can be switched on and off to regulate the pump.

[0020] Furthermore, the hydraulic system preferably comprises a plurality of supply pumps, whereby each supply pump is connected to the tank and to a respective consumer connection. Depending on the configuration of each supply pump, a corresponding displacement line, a bypass line or a displacement device with a switching valve is therefore provided. Preferably, a supply pump is provided for each hydraulic consumer to be controlled.

[0021] Furthermore, the hydraulic system may also comprise a plurality of cooling circuits, each preferably assigned to a supply pump, such that by deactivating the respective cooling circuit, the respective cooling pump can provide an additional dynamic volume flow rate for each supply pump circuit.

[0022] The solution to this problem is further achieved by a machine tool comprising at least one hydraulic consumer and a hydraulic system as described above. The hydraulic consumer is connected to the consumer and return connections of the hydraulic system. The machine tool can be, for example, a lathe, milling machine, machining center, hollow molding machine, or drilling machine. [Brief explanation of the drawings]

[0023] The invention will now be described in more detail with reference to embodiments shown in the drawings. [Figure 1] FIG. 1 is a hydraulic circuit diagram of a machine tool equipped with a hydraulic system according to a first embodiment of the present invention. [Figure 2] FIG. 2 is a hydraulic circuit diagram of a machine tool equipped with a hydraulic system according to a second embodiment of the present invention. [Figure 3] FIG. 3 is a hydraulic circuit diagram of a machine tool equipped with a hydraulic system according to a third embodiment.

[0024] Detailed Description

[0025] Figure 1 shows a hydraulic circuit diagram of a machine tool 100 with a hydraulic consumer 110, which is only shown diagrammatically in Figure 1. The machine tool 100 can be, for example, a lathe. The hydraulic consumer 110 can be, for example, a hydraulically actuated clamping device for a workpiece. The machine tool 100 also comprises a hydraulic system 10.

[0026] As shown, the hydraulic system 10 comprises a supply pump 12, a tank T, a consumer connection 14, a return connection 16, and a cooling circuit 18. A hydraulic consumer 110 is connected to the consumer connection 14 and the return connection 16. The supply pump 12 is connected to the tank T and the consumer connection 14 and is able to supply pressurized hydraulic fluid to the hydraulic consumer 110 via the supply pump 12.

[0027] The cooling circuit 18 includes a cooling pump 20, a circulating cooling line 22, and a heat exchanger 24 to maintain the hydraulic fluid at a predetermined temperature range, for example, 20°C to 40°C. As shown in FIG. 1, the cooling pump 20 and the heat exchanger 24 are arranged in the circulating cooling line 22. The circulating cooling line 22 is connected to a tank T, and the cooling pump 20 pumps the heated hydraulic fluid through the heat exchanger 24, where it is cooled and then returned to the tank T. In this embodiment, the cooling pump 20 is configured as a gear pump.

[0028] A branch line 26 is provided between the cooling pump 20 and the heat exchanger 24, branching off from the circulating cooling line 22. In other words, the branch line 26 branches off from the circulating cooling line 22 to the upstream side of the cooling pump 20 and downstream side of the heat exchanger 24. As shown in Fig. 1, the branch line 26 opens upstream of the supply pump 12 and is therefore connected to the consumer connection 14. A check valve 30, which opens in the direction of flow towards the consumer connection 14, is arranged in the branch line 26 to prevent undesired backflow via the branch line 26 to the heat exchanger 24.

[0029] The first switching valve 28 is arranged in the circulation cooling line 22 between the cooling pump 20 and the heat exchanger 24. In this exemplary embodiment, the first switching valve 28 is configured as a 2 / 2-way valve. In the closed position 28.1 of the first switching valve 28, the circulation cooling line 22 is closed and the cooling pump 20 is no longer connected to the heat exchanger 24 but is connected only to the branch line 26. In the open position 28.2 of the first switching valve 28, the circulation cooling line 22 is opened and the cooling circuit 18 can operate to supply hydraulic fluid to the heat exchanger 24 via the cooling pump 20.

[0030] In this exemplary embodiment, the first switching valve 28 is preloaded to a closed position 28.1 via a spring 50. The first switching valve 28 can be pressurized against the force of the spring 50 via a first control line 32 on the open side. The first control line 32 is connected to the consumer connection 14, whereby the system pressure present at the consumer connection 14 is reported to the first switching valve 28 via the first control line 32. As shown, a pressure gauge 54 may be provided to indicate the system pressure present at the consumer connection 14. It is conceivable that the first switching valve 28 and the check valve 30 may be configured as a combined valve, for example a 3 / 2-way valve.

[0031] In this exemplary embodiment, the feed pump 12 is configured as a variable displacement radial piston pump. Preferably, the feed pump 12 comprises a plurality of pump elements that can be switched on and off as required. To adjust the delivery rate of the feed pump 12, the feed pump 12 comprises a displacement device 38 and a bypass line 42 connecting the displacement device 38 to the tank T. In this exemplary embodiment, the displacement device 38 is configured as a displacement cylinder. A nozzle 44 is arranged in the bypass line 42, via which the displacement device 38 is released into the tank T.

[0032] A displacement line 40 branches off between the first switching valve 28 and the heat exchanger 24. The displacement line 40 is connected to the displacement device 38. A second switching valve 46, which can be switched between a closed position 46.1 and an open position 46.2, is arranged in the displacement line 40. The second switching valve 46 is preloaded to the closed position 46.1 via a spring 52. On the open side, the system pressure present at the supply connection 14 is transmitted to the second switching valve 46 via a second control line 48. In this exemplary embodiment, the second switching valve 46 is configured as a 2 / 2-way valve. However, the second switching valve 46 may also be configured as a proportional valve. The second switching valve 46 is therefore configured to dynamically control the displacement device 38 depending on the system pressure applied to the consumer connection 14.

[0033] Next, the function of the hydraulic system 10 of the present invention shown in FIG. 1 will be described.

[0034] During normal operation of the hydraulic system 10, a constant system pressure of, for example, 100 bar is present at the consumer connection 14, with a flow rate of, for example, 2 to 6 liters per minute, in order to maintain the pressure required for the hydraulic consumer 110 (e.g., clamping pressure). The system pressure is transmitted via the open side of the first control line 32 to the first switching valve 28, which is switched to its open position 28.2 against the force of a spring 50. The cooling circuit 18 is activated because the cooling pump 20 pumps hydraulic fluid to the heat exchanger 24 via the first switching valve 28, which is switched to its open position 28.2. The system pressure is applied via the open side of the second control line 48 to the second switching valve 46, against the force of a spring 52, so that the pressure present in the displacement line 40, and thus the delivery rate of the supply pump 12, is controlled via the displacement device 38.

[0035] If an additional dynamic volume flow occurs, for example due to a change in hydraulically operated tools, this may lead to a pressure drop in the system pressure. However, the system pressure must not drop to a critical range where the required clamping pressure at the hydraulic consumer 110 can no longer be maintained. For example, a pressure drop of less than 10 bar may be acceptable.

[0036] If the system pressure drops more suddenly, this larger pressure drop is transmitted via the first control line 32 to the first directional control valve 28, and the spring force of the spring 50 exceeds the pressure transmitted via the first control line 32. This causes the first directional control valve 28 to switch from the open position 28.2 to the closed position 28.1, connecting the cooling pump 20 only to the branch line 26. The check valve 30 opens, and the full volumetric flow of the cooling pump 20 is applied to the consumer connection 14.

[0037] The pressure drop in the system pressure is transmitted to the second switching valve 46 via the second control line 48. The spring force of the spring 52 exceeds the pressure transmitted via the second control line 48, and the second switching valve 46 switches from the open position 46.2 to the closed position 46.1. The displacement device 38 is released via the bypass line 42, and the supply pump 12 is thus controlled to maximum power. The maximum volumetric flow rates of both pumps, i.e., the cooling pump 20 and the supply pump 12, are therefore applied at the supply connection 14.

[0038] As soon as no additional dynamic volume flow is generated, the first switching valve 28 is returned to the open position 28.2 and the cooling circuit 18 is activated again. The flow rate of the feed pump 12 is therefore also controlled via the second switching valve 46 and the displacement device 38.

[0039] 2 shows a hydraulic circuit diagram of a second embodiment of a machine tool 100 equipped with a hydraulic system 10 according to the present invention. Only differences from the embodiment shown in FIG. 1 will be described below.

[0040] The embodiment shown in Figure 2 differs from the embodiment shown in Figure 1 in the configuration of the first switching valve 28 and the second switching valve 46 and the operation of these two valves. In this embodiment, no control line is provided to transfer the pressure at the supply connection 14 to the open side of the first switching valve 28 or the second switching valve 46. The first switching valve 28 in this exemplary embodiment is configured as a solenoid 2 / 2-way valve, whereby the first switching valve 28 is preloaded into the closed position 28.1 via a spring 50. The second switching valve 46 in this exemplary embodiment is also configured as a solenoid 2 / 2-way valve and is preloaded into the closed position 46.1 via a spring 52.

[0041] The hydraulic system 10 includes a control unit 34 for energizing the electromagnets of the first and second switching valves 28, 46 to switch the first and second switching valves 28, 46 to an open position 28.2 and an open position 46.2, respectively. The hydraulic system 10 further includes a sensor 36 for measuring at least one parameter of the hydraulic system 10 and communicating it to the control unit 34 for controlling the first and second switching valves 28, 46. The sensor 36 can be, for example, a pressure sensor, a volumetric flow sensor, or a combined pressure and volumetric flow sensor.

[0042] If the control unit 34 detects an additional dynamic volume flow via the sensor 36, the first switching valve 28 is switched to the closed position 28.1 by de-energizing its magnet. The cooling circuit 18 is deactivated and the cooling pump 20 is connected only to the branch line 26. The second switching valve 46 is then switched to the closed position 46.1 by de-energizing its magnet, the displacement device 38 is released via the bypass line 42 and the supply pump 12 is controlled to maximum power.

[0043] As soon as no additional dynamic volume flow is generated, the first switching valve 28 is switched to the open position 28.2 by energizing the magnet and the cooling circuit 18 is activated again. Thus, by energizing the second switching valve 46 and the displacement device 38, the flow rate of the supply pump 12 is also controlled.

[0044] 3 shows a hydraulic circuit diagram of a third embodiment of a machine tool 100 equipped with a hydraulic system 10 according to the present invention. Only differences from the embodiment shown in FIG. 2 will be described below.

[0045] In the embodiment shown in Fig. 3, the supply pump 12 is configured as a direct electrical variable displacement pump. In this respect, a second switching valve, a displacement line, and a displacement device are not provided in this exemplary embodiment. The supply pump is directly connected to a control unit 34, which controls the supply speed based on parameters measured by a sensor 36 so that the supply speed is controlled conventionally during normal operation and at maximum output when an additional dynamic volume flow occurs. At the same time, when an additional dynamic volume flow occurs, the control unit switches the first switching valve 28 to its closed position 28.1 so that the cooling pump 20 supplies pressure to the hydraulic consumer 110 only via the branch line 26.

[0046] As soon as no additional dynamic volume flow is generated, the first switching valve 28 is switched to the open position 28.2 by energizing the magnet and the cooling circuit 18 is activated again. The flow rate of the supply pump 12 is therefore also controlled via a corresponding direct electrical regulation.

[0047] Furthermore, in principle, it is possible to combine the above embodiments, such as by pressurizing the first switching valve 28 via the open side control lines and making the second switching valve 46 an electromagnetic switching valve operated via the control unit 34. It should therefore be pointed out that terms such as "first," "second," or "third" used herein do not specify a specific order but serve only to distinguish corresponding features. [Explanation of symbols]

[0048] 10...hydraulic system, 12...supply pump, 14...Consumer connection part, 16...return connection, 18...Cooling circuit, 20...cooling pump, 22...Circulating cooling line, 24...heat exchanger, 26...branch line, 28...first switching valve, 28.1...Closed position of the first switching valve, 28.2...first switching valve open position, 30...Check valve, 32 first control line, 34...control unit, 36...sensor, 38...Displacement device, 40...displacement line, 42...Bypass line, 44...Nozzle, 46...second switching valve, 46.1...Second switching valve closed position, 46.2...open position of second switching valve, 48...second control line, 50...first switching valve spring, 52...second switching valve spring, 54...Pressure gauge, 100...Machine tools, 110...hydraulic pressure consumer, 112...hydraulic pressure consumer, T...Tank.

Claims

1. A hydraulic system (10) for supplying at least one hydraulic consumer (110) with at least one supply pump (12), a consumer connection (14), a return connection (16), at least one cooling circuit (18) and a tank (T), The supply pump (12) is connected to the tank (T) and to the consumer connection (14), The return connection (16) is connected to the tank (T), At least one of the cooling circuits (18) comprises a cooling pump (20), a circulating cooling line (22) connected to the tank (T), and a heat exchanger (24); The cooling pump (20) and the heat exchanger (24) are arranged in the circulating cooling line (22); A hydraulic system (10) characterized in that a branch line (26) connected to the consumer connection (14) branches off from the circulating cooling line (22) downstream of the cooling pump (20) and upstream of the heat exchanger (24), The cooling circuit (18) is provided with a first switching valve (28), The first switching valve (28) is switchable between a closed position (28.1) and an open position (28.2); the circulating cooling line (22) is closed when the first switching valve (28) is in the closed position (28.1), and the cooling pump (20) is connected only to the branch line (26) when the first switching valve (28) is in the closed position (28.1); The hydraulic system (10) is configured such that the cooling pump (20) is connected to the heat exchanger (24) in the open position (28.2) of the first switching valve (28).

2. 2. A hydraulic system (10) according to claim 1, characterized in that the branch line (26) is arranged with a check valve (30) which opens in the flow direction towards the consumer connection (14).

3. 3. The hydraulic system (10) according to claim 1, wherein the first switching valve (28) is pre-pressurized in the closed position (28.1), and the hydraulic system (10) comprises a first control line (32) connected to the consumer connection (14), and the pressure in the first control line (32) is applied to the open side of the first switching valve (28).

4. The hydraulic system (10) according to any one of claims 1 to 2, characterized in that the hydraulic system (10) comprises a control unit (34), the first switching valve (28) is an electromagnetically controlled switching valve, the control unit (34) controls the first switching valve based on at least one determined parameter of the hydraulic system (10), and the first switching valve (28) is preferably pre-pressurized to the closed position.

5. Hydraulic system (10) according to any one of claims 1 to 4, characterized in that at least one supply pump (12) is a variable displacement pump.

6. 6. The hydraulic system (10) according to claim 5, characterized in that the at least one supply pump (12) comprises a displacement device (38), a regulating line (40) connected to the displacement device (38) branches off from the circulating cooling line (22) between the first switching valve (28) and the heat exchanger (24), and a bypass line (42) connects the displacement device (38) to the tank (T).

7. 7. The hydraulic system (10) according to claim 6, characterized in that a second switching valve (46) switchable between an open position (46.2) and a closed position (46.1) is arranged in the displacement line (40), the second switching valve (46) being switchable between an open position (46.2) and a closed position (46.1) of the second switching valve (46), the displacement line (40) being open and the displacement line (40) being closed in the closed position (46.1) of the second switching valve (46).

8. 8. The hydraulic system (10) according to claim 7, characterized in that the second switching valve (46) is pre-pressurized to the closed position (46.1), the hydraulic system (10) comprises a second control line (48) connected to the consumer connection (14), and the pressure in the second control line (48) is applied to the open side of the second switching valve (46).

9. 8. The hydraulic system according to claim 7, wherein the hydraulic system comprises a control unit, the second switching valve is an electromagnetically controlled switching valve, the control unit controls the second switching valve based on at least one determined parameter of the hydraulic system, and the second switching valve is preferably pre-pressurized to the closed position.

10. A hydraulic system (10) according to any one of claims 1 to 4, characterized in that at least one of the supply pumps (12) is a direct electric variable displacement pump.

11. 11. The hydraulic system (10) according to any one of claims 1 to 10, characterized in that the cooling pump (24) is a gear pump and / or at least one of the supply pumps (12) is a radial piston pump.

12. The hydraulic system (10) according to any one of claims 1 to 11, characterized in that the hydraulic system (10) comprises a plurality of supply pumps (12), each supply pump (12) being connected to the tank (T) and to the consumer connection (14).

13. A machine tool (100) having at least one hydraulic consumer (110) and a hydraulic system (10) according to any one of claims 1 to 12, wherein the hydraulic consumer (110) is connected to the consumer connection (14) and the return connection (16).

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