Hydraulic Drive System Having a 2X2Q Pump Unit

Abstract

A hydraulic drive system for operating a hydraulic cylinder in first and second movement profiles. A hydraulic drive unit includes first and second hydraulic machines, each with first and second connections. In the first movement profile, a first cylinder chamber of the hydraulic cylinder is fluidly connected to a first fluid reservoir and a second cylinder chamber is fluidly connected to the second connection of the second hydraulic machine. In the second movement profile, the first connection of the first hydraulic machine is connected to the second connection of the second hydraulic machine.

Claims

1. A hydraulic drive system for operating a hydraulic cylinder in a first movement profile and in a second movement profile, the system comprising: a hydraulic cylinder including a first cylinder chamber and a second cylinder chamber; a first fluid-hydraulic reservoir; a hydraulic drive unit having a first hydraulic machine having a first connection and a second connection and a second hydraulic machine having a first connection and a second connection; a first controllable valve, wherein the first controllable valve creates a fluid-hydraulic connection between the first cylinder chamber of the hydraulic cylinder and the first fluid-hydraulic reservoir in accordance with a movement profile; a second controllable valve, wherein the second controllable valve creates a fluid-hydraulic connection between the second connection of the second hydraulic machine and the second cylinder chamber of the hydraulic cylinder or with the first connection of the first hydraulic machine in accordance with the movement profile; wherein the first hydraulic machine and the second hydraulic machine are mechanically interconnected and are operated jointly by a variable-speed drive; wherein the second connection of the first hydraulic machine and the first connection of the second hydraulic machine are fluid-hydraulically connected to the first fluid-hydraulic reservoir; wherein, in the first movement profile, the first cylinder chamber is fluid-hydraulically connected to the first fluid-hydraulic reservoir and the second cylinder chamber is fluid-hydraulically connected to the second connection of the second hydraulic machine; and wherein, in the second movement profile, the first connection of the first hydraulic machine is connected to the second connection of the second hydraulic machine.

2. The hydraulic drive system according to claim 1, wherein the hydraulic drive system furthermore comprises a pressure relief valve fluid-hydraulic connected between the second cylinder chamber and the fluid-hydraulic reservoir.

3. The hydraulic drive system according to claim 1, wherein the first fluid-hydraulic reservoir is designed as a non-pressurized fluid-hydraulic reservoir.

4. The hydraulic drive system according to claim 1, wherein, to switch the switching position, the second controllable valve is in fluid-hydraulic communication with the first cylinder chamber of the hydraulic cylinder via a pilot line.

5. The hydraulic drive system according to claim 1, wherein, to switch the switching position, the first controllable valve is in fluid-hydraulic communication with the second cylinder chamber of the hydraulic cylinder via a pilot line.

6. The hydraulic drive system according to claim 1, wherein the first controllable valve switches the switching position as a result of a received control signal.

7. The hydraulic drive system according to claim 1, wherein the second controllable valve switches the switching position as a result of a received control signal.

8. The hydraulic drive system according to claim 1, wherein the hydraulic cylinder comprises a first hydraulic cylinder surface and a second hydraulic cylinder surface and the first hydraulic cylinder surface and the second hydraulic cylinder surface are different.

9. The hydraulic drive system according to claim 1, wherein the hydraulic drive system comprises a third valve and the third valve is connected between the second cylinder chamber of the hydraulic cylinder and the second controllable valve.

10. The hydraulic drive system according to claim 1, wherein the hydraulic drive system comprises a fourth valve and the fourth valve is connected between the second cylinder chamber of the hydraulic cylinder and a second fluid-hydraulic reservoir.

11. The hydraulic drive system according to claim 1, wherein the second fluid-hydraulic reservoir is designed as a pressurized fluid-hydraulic reservoir.

12. The hydraulic drive system according to claim 1, wherein the pressurized fluid-hydraulic reservoir has a pressure which is greater than the pressure resulting from the moving mass actively acting on the cylinder and from the cylinder surface in the cylinder chamber of the cylinder.

13. The hydraulic drive system according to claim 1, wherein the third valve and the fourth valve are designed as a 2/2-way valve.

14. The hydraulic drive system according to claim 1, wherein the first hydraulic machine has a greater delivery volume than the second hydraulic machine.

15. The hydraulic drive system according to claim 1 configured to control a hydraulic cylinder in a press system.

Description

[0033] In the figures of the drawing, similar, functionally similar and similarly acting elements, features and components are each denoted by the same reference signs-unless stated otherwise. In the drawing:

[0034] FIG. 1 shows a first embodiment of the hydraulic drive system according to the present invention;

[0035] FIG. 2 shows a further embodiment of the hydraulic drive system according to the present invention;

[0036] FIG. 3 shows a further embodiment of the hydraulic drive system according to the present invention; and

[0037] FIG. 4 shows a further embodiment of a hydraulic drive system according to the present invention, for use in controlling a hydraulic cylinder in a folding press system.

[0038] FIG. 1 shows an embodiment of the hydraulic drive system 100 according to the present invention. The hydraulic drive system 100 is designed to be operated in a first movement profile and in a second movement profile. In the first movement profile, the movement speed during the extension and retraction of the hydraulic cylinder 10 is greater than in the second movement profile.

[0039] The hydraulic drive system 100 comprises a hydraulic cylinder 10. The hydraulic cylinder 10 has a first cylinder chamber 11 (piston side) and a second cylinder chamber 12 (ring side). The hydraulic cylinder 10 has a first hydraulic cylinder surface and a second hydraulic cylinder surface. The first hydraulic cylinder surface and the second hydraulic cylinder surface are designed to be different. The hydraulic cylinder 10 is preferably designed as at least a differential cylinder.

[0040] Furthermore, a fluid-hydraulic reservoir 50 is provided. The fluid-hydraulic reservoir 50 has fluid-hydraulic connections to a first hydraulic machine 21 and to a second hydraulic machine 24.

[0041] Furthermore, the hydraulic drive system 100 has a hydraulic drive unit 20. The hydraulic drive unit 20 comprises the first hydraulic machine 21 and the second hydraulic machine 24. The first hydraulic machine 21 has a first connection 22 and a second connection 23. The second hydraulic machine 24 has a first connection 25 and a second connection 26. The connections of the first hydraulic machine 21 and the second hydraulic machine 24 may be designed as a high pressure connection and a low pressure connection. In particular, the first connection 22 of the first hydraulic machine 21 and the second connection 26 of the second hydraulic machine 24 are designed as a high pressure connection. The second connection 23 of the first hydraulic machine 21 and the first connection 25 of the second hydraulic machine 24 are designed as a low pressure connection. In one embodiment, the first hydraulic machine 21 and the second hydraulic machine 24 have different delivery volumes. The first hydraulic machine 21 preferably has a higher delivery volume than the second hydraulic machine 24. The first hydraulic machine 21 and the second hydraulic machine 24 are mechanically interconnected. In particular, the first hydraulic machine 21 and the second hydraulic machine 24 may be mechanically interconnected (coupled) via a shaft. The first hydraulic machine 21 and the second hydraulic machine 24 are operated jointly by a variable-speed drive 27 of the hydraulic drive unit 20. The variable-speed drive 27 may be designed as a variable-speed electric motor or an electric motor with a variable direction of rotation. Variable-speed drives 27 substantially comprise an electric motor, a hydraulic pump and a frequency converter, for which the software sets the motor speed. Furthermore, the direction of rotation of the drive 27 may be specified via the frequency converter. A retraction and extension of the hydraulic cylinder 10 may thus be provided.

[0042] The hydraulic drive system 100 furthermore comprises a first controllable valve 30. The first controllable valve 30 may create a fluid-hydraulic connection between the first cylinder chamber 11 of the hydraulic cylinder 10 and the first fluid-hydraulic reservoir 50 in accordance with a movement profile. The first controllable valve 30 has a pilot line 31. The pilot line 31 may be designed as a hydraulic pilot line or as an electric pilot line. A change in the switching state of the first controllable valve 30 may take place as a result of connecting the pilot line 31.

[0043] The hydraulic drive system 100 furthermore comprises a second controllable valve 60. The second controllable valve 60 may create a fluid-hydraulic connection between the second connection 26 of the second hydraulic machine 24 and the second cylinder chamber 12 of the hydraulic cylinder 10 in accordance with the movement profile. Alternatively, the second controllable valve 60 may create a fluid-hydraulic connection between the second connection 26 of the second hydraulic machine 24 and the first connection 22 of the hydraulic machine 21. Furthermore, the movement profile may be selected via the second controllable valve 60. It is provided that the drive system according to the invention is operated in bump bending mode. This mode enables a smooth, wide radius to be produced in thick, high-strength plate, for example. This places high technical demands on the hydraulic drive system 100 since bump bending involves dozens of bends bent by the brake punch a few degrees at a time. The dozens of bends are realized by small upward and downward movements of the hydraulic cylinder 10.

[0044] To this end, during the downward movement of the hydraulic cylinder 10, a fluid-hydraulic connection is created between the second cylinder chamber 12 of the hydraulic cylinder 10 and the pressurized fluid-hydraulic reservoir 90. Furthermore, the second connection 26 of the second hydraulic machine 24 is fluid-hydraulically connected to the first connection 22 of the hydraulic machine 21. The hydraulic cylinder 10, in particular the piston rod of the hydraulic cylinder 10, moves with a uniform upward and downward movement (bump bending).

[0045] The second controllable valve 60 has a pilot line 61. The pilot line 61 may be designed as a hydraulic pilot line or as an electric pilot line. A change in the switching state of the second controllable valve 60 may take place as a result of connecting the pilot line 61.

[0046] It is provided that the second connection 23 of the first hydraulic machine 21 and the first connection 25 of the second hydraulic machine are fluid-hydraulically connected to the first fluid-hydraulic reservoir 50. In one embodiment, it is provided that the fluid-hydraulic reservoir 50 is designed as a non-pressurized hydraulic reservoir.

[0047] Furthermore, it is provided that, in a first movement profile, the first cylinder chamber 11 is fluid-hydraulically connected to the first fluid-hydraulic reservoir 50. In particular, the first cylinder chamber 11 of the hydraulic cylinder 10 is fluid-hydraulically connected to the first fluid-hydraulic reservoir 50 via the first controllable valve 30. Moreover, the second cylinder chamber 12 is fluid-hydraulically connected to the second connection 26 of the hydraulic machine 24. In particular, the second cylinder chamber 12 of the hydraulic cylinder 10 is fluid-hydraulically connected to the second connection 26 of the second hydraulic machine 24 via the second controllable valve 60.

[0048] It is furthermore provided that, in a second movement profile, the first connection 22 of the first hydraulic machine 21 is connected, in particular fluid-hydraulically connected, to the second connection 26 of the second hydraulic machine 24. Furthermore, in the second movement profile, the first controllable valve 30 is switched so that there is no fluid-hydraulic connection to the first fluid-hydraulic reservoir 50.

[0049] FIG. 2 shows a further embodiment of a hydraulic drive system 100 according to the present invention. The hydraulic drive system 100 has the same components as the embodiment illustrated in FIG. 1. Furthermore, the hydraulic drive system 100 according to FIG. 2 has a pressure relief valve (PRV) 63. The pressure relief valve 63 has a fluid-hydraulic connection to the fluid-hydraulic reservoir 50. Fluid may be transferred into the fluid-hydraulic reservoir 50 via the fluid-hydraulic connection to the fluid-hydraulic reservoir 50. The pressure relief valve 63 in the embodiment represents an advantageous configuration in the hydraulic drive system 100. By means of the pressure relief valve 63, the maximum permissible fluid pressure is limited in order to protect the hydraulic drive system 100 and, in particular, the hydraulic cylinder 10 against too high a pressure (overpressure protection) and to avoid damage. Via a spring in the PRV, for example, the PRV enables the fluid to flow from the fluid connection into the fluid-hydraulic reservoir 50 if the pressure in the hydraulic drive system 100 exceeds a desired (set) value. It is generally possible to protect against exceeding the maximum permissible pump or system pressure by means of such a PRV.

[0050] FIG. 3 shows a further embodiment of a hydraulic drive system 100 according to the present invention. The hydraulic drive system 100 has the same components as the embodiment illustrated in FIG. 1. Furthermore, the hydraulic drive system 100 according to FIG. 3 has a third valve 70. The third valve 70 is connected between the second cylinder chamber 12 of the hydraulic cylinder 10 and the second controllable valve 60. Moreover, the embodiment of the hydraulic drive system 100 illustrated in FIG. 3 has a fourth valve 80. The fourth valve 80 is connected between the second cylinder chamber 12 of the hydraulic cylinder 10 and a second fluid-hydraulic reservoir 90. The second fluid-hydraulic reservoir 90 may be designed as a pressurized fluid-hydraulic reservoir 90. In particular, the fluid released by the cylinder chamber 12 of the hydraulic cylinder 10 may be discharged into the pressurized fluid-hydraulic reservoir 90 in a corresponding switching position of the third valve 70 and the fourth valve 80. Process energy, in particular energy present in the ring side, may thus be advantageously discharged into the pressurized fluid-hydraulic reservoir 90 during the downward movement of the hydraulic cylinder 10 and may be recuperated as needed. The energy stored in the form of pressurized fluid may be used for the downward movement of the hydraulic cylinder 10. The energy consumption of the hydraulic system 100 may thus be reduced.

[0051] FIG. 4 shows a further embodiment of a hydraulic drive system 100 according to the present invention for use in controlling a hydraulic cylinder 10 in a press system, for example in a folding press system. Reference sign 200 denotes the press system. When using folding press systems, plate to be treated is placed between a die with a V-shaped opening and a hydraulic cylinder 10 with a conical workpiece. If the hydraulic cylinder 10 is lowered with a certain force, the workpiece is pressed into the opening and bent to the required angle.

[0052] Furthermore, the first controllable valve 30 illustrated in the embodiment of FIG. 4 is depicted as a controllable non-return valve 30. The controllable non-return valve 30 has a first switching position blocked and a second switching position open. In the second switching position, fluid may escape from the non-pressurized fluid-hydraulic reservoir 50. In the embodiment illustrated in FIG. 4, to switch the switching position, the controllable non-return valve 30 is in fluid-hydraulic communication with the second cylinder chamber 12 of the hydraulic cylinder 10 via a pilot line 31. In an embodiment which is not shown, the switching position may be switched via a received control signal 31, in particular an electrical control signal 31.

[0053] Furthermore, the second controllable valve 60 is designed as a 3/2-way valve. The 3/2-way valve has a first and a second switching position. A first switching position provides a fluid-hydraulic connection between the second cylinder chamber 12 of the hydraulic cylinder 10 and the second connection 26 of the second hydraulic machine 24 (c.f. FIG. 4). A second switching position creates a fluid-hydraulic connection between a first cylinder chamber 11 of the hydraulic cylinder 10 and the second connection 26 of the second hydraulic machine 24. In FIG. 4, to switch the switching position, the second controllable valve 60 is in fluid-hydraulic communication with the first cylinder chamber 11 of the hydraulic cylinder 10 via a pilot line 61. In an alternative configuration, the second controllable valve 60 may also be switched via an electrical signal. Furthermore, the controllable valve 60 in the illustrated embodiment has a spring reset function. Alternatively, a pulse reset function may also be provided.

[0054] Furthermore, the third valve 70 and the fourth valve 80 are designed as 2/2-way valves. The third valve 70 and the fourth valve 80 have two switching positions, in which the valve is blocked and opened respectively in one direction. The third valve 70 and the fourth valve 80 may be electrically and hydraulically switched and have a spring reset function in the illustrated embodiment.

[0055] In the basic position of the third valve 70 and the fourth valve 80 (c.f. FIG. 4), hydraulic fluid may be transferred into the pressurized fluid-hydraulic reservoir 90.

[0056] Furthermore, a non-return valve 40 is provided in the embodiment of FIG. 4. The non-return valve 40 has a hydraulic connection to the node between the second connection 23 of the first hydraulic machine 21 and the first connection 25 of the second hydraulic machine 24 and the second connection 26 of the second hydraulic machine 24 and to the first fluid-hydraulic reservoir 50. The non-return valve 40 is a safety valve for the second hydraulic machine 24 and prevents the cavitation of the second hydraulic machine 24. This is especially advantageous if, in an alternative embodiment, the fluid-hydraulic reservoir 50 is designed as a pressurized fluid-hydraulic reservoir 50.

[0057] The hydraulic drive system 100 is provided for operating the hydraulic cylinder 10 in a first movement profile and in a second movement profile. The movement speed of the hydraulic cylinder 10 is preferably greater in the first movement profile than during the movement using the second movement profile. The provision of a power movement is greatest when using the second movement profile.

[0058] In the first movement profile, the first cylinder chamber 11 of the hydraulic cylinder 10 is fluid-hydraulically connected to the first fluid-hydraulic reservoir 50. Furthermore, the connection 22 of the first hydraulic machine 21 is connected to the first cylinder chamber 11 of the hydraulic cylinder 10. During the first movement profile in the downward stroke of the hydraulic cylinder 10, the first hydraulic machine 21 pumps fluid into the first cylinder chamber 11. Since the volume on the piston side is greater than the volume on the ring side and therefore further fluid is required, the cylinder chamber 11 of the hydraulic cylinder 10 may take in fluid from the non-pressurized reservoir 50 via the non-return valve 30. Furthermore, the second cylinder chamber 12 of the hydraulic cylinder 10 is fluid-hydraulically connected to the second connection 26 of the second hydraulic machine 24 via the valve 60. The fluid taken from the hydraulic cylinder 10 is supplied to the cylinder chamber 11 via the first hydraulic machine 21 and to the second hydraulic machine 24.

[0059] As previously illustrated, the first movement profile in one embodiment may likewise be used for the upward stroke of the hydraulic cylinder 10. The switching position of the valves involved remains unchanged and only the direction of rotation of the drive 27 changes. To this end, the excess fluid which may not be received by the ring side (piston side has a greater surface and therefore more volume) is supplied to the non-pressurized fluid reservoir 50 via the activated non-return valve 30.

[0060] Via the second controllable valve 60, it is possible to determine the movement profile in which the hydraulic drive system 100 is operating. If the second controllable valve 60 is activated, for example, then the hydraulic drive system 100 is in the second movement profile. If the second controllable valve 60 is in the idle position, then the hydraulic drive system 100 is in the first movement profile. The second controllable valve 60 may subsequently remain in the switching position. Active switching of the movement profile takes place via the third valve 70. It is possible to actively switch between the first movement profile and the second movement profile. The second controllable valve 60 switches as a result of the active switching of valve 70. There is a positive control between the second controllable valve 60 and the third valve 70. In the second movement profile, a power-transmitting movement of the hydraulic cylinder 10 is executed with the tool inserted. To this end, the first connection 22 of the first hydraulic machine 21 is fluid-hydraulically connected to the second connection 26 of the second hydraulic machine 24 via the 3/2-way valve 60.

[0061] The effective pump volume is decreased as a result of the switching of the second controllable valve 60. During the hydraulic motor operation, the second hydraulic machine 24 discharges some of the volume flow which is provided by the first hydraulic machine 21. The resultant reactive output torque of the second hydraulic machine 24 is provided as a driving torque via the mechanical connection of the hydraulic machines. The effectively delivered volume flow in the direction of the first cylinder chamber 11 is therefore decreased. The required driving torque is therefore likewise reduced. Moreover, the first connection 22 of the first hydraulic machine 21 is hydraulically connected to the first cylinder chamber 11 of the hydraulic cylinder 10. The non-return valve 30 is closed. The first hydraulic machine 21 is connected to the non-pressurized fluid-hydraulic reservoir 50 via the second connection 23. Moreover, the first connection 25 of the second hydraulic machine 24 is connected to the non-pressurized fluid-hydraulic reservoir 50. Via these fluid-hydraulic connections, fluid is taken from the non-pressurized fluid-hydraulic reservoir 50 via the low pressure side of the hydraulic machines 21, 24. The fluid which is transported away from the second cylinder chamber 12 of the hydraulic cylinder may be transferred to, and stored in, the pressurized fluid-hydraulic reservoir 90 via the 2/2-way valves 70/80 in a corresponding switching position. By way of example, the energy stored in this way may be used for the bump bending. The stored energy may be supplied for the upward movement in the first movement profile.

LIST OF REFERENCE SIGNS

[0062] 100 Hydraulic drive system [0063] 200 Folding press system [0064] 10 Hydraulic cylinder [0065] 11 First cylinder chamber [0066] 12 Second cylinder chamber [0067] 20 Hydraulic drive unit [0068] 21 First hydraulic machine [0069] 22 First connection of the first hydraulic machine [0070] 23 Second connection of the first hydraulic machine [0071] 24 Second hydraulic machine [0072] 25 First connection of the second hydraulic machine [0073] 26 Second connection of the second hydraulic machine [0074] 27 Variable-speed drive [0075] 30 First controllable valve [0076] 31 Pilot line [0077] 40 Non-return valve [0078] 50 First fluid-hydraulic reservoir [0079] 60 Second controllable valve [0080] 61 Pilot line [0081] 63 Pressure relief valve [0082] 70 Third controllable valve [0083] 80 Fourth controllable valve [0084] 90 Second fluid-hydraulic reservoir