ELECTROHYDROSTATIC SYSTEM WITH PRESSURE SENSOR

Abstract

The present invention relates to an electrohydrostatic system having a hydraulic cylinder comprising a first cylinder chamber and a second cylinder chamber. Furthermore, the electrohydrostatic system has a fluid hydraulic supply device for providing a hydraulic fluid, a fluid hydraulic motor pump unit, designed to provide a fluid hydraulic volume flow in order to move the hydraulic cylinder. A motor control device is designed to provide a rated current for an electrical drive of the fluid hydraulic motor pump unit. Moreover, the electrohydrostatic system has at least one fluid hydraulic safety valve, which on a first valve side is connected to one of the cylinder chambers of the hydraulic cylinder and on a second valve side is connected to the fluid hydraulic motor pump unit. The fluid hydraulic safety valve can be bridged via a bypass connection with a fixed orifice plate, wherein the bypass connection is connected to the first valve side and to the second valve side of the at least one fluid hydraulic safety valve. Moreover, the electrohydrostatic system has a pressure sensor that is connected to one of the cylinder chambers of the hydraulic cylinder. The pressure sensor is designed to detect a fluid hydraulic pressure on one of the cylinder chambers and, according to the detected fluid hydraulic pressure, to provide an enabling signal for the motor control device to provide the rated current for the electrical drive of the fluid hydraulic motor pump unit.

Claims

1. An electrohydrostatic system comprising: a hydraulic cylinder having a first cylinder chamber and a second cylinder chamber; a fluid hydraulic supply device for providing a hydraulic fluid; a fluid hydraulic motor pump unit designed to provide a fluid hydraulic volume flow in order to move the hydraulic cylinder; a motor control device designed to provide a rated current for an electrical drive of the fluid hydraulic motor pump unit; at least one fluid hydraulic safety valve, which on a first valve side is connected to one of the cylinder chambers of the hydraulic cylinder and on a second valve side is connected to the fluid hydraulic motor pump unit; a bypass connection having a fixed orifice plate for bridging the at least one fluid hydraulic safety valve, wherein the bypass connection is connected to the first valve side and to the second valve side of the at least one fluid hydraulic safety valve; a pressure sensor, which is connected to the second cylinder chamber of the hydraulic cylinder and is designed to detect a fluid hydraulic pressure on one of the cylinder chambers and, corresponding to the detected fluid hydraulic pressure, to provide an enabling signal for the motor control device to provide the rated current for the electrical drive of the fluid hydraulic motor pump unit; and the resistance of the fixed orifice plate having at least one value that in the hydraulic cylinder is determined by pressure generated by a suspended load of the hydraulic cylinder.

2. The electrohydrostatic system according to claim 1, wherein the electrohydrostatic system comprises a first safety device that is designed to receive an electrical signal corresponding to a detected fluid hydraulic pressure from the pressure sensor and to provide an enabling signal for the motor control device to provide the rated current for the electrical drive of the fluid hydraulic motor pump unit.

3. The electrohydrostatic system according to claim 1, wherein the hydraulic cylinder is designed as a differential cylinder, synchronous cylinder, multi-surface cylinder or a detached cylinder arrangement.

4. The electrohydrostatic system according to claim 1, wherein the fluid hydraulic supply device comprises a pressure accumulator, a safety valve, a fluid source, at least one check valve and a fluid reservoir.

5. The electrohydrostatic system according to claim 1, wherein the motor control device provides a safe torque off safety function.

6. The electrohydrostatic system according to claim 1, wherein the pressure sensor is designed as a pressure sensor with increased functional safety.

7. (canceled)

8. The electrohydrostatic system according to claim 1, wherein the resistance of the fixed orifice plate to a pressure for providing a setup speed of the hydraulic cylinder is set in a range from 5 to 40 mm/s.

9. The electrohydrostatic system according to claim 1, wherein the pressure sensor is connected to the second cylinder chamber of the hydraulic cylinder.

10. The electrohydrostatic system according to claim 1, wherein a fluid hydraulic setup valve is switched in the bypass connection.

11. The electrohydrostatic system according to claim 1, wherein a pressure relief valve is connected in the bypass connection.

12. The electrohydrostatic system according to claim 11, wherein a check valve is connected in parallel to the pressure relief valve.

13. The electrohydrostatic system according to claim 1, wherein the electrohydrostatic system comprises a second safety device that includes a distance measuring system and/or a mechanical safety.

14. The electrohydrostatic system according to claim 1, wherein the first cylinder chamber of the hydraulic cylinder with the fluid hydraulic motor pump unit and the second cylinder chamber of the hydraulic cylinder is connected to the at least one fluid hydraulic safety valve.

15. The electrohydrostatic system according to claim 1, wherein the first cylinder chamber of the hydraulic cylinder is connected to the at least one fluid hydraulic safety valve and the second cylinder chamber of the hydraulic cylinder is connected to the fluid hydraulic motor pump unit.

16. The electrohydrostatic system according to claim 1 for controlling the setup speed in a powder press, forging press and/or forming press.

17. The electrohydrostatic system according to claim 1, wherein the resistance of the fixed orifice plate to a pressure for providing a setup speed of the hydraulic cylinder is set at or below 10 mm/s.

Description

[0030] In the figures of the drawing, identical, functionally identical, and identically acting elements, features and components are respectively provided with the same reference signs, insofar as is not stated otherwise.

[0031] The following are shown:

[0032] FIG. 1 is a schematic representation of an electrohydrostatic system according to a first embodiment;

[0033] FIG. 2 is a schematic representation of a known electrohydrostatic system from the prior art;

[0034] FIG. 3 is a schematic representation of a classic hydraulic system known in the art;

[0035] FIG. 4 is a schematic representation of an extrusion press with an electrohydrostatic system according to a second embodiment;

[0036] FIG. 5 is a schematic representation of an electrohydrostatic system according to a third embodiment;

[0037] FIG. 6 is a schematic representation of an electrohydrostatic system according to a fourth embodiment;

[0038] FIG. 7 is a schematic representation of an electrohydrostatic system according to a fifth embodiment;

[0039] FIG. 8 is a schematic representation of an electrohydrostatic system according to a sixth embodiment;

[0040] FIG. 1 shows a schematic representation of an electrohydrostatic system 1 according to a first embodiment. The electrohydrostatic system 1 has a hydraulic cylinder 10 with a first cylinder chamber 11 and a second cylinder chamber 12. Furthermore, the electrohydrostatic system 1 has a motor pump unit 15 for the pressure supply and a supply device 90 for fluid supply. The motor pump unit 15 is connected to the first cylinder chamber 11 of the hydraulic cylinder 10 and the supply device 90 via a check valve 93 at a first terminal in the embodiment shown in FIG. 1. At a second connection, the motor pump unit 15 has a connection to a safety valve 16, which is in turn connected to the second cylinder chamber 12 of the hydraulic cylinder 10. The supply device 90 comprises a safety valve 91, a fluid source 92, a check valve 93, a pressure accumulator 95 and a fluid reservoir 96. Furthermore, the electrohydrostatic system 1 has a motor control device 20 that can be designed as a frequency converter. In addition, the electrohydrostatic system 1 has a pressure sensor 60, especially a pressure sensor with increased functional safety. The pressure sensor 60 provides a pressure value of a first safety device 30 determined at the fixed orifice plate 13, preferably a safety PLC, as a safety control 30. The first safety device 30 is electrically coupled to the motor controller 20 and is designed to receive an electrical signal from the safety device 30 in response to an increased pressure corresponding to a setup speed outside the requirement. Preferably, the frequency converter 20 has a “safe torque off” (STO) function for switching off the torque of the motor pump unit in order to set the setup speed according to the requirements. The present invention is characterized by the pressure sensor with increased functional safety. Alternatively, two pressure sensors of simple design can be used in redundant combination, with which an evaluation of the provided signals is analogous to the pressure sensor with increased functional safety. Alternatively, a pressure sensor of simple design without a redundant design can be used and evaluated. The pressure sensors 60 in the embodiment, and in the alternative embodiment as shown above, can be introduced into the electrohydrostatic system 1 on the first cylinder chamber 11 and/or the second cylinder chamber 12 of the hydraulic cylinder 10. The hydraulic cylinder 10 can be used as a differential cylinder, synchronous cylinder, multi-surface cylinder or as a detached cylinder arrangement. Unintentional pressure buildup in the electrohydrostatic system 1 can be secured via the STO safety function of the frequency converter 20 and the motor pump unit 15. The protection against the suspended load dropping can be ensured by one safety-relevant valve or a plurality of safety-relevant valves 16. The setting of the safe speed in the setup process is carried out via the fixed orifice plate 13. The fixed orifice plate 13 represents a bypass of the safety valve 16 and is connected to the second cylinder chamber 12 of the hydraulic cylinder 10 and the motor pump unit 15 or the supply device 90. Furthermore, the fixed orifice plate 13 has a connection to the pressure sensor 60 with increased functional safety. In the embodiment of FIG. 1, the fixed orifice plate 13 is designed without an additional setup valve. The pressure difference for which the fixed orifice plate 13 is designed is set by the pressure sensor 60 with increased functional safety as the upper limit in setup mode. If this defined pressure value is exceeded, the first safety device 30 triggers the STO safety function of the frequency converter 20. By triggering of the STO safety function, the safe setup speed is not exceeded. With the embodiment according to the invention, a safe setup speed can be realized, although pressure differences occurring on the hydraulic chambers prevail due to unequal surfaces or other reasons. Thus, no pressure limiting device is subjected to excess pressure and the maximum set-up speed is limited. The setup speed is predetermined by the rotational speed and/or the delivery volume of the variable-speed motor pump unit 15, wherein the maximum setup speed can be freely defined by the resistance and the pressure sensor 60 with increased functional safety between the pressure of the suspended load and the maximum pressure of the pressure relief valves.

[0041] FIG. 4 shows a schematic representation of an electrohydrostatic system 1 according to a second embodiment. In the embodiment according to FIG. 4, the electrohydrostatic system 1 is expanded by a setup valve 14 in the bypass connection of the safety valve 16 or the safety valves 16 with reference to the embodiment of FIG. 1. The setup valve 14 is introduced between the fixed orifice plate 13 and the second cylinder chamber 12 of the hydraulic cylinder 10. The pressure sensor 60 with increased functionality determines the pressure at the fixed orifice plate 13 via the setup valve 14. Setup mode can be switched on or off via setup valve 14. In addition, a sagging of the hydraulic cylinder due to its own weight can be prevented in the event of failure of the motor pump unit 15.

[0042] FIG. 5 shows a schematic representation of an electrohydrostatic system 1 according to a third embodiment. In the embodiment according to FIG. 5, the electrohydrostatic system 1 is expanded by a pressure relief valve 70 in the bypass connection of the safety valve 16 or the safety valves 16 with reference to the embodiment of FIG. 1. The pressure relief valve 70 is introduced between the fixed orifice plate 13 and the second cylinder chamber 12 of the hydraulic cylinder 10. The pressure sensor 60 with increased functionality determines the pressure at the fixed orifice plate 13 via the pressure relief valve 70. The pressure relief valve 70 serves as a load holding valve in order to prevent a lowering of the piston of the hydraulic cylinder 10 due to the dead weight. A setup in the extending direction of the hydraulic cylinder 10 is made possible by the pressure relief valve 70.

[0043] FIG. 6 shows a schematic representation of an electrohydrostatic system 1 according to a fourth embodiment. In the embodiment according to FIG. 6, the electrohydrostatic system 1 is expanded by a pressure relief valve 80 in the bypass connection of the safety valve 16 or the safety valves 16 with reference to the embodiment of FIG. 1. The pressure relief valve 80 is introduced between the fixed orifice plate 13 and the second cylinder chamber 12 of the hydraulic cylinder 10. The pressure sensor 60 with increased functionality determines the pressure at the fixed orifice plate 13 via the pressure relief valve 80. In addition, a check valve 81 is provided in a bypass connection to the pressure relief valve 80. The pressure relief valve 80 serves as a load holding valve in order to prevent a lowering of the piston of the hydraulic cylinder 10 due to the dead weight. The function of the setup valve 14 is replaced by the pressure holding valve 80 in combination with the check valve 81. The pressure relief valve 80 is set for the suspended load.

[0044] FIG. 7 shows a schematic representation of an electrohydrostatic system 1 according to a fifth embodiment. In the embodiment according to FIG. 7, the pressure sensor 60 is connected with increased functional safety to the cylinder chamber of the hydraulic cylinder 10, which has no connection to the safety valve 16. The exact position of the pressure sensor 60 with increased functionality can be selected in dependence on the overall system and thus the orientation and the type of the hydraulic cylinders, further axes that can apply excess pressure to these axes and/or the acting weight force. Thus, a safe setup speed for each system can be provided efficiently and flexibly.

[0045] FIG. 8 shows a schematic representation of an electrohydrostatic system 1 according to a sixth embodiment. In the embodiment according to FIG. 8, the electrohydrostatic system 1 additionally comprises a second safety device 50. The second safety device 50 can comprise a distance measuring system and/or a mechanical safety. A redundant safety can be provided by the second safety device 50 in combination with the first safety device 30. A defect of one of the two safety devices 30, 50 can be compensated by the other functional safety device 30, 50, thereby ensuring the full safety. Alternatively, the second safety device 50 can also be designed as a second hydraulic safety valve 16. As an alternative to the pressure sensor 60, the distance measuring system supplies information about the actual movement speed of the hydraulic cylinder 10 with increased functional safety. The determined actual movement speed can be used for limiting the same via the frequency converter 20 in combination with the motor pump unit 15. For determining the actual movement speed, the path signal is derived over time. The mechanical safety can be set up via a mechanical brake and/or clamping device. This increases the safety of the electrohydrostatic system 1.

LIST OF REFERENCE SIGNS

[0046] 1 Electrohydrostatic system [0047] 10 Hydraulic cylinder [0048] 11 First cylinder chamber [0049] 12 Second cylinder chamber [0050] 13 Fixed orifice plate [0051] 14 Setup valve [0052] 15 Motor pump unit [0053] 16 Safety valve [0054] 17 Setup valve [0055] 18 Directional valve [0056] 20 Motor control device [0057] 30 First safety device [0058] 50 Second safety device [0059] 60 Pressure sensor [0060] 70 Pressure relief valve [0061] 80 Pressure relief valve [0062] 81 Check valve [0063] 90 Supply device [0064] 91 Safety valve [0065] 92 Fluid source [0066] 93 Check valve [0067] 94 Pressure relief valve [0068] 95 Pressure accumulator [0069] 96 Fluid reservoir