Hydraulic system

Abstract

A hydraulic system (1) according to one embodiment comprises: a hydraulic cylinder (4A) that includes a cylinder tube (41), covers (42), (43), and a piston (44); a position detector (8A) that detects the position of the piston (44); a driving apparatus (7) that alternately supplies hydraulic oil to a drive chamber (4a) of the hydraulic cylinder (4A) and discharges hydraulic oil from the drive chamber (4a); and a processing circuit (91). The processing circuit (91) applies an inversion command to the driving apparatus (7) when the piston (44) moves toward the cover (42) and reaches an inversion command application position. Further, the processing circuit (91) updates the inversion command application position on the basis of the deviation between a target inversion position and an actual inversion position of the piston (44) detected by the position detector (8A).

Description

Hydraulic system

[0001] The present disclosure relates to a hydraulic system including a hydraulic cylinder.

[0002] Conventionally, hydraulic cylinders such as single-rod and double-rod types have been known. Such hydraulic cylinders include a cylinder tube and a piston disposed within the cylinder tube. Hydraulic cylinders are sometimes used in applications where the piston repeatedly reciprocates at a predetermined cycle.

[0003] For example, Patent Document 1 discloses a hydraulically driven gas booster 100 for compressing gas as shown in Fig. 6. The gas booster 100 includes a first structure 110 and a second structure 120. Each of the first structure 110 and the second structure 120 includes a gas cylinder 200 and a hydraulic cylinder 300 arranged coaxially.

[0004] Each gas cylinder 200 includes a gas cylinder tube 210 and a gas cover 220 that closes the opening of the gas cylinder tube 210 on the side opposite to the hydraulic cylinder 300. Furthermore, the gas cylinder 200 includes a gas piston 230 disposed within the gas cylinder tube 210. A compression chamber 240 is formed between the gas piston 230 and the gas cover 220.

[0005] Each hydraulic cylinder 300 includes a hydraulic cylinder tube 310 and a pair of hydraulic covers 320, 330 that close openings on both sides of the hydraulic cylinder tube 310. Furthermore, the hydraulic cylinder 300 includes a hydraulic piston 340 disposed within the hydraulic cylinder tube 310. A first drive chamber 350 is formed between the hydraulic piston 340 and the hydraulic cover 320, and a second drive chamber 360 is formed between the hydraulic piston 340 and the hydraulic cover 330. The hydraulic piston 340 is connected to the gas piston 230 by a rod 400 that passes through the hydraulic cover 330.

[0006] The second drive chamber 360 of the first structure 110 and the second drive chamber 360 of the second structure 120 are communicated with each other via a communication passage 500. In the gas booster 100, the supply of hydraulic oil to the first drive chamber 350 of the first structure 110 and the discharge of hydraulic oil from the first drive chamber 350 of the second structure 120, and the discharge of hydraulic oil from the first drive chamber 350 of the first structure 110 and the supply of hydraulic oil to the first drive chamber 350 of the second structure 120 are performed alternately.

[0007] Furthermore, in the gas booster 100 of Patent Document 1, a position sensor 600 is attached to the hydraulic cylinder tube 310 of each hydraulic cylinder 300 .

[0008] Special Publication No. 2021-522446

[0009] In Patent Document 1, the position sensor 600 is attached to the hydraulic cylinder tube 310, and therefore it is assumed that the position sensor 600 is a proximity sensor. In other words, the position sensor 600 detects when the hydraulic piston 340 approaches the position sensor 600.

[0010] However, a proximity sensor cannot accurately determine the position of the hydraulic piston 340. Therefore, if the movement direction of the hydraulic piston 340 is reversed based on the detection result of the proximity sensor, the hydraulic piston 340 may hit the hydraulic cover 320 or 330, which defines the stroke end, or the distance from the reversal position to the stroke end may become longer. If the hydraulic piston 340 hits the hydraulic cover 320 or 330, noise may be generated and the risk of hydraulic oil leakage due to surge pressure may increase, and if the distance from the reversal position to the stroke end becomes longer, the power may decrease.

[0011] Therefore, an object of the present disclosure is to provide a hydraulic system that can reverse the piston of a hydraulic cylinder near the end of its stroke without hitting the cover.

[0012] The present disclosure provides a hydraulic system including: a hydraulic cylinder including a cylinder tube, a cover closing one opening of the cylinder tube, and a piston disposed within the cylinder tube to form a drive chamber between itself and the cover; a position detector detecting a position of the piston; a drive machine that alternately supplies hydraulic oil to the drive chamber and discharges hydraulic oil from the drive chamber; and a processing circuit that applies a reverse command to the drive machine when the piston moves toward the cover and reaches a reverse command application position, wherein the processing circuit updates the reverse command application position based on a deviation between a target reverse position and an actual reverse position of the piston detected by the position detector.

[0013] According to the present disclosure, a hydraulic system is provided that can reverse the piston of a hydraulic cylinder near the end of its stroke without hitting a cover.

[0014] It is a schematic configuration diagram of a hydraulic system according to a first embodiment. It is a graph showing the relationship between the position of a hydraulic piston and a stroke end. It is a schematic configuration diagram of a hydraulic system of a modified example. It is a schematic configuration diagram of a hydraulic system of another modified example. It is a schematic configuration diagram of a hydraulic system according to a second embodiment. It is a cross-sectional view of a conventional gas booster.

[0015] 1 shows a hydraulic system 1 according to a first embodiment. The hydraulic system 1 includes a gas booster 2 that compresses gas, a driver 7 that drives the gas booster 2, and a control device 9 that controls the driver 7.

[0016] The gas booster 2 is an example of a booster that pressurizes a fluid, and it is also possible to pressurize a liquid with the same structure as the gas booster 2. In this case, compression chambers 3a and 3b, which will be described later, become pressurization chambers.

[0017] In this embodiment, the gas booster 2 is a twin-shaft type, and compresses gas in two stages. The gas to be compressed is not particularly limited, but is, for example, hydrogen. Specifically, the gas booster 2 includes a first structure 21 and a second structure 22.

[0018] The first structure 21 includes the first gas cylinder 3A, the first hydraulic cylinder 4A, and the rod 65, and the second structure 22 includes the second gas cylinder 3B, the second hydraulic cylinder 4B, and the rod 67. In other words, the first hydraulic cylinder 4A and the second hydraulic cylinder 4B are part of the gas booster 2.

[0019] The first structure 21 and the second structure 22 differ significantly in the size of the first gas cylinder 3A and the second gas cylinder 3B. Specifically, the diameter of a gas piston 37 (described later) of the second gas cylinder 3B is smaller than the diameter of a gas piston 33 (described later) of the first gas cylinder 3A. For example, the area of ​​the gas piston 33 is between two and ten times the area of ​​the gas piston 37.

[0020] In the first structure 21, the first gas cylinder 3A and the first hydraulic cylinder 4A are aligned coaxially, and in the second structure 22, the second gas cylinder 3B and the second hydraulic cylinder 4B are aligned coaxially. In this embodiment, the axial directions of the first gas cylinder 3A and the first hydraulic cylinder 4A and the second gas cylinder 3B and the second hydraulic cylinder 4B are vertical. Also, in this embodiment, the first hydraulic cylinder 4A is disposed below the first gas cylinder 3A, and the second hydraulic cylinder 4B is disposed below the second gas cylinder 3B. However, the axial directions of the first gas cylinder 3A and the first hydraulic cylinder 4A and the second gas cylinder 3B and the second hydraulic cylinder 4B may be horizontal.

[0021] With respect to the first structure 21, the first gas cylinder 3A includes a gas cylinder tube 31, a gas cover 32, and a gas piston 33. The gas cylinder tube 31 is cylindrical and extends vertically, and the gas cover 32 closes the upper opening of the gas cylinder tube 31, which is the opposite side to the first hydraulic cylinder 4A. The gas piston 33 is disposed within the gas cylinder tube 31 and forms a compression chamber 3a between itself and the gas cover 32.

[0022] The first gas cylinder 3A also includes a cylindrical jacket 34 that houses the gas cylinder tube 31 and extends from the gas cover 32 to a hydraulic cover 42 (described later). An annular cooling chamber is formed between the gas cylinder tube 31 and the jacket 34, and a coolant is supplied to and discharged from the cooling chamber. However, the jacket 34 may be omitted.

[0023] The gas cover 32 has, for example, a disk shape. In this embodiment, the gas cover 32 has an intake port 5 a and an exhaust port 5 b on an end surface facing radially outward. However, one or both of the intake port 5 a and the exhaust port 5 b may be located on the upper surface of the gas cover 32.

[0024] A gas flow path 51 extending from the suction port 5a to the compression chamber 3a and a gas flow path 53 extending from the compression chamber 3a to the discharge port 5b are formed in the gas cover 32. Check valves 52 and 54 are provided in the gas flow paths 51 and 53, respectively.

[0025] However, the check valve 52 may be provided in the gas supply path 11, which will be described later, and the check valve 54 may be provided in the gas communication path 12, which will be described later. In this case, the suction port 5a and the discharge port 5b may be provided in the upper part of the gas cylinder tube 31, and the gas flow paths 51, 53 may be omitted. When the suction port 5a and the discharge port 5b are provided in the gas cylinder tube 31, the piping that constitutes the gas supply path 11 may pass through the jacket 34 and connect to the suction port 5a, and the piping that constitutes the gas communication path 12 may pass through the jacket 34 and connect to the discharge port 5b.

[0026] The first hydraulic cylinder 4A includes a hydraulic cylinder tube 41, a pair of hydraulic covers 42, 43, and a hydraulic piston 44. The hydraulic cylinder tube 41 is cylindrical and extends vertically, with the hydraulic cover 42 closing the upper opening of the hydraulic cylinder tube 41 and the hydraulic cover 43 closing the lower opening of the hydraulic cylinder tube 41. The hydraulic piston 44 is disposed within the hydraulic cylinder tube 41 and forms a first drive chamber 4a with the upper hydraulic cover 42, and a second drive chamber 4b with the lower hydraulic cover 43.

[0027] In this embodiment, the lower opening of the gas cylinder tube 31 is closed by the hydraulic cover 42. The rod 65 traverses the first drive chamber 4a and passes through the hydraulic cover 42 to connect the hydraulic piston 44 and the gas piston 33. However, similar to the gas booster 100 shown in Figure 6, the lower opening of the gas cylinder tube 31 may be closed by an intermediate cover, and an intermediate tube may be provided between the intermediate cover and the hydraulic cover 42 to surround the space around the rod 65.

[0028] The hydraulic covers 42, 43 are, for example, disk-shaped. In this embodiment, the hydraulic cover 42 has a supply / discharge port 6a on its end surface facing radially outward, and the hydraulic cover 43 has a supply / discharge port 6b on its end surface facing radially outward. However, the positions of the supply / discharge ports 6a, 6b are not limited to this. For example, the supply / discharge port 6a may be provided in the upper part of the hydraulic cylinder tube 41, thereby omitting a hydraulic flow path 61, which will be described later, or the supply / discharge port 6b may be provided in the lower part of the hydraulic cylinder tube 41, thereby omitting a hydraulic flow path 62, which will be described later.

[0029] The hydraulic cover 42 has a hydraulic flow path 61 formed from the supply / discharge port 6a to the first drive chamber 4a, and the hydraulic cover 43 has a hydraulic flow path 62 formed from the supply / discharge port 6b to the second drive chamber 4b.

[0030] With respect to the second structure 22, the second gas cylinder 3B includes a gas cylinder tube 35, a gas cover 36, and a gas piston 37. The gas cylinder tube 35 is cylindrical and extends vertically, and the gas cover 36 closes the upper opening of the gas cylinder tube 35, which is the opposite side to the second hydraulic cylinder 4B. The gas piston 37 is disposed within the gas cylinder tube 35 and forms a compression chamber 3b between itself and the gas cover 36.

[0031] The second gas cylinder 3B also includes a cylindrical jacket 38 that houses the gas cylinder tube 35 and extends from the gas cover 36 to a hydraulic cover 46 (described later). An annular cooling chamber is formed between the gas cylinder tube 35 and the jacket 38, and a coolant is supplied to and discharged from the cooling chamber. However, the jacket 38 may be omitted.

[0032] The gas cover 36 has, for example, a disk shape. In this embodiment, the gas cover 36 has an intake port 5c and an exhaust port 5d on an end surface facing radially outward. However, one or both of the intake port 5c and the exhaust port 5d may be located on the upper surface of the gas cover 36.

[0033] A gas flow path 55 extending from the suction port 5c to the compression chamber 3b and a gas flow path 57 extending from the compression chamber 3b to the discharge port 5d are formed in the gas cover 36. Check valves 56 and 58 are provided in the gas flow paths 55 and 57, respectively.

[0034] However, the check valve 56 may be provided in the gas communication passage 12, which will be described later, and the check valve 58 may be provided in the gas discharge passage 13, which will be described later. In this case, the suction port 5c and the discharge port 5d may be provided in the upper part of the gas cylinder tube 35, and the gas flow passages 55, 57 may be omitted. When the suction port 5c and the discharge port 5d are provided in the gas cylinder tube 35, the piping that constitutes the gas communication passage 12 may pass through the jacket 38 and connect to the suction port 5c, and the piping that constitutes the gas discharge passage 13 may pass through the jacket 38 and connect to the discharge port 5d.

[0035] The second hydraulic cylinder 4B includes a hydraulic cylinder tube 45, a pair of hydraulic covers 46, 47, and a hydraulic piston 48. The hydraulic cylinder tube 45 is cylindrical and extends vertically, with the hydraulic cover 46 closing the upper opening of the hydraulic cylinder tube 45 and the hydraulic cover 47 closing the lower opening of the hydraulic cylinder tube 45. The hydraulic piston 48 is disposed within the hydraulic cylinder tube 45 and forms a first drive chamber 4c between itself and the upper hydraulic cover 46, and a second drive chamber 4d between itself and the lower hydraulic cover 47.

[0036] In this embodiment, the lower opening of the gas cylinder tube 35 is closed by the hydraulic cover 46. The rod 67 traverses the first drive chamber 4c and passes through the hydraulic cover 46 to connect the hydraulic piston 48 and the gas piston 37. However, similar to the gas booster 100 shown in FIG. 6 , the lower opening of the gas cylinder tube 35 may be closed by an intermediate cover, and an intermediate tube may be provided between the intermediate cover and the hydraulic cover 46 to surround the space around the rod 67.

[0037] The hydraulic covers 46, 47 are, for example, disk-shaped. In this embodiment, the hydraulic cover 46 has a supply / discharge port 6c on its end surface facing radially outward, and the hydraulic cover 47 has a supply / discharge port 6d on its end surface facing radially outward. However, the positions of the supply / discharge ports 6c, 6d are not limited to this. For example, the supply / discharge port 6c may be provided in the upper part of the hydraulic cylinder tube 45, thereby omitting a hydraulic flow path 63 (described later), or the supply / discharge port 6d may be provided in the lower part of the hydraulic cylinder tube 45, thereby omitting a hydraulic flow path 64 (described later).

[0038] The hydraulic cover 46 has a hydraulic flow path 63 formed therein that runs from the supply / discharge port 6c to the first drive chamber 4c, and the hydraulic cover 47 has a hydraulic flow path 64 formed therein that runs from the supply / discharge port 6d to the second drive chamber 4d.

[0039] A gas supply passage 11 is connected to the suction port 5a of the first gas cylinder 3A, and a gas discharge passage 13 is connected to the discharge port 5d of the second gas cylinder 3B. The discharge port 5b of the first gas cylinder 3A and the suction port 5c of the second gas cylinder 3B are connected to each other by a gas communication passage 12. Therefore, gas is supplied from the compression chamber 3a of the first gas cylinder 3A to the compression chamber 3b of the second gas cylinder 3B.

[0040] The gas piston 33 of the first gas cylinder 3A and the gas piston 37 of the second gas cylinder 3B move alternately. When the gas piston 33 of the first gas cylinder 3A descends, gas is supplied from the gas supply line 11 to the compression chamber 3a through the gas flow path 51. When the gas piston 33 of the first gas cylinder 3A ascends and the gas piston 37 of the second gas cylinder 3B descends, gas is supplied from the compression chamber 3a of the first gas cylinder 3A through the gas flow path 53, the gas communicating passage 12, and the gas flow path 55 to the compression chamber 3b of the second gas cylinder 3B. At this time, the gas is compressed due to the area difference between the compression chambers 3a and 3b. That is, when the pressure in the compression chamber 3a is lower than the pressure in the compression chamber 3b, the gas is compressed in the compression chamber 3a, the gas flow path 53, and the gas communicating passage 12. When the pressure in the compression chamber 3a is equal to or greater than the pressure in the compression chamber 3b, the gas is compressed in the compression chamber 3a, the gas flow path 53, the gas communicating passage 12, the gas flow path 55, and the compression chamber 3b. When the gas piston 37 of the second gas cylinder 3B rises, the gas in the compression chamber 3b is compressed to at least the pressure downstream of the check valve 58, and the compressed gas is discharged through the gas flow path 57 and the gas discharge path 13.

[0041] The supply / discharge port 6b of the first hydraulic cylinder 4A and the supply / discharge port 6d of the second hydraulic cylinder 4B are connected to each other by a hydraulic communication passage 14. Therefore, the second drive chamber 4b of the first hydraulic cylinder 4A and the second drive chamber 4d of the second hydraulic cylinder 4B are in communication with each other via the hydraulic flow path 62, the hydraulic communication passage 14, and the hydraulic flow path 64.

[0042] The diameter of the hydraulic piston 44 of the first hydraulic cylinder 4A and the diameter of the hydraulic piston 48 of the second hydraulic cylinder 4B are equal. Therefore, the stroke of the hydraulic piston 44 and the gas piston 33 in the first structure 21 and the stroke of the hydraulic piston 48 and the gas piston 37 in the second structure 22 are equal. However, the diameter of the hydraulic piston 44 of the first hydraulic cylinder 4A and the diameter of the hydraulic piston 48 of the second hydraulic cylinder 4B may be different, and the stroke of the hydraulic piston 44 and the gas piston 33 in the first structure 21 and the stroke of the hydraulic piston 48 and the gas piston 37 in the second structure 22 may be different.

[0043] The above-mentioned driving machine 7 alternately supplies hydraulic oil to the first drive chamber 4a of the first hydraulic cylinder 4A and discharges hydraulic oil from the first drive chamber 4c of the second hydraulic cylinder 4B, and discharges hydraulic oil from the first drive chamber 4a of the first hydraulic cylinder 4A and supplies hydraulic oil to the first drive chamber 4c of the second hydraulic cylinder 4B.

[0044] In this embodiment, the driving machine 7 includes a hydraulic pump 71 that can switch the discharge direction of hydraulic oil, and an electric motor 72 that drives the hydraulic pump 71. The electric motor 72 is, for example, a servo motor. The control device 9 described above includes a processing circuit 91 that controls the rotation direction and rotation speed of the electric motor 72. For example, if the electric motor 72 is a servo motor, the processing circuit 91 includes a servo amplifier. If the electric motor 72 is an induction motor, the processing circuit 91 may include an inverter.

[0045] In this embodiment, the hydraulic pump 71 is a bidirectional pump that can switch the discharge direction of hydraulic oil depending on the rotation direction. Also, in this embodiment, the hydraulic pump 71 is a variable displacement pump that can change the tilt angle, and the driving machine 7 includes a regulator 70 that changes the tilt angle of the hydraulic pump 71. The regulator 70 is controlled by the control device 9. For example, the hydraulic pump 71 is an axial piston pump such as a swash plate pump or a bent-axis pump. However, the hydraulic pump 71 may also be a fixed displacement pump that does not require the regulator 70.

[0046] The hydraulic pump 71 is connected to the supply / discharge port 6a of the first hydraulic cylinder 4A by the supply / discharge path 15, and is connected to the supply / discharge port 6c of the second hydraulic cylinder 4B by the supply / discharge path 16. In other words, the hydraulic pump 71 is connected to the first drive chamber 4a of the first hydraulic cylinder 4A via the supply / discharge path 15 and the hydraulic flow path 61, and is connected to the first drive chamber 4c of the second hydraulic cylinder 4B via the supply / discharge path 16 and the hydraulic flow path 63.

[0047] When hydraulic oil is supplied from the hydraulic pump 71 to the first drive chamber 4a of the first hydraulic cylinder 4A through the supply and discharge path 15 and the hydraulic flow path 61, the hydraulic piston 44 in the first structure 21 moves down together with the gas piston 33, and hydraulic oil is supplied from the second drive chamber 4b of the first hydraulic cylinder 4A to the second drive chamber 4d of the second hydraulic cylinder 4B through the hydraulic flow path 62, the hydraulic communicating path 14, and the hydraulic flow path 64. When hydraulic oil is supplied to the second drive chamber 4d, the hydraulic piston 48 in the second structure 22 moves up together with the gas piston 37, and hydraulic oil flows out from the first drive chamber 4c through the hydraulic flow path 63, and the flowed-out hydraulic oil is sucked into the hydraulic pump 71 through the supply and discharge path 16.

[0048] Conversely, when hydraulic oil is supplied from the hydraulic pump 71 to the first drive chamber 4c of the second hydraulic cylinder 4B through the supply and discharge path 16 and the hydraulic flow path 63, the hydraulic piston 48 in the second structure 22 moves down together with the gas piston 37, and hydraulic oil is supplied from the second drive chamber 4d of the second hydraulic cylinder 4B to the second drive chamber 4b of the first hydraulic cylinder 4A through the hydraulic flow path 64, the hydraulic communicating path 14, and the hydraulic flow path 62. When hydraulic oil is supplied to the second drive chamber 4b, the hydraulic piston 44 in the first structure 21 moves up together with the gas piston 33, and hydraulic oil flows out of the first drive chamber 4a through the hydraulic flow path 61, and the flowed-out hydraulic oil is sucked into the hydraulic pump 71 through the supply and discharge path 15.

[0049] Furthermore, in this embodiment, the first hydraulic cylinder 4A is provided with a first position detector 8A that detects the position of the hydraulic piston 44, and the second hydraulic cylinder 4B is provided with a second position detector 8B that detects the position of the hydraulic piston 48. The first position detector 8A and the second position detector 8B are electrically connected to the control device 9. Note that in Fig. 1, some signal lines are omitted to simplify the drawing.

[0050] In this embodiment, the first position detector 8A is a stroke sensor that detects the position of the hydraulic piston 44 over the entire length between the stroke ends defined by the hydraulic covers 42, 43 of the first hydraulic cylinder 4A. However, it is sufficient that the first position detector 8A is able to detect the position of the hydraulic piston 44 within a predetermined range from at least one of the stroke ends.

[0051] Similarly, in this embodiment, the second position detector 8B is a stroke sensor that detects the position of the hydraulic piston 48 over the entire length between the stroke ends defined by the hydraulic covers 46, 47 of the second hydraulic cylinder 4B. However, it is sufficient that the second position detector 8B is able to detect the position of the hydraulic piston 48 within a predetermined range from at least one of the stroke ends.

[0052] The first position detector 8A and the second position detector 8B have the same structure. In this embodiment, the first position detector 8A and the second position detector 8B are each a magnetostrictive linear sensor. However, the first position detector 8A and the second position detector 8B may each be another type of sensor, such as a laser type or an infrared type.

[0053] More specifically, the first position detector 8A includes a probe 81 attached to the hydraulic cover 43 and extending through the hydraulic piston 44, and a magnet 84 attached to the hydraulic piston 44. The probe 81 includes a head 82 located outside the hydraulic cover 43, and a sensor rod 83 extending from the head 82. In this embodiment, the magnet 84 is ring-shaped and is passed through by the sensor rod 83. The hydraulic piston 44 and the rod 65 are provided with holes 66 to avoid interference with the sensor rod 83.

[0054] Similarly, the second position detector 8B includes a probe 81 attached to the hydraulic cover 47 and extending through the hydraulic piston 48, and a magnet 84 attached to the hydraulic piston 48. The probe 81 includes a head 82 located outside the hydraulic cover 47, and a sensor rod 83 extending from the head 82. In this embodiment, the magnet 84 is ring-shaped, and is passed through by the sensor rod 83. The hydraulic piston 48 and the rod 67 are provided with holes 68 to avoid interference with the sensor rod 83.

[0055] With respect to the control device 9, the functions of the elements disclosed herein can be performed using circuits or processing circuits, including general-purpose processors, special-purpose processors, integrated circuits, application-specific integrated circuits (ASICs), conventional circuits, and / or combinations thereof, configured or programmed to perform the disclosed functions. A processor is considered a processing circuit or circuit because it includes transistors and other circuitry. In this disclosure, a circuit, unit, or means is hardware that performs the recited functions or hardware that is programmed to perform the recited functions. The hardware may be hardware disclosed herein or other known hardware that is programmed or configured to perform the recited functions. Where the hardware is a processor, which is considered a type of circuit, the circuit, means, or unit is a combination of hardware and software, and the software is used to configure the hardware and / or processor.

[0056] The processing circuit 91 of the control device 9 reverses the rotation direction of the electric motor 72 based on the detection results of the first position detector 8A and the second position detector 8B. The command to reverse the rotation direction of the electric motor 72 given to the driving machine 7 by the processing circuit 91 is the reversal command that the processing circuit 91 applies to the driving machine 7.

[0057] More specifically, when the hydraulic piston 44 of the first hydraulic cylinder 4A rises, in other words, moves toward the hydraulic cover 42, the processing circuit 91 applies a reverse rotation command to the driving machine 7 when the hydraulic piston 44 reaches a reverse rotation command application position CP. In other words, when the position of the hydraulic piston 44 detected by the first position detector 8A coincides with the reverse rotation command application position CP, the processing circuit 91 reverses the rotation direction of the electric motor 72 from the direction in which the hydraulic pump 71 discharges hydraulic oil to the supply and discharge path 16 to the direction in which the hydraulic pump 71 discharges hydraulic oil to the supply and discharge path 15.

[0058] Furthermore, when the hydraulic piston 48 of the second hydraulic cylinder 4B rises, in other words, moves toward the hydraulic cover 46, the processing circuit 91 applies a reverse rotation command to the driving machine 7 when the hydraulic piston 48 reaches a reverse rotation command application position CP. In other words, when the position of the hydraulic piston 48 detected by the second position detector 8B matches the reverse rotation command application position CP, the processing circuit 91 reverses the rotation direction of the electric motor 72 from the direction in which the hydraulic pump 71 discharges hydraulic oil to the supply and discharge path 15 to the direction in which the hydraulic pump 71 discharges hydraulic oil to the supply and discharge path 16.

[0059] Furthermore, when the hydraulic piston 44 of the first hydraulic cylinder 4A rises, the processing circuit 91 updates the reverse command application position CP based on the deviation ΔL (= TP - RP) between the target reverse position TP and the actual reverse position RP of the hydraulic piston 44 detected by the first position detector 8A, as shown in Figure 2. The target reverse position TP is a position several millimeters away from the stroke end.

[0060] In this embodiment, the processing circuit 91 calculates the current reverse command application position CP(n) by adding the previous reverse command application position CP(n-1) to a correction value CV (= ΔL × K) obtained by multiplying the deviation ΔL (= TP - RP(n-1)) between the target reverse position TP and the previous actual reverse position RP(n-1) of the hydraulic piston 44 by a gain K (CP(n) = CP(n-1) + CV). This makes it possible to update the reverse command application position CP with a simple calculation. The gain K is a value between 0 and 1 and may be a fixed value or may vary depending on the deviation ΔL.

[0061] Similarly, when the hydraulic piston 48 of the second hydraulic cylinder 4B rises, the processing circuit 91 updates the reverse command application position CP based on the deviation ΔL (= TP - RP) between the target reverse position TP and the actual reverse position RP of the hydraulic piston 48 detected by the second position detector 8B, as shown in Figure 2. The target reverse position TP is a position several millimeters away from the stroke end.

[0062] In this embodiment, the processing circuit 91 calculates the current reverse command application position CP(n) by adding the previous reverse command application position CP(n-1) to a correction value CV (= ΔL × K) obtained by multiplying the deviation ΔL (= TP - RP(n-1)) between the target reverse position TP and the previous actual reverse position RP(n-1) of the hydraulic piston 48 by a gain K (CP(n) = CP(n-1) + CV). This makes it possible to update the reverse command application position CP with a simple calculation. The gain K is a value ranging from 0 to 1 and may be a fixed value or may vary depending on the deviation ΔL.

[0063] As described above, in the hydraulic system 1 of this embodiment, the first position detector 8A is used in the first hydraulic cylinder 4A, so it is possible to accurately grasp the position of the hydraulic piston 44. Moreover, since the reverse command application position CP is updated based on the deviation ΔL between the target reverse position TP and the actual reverse position RP of the hydraulic piston 44 detected by the first position detector 8A, it is possible to reverse the hydraulic piston 44 of the first hydraulic cylinder 4A near the stroke end without hitting the hydraulic cover 42.

[0064] Furthermore, since the second hydraulic cylinder 4B uses the second position detector 8B, it is possible to accurately grasp the position of the hydraulic piston 48. Moreover, since the reverse command application position CP is updated based on the deviation ΔL between the target reverse position TP and the actual reverse position RP of the hydraulic piston 448 detected by the second position detector 8B, it is possible to reverse the hydraulic piston 48 of the second hydraulic cylinder 4B near the stroke end without hitting the hydraulic cover 46.

[0065] Furthermore, in this embodiment, the first hydraulic cylinder 4A and the second hydraulic cylinder 4B are part of the gas booster 2. In the gas booster 2, the hydraulic load may fluctuate when compressing gas, in other words, when the fluid is pressurized, but even if the hydraulic load fluctuates in this way, the hydraulic piston 44 of the first hydraulic cylinder 4A can be reversed near the stroke end without hitting the hydraulic cover 42, and the hydraulic piston 48 of the second hydraulic cylinder 4B can be reversed near the stroke end without hitting the hydraulic cover 46.

[0066] 3 , the supply / discharge port 6a of the first hydraulic cylinder 4A and the supply / discharge port 6c of the second hydraulic cylinder 4B may be connected to each other by a hydraulic communication passage 14, and a hydraulic pump 71 may be connected to the supply / discharge port 6b of the first hydraulic cylinder 4A by a supply / discharge passage 15 and to the supply / discharge port 6d of the second hydraulic cylinder 4B by a supply / discharge passage 16. In this case, the driver 7 alternately supplies hydraulic oil to the second drive chamber 4b of the first hydraulic cylinder 4A and discharges hydraulic oil from the second drive chamber 4d of the second hydraulic cylinder 4B, and discharges hydraulic oil from the second drive chamber 4b of the first hydraulic cylinder 4A and supplies hydraulic oil to the second drive chamber 4d of the second hydraulic cylinder 4B.

[0067] 1 or the hydraulic system 1A shown in FIG. 3, when the hydraulic piston 44 of the first hydraulic cylinder 4A descends, the processing circuit 91 may reverse the rotation direction of the electric motor 72 when the position of the hydraulic piston 44 detected by the first position detector 8A coincides with the reverse command application position CP, as in the above embodiment. This allows the hydraulic piston 44 of the first hydraulic cylinder 4A to reverse the rotation direction near the stroke end without hitting the hydraulic cover 43.

[0068] 1 or the hydraulic system 1A shown in Fig. 3, when the hydraulic piston 48 of the second hydraulic cylinder 4B descends, the processing circuit 91 may reverse the rotation direction of the electric motor 72 when the position of the hydraulic piston 48 detected by the second position detector 8B coincides with the reverse command application position CP, as in the above embodiment. This allows the hydraulic piston 48 of the second hydraulic cylinder 4B to reverse the rotation direction near the stroke end without hitting the hydraulic cover 47.

[0069] 4, the first gas cylinder 3A and the second gas cylinder 3B may be connected in parallel by a gas supply line 17 and a gas discharge line 18, and the gas booster 2 may compress the gas in a single stage. In this case, the diameter of the gas piston 37 of the second gas cylinder 3B is equal to the diameter of the gas piston 33 of the first gas cylinder 3A.

[0070] 1, 3, and 4, the hydraulic pump 71 may be a bi-directional tilt pump that rotates in one direction and whose discharge direction of hydraulic oil can be switched depending on the tilt direction of the swash plate or inclined axis from the center. In this case, the reversal command applied to the driver 7 by the processing circuit 91 of the control device 9 is a command to reverse the tilt direction of the bi-directional tilt pump. Furthermore, when the hydraulic pump 71 is a bi-directional tilt pump, the processing circuit 91 of the control device 9 may keep the rotation speed of the electric motor 74 constant and adjust the tilt angle of the bi-directional tilt pump.

[0071] Second Embodiment A hydraulic system 1C according to a second embodiment is shown in Fig. 5. In this embodiment, the same components as those in the first embodiment are denoted by the same reference numerals, and redundant explanations will be omitted.

[0072] In this embodiment, the driving machine 7 includes a hydraulic pump 73 that rotates in only one direction, an electric motor 74 that drives the hydraulic pump 73, and a switching valve 76. In this embodiment, the hydraulic pump 73 is a variable displacement pump whose tilt angle is changed by a regulator 70, but the hydraulic pump 73 may also be a fixed displacement pump that does not require the regulator 70.

[0073] The switching valve 76 is connected to the hydraulic pump 73 via a pump line 75 and to a tank via a tank line 77. The switching valve 76 is also connected to the supply / discharge port 6a of the first hydraulic cylinder 4A via the supply / discharge line 15 and to the supply / discharge port 6c of the second hydraulic cylinder 4B via the supply / discharge line 16. In other words, the switching valve 76 is connected to the first drive chamber 4a of the first hydraulic cylinder 4A via the supply / discharge line 15 and the hydraulic flow path 61, and is connected to the first drive chamber 4c of the second hydraulic cylinder 4B via the supply / discharge line 16 and the hydraulic flow path 63.

[0074] In this embodiment, the processing circuit 91 of the control device 9 switches the switching valve 76 between a neutral position, a first operating position, and a second operating position. A relief path provided with a relief valve branches off from the pump path 75 and leads to a tank, and the relief valve maintains the discharge pressure of the hydraulic pump 73 at or below a certain value.

[0075] In the neutral position, the switching valve 76 blocks all of the pump line 75, the tank line 77, and the supply and discharge lines 15 and 16. This prohibits the supply of hydraulic oil from the hydraulic pump 73 to the first drive chamber 4a of the first hydraulic cylinder 4A and the first drive chamber 4c of the second hydraulic cylinder 4B. In the first operating position shown on the left in FIG. 5 , the switching valve 76 connects the pump line 75 to the supply and discharge line 16 and connects the supply and discharge line 15 to the tank line 77. This allows the supply of hydraulic oil from the hydraulic pump 73 to the first drive chamber 4c of the second hydraulic cylinder 4B and the discharge of hydraulic oil from the first drive chamber 4a of the first hydraulic cylinder 4A to the tank. In the second operating position shown on the right in FIG. 5 , the switching valve 76 connects the pump line 75 to the supply and discharge line 15 and connects the supply and discharge line 16 to the tank line 77. This allows the hydraulic pump 73 to supply hydraulic oil to the first drive chamber 4a of the first hydraulic cylinder 4A and the hydraulic oil to be discharged from the first drive chamber 4c of the second hydraulic cylinder 4B to the tank.

[0076] In this embodiment, the opening area of ​​the switching valve 76 in the first operating position and the second operating position is a fixed value, and the processing circuit 91 of the control device 9 adjusts the rotation speed of the electric motor 74. However, the switching valve 76 may be a proportional valve whose opening area in the first operating position and the second operating position is variable, and the processing circuit 91 may keep the rotation speed of the electric motor 74 constant and adjust the opening area of ​​the switching valve 76 in the first operating position or the second operating position.

[0077] In this embodiment, the reverse rotation command applied by the processing circuit 91 of the control device 9 to the driving machine 7 is a command to switch the switching valve 76 from one of the first operating position and the second operating position to the other. As in the first embodiment, the processing circuit 91 applies the reverse rotation command to the driving machine 7 when the hydraulic piston 44 of the first hydraulic cylinder 4A or the hydraulic piston 48 of the second hydraulic cylinder 4B reaches the reverse rotation command application position CP. Furthermore, the processing circuit 91 updates the reverse rotation command application position CP based on the deviation ΔL between the target reverse position TP and the actual reverse position RP of the hydraulic piston 44 or the deviation ΔL between the target reverse position TP and the actual reverse position RP of the hydraulic piston 48. As a result, the same effects as those of the first embodiment can be achieved in this embodiment.

[0078] However, in a rotation speed control method in which the hydraulic pump 71 is a bidirectional pump as in the first embodiment, fluctuations in the deceleration distance from the reverse command application position CP to the reverse position tend to be greater than in a switching valve control method as in this embodiment or a tilt angle control method in which the hydraulic pump 71 is a bidirectional tilt pump as in the modified example of the first embodiment. Therefore, the present disclosure is particularly useful for rotation speed control methods. The configuration of the driving machine 7 shown in Figure 5 can be used not only in the hydraulic system 1 shown in Figure 1, but also in the hydraulic system 1A shown in Figure 3 or the hydraulic system 1B shown in Figure 4.

[0079] Other Embodiments The present disclosure is not limited to the above-described embodiments, and various modifications are possible without departing from the gist of the present disclosure.

[0080] For example, the gas booster 2 may be a uniaxial type in which a double-rod hydraulic cylinder is disposed between two gas cylinders. This configuration is also applicable to a booster that pressurizes a liquid.

[0081] <Summary> In a first aspect, the present disclosure provides a hydraulic system including: a hydraulic cylinder including a cylinder tube, a cover closing one opening of the cylinder tube, and a piston disposed within the cylinder tube to form a drive chamber between itself and the cover; a position detector detecting a position of the piston; a driver that alternately supplies hydraulic oil to the drive chamber and discharges hydraulic oil from the drive chamber; and a processing circuit that applies a reverse command to the driver when the piston moves toward the cover and reaches a reverse command application position, wherein the processing circuit updates the reverse command application position based on a deviation between a target reverse position and an actual reverse position of the piston detected by the position detector.

[0082] According to the above configuration, since the position detector is used, the position of the piston can be accurately grasped. Moreover, since the reverse command application position is updated based on the deviation between the target reverse position and the actual reverse position of the piston detected by the position detector, the piston of the hydraulic cylinder can be reversed near the stroke end without hitting the cover.

[0083] In a second aspect, in the first aspect, the hydraulic cylinder may be part of a booster that boosts the fluid. In a booster, the hydraulic load may fluctuate when the fluid is boosted, but even if the hydraulic load fluctuates, with this configuration, the piston of the hydraulic cylinder can reverse near the stroke end without hitting the cover.

[0084] In a third aspect, the booster according to the second aspect may include a first hydraulic cylinder and a second hydraulic cylinder as the hydraulic cylinders, the position detector may include a first position detector that detects the position of the piston of the first hydraulic cylinder and a second position detector that detects the position of the piston of the second hydraulic cylinder, the driver may include a bidirectional pump connected to the drive chamber of the first hydraulic cylinder and the drive chamber of the second hydraulic cylinder, and an electric motor that drives the bidirectional pump, and the reverse command may be a command to reverse the rotation direction of the electric motor. With this configuration, the present disclosure is particularly useful for a rotation speed control method, because fluctuations in the deceleration distance from the position where the reverse command is applied to the position where the reverse rotation occurs tend to be greater with a rotation speed control method than with a tilt angle control method or a switching valve control method.

[0085] As a fourth aspect, in the second aspect, for example, the booster may include a first hydraulic cylinder and a second hydraulic cylinder as the hydraulic cylinders, the position detector may include a first position detector that detects the position of the piston of the first hydraulic cylinder and a second position detector that detects the position of the piston of the second hydraulic cylinder, the driver may include a double-tilt pump connected to the drive chamber of the first hydraulic cylinder and the drive chamber of the second hydraulic cylinder, and a regulator that changes the tilt angle of the double-tilt pump, and the reversal command may be a command to reverse the tilt direction of the double-tilt pump.

[0086] As a fifth aspect, in the second aspect, for example, the booster may include a first hydraulic cylinder and a second hydraulic cylinder as the hydraulic cylinders, the position detector may include a first position detector that detects a position of the piston of the first hydraulic cylinder and a second position detector that detects a position of the piston of the second hydraulic cylinder, the driving machine may include a switching valve connected to the drive chamber of the first hydraulic cylinder and the drive chamber of the second hydraulic cylinder, and a hydraulic pump connected to the switching valve, the switching valve may be switched between a neutral position that prohibits the supply of hydraulic oil from the hydraulic pump to the drive chamber of the first hydraulic cylinder and the drive chamber of the second hydraulic cylinder, a first operating position that allows the supply of hydraulic oil from the hydraulic pump to the drive chamber of the second hydraulic cylinder, and a second operating position that allows the supply of hydraulic oil from the hydraulic pump to the drive chamber of the first hydraulic cylinder, and the reversal command may be a command to switch the switching valve from one of the first operating position and the second operating position to the other.

[0087] As a sixth aspect, in any of the first to fifth aspects, the deviation may be a deviation between the target reverse rotation position and a previous actual reverse rotation position of the piston, and the processing circuit may calculate the current reverse rotation command application position by adding a correction value obtained by multiplying the deviation by a gain to the previous reverse rotation command application position. With this configuration, the reverse rotation command application position can be updated with a simple calculation.

Claims

1. A hydraulic system comprising: a hydraulic cylinder including a cylinder tube, a cover closing one opening of the cylinder tube, and a piston disposed within the cylinder tube to form a drive chamber between the cover and the cylinder tube; a position detector detecting the position of the piston; a drive machine that alternately supplies hydraulic oil to the drive chamber and discharges hydraulic oil from the drive chamber; and a processing circuit that applies a reverse command to the drive machine when the piston moves toward the cover and reaches a reverse command application position, wherein the processing circuit updates the reverse command application position based on the deviation between a target reverse position and the actual reverse position of the piston detected by the position detector.

2. The hydraulic system of claim 1, wherein the hydraulic cylinder is part of a booster that pressurizes a fluid.

3. The hydraulic system according to claim 2, wherein the booster includes a first hydraulic cylinder and a second hydraulic cylinder as the hydraulic cylinders, the position detector includes a first position detector that detects the position of the piston of the first hydraulic cylinder and a second position detector that detects the position of the piston of the second hydraulic cylinder, the driver includes a bidirectional pump connected to the drive chamber of the first hydraulic cylinder and the drive chamber of the second hydraulic cylinder, and an electric motor that drives the bidirectional pump, and the reversal command is a command to reverse the rotation direction of the electric motor.

4. The hydraulic system according to claim 2, wherein the booster includes a first hydraulic cylinder and a second hydraulic cylinder as the hydraulic cylinders, the position detector includes a first position detector that detects the position of the piston of the first hydraulic cylinder and a second position detector that detects the position of the piston of the second hydraulic cylinder, the driver includes a double tilt pump connected to the drive chamber of the first hydraulic cylinder and the drive chamber of the second hydraulic cylinder, and a regulator that changes the tilt angle of the double tilt pump, and the reversal command is a command to reverse the tilt direction of the double tilt pump.

5. The hydraulic system according to claim 2, wherein the booster includes a first hydraulic cylinder and a second hydraulic cylinder as the hydraulic cylinders, the position detector includes a first position detector that detects the position of the piston of the first hydraulic cylinder and a second position detector that detects the position of the piston of the second hydraulic cylinder, the driver includes a changeover valve connected to the drive chamber of the first hydraulic cylinder and the drive chamber of the second hydraulic cylinder, and a hydraulic pump connected to the changeover valve, the changeover valve being switched between a neutral position that prohibits the supply of hydraulic oil from the hydraulic pump to the drive chamber of the first hydraulic cylinder and the drive chamber of the second hydraulic cylinder, a first operating position that allows the supply of hydraulic oil from the hydraulic pump to the drive chamber of the second hydraulic cylinder, and a second operating position that allows the supply of hydraulic oil from the hydraulic pump to the drive chamber of the first hydraulic cylinder, and the reversal command is a command to switch the changeover valve from one of the first operating position and the second operating position to the other.

6. A hydraulic system according to any one of claims 1 to 5, wherein the deviation is a deviation between the target reversal position and the previous actual reversal position of the piston, and the processing circuit calculates the current reversal command application position by adding a correction value obtained by multiplying the deviation by a gain to the previous reversal command application position.

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