JP2024086360A - Hydraulic drive system and method for controlling hydraulic drive system - Google Patents

Abstract

To expand a range of pressure supplied to a hydraulic oil chamber of a hydraulic cylinder.SOLUTION: A hydraulic drive device 100 includes: a hydraulic cylinder 120 having a hydraulic oil chamber 121; a first accumulator 130 partitioned to a first oil chamber 131 communicated with the hydraulic oil chamber 121 and a first gas chamber 132; a second accumulator 140 partitioned to a second oil chamber 141 to which a hydraulic oil is supplied from an oil supply part 110 and a second gas chamber 142; a hydraulic booster 150 for adjusting the capacity of the second oil chamber 141; a gas flow passage 160 for communicating the first gas chamber 132 and the second gas chamber 142; a gas on-off valve 170 disposed in the gas flow passage 160; and a control part 190 for switching the gas on-off valve 170 to the on state in response to a fact that the capacity of the first gas chamber 132 has become first predetermined capacity or less when increasing the pressure of the hydraulic oil chamber 121 gradually, and increasing the capacity of the second oil chamber 141 until the capacity of the second gas chamber 142 becomes a second predetermined capacity or less.SELECTED DRAWING: Figure 2

Description

This disclosure relates to a hydraulic drive system and a method for controlling the hydraulic drive system.

Crushers such as vertical mills are configured to crush raw materials such as biomass pellets and coal supplied to them by pressing a rotatably supported crushing roller against a crushing table that rotates by power (for example, Patent Document 1). The crusher disclosed in Patent Document 1 has an accumulator with a gas-filled bladder placed in the piping for hydraulic oil supplied to the hydraulic cylinder to suppress hydraulic pulsation.

Japanese Patent Application Laid-Open No. 62-38254

The pulverizer pulverizes the solid fuel supplied to the boiler. The amount of fuel supplied to the boiler varies between approximately 100% and 15% depending on the load required of the boiler. Meanwhile, the operable range of conventional pulverizers is around 100% to 30%. This is because, while it is necessary to change the driving force that presses the pulverizer roller against the pulverizer table depending on the amount of solid fuel supplied to the pulverizer, it is necessary to limit the pressure range of the hydraulic oil supplied to the hydraulic cylinder that generates the driving force.

The hydraulic oil supplied to the hydraulic cylinder is incompressible, so when the hydraulic cylinder is displaced, a hammer phenomenon occurs in which high pressure is generated instantaneously. To suppress the hydraulic pulsation caused by this hammer phenomenon, an accumulator is used that contains a bladder filled with a compressible fluid gas (e.g., nitrogen gas).

The volume of gas sealed in the bladder built into the accumulator changes according to changes in hydraulic oil pressure. If the hydraulic oil pressure drops and the volume of the bladder becomes too large, the bladder will come into contact with the valve that directs the hydraulic oil to the accumulator, and if the hydraulic oil pressure increases and the volume of the bladder becomes too small, the bladder will come into contact with the valve that directs gas to the bladder, which may damage the bladder. Therefore, to prevent damage to the bladder, the range of hydraulic oil pressure supplied to the hydraulic cylinder is limited. If the amount of fuel supplied to the boiler is excessively small, this restriction on the hydraulic pressure range makes it impossible to lower the pressure further below the lower limit of the hydraulic oil pressure range, and it is necessary, for example, to stop some of the multiple pulverizers in operation and increase the amount of fuel supplied to each pulverizer.

The present disclosure has been made in consideration of these circumstances, and aims to provide a hydraulic drive device and a control method for a hydraulic drive device that can expand the range of pressure supplied to the hydraulic oil chamber of a hydraulic cylinder.

In order to solve the above problems, the hydraulic drive system and the control method for the hydraulic drive system of the present disclosure employ the following measures.
A hydraulic drive device according to one aspect of the present disclosure includes an oil supply unit, a hydraulic cylinder having a piston that forms a hydraulic oil chamber to which hydraulic oil is supplied from the oil supply unit, and drives the piston by the pressure of the hydraulic oil supplied to the hydraulic oil chamber, a first accumulator in which a first oil chamber communicating with the hydraulic oil chamber and a first gas chamber in which a first gas is sealed are partitioned by a first partition, a second accumulator in which a second oil chamber to which the hydraulic oil is supplied from the oil supply unit and a second gas chamber in which a second gas is sealed are partitioned by a second partition, and a pressure regulator that adjusts the volume of the second oil chamber. the control unit controls the gas on-off valve and the adjustment unit to switch the gas on-off valve from a closed state to an open state when the volume of the first gas chamber becomes equal to or less than a first predetermined volume when the pressure of the hydraulic oil chamber is gradually increased, and to increase the volume of the second oil chamber until the volume of the second gas chamber becomes equal to or less than a second predetermined volume.

In addition, in a control method for a hydraulic drive device according to one aspect of the present disclosure, the hydraulic drive device includes an oil supply unit, a piston that forms a hydraulic oil chamber to which hydraulic oil is supplied from the oil supply unit, a hydraulic cylinder that drives the piston by the pressure of the hydraulic oil supplied to the hydraulic oil chamber, a first accumulator that is partitioned by a first partition between a first oil chamber that communicates with the hydraulic oil chamber and a first gas chamber in which a first gas is sealed, and a second oil chamber to which the hydraulic oil is supplied from the oil supply unit and a second gas chamber in which a second gas is sealed, which are partitioned by a second partition. The pressure control device includes a second accumulator, an adjustment unit that adjusts the volume of the second oil chamber, a gas flow path that connects the first gas chamber and the second gas chamber, and a gas on-off valve that is arranged in the gas flow path, and includes an adjustment process that switches the gas on-off valve from a closed state to an open state when the volume of the first gas chamber becomes equal to or less than a first predetermined volume, and controls the gas on-off valve and the adjustment unit to increase the volume of the second oil chamber until the volume of the second gas chamber becomes equal to or less than a second predetermined volume, when the pressure of the hydraulic oil chamber is gradually increased.

The present disclosure provides a hydraulic drive system and a method for controlling the hydraulic drive system that can expand the range of pressure supplied to the hydraulic oil chamber of a hydraulic cylinder.

FIG. 1 is a vertical cross-sectional view showing a crusher according to a first embodiment of the present disclosure. 1 is a configuration diagram showing a hydraulic drive device according to a first embodiment of the present disclosure, illustrating a state in which pressurization of a hydraulic oil chamber of a hydraulic cylinder is started. FIG. 4 is a flowchart showing a control method for the hydraulic drive system according to the first embodiment of the present disclosure. 1 is a configuration diagram showing a hydraulic drive device according to a first embodiment of the present disclosure, illustrating a state in which the pressure of hydraulic oil in a first oil chamber has reached or exceeded a switching pressure. 1 is a configuration diagram showing a hydraulic drive device according to a first embodiment of the present disclosure, illustrating a state in which the transfer of hydraulic oil to a second oil chamber is completed. FIG. 1 is a configuration diagram showing a hydraulic drive system according to a first embodiment of the present disclosure, illustrating a state in which the pressure in a first oil chamber has reached or exceeded an upper limit pressure. FIG. 11 is a configuration diagram showing a hydraulic drive device according to a second embodiment of the present disclosure, illustrating a state in which the pressure of the hydraulic oil in the first oil chamber has reached or exceeded the switching pressure. 13 is a diagram showing a modified example in which the first accumulator and the second accumulator are accommodated inside a single housing. FIG.

First Embodiment
Hereinafter, a hydraulic drive system 100 and a control method for the hydraulic drive system 100 according to a first embodiment of the present disclosure will be described with reference to the drawings. The hydraulic drive system 100 according to the present disclosure is a device used in a mill (pulverizer) 10 that supplies pulverized fuel to a boiler (not shown) of a power generation plant (not shown). Fig. 1 is a vertical cross-sectional view showing the mill 10 according to the first embodiment of the present disclosure.

The mill 10 includes a housing 11, a grinding table 12, grinding rollers 13, a reducer 14, a mill motor 15 connected to the reducer 14 to rotate the grinding table 12, a rotary classifier 16, a coal supply pipe 17, and a classifier motor 18 to rotate the rotary classifier 16.

The housing 11 is a cylindrical case with a central axis Ch extending in the vertical direction, and is a case that houses the grinding table 12, the grinding roller 13, the rotary classifier 16, and the coal feed pipe 17. An opening 11a is formed in the peripheral wall of the housing 11, and the grinding roller 13 and the journal head 45 that supports the grinding roller 13 are installed near the opening 11a. When the grinding roller 13 and the like are installed, the opening 11a is covered by a roller cover 70 that, together with the housing 11, forms the outer wall of the mill 10.

A coal feed pipe 17 is attached to the center of the ceiling 42 of the housing 11. This coal feed pipe 17 supplies solid fuel introduced through a coal feeder (not shown) into the housing 11, and is positioned vertically at the center of the housing 11 with its lower end extending into the interior of the housing 11.

A reduction gear 14 is installed near the bottom surface 41 of the housing 11, and a grinding table 12 is arranged to rotate freely around an axis Ch by a driving force transmitted from a mill motor 15 connected to the reduction gear 14.

The grinding table 12 is a circular member in plan view, and is arranged so that the lower end of the coal supply pipe 17 faces it. The coal supply pipe 17 supplies solid fuel (for example, coal or biomass fuel in this embodiment) from above toward the grinding table 12 below. The grinding table 12 grinds the supplied solid fuel by sandwiching it between the grinding rollers 13.

When solid fuel is fed from the coal feed pipe 17 toward the center of the grinding table 12, the centrifugal force generated by the rotation of the grinding table 12 guides the solid fuel to the outer periphery of the grinding table 12, where it is pinched between the grinding table 12 and the grinding roller 13 and pulverized. The pulverized solid fuel is guided through a carrier gas flow path (not shown) and blown upward by the carrier gas (hereinafter referred to as "primary air") blown out from the blowing port 12b, and is guided to the rotary classifier 16.

Between the outer circumferential surface of the grinding table 12 and the inner circumferential surface of the housing 11, there is an air outlet 12b that allows the primary air flowing into the lower part of the housing 11 to flow out into the space above the grinding table 12 within the housing 11. A swirling blade 12a is installed on the outer circumferential side of the grinding table 12 located at the outlet of the air outlet 12b, and applies a swirling force to the primary air blown upward from the air outlet 12b.

The primary air, given a swirling force by the swirling blades 12a, becomes an airflow with a swirling velocity component, and transports the solid fuel pulverized on the grinding table 12 to the rotary classifier 16 located at the top inside the housing 11. Among the pulverized solid fuel, particles larger than a predetermined particle size are classified by the rotary classifier 16, or fall without reaching the rotary classifier 16 and are returned to the grinding table 12, where they are pulverized again between the grinding table 12 and the grinding roller 13.

The crushing roller 13 is a rotating body that crushes the solid fuel supplied onto the crushing table 12 from the coal supply pipe 17. The crushing roller 13 is pressed against the upper surface of the crushing table 12 to crush the solid fuel in cooperation with the crushing table 12. Although only one representative crushing roller 13 is shown in FIG. 1, multiple crushing rollers 13 are arranged at regular intervals in the circumferential direction so as to press against the upper surface of the crushing table 12.

For example, three crushing rollers 13 are arranged on the outer periphery at equal intervals in the circumferential direction, with an angular interval of 120°. In this case, the portions where the three crushing rollers 13 come into contact with the upper surface of the crushing table 12 (the portions that press against each other) are equidistant from the central axis of rotation of the crushing table 12. In addition, three openings 11a are formed in the housing 11 at equal intervals in the circumferential direction.

The grinding roller 13 is supported by a journal head 45 having a support arm 47 and a support shaft 48. The grinding roller 13 supported by the journal head 45 can be swung and displaced up and down as the journal head 45 rotates around the support shaft 48 that extends horizontally, and can move closer to and away from the top surface of the grinding table 12.

When the grinding table 12 rotates, the grinding roller 13 receives a rotational force from the grinding table 12 and rotates with the grinding table 12 while the outer circumferential surface is in contact with the solid fuel on the upper surface of the grinding table 12. When solid fuel is supplied from the coal supply pipe 17, the solid fuel is pressed between the grinding roller 13 and the grinding table 12 and crushed. This pressing force is called the grinding load.

The intermediate piston 61 of the load application device 60 is in contact with the upper end (at least the portion above the support shaft 48) of the support arm 47 of the journal head 45. The load application device 60 is a device that applies a load (crushing load) to the support arm 47 so as to press the crushing roller 13 against the crushing table 12, and is fixed to the roller cover 70.

The load application device 60 is a device that applies a crushing load along the axis Cf to the upper end of the support arm 47. The load application device 60 has an intermediate piston 61 and a piston housing 62, and is configured so that the operating force generated in the hydraulic cylinder 120 is transmitted from the piston 122 of the hydraulic cylinder 120 to the upper end of the support arm 47 via the intermediate piston 61. The intermediate piston 61 is housed in the piston housing 62 and is slidable along the direction of the axis Cf.

A gap bolt 80 is in contact with the lower end (at least the portion below the support shaft 48) of the support arm 47 of the journal head 45. The gap bolt 80 is a device that provides a gap between the grinding roller 13 and the grinding table 12 so that the grinding roller 13 does not come into contact with the grinding table 12 when there is no solid fuel on the upper surface of the grinding table 12, and is fixed to the roller cover 70. The size of the gap is determined by the amount of protrusion of the gap bolt 80.

The reducer 14 is connected to the mill motor 15 and transmits the driving force of the mill motor 15 to the grinding table 12, causing the grinding table 12 to rotate around its central axis.

The rotary classifier 16 is mounted on the upper part of the housing 11 and has a hollow inverted cone-shaped exterior. The rotary classifier 16 is equipped with a number of blades extending vertically around its outer periphery. The blades are provided at a predetermined interval (even interval) around the central axis of the rotary classifier 16. The rotary classifier 16 classifies the solid fuel (hereinafter, the pulverized solid fuel is referred to as "pulverized fuel") pulverized by the pulverizing table 12 and the pulverizing roller 13 into particles larger than a predetermined particle size (for example, 70 to 100 μm for coal) (hereinafter, the pulverized fuel exceeding the predetermined particle size is referred to as "coarse fuel") and particles smaller than the predetermined particle size (hereinafter, the pulverized fuel smaller than the predetermined particle size is referred to as "fine fuel").

The rotary classifier 16 is given a rotational driving force by the classifier motor 18 and rotates around the coal feed pipe 17 around a cylindrical axis (not shown) that extends in the vertical direction of the housing 11. In this embodiment, a rotary classifier 16 is used, but a fixed classifier having a fixed hollow inverted cone-shaped casing and multiple fixed swirling blades on the outer periphery of the casing may also be used.

When the pulverized fuel reaches the rotary classifier 16, due to the relative balance between the centrifugal force generated by the rotation of the blades and the centripetal force of the primary air flow, large diameter coarse pulverized fuel particles are knocked down by the blades and returned to the grinding table 12 for re-pulverization, while the fine pulverized fuel is directed to the outlet port 19 in the ceiling 42 of the housing 11. The fine pulverized fuel classified by the rotary classifier 16 is discharged from the outlet port 19 together with the primary air into the fine fuel supply passage (not shown) and supplied to the boiler burner.

The coal supply pipe 17 is attached so that its lower end extends vertically into the interior of the housing 11, penetrating the ceiling 42 of the housing 11, and supplies solid fuel fed from the top of the coal supply pipe 17 to the center of the grinding table 12. A coal supply machine (not shown) is connected to the upper end of the coal supply pipe 17, and solid fuel is supplied.

Next, the hydraulic drive system 100 of this embodiment will be described with reference to FIG. 2. FIG. 2 is a configuration diagram showing the hydraulic drive system 100 according to the first embodiment of the present disclosure. The hydraulic drive system 100 of this embodiment is a device that applies a load to the support arm 47 of the crushing roller 13 via the intermediate piston 61 of the load application device 60.

As shown in FIG. 2, the hydraulic drive system 100 includes an oil supply unit 110, a hydraulic cylinder 120, a first accumulator 130, a second accumulator 140, a hydraulic booster (adjustment unit) 150, a gas flow path 160, a gas on-off valve 170, a pressure sensor 180, and a control unit 190.

The oil supply unit 110 is a device that supplies hydraulic oil to the hydraulic cylinder 120. The oil supply unit 110 includes an oil pump 111, a check valve 112, a solenoid valve 113, an oil tank 114, an oil supply passage 115, an oil discharge passage 116, and an oil passage 117.

The oil pump 111 pumps hydraulic oil from the oil tank 114 and discharges it to the oil supply passage 115. The hydraulic oil discharged from the oil pump 111 flows into the solenoid valve 113 via the check valve 112. Note that due to the presence of the check valve 112, the hydraulic oil supplied from the oil pump 111 to the solenoid valve 113 does not return from the oil supply passage 115 to the oil pump 111.

When the oil pump 111 starts operating in response to an instruction from the control unit 190, hydraulic oil is supplied to the solenoid valve 113. In response to an instruction from the control unit 190, the solenoid valve 113 can switch between supplying the hydraulic oil supplied from the oil pump 111 to the hydraulic cylinder 120 via the oil passage 117 or returning it to the oil tank 114 via the oil drain passage 116.

The hydraulic cylinder 120 is a device that generates a driving force to drive the intermediate piston 61 of the load application device 60 by the pressure of the hydraulic oil supplied from the oil supply unit 110. The hydraulic cylinder 120 has a piston 122 that forms a hydraulic oil chamber 121 to which hydraulic oil is supplied from the oil supply unit 110. The hydraulic cylinder 120 drives the piston 122 by the pressure of the hydraulic oil supplied to the hydraulic oil chamber 121.

The first accumulator 130 is a device for maintaining a constant oil pressure in the hydraulic oil chamber 121. The first accumulator 130 is a device in which a first oil chamber 131 communicating with the hydraulic oil chamber 121 and a first gas chamber 132 filled with an inert gas (first gas) such as nitrogen gas are separated by a rubber bladder (first partition) 133.

The first accumulator 130 allows hydraulic oil to flow from the hydraulic oil chamber 121 to the first oil chamber 131 when the volume of the hydraulic oil chamber 121 decreases due to the movement of the piston 122, and allows hydraulic oil to flow from the first oil chamber 131 to the hydraulic oil chamber 121 when the volume of the hydraulic oil chamber 121 increases due to the movement of the piston 122. The first accumulator 130 has a poppet valve 134 that blocks the flow of hydraulic oil between the first oil chamber 131 and the hydraulic oil chamber 121 when the bladder 133 comes into contact with it.

The second accumulator 140 is a device used to change the volume of the first gas chamber 132 of the first accumulator 130. The second accumulator 140 is a device in which a second oil chamber 141 that communicates with the first oil adjustment chamber 151 of the hydraulic booster 150 and a second gas chamber 142 that contains an inert gas (second gas) such as nitrogen gas are separated by a rubber bladder (second partition) 143.

The second accumulator 140 allows hydraulic oil to flow from the first oil adjustment chamber 151 to the second oil chamber 141 when the volume of the first oil adjustment chamber 151 decreases, and allows hydraulic oil to flow from the second oil chamber 141 to the first oil adjustment chamber 151 when the volume of the first oil adjustment chamber 151 increases. The second accumulator 140 has a poppet valve 144 that blocks the flow of hydraulic oil between the second oil chamber 141 and the first oil adjustment chamber 151 when the bladder 143 comes into contact with it.

The hydraulic booster 150 is a device that adjusts the volume of the second oil chamber 141 of the second accumulator 140. The hydraulic booster 150 includes a first oil adjustment chamber 151, a second oil adjustment chamber 152, a pressure-receiving piston 153, a first switching valve (oil supply valve) 154, a second switching valve 155, and a discharge valve 156.

The first oil adjustment chamber 151 is a space to which hydraulic oil is supplied from the oil supply unit 110 when the first switching valve (oil refill valve) 154 is open, and which is in communication with the second oil chamber 141 of the second accumulator 140. The second oil adjustment chamber 152 is a space to which hydraulic oil is supplied from the oil supply unit 110 when the second switching valve 155 is open.

The pressure-receiving piston 153 has a first pressure-receiving portion 153a arranged on the first oil adjustment chamber 151 side and a second pressure-receiving portion 153b arranged on the second oil adjustment chamber 152 side. The first pressure-receiving area of the first pressure-receiving portion 153a relative to the first oil adjustment chamber 151 is smaller than the second pressure-receiving area of the second pressure-receiving portion 153b relative to the second oil adjustment chamber 152.

The first switching valve (oil supply valve) 154 is a device that switches the supply state of hydraulic oil from the oil supply unit 110 to the first oil adjustment chamber 151. The second switching valve 155 is a device that switches the supply state of hydraulic oil from the oil supply unit 110 to the second oil adjustment chamber 152.

The gas flow passage 160 is a flow passage that connects the first gas chamber 132 of the first accumulator 130 and the second gas chamber 142 of the second accumulator 140 .
The gas on-off valve 170 is a device disposed in the gas flow path 160 and switches between a connected state in which the first gas chamber 132 and the second gas chamber 142 are connected to each other, and a blocked state in which the first gas chamber 132 and the second gas chamber 142 are not connected to each other.

The pressure sensor 180 is a sensor that detects the pressure of the hydraulic oil flowing through the oil passage 117. The pressure sensor 180 transmits the detected hydraulic oil pressure to the control unit 190.

The control unit 190 is a device that controls each part of the hydraulic drive system 100, including the oil supply unit 110, the hydraulic booster 150, and the gas on-off valve 170. The control unit 190 controls each part of the hydraulic drive system 100, for example, by reading and executing a program stored in a memory unit (not shown).

Next, a method for controlling a hydraulic drive device according to the first embodiment of the present disclosure will be described with reference to the drawings. FIG. 3 is a flowchart showing a method for controlling a hydraulic drive device according to the first embodiment of the present disclosure. The control unit 190 reads and executes a program to perform each process shown in FIG. 3. The process shown in FIG. 3 is a process that is executed when the amount of solid fuel supplied from the coal supply pipe 17 to the mill 10 gradually increases, and accordingly the pressure in the hydraulic oil chamber 121 of the hydraulic cylinder 120 is gradually increased.

In step S<b>101 , the control unit 190 controls the gas on-off valve 170 to be in a closed state before the oil supply unit 110 pressurizes the hydraulic oil chamber 121 .
In step S102, the control unit 190 controls the first switching valve (oil supply valve) 154 to be in a closed state before the oil supply unit 110 pressurizes the hydraulic oil chamber 121.

In step S<b>103 , the control unit 190 controls the second switching valve 155 to be in a closed state before the oil supply unit 110 pressurizes the hydraulic oil chamber 121 .
In step S<b>104 , the control unit 190 operates the oil pump 111 of the oil supply unit 110 to start pressurizing the hydraulic oil chamber 121 of the hydraulic cylinder 120 .

With the gas on-off valve 170 in a closed state, the first gas chamber 132 of the first accumulator 130 is filled with a first gas at a first pressure (e.g., 1.8 MPa), and the second gas chamber 142 of the second accumulator 140 is filled with a second gas at a second pressure (e.g., 6.5 MPa) that is higher than the first pressure.

Figure 2 is a schematic diagram showing the hydraulic drive system 100 when pressurization of the hydraulic oil chamber 121 of the hydraulic cylinder 120 has begun, and shows the state in which pressurization of the hydraulic oil chamber 121 of the hydraulic cylinder 120 has begun. In the state shown in Figure 2, the pressure of the second oil chamber 141 and the second gas chamber 142 of the second accumulator 140 (e.g., 7.2 MPa) is higher than the pressure of the first oil chamber 131 and the first gas chamber 132 of the first accumulator 130 (e.g., 2.0 MPa).

In step S105, the control unit 190 determines whether the pressure of the working oil detected by the pressure sensor 180 is equal to or greater than the switching pressure (e.g., 7.2 MPa), and if YES, proceeds to step S106, and if NO, repeats the determination in step S105. Here, the switching pressure is the pressure in the first oil chamber 131 at which the volume of the first gas chamber 132 is equal to or less than the first predetermined volume. If the volume of the first gas chamber 132 becomes excessively small, the bladder 133, etc. may be damaged, so the volume of the first gas chamber 132 is limited so as not to fall below the first predetermined volume.

The first predetermined volume is preferably set to a volume that is, for example, 0.25 times the total volume of the first accumulator 130 (the minimum volume of the first gas chamber 132 to prevent damage to the bladder 133) that is larger than the maximum volume of the hydraulic oil chamber 121 (the stroke volume of the piston 122). This is to prevent the volume of the first gas chamber 132 of the first accumulator 130 from shrinking to 0.25 times the total volume of the first accumulator 130 or less, which would damage the bladder 133, even if hydraulic oil flows from the hydraulic oil chamber 121 to the first oil chamber 131 due to the forced displacement of the piston 122 when the first accumulator 130 is operating at the upper limit pressure.

In step S106, in response to the pressure of the hydraulic oil in the first oil chamber 131 becoming equal to or greater than the switching pressure (the volume of the first gas chamber 132 becoming equal to or less than the first predetermined volume), the control unit 190 controls the first switching valve (oil supply valve) 154 to be open in order to make the first oil chamber 131 of the first accumulator 130 and the second oil chamber 141 of the second accumulator 140 have the same pressure.

In step S107, when the pressure of the hydraulic oil in the first oil chamber 131 becomes equal to or greater than the switching pressure (the volume of the first gas chamber 132 becomes equal to or less than the first predetermined volume), the control unit 190 controls the gas on-off valve 170 to open in order to allow gas to move between the first gas chamber 132 of the first accumulator 130 and the second gas chamber 142 of the second accumulator 140.

Figure 4 is a schematic diagram showing the hydraulic drive system 100 according to the first embodiment of the present disclosure, showing a state in which the pressure of the hydraulic oil in the first oil chamber 131 is equal to or higher than the switching pressure. As shown in Figure 4, because the first switching valve (oil supply valve) 154 is in an open state, hydraulic oil is supplied to both the hydraulic oil chamber 121 of the hydraulic cylinder 120 and the first oil adjustment chamber 151 of the hydraulic booster 150, resulting in the same pressure.

Since the pressure in the hydraulic oil chamber 121 and the first oil adjustment chamber 151 are the same, the pressure in the first gas chamber 132 of the first accumulator 130 and the second gas chamber 142 of the second accumulator 140 are the same. Therefore, even if the gas on-off valve 170 is opened in step S107, no gas movement occurs between the first gas chamber 132 and the second gas chamber 142.

In step S108, the control unit 190 controls the first switching valve (oil supply valve) 154 to be switched from the open state to the closed state in order to increase the volume of the second oil chamber 141 of the second accumulator 140.
In step S109, the control unit 190 controls the second switching valve 155 to be switched from a closed state to an open state in order to increase the volume of the second oil chamber 141 of the second accumulator 140. In addition, the control unit 190 switches the discharge valve 156 from an open state to a closed state in order to seal off the hydraulic oil supplied from the oil passage 117 to the second oil adjustment chamber 152.

By opening the second switching valve 155, hydraulic oil is supplied from the oil passage 117 to the second oil adjustment chamber 152. The first oil adjustment chamber 151 and the second oil adjustment chamber 152 are at the same pressure due to the hydraulic oil supplied from the oil supply unit 110, but the second pressure receiving area of the second pressure receiving portion 153b is larger than the first pressure receiving area of the first pressure receiving portion 153a of the pressure receiving piston 153.

As a result, the pressure-receiving piston 153 moves toward the first oil adjustment chamber 151, and the volume of the second oil chamber 141 of the second accumulator 140, which is connected to the first oil adjustment chamber 151, increases. In addition, as the volume of the second oil chamber 141 increases, the volume of the second gas chamber 142 decreases, and the second gas in the second gas chamber 142 moves to the first gas chamber 132 via the gas flow path 160, and the volume of the first gas chamber 132 increases.

In step S110, the control unit 190 determines whether the transfer of hydraulic oil from the first oil adjustment chamber 151 to the second oil chamber 141 is complete. If the result is YES, the process proceeds to step S111. If the result is NO, the determination in step S110 is repeated. The amount of hydraulic oil transferred from the first oil adjustment chamber 151 to the second oil chamber 141 is set so that the volume of the second gas chamber 142 becomes the second predetermined volume. If the volume of the second gas chamber 142 becomes too small, the bladder 143, etc. may be damaged, so the volume of the second gas chamber 142 is limited so as not to fall below the second predetermined volume.

The second predetermined volume is preferably set to a volume that is, for example, 0.25 times the total volume of the second accumulator 140 (the minimum volume of the second gas chamber 142 to prevent damage to the bladder 143) that is larger than the maximum volume of the first oil adjustment chamber 151 (the stroke volume of the pressure-receiving piston 153). This is to prevent the volume of the second gas chamber 142 of the second accumulator 140 from shrinking to 0.25 times the total volume of the second accumulator 140 or less, which would damage the bladder 143, even if hydraulic oil flows from the first oil adjustment chamber 151 to the second oil chamber 141 due to the forced displacement of the pressure-receiving piston 153 when the second accumulator 140 is operating at the upper limit pressure.

Figure 5 is a schematic diagram showing the hydraulic drive system 100 according to the first embodiment of the present disclosure, showing the state in which the transfer of hydraulic oil to the second oil chamber 141 has been completed. As shown in Figure 5, compared to Figure 4, the volume of the second gas chamber 142 has decreased, while the volume of the first gas chamber 132 has increased.

In step S111, the control unit 190 controls the second switching valve 155 to switch from an open state to a closed state in response to completion of the transfer of hydraulic oil to the second oil chamber 141, in order to prevent a further increase in the volume of the second oil chamber 141 that could damage the bladder 143, etc. By closing the second switching valve 155, a further increase in the volume of the second oil chamber 141 is prevented.

In step S112, the control unit 190 controls the gas on-off valve 170 to close in response to completion of the transfer of hydraulic oil to the second oil chamber 141, in order to disable the movement of gas between the first gas chamber 132 of the first accumulator 130 and the second gas chamber 142 of the second accumulator 140.

In step S113, the control unit 190 determines whether the pressure of the hydraulic oil detected by the pressure sensor 180 is equal to or greater than the upper limit pressure (e.g., 25.9 MPa), and if YES, proceeds to step S114, and if NO, repeats the determination in step S113. Here, the upper limit pressure is the hydraulic oil pressure at which the volume of the first gas chamber 132 is equal to or less than the first predetermined volume. If the volume of the first gas chamber 132 becomes excessively small, the bladder 133, etc. may be damaged, so the volume of the first gas chamber 132 is limited so as not to fall below the first predetermined volume.

Figure 6 is a schematic diagram showing the hydraulic drive system 100 according to the first embodiment of the present disclosure, showing a state in which the pressure in the first oil chamber 131 has reached the upper limit pressure. As shown in Figure 6, compared to Figure 5, the volume of the first gas chamber 132 has decreased while the volume of the second gas chamber 142 has not changed.

In step S114, the control unit 190 controls the oil supply unit 110 to stop pressurizing the hydraulic oil chamber 121 by the oil supply unit 110 in order to prevent the volume of the first gas chamber 132 from further decreasing and damaging the bladder 133, etc., and ends the processing of this flowchart.

As described above, in steps S101 to S105 (first pressurization step), when the control unit 190 gradually increases the pressure in the hydraulic oil chamber 121 of the hydraulic cylinder 120, the control unit 190 controls the gas on-off valve 170 to be in a closed state and the oil supply unit 110 to supply hydraulic oil from the oil supply unit 110 to the hydraulic oil chamber 121 to increase the pressure in the hydraulic oil chamber 121 until the volume of the first gas chamber 132 becomes equal to or less than the first predetermined volume.

In addition, in steps S106 to S110 (adjustment process), when the pressure in the hydraulic oil chamber 121 is gradually increased, the control unit 190 switches the gas on-off valve 170 from a closed state to an open state in response to the volume of the first gas chamber 132 becoming equal to or less than a first predetermined volume, and controls the gas on-off valve 170 and the hydraulic booster 150 to increase the volume of the second oil chamber 141 until the volume of the second gas chamber 142 becomes equal to or less than a second predetermined volume.

In addition, in steps S111 to S114 (second pressurization step), the control unit 190 switches the gas on-off valve 170 from an open state to a closed state in response to the volume of the second gas chamber 142 becoming equal to or less than the second predetermined volume, and controls the gas on-off valve 170 and the oil supply unit 110 to supply hydraulic oil to the hydraulic oil chamber 121 until the volume of the first gas chamber 132 becomes equal to or less than the first predetermined volume, thereby increasing the pressure of the hydraulic oil chamber 121.

The process of FIG. 3 described above is a process executed when the supply amount of solid fuel supplied from the coal supply pipe 17 to the mill 10 gradually increases, and the pressure in the hydraulic oil chamber 121 of the hydraulic cylinder 120 is gradually increased accordingly. The process executed when the supply amount of solid fuel supplied from the coal supply pipe 17 to the mill 10 gradually decreases, and the pressure in the hydraulic oil chamber 121 of the hydraulic cylinder 120 is gradually decreased accordingly, is the opposite of the process described above.

Specifically, the control unit 190 gradually reduces the pressure in the hydraulic oil chamber 121 from the state shown in FIG. 6 to increase the volume of the first gas chamber 132 to a predetermined upper limit value. This upper limit value is set so that the bladder 133 does not contact the poppet valve 134. The control unit 190 then opens the gas on-off valve 170, discharges the hydraulic oil from the second oil adjustment chamber 152 of the hydraulic booster 150, and transfers the hydraulic oil from the second oil chamber 141 to the first oil adjustment chamber 151, thereby increasing the volume of the second gas chamber 142. As the volume of the second gas chamber 142 increases, the volume of the first gas chamber 132 decreases.

Then, the control unit 190 closes the gas on-off valve 170 and gradually reduces the pressure in the hydraulic oil chamber 121 to increase the volume of the first gas chamber 132 to a predetermined upper limit value. In this way, the pressure in the hydraulic oil chamber 121 can be reduced in two stages.

The operation and effects of the present embodiment described above will now be described.
According to the hydraulic drive system 100 of this embodiment, when the pressure of the hydraulic oil chamber 121 that drives the piston 122 of the hydraulic cylinder 120 is gradually increased, the gas on-off valve 170 is switched from the closed state to the open state in response to the volume of the first gas chamber 132 becoming equal to or smaller than a first predetermined volume. By opening the gas on-off valve 170, the first gas chamber 132 of the first accumulator 130 and the second gas chamber 142 of the second accumulator 140 are brought into communication with each other.

The hydraulic booster 150 is controlled to increase the volume of the second oil chamber 141 until the volume of the second gas chamber 142 becomes equal to or less than the second predetermined volume. When the hydraulic booster 150 increases the volume of the second oil chamber 141, the second gas moves from the second gas chamber 142 partitioned by the bladder 143 to the first gas chamber 132, decreasing the volume of the second gas chamber 142. The second gas that moves from the second gas chamber 142 to the first gas chamber 132 increases the volume of the first gas chamber 132, making it larger than the first predetermined volume.

Because the volume of the first gas chamber 132 becomes larger than the first predetermined volume, it is possible to supply more hydraulic oil from the oil supply unit 110 to the hydraulic oil chamber 121 to increase the pressure generated by the hydraulic oil chamber 121 until the volume of the first gas chamber 132 again becomes equal to or smaller than the first predetermined volume. This makes it possible to expand the range of pressure supplied to the hydraulic oil chamber 121 of the hydraulic cylinder 120.

In addition, according to the hydraulic drive device 100 of this embodiment, when the pressure of the hydraulic oil chamber 121 is gradually increased, the gas on-off valve 170 is closed until the volume of the first gas chamber 132 becomes equal to or less than the first predetermined volume, and hydraulic oil is supplied from the oil supply unit 110 to the hydraulic oil chamber 121 to increase the pressure of the hydraulic oil chamber 121. In addition, when the volume of the second gas chamber 142 becomes equal to or less than the second predetermined volume, the gas on-off valve 170 is switched from the open state to the closed state to block the first gas chamber 132, which has become larger than the first predetermined volume.

Then, hydraulic oil can be supplied to the hydraulic oil chamber 121 until the volume of the first gas chamber 132 becomes equal to or less than the first predetermined volume, thereby increasing the pressure of the hydraulic oil chamber 121. In this way, the hydraulic booster 150 restores the volume of the first gas chamber 132 to a volume greater than the first predetermined volume after it becomes equal to or less than the first predetermined volume, thereby increasing the pressure of the hydraulic oil chamber 121 in two stages and expanding the range of pressure supplied to the hydraulic oil chamber 121 of the hydraulic cylinder 120.

According to the hydraulic drive system 100 of this embodiment, the first switching valve (oil supply valve) 154 and the second switching valve 155 are controlled so that hydraulic oil is supplied from the oil supply unit 110 to the first oil adjustment chamber 151 and the second oil adjustment chamber 152. The first oil adjustment chamber 151 and the second oil adjustment chamber 152 are at the same pressure due to the hydraulic oil supplied from the oil supply unit 110, but the second pressure receiving area of the second pressure receiving portion 153b is larger than the first pressure receiving area of the first pressure receiving portion 153a of the pressure receiving piston 153. Therefore, the pressure receiving piston 153 moves toward the first oil adjustment chamber 151 side, and the volume of the second oil chamber 141 of the second accumulator 140 connected to the first oil adjustment chamber 151 can be increased.

In addition, according to the hydraulic drive system 100 of this embodiment, the rubber bladder 133 can appropriately absorb pressure pulsations in the hydraulic oil chamber 121.

Second Embodiment
Next, a hydraulic drive system 100A according to a second embodiment of the present disclosure will be described with reference to the drawings. This embodiment is a modified example of the first embodiment, and is the same as the first embodiment except as otherwise specifically described below, and therefore will not be described below.

The hydraulic drive system 100 of the first embodiment uses the hydraulic booster 150 to restore the volume of the first gas chamber 132 to a volume greater than the first predetermined volume after it has fallen below the first predetermined volume, thereby increasing the pressure of the hydraulic oil chamber 121 in two stages and expanding the range of pressure supplied to the hydraulic oil chamber 121 of the hydraulic cylinder 120. In contrast, the hydraulic drive system 100A of the present embodiment increases the pressure of the hydraulic oil chamber 121 in three stages, further expanding the range of pressure supplied to the hydraulic oil chamber 121 of the hydraulic cylinder 120.

Figure 7 is a configuration diagram showing a hydraulic drive system 100A according to a second embodiment of the present disclosure, showing a state in which the pressure of the hydraulic oil in the first oil chamber 131 is equal to or higher than the switching pressure. In Figure 7, the third accumulator 140A has a configuration similar to that of the second accumulator 140. The third oil chamber 141A of the third accumulator 140A is similar to the second oil chamber 141 of the second accumulator 140. The third gas chamber 142A of the third accumulator 140A is similar to the second gas chamber 142 of the second accumulator 140. The bladder 143A of the third accumulator 140A is similar to the bladder 143 of the second accumulator 140. The poppet valve 144A of the third accumulator 140A is similar to the poppet valve 144 of the second accumulator 140.

Also, in FIG. 7, the hydraulic booster 150A has a similar configuration to the hydraulic booster 150. The first oil adjustment chamber 151A and the second oil adjustment chamber 152A of the hydraulic booster 150A are similar to the first oil adjustment chamber 151 and the second oil adjustment chamber of the hydraulic booster 150. The pressure-receiving piston 153A of the hydraulic booster 150A is similar to the pressure-receiving piston 153 of the hydraulic booster 150. The first switching valve (oil supply valve) 154A and the second switching valve 155A of the hydraulic booster 150A are similar to the first switching valve (oil supply valve) 154 and the second switching valve 155 of the hydraulic booster 150. The discharge valve 156A of the hydraulic booster 150A is similar to the discharge valve 156 of the hydraulic booster 150.

The hydraulic booster 150A of this embodiment increases the pressure of the hydraulic oil chamber 121 in three stages by restoring the volume of the first gas chamber 132 to a volume larger than the first predetermined volume when the first oil chamber 131 reaches or exceeds the upper limit pressure in step S113 of the first embodiment and the volume of the first gas chamber 132 falls to or below the first predetermined volume.

In this embodiment, when the volume of the first gas chamber 132 becomes equal to or less than the first predetermined volume, the control unit 190 controls the first switching valve (oil supply valve) 154A to be open in order to make the first oil chamber 131 of the first accumulator 130 and the third oil chamber 141A of the third accumulator 140A have the same pressure.

In addition, when the volume of the first gas chamber 132 becomes equal to or less than the first predetermined volume, the control unit 190 controls the gas on-off valve 170A to open in order to allow gas to move between the first gas chamber 132 of the first accumulator 130 and the third gas chamber 142A of the third accumulator 140A.

As shown in FIG. 7, the first switching valve (oil supply valve) 154A is open, so hydraulic oil is supplied to both the hydraulic oil chamber 121 of the hydraulic cylinder 120 and the first oil adjustment chamber 151A of the hydraulic booster 150A, resulting in the same pressure.

Because the pressure in the hydraulic oil chamber 121 and the first oil adjustment chamber 151A are the same, the pressure in the first gas chamber 132 of the first accumulator 130 and the third gas chamber 142A of the third accumulator 140A are the same. Therefore, even if the gas on-off valve 170A is open, no gas movement occurs between the first gas chamber 132 and the third gas chamber 142A.

Thereafter, the control unit 190 controls the first switching valve (oil supply valve) 154A to be switched from the open state to the closed state in order to increase the volume of the third oil chamber 141A of the third accumulator 140A.
The control unit 190 controls the second switching valve 155A to be switched from a closed state to an open state in order to increase the volume of the third oil chamber 141A of the third accumulator 140A. The control unit 190 also controls the discharge valve 156A to be switched from an open state to a closed state in order to seal off the hydraulic oil supplied from the oil passage 117 to the second oil adjustment chamber 152A.

By opening the second switching valve 155A, hydraulic oil is supplied from the oil passage 117 to the second oil adjustment chamber 152A. The first oil adjustment chamber 151A and the second oil adjustment chamber 152A are at the same pressure due to the hydraulic oil supplied from the oil supply unit 110, but the second pressure receiving area of the second pressure receiving part on the second oil adjustment chamber 152A side of the pressure receiving piston 153 is larger than the first pressure receiving area of the first pressure receiving part on the first oil adjustment chamber 151A side.

As a result, the pressure-receiving piston 153A moves toward the first oil adjustment chamber 151A, and the volume of the third oil chamber 141A of the third accumulator 140A, which is connected to the first oil adjustment chamber 151A, increases. In addition, as the volume of the third oil chamber 141A increases, the volume of the third gas chamber 142A decreases, and the third gas in the third gas chamber 142A moves to the first gas chamber 132 via the gas flow path 160A, and the volume of the first gas chamber 132 increases.

The control unit 190 then determines whether the transfer of hydraulic oil from the first oil adjustment chamber 151A to the third oil chamber 141A is complete, and if the transfer of hydraulic oil is complete, controls the second switching valve 155A to switch from an open state to a closed state to prevent the volume of the third oil chamber 141A from increasing further and damaging the bladder 143A, etc. By closing the second switching valve 155A, the volume of the third oil chamber 141A is prevented from increasing further.

In addition, upon completion of the transfer of hydraulic oil to the third oil chamber 141A, the control unit 190 controls the gas on-off valve 170A to a closed state in order to disable the movement of gas between the first gas chamber 132 of the first accumulator 130 and the third gas chamber 142A of the third accumulator 140A.

Then, the control unit 190 determines whether the pressure of the hydraulic oil detected by the pressure sensor 180 is equal to or greater than the upper limit pressure, and if so, controls the oil supply unit 110 to stop pressurizing the hydraulic oil chamber 121 by the oil supply unit 110 in order to prevent a further decrease in the volume of the first gas chamber 132, which could damage the bladder 133, etc.

As described above, the hydraulic drive system 100A of this embodiment increases the pressure in the hydraulic oil chamber 121 in three stages and further expands the range of pressure supplied to the hydraulic oil chamber 121 of the hydraulic cylinder 120, but other configurations are also possible. Another accumulator similar to the third accumulator 140A and another hydraulic booster similar to the hydraulic booster 150A may be further provided to further increase the pressure in the hydraulic oil chamber 121 in four or more stages.

Other Embodiments
In the above description, the control unit 190 controls each part of the hydraulic drive system 100 including the oil supply unit 110, the hydraulic booster 150, and the gas on-off valve 170, but other configurations are also possible. For example, the control unit 190 may be divided into two control units: a first control unit that controls the oil supply unit 110 according to the pressure of the hydraulic oil supplied to the hydraulic oil chamber 121, and a second control unit that controls the hydraulic booster 150 and the gas on-off valve 170 according to the pressure of the hydraulic oil supplied to the hydraulic oil chamber 121. In this way, for example, when a first control unit for controlling a single first accumulator 130 is provided in an existing hydraulic drive system, it is possible to expand the range of pressure supplied to the hydraulic oil chamber 121 of the hydraulic cylinder 120 by making a small-scale modification to add only the second control unit.

The first accumulator 130 and the second accumulator 140 described above may be housed inside a single housing 200, as shown in the modified example of FIG. 8. In this case, the partition separating the second oil chamber 141 and the second gas chamber 142 of the second accumulator 140 may be the rubber bladder 143 of the first embodiment, or may be the piston 143B shown in FIG. 8.

In the above description, the hydraulic booster 150 is an opposed cylinder type in which the first oil adjustment chamber 151 and the second oil adjustment chamber 152 are arranged at both ends of the pressure-receiving piston 153, but other configurations are also possible. For example, it may be a hydraulic pump type or other type.

In addition, in the above description, to prevent the bladder 143 of the second accumulator 140 from over-expanding, hydraulic oil of about 10% of the volume of the second accumulator 140 may be sealed in the second oil chamber 141 in advance.

In addition, in the above explanation, it is preferable to set the switching pressure when the pressure in the hydraulic oil chamber 121 is gradually decreased to be lower than the switching pressure when the pressure in the hydraulic oil chamber 121 is gradually increased. In this way, a hysteresis characteristic can be provided, so that when operating near the switching pressure, it is possible to prevent control hunting due to slight pressure fluctuations caused by forced displacement of the piston 122 of the hydraulic cylinder 120.

In the above description, it is preferable that the total capacity of the first accumulator 130 and the total capacity of the second accumulator 140 are the same, but they may be different. Although the mill 10 is usually equipped with multiple hydraulic cylinders 120 and first accumulators 130, a single second accumulator 140 and multiple first accumulators 130 may be connected by multiple gas flow paths 160. In this case, it is preferable that the sum of the total capacities of the multiple first accumulators 130 is equal to the total capacity of the second accumulator 140.

In addition, in the above description, the hydraulic booster 150 may be provided with a relief valve (not shown) that releases hydraulic oil to the oil tank 114 when abnormally high pressure occurs on the high-pressure side of the hydraulic booster 150, and an oil supply valve (corresponding to the first switching valve 154, 154A) that supplies hydraulic oil from the hydraulic oil chamber 121 to the second accumulator via the high-pressure side of the hydraulic booster. However, these valves are always closed except when necessary and are independent of the hydraulic system on the cylinder head side of the hydraulic cylinder 120.

In the above description, the second switching valve 155 is preferably an electromagnetic valve or the like that can be remotely operated from the control unit 190, but it may also be mechanically operated by the pressure of the hydraulic system on the head side of the hydraulic cylinder 120. When the hydraulic booster 150 is not in operation, the exhaust valves 156, 156A are opened to release the pressure on the low pressure side of the hydraulic booster 150 to the atmosphere, so that the hydraulic oil leaking from the second switching valve 155 in the closed state promotes pressurization of the hydraulic booster 150, and damage to the second accumulator 140 due to excessive pressure can be prevented.

Furthermore, a pilot check valve (not shown) for the purpose of maintaining hydraulic pressure may be provided between the outlet of the hydraulic booster 150 and the inlet of the second accumulator 140 so that hydraulic oil is supplied to the second accumulator only when pressure is applied from the hydraulic booster 150 side, and the return of hydraulic oil from the second accumulator 140 to the hydraulic booster 150 may be controlled by pilot pressure. As a result, even if oil leakage occurs from the hydraulic booster 150 and the outlet pressure of the hydraulic booster 50 drops, hydraulic oil will not return from the second accumulator 140 to the hydraulic booster 150 unless the pilot pressure is applied to the pilot check valve, so the hydraulic pressure in the second accumulator 140 is maintained and operation can continue.

In addition, the above description may be further modified as follows. The mill control device often has an input from a pressure transmitter for detecting the pressure of the hydraulic oil chamber 121 of the hydraulic cylinder 120, and an output to a solenoid valve that controls the charging and discharging of the hydraulic oil chamber 121. The pressure signal from the pressure transmitter is input to the control device, and the hydraulic pressure is controlled by switching the solenoid valve according to the hydraulic pressure target value corresponding to the pre-programmed mill load (amount of coal supply). When modifying an existing mill, it is necessary to add a remotely operable gas opening and closing valve 170 between the first accumulator 130 and the second accumulator 140, and a remotely operable first switching valve (oil supply valve) 154, a second switching valve 155, and a discharge valve 156 attached to the hydraulic booster 150.

When increasing the input/output from the control device by reusing the existing control device, it becomes necessary to run wiring from the control device to the site and modify the control logic, which increases the scope of modification. Therefore, an additional control device that controls the additional equipment may be installed, and the signal from the pressure transmitter may be branched and input to the additional control device to control the gas on-off valve 170, the first switching valve (oil supply valve) 154, the second switching valve 155, and the discharge valve 156. In this case, the modification of the existing control device is only required to change the program for the target value of the hydraulic pressure according to the mill load (coal supply amount), which reduces the scope of modification of the existing control device.

The control device may also be provided with an oil level maintenance function for the second accumulator 140, which opens the oil supply valve (first switching valve) 154 before the hydraulic booster is activated and supplies hydraulic oil to the second accumulator 140. The control device may also be provided with a function for detecting large fluctuations in oil pressure that occur when the bladder 133 of the first accumulator 130 is damaged and is no longer able to absorb hydraulic pressure pulsations, and for outputting an alarm or the like.

In addition, if the bladder 133 is damaged, the gas (first gas) sealed in the first gas chamber 132 may flow into the hydraulic oil system, and the first gas may be ejected from the oil tank 114 of the oil supply unit 110. Therefore, a device may be provided that determines whether damage has occurred to the bladder 133 by checking the gas composition in the oil tank 114. This allows for early detection of an abnormality before the first gas is completely released from the first gas chamber 132 of the first accumulator 130, thereby suppressing the occurrence of hammering and cavitation in the hydraulic oil system, preventing damage to equipment, and ensuring safety.

As in the case where the bladder 133 is damaged, if the bladder 143 is damaged, the gas (second gas) sealed in the second gas chamber 142 may flow into the hydraulic oil system and may erupt from the oil tank 114 of the oil supply unit 110. Therefore, by examining the gas composition in the oil tank 114, the device may be used to determine whether damage has occurred to either or both of the bladders 133, 143 installed in the system.

In addition, in the above description, it is preferable to provide a gas supply port in the first gas chamber 132 of the first accumulator 130 and the second gas chamber 142 of the second accumulator 140, and to install a floor, ladder, or the like for accessing the gas supply port. In this way, gas can be periodically supplied to the first gas chamber 132 and the second gas chamber 142.

In the above description, the second accumulator 40 may be a piston type instead of a bladder type. Since the second accumulator is not intended to absorb hydraulic oil pressure pulsations, it does not have to be a bladder type accumulator with good pulsation absorption properties. By adopting a piston type accumulator that is free from concerns about overcompression and overexpansion, the entire internal volume of the accumulator can be used effectively, making it possible to make the second accumulator smaller than a bladder type accumulator. In addition, by installing a position detection sensor on the piston, it becomes possible to detect leakage of the enclosed gas or leakage of hydraulic oil on the high pressure side of the hydraulic booster 150, making it possible to know when maintenance of the hydraulic oil system is required.

The hydraulic drive system and the control method for the hydraulic drive system according to the present embodiment described above can be understood, for example, as follows.
A hydraulic drive system (100) according to a first aspect of the present disclosure includes an oil supply unit (110), a hydraulic cylinder (120) having a piston (122) forming a hydraulic oil chamber (121) to which hydraulic oil is supplied from the oil supply unit, and driving the piston by the pressure of the hydraulic oil supplied to the hydraulic oil chamber, a first accumulator (130) having a first oil chamber (131) communicating with the hydraulic oil chamber and a first gas chamber (132) in which a first gas is sealed, a second accumulator (140) having a second oil chamber (141) to which the hydraulic oil is supplied from the oil supply unit and a second gas chamber (142) in which a second gas is sealed, and The hydraulic oil chamber is provided with an adjustment unit (150) that adjusts the volume of a second oil chamber, a gas flow path (160) that connects the first gas chamber and the second gas chamber, a gas on-off valve (170) arranged in the gas flow path, and a control unit (190) that controls the oil supply unit, the adjustment unit, and the gas on-off valve, and when the pressure of the hydraulic oil chamber is gradually increased, the control unit controls the gas on-off valve and the adjustment unit to switch the gas on-off valve from a closed state to an open state in response to the volume of the first gas chamber becoming equal to or less than a first predetermined volume, and to increase the volume of the second oil chamber until the volume of the second gas chamber becomes equal to or less than a second predetermined volume.

According to the hydraulic drive device according to the first aspect of the present disclosure, when the pressure of the hydraulic oil chamber that drives the piston of the hydraulic cylinder is gradually increased, the gas on-off valve is switched from a closed state to an open state in response to the volume of the first gas chamber becoming equal to or less than a first predetermined volume. By opening the gas on-off valve, the first gas chamber of the first accumulator and the second gas chamber of the second accumulator are brought into communication with each other.

The adjustment unit is controlled to increase the volume of the second oil chamber until the volume of the second gas chamber becomes equal to or less than the second predetermined volume. By increasing the volume of the second oil chamber by the adjustment unit, the second gas moves from the second gas chamber partitioned by the second partition to the first gas chamber, and the volume of the second gas chamber decreases. The second gas that moves from the second gas chamber to the first gas chamber increases the volume of the first gas chamber, making it larger than the first predetermined volume.

Because the volume of the first gas chamber becomes larger than the first predetermined volume, the pressure generated by the hydraulic oil chamber can be increased by supplying more hydraulic oil from the oil supply unit to the hydraulic oil chamber until the volume of the first gas chamber again becomes equal to or smaller than the first predetermined volume. This makes it possible to expand the range of pressure supplied to the hydraulic oil chamber of the hydraulic cylinder.

In the first aspect, the hydraulic drive device according to the second aspect of the present disclosure further includes the following configuration. That is, when the pressure of the hydraulic oil chamber is gradually increased, the control unit controls the gas on-off valve and the oil supply unit to keep the gas on-off valve in the closed state and supply the hydraulic oil from the oil supply unit to the hydraulic oil chamber to increase the pressure of the hydraulic oil chamber until the volume of the first gas chamber becomes equal to or less than the first predetermined volume, and controls the gas on-off valve and the oil supply unit to switch the gas on-off valve from the open state to the closed state in response to the volume of the second gas chamber becoming equal to or less than the second predetermined volume, and to supply the hydraulic oil to the hydraulic oil chamber until the volume of the first gas chamber becomes equal to or less than the first predetermined volume to increase the pressure of the hydraulic oil chamber.

According to the hydraulic drive device according to the second aspect of the present disclosure, when the pressure in the hydraulic oil chamber is gradually increased, the gas on-off valve is closed until the volume of the first gas chamber becomes equal to or less than the first predetermined volume, and hydraulic oil is supplied from the oil supply unit to the hydraulic oil chamber to increase the pressure in the hydraulic oil chamber. In addition, when the volume of the second gas chamber becomes equal to or less than the second predetermined volume, the gas on-off valve is switched from the open state to the closed state to block the first gas chamber, which has become larger than the first predetermined volume.

Then, hydraulic oil can be supplied to the hydraulic oil chamber until the volume of the first gas chamber becomes equal to or less than the first predetermined volume, thereby increasing the pressure in the hydraulic oil chamber. In this way, the adjustment unit restores the volume of the first gas chamber to a volume greater than the first predetermined volume after the volume becomes equal to or less than the first predetermined volume, thereby increasing the pressure in the hydraulic oil chamber in two stages and expanding the range of pressure supplied to the hydraulic oil chamber of the hydraulic cylinder.

The hydraulic drive device according to the third aspect of the present disclosure, in the first or second aspect, further comprises the following configuration. That is, the adjustment unit comprises a first oil adjustment chamber (151) to which the hydraulic oil is supplied from the oil supply unit and which communicates with the second oil chamber, a second oil adjustment chamber (152) to which the hydraulic oil is supplied from the oil supply unit, a first switching valve (154) that switches the supply state of the hydraulic oil from the oil supply unit to the first oil adjustment chamber, a second switching valve (155) that switches the supply state of the hydraulic oil from the oil supply unit to the second oil adjustment chamber, and a pressure-receiving piston having a first pressure-receiving portion having a first pressure-receiving area with respect to the first oil adjustment chamber and a second pressure-receiving portion having a second pressure-receiving area larger than the first pressure-receiving area with respect to the second oil adjustment chamber, and the control unit controls the first switching valve and the second switching valve so that the hydraulic oil is supplied from the oil supply unit to the first oil adjustment chamber and the second oil adjustment chamber to increase the volume of the second oil chamber.

According to the hydraulic drive device of the third aspect of the present disclosure, the first and second switching valves are controlled so that hydraulic oil is supplied from the oil supply unit to the first and second oil adjustment chambers. The first and second oil adjustment chambers are at the same pressure due to the hydraulic oil supplied from the oil supply unit, but the second pressure receiving area of the second pressure receiving part is larger than the first pressure receiving area of the first pressure receiving part of the pressure receiving piston. Therefore, the pressure receiving piston moves toward the first oil adjustment chamber, and the volume of the second oil chamber of the second accumulator connected to the first oil adjustment chamber can be increased.

The hydraulic drive system according to a fourth aspect of the present disclosure is the first or second aspect, further including the following configuration: That is, the first partition is a rubber bladder.
According to the hydraulic drive device according to the fourth aspect of the present disclosure, the rubber bladder can appropriately absorb pressure pulsations in the hydraulic oil chamber.

The hydraulic drive device according to the fifth aspect of the present disclosure, in the first or second aspect, further comprises the following configuration. That is, the control unit comprises a first control device that controls the oil supply unit according to the pressure of the hydraulic oil supplied to the hydraulic oil chamber, and a second control device that controls the adjustment unit and the gas on-off valve according to the pressure of the hydraulic oil supplied to the hydraulic oil chamber.

According to the hydraulic drive system of the fifth aspect of the present disclosure, a first control device is provided that controls the oil supply unit in response to the pressure of the hydraulic oil supplied to the hydraulic oil chamber, and a second control device is provided that controls the adjustment unit and the gas on-off valve in response to the pressure of the hydraulic oil supplied to the hydraulic oil chamber. For example, if an existing hydraulic drive system is provided with a first control device for controlling a single accumulator, a small-scale modification that adds only the second control device makes it possible to expand the range of pressures supplied to the hydraulic oil chamber of the hydraulic cylinder.

In the control method for a hydraulic drive device according to the sixth aspect of the present disclosure, the hydraulic drive device includes an oil supply unit, a hydraulic cylinder having a piston that forms a hydraulic oil chamber to which hydraulic oil is supplied from the oil supply unit and that drives the piston by the pressure of the hydraulic oil supplied to the hydraulic oil chamber, a first accumulator that is partitioned by a first partition into a first oil chamber that communicates with the hydraulic chamber and a first gas chamber in which a first gas is sealed, a second accumulator that is partitioned by a second partition into a second oil chamber to which the hydraulic oil is supplied from the oil supply unit and a second gas chamber in which a second gas is sealed, an adjustment unit that adjusts the volume of the second oil chamber, a gas flow path that communicates between the first gas chamber and the second gas chamber, and a gas on-off valve that is arranged in the gas flow path. The control method for the hydraulic drive device includes an adjustment step of controlling the gas on-off valve and the adjustment unit to switch the gas on-off valve from a closed state to an open state in response to the volume of the first gas chamber becoming equal to or less than a first predetermined volume when the pressure of the hydraulic oil chamber is gradually increased, and to increase the volume of the second oil chamber until the volume of the second gas chamber becomes equal to or less than a second predetermined volume.

According to the control method for a hydraulic drive device according to the sixth aspect of the present disclosure, when the pressure of the hydraulic oil chamber that drives the piston of the hydraulic cylinder is gradually increased, the gas on-off valve is switched from a closed state to an open state in response to the volume of the first gas chamber becoming equal to or less than a first predetermined volume. By opening the gas on-off valve, the first gas chamber of the first accumulator and the second gas chamber of the second accumulator are brought into communication with each other.

The adjustment unit is controlled to increase the volume of the second oil chamber until the volume of the second gas chamber becomes equal to or less than the second predetermined volume. By increasing the volume of the second oil chamber by the adjustment unit, the second gas moves from the second gas chamber partitioned by the second partition to the first gas chamber, decreasing the volume of the second gas chamber. The second gas that moves from the second gas chamber to the first gas chamber increases the volume of the first gas chamber, making it larger than the first predetermined volume.

Because the volume of the first gas chamber becomes larger than the first predetermined volume, the pressure generated by the hydraulic oil chamber can be increased by supplying more hydraulic oil from the oil supply unit to the hydraulic oil chamber until the volume of the first gas chamber again becomes equal to or smaller than the first predetermined volume. This makes it possible to expand the range of pressure supplied to the hydraulic oil chamber of the hydraulic cylinder.

The control method for a hydraulic drive device according to the seventh aspect of the present disclosure further includes the following configuration in the sixth aspect. That is, when the pressure of the hydraulic oil chamber is gradually increased, the gas on-off valve is kept in the closed state until the volume of the first gas chamber becomes equal to or less than the first predetermined volume, and the gas on-off valve and the oil supply unit are controlled to supply the hydraulic oil from the oil supply unit to the hydraulic oil chamber to increase the pressure of the hydraulic oil chamber; and when the pressure of the hydraulic oil chamber is gradually increased, the gas on-off valve is switched from the open state to the closed state in response to the volume of the second gas chamber becoming equal to or less than the second predetermined volume, and the gas on-off valve and the oil supply unit are controlled to supply the hydraulic oil to the hydraulic oil chamber until the volume of the first gas chamber becomes equal to or less than the first predetermined volume to increase the pressure of the hydraulic oil chamber.

According to the control method for a hydraulic drive device according to the seventh aspect of the present disclosure, when the pressure in the hydraulic oil chamber is gradually increased, the gas on-off valve is closed until the volume of the first gas chamber becomes equal to or less than a first predetermined volume, and the hydraulic oil is supplied from the oil supply unit to the hydraulic oil chamber to increase the pressure in the hydraulic oil chamber. In addition, when the volume of the second gas chamber becomes equal to or less than the second predetermined volume, the gas on-off valve is switched from an open state to a closed state to block the first gas chamber, which has become larger than the first predetermined volume.

Then, hydraulic oil can be supplied to the hydraulic oil chamber until the volume of the first gas chamber becomes equal to or less than the first predetermined volume, thereby increasing the pressure in the hydraulic oil chamber. In this way, the adjustment unit restores the volume of the first gas chamber to a volume greater than the first predetermined volume after the volume becomes equal to or less than the first predetermined volume, thereby increasing the pressure in the hydraulic oil chamber in two stages and expanding the range of pressure supplied to the hydraulic oil chamber of the hydraulic cylinder.

10 Mill 60 Loading device 61 Intermediate piston 100, 100A Hydraulic drive device 110 Oil supply section 111 Oil pump 112 Check valve 113 Solenoid valve 114 Oil tank 115 Oil supply passage 116 Oil discharge passage 117 Oil passage 120 Hydraulic cylinder 121 Hydraulic oil chamber 122 Piston 130 First accumulator 131 First oil chamber 132 First gas chamber 133 Bladder 134 Poppet valve 140 Second accumulator 140A Third accumulator 141 Second oil chamber 141A Third oil chamber 142 Second gas chamber 142A Third gas chamber 143, 143A Bladder 143B Piston 144, 144A Poppet valve 150, 150A Hydraulic booster 151, 151A First oil adjustment chamber 152, 152A Second oil adjustment chamber 153, 153A Pressure receiving piston 153a First pressure receiving portion 153b Second pressure receiving portion 154, 154A First switching valve (oil supply valve)
155, 155A Second switching valve 156, 156A Exhaust valve 160, 160A Gas flow path 170, 170A Gas on-off valve 180 Pressure sensor 190 Control unit 200 Housing Cf, Ch Axis

Claims (7)

An oil supply unit;
a hydraulic cylinder having a piston that forms a hydraulic oil chamber to which hydraulic oil is supplied from the oil supply unit, the hydraulic cylinder driving the piston by the pressure of the hydraulic oil supplied to the hydraulic oil chamber;
a first accumulator, the first oil chamber being communicated with the hydraulic oil chamber and the first gas chamber being sealed with a first gas, the first oil chamber being partitioned by a first partition;
a second accumulator in which a second oil chamber to which the hydraulic oil is supplied from the oil supply unit and a second gas chamber in which a second gas is sealed are partitioned by a second partition;
an adjustment unit that adjusts the volume of the second oil chamber;
a gas flow passage that communicates the first gas chamber with the second gas chamber;
a gas on-off valve disposed in the gas flow path;
a control unit that controls the oil supply unit, the adjustment unit, and the gas on-off valve,
The control unit is a hydraulic drive device that, when the pressure of the hydraulic oil chamber is gradually increased, switches the gas on-off valve from a closed state to an open state in response to the volume of the first gas chamber becoming equal to or less than a first predetermined volume, and controls the gas on-off valve and the adjustment unit to increase the volume of the second oil chamber until the volume of the second gas chamber becomes equal to or less than a second predetermined volume. When the control unit gradually increases the pressure in the hydraulic oil chamber,
until the volume of the first gas chamber becomes equal to or less than the first predetermined volume, the gas on-off valve is kept in the closed state, and the gas on-off valve and the oil supply unit are controlled so as to supply the hydraulic oil from the oil supply unit to the hydraulic oil chamber to increase the pressure of the hydraulic oil chamber;
2. The hydraulic drive system according to claim 1, wherein the gas on-off valve and the oil supply unit are controlled so as to switch the gas on-off valve from the open state to the closed state in response to the volume of the second gas chamber becoming equal to or less than the second predetermined volume, and to supply the hydraulic oil to the hydraulic oil chamber until the volume of the first gas chamber becomes equal to or less than the first predetermined volume, thereby increasing the pressure of the hydraulic oil chamber. The adjustment unit is
a first oil adjustment chamber to which the hydraulic oil is supplied from the oil supply unit and which communicates with the second oil chamber;
a second oil adjusting chamber to which the hydraulic oil is supplied from the oil supply unit;
a pressure-receiving piston having a first pressure-receiving portion having a first pressure-receiving area with respect to the first oil adjustment chamber and a second pressure-receiving portion having a second pressure-receiving area with respect to the second oil adjustment chamber that is larger than the first pressure-receiving area;
a first switching valve that switches a supply state of the hydraulic oil from the oil supply unit to the first oil adjustment chamber;
a second switching valve that switches a supply state of the hydraulic oil from the oil supply unit to the second oil adjustment chamber,
3. The hydraulic drive system according to claim 1, wherein the control unit controls the first switching valve and the second switching valve so that the hydraulic oil is supplied from the oil supply unit to the first oil adjustment chamber and the second oil adjustment chamber to increase a volume of the second oil chamber. The hydraulic drive device according to claim 1 or 2, wherein the first bulkhead is a rubber bladder. The control unit is
a first control device that controls the oil supply unit in response to a pressure of the hydraulic oil supplied to the hydraulic oil chamber;
3. The hydraulic drive system according to claim 1, further comprising: a second control device that controls the adjustment unit and the gas on-off valve in response to a pressure of the hydraulic oil supplied to the hydraulic oil chamber. A method for controlling a hydraulic drive system, comprising:
The hydraulic drive device is
An oil supply unit;
a hydraulic cylinder having a piston that forms a hydraulic oil chamber to which hydraulic oil is supplied from the oil supply unit, the hydraulic cylinder driving the piston by the pressure of the hydraulic oil supplied to the hydraulic oil chamber;
a first oil chamber communicating with the hydraulic oil chamber, a first gas chamber containing a first gas, and a first accumulator partitioned by a first partition;
a second accumulator in which a second oil chamber to which the hydraulic oil is supplied from the oil supply unit and a second gas chamber in which a second gas is sealed are partitioned by a second partition;
an adjustment unit that adjusts the volume of the second oil chamber;
a gas flow passage that communicates the first gas chamber with the second gas chamber;
a gas on-off valve disposed in the gas flow path,
A method for controlling a hydraulic drive system comprising an adjustment process for controlling the gas on-off valve and the adjustment unit to switch the gas on-off valve from a closed state to an open state in response to the volume of the first gas chamber becoming equal to or less than a first predetermined volume when the pressure of the hydraulic oil chamber is gradually increased, and to increase the volume of the second oil chamber until the volume of the second gas chamber becomes equal to or less than a second predetermined volume. a first pressurizing step of controlling the gas on-off valve and the oil supply unit so as to gradually increase the pressure of the hydraulic oil chamber by supplying the hydraulic oil from the oil supply unit to the hydraulic oil chamber while keeping the gas on-off valve in the closed state until the volume of the first gas chamber becomes equal to or less than the first predetermined volume;
7. The method for controlling a hydraulic drive system according to claim 6, further comprising: a second pressurizing step of controlling the gas on-off valve and the oil supply unit to switch the gas on-off valve from the open state to the closed state in response to a volume of the second gas chamber becoming equal to or less than the second predetermined volume when the pressure of the hydraulic oil chamber is gradually increased, and to supply the hydraulic oil to the hydraulic oil chamber until the volume of the first gas chamber becomes equal to or less than the first predetermined volume, thereby increasing the pressure of the hydraulic oil chamber.