Hydraulic drive device and hydraulic machine

Abstract

To accurately control a hydraulic actuator 11 in driving operation.SOLUTION: The relief valves (35) operate to return the hydraulic fluid in the first flow path (35c) to the fluid tank (12) when the pressure (P2) of the hydraulic fluid in the first flow path (P3) exceeds a set pressure (21a) corresponding to a vent pressure (P1), which is the pressure of the hydraulic fluid at the vent port (21a). The second pump (36) is connected between the vent port (35c) of the relief value (35) and the oil tank (12). The control unit (50) controls the second pump (36) such that the vent pressure (P2) detected by the vent pressure sensor (42) is maintained at a predetermined pressure in the driving operation of supplying the hydraulic fluid from the fluid tank (12) to the hydraulic actuators (11) via the first pump (31).SELECTED DRAWING: Figure 1

Description

[Technical Field]

[0001] The present disclosure relates to hydraulic drive technology. [Background technology]

[0002] Patent Document 1 discloses a hydraulic control circuit for an injection molding machine. In this hydraulic control circuit, a main line is connected to the discharge side of a pump, and a branch line branches from the main line toward a tank. A relief valve equipped with a pilot valve is provided in the branch line. An electromagnetic proportional pilot relief valve is provided in the vent path of the relief valve. The set pressure of the relief valve is controlled by the electromagnetic proportional pilot relief valve. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Utility Model Application Publication No. 55-8170 Summary of the Invention [Problem to be solved by the invention]

[0004] In the hydraulic control circuit of Patent Document 1, the electromagnetic proportional pilot relief valve generates a pilot pressure for controlling itself using the pressure it controls, which makes it difficult to stabilize the set pressure of the relief valve controlled by the electromagnetic proportional pilot relief valve, and therefore difficult to improve the stability of the operation of the relief valve.

[0005] As described above, in the hydraulic control circuit of Patent Document 1, it is difficult to improve the stability of the operation of the relief valve, and therefore, in the drive operation of supplying hydraulic oil from the oil tank via the pump to the hydraulic actuator, it is not possible to accurately control the pressure of the hydraulic oil supplied to the hydraulic actuator, and it is not possible to accurately control the hydraulic actuator. [Means for solving the problem]

[0006] A first aspect of the present disclosure relates to a hydraulic drive system for driving a hydraulic actuator (11). The hydraulic drive system includes: a first pump (31) connected between the hydraulic actuator (11) and an oil tank (12); a first flow path (21a) that is a flow path between the hydraulic actuator (11) and the first pump (31) and that is connected between the oil tank (12) and the first pump (31); and a vent port (35c) that is connected between the first flow path (21a) and the oil tank (12). When a pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds a set pressure (P3) that corresponds to a vent pressure (P2) that is a pressure of the hydraulic oil in the vent port (35c), the first flow path (21a) is opened. a relief valve (35) that operates to return hydraulic oil in a vent port (35c) of the relief valve (35) to the oil tank (12); a second pump (36) that is connected between a vent port (35c) of the relief valve (35) and the oil tank (12); a vent pressure sensor (42) that detects the vent pressure (P2); and a control unit (50) that controls the second pump (36) so that the vent pressure (P2) detected by the vent pressure sensor (42) is maintained at a predetermined pressure during a drive operation of supplying hydraulic oil from the oil tank (12) to the hydraulic actuator (11) via the first pump (31).

[0007] In the first aspect, the set pressure (P3) of the relief valve (35) can be controlled by using the second pump (36) without using a pilot relief valve that controls itself using the pressure that it controls. This makes it possible to stabilize the set pressure (P3) of the relief valve (35) more than when using the above-described pilot relief valve, thereby improving the stability of the operation of the relief valve (35). Since the stability of the operation of the relief valve (35) can be improved in this way, the pressure (P1) of the hydraulic oil in the first flow path (21a), which is the pressure of the hydraulic oil supplied to the hydraulic actuator (11), can be accurately controlled in the driving operation, and the hydraulic actuator (11) can be accurately controlled.

[0008] A second aspect of the present disclosure is the hydraulic drive device of the first aspect, wherein the relief valve (35) is configured to increase the vent pressure (P2) when the pressure (P1) of the hydraulic oil in the first flow path (21 a) exceeds the set pressure (P3) of the relief valve (35) and the relief valve (35) attempts to operate, and the control unit (50) controls the second pump (36) in the driving operation so that the vent pressure (P2) returns to the predetermined pressure when the pressure (P1) of the hydraulic oil in the first flow path (21 a) exceeds the set pressure (P3) of the relief valve (35) and the relief valve (35) attempts to operate and the vent pressure (P2) becomes higher than the predetermined pressure.

[0009] In the second mode, when the relief valve (35) is about to operate and the vent pressure (P2) becomes higher than a predetermined pressure, the second pump (36) is controlled so that the vent pressure (P2) returns to the predetermined pressure, thereby stabilizing the set pressure (P3) of the relief valve (35).

[0010] A third aspect of the present disclosure relates to a hydraulic machine including the hydraulic drive device of the first or second aspect. [Brief explanation of the drawings]

[0011] [Figure 1] FIG. 1 is a hydraulic circuit diagram illustrating the configuration of a hydraulic machine according to an embodiment. [Figure 2] FIG. 2 is a schematic diagram illustrating the structure of a relief valve. [Figure 3] FIG. 3 is a timing chart illustrating the driving operation. [Figure 4] FIG. 4 is a timing chart illustrating the depressurization operation. [Figure 5] FIG. 5 is a timing chart illustrating a modified example of the depressurization operation. [Figure 6] FIG. 6 is a hydraulic circuit diagram for explaining a modified example of the hydraulic actuator and the hydraulic drive device. DETAILED DESCRIPTION OF THE INVENTION

[0012] Hereinafter, the embodiments will be described in detail with reference to the drawings. In the drawings, the same or corresponding parts are designated by the same reference numerals and their description will not be repeated.

[0013] (Embodiment) 1 illustrates the configuration of a hydraulic machine 10 according to an embodiment. The hydraulic machine 10 includes a hydraulic actuator 11, an oil tank 12, and a hydraulic drive unit 20.

[0014] The hydraulic actuator 11 is supplied with hydraulic oil and operates using the energy of the hydraulic oil. The hydraulic oil is drained from the hydraulic actuator 11 after the hydraulic actuator 11 is operated. For example, the hydraulic actuator 11 is a single-acting hydraulic cylinder. Such hydraulic cylinders are used in die-casting machines, injection molding machines, etc. The oil tank 12 stores the hydraulic oil.

[0015] The hydraulic drive unit (20) drives the hydraulic actuator (11) using hydraulic oil in the oil tank (12). Specifically, the hydraulic drive unit (20) operates the hydraulic actuator (11) by supplying the hydraulic oil in the oil tank (12) to the hydraulic actuator (11), and after the hydraulic actuator (11) operates, the hydraulic oil in the hydraulic actuator (11) is drained from the hydraulic actuator (11) and returned to the oil tank (12).

[0016] In this example, the hydraulic drive unit (20) includes a first pump (31), a first motor (32), a relief valve (35), a second pump (36), a second motor (37), a first pressure sensor (41), a second pressure sensor (42), and a control unit (50).

[0017] [First pump] The first pump (31) is connected between the hydraulic actuator (11) and the oil tank (12) and transports hydraulic oil between the hydraulic actuator (11) and the oil tank (12). In this example, the first pump (31) is provided in a main flow path (21) that connects the hydraulic actuator (11) and the oil tank (12). The main flow path (21) has a first flow path (21a) that connects the hydraulic actuator (11) and an outlet of the first pump (31) and a second flow path (21b) that connects the inlet of the first pump (31) and the oil tank (12).

[0018] In addition, the first pump (31) can be switched between a forward rotation state in which the hydraulic oil is transported from the inlet side, which is the oil tank (12) side, to the outlet side, which is the hydraulic actuator (11) side, and a reverse rotation state in which the hydraulic oil is transported from the outlet side to the inlet side.

[0019] [First motor] The first motor (32) is coupled to the first pump (31) and drives the first pump (31). In this example, the first motor (32) is switchable between forward rotation drive, in which the first pump (31) is rotated in a forward direction to drive the first pump (31) in a forward rotation state, and reverse rotation drive, in which the first pump (31) is rotated in a reverse rotation direction (the direction opposite to the forward rotation direction) to drive the first pump (31) in a reverse rotation state. The first motor (32) is a motor whose rotation speed is changeable. For example, the first motor (32) is a servo motor. Hereinafter, the operation of "controlling the first pump (31) by controlling the first motor (32)" will be simply referred to as "controlling the first pump (31)."

[0020] [Relief valve] The relief valve (35) is connected between the first flow path (21a), which is a flow path between the hydraulic actuator (11) and the first pump (31), and the oil tank (12). The relief valve (35) has an inlet port (35a), an outlet port (35b), and a vent port (35c). In this example, the relief valve (35) is provided in a relief flow path (22) that connects the first flow path (21a) and the oil tank (12). The relief flow path (22) has an inlet path (22a) that connects the first flow path (21a) and the inlet port (35a) and an outlet path (22b) that connects the outlet port (35b) and the oil tank (12).

[0021] When the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds a set pressure (P3) corresponding to a vent pressure (P2), which is the pressure of the hydraulic oil in the vent port (35c), the relief valve (35) operates to return the hydraulic oil in the first flow path (21a) to the oil tank (12). When the pressure (P1) of the hydraulic oil in the first flow path (21a) no longer exceeds the vent pressure (P2), the relief valve (35) ceases to operate.

[0022] The relief valve (35) is configured so that when the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds the set pressure (P3) of the relief valve (35) and the relief valve (35) is about to operate, the vent pressure (P2) increases. The structure of the relief valve (35) will be described in detail later.

[0023] [Second pump] The second pump (36) is connected between the vent port (35c) of the relief valve (35) and the oil tank (12) and transports hydraulic oil between the vent port (35c) of the relief valve (35) and the oil tank (12). In this example, the second pump (36) is provided in a vent flow path (23) that connects the vent port (35c) of the relief valve (35) and the oil tank (12). The vent flow path (23) has a first vent flow path (23a) that connects the vent port (35c) and an outlet of the second pump (36) and a second vent flow path (23b) that connects the inlet of the second pump (36) and the oil tank (12).

[0024] The second pump (36) is switchable between a forward rotation state in which the hydraulic oil is conveyed from an inlet side, which is the oil tank (12) side, to an outlet side, which is the vent port (35c) side of the relief valve (35), and a reverse rotation state in which the hydraulic oil is conveyed from the outlet side to the inlet side. The capacity of the second pump (36) is smaller than the capacity of the first pump (31).

[0025] [Second motor] The second motor (37) is coupled to the second pump (36) and drives the second pump (36). In this example, the second motor (37) is switchable between forward rotation drive, in which the second pump (36) is rotated in a forward direction to drive the second pump (36) in a forward rotation state, and reverse rotation drive, in which the second pump (36) is rotated in a reverse rotation direction (the direction opposite to the forward rotation direction) to drive the second pump (36) in a reverse rotation state. The second motor (37) is a motor whose rotation speed is changeable. Hereinafter, the operation of "controlling the second pump (36) by controlling the second motor (37)" will be simply referred to as "controlling the second pump (36)."

[0026] [First pressure sensor] The first pressure sensor (41) detects the pressure (P1) of the hydraulic oil in the first flow path (21a). In this example, the first pressure sensor (41) is connected to the first flow path (21a). The first pressure sensor (41) transmits a pressure signal indicating the “pressure (P1) of the hydraulic oil in the first flow path (21a)” detected by the first pressure sensor (41) to the control unit (50).

[0027] [Second pressure sensor (vent pressure sensor)] The second pressure sensor (42) detects the vent pressure (P2). In this example, the second pressure sensor (42) is connected to the first vent flow path (23a). The second pressure sensor (42) transmits a pressure signal indicating the "vent pressure (P2)" detected by the second pressure sensor (42) to the control unit (50). The second pressure sensor (42) is an example of a vent pressure sensor that detects the vent pressure (P2).

[0028] [Control Unit] The control unit (50) performs various operations (processing). Specifically, the control unit (50) acquires information and data from each part of the hydraulic machine (10) and performs various operations based on the information and data.

[0029] For example, the control unit (50) is configured by a computer (e.g., a microcomputer) including a processor, a memory, an input / output interface, etc. The memory is electrically connected to the processor and stores a program for operating the processor. The processor executes the program to realize various functions of the control unit (50). The control unit (50) also includes components for control (e.g., an electric circuit, an electronic circuit, etc.).

[0030] The memory of the control unit (50) also stores information and data used to control the hydraulic machine (10) (for example, set values ​​and control patterns such as thresholds, upper limits, lower limits, and target values), information and data (for example, measurement values) obtained by various sensors provided in the hydraulic machine (10), information and data (for example, command values) input from outside the hydraulic machine (10), and the like.

[0031] [Operation of the control unit] In this example, the control unit (50) performs a driving operation and a depressurizing operation. The driving operation is an operation of supplying hydraulic oil from the oil tank (12) to the hydraulic actuator (11) via the first pump (31). The depressurizing operation is an operation of returning hydraulic oil to the oil tank (12) via the hydraulic actuator (11) or the relief valve (35).

[0032] [Driving operation] In the driving operation, the control unit (50) controls the first pump (31) so that the pressure (P1) of the hydraulic oil in the first flow path (21a) becomes a predetermined target pressure by driving the first pump (31) in a forward rotation state. In this example, the control unit (50) controls the rotation direction and the rotation speed of the first motor (32) to control the rotation direction and the rotation speed of the first pump (31).

[0033] The target pressure is determined based on the control of the hydraulic actuator (11) (how the hydraulic actuator (11) is controlled). The hydraulic actuator (11) can be controlled by controlling the “pressure (P1) of the hydraulic oil in the first flow path (21a)” which is the pressure of the hydraulic oil supplied to the hydraulic actuator (11).

[0034] Furthermore, in the driving operation, the control unit (50) controls the second pump (36) so that the vent pressure (P2) detected by the vent pressure sensor (42) is maintained at a predetermined pressure. In this example, the control unit (50) controls the rotation direction and the rotation speed of the second pump (36) by controlling the rotation direction and the rotation speed of the second motor (37).

[0035] Specifically, in the driving operation, when the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds the set pressure (P3) of the relief valve (35), causing the relief valve (35) to operate and causing the vent pressure (P2) to exceed a predetermined pressure, the control unit (50) controls the second pump (36) to return the vent pressure (P2) to the predetermined pressure.

[0036] The predetermined pressure is a target value of the vent pressure (P2) and is determined based on a target value of the set pressure (P3) of the relief valve (35). For example, the target value of the vent pressure (P2) is set to a pressure obtained by subtracting a "pressure (K) corresponding to the biasing force of the pilot spring (304)," which will be described later, from the target value of the set pressure (P3) of the relief valve (35). The target value of the set pressure (P3) of the relief valve (35) is determined based on the allowable upper limit of the pressure (P1) of the hydraulic oil in the first flow path (21a). For example, the target value of the set pressure (P3) of the relief valve (35) is set to a pressure that is lower by a predetermined amount than the allowable upper limit of the pressure (P1) of the hydraulic oil in the first flow path (21a).

[0037] In this example, the control unit (50) monitors the vent pressure (P2) by continuously determining whether the vent pressure (P2) detected by the second pressure sensor (42) is within a predetermined range during the driving operation, and controls the second pump (36) during the driving operation so that the vent pressure (P2) is within the predetermined range.

[0038] The predetermined range is a range of pressures that includes the predetermined pressure, for example, a range of pressures with the predetermined pressure as a median. The predetermined range is defined by a predetermined upper limit pressure and a predetermined lower limit pressure. For example, the upper limit pressure is set to a pressure that is higher than the predetermined pressure by a predetermined amount, and the lower limit pressure is set to a pressure that is lower than the predetermined pressure by a predetermined amount.

[0039] Specifically, when the vent pressure (P2) exceeds the upper limit pressure during the driving operation, the control unit (50) controls the second pump (36) so that the second pump (36) is driven in a reverse rotation state, thereby decreasing the vent pressure (P2) by a predetermined control amount. Furthermore, when the vent pressure (P2) falls below the lower limit pressure during the driving operation, the control unit (50) controls the second pump (36) so that the second pump (36) is driven in a forward rotation state, thereby increasing the vent pressure (P2) by a predetermined control amount. Then, when the vent pressure (P2) reaches a predetermined pressure (or falls within a predetermined range) during the driving operation, the control unit (50) controls the second pump (36) so that the second pump (36) is stopped.

[0040] The control amount may be a fixed amount set in advance. Alternatively, the control amount may be a variable amount that changes depending on the absolute value of the difference between the vent pressure (P2) and a predetermined pressure. For example, the control amount may increase as the absolute value of the difference between the vent pressure (P2) and the predetermined pressure increases.

[0041] [Pressure release operation] In the depressurization operation, the control unit (50) controls the second pump (36) so that the vent pressure (P2) decreases from a “first pressure, which is the initial pressure in the depressurization operation,” to a “second pressure lower than the first pressure.” For example, the second pressure is set to the minimum value of the vent pressure (P2) (the minimum expected vent pressure (P2)).

[0042] In this example, the control unit (50) controls the second pump (36) in the depressurization operation so that the change over time of the vent pressure (P2) becomes a preset change over time.

[0043] [Relief valve structure] Next, the structure of the relief valve (35) will be described with reference to Fig. 2. The relief valve (35) is a balanced piston type relief valve. The relief valve (35) includes a casing (300), a main valve (301), a main spring (302), a pilot valve (303), and a pilot spring (304).

[0044] The casing (300) is formed with an inlet port (35a), an outlet port (35b), a vent port (35c), a main valve chamber (300a), a pilot valve chamber (300b), a communication chamber (300c), and a communication passage (300d).

[0045] The main valve chamber (300a) is a cylindrical space and accommodates the main valve (301) and the main spring (302). Hereinafter, the axial direction of the main valve chamber (300a) (the direction in which the axis extends, the up-down direction in FIG. 2) will be referred to as the "first direction," and the direction perpendicular to the first direction (the left-right direction in FIG. 2) will be referred to as the "second direction."

[0046] An inlet port (35a) and an outlet port (35b) are in communication with one axial end (lower end in FIG. 2) of the main valve chamber (300a). In this example, the inlet port (35a) penetrates the casing (300) in the second direction and is in communication with one axial end of the main valve chamber (300a). The outlet port (35b) penetrates the casing (300) in the first direction and is in communication with one axial end of the main valve chamber (300a).

[0047] The pilot valve chamber (300b) is a cylindrical space and accommodates the pilot valve (303) and the pilot spring (304). In this example, the axial direction of the pilot valve chamber (300b) intersects with the axial direction of the main valve chamber (300a). Specifically, the axial direction of the main valve chamber (300a) is a first direction, and the axial direction of the pilot valve chamber (300b) is a second direction.

[0048] The communication chamber (300c) is in communication with the main valve chamber (300a), the pilot valve chamber (300b), and the vent port (35c). In this example, the other axial end (upper end in FIG. 2) of the main valve chamber (300a) is in communication with the communication chamber (300c) via a communication passage (300e) extending in the first direction. One axial end (right end in FIG. 2) of the pilot valve chamber (300b) is in communication with the communication chamber (300c). The vent port (35c) passes through the casing (300) in the second direction and is in communication with the communication chamber (300c).

[0049] The communication passage (300d) connects the main valve chamber (300a) and the pilot valve chamber (300b). In this example, the communication passage (300d) extends in a first direction and connects the other axial end (upper end in FIG. 2) of the main valve chamber (300a) to one axial end of the pilot valve chamber (300b).

[0050] The main valve (301) opens and closes a communication portion (hereinafter referred to as a “main communication portion (351)”) between the main valve chamber (300a) and the outlet port (35b). In this example, the main valve (301) has a cylindrical valve body (301a) extending in a first direction and an annular portion (301b) protruding radially outward from the axial center of the valve body (301a). When one axial end of the valve body (301a) comes into contact with the main communication portion (351), the main communication portion (351) is in a “closed state.” When the contact between the one axial end of the valve body (301a) and the main communication portion (351) is released, the main communication portion (351) is in an “open state.” The main valve (301) is slidable in a first direction with the peripheral wall of the annular portion (301b) in contact with the peripheral wall of the main valve chamber (300a).

[0051] A through-passage (301c) penetrating the valve body (301a) in a first direction is formed in the valve body (301a) of the main valve (301). A throttle passage (301d) penetrating the annular portion (301b) of the main valve (301) in the first direction is formed in the annular portion (301b).

[0052] The main spring (302) biases the main valve (301) toward the main communication portion with a preset biasing force.

[0053] The pilot valve (303) opens and closes a communication portion (hereinafter referred to as a "pilot communication portion (352)") between the pilot valve chamber (300b) and the communication chamber (300c). In this example, one axial end of the pilot valve (303) comes into contact with the pilot communication portion (352), causing the pilot communication portion (352) to enter a "closed state." When the contact between the one axial end of the pilot valve (303) and the pilot communication portion (352) is released, the pilot communication portion (352) enters an "open state."

[0054] The pilot spring (304) biases the pilot valve (303) toward the pilot communication portion with a preset biasing force. The biasing force of the pilot spring (304) can be adjusted by turning the handle. The biasing force of the pilot spring (304) changes by turning the handle.

[0055] [Relief valve setting pressure] Next, the set pressure (P3) of the relief valve (35) shown in FIG. 2 will be described. The set pressure (P3) of the relief valve (35) is a pressure corresponding to the "vent pressure (P2)" which is the pressure of the hydraulic oil at the vent port (35c) of the relief valve (35) and the "biasing force of the pilot spring (304)." The set pressure (P3) of the relief valve (35) increases as the vent pressure (P2) or the biasing force of the pilot spring (304) increases. Specifically, if the pressure corresponding to the biasing force of the pilot spring (304) is "pressure (K)," the set pressure (P3) of the relief valve (35) is a pressure obtained by adding the "vent pressure (P2)" and the "pressure (K)."

[0056] [Relief valve behavior] Next, a description will be given of the behavior of the relief valve (35) shown in Fig. 2. The pressure of the hydraulic oil at the inlet port (35a) of the relief valve (35) is the pressure (P1) of the hydraulic oil in the first flow path (P21).

[0057] When the pressure (P1) of the hydraulic oil in the first flow path (P21) exceeds the set pressure (P3) of the relief valve (35), the pilot valve (303) moves away from the pilot communication part (352), and the pilot communication part (352) enters an "open state." This causes hydraulic oil to flow through the throttle passage (301d) of the main valve (301), and a pressure difference occurs between both axial end faces (the upper end face and the lower end face in FIG. 2) of the annular part (301b) of the main valve (301). As a result, the main valve (301) moves away from the main communication part (351), and the main communication part (351) enters an "open state." This causes hydraulic oil to flow from the inlet port (35a) to the outlet port (35b), and the pressure of the hydraulic oil at the inlet port (35a) (the pressure (P1) of the hydraulic oil in the first flow path (P21)) decreases.

[0058] When the pressure (P1) of the hydraulic oil in the first flow path (P21) exceeds the set pressure (P3) of the relief valve (35) and the main valve (301) starts to move away from the main communication part (351), the volume of the space surrounded by the other axial end face (upper end face in FIG. 2) of the annular part (301b) of the main valve (301) and the main valve chamber (300a) decreases. As a result, the hydraulic oil in the vent flow path (23) connected to the vent port (35c) of the relief valve (35) is compressed, and the vent pressure (P2), which is the pressure of the hydraulic oil in the vent port (35c) of the relief valve (35), increases. This increase in vent pressure (P2) increases the set pressure (P3) of the relief valve (35), thereby inhibiting the operation of the relief valve (35) (specifically, the movement of the main valve (301) away from the main communication part (351)).

[0059] Furthermore, the above-mentioned operation in which “the pressure (P1) of the hydraulic oil in the first flow path (P21) exceeds the set pressure (P3) of the relief valve (35), and the main valve (301) begins to move in a direction away from the main communication part (351)” is an example of the operation in which “the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds the set pressure (P3) of the relief valve (35), and the relief valve (35) tries to operate (begins to operate).”

[0060] [Driving operation] Next, the driving operation will be described with reference to Fig. 3. The following describes an example in which surge pressure (sudden pressure fluctuation of the hydraulic oil) occurs in the first flow path (21a) when hydraulic oil is supplied from the oil tank (12) to the hydraulic actuator (11) via the first pump (31).

[0061] 3 shows the “first flow path pressure” which is the pressure (P1) of the hydraulic oil in the first flow path (21a), the “vent pressure (P2)” detected by the second pressure sensor (42), the “second pump flow rate (Q2)” which is the flow rate of the hydraulic oil conveyed by the second pump (36), and the “relief flow rate (QR)” which is the flow rate of the hydraulic oil flowing through the relief valve (35). The signs (positive and negative) of the second pump flow rate (Q2) and the relief flow rate (QR) indicate that the direction of the hydraulic oil toward the oil tank (12) is “negative.”

[0062] At time (t0), the control unit (50) controls the first pump (31) so that the pressure (P1) of the hydraulic oil in the first flow path (21a) becomes a predetermined target pressure by driving the first pump (31) in the forward rotation state. As a result, the hydraulic oil starts to be supplied from the oil tank (12) to the hydraulic actuator (11) via the first pump (31), and the pressure (P1) of the hydraulic oil in the first flow path (21a) increases. When the hydraulic oil is supplied from the oil tank (12) to the hydraulic actuator (11) via the first pump (31), a surge pressure (a sudden increase in the pressure of the hydraulic oil) occurs in the first flow path (21a).

[0063] At time t1, the pressure P1 of the hydraulic oil in the first flow path 21a exceeds the set pressure P3 of the relief valve 35. This causes the relief valve 35 to operate, and as a result, the vent pressure P2 detected by the second pressure sensor 42 increases.

[0064] The increase in the vent pressure (P2) increases the set pressure (P3) of the relief valve (35), and the pressure (P1) of the hydraulic oil in the first flow path (21a) does not exceed the set pressure (P3). As a result, the relief valve (35) does not operate, and the hydraulic oil remains in a state where it does not flow from the first flow path (21a) through the relief valve (35) to the oil tank (12).

[0065] At time (t2), the vent pressure (P2) exceeds the upper limit pressure (the upper limit pressure that defines the upper limit of a predetermined range). The control unit (50) controls the second pump (36) so that the second pump (36) is driven in reverse rotation to reduce the vent pressure (P2) by a predetermined control amount. As a result, the second pump (36) starts to drive in reverse rotation, and hydraulic oil starts to flow from the vent port (35c) of the relief valve (35) through the second pump (36) toward the oil tank (12). As a result, the vent pressure (P2) decreases.

[0066] Due to the decrease in the vent pressure (P2), the set pressure (P3) of the relief valve (35) decreases, and the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds the set pressure (P3) of the relief valve (35). This activates the relief valve (35), and the hydraulic oil starts to flow from the first flow path (21a) through the relief valve (35) toward the oil tank (12). This activation of the relief valve (35) causes the pressure (P1) of the hydraulic oil in the first flow path (21a) to start decreasing.

[0067] During the period from time (t2) to time (t3), the set pressure (P3) of the relief valve (35) decreases as the vent pressure (P2) decreases, and the pressure (P1) of the hydraulic oil in the first flow path (21a) also decreases.

[0068] At time (t3), the vent pressure (P2) returns to the predetermined pressure. The control unit (50) controls the second pump (36) to stop the second pump (36). As a result, the second pump (36) stops, and the hydraulic oil stops flowing from the vent port (35c) of the relief valve (35) through the second pump (36) to the oil tank (12).

[0069] Furthermore, by maintaining the vent pressure (P2) at a predetermined pressure, the set pressure (P3) of the relief valve (35) is also maintained at a pressure corresponding to the predetermined pressure. When the pressure (P1) of the hydraulic oil in the first flow path (21a) does not exceed the set pressure (P3) of the relief valve (35), the relief valve (35) is deactivated, and the hydraulic oil does not flow from the first flow path (21a) through the relief valve (35) toward the oil tank (12).

[0070] As described above, even if a surge pressure (a sudden increase in pressure of the hydraulic oil) occurs in the first flow path (21a) when the hydraulic oil is supplied from the oil tank (12) to the hydraulic actuator (11) via the first pump (31), the set pressure (P3) of the relief valve (35) can be stabilized to stabilize the operation of the relief valve (35), thereby suppressing the surge pressure in the first flow path (21a).

[0071] [Pressure release operation] Next, the depressurization operation will be described with reference to Fig. 4. In the following, an example will be described in which the time change of the preset vent pressure (P2) is a time change in which "the pressure changes sharply from the first pressure to the second pressure."

[0072] 4 shows the “first flow path pressure” which is the pressure (P1) of the hydraulic oil in the first flow path (21a), the “vent pressure (P2)” detected by the second pressure sensor (42), the “second pump flow rate (Q2)” which is the flow rate of the hydraulic oil conveyed by the second pump (36), and the “relief flow rate (QR)” which is the flow rate of the hydraulic oil flowing through the relief valve (35). The signs (positive and negative) of the second pump flow rate (Q2) and the relief flow rate (QR) indicate that the direction of the hydraulic oil toward the oil tank (12) is “negative.”

[0073] At time (t1), the control unit (50) controls the second pump (36) to operate in reverse rotation to reduce the vent pressure (P2) from the first pressure (initial pressure) to the second pressure. In this example, the second pressure is the final pressure in the depressurization operation and is set to, for example, the minimum value of the vent pressure (P2). Through the above control, the vent pressure (P2) is reduced, and the set pressure (P3) of the relief valve (35) is reduced. As a result, the pressure of the hydraulic oil in the first flow path (21a) exceeds the set pressure (P3) of the relief valve (35). This activates the relief valve (35), and the hydraulic oil returns from the hydraulic actuator (11) to the oil tank (12) via the relief valve (35). As the vent pressure (P2) decreases, the pressure of the hydraulic oil in the first flow path (21a) decreases.

[0074] At time (t2), the vent pressure (P2) becomes the second pressure. The control unit (50) controls the second pump (36) to stop the second pump (36). As a result, the second pump (36) stops, and the hydraulic oil stops flowing from the vent port (35c) of the relief valve (35) through the second pump (36) to the oil tank (12).

[0075] Furthermore, by maintaining the vent pressure (P2) at the second pressure, the set pressure (P3) of the relief valve (35) is also maintained at a pressure corresponding to the second pressure (in this example, the minimum value of the set pressure (P3)). When the pressure (P1) of the hydraulic oil in the first flow path (21a) no longer exceeds the set pressure (P3) of the relief valve (35), the relief valve (35) is no longer activated, and the hydraulic oil no longer flows from the first flow path (21a) through the relief valve (35) toward the oil tank (12).

[0076] [Effects of the embodiment] As described above, in the hydraulic drive device (20) of the embodiment, when the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds the set pressure (P3) corresponding to the vent pressure (P2), which is the pressure of the hydraulic oil in the vent port (35c), the relief valve (35) operates to return the hydraulic oil in the first flow path (21a) to the oil tank (12). The second pump (36) is connected between the vent port (35c) of the relief valve (35) and the oil tank (12). Then, during the drive operation of supplying the hydraulic oil from the oil tank (12) to the hydraulic actuator (11) via the first pump (31), the control unit (50) controls the second pump (36) so that the vent pressure (P2) detected by the vent pressure sensor (42) is maintained at a predetermined pressure.

[0077] In the above configuration, the set pressure (P3) of the relief valve (35) can be controlled by using the second pump (36) without using a pilot relief valve (e.g., the electromagnetic proportional pilot relief valve of Patent Document 1) that controls itself using the pressure it controls. This makes it possible to stabilize the set pressure (P3) of the relief valve (35) more than when using the above-mentioned pilot relief valve, thereby improving the stability of the operation of the relief valve (35). Since the stability of the operation of the relief valve (35) can be improved in this way, the pressure (P1) of the hydraulic oil in the first flow path (21a), which is the pressure of the hydraulic oil supplied to the hydraulic actuator (11), can be accurately controlled during the driving operation, and the hydraulic actuator (11) can be accurately controlled.

[0078] In addition, in the hydraulic drive device (20) of the embodiment, when the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds the set pressure (P3) of the relief valve (35) during the drive operation, the relief valve (35) operates and the vent pressure (P2) becomes higher than a predetermined pressure, the control unit (50) controls the second pump (36) to return the vent pressure (P2) to the predetermined pressure.

[0079] In the above configuration, when the relief valve (35) is activated and the vent pressure (P2) becomes higher than a predetermined pressure, the second pump (36) is controlled so that the vent pressure (P2) returns to the predetermined pressure, thereby stabilizing the set pressure (P3) of the relief valve (35).

[0080] In addition, in the hydraulic drive system (20) of the embodiment, the control unit (50) controls the second pump (36) in a depressurization operation of returning hydraulic oil from the hydraulic actuator (11) to the oil tank (12) via the relief valve (35) so that the vent pressure (P2) decreases from the first pressure (initial pressure in the depressurization operation) to the second pressure (pressure lower than the first pressure).

[0081] In the above configuration, the set pressure of the relief valve (35) can be reduced by reducing the vent pressure (P2), and as a result, the pressure of the hydraulic oil in the first flow path (21a) can exceed the set pressure (P3) of the relief valve (35). This allows the relief valve (35) to be operated in the depressurization operation, and allows the hydraulic oil to be returned from the hydraulic actuator (11) to the oil tank (12) via the relief valve (35).

[0082] Furthermore, in the above configuration, the set pressure (P3) of the relief valve (35) can be controlled by the second pump (36) without using a pilot relief valve that controls itself using the pressure it controls. This makes it possible to stabilize the set pressure (P3) of the relief valve (35) more than when using the above-described pilot relief valve, thereby improving the stability of the operation of the relief valve (35). In this way, the stability of the operation of the relief valve (35) during the depressurization operation can be improved, and the depressurization operation can be performed with high accuracy.

[0083] In the hydraulic drive system (20) of the embodiment, the control unit (50) controls the second pump (36) in the depressurization operation so that the change over time of the vent pressure (P2) becomes a preset change over time.

[0084] In the above configuration, by setting the change in the vent pressure (P2) over time during the depressurization operation to a predetermined time change, the change in the set pressure (P3) of the relief valve (35) over time during the depressurization operation can be set to a predetermined time change. This makes it possible to control the return of the hydraulic oil from the hydraulic actuator (11) to the oil tank (12) during the depressurization operation, and thereby to accurately control the operation of the hydraulic actuator (11) during the depressurization operation.

[0085] (Modification of pressure release operation) Note that the "change over time of the preset vent pressure (P2)" in the depressurization operation is not limited to a "sharp change from the first pressure (initial pressure) to the second pressure (final pressure)." Hereinafter, the "change over time of the preset vent pressure (P2)" in the depressurization operation will be simply referred to as the "change over time of the vent pressure (P2) in the depressurization operation."

[0086] For example, as shown in FIG. 5, the change over time of the vent pressure (P2) during the depressurization operation may be such that "a maintenance period in which the vent pressure (P2) is maintained at a constant value and a change period in which the vent pressure (P2) decreases alternately occur, resulting in a stepwise change from the first pressure to the second pressure."

[0087] Furthermore, the change over time of the vent pressure (P2) during the depressurization operation may be a change over time in which the vent pressure (P2) "slowly changes from the first pressure to the second pressure," or a change over time in which the vent pressure (P2) "continuously changes from the first pressure to the second pressure without any period in which the vent pressure (P2) is maintained at a constant value," or any other change over time.

[0088] Furthermore, the temporal change in the vent pressure (P2) during the depressurization operation may be settable by at least one of the following elements: "whether or not a maintenance period is included," "the duration of the maintenance period and the change period," and "the amount of decrease in the vent pressure (P2) per unit time during the change period." For example, the control unit (50) may set at least one of the above elements in the temporal change in the vent pressure (P2) during the depressurization operation in response to a setting operation (an operation for setting at least one of the above elements) by the operator of the hydraulic machine (10).

[0089] Furthermore, the change over time of the vent pressure (P2) in the depressurization operation may be selected from a plurality of candidates (candidates for the change over time of the vent pressure (P2) in the depressurization operation) prepared in advance. Each of the plurality of candidates differs from the other candidates in at least one element of “presence or absence of a maintenance period,” “duration of the maintenance period and the change period,” and “amount of decrease in the vent pressure (P2) per unit time in the change period.” For example, in response to a selection operation (an operation for selecting one candidate from the plurality of candidates) by the operator of the hydraulic machine (10), the control unit (50) may set a candidate selected from the plurality of candidates as the “change over time of the vent pressure (P2) in the depressurization operation.”

[0090] The setting operation and the selection operation may be input to an operation unit (such as an operation panel operated by an operator, not shown) provided in the hydraulic machine 10. The control unit 50 may be configured to perform the setting operation (or the selection operation) in response to the setting operation (or the selection operation) input to the operation unit.

[0091] (Other embodiments) The above embodiment and modified examples may be configured or processed as follows.

[0092] Although the hydraulic actuator (11) is a "single-acting hydraulic cylinder" in the above example, the present invention is not limited to this. For example, as shown in Fig. 6, the hydraulic actuator (11) may be a double-acting hydraulic cylinder.

[0093] The hydraulic actuator (11) shown in FIG. 6 includes a cylinder tube (101), a piston (102), and a rod (103). The piston (102) is housed in the cylinder tube (101) so as to be slidable in the extension direction of the cylinder tube (101), and divides the internal space of the cylinder tube (101) into a "head chamber (104) at one end side of the sliding direction of the piston (102)" and a "rod chamber (105) at the other end side of the sliding direction of the piston (102)." The rod (103) is disposed in the rod chamber (105). One end of the rod (103) is connected to the other end side of the sliding direction of the piston (102), and the other end of the rod (103) is connected to a mechanical element.

[0094] When hydraulic oil is supplied to the head chamber (104) and the hydraulic oil is discharged from the rod chamber (105), the piston (102) moves toward the rod chamber (105) and the rod (103) is pushed out of the cylinder tube (101). When hydraulic oil is supplied to the rod chamber (105) and the hydraulic oil is discharged from the head chamber (104), the piston (102) moves toward the head chamber (104) and the rod (103) is pulled back toward the head chamber (104).

[0095] As shown in FIG. 6, the hydraulic drive unit (20) may include a directional control valve (38). The directional control valve (38) has a drive solenoid and is switchable between a first state, a second state, and a closed state. In the first state, the first port (A) and the third port (P) communicate with each other, and the second port (B) and the fourth port (T) communicate with each other. In the second state, the first port (A) and the fourth port (T) communicate with each other, and the second port (B) and the third port (P) communicate with each other. In the closed state, the first port (A), the second port (B), the third port (P), and the fourth port (T) are each isolated from the other ports.

[0096] 6, the first port (A) of the directional control valve (38) is connected to the head chamber (104) of the hydraulic actuator (11), and the second port (B) of the directional control valve (38) is connected to the rod chamber (105) of the hydraulic actuator (11). The third port (P) of the directional control valve (38) is connected to the first flow path (21a), and the fourth port (T) of the directional control valve (38) is connected to the oil tank (12).

[0097] When the directional control valve (38) is in the first state, the hydraulic oil in the first flow path (21a) is supplied to the head chamber (104) of the hydraulic actuator (11), and the hydraulic oil in the rod chamber (105) of the hydraulic actuator (11) is returned to the oil tank (12). As a result, the rod (103) of the hydraulic actuator (11) is pushed out of the cylinder tube (101).

[0098] When the directional control valve (38) is in the second state, the hydraulic oil in the first flow path (21a) is supplied to the rod chamber (105) of the hydraulic actuator (11), and the hydraulic oil in the head chamber (104) of the hydraulic actuator (11) is returned to the oil tank (12). As a result, the rod (103) of the hydraulic actuator (11) is pulled back toward the head chamber (104).

[0099] In the depressurization operation, the control unit (50) may control the first pump (31) to operate in a reverse rotation state, thereby returning the hydraulic oil from the hydraulic actuator (11) to the oil tank (12) via the first pump (31), thereby quickly completing the depressurization operation.

[0100] Although the embodiments and modifications have been described, it will be understood that various modifications in form and details are possible without departing from the spirit and scope of the claims. Furthermore, elements of the above-described embodiments, modifications, and other embodiments may be combined or substituted as appropriate. [Industrial Applicability]

[0101] As described above, the present disclosure is useful as a hydraulic drive technology. [Explanation of symbols]

[0102] 10 Hydraulic Machinery 11 Hydraulic Actuator 12 Oil Tank 20 Hydraulic drive unit 21 Main Channel 21a First flow path 22 Relief channel 23 Vent channel 31 First Pump 32 First motor 35 Relief valve 35a inlet port 35b Exit Port 35c vent port 36 Second Pump 37 Second motor 41 First pressure sensor 42 Second pressure sensor (vent pressure sensor) 50 control section 300 casing 301 Main valve 302 Main spring 303 Pilot valve 304 Pilot Spring

Claims

1. A hydraulic drive device that drives a hydraulic actuator (11), a first pump (31) connected between the hydraulic actuator (11) and an oil tank (12); a relief valve (35) connected between the oil tank (12) and a first flow path (21a) that is a flow path between the hydraulic actuator (11) and the first pump (31), the relief valve (35) having a vent port (35c), and operating to return the hydraulic oil in the first flow path (21a) to the oil tank (12) when the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds a set pressure (P3) that corresponds to a vent pressure (P2) that is the pressure of the hydraulic oil in the vent port (35c); a second pump (36) connected between the vent port (35c) of the relief valve (35) and the oil tank (12); a vent pressure sensor (42) for detecting the vent pressure (P2); a control unit (50) that controls the second pump (36) so that the vent pressure (P2) detected by the vent pressure sensor (42) is maintained at a predetermined pressure during a driving operation of supplying hydraulic oil from the oil tank (12) to the hydraulic actuator (11) via the first pump (31). Hydraulic drive unit.

2. The hydraulic drive system of claim 1, The relief valve (35) is configured so that when the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds a set pressure (P3) of the relief valve (35) and the relief valve (35) is activated, the vent pressure (P2) increases, In the driving operation, when the pressure (P1) of the hydraulic oil in the first flow path (21a) exceeds the set pressure (P3) of the relief valve (35), the relief valve (35) operates, and the vent pressure (P2) becomes higher than the predetermined pressure, the control unit (50) controls the second pump (36) so that the vent pressure (P2) returns to the predetermined pressure. Hydraulic drive unit.

3. A hydraulic machine comprising the hydraulic drive system of claim 1 or 2.

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