Hydraulic drive device

Abstract

To provide a hydraulic driving device capable of inhibiting an excessive load from working on an electric motor during regeneration.SOLUTION: The hydraulic driving device for supplying / discharging working liquid to each of a head side port and a rod side port to drive a hydraulic cylinder includes a hydraulic pump motor to be rotationally driven by discharging the working liquid and supplying working liquid, the electric motor connected to the hydraulic pump motor, a direction control valve for switching the direction of the working liquid flowing between the hydraulic pump motor and the head side port, a regeneration valve for opening / closing a regeneration passage linking the head side port to the rod side port, a pressure sensor for detecting an inflow pressure to the hydraulic pump motor, and a control device for controlling the operation of each of the direction control valve and the regeneration valve. The control device controls the opening of the regeneration valve in response to the inflow pressure of the working liquid detected by the pressure sensor when the regeneration passage is opened by the regeneration valve and the head side port and the hydraulic pump motor are connected by the direction control valve.SELECTED DRAWING: Figure 1

Description

Technical Field

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[0001] The present disclosure relates to a hydraulic drive device that supplies and discharges hydraulic fluid to each of a head-side port and a rod-side port of a hydraulic cylinder.

Background Art

[0002] As a hydraulic drive device for driving a hydraulic cylinder, for example, a hydraulic drive device as disclosed in Patent Document 1 is known. In the hydraulic drive device as disclosed in Patent Document 1, in a boom lowering operation, a hydraulic pump motor is rotationally driven by the hydraulic oil discharged from the head-side port of the boom cylinder. Thereby, the potential energy of the boom can be regenerated into electrical energy.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

[0007] According to this disclosure, the opening degree of the regeneration valve is controlled according to the inflow pressure. Therefore, when an excessive load is generated on the motor during regeneration, the regeneration valve can generate a pressure loss. This suppresses the excessive load acting on the motor during regeneration. [Effects of the Invention]

[0008] According to this disclosure, it is possible to suppress excessive load on the motor during regeneration. [Brief explanation of the drawing]

[0009] [Figure 1] This is a circuit diagram showing the configuration of a hydraulic drive device according to the first embodiment of the present disclosure. [Figure 2] Figure 1 is a flowchart showing the procedure for the boom cylinder extension and retraction process performed by the hydraulic drive device. [Figure 3] Figure 1 is a circuit diagram showing the flow of the working fluid when extending the boom cylinder in the hydraulic drive device. [Figure 4] Figure 1 is a circuit diagram showing the flow of the working fluid when the boom cylinder is retracted in the hydraulic drive device. [Figure 5] This is a circuit diagram showing the configuration of a hydraulic drive device according to a second embodiment of the present disclosure. [Modes for carrying out the invention]

[0010] Hereinafter, the hydraulic drive devices 1 and 1A of the first and second embodiments of this disclosure will be described with reference to the aforementioned drawings. Note that the concept of direction used in the following description is for convenience of explanation and does not limit the orientation of the invention's configuration to that direction. Furthermore, the hydraulic drive devices 1 and 1A described below are merely one embodiment of this disclosure. Therefore, this disclosure is not limited to these embodiments, and additions, deletions, and modifications are permitted without departing from the spirit of the invention.

[0011] [First Embodiment] The hydraulic drive device 1 shown in Figure 1 is installed in, for example, a work vehicle (not shown). The work vehicle is, for example, a construction vehicle such as a hydraulic excavator and a hydraulic crane, and an industrial vehicle such as a lift. In this embodiment, the work vehicle is a hydraulic excavator. The hydraulic excavator is equipped with a boom, an arm, and an attachment (for example, a bucket). The hydraulic excavator can perform various tasks by moving the boom, arm, and attachment (for example, a bucket). The hydraulic excavator is equipped with a boom cylinder 2.

[0012] A boom cylinder 2, an example of a hydraulic cylinder, has a head-side port 2a and a rod-side port 2b. The boom cylinder 2 is installed on the boom. The boom cylinder 2 moves the boom by extending and retracting. The boom cylinder 2 is driven by the supply and discharge of working fluid (e.g., oil or water) to and from the head-side port 2a and the rod-side port 2b, respectively. More specifically, the boom cylinder 2 extends when working fluid is supplied to the head-side port 2a and working fluid is discharged from the rod-side port 2b. This causes the boom to rise. On the other hand, the boom cylinder 2 contracts when working fluid is discharged from the head-side port 2a and working fluid is supplied to the rod-side port 2b. This causes the boom to lower. In this embodiment, the boom cylinder 2 is supported by the weight of the boom in the direction of contraction. Therefore, the boom cylinder 2 contracts by discharging working fluid from the head-side port 2a and drawing working fluid in from the rod-side port 2b due to the weight of the boom.

[0013] <Hydraulic drive device> The hydraulic drive unit 1 supplies and discharges working fluid to the head-side port 2a and the rod-side port 2b, respectively. This allows the hydraulic drive unit 1 to drive the boom cylinder 2, i.e., extend and retract the boom cylinder 2. The hydraulic drive unit 1 also regenerates energy from the working fluid discharged from the head-side port 2a of the boom cylinder 2. The hydraulic drive unit 1, which functions in this way, comprises a hydraulic pump motor 11, an electric motor 12, a directional control valve 13, a regeneration valve 14, and an unload valve 15. The hydraulic drive unit 1 also includes an operating device 16, an intake-side pressure sensor 17, a stroke sensor 18, and a control device 19.

[0014] <Hydraulic pump motor> The hydraulic pump motor 11 has an intake port 11a and a discharge port 11b. The hydraulic pump motor 11 also has a shaft 11c. The intake port 11a is connected to the tank 20 via an intake passage 21. A check valve 24 is interposed in the intake passage 21. The check valve 24 allows the flow of working fluid from the tank 20 to the intake port 11a and prevents flow in the reverse direction.

[0015] When the shaft 11c is rotated, the hydraulic pump motor 11 operates as follows: The hydraulic pump motor 11 draws in working fluid from the suction port 11a. The hydraulic pump motor 11 then discharges working fluid from the discharge port 11b. On the other hand, when working fluid is supplied to the suction port 11a, the hydraulic pump motor 11 rotates the shaft 11c. The hydraulic pump motor 11 then discharges working fluid from the discharge port 11b. In this embodiment, the hydraulic pump motor 11 is a variable displacement swashplate pump and has a regulator 11d. The regulator 11d changes the tilt angle of the swashplate according to the input displacement command. This changes the pump capacity of the hydraulic pump motor 11. That is, the hydraulic pump motor 11 can change the discharge flow rate and the suction flow rate.

[0016] <Electric motor> The electric motor 12 is connected to the hydraulic pump motor 11. More specifically, the electric motor 12 is connected to the shaft 11c. The electric motor 12 rotates the hydraulic pump motor 11, thereby discharging working fluid from the hydraulic pump motor 11. More specifically, the electric motor 12 rotates the shaft 11c, thereby discharging working fluid from the discharge port 11b. The electric motor 12 also generates electricity by receiving the supply of working fluid, which causes the hydraulic pump motor 11 (more specifically, the shaft 11c) to rotate. In other words, the electric motor 12 works in cooperation with the hydraulic pump motor 11 to regenerate the fluid energy of the working fluid into electrical energy. Furthermore, the electric motor 12 changes its rotational speed (more specifically, the rotational speed of the shaft 11c) according to the input rotational speed command.

[0017] <Direction control valve> The direction control valve 13 switches the direction of the working fluid flowing between the hydraulic pump motor 11 and the head side port 2a. The direction control valve 13 is connected to the suction port 11a and the discharge port 11b of the hydraulic pump motor 11, respectively. More specifically, the direction control valve 13 is connected to the suction port 11a side of the hydraulic pump motor 11 from the check valve 24 in the suction passage 21. Also, the direction control valve 13 is connected to the discharge port 11b via the discharge passage 22. Further, the direction control valve 13 is connected to the head side port 2a of the boom cylinder 2. Also, the direction control valve 13 is connected to the rod side port 2b and the tank 20 of the boom cylinder 2.

[0018] The direction control valve 13 switches the connection destination of the head side port 2a to the discharge port 11b and the suction port 11a, respectively, according to the input operation command. Further, when the direction control valve 13 connects the head side port 2a to the discharge port 11b, it connects the rod side port 2b to the tank 20. On the other hand, when the direction control valve 13 connects the head side port 2a to the suction port 11a, it connects the rod side port 2b to the discharge port 11b. Note that when the direction control valve 13 connects the rod side port 2b to the discharge port 11b, it allows the flow of the working fluid from the discharge port 11b to the rod side port 2b and blocks the reverse flow of the working fluid. Also, when the direction control valve 13 connects the head side port 2a to the suction port 11a, it controls the opening degree between the head side port 2a and the suction port 11a (hereinafter, also referred to as the "opening degree of the direction control valve 13") according to the operation command. In the present embodiment, the direction control valve 13 is an electric spool valve. However, the direction control valve 13 is not limited to an electric spool valve.

[0019] <Regenerative valve> The regeneration valve 14 opens and closes a regeneration passage 23 that connects the head-side port 2a and the rod-side port 2b. The regeneration valve 14 is interposed in the regeneration passage 23. The regeneration valve 14 opens and closes the regeneration passage 23 in response to a regeneration command. Further, the regeneration valve 14 allows the flow of the hydraulic fluid in the regeneration direction in the open state of the regeneration passage 23 and blocks the reverse flow. The regeneration direction is the flow from the head-side port 2a to the rod-side port 2b. Thereby, the regeneration valve 14 regenerates the hydraulic fluid discharged from the head-side port 2a to the rod-side port 2b. The regeneration valve 14 reduces the opening degree in response to a regeneration command. The regeneration valve 14 is, for example, an electromagnetic proportional control valve.

[0020] <Unloading valve> The unloading valve 15 connects a discharge passage 22 that connects the discharge port 11b and the direction control valve 13 to the tank 20. More specifically, the unloading valve 15 connects the discharge passage 22 to the tank 20 in response to an input unloading command. Thereby, the hydraulic pump motor 11 can be unloaded. In the present embodiment, the unloading valve 15 is an electromagnetic on-off valve. However, the unloading valve 15 may be an electromagnetic proportional control valve capable of controlling the opening degree.

[0021] <Operating device> The operating device 16 is for operating the boom (more specifically, the boom cylinder 2). The operating device 16 has an operating lever 16a. The operating lever 16a is configured to be operable. The operating device 16 outputs an operation signal according to the operation direction and operation amount of the operating lever 16a. The operating device 16 is, for example, an electric joystick. However, the operating device 16 may be a pilot-operated valve. In this case, the operating device 16 outputs an operation signal according to the output pressure of the pilot-operated valve. Further, the operating device 16 may be a touch panel. In this case, the operating device 16 outputs an operation signal according to the input operation and program.

[0022] <Suction-side pressure sensor> The suction-side pressure sensor 17 detects the inflow pressure of the hydraulic pump motor 11. The inflow pressure is the pressure of the working fluid flowing into the suction port 11a of the hydraulic pump motor 11, and is also called the suction pressure. More specifically, the suction-side pressure sensor 17 is connected to the suction passage 21. The suction-side pressure sensor 17 detects the fluid pressure in the suction passage 21 as the inflow pressure. The suction-side pressure sensor 17 then outputs the detected inflow pressure.

[0023] <Stroke sensor> The stroke sensor 18, an example of a speed sensor, is a sensor for detecting the speed of the boom cylinder 2. More specifically, the stroke sensor 18 detects the stroke amount of the boom cylinder 2. The stroke sensor 18 then outputs the detected stroke amount. The speed sensor may also be a speed sensor, acceleration sensor, angle sensor, or inertial measurement unit (IMU), as long as it is a sensor that can calculate the speed of the boom cylinder 2 based on other detection results. The speed sensor detects the stroke speed of the boom cylinder 2. The acceleration sensor detects the stroke acceleration of the boom cylinder 2. The angle sensor detects the angle of the boom. The IMU detects the acceleration and rotational speed of the boom.

[0024] <Control device> The control device 19 controls the operation of the directional control valve 13, the regeneration valve 14, and the unload valve 15 in response to the input operation signals. More specifically, the control device 19 controls the operation of the directional control valve 13, the regeneration valve 14, and the unload valve 15 by outputting operation commands, regeneration commands, and unload commands in response to the operation signals. In this way, the control device 19 controls the flow of the working fluid in the hydraulic drive device 1. The control device 19 also controls the operation of the hydraulic pump motor 11 and the electric motor 12 in response to the operation signals. More specifically, the control device 19 controls the operation of the hydraulic pump motor 11 and the electric motor 12 by outputting capacity commands and rotational speed commands in response to the operation signals. In this way, the control device 19 controls the discharge flow rate and suction flow rate of the hydraulic pump motor 11.

[0025] Furthermore, in this embodiment, the control device 19 changes the discharge flow rate and suction flow rate of the hydraulic pump motor 11 according to the detection result of the stroke sensor 18. As a result, the control device 19 provides feedback control of the speed or acceleration (speed in this embodiment) of the boom cylinder 2. In addition, the control device 19 controls the operation of the directional control valve 13 and the regeneration valve 14 according to the inflow pressure detected by the suction-side pressure sensor 17. More specifically, the control device 19 controls the opening degree of the directional control valve 13 and the regeneration valve 14 according to the inflow pressure detected by the suction-side pressure sensor 17.

[0026] <Operation of the hydraulic drive device> In the hydraulic drive device 1, when the operating device 16 is operated (in this embodiment, the operating lever 16a is operated), an operation signal is output from the operating device 16. The control device 19 controls the operation of the directional control valve 13, the regeneration valve 14, and the unload valve 15 according to the operation signal. The control device 19 also controls the operation of the electric motor 12 and the hydraulic pump motor 11 according to the operation signal and the detection result of the stroke sensor 18. As a result, the control device 19 extends and retracts the boom cylinder 2 in a direction and speed corresponding to the operation signal (in this embodiment, the operating direction and amount of the operating lever 16a). In the hydraulic drive device 1, when the boom is lowered (i.e., when the boom cylinder 2 is retracted), a portion of the working fluid discharged from the head-side port 2a of the boom cylinder 2 is regenerated into the rod-side port 2b. In addition, the remaining portion of the working fluid discharged from the head-side port 2a is used for energy recovery in the hydraulic drive device 1. Furthermore, the control device 19 controls the opening of the directional control valve 13 and the regeneration valve 14 according to the inflow pressure of the hydraulic pump motor 11. This prevents the load on the electric motor 12 from increasing excessively.

[0027] The boom cylinder extension and retraction process, which extends and retracts the boom cylinder 2, will be explained in more detail below with reference to the flowchart in Figure 2. In the hydraulic drive device 1, when the operating device 16 is operated to extend or retract the boom cylinder 2, an operation signal is output from the operating device 16. Then the boom cylinder extension and retraction process starts and proceeds to step S1. In step S1, which is the boom lowering operation determination process, the control device 19 determines whether the operation on the operating device 16 is a boom lowering operation (i.e., an operation to retract the boom cylinder 2). More specifically, the control device 19 detects the direction of operation of the operating lever 16a based on the operation signal. Then, the control device 19 determines whether it is a boom lowering operation or not according to the direction of operation of the operating lever 16a. For example, if the operating lever 16a is operated in the first direction, the control device 19 determines it is a boom raising operation. Then it proceeds to step S2. On the other hand, if the operating lever 16a is operated in the second direction, the control device 19 determines it is a boom lowering operation. Then it proceeds to step S3.

[0028] In step S2, which is the boom cylinder extension process, the control device 19 extends the boom cylinder 2. More specifically, the control device 19 operates the directional control valve 13 in response to the operation signal. For example, the control device 19 outputs an operation command to the directional control valve 13 in response to the operation signal. As a result, the directional control valve 13 connects the discharge port 11b to the head-side port 2a and the rod-side port 2b to the tank 20, as shown in Figure 3. In this embodiment, the opening between the discharge port 11b and the head-side port 2a in the directional control valve 13 is fully open. The suction port 11a is then blocked from the head-side port 2a and the rod-side port 2b by the directional control valve 13. The control device 19 also outputs a rotation speed command and a capacity command in response to the operation signal. As a result, the hydraulic pump motor 11 discharges working fluid at a flow rate corresponding to the operation signal from the discharge port 11b. The discharged working fluid is guided to the head-side port 2a via the directional control valve 13 (arrow A1 in Figure 3). On the other hand, working fluid is discharged from the rod-side port 2b to the tank 20 via the directional control valve 13 (arrow A2 in Figure 3). This causes the boom cylinder 2 to extend at a speed corresponding to the operation signal (see arrow A and dashed line in Figure 3). Therefore, the boom can be raised at a speed corresponding to the operation signal. After the boom raising operation is completed, the control device 19 terminates the boom cylinder extension / retraction process.

[0029] In step S3, which is the boom cylinder retraction process, the control device 19 retracts the boom cylinder 2. More specifically, the control device 19 operates the directional control valve 13, the regeneration valve 14, and the unload valve 15 in response to the operation signal. For example, the control device 19 outputs an operation command to the directional control valve 13 in response to the operation signal. As a result, the control device 19 connects the head-side port 2a to the suction port 11a via the directional control valve 13, as shown in Figure 4. The control device 19 also outputs a regeneration command to the regeneration valve 14. As a result, the control device 19 opens the regeneration passage 23 via the regeneration valve 14. This connects the head-side port 2a and the rod-side port 2b. Furthermore, the control device 19 outputs an unload command to the unload valve 15. As a result, the control device 19 connects the discharge passage 22 to the tank 20 via the unload valve 15. This unloads the hydraulic pump motor 11.

[0030] As described above, when the directional control valve 13, regeneration valve 14, and unload valve 15 are operated, the working fluid flows as follows. That is, the boom cylinder 2 is subjected to the weight of the boom in the direction of contraction. Therefore, the boom cylinder 2 is contracted by the weight of the boom. As a result, working fluid is discharged from the head-side port 2a. A portion of the discharged working fluid is supplied to the rod-side port 2b through the regeneration passage 23. That is, a portion of the working fluid is regenerated from the head-side port 2a to the rod-side port 2b (see arrow B1 in Figure 4). On the other hand, the remaining portion is supplied to the suction port 11a of the hydraulic pump motor 11 via the directional control valve 13 (see arrow B2 in Figure 4). The remaining portion then rotates the electric motor 12 via the hydraulic pump motor 11 and is discharged from the discharge port 11b to the tank 20 via the unload valve 15. By rotating the electric motor 12, the electric motor 12 generates electricity. As a result, the fluid energy of the remaining portion is recovered as electrical energy. In other words, the potential energy of the boom is regenerated into electrical energy. Thus, energy can be recovered from the discharged working fluid.

[0031] Furthermore, the control device 19 retracts the boom cylinder 2 at a speed corresponding to the operation signal by controlling the suction flow rate of the hydraulic pump motor 11. More specifically, the control device 19 outputs a rotation speed command and a volume command corresponding to the operation signal. This allows the hydraulic pump motor 11 to flow working fluid at a flow rate corresponding to the operation signal into the suction port 11a, thereby controlling the flow rate of working fluid discharged from the head-side port 2a of the boom cylinder 2 to a flow rate corresponding to the operation signal. As a result, the flow rate of working fluid regenerated at the rod-side port 2b is controlled to a flow rate corresponding to the operation signal, allowing the boom cylinder 2 to retract at a speed corresponding to the operation signal (see arrow B and dashed line in Figure 4). This allows the boom to be lowered at a speed corresponding to the operation signal. Once the boom cylinder 2 is retracted in response to the boom lowering operation, the process proceeds to step S4.

[0032] Furthermore, the control device 19 performs the following feedback control during boom lowering operations. Specifically, the control device 19 changes the suction flow rate of the hydraulic pump motor 11 according to the detection result of the stroke sensor 18. More specifically, the control device 19 changes the suction flow rate of the hydraulic pump motor 11 by outputting a capacity command and a rotational speed command according to the detection result of the stroke sensor 18. In this way, the speed of the boom cylinder 2 is feedback controlled by the control device 19. This suppresses hunting that occurs in the boom cylinder 2.

[0033] In step S4, which is the inflow load determination process, the control device 19 determines whether the inflow load, which is the load flowing into the electric motor 12, is greater than or equal to a predetermined value I1. More specifically, the control device 19 estimates the inflow load I based on the inflow pressure detected by the suction-side pressure sensor 17. Specifically, the control device 19 calculates the suction flow rate of the hydraulic pump motor 11 based on the rotation speed command and the capacity command. The control device 19 then estimates the inflow load I based on the suction flow rate and the inflow pressure. The control device 19 determines whether the inflow load I is greater than or equal to a predetermined value I1. If the inflow load I is less than the predetermined value I1, the process proceeds to step S5. On the other hand, if the inflow load I is greater than or equal to the predetermined value I1, the process proceeds to step S6.

[0034] In step S5, which is the first opening degree control process, the control device 19 controls the opening degree of the regeneration valve 14 according to the inflow load I. More specifically, the control device 19 sets the opening degree R of the regeneration valve 14 to a predetermined first regeneration opening degree R1 or greater, for example, fully open. The control device 19 also sets the opening degree D of the directional control valve 13, i.e., the opening degree between the head-side port 2a and the suction port 11a, to a predetermined first regeneration opening degree D1 or greater, for example, fully open. By keeping the regeneration valve 14 and the directional control valve 13 fully open in this way, the pressure loss in the working fluid can be suppressed, and thus a greater amount of energy can be recovered as electrical energy. Note that the first regeneration opening degree R1 and the first regeneration opening degree D1 do not necessarily have to be fully open; they should be 85% or more of the fully open value. After the boom lowering operation is completed, the control device 19 terminates the boom cylinder extension / retraction process.

[0035] In step S6, which is the second opening degree control process, the control device 19 restricts the opening degree of the regeneration valve 14. More specifically, the control device 19 restricts the opening degree R of the regeneration valve 14 from the first regeneration opening degree R1. That is, the control device 19 restricts the opening degree R of the regeneration valve 14 to the second regeneration opening degree R2 (for example, an opening degree between 20% and less than 85% of the fully open state). This causes a pressure loss in the working fluid flowing through the hydraulic drive device 1. Therefore, the fluid energy of the working fluid supplied to the hydraulic pump motor 11 can be reduced. Note that the second regeneration opening degree R2 is not limited to the numerical range described above, and only needs to be smaller than the first regeneration opening degree R1.

[0036] Furthermore, the control device 19 restricts the opening of the directional control valve 13. More specifically, the control device 19 restricts the opening D of the directional control valve 13 from the first raw opening D1. That is, the control device 19 restricts the opening D of the directional control valve 13 to the second raw opening D2 (for example, an opening between 20% and less than 85% of the fully open state). This suppresses the reduction in the hydraulic pressure of the working fluid supplied to the rod-side port 2b while causing a pressure loss in the working fluid supplied to the hydraulic pump motor 11. Therefore, the fluid energy of the working fluid supplied to the hydraulic pump motor 11 can be reduced. Note that the second raw opening D2 is not limited to the numerical range described above, and only needs to be smaller than the first raw opening D1.

[0037] In this way, the hydraulic drive device 1 reduces the fluid energy of the working fluid by the regeneration valve 14 and the directional control valve 13. As a result, the fluid energy flowing into the hydraulic pump motor 11 is reduced. Therefore, the inflow load to the electric motor 12 is suppressed during regeneration. After the opening of the regeneration valve 14 and the directional control valve 13 is reduced and the boom lowering operation is completed, the control device 19 terminates the boom cylinder extension and retraction process.

[0038] Furthermore, the control device 19 controls the pump capacity of the hydraulic pump motor 11 and the rotational speed of the electric motor 12 according to the inflow load during regeneration. More specifically, the control device 19 limits the output capacity command and rotational speed command according to the estimated inflow load. This limits the pump capacity of the hydraulic pump motor 11 and the rotational speed of the electric motor 12. As a result, the suction flow rate of the hydraulic pump motor 11 can be suppressed. This reduces the amount of energy regenerated by the electric motor 12 during regeneration. Therefore, it is possible to prevent excessive load (for example, output exceeding the rated output) from acting on the electric motor 12.

[0039] In the hydraulic drive device 1 of this embodiment, the opening degree of the regeneration valve 14 is controlled according to the inflow pressure. Therefore, when an excessive load is generated on the motor 12 during regeneration, the regeneration valve 14 can generate a pressure loss. This suppresses the application of an excessive load to the motor 12 during regeneration.

[0040] Furthermore, in the hydraulic drive device 1 of this embodiment, when the inflow load exceeds a predetermined value, the control device 19 restricts the opening of the regeneration valve 14. Therefore, pressure loss can be generated. This reduces the load on the electric motor 12 during regeneration. Therefore, it is possible to prevent the electric motor 12 from becoming overloaded. On the other hand, by keeping the opening of the regeneration valve 14 wide open when the inflow load is below a predetermined value, pressure loss during regeneration can be suppressed. This makes it possible to maintain a high regeneration efficiency in the hydraulic drive device 1.

[0041] Furthermore, in the hydraulic drive device 1 of this embodiment, when the inflow load exceeds a predetermined value, the control device 19 restricts the opening of the directional control valve 13. Therefore, pressure loss can be generated. This reduces the load on the motor 12 during regeneration. Therefore, it is possible to prevent the motor 12 from becoming overloaded. On the other hand, by keeping the opening of the directional control valve 13 large when the inflow load is below a predetermined value, pressure loss during regeneration can be suppressed. This makes it possible to maintain a high regeneration efficiency in the hydraulic drive device 1.

[0042] Furthermore, in the hydraulic drive device 1 of this embodiment, the control device 19 controls the rotational speed of the electric motor 12 according to the inflow pressure. Therefore, by reducing the rotational speed of the electric motor 12, the suction flow rate of the hydraulic pump motor 11 can be suppressed. This reduces the load on the electric motor 12. Therefore, the electric motor 12 is less likely to become overloaded.

[0043] Furthermore, in the hydraulic drive device 1 of this embodiment, the control device 19 controls the pump capacity of the hydraulic pump motor 11 according to the inflow pressure. Therefore, by reducing the pump capacity of the hydraulic pump motor 11, the suction flow rate of the hydraulic pump motor 11 can be suppressed. This reduces the load on the electric motor 12. Therefore, the electric motor 12 is less likely to become overloaded.

[0044] Furthermore, in the hydraulic drive device 1 of this embodiment, when regeneration is performed by the electric motor 12, the discharge passage 22 is connected to the tank 20 by the unload valve 15. This makes it possible to suppress the rise in the discharge pressure of the hydraulic pump motor 11. Therefore, the regenerative efficiency of the electric motor 12 can be maintained at a high level.

[0045] [Second Embodiment] The hydraulic drive device 1A of the second embodiment has a similar configuration to the hydraulic drive device 1 of the first embodiment. Therefore, the configuration of the hydraulic drive device 1A of the second embodiment will mainly be described in terms of the differences from the hydraulic drive device 1 of the first embodiment, and identical components will be denoted by the same reference numerals and their description will be omitted.

[0046] The hydraulic drive device 1A of the second embodiment shown in Figure 5 comprises a hydraulic pump motor 11A, an electric motor 12, a directional control valve 13A, and a regeneration valve 14. The hydraulic drive device 1A also comprises an operating device 16, a pressure sensor 17A, a stroke sensor 18, and a control device 19A.

[0047] <Hydraulic pump motor> The hydraulic pump motor 11A has a first port 11Aa, a second port 11Ab, and a shaft 11c. The first port 11Aa is connected to the tank 20 via a tank passage 21A. The second port 11Ab is connected to a pump passage 22A. When the shaft 11c of the hydraulic pump motor 11A is rotated in the forward direction, it draws in working fluid from the first port 11Aa and discharges working fluid from the second port 11Ab. On the other hand, when working fluid is supplied to the second port 11Ab, the hydraulic pump motor 11A rotates the shaft 11c in the reverse direction. The hydraulic pump motor 11A then discharges working fluid from the first port 11Aa. In this embodiment, the hydraulic pump motor 11A is a variable displacement swashplate pump and has a regulator 11d.

[0048] <Directional control valve> The directional control valve 13A switches the direction of the working fluid flowing between the hydraulic pump motor 11A and the head-side port 2a. The directional control valve 13A is connected to the second port 11Ab of the hydraulic pump motor 11A via the pump passage 22A. The directional control valve 13A is also connected to the head-side port 2a and the rod-side port 2b of the boom cylinder 2. Furthermore, the directional control valve 13A is connected to the tank 20.

[0049] When an operation command is input, the directional control valve 13A connects its second port 11Ab to the head-side port 2a. Furthermore, the directional control valve 13A opens and closes the connection between the rod-side port 2b and the tank 20 according to the input operation command. This allows the directional control valve 13A to switch the direction of the working fluid flowing between the hydraulic pump motor 11A and the head-side port 2a. In addition, when the working fluid flows from the head-side port 2a to the second port 11Ab, the directional control valve 13A controls the opening degree between the head-side port 2a and the second port 11Ab (i.e., the opening degree of the directional control valve 13A) according to the operation command. In this embodiment, the directional control valve 13A is an electric spool valve. However, the directional control valve 13A is not limited to an electric spool valve.

[0050] <Pressure Sensor> The pressure sensor 17A detects the inflow pressure of the hydraulic pump motor 11A. More specifically, the pressure sensor 17A is connected to the pump passage 22A. The pressure sensor 17A detects the hydraulic pressure of the working fluid flowing through the pump passage 22A. Therefore, during regeneration, the pressure sensor 17A detects the hydraulic inflow pressure of the working fluid flowing through the pump passage 22A. The pressure sensor 17A outputs the detected inflow pressure.

[0051] <Control device> The control device 19A controls the operation of the directional control valve 13A, the regeneration valve 14, and the unload valve 15 in accordance with the input operation signals, similar to the control device 19 in the first embodiment. In this embodiment, the control device 19A also changes the discharge flow rate and suction flow rate of the hydraulic pump motor 11A in accordance with the detection result of the stroke sensor 18. Furthermore, the control device 19A controls the opening degree of the directional control valve 13A and the regeneration valve 14 in accordance with the inflow pressure detected by the pressure sensor 17A.

[0052] <Operation of the hydraulic drive device> In the hydraulic drive device 1A, when the operating device 16 is operated (in this embodiment, the operating lever 16a is operated), the boom cylinder extension and retraction process is performed in the same way as in the hydraulic drive device 1 of the first embodiment. The boom cylinder extension and retraction process performed by the control device 19A is similar to the boom cylinder extension and retraction process performed by the control device 19 of the first embodiment. The following will mainly describe the differences between the boom cylinder extension and retraction process performed by the control device 19A and the boom cylinder extension and retraction process performed by the control device 19 of the first embodiment.

[0053] In step S2, which is the boom cylinder extension process, the control device 19A extends the boom cylinder 2. More specifically, the control device 19A operates the directional control valve 13A in response to the operation signal. For example, the control device 19A outputs an operation command to the directional control valve 13A in response to the operation signal. As a result, the directional control valve 13A connects its second port 11Ab to the head-side port 2a and its rod-side port 2b to the tank 20. The control device 19A then outputs a rotation speed command and a capacity command in response to the operation signal. As a result, the hydraulic pump motor 11A discharges working fluid at a flow rate corresponding to the operation signal from the second port 11Ab. Therefore, the boom can be raised at a speed corresponding to the operation signal. After the boom raising operation is completed, the control device 19A terminates the boom cylinder extension / retraction process.

[0054] In step S3, which is the boom cylinder retraction process, the control device 19A retracts the boom cylinder 2. More specifically, the control device 19A operates the directional control valve 13A and the regeneration valve 14 in response to the operation signal. For example, the control device 19A outputs an operation command to the directional control valve 13A in response to the operation signal. As a result, the control device 19A connects the head-side port 2a to the second port 11Ab via the directional control valve 13A, and blocks the connection between the rod-side port 2b and the tank 20. The control device 19A also outputs a regeneration command to the regeneration valve 14, which opens the regeneration passage 23. As a result, in the boom cylinder 2, which is subjected to the weight of the boom in the direction of retraction, the working fluid is pushed out from the head-side port 2a. A portion of the pushed-out working fluid is regenerated at the rod-side port 2b. The remaining portion is guided to the hydraulic pump motor 11A. Energy regeneration is then performed in the electric motor 12. Furthermore, the control device 19A, similar to the control device 19 of the first embodiment, retracts the boom cylinder 2 at a speed corresponding to the operation signal by controlling the suction flow rate, and also provides feedback control of the speed or acceleration of the boom cylinder 2 according to the detection result of the stroke sensor 18. When the boom cylinder 2 is retracted in response to the boom lowering operation in this manner, the process proceeds to step S4.

[0055] In step S4, which is the inflow load determination process, the control device 19A estimates the inflow load I based on the inflow pressure detected by the pressure sensor 17A. Specifically, the control device 19A calculates the suction flow rate of the hydraulic pump motor 11A based on the rotation speed command and the capacity command. Then, the control device 19A estimates the inflow load I based on the suction flow rate and the inflow pressure. If the estimated inflow load I is less than a predetermined value I1, the process proceeds to step S5. On the other hand, if the inflow load I is greater than or equal to the predetermined value I1, the process proceeds to step S6.

[0056] The hydraulic drive device 1A of this embodiment provides the same effects and advantages as the hydraulic drive device 1 of the first embodiment.

[0057] <Other Embodiments> In the hydraulic drive devices 1 and 1A of this embodiment, the hydraulic cylinder supplying the working fluid may be a hydraulic cylinder other than the boom cylinder 2, such as an arm cylinder and a lift cylinder. The directional control valves 13 and 13A and the regeneration valve 14 do not necessarily both need to have adjustable opening degrees; it is sufficient if at least one of the directional control valves 13 and 13A and the regeneration valve 14 is configured to have adjustable opening degrees. The control devices 19 and 19A do not necessarily need to restrict the opening degrees of both the directional control valves 13 and 13A and the regeneration valve 14 when the inflow load increases. The control devices 19 and 19A only need to restrict the opening degree of at least one of the directional control valves 13 and 13A and the regeneration valve 14. Furthermore, the control devices 19 and 19A may selectively restrict the opening degrees of the directional control valves 13 and 13A and the regeneration valve 14 according to the inflow load. For example, the control devices 19 and 19A first reduce the opening of the regeneration valve 14 as the inflow load increases, and then reduce the opening of the directional control valves 13 and 13A. Furthermore, the control devices 19 and 19A do not necessarily need to limit the pump capacity of the hydraulic pump motors 11 and 11A and the rotational speed of the electric motor 12 when the inflow load increases. Moreover, the control devices 19 and 19A do not necessarily need to provide feedback control of the speed or acceleration of the boom cylinder 2. Furthermore, the drive source for the hydraulic pump motors 11 and 11A is not limited to the electric motor 12, but may be a hybrid drive source of the electric motor 12 and an engine.

[0058] <Exemplary Embodiment> The hydraulic drive device in the first phase is a hydraulic drive device that drives a hydraulic cylinder by supplying and discharging working fluid to and from the head-side port and the rod-side port, and comprises a hydraulic pump motor that discharges and is rotationally driven by the supplied working fluid, an electric motor connected to the hydraulic pump motor, a directional control valve that switches the direction of the working fluid flowing between the hydraulic pump motor and the head-side port, a regeneration valve that opens and closes a regeneration passage connecting the head-side port and the rod-side port, a pressure sensor that detects the inflow pressure of the hydraulic pump motor, and a control device that controls the operation of the directional control valve and the regeneration valve, respectively, wherein the control device controls the opening degree of the regeneration valve according to the inflow pressure of the working fluid detected by the pressure sensor when the regeneration passage is opened by the regeneration valve and the head-side port and the hydraulic pump motor are connected by the directional control valve.

[0059] According to the above procedure, the opening of the regeneration valve is controlled according to the inflow pressure. Therefore, when an excessive load is generated on the motor during regeneration, the regeneration valve can generate a pressure loss. This suppresses the excessive load acting on the motor during regeneration.

[0060] In the second phase, the hydraulic drive device, in the first phase, may, when the inflow load calculated according to the inflow pressure detected by the pressure sensor and the rotational speed of the electric motor exceeds a predetermined value, reduce the opening of the regeneration valve.

[0061] According to the above procedure, when the inflow load exceeds a predetermined value, the control device restricts the opening of the regeneration valve. Therefore, pressure loss can be generated. This reduces the load on the motor during regeneration, thus preventing the motor from becoming overloaded. On the other hand, by keeping the opening of the regeneration valve wide open when the inflow load is below a predetermined value, pressure loss during regeneration can be suppressed. This allows for maintaining high regeneration efficiency in the hydraulic drive device.

[0062] In the third phase, the hydraulic drive device, in the hydraulic drive device of the first or second phase, may cause the control device to restrict the opening between the head-side port and the hydraulic pump motor using the directional control valve when the inflow load, calculated according to the inflow pressure detected by the pressure sensor and the rotational speed of the electric motor, exceeds a predetermined value.

[0063] According to the above procedure, when the inflow load exceeds a predetermined value, the control device reduces the opening of the directional control valve. Therefore, pressure loss can be generated. This reduces the load on the motor during regeneration. Therefore, it is possible to prevent the motor from becoming overloaded. On the other hand, by keeping the opening of the directional control valve wide open when the inflow load is below a predetermined value, pressure loss during regeneration can be suppressed. This allows for maintaining high regenerative efficiency in the hydraulic drive system.

[0064] In the fourth phase, the hydraulic drive device is one in which the control device controls the rotational speed of the electric motor in accordance with the inflow pressure detected by the pressure sensor.

[0065] According to the above procedure, the control device controls the rotational speed of the electric motor in accordance with the inflow pressure. Therefore, by reducing the rotational speed of the electric motor, the suction flow rate of the hydraulic pump motor can be reduced. This reduces the load on the electric motor, and thus prevents the electric motor from becoming overloaded.

[0066] In the fifth phase, the hydraulic drive device is a hydraulic drive device in any one of the first to fourth phases, wherein the hydraulic pump motor can change the pump capacity, and the control device may control the pump capacity of the hydraulic pump motor according to the inflow pressure detected by the pressure sensor.

[0067] In the above scenario, the control device controls the pump capacity of the hydraulic pump motor according to the inflow pressure. Therefore, by reducing the pump capacity of the hydraulic pump motor, the suction flow rate of the hydraulic pump motor can be suppressed. This reduces the load on the motor, thus preventing the motor from becoming overloaded.

[0068] The hydraulic drive device in the sixth phase further comprises an unload valve in the hydraulic drive device in any one of the first to fifth phases, the hydraulic pump motor includes a discharge port for discharging working fluid and an intake port for drawing in working fluid, the directional control valve switches the connection destinations of the head-side port and the rod-side port to the discharge port and the intake port, respectively, the unload valve connects the discharge passage connecting the discharge port and the directional control valve to a tank, and the control device may operate the unload valve when the directional control valve connects the head-side port to the intake port.

[0069] According to the above procedure, when regenerative braking is performed by the electric motor, the discharge passage is connected to the tank by an unload valve. This suppresses the rise in discharge pressure of the hydraulic pump motor. Therefore, the regenerative efficiency of the electric motor can be maintained at a high level. [Explanation of Symbols]

[0070] 1.1A Hydraulic drive device 2. Boom Cylinder (Hydraulic Cylinder) 2a Head-side port 2b Rod-side port 11,11A Hydraulic pump motor 11a Inhalation port 11b Discharge port 12 Electric motor 13,13A Directional control valve 14 Regeneration valve 15 Unload valve 17,17A pressure sensor 18 Stroke Sensor 19,19A Control device 20 tanks 22 Discharge passage 23 Regeneration passage

Claims

1. A hydraulic drive device that drives a hydraulic cylinder by supplying and discharging working fluid to the head-side port and the rod-side port, A hydraulic pump motor that discharges and is rotationally driven by the supplied hydraulic fluid, An electric motor connected to the aforementioned hydraulic pump motor, A directional control valve that switches the direction of the working fluid flowing between the hydraulic pump motor and the head-side port, A regeneration valve that opens and closes the regeneration passage connecting the head-side port and the rod-side port, A pressure sensor that detects the inflow pressure of the hydraulic pump motor, The system includes a control device that controls the operation of the directional control valve and the regeneration valve, respectively. The control device is a hydraulic drive device that, when opening the regeneration passage with the regeneration valve and connecting the head-side port and the hydraulic pump motor with the directional control valve, controls the opening degree of the regeneration valve according to the inflow pressure of the working fluid detected by the pressure sensor.

2. The hydraulic drive device according to claim 1, wherein the control device restricts the opening of the regeneration valve when the inflow load, calculated according to the inflow pressure detected by the pressure sensor and the rotational speed of the electric motor, exceeds a predetermined value.

3. The hydraulic drive device according to claim 1 or 2, wherein the control device causes the directional control valve to restrict the opening between the head-side port and the hydraulic pump motor when the inflow load, calculated according to the inflow pressure detected by the pressure sensor and the rotational speed of the electric motor, exceeds a predetermined value.

4. The hydraulic drive device according to claim 1 or 2, wherein the control device controls the rotational speed of the electric motor in accordance with the inflow pressure detected by the pressure sensor.

5. The aforementioned hydraulic pump motor can change the pump capacity, The hydraulic drive device according to claim 1 or 2, wherein the control device controls the pump capacity of the hydraulic pump motor according to the inflow pressure detected by the pressure sensor.

6. It also includes an unload valve, The hydraulic pump motor includes a discharge port for discharging working fluid and a suction port for drawing in working fluid. The directional control valve switches the connection destinations of the head-side port and the rod-side port to the discharge port and the suction port, respectively. The unload valve connects the discharge passage between the discharge port and the directional control valve to the tank. The hydraulic drive device according to claim 1 or 2, wherein the control device operates the unload valve when the directional control valve connects the head-side port to the suction port.

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