Hydraulic drive device

Abstract

To provide a regenerative hydraulic driving device capable of downsizing a hydraulic pump motor.SOLUTION: The hydraulic driving device for supplying / discharging working liquid to / from a hydraulic cylinder includes a plurality of hydraulic pump motors each having a suction port and a discharge port, a plurality of electric motors connected to the plurality of hydraulic pump motors, respectively, and a direction control valve connected to a meter-out passage for connecting the hydraulic cylinder to the meter-out passage to discharge the working liquid from the hydraulic cylinder to the meter-out passage, the suction port of each of the plurality of hydraulic pump motors being connected in parallel to the meter-out passage.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to a hydraulic drive device that supplies and discharges hydraulic fluid to and from the hydraulic cylinder.

Background Art

[0002] As a hydraulic drive device for driving a hydraulic cylinder, a hydraulic drive device such as Patent Document 1 is known. In the hydraulic drive device such as Patent Document 1, in the boom lowering operation, the 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 electric energy.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the hydraulic drive device of Patent Document 1, the potential energy of the boom is regenerated into electric energy by one hydraulic pump motor with respect to the boom cylinder. Therefore, in the hydraulic drive device of Patent Document 1, if all the hydraulic fluid discharged from the boom cylinder during regeneration is to be sucked by one hydraulic pump motor, the hydraulic pump motor will increase in size.

[0005] Therefore, an object of the present invention is to provide a hydraulic drive device that can regenerate and can reduce the size of the hydraulic pump motor.

Means for Solving the Problems

[0006] The hydraulic drive device of the first invention is a hydraulic drive device for supplying and discharging working fluid to and from a hydraulic cylinder, comprising: a plurality of hydraulic pump motors having an intake port and a discharge port; a plurality of electric motors connected to each of the plurality of hydraulic pump motors; and a directional control valve connected to a meter-out passage, which discharges working fluid from the hydraulic cylinder to the meter-out passage by connecting the hydraulic cylinder to the meter-out passage, wherein the intake port of each of the plurality of hydraulic pump motors is connected in parallel to the meter-out passage.

[0007] According to the first invention, the suction ports of each of the multiple hydraulic pump motors are connected in parallel to the meter-out passage. Therefore, the fluid energy of the working fluid discharged from the hydraulic cylinder can be regenerated into electrical energy by the multiple hydraulic pump motors. Consequently, during regeneration, the flow rate of the working fluid drawn into each of the hydraulic pump motors, i.e., the suction flow rate, can be reduced. This makes it possible to miniaturize each of the hydraulic pump motors.

[0008] The hydraulic drive device of the second invention is a hydraulic drive device for supplying and discharging working fluid to a plurality of hydraulic actuators, including a first hydraulic actuator which is a hydraulic cylinder, and comprises a plurality of hydraulic pump motors having an intake port and a discharge port, the discharge port of which is connected to each of the plurality of hydraulic actuators, a plurality of electric motors connected to each of the plurality of hydraulic pump motors, and a directional control valve connected to a meter-out passage, which discharges working fluid from the first hydraulic actuator to the meter-out passage by connecting the first hydraulic actuator to the meter-out passage, wherein the intake port of each of the plurality of hydraulic pump motors is connected in parallel to the meter-out passage

[0009] According to the second invention, since each discharge port of the hydraulic pump motor is connected to a different hydraulic actuator, multiple hydraulic actuators can be operated simultaneously. On the other hand, each suction port of the hydraulic pump motor is connected in parallel to the meter-out passage. Therefore, the fluid energy of the working fluid discharged from the first hydraulic actuator can be regenerated into electrical energy by multiple hydraulic pump motors. Consequently, during regeneration, the flow rate of the working fluid drawn into each hydraulic pump motor, i.e., the suction flow rate, can be reduced. This makes it possible to miniaturize each hydraulic pump motor. [Effects of the Invention]

[0010] According to the first and second inventions, the hydraulic pump motor can be miniaturized and regenerative. [Brief explanation of the drawing]

[0011] [Figure 1] This is a circuit diagram showing the configuration of the hydraulic drive device of this embodiment. [Figure 2] In the hydraulic drive device of this embodiment, the graphs show the flow rates that each hydraulic cylinder requests from the first to third hydraulic pump motors for each operation amount, where (a) is a graph showing the boom's requested flow rate, (b) is a graph showing the arm's requested flow rate, and (c) is a graph showing the bucket's requested flow rate. [Figure 3] This flowchart shows the procedure for extending and retracting each hydraulic cylinder in the hydraulic drive device of this embodiment. [Figure 4] Figures 4(a) to 4(c) are graphs showing the required flow rates for each of the first to third hydraulic pump motors in relation to the amount of operation for each operation when the second operation is performed simultaneously with the boom lowering operation. [Figure 5] Figures 5(a) to 5(c) are graphs showing the required flow rates for each of the first to third hydraulic pump motors in relation to the amount of operation for each operation when the third operation is performed along with the boom lowering operation. [Modes for carrying out the invention]

[0012] Hereinafter, a hydraulic drive device 1 according to an embodiment of the present invention 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 device 1 described below is merely one embodiment of the present invention. Therefore, the present invention is not limited to this embodiment, and additions, deletions, and modifications are possible without departing from the spirit of the invention.

[0013] The hydraulic drive device 1 shown in Figure 1 is installed in, for example, a work vehicle (not shown). The work vehicle is a construction vehicle such as a hydraulic excavator and 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 plurality of hydraulic actuators 3 to 5 to move the attachment. In this embodiment, the attachment of the hydraulic excavator is a bucket, and it is equipped with at least a boom cylinder 3 which is the first hydraulic actuator, an arm cylinder 4 which is the second hydraulic actuator, and a bucket cylinder 5 which is the third hydraulic actuator. Each of the hydraulic cylinders 3 to 5 is provided on the boom, arm, and bucket, respectively. The hydraulic excavator moves the boom, arm, and bucket, respectively, by extending and retracting the three hydraulic cylinders 3 to 5. As a result, the hydraulic excavator can perform various tasks.

[0014] The hydraulic drive unit 1 supplies and discharges working fluid to a plurality of hydraulic cylinders 3 to 5. In this embodiment, the hydraulic drive unit 1 supplies and discharges working fluid to at least the boom cylinder 3, arm cylinder 4, and bucket cylinder 5 described above. The hydraulic drive unit 1 comprises a plurality of hydraulic pump motors 11 to 13, a plurality of electric motors 14 to 16, and a first directional control valve 17. More specifically, the hydraulic drive unit 1 is equipped with at least the same number of hydraulic pump motors 11 to 13 and electric motors 14 to 16 as the number of hydraulic cylinders 3 to 5. In this embodiment, the hydraulic drive unit 1 comprises three hydraulic pump motors (i.e., first to third hydraulic pump motors) 11 to 13 and three electric motors (i.e., first to third electric motors) 14 to 16. Furthermore, the hydraulic drive device 1 further includes a second directional control valve 18, a third directional control valve 19, a regeneration valve 20, a plurality of unload valves 21 to 23, and a merging mechanism 24. In this embodiment, the hydraulic drive device 1 is equipped with the same number of unload valves (i.e., first to third unload valves) 21 to 23 as the hydraulic pump motors 11 to 13. The hydraulic drive device 1 also includes an operating device 26 and a control device 27.

[0015] [Hydraulic pump motor] Each of the first to third hydraulic pump motors 11 to 13 has an intake port 11a to 13a and a discharge port 11b to 13b. The intake ports 11a to 13a of each of the first to third hydraulic pump motors 11 to 13 are connected in parallel to the meter-out passage 31, which will be described later. The intake ports 11a to 13a of each of the first to third hydraulic pump motors 11 to 13 are also connected to the tank 28 via the meter-out passage 31 and tank passages 28a to 28c. The tank passages 28a to 28c connect the tank 28 to the meter-out passage 31. Check valves 29a to 29c are interposed in the tank passages 28a to 28c. The check valves 29a to 29c allow the flow of working fluid from the tank 28 to the meter-out passage 31 and prevent reverse flow.

[0016] The discharge ports 11b to 13b of the first to third hydraulic pump motors 11 to 13 are respectively connected to the hydraulic cylinders 3 to 5. In the present embodiment, the discharge port 11b of the first hydraulic pump motor 11 is connected to the boom cylinder 3. The discharge port 12b of the second hydraulic pump motor 12 is connected to the arm cylinder 4. The discharge port 13b of the third hydraulic pump motor 13 is connected to the bucket cylinder 5.

[0017] Also, the first to third hydraulic pump motors 11 to 13 have shafts 11c to 13c. Each of the first to third hydraulic pump motors 11 to 13 sucks the hydraulic fluid from the suction ports 11a to 13a and discharges the hydraulic fluid from the discharge ports 11b to 13b when the shafts 11c to 13c are rotationally driven. On the other hand, each of the first to third hydraulic pump motors 11 to 13 rotates the shafts 11c to 13c when the hydraulic fluid is supplied to the suction ports 11a to 13a.

[0018] Furthermore, the first to third hydraulic pump motors 11 to 13 are variable displacement swash plate pumps in the present embodiment. That is, each of the first to third hydraulic pump motors 11 to 13 has regulators 11d to 13d. Each of the regulators 11d to 13d changes the pump capacity of each of the first to third hydraulic pump motors 11 to 13 based on the input first to third capacity commands.

[0019] [Electric motor] The first to third electric motors 14 to 16 are each connected to each of the first to third hydraulic pump motors 11 to 13. More specifically, the first to third electric motors 14 to 16 are each connected to each of the first to third hydraulic pump motors 11 to 13 via shafts 11c to 13c. Each of the first to third electric motors 14 to 16 discharges hydraulic fluid from each of them by rotationally driving each of the first to third hydraulic pump motors. Further, each of the first to third electric motors 14 to 16 generates electricity by being rotationally driven by each of the first to third hydraulic pump motors 11 to 13. That is, each of the first to third electric motors 14 to 16 regenerates the fluid energy of the hydraulic fluid into electrical energy by cooperating with each of the first to third hydraulic pump motors 11 to 13. Each of the first to third electric motors 14 to 16 changes its rotational speed according to each of the input first to third rotational speed commands.

[0020] [First Direction Control Valve] The first direction control valve 17 is connected to the meter-out passage 31. Further, the first direction control valve 17 is connected to the boom cylinder 3. The first direction control valve 17 discharges the hydraulic fluid from the boom cylinder 3 to the meter-out passage 31 by connecting the boom cylinder 3 to the meter-out passage 31. More specifically, the first direction control valve 17 is connected to each of the head-side port 3a and the rod-side port 3b of the boom cylinder 3. The first direction control valve 17 connects the head-side port 3a to the meter-out passage 31. Thereby, the hydraulic fluid is discharged from the head-side port 3a of the boom cylinder 3 to the meter-out passage 31. The first to third hydraulic pump motors 11 to 13 (more specifically, the suction ports 11a to 13a) are connected in parallel to the meter-out passage 31. Further, the first direction control valve 17 is connected to the first hydraulic pump motor 11 via the first pump passage 32. Furthermore, the first direction control valve 17 is connected to the tank 28.

[0021] The first directional control valve 17 switches the direction of flow of the working fluid between the first hydraulic pump motor 11 and the boom cylinder 3 in response to the input first operation command. More specifically, the first directional control valve 17 switches the connection destinations of the respective ports 3a and 3b of the boom cylinder 3 in response to the first operation command. For example, in response to the first operation command, the first directional control valve 17 connects the head-side port 3a of the boom cylinder 3 to the meter-out passage 31 and connects the discharge port 11b of the first hydraulic pump motor 11 to the rod-side port 3b of the boom cylinder 3. In this embodiment, a check valve 17a is interposed between the discharge port 11b and the rod-side port 3b in the first directional control valve 17. The check valve 17a allows flow from the discharge port 11b to the rod-side port 3b and prevents flow in the reverse direction. Furthermore, the first directional control valve 17 connects the rod-side port 3b of the boom cylinder 3 to the tank 28 and the discharge port 11b of the first hydraulic pump motor 11 to the head-side port 3a of the boom cylinder 3 in response to the first operation command. In addition, the first directional control valve 17 can shut off the connection between the first hydraulic pump motor 11 and the boom cylinder 3.

[0022] [Second Directional Control Valve] The second directional control valve 18 is connected to the second hydraulic pump motor 12 via the second pump passage 33. More specifically, the second directional control valve 18 is connected to the discharge port 12b of the second hydraulic pump motor 12. The second directional control valve 18 is also connected to the arm cylinder 4. The second directional control valve 18 switches the direction of the flow of the hydraulic fluid between the second hydraulic pump motor 12 and the arm cylinder 4 in response to the second operation command. More specifically, in response to the second operation command, the second directional control valve 18 connects the discharge port 12b of the second hydraulic pump motor 12 to one of the rod-side port 4a and head-side port 4b of the arm cylinder 4. The second directional control valve 18 also connects the other of the rod-side port 4a and head-side port 4b to the tank 28 in response to the second operation command. As a result, the second directional control valve 18 directs the working fluid discharged from the second hydraulic pump motor 12 to either the rod-side port 4a or the head-side port 4b. The second directional control valve 18 can also shut off the connection between the second hydraulic pump motor 12 and the arm cylinder 4.

[0023] [Third Directional Control Valve] The third directional control valve 19 is connected to the third hydraulic pump motor 13 via the third pump passage 34. More specifically, the third directional control valve 19 is connected to the discharge port 13b of the third hydraulic pump motor 13. The third directional control valve 19 is also connected to the bucket cylinder 5. The third directional control valve 19 switches the direction of the hydraulic fluid flowing between the third hydraulic pump motor 13 and the bucket cylinder 5 in response to the third operation command. Specifically, in response to the third operation command, the third directional control valve 19 connects the discharge port 13b of the third hydraulic pump motor 13 to one of the rod-side port 5a and head-side port 5b of the bucket cylinder 5. In addition, in response to the third operation command, the third directional control valve 19 connects the other of the rod-side port 5a and head-side port 5b to the tank 28. Furthermore, the third directional control valve 19 can shut off the connection between the third hydraulic pump motor 13 and the bucket cylinder 5.

[0024] [Regenerative valve] The regeneration valve 20 is connected to the head-side port 3a and the rod-side port 3b of the boom cylinder 3. The regeneration valve 20 connects the head-side port 3a and the rod-side port 3b in response to a regeneration command. The regeneration valve 20 also allows the flow of working fluid from the head-side port 3a to the rod-side port 3b while maintaining communication between the two ports, and prevents flow in the reverse direction. As a result, when the regeneration valve 20 supplies working fluid to the rod-side port 3b, it regenerates the working fluid discharged from the head-side port 3a into the rod-side port 3b.

[0025] [Unload valve] Each of the first to third unload valves 21 to 23 discharges at least a portion of the working fluid discharged from the respective discharge ports 11b to 13b of the first to third hydraulic pump motors 11 to 13 into the tank 28. More specifically, each of the first to third unload valves 21 to 23 is connected to each of the first to third pump passages 32 to 34. Each of the first to third unload valves 21 to 23 operates in response to each of the input first to third unload commands. Each of the first to third unload valves 21 to 23 adjusts the opening between each of the discharge ports 11b to 13b and the tank 28 in response to each of the input first to third unload commands.

[0026] [Confluence mechanism] The merging mechanism 24 merges the working fluid discharged from the respective discharge ports 11b to 13b of the first to third hydraulic pump motors 11 to 13. More specifically, the merging mechanism 24 is connected to three pump passages 32 to 34. The merging mechanism 24 connects the first pump passage 32 and the third pump passage 34, and also connects the second pump passage 33 and the third pump passage 34. The merging mechanism 24 merges the working fluid discharged from each of the first to third hydraulic pump motors 11 to 13 by switching the connection state of the three pump passages 32 to 34. In this embodiment, the merging mechanism 24 includes a first merging valve 41 and a second merging valve 42.

[0027] The first merging valve 41 merges the working fluid discharged from the discharge ports 11b and 13b of the first and third hydraulic pump motors 11 and 13, respectively. More specifically, the first merging valve 41 is connected to the first pump passage 32 and the third pump passage 34. The first merging valve 41 opens in response to the input first merging command. This connects the first pump passage 32 and the third pump passage 34, allowing the working fluid to flow back and forth between the two pump passages 32 and 34.

[0028] The second merging valve 42 merges the working fluid discharged from the discharge ports 12b and 13b of the second and third hydraulic pump motors 12 and 13, respectively. More specifically, the second merging valve 42 is connected to the second pump passage 33 and the third pump passage 34. The second merging valve 42 opens in response to the input second merging command. This connects the second pump passage 33 and the third pump passage 34, allowing working fluid to flow between the two pump passages 33 and 34.

[0029] <Operating device> The operating device 26 is operated by an operator or the like to move the boom cylinder 3, arm cylinder 4, and bucket cylinder 5. More specifically, the operating device 26 outputs an operation signal corresponding to the direction and amount of operation (hereinafter referred to as the "operation state") of each operation (hereinafter referred to as "each operation") of each hydraulic cylinder 3 to 5. The operating device 26 includes, for example, a plurality of operating levers 26a, 26b. In this embodiment, the operating device 26 includes two operating levers 26a, 26b. The operating levers 26a, 26b can be operated in various directions (e.g., tilting). The operating device 26 outputs an operation signal with the respective operating direction (e.g., tilting direction) and amount of operation (e.g., tilting amount) of each operating lever 26a, 26b as the operation state for each operation. Note that the operating device 26 may be in other forms such as an operation panel, and may output operation signals according to operations on the operation panel or a pre-stored program.

[0030] <Control device> The control device 27 receives an operation signal from the operating device 26. The control device 27 then operates the first to third directional control valves 17 to 19 in accordance with the input operation signal. More specifically, the control device 27 operates the first directional control valve 17 by outputting a first operation command in accordance with the operation state of the first operation, which is an operation on the boom cylinder 3. The control device 27 also operates the second directional control valve 18 by outputting a second operation command in accordance with the operation state of the second operation, which is an operation on the arm cylinder 4. Furthermore, the control device 27 operates the third directional control valve 19 by outputting a third operation command in accordance with the operation state of the third operation, which is an operation on the bucket cylinder 5. The control device 27 outputs a regeneration command in accordance with the operation state of the first operation. This causes the control device 27 to operate the regeneration valve 20. The control device 27 also outputs first and second communication commands. This causes the control device 27 to open the first and second merging valves 41 and 42.

[0031] The control device 27 controls the discharge flow rate or suction flow rate of each of the first to third hydraulic pump motors 11 to 13 in accordance with the input operation signal. More specifically, the control device 27 sets the flow rate that each hydraulic cylinder 3 to 5 requests from the first to third hydraulic pump motors 11 to 13 for each operation amount, as shown in the graphs in Figures 2(a) to 2(c). For example, Figure 2(a) shows the boom request flow rate. Figure 2(b) shows the arm request flow rate. Figure 2(c) shows the bucket request flow rate. The boom request flow rate is the flow rate that boom cylinder 3 requests from the first to third hydraulic pump motors 11 to 13 for the operation amount of the first operation. The arm request flow rate is the flow rate that arm cylinder 4 requests from the first to third hydraulic pump motors 11 to 13 for the operation amount of the second operation. The bucket request flow rate is the flow rate that bucket cylinder 5 requests from the second and third hydraulic pump motors 12 and 13 for the operation amount of the third operation. In Figures 2(a) to 2(c), the solid lines represent the required flow rates for the first hydraulic pump motor 11, the dashed lines represent the required flow rates for the second hydraulic pump motor 12, and the double dashed lines represent the required flow rates for the third hydraulic pump motor 13.

[0032] The control device 27 calculates the required discharge flow rate and required regenerative flow rate for each of the first to third hydraulic pump motors 11 to 13 based on the required flow rate and the operating status of each operation. The required discharge flow rate is the discharge flow rate required for each of the first to third hydraulic pump motors 11 to 13. The required regenerative flow rate is the regenerative flow rate, i.e., suction flow rate, required for each of the first to third hydraulic pump motors 11 to 13. The method for calculating the required discharge flow rate and required regenerative flow rate will be described in detail later. Based on the calculated required discharge flow rate and required regenerative flow rate, the control device 27 calculates the rotational speed of each electric motor 14 to 16 and the pump capacity of each of the first to third hydraulic pump motors 11 to 13. Then, the control device 27 outputs first to third rotational speed commands to each electric motor 14 to 16 according to the rotational speed, and outputs first to third capacity commands to the first to third hydraulic pump motors 11 to 13 according to the pump capacity. As a result, the control device 27 controls the discharge flow rate of each of the first to third hydraulic pump motors 11 to 13 to the required discharge flow rate (or suction flow rate to the required regenerative flow rate) according to the operating status of each operation.

[0033] The control device 27 controls the operation of the first to third unload valves 21 to 23 in accordance with the input operation signal. More specifically, as described above, the control device 27 calculates the required discharge flow rate and the required regenerative flow rate for each of the first to third hydraulic pump motors 11 to 13. Then, the control device 27 controls the opening degree of each of the first to third unload valves 21 to 23 by outputting first to third unload commands for each of the first to third hydraulic pump motors 11 to 13 according to the difference between the required discharge flow rate and the required regenerative flow rate.

[0034] <Operation of the hydraulic drive device> In the hydraulic drive device 1, when the operating device 26 is operated (in this embodiment, the operating levers 26a and 26b are operated), an operation signal corresponding to the operating state of each operation is output from the operating device 26. When an operation signal is output, the control device 27 extends and retracts each hydraulic cylinder 3 to 5 in a direction corresponding to the operating direction of each operation and at a speed corresponding to the amount of operation of each operation.

[0035] More specifically, the control device 27 outputs rotational speed commands to each of the first to third electric motors 14-16 according to the operating state of each operation. The control device 27 also outputs capacity commands to each of the first to third hydraulic pump motors 11-13 according to the operating state of each operation. As a result, the control device 27 causes the first to third hydraulic pump motors 11-13 to discharge or draw in working fluid at a flow rate corresponding to the amount of operation for each operation. The control device 27 also outputs first to third operation commands according to the operating state of each operation. Then, the first to third directional control valves 17-19 connect each of the first to third hydraulic pump motors 11-13 to the corresponding hydraulic cylinders 3-5. As a result, each hydraulic cylinder 3-5 expands and contracts in the direction corresponding to the operating direction of each operation and at a speed corresponding to the amount of operation. The expansion and contraction of each hydraulic cylinder 3-5 due to each operation will be explained below with reference to the flow chart in Figure 3.

[0036] When the operating device 26 is operated (in this embodiment, the operating levers 26a and 26b are operated), the control device 27 starts the flow shown in Figure 3. Then, it proceeds to step S1. In step S1, which is the boom lowering operation determination process, it is determined whether or not the boom lowering operation, which is one of the first operations, has been performed. In this embodiment, the control device 27 determines whether or not one of the operating levers 26a has been tilted forward to lower the boom. If one of the operating levers 26a has been tilted forward, the control device 27 determines that the boom lowering operation has been performed. Then, it proceeds to step S2. On the other hand, if one of the operating levers 26a has not been operated or has been tilted backward, the control device 27 determines that the boom lowering operation has not been performed. Then, it proceeds to step S7. Note that the boom lowering operation is not limited to tilting the operating lever 26a forward. The boom lowering operation determination method described above is merely an example, and the control device 27 only needs to determine that the boom lowering operation has been performed when an operation corresponding to the boom lowering operation is performed on the operating device 26.

[0037] In step S2, which is the process of fully opening the unload valves, the control device 27 fully opens each of the first to third unload valves 21 to 23. The control device 27 then recovers the fluid energy of the working fluid discharged from the head-side port 3a of the boom cylinder 3 when the boom is lowered into electrical energy, that is, boom lowering regeneration is performed. The boom lowering regeneration will be explained in more detail below.

[0038] The control device 27 activates the first directional control valve 17 by outputting a first operation command. As a result, the first directional control valve 17 connects the head-side port 3a of the boom cylinder 3 to the meter-out passage 31. In addition, the discharge port 11b of the first hydraulic pump motor 11 is connected to the rod-side port 3b of the boom cylinder 3 via a check valve 17a. Furthermore, the control device 27 calculates the required regenerative flow rate for each of the first to third hydraulic pump motors 11 to 13 based on the amount of boom lowering operation. In this embodiment, the required regenerative flow rate for each of the first to third hydraulic pump motors 11 to 13 is calculated according to the respective boom required flow rate and the amount of boom lowering operation for each of the first to third hydraulic pump motors 11 to 13. The control device 27 then outputs first to third rotational speed commands and first to third capacity commands corresponding to the required regenerative flow rate for each of the first to third hydraulic pump motors 11 to 13. As a result, the suction flow rates of the first to third hydraulic pump motors 11-13 are controlled to their respective required regenerative flow rates. Furthermore, the control device 27 fully opens the first to third unload valves 21-23. Then, the working fluid flows as follows.

[0039] Specifically, the working fluid is discharged from the head-side port 3a of the boom cylinder 3. The discharged working fluid flows from the head-side port 3a to the meter-out passage 31. The working fluid is then supplied to each of the first to third hydraulic pump motors 11 to 13 via the meter-out passage 31. The first to third hydraulic pump motors 11 to 13 are driven by the supplied working fluid. Therefore, the first to third electric motors 14 to 16 generate electricity. As a result, the fluid energy of the working fluid is regenerated into electrical energy using the first to third hydraulic pump motors 11 to 13 and the first to third electric motors 14 to 16. At this time, the first to third unload valves 21 to 23 are fully open by the control device 27. Therefore, the working fluid discharged from the first to third hydraulic pump motors 11 to 13 is discharged directly into the tank 28. That is, the first to third hydraulic pump motors 11 to 13 are in an unloaded state. Therefore, the fluid energy of the working fluid is efficiently regenerated into electrical energy. In addition, the control device 27 outputs a first operation command and a regeneration command when the boom is lowered and regenerated. As a result, the regeneration valve 20 opens, and the rod-side port 3b and the head-side port 3a come into contact. As a result, a portion of the working fluid discharged from the head-side port 3a is regenerated into the rod-side port 3b.

[0040] In this way, in the hydraulic drive device 1, a portion of the working fluid discharged from the head-side port 3a of the boom cylinder 3 is regenerated to the rod-side port 3b, while the remaining portion is returned to the first to third hydraulic pump motors 11 to 13. As a result, the boom cylinder 3 contracts, and the boom lowers. The control device 27 controls the flow rate of the working fluid that flows to the rod-side port 3b via the regeneration valve 20 by controlling the suction flow rate of each of the first to third hydraulic pump motors 11 to 13 to their respective required regenerative flow rates. This allows the working fluid to flow to the rod-side port 3b at a flow rate corresponding to the operating state of the first operation. This allows the boom cylinder 3 to contract at a speed corresponding to the operating state of the first operation. In other words, the boom can be lowered at a speed corresponding to the operating state of the first operation. In addition, the amount of power generated by the first to third electric motors 14 to 16 is controlled by controlling the suction flow rate of each of the first to third hydraulic pump motors 11 to 13 to their respective required regenerative flow rates. When boom lowering regeneration starts, the process moves to step S3.

[0041] In step S3, which is a simultaneous operation determination process, it is determined whether or not at least one of the second and third operations is being performed along with the boom lowering operation. More specifically, the control device 27 acquires the operation status of each operation according to the input operation signal. Then, the control device 27 determines, according to the operation status of each operation, whether or not either the second or third operation is being performed along with the boom lowering operation. If it is determined that at least one of the second and third operations is not being performed along with the boom lowering operation, the boom lowering regeneration described above continues until the boom lowering operation is completed or at least one of the second and third operations is performed along with the boom lowering operation, and the flow ends. On the other hand, if it is determined that at least one of the second and third operations is being performed along with the boom lowering operation, the process proceeds to step S4.

[0042] In step S4, which is a hydraulic pump motor flow rate control process, the discharge flow rate or regenerative flow rate of each of the first to third hydraulic pump motors 11 to 13 is controlled according to the operating state of each operation. More specifically, the control device 27 calculates the required discharge flow rate and the required regenerative flow rate for each of the first to third hydraulic pump motors 11 to 13 based on the required flow rate and the operating state of each operation. In this embodiment, the required regenerative flow rate for each of the first and third hydraulic pump motors 11 to 13 is the required boom flow rate for each of the first and third hydraulic pump motors 11 to 13. On the other hand, the discharge flow rate for each of the first to third hydraulic pump motors 11 to 13 is the sum of the arm required flow rate and the bucket required flow rate for each of the first and third hydraulic pump motors 11 to 13.

[0043] The control device 27 calculates the control flow rate for each of the first and third hydraulic pump motors 11-13. More specifically, the control device 27 selects the larger of the required discharge flow rate and the required regenerative flow rate as the control flow rate. Then, the control device 27 controls the operation of each of the first and third hydraulic pump motors 11-13 and the first to third electric motors 14-16 based on the control flow rate. More specifically, the control device 27 outputs first to third rotational speed commands and first to third capacity commands according to the control flow rate. As a result, the discharge flow rate or suction flow rate of the first to third hydraulic pump motors 11-13 is controlled to the control flow rate. For example, for the first to third hydraulic pump motors 11-13 where the required discharge flow rate is selected, the discharge flow rate is controlled to the required discharge flow rate. On the other hand, for the first to third hydraulic pump motors 11-13 where the required regenerative flow rate is selected, the suction inflow is controlled to the required regenerative flow rate. Once the discharge flow rate or regenerative flow rate is controlled, the process proceeds to step S5.

[0044] Step S5, which is the opening and closing process of the merging mechanism, involves opening and closing the merging mechanism 24 according to the respective required flow rates. More specifically, the control device 27 opens and closes the first and second merging valves 41 and 42 according to the arm required flow rates and bucket required flow rates for each of the first to third hydraulic pump motors 11 to 13, and the operating status of each operation. For example, when the operating amounts for the second and third operations are small, the second and third hydraulic pump motors 12 and 13 supply working fluid to each hydraulic cylinder 4 and 5 independently of each other. Therefore, the control device 27 keeps the first and second merging valves 41 and 42 closed.

[0045] On the other hand, when the operating amount of the second operation increases, the arm cylinder 4 is required to receive hydraulic fluid from the first and third hydraulic pump motors 11 and 13 in addition to the second hydraulic pump motor 12 in stages. The control device 27 first opens the second merging valve 42 to combine the hydraulic fluid from the third hydraulic pump motor 13 with the hydraulic fluid from the second hydraulic pump motor 12 and supply it to the arm cylinder 4. Furthermore, when a higher hydraulic fluid flow rate is required, the control device 27 opens the first merging valve 41 in stages to further combine the hydraulic fluid from the first hydraulic pump motor 11 with the hydraulic fluid from the second hydraulic pump motor 12 and supply it to the arm cylinder 4. Also, when the operating amount of the third operation increases, the bucket cylinder 5 is required to receive hydraulic fluid from the second hydraulic pump motor 12 in addition to the third hydraulic pump motor 13. Therefore, the control device 27 opens the second merging valve 42. As a result, the working fluid from the second hydraulic pump motor 12 is merged with the working fluid from the third hydraulic pump motor 13 and supplied to the bucket cylinder 5. When the merging mechanism 24 opens and closes according to the amount of operation of the second and third operations, the process proceeds to step S6.

[0046] In step S6, which is the unload valve opening control process, the opening of the first to third unload valves 21 to 23 is controlled according to the difference between the required discharge flow rate and the required regenerative flow rate for each of the first to third hydraulic pump motors 11 to 13. This controls the flow rate from the first to third hydraulic pump motors 11 to 13 to each of the hydraulic cylinders 3 to 5. In other words, the control device 27 controls the discharge of excess flow rate using the first to third unload valves 21 to 23. To explain the excess flow rate discharge control in more detail, the control device 27 calculates the difference between the required regenerative flow rate and the required discharge flow rate (for example, the value obtained by subtracting the required discharge flow rate from the required regenerative flow rate) for each of the first to third hydraulic pump motors 11 to 13. Then, the control device 27 controls the opening of the first to third unload valves 21 to 23 according to the difference between the required discharge flow rate and the required regenerative flow rate for each of the first to third hydraulic pump motors 11 to 13.

[0047] More specifically, the control device 27 closes the corresponding first to third unload valves 21 to 23 for each of the first to third hydraulic pump motors 11 to 13 where the requested discharge flow rate is greater than the requested regenerative flow rate (i.e., the difference is negative). This allows the entire requested discharge flow rate to be used to drive the hydraulic cylinders 3 to 5 for those where the requested discharge flow rate is greater than the requested regenerative flow rate. On the other hand, the control device 27 controls the opening degree of the corresponding first to third unload valves 21 to 23 for each of the first to third hydraulic pump motors 11 to 13 where the requested discharge flow rate is less than the requested regenerative flow rate (i.e., the difference is positive). More specifically, the control device 27 controls the opening degree of each of the first to third unload valves 21 to 23 according to the first to third difference. As a result, the control device 27 discharges the excess flow rate, obtained by subtracting the required discharge flow rate from the required regenerative flow rate, from the corresponding first to third unload valves 21 to 23 into the tank 28 in each of the first to third hydraulic pump motors 11 to 13. In doing so, the control device 27 supplies the required flow rate of working fluid to each hydraulic cylinder 3 to 5. When the opening degree of the first to third unload valves 21 to 23 is controlled according to the first to third difference, the flow ends.

[0048] In step S7, which is the unload valve full closing process, the control device 27 fully closes the first to third unload valves 21 to 23. Then, the control device 27 operates (extends or retracts) each hydraulic cylinder 3 to 5 according to the operating state of each operation. For example, when each operation is performed to operate the hydraulic cylinders 3 to 5, the control device 27 calculates the required discharge flow rate of the first to third hydraulic pump motors 11 to 13 based on the required flow rate and the operating state of each operation. The control device 27 outputs first to third rotational speed commands and first to third capacity commands corresponding to the required discharge flow rate of the first to third hydraulic pump motors 11 to 13. As a result, hydraulic fluid at a flow rate corresponding to the amount of operation performed in each operation is discharged from the first to third hydraulic pump motors 11 to 13. The control device 27 also outputs first to third operation commands according to the operating state of each operation. Then, the corresponding first to third directional control valves 17 to 19 are operated. In this embodiment, the first to third directional control valves 17 to 19 are fully open when activated. Therefore, a flow rate of working fluid corresponding to the amount of operation of each operation flows to the hydraulic cylinders 3 to 5. Consequently, the hydraulic cylinders 3 to 5 operate at a speed corresponding to the amount of operation of each operation.

[0049] Furthermore, when the amount of operation for each operation increases, the control device 27 opens the merging mechanism 24, more specifically the first and second merging valves 41 and 42. By opening the first merging valve 41, the working fluids from the first and third hydraulic pump motors 11 and 13 merge. This allows more working fluid to be supplied to, for example, the bucket cylinder 5. Also, by opening the second merging valve 42, the working fluids from the second and third hydraulic pump motors 12 and 13 merge. This allows more working fluid to be supplied to, for example, the arm cylinder 4. Furthermore, by opening the first and second merging valves 41 and 42, the working fluids from the first to third hydraulic pump motors 11 to 13 merge. This allows even more working fluid to be supplied to, for example, the arm cylinder 4. By supplying a large amount of working fluid in this way, the hydraulic cylinders 3 to 5 can be operated at a speed that is appropriate to the amount of operation for each operation and is even faster.

[0050] The following describes the operation of the hydraulic drive device 1 when a boom lowering operation is performed independently. When a boom lowering operation is performed independently, in step S1 the control device 27 determines that the boom lowering operation has been performed. Then, in step S2 the control device 27 fully opens the first to third unload valves 21 to 23. Furthermore, the control device 27 performs boom lowering regeneration. As a result, the fluid energy of the working fluid discharged from the head-side port 3a of the boom cylinder 3 can be regenerated into electrical energy by the first to third hydraulic pump motors 11 to 13 and the first to third electric motors 14 to 16. Since it is a boom lowering operation performed independently, in step S3 the control device 27 determines that at least one of the second and third operations has not been performed along with the boom lowering operation. Then the flow ends.

[0051] Next, the operation of the hydraulic drive device 1 when the second operation is performed along with the boom lowering operation will be explained with reference to Figure 4. Figures 4(a) to 4(c) are graphs showing the required flow rates of the first to third hydraulic pump motors 11 to 13 in relation to the amount of operation for each operation when the second operation is performed along with the boom lowering operation. When the second operation is performed along with the boom lowering operation, in step S1 the control device 27 determines that the boom lowering operation has been performed. Then, in step S2 the control device 27 fully opens the first to third unload valves 21 to 23. Then, the control device 27 performs boom lowering regeneration. In step S3 the control device 27 determines that the second operation is being performed along with the boom lowering operation. In step S4 the control device 27 calculates the control flow rates of the first to third hydraulic pump motors 11 to 13 based on the required flow rates and the respective amounts of operation for the boom lowering operation and the second operation. In this embodiment, the control flow rate for the first hydraulic pump motor 11 is calculated as the required regenerative flow rate (i.e., the boom required flow rate), and the control flow rate for the second hydraulic pump motor 12 is calculated as the required discharge flow rate (arm required flow rate). On the other hand, for the third hydraulic pump motor 13, the control flow rate is calculated as the required regenerative flow rate when the operation amount of the second operation is small, and as the operation amount of the second operation is large, the required discharge flow rate is calculated.

[0052] In step S5, the control device 27 keeps the first and second merging valves 41 and 42 closed when the amount of operation for the second operation is small. On the other hand, when the amount of operation for the second operation increases, the control device 27 opens the second merging valve 42. As a result, the working fluid from the third hydraulic pump motor 13 is merged with the working fluid from the second hydraulic pump motor 12. Furthermore, when the amount of operation for the second operation increases even more, the control device 27 opens the first merging valve 41. As a result, in addition to the working fluid from the third hydraulic pump motor 13, the working fluid from the first hydraulic pump motor 11 is also merged with the working fluid from the second hydraulic pump motor 12. By merging the fluids in this way, the arm cylinder 4 can be operated more quickly.

[0053] In step S6, the control device 27 controls the opening degrees of the first to third unload valves 21 to 23 according to the first to third differences. For example, in the second hydraulic pump motor 12, the required discharge flow rate is always greater than the required regenerative flow rate (i.e., the second difference is negative), so the second unload valve 22 is fully closed. On the other hand, the relationship between the required discharge flow rate and the required regenerative flow rate of the first and third hydraulic pump motors 11 and 13 changes according to the amount of the second operation. When the amount of the second operation is small, the required discharge flow rate is less than the required regenerative flow rate in each of the first and third hydraulic pump motors 11 and 13 (i.e., the first and third differences are positive). Therefore, the control device 27 controls the opening degrees of the first and third unload valves 21 and 23 according to the first and third differences.

[0054] For example, when the required discharge flow rate of the first and third hydraulic pump motors 11 and 13 is zero, the first and third unload valves 21 and 23 are fully open. Then, as the amount of operation in the second operation increases, the control device 27 closes the opening of the first and third unload valves 21 and 23 in accordance with the difference between the first and third operations, as the required discharge flow rate increases. This makes it possible to increase the flow rate of the working fluid that is joined with the working fluid from the second hydraulic pump motor 12 while maintaining the suction flow rate of the first and third hydraulic pump motors 11 and 13 at the required regenerative flow rate. Subsequently, when the amount of operation in the second operation increases further and the required discharge flow rate of each of the first and third hydraulic pump motors 11 and 13 becomes greater than the required regenerative flow rate, the corresponding first and third unload valves 21 and 23 are closed. Conversely, as the amount of operation in the second operation decreases, the opening of each of the first and third unload valves 21 and 23 changes from a fully closed state to a fully open state in accordance with the difference between the first and third operations. The flow then ends.

[0055] Furthermore, the operation of the hydraulic drive device 1 when the third operation is performed along with the boom lowering operation will be explained with reference to Figure 5. Figures 5(a) to (c) are graphs showing the respective required flow rates of the first to third hydraulic pump motors 11 to 13 in relation to the amount of operation for each operation when the third operation is performed along with the boom lowering operation. When the third operation is performed along with the boom lowering operation, in step S1 the control device 27 determines that the boom lowering operation has been performed. Then, in step S2 the control device 27 fully opens the first to third unload valves 21 to 23. Then, the control device 27 performs boom lowering regeneration. In step S3 the control device 27 determines that the third operation has been performed along with the boom lowering operation. In step S4 the control device 27 calculates the respective control flow rates of the first to third hydraulic pump motors 11 to 13 based on each required flow rate and the amount of operation for the boom lowering operation and each operation. In this embodiment, the control flow rate for the first hydraulic pump motor 11 is calculated as the required regenerative flow rate (i.e., the boom required flow rate), and the control flow rate for the third hydraulic pump motor 13 is calculated as the required discharge flow rate (bucket required flow rate). On the other hand, for the second hydraulic pump motor 12, the control flow rate is calculated as the required regenerative flow rate when the operation amount of the third operation is small, and as the operation amount of the third operation is large, the required discharge flow rate is calculated.

[0056] In step S5, when the amount of operation for the third operation is small, the control device 27 keeps the first and second merging valves 41 and 42 closed. On the other hand, when the amount of operation for the third operation increases, the control device 27 opens the second merging valve 42. As a result, the working fluid from the second hydraulic pump motor 12 is merged with the working fluid from the third hydraulic pump motor 13. This allows the bucket cylinder 5 to be operated more quickly.

[0057] In step S6, the control device 27 controls the opening degrees of the second and third unload valves 22 and 23 according to the second and third differences. For example, in the third hydraulic pump motor 13, the required discharge flow rate is always greater than the required regenerative flow rate (i.e., the third difference is negative), so the third unload valve 23 is fully closed. On the other hand, the relationship between the required discharge flow rate and the required regenerative flow rate of the second hydraulic pump motor 12 changes according to the amount of the third operation. When the amount of the third operation is small, the required discharge flow rate of the second hydraulic pump motor 12 is less than the required regenerative flow rate (i.e., the second difference is positive). Therefore, the control device 27 controls the opening degree of the second unload valve 22 to an opening degree corresponding to the second difference.

[0058] For example, if the requested discharge flow rate is zero, the second unload valve 22 is fully open. Then, as the amount of the operation in the third operation increases, the control device 27 closes the opening of the second unload valve 22 in accordance with the second difference, because the requested discharge flow rate increases. This makes it possible to increase the flow rate of the working fluid that is joined with the working fluid from the third hydraulic pump motor 13 while maintaining the suction flow rate of the second hydraulic pump motor 12 at the requested regenerative flow rate. Subsequently, when the amount of the operation in the third operation increases further and the requested discharge flow rate becomes greater than the requested regenerative flow rate, the second unload valve 22 is closed. Conversely, as the amount of the operation in the third operation decreases, the opening of the second unload valve 22 changes from a fully closed state to a fully open state in accordance with the second difference, the opposite of the procedure described above. After that, the flow ends.

[0059] In the hydraulic drive device 1 of this embodiment, the suction ports 11a to 13a of the first to third hydraulic pump motors 11 to 13 are connected in parallel to the meter-out passage 31. Therefore, the fluid energy of the working fluid discharged from the boom cylinder 3 can be regenerated into electrical energy by the first to third hydraulic pump motors 11 to 13. Consequently, the suction flow rate in each of the first to third hydraulic pump motors 11 to 13 can be reduced during regeneration. This makes it possible to miniaturize each of the first to third hydraulic pump motors 11 to 13.

[0060] Furthermore, in the hydraulic drive device 1 of this embodiment, the confluence mechanism 24 combines the working fluid discharged from the respective discharge ports 11b to 13b of the first to third hydraulic pump motors 11 to 13 and supplies it to the respective hydraulic cylinders 3 to 5. Therefore, the discharge flow rate from each of the first to third hydraulic pump motors 11 to 13 can be reduced. As a result, the first to third hydraulic pump motors 11 to 13 can be made smaller.

[0061] Furthermore, in the hydraulic drive device 1 of this embodiment, the opening degree of each of the first to third unload valves 21 to 23 can be adjusted. Therefore, the flow rate of the residual portion of the working fluid discharged from the discharge ports 11b to 13b of the first to third hydraulic pump motors 11 to 13 that is not discharged into the tank 28 can be controlled by the opening degree of the first to third unload valves 21 to 23, i.e., the flow rate of the working fluid supplied to each hydraulic cylinder 4 and 5. As a result, during regeneration, while regeneration is performed by the first to third hydraulic pump motors 11 to 13, the flow rate of the residual portion of the working fluid that is not discharged into the tank 28 can be precisely controlled and utilized. In other words, working fluid with precisely controlled flow rate can be supplied from the second and third hydraulic pump motors 12 and 13 to the arm cylinder 4 and the bucket cylinder 5, respectively.

[0062] Furthermore, in the hydraulic drive device 1 of this embodiment, the discharge ports 11b and 12b of the first and second hydraulic pump motors 11 and 12 are connected to the boom cylinder 3 and the arm cylinder 4, respectively, so that the boom cylinder 3 and the arm cylinder 4 can be operated simultaneously. On the other hand, the suction ports 11a and 12a of the first and second hydraulic pump motors 11 and 12 are connected in parallel to the meter-out passage 31. Therefore, the fluid energy of the working fluid discharged from the boom cylinder 3 can be regenerated into electrical energy by the first and second hydraulic pump motors 11 and 12. Therefore, the suction flow rate of the first and second hydraulic pump motors 11 and 12 can be reduced during regenerative operation. Consequently, the first and second hydraulic pump motors 11 and 12 can be made smaller.

[0063] Furthermore, in the hydraulic drive device 1 of this embodiment, the opening degree of the first unload valve 21 can be adjusted. Therefore, the flow rate of the working fluid discharged from the discharge port 11b of the first hydraulic pump motor 11 (i.e., the flow rate of the remaining portion not discharged into the tank 28) can be controlled by the opening degree of the first unload valve 21. This allows for precise control and utilization of the flow rate of the remaining portion of the working fluid that is not discharged into the tank 28 while regeneration is performed by the first and second hydraulic pump motors 11 and 12 during regeneration. For example, the remaining portion of the working fluid can be combined with the working fluid from the first hydraulic pump motor 11 by the merging mechanism 24 and supplied to the arm cylinder 4, and the flow rate of the combined working fluid can be precisely controlled.

[0064] Furthermore, in the hydraulic drive device 1 of this embodiment, the opening degree of the second unload valve 22 can be adjusted. This allows a portion of the working fluid guided from the boom cylinder 3 to the second hydraulic pump motor 12 to be supplied to the arm cylinder 4, while the fluid energy of the remaining working fluid is regenerated as electrical energy. Therefore, the working fluid discharged from the boom cylinder 3 can be effectively utilized.

[0065] Furthermore, in the hydraulic drive device 1 of this embodiment, the merging mechanism 24 can merge the working fluid discharged from the respective discharge ports 11b and 12b of the first and second hydraulic pump motors 11 and 12. Therefore, the discharge flow rate from each of the first and second hydraulic pump motors 11 and 12 can be reduced. This makes it possible to miniaturize each of the first and second hydraulic pump motors 11 and 12. In addition, since the flow rate of the working fluid merged from the first hydraulic pump motor 11 can be controlled by the first unload valve 21, the controllability of the arm cylinder 4 can be ensured even when merging is performed.

[0066] Furthermore, in the hydraulic drive device 1 of this embodiment, the control device 27 controls the opening degree of the second unload valve 22 according to the difference between the required regenerative flow rate and the required discharge flow rate. This allows the excess flow rate that is not supplied to the arm cylinder 4 to be regenerated as electrical energy. This reduces energy consumption in the hydraulic drive device 1.

[0067] Furthermore, in the hydraulic drive device 1 of this embodiment, the control device 27 controls the opening degree of the first unload valve 21 according to the first difference and controls the opening degree of the second unload valve 22 according to the second difference. As a result, the excess flow rate that is not supplied to the arm cylinder 4 from each of the first and second hydraulic pump motors 11 and 12 can be regenerated as electrical energy. This reduces energy consumption in the hydraulic drive device 1.

[0068] Furthermore, in the hydraulic drive device 1 of this embodiment, the control device 27 controls the opening degree of the second unload valve 22 according to the second difference and controls the opening degree of the third unload valve 23 according to the third difference. As a result, excess flow rate that is not supplied from the second and third hydraulic pump motors 12 and 13 to the arm cylinder 4 and bucket cylinder 5 can be regenerated as electrical energy. This reduces energy consumption in the hydraulic drive device 1.

[0069] Furthermore, in the hydraulic drive device 1 of this embodiment, the control device 27 controls the opening degree of the second unload valve 22 according to the second difference and controls the opening degree of the third unload valve 23 according to the third difference. As a result, excess flow rate that is not supplied from the second and third hydraulic pump motors 12 and 13 to the arm cylinder 4 and bucket cylinder 5 can be regenerated as electrical energy. This reduces energy consumption in the hydraulic drive device 1. In addition, since the flow rate of the working fluid merged from the second and third hydraulic pump motors 12 and 13 can be controlled by the second and third unload valves 22 and 23, controllability of the flow rate of the working fluid after merging can be ensured.

[0070] <Other Embodiments> The hydraulic drive system 1 of this embodiment may be applied to construction vehicles and industrial vehicles other than hydraulic excavators, and may also be applied to other work machines. Furthermore, the hydraulic drive system 1 may be applied to any vehicle or machine that supplies working fluid to drive multiple hydraulic cylinders. The number of hydraulic cylinders supplied by the hydraulic drive system 1 may be two or four or more. In the case of two hydraulic cylinders, the number of merging valves will be one. Also, the number of hydraulic pump motors provided in the hydraulic drive system 1 does not necessarily have to be the same as the number of hydraulic actuators. Moreover, the hydraulic cylinders 3 to 5 are not limited to the boom cylinder 3, arm cylinder 4, and bucket cylinder 5, but may be other hydraulic cylinders.

[0071] In the hydraulic drive device 1 of this embodiment, the first to third hydraulic pump motors 11 to 13 are connected in parallel to the meter-out passage 31, but the number of hydraulic pump motors connected in parallel to the meter-out passage 31 may be two or four or more. Also, the second hydraulic actuator to which the second hydraulic pump motor 12 supplies working fluid may be a bucket cylinder 5. Similarly, the third hydraulic actuator to which the third hydraulic pump motor 13 supplies working fluid may be an arm cylinder 4. The flow described above for the extension and retraction operation of each cylinder is merely an example, and other flows may be used. Furthermore, the hydraulic drive device 1 does not necessarily need to be equipped with a regeneration valve 20, and may also be equipped with a regeneration valve that connects the two ports 4a and 4b of the arm cylinder 4 in addition to the regeneration valve 20. Moreover, the first to third hydraulic pump motors 11 to 13 may be fixed-displacement pumps, or they may be oblique-axis pumps, gear pumps, etc. If the first to third hydraulic pump motors 11 to 13 are fixed-displacement pumps, the control device 27 controls the discharge flow rate and suction flow rate according to the rotational speed of the electric motors 14 to 16.

[0072] <Exemplary Embodiment> The hydraulic drive device in the first phase is a hydraulic drive device for supplying and discharging working fluid to and from a hydraulic cylinder, comprising: a plurality of hydraulic pump motors having an intake port and a discharge port; a plurality of electric motors connected to each of the plurality of hydraulic pump motors; and a directional control valve connected to a meter-out passage, which discharges working fluid from the hydraulic cylinder to the meter-out passage by connecting the hydraulic cylinder to the meter-out passage, wherein the intake port of each of the plurality of hydraulic pump motors is connected in parallel to the meter-out passage.

[0073] In the above scenario, the suction ports of each of the multiple hydraulic pump motors are connected in parallel to the meter-out passage. Therefore, the fluid energy of the working fluid discharged from the hydraulic cylinder can be regenerated into electrical energy by the multiple hydraulic pump motors. Consequently, during regeneration, the flow rate of the working fluid drawn into each hydraulic pump motor, i.e., the suction flow rate, can be reduced. This allows for miniaturization of each hydraulic pump motor.

[0074] The hydraulic drive device in the second phase may include a merging mechanism in the hydraulic drive device in the first phase that combines the working fluid discharged from each of the discharge ports of the plurality of hydraulic pump motors and supplies it to the hydraulic cylinder.

[0075] According to the above procedure, the confluence mechanism combines the working fluid discharged from each discharge port of the hydraulic pump motor and supplies it to the hydraulic cylinder. Therefore, the discharge flow rate from each hydraulic pump motor can be reduced. This makes it possible to miniaturize multiple hydraulic pump motors.

[0076] The hydraulic drive device in the third phase further comprises a plurality of unload valves that discharge at least a portion of the working fluid discharged from each of the discharge ports of the plurality of hydraulic pump motors into a tank, in addition to the hydraulic drive device in the first or second phase. The opening degree of the aforementioned multiple unload valves may be adjusted.

[0077] Following the above procedure, the opening degree of each unload valve can be adjusted. Therefore, the flow rate of the working fluid discharged from each discharge port of the hydraulic pump motor (i.e., the flow rate of the remaining portion not discharged into the tank) can be controlled by the opening degree of the unload valve. This allows for precise control and utilization of the flow rate of the remaining working fluid not discharged into the tank while regenerating with multiple hydraulic pump motors during regeneration.

[0078] The hydraulic drive device in the fourth phase is a hydraulic drive device that supplies and discharges working fluid to a plurality of hydraulic actuators, including a first hydraulic actuator which is a hydraulic cylinder, and comprises a plurality of hydraulic pump motors having an intake port and a discharge port, the discharge port of which is connected to each of the plurality of hydraulic actuators, a plurality of electric motors connected to each of the plurality of hydraulic pump motors, and a directional control valve connected to a meter-out passage, which discharges working fluid from the first hydraulic actuator to the meter-out passage by connecting the first hydraulic actuator to the meter-out passage, wherein the intake port of each of the plurality of hydraulic pump motors is connected in parallel to the meter-out passage.

[0079] Following the above configuration, since each discharge port of the hydraulic pump motor is connected to a different hydraulic actuator, multiple hydraulic actuators can be operated simultaneously. On the other hand, each suction port of the hydraulic pump motor is connected in parallel to the meter-out passage. Therefore, the fluid energy of the working fluid discharged from the first hydraulic actuator can be regenerated into electrical energy by multiple hydraulic pump motors. Consequently, during regeneration, the flow rate of the working fluid drawn into each hydraulic pump motor, i.e., the suction flow rate, can be reduced. This allows each hydraulic pump motor to be miniaturized.

[0080] The hydraulic drive device in the fifth phase may be the hydraulic drive device in the fourth phase, further comprising a first unload valve, wherein the plurality of hydraulic pump motors include a first hydraulic pump motor connected to the first hydraulic actuator, and the first unload valve discharges at least a portion of the working fluid discharged from the discharge port of the first hydraulic pump motor into a tank and adjusts its opening.

[0081] According to the above procedure, the opening degree of the first unload valve can be adjusted. Therefore, the flow rate of the working fluid discharged from the discharge port of the first hydraulic pump motor (i.e., the flow rate of the remaining portion not discharged into the tank) can be controlled by the opening degree of the first unload valve. This allows for precise control and utilization of the flow rate of the remaining portion of the working fluid not discharged into the tank while regenerating with multiple hydraulic pump motors during regeneration.

[0082] The hydraulic drive device in the sixth phase is the hydraulic drive device in the fifth phase, further comprising a second unload valve, wherein the plurality of hydraulic pump motors include a second hydraulic pump motor connected to a second hydraulic actuator which is one of the plurality of hydraulic actuators, and the second unload valve may discharge at least a portion of the working fluid discharged from the discharge port of the second hydraulic pump motor into a tank and adjust the degree of opening.

[0083] Following the above procedure, the opening degree of the second unload valve can be adjusted. This allows a portion of the working fluid guided from the first hydraulic actuator to the second hydraulic pump motor to be supplied to the second hydraulic actuator, while the fluid energy of the remaining working fluid is recovered as electrical energy. Therefore, the working fluid discharged from the first hydraulic actuator can be effectively utilized.

[0084] The hydraulic drive device in the seventh phase is a hydraulic drive device in the sixth phase that includes a merging mechanism, wherein the discharge port of the first hydraulic pump motor is connected to the first hydraulic actuator, the discharge port of the second hydraulic pump motor is connected to the second hydraulic actuator, and the merging mechanism merges the working fluid discharged from the respective discharge ports of the first hydraulic pump motor and the second hydraulic pump motor.

[0085] Following the above procedure, the merging mechanism can merge the working fluid discharged from the respective discharge ports of the first and second hydraulic pump motors. Therefore, the discharge flow rates from each of the first and second hydraulic pump motors can be reduced. This allows for miniaturization of both the first and second hydraulic pump motors. Furthermore, since the flow rate of the working fluid merged from the first hydraulic pump motor can be controlled by the first unload valve, the controllability of the second hydraulic actuator can be ensured even during merging.

[0086] The hydraulic drive device in the eighth phase includes a control device that controls the operation of the directional control valve and the second unload valve in accordance with an input signal, wherein the control device activates the directional control valve in accordance with an input signal to connect the first hydraulic actuator to the meter-out passage, and calculates a required regenerative flow rate, which is the flow rate to be regenerated from the first hydraulic actuator to the second hydraulic pump motor, and a required discharge flow rate, which is the flow rate to be discharged from the second hydraulic pump motor, based on the input signal, and controls the opening degree of the second unload valve according to the difference between the required regenerative flow rate and the required discharge flow rate.

[0087] In accordance with the above scenario, the control device controls the opening degree of the second unload valve according to the difference between the required regenerative flow rate and the required discharge flow rate. This allows the excess flow rate not supplied to the second hydraulic actuator to be regenerated as electrical energy. This reduces energy consumption in the hydraulic drive device.

[0088] The hydraulic drive device in the ninth phase includes a control device that controls the operation of the directional control valve, the merging mechanism, the first unload valve, and the second unload valve in accordance with an input signal, wherein the control device operates the directional control valve in accordance with an input signal to connect the first hydraulic actuator to the meter-out passage and the merging mechanism combines the working fluid discharged from the respective discharge ports of the first hydraulic pump motor and the second hydraulic pump motor and supplies it to the second hydraulic actuator, and the input signal is Based on the signal, the system may calculate the required regenerative flow rate, which is the flow rate to be regenerated from the first hydraulic actuator to the first hydraulic pump motor and the second hydraulic pump motor, respectively, and the required discharge flow rate, which is the flow rate to be discharged from the first hydraulic pump motor and the second hydraulic pump motor, respectively. The system may then control the opening degree of the first unload valve according to the first difference, which is the difference between the required regenerative flow rate and the required discharge flow rate for the first hydraulic pump motor, and control the opening degree of the second unload valve according to the second difference, which is the difference between the required regenerative flow rate and the required discharge flow rate for the second hydraulic pump motor.

[0089] According to the above procedure, the control device controls the opening degree of the first unload valve according to the first difference and the opening degree of the second unload valve according to the second difference. This allows the excess flow rate that is not supplied to the hydraulic actuator from each of the two hydraulic pump motors to be regenerated as electrical energy. This reduces energy consumption in the hydraulic drive system.

[0090] The hydraulic drive device in the tenth phase further comprises, in any one of the sixth to ninth phases, a third unload valve, and a control device that controls the operation of the directional control valve, the second unload valve, and the third unload valve in response to an input signal, the plurality of hydraulic pump motors further include a third hydraulic pump motor connected to a third hydraulic actuator which is one of the plurality of hydraulic actuators, the third unload valve discharges at least a portion of the working fluid discharged from the discharge port of the third hydraulic pump motor into a tank and adjusts its opening, and the control device controls the operation of the directional control valve, the second unload valve, and the third unload valve in response to an input signal When the directional control valve is activated to connect the first hydraulic actuator to the meter-out passage, the required regenerative flow rate, which is the flow rate to be regenerated from the first hydraulic actuator to the second and third hydraulic pump motors, and the required discharge flow rate, which is the flow rate to be discharged from the second and third hydraulic pump motors, are calculated based on the input signal. The opening degree of the second unload valve may be controlled according to the second difference, which is the difference between the required regenerative flow rate and the required discharge flow rate for the second hydraulic pump motor, and the opening degree of the third unload valve may be controlled according to the third difference, which is the difference between the required regenerative flow rate and the required discharge flow rate for the third hydraulic pump motor.

[0091] In the above scenario, the control device controls the opening degree of the second unload valve according to the second difference and the opening degree of the third unload valve according to the third difference. This allows the excess flow rate not supplied from each of the two hydraulic pump motors to the second and third hydraulic actuators to be regenerated as electrical energy. This reduces energy consumption in the hydraulic drive system.

[0092] The hydraulic drive device in the 11th phase further comprises a merging mechanism in the hydraulic drive device in the 10th phase, the merging mechanism merges the working fluid discharged from the respective discharge ports of the second hydraulic pump motor and the third hydraulic pump motor and supplies it to the second hydraulic actuator or the third hydraulic actuator, and the control device operates the directional control valve in response to an input signal to connect the first hydraulic actuator to the meter-out passage and merges the working fluid discharged from the respective discharge ports of the second hydraulic pump motor and the third hydraulic pump motor by the merging mechanism, and may control the opening degree of the second unload valve according to the second difference and the opening degree of the third unload valve according to the third difference.

[0093] In the above scenario, the control device controls the opening degree of the second unload valve according to the second difference and the opening degree of the third unload valve according to the third difference. This allows the excess flow rate that is not supplied to the hydraulic actuator from each of the two hydraulic pump motors to be regenerated as electrical energy. This reduces energy consumption in the hydraulic drive system. Furthermore, since the flow rate of the working fluid merged from each of the second and third hydraulic pump motors can be controlled by each of the second and third unload valves, controllability of the flow rate of the working fluid after merging can be ensured. [Explanation of symbols]

[0094] 1. Hydraulic drive device 3. Boom Cylinder (First Hydraulic Actuator) 4. Arm cylinder (second hydraulic actuator) 5. Bucket cylinder (third hydraulic actuator) 11. First hydraulic pump motor 11a Inhalation port 11b Discharge port 12. Second hydraulic pump motor 12a Inhalation port 12b Discharge port 13. Third hydraulic pump motor 13a Inhalation port 13b Discharge port 14 Electric motor 15 Electric motor 16 Electric motor 17. First Directional Control Valve 21. First unloading valve 22. Second unloading valve 23. Third unloading valve 24 Merging mechanism 27 Control device 28 tanks 31 Meter Out Passage

Claims

1. A hydraulic drive device that supplies and discharges working fluid to a hydraulic cylinder, Multiple hydraulic pump motors having suction ports and discharge ports, Multiple electric motors connected to each of the aforementioned multiple hydraulic pump motors, A directional control valve connected to a meter-out passage, which discharges working fluid from the hydraulic cylinder to the meter-out passage by connecting the hydraulic cylinder to the meter-out passage, The system includes a plurality of unload valves that discharge at least a portion of the working fluid discharged from each of the discharge ports of the plurality of hydraulic pump motors into a tank. Each of the aforementioned multiple hydraulic pump motors has a suction port connected in parallel to the meter-out passage. The aforementioned multiple unload valves are hydraulically driven devices that adjust the degree of opening.

2. The hydraulic drive device according to claim 1, further comprising a confluence mechanism that combines the working fluid discharged from each of the multiple hydraulic pump motors and supplies it to the hydraulic cylinder.

3. A hydraulic drive device that supplies and discharges working fluid to a plurality of hydraulic actuators, including a first hydraulic actuator which is a hydraulic cylinder, A plurality of hydraulic pump motors having an intake port and a discharge port, the discharge port of which is connected to each of the plurality of hydraulic actuators, Multiple electric motors connected to each of the aforementioned multiple hydraulic pump motors, A directional control valve connected to a meter-out passage, which discharges working fluid from the first hydraulic actuator to the meter-out passage by connecting the first hydraulic actuator to the meter-out passage, Equipped with a first unload valve, Each of the aforementioned multiple hydraulic pump motors has a suction port connected in parallel to the meter-out passage. The plurality of hydraulic pump motors include a first hydraulic pump motor connected to the first hydraulic actuator, The first unload valve is a hydraulically driven device that discharges at least a portion of the working fluid discharged from the discharge port of the first hydraulic pump motor into a tank and adjusts the degree of opening.

4. Equipped with a second unload valve, The plurality of hydraulic pump motors include a second hydraulic pump motor connected to a second hydraulic actuator, which is one of the plurality of hydraulic actuators. The hydraulic drive device according to claim 3, wherein the second unload valve discharges at least a portion of the working fluid discharged from the discharge port of the second hydraulic pump motor into a tank and adjusts the degree of opening.

5. Equipped with a merging mechanism, The discharge port of the first hydraulic pump motor is connected to the first hydraulic actuator. The discharge port of the second hydraulic pump motor is connected to the second hydraulic actuator. The hydraulic drive device according to claim 4, wherein the merging mechanism merges the working fluid discharged from the respective discharge ports of the first hydraulic pump motor and the second hydraulic pump motor.

6. The system includes a control device that controls the operation of the directional control valve and the second unload valve in accordance with the input signal. The hydraulic drive device according to claim 4, wherein the control device operates the directional control valve in response to an input signal to connect the first hydraulic actuator to the meter-out passage, and calculates a required regenerative flow rate, which is the flow rate to be regenerated from the first hydraulic actuator to the second hydraulic pump motor, and a required discharge flow rate, which is the flow rate to be discharged from the second hydraulic pump motor, based on the input signal, and controls the opening degree of the second unload valve according to the difference between the required regenerative flow rate and the required discharge flow rate.

7. The system includes a control device that controls the operation of the directional control valve, the merging mechanism, the first unload valve, and the second unload valve in accordance with the input signal. The control device, in response to an input signal, operates the directional control valve to connect the first hydraulic actuator to the meter-out passage and combines the working fluid discharged from the respective discharge ports of the first hydraulic pump motor and the second hydraulic pump motor by the confluence mechanism and supplies it to the second hydraulic actuator, calculates the required regenerative flow rate, which is the flow rate to be regenerated from the first hydraulic actuator to the first hydraulic pump motor and the second hydraulic pump motor, and the required discharge flow rate, which is the flow rate to be discharged from the first hydraulic pump motor and the second hydraulic pump motor, respectively, based on the input signal, controls the opening degree of the first unload valve according to the first difference, which is the difference between the required regenerative flow rate and the required discharge flow rate for the first hydraulic pump motor, and controls the opening degree of the second unload valve according to the second difference, which is the difference between the required regenerative flow rate and the required discharge flow rate for the second hydraulic pump motor, as described in claim 5.

8. The third unload valve, The system further includes a control device that controls the operation of the directional control valve, the second unload valve, and the third unload valve in accordance with the input signal, The plurality of hydraulic pump motors further include a third hydraulic pump motor connected to a third hydraulic actuator, which is one of the plurality of hydraulic actuators. The third unload valve discharges at least a portion of the working fluid discharged from the discharge port of the third hydraulic pump motor into a tank and adjusts its opening degree. The control device, when operating the directional control valve in response to an input signal to connect the first hydraulic actuator to the meter-out passage, calculates a required regenerative flow rate, which is the flow rate to be regenerated from the first hydraulic actuator to the second and third hydraulic pump motors, and a required discharge flow rate, which is the flow rate to be discharged from the second and third hydraulic pump motors, respectively, based on the input signal, controls the opening degree of the second unload valve in accordance with the second difference, which is the difference between the required regenerative flow rate and the required discharge flow rate for the second hydraulic pump motor, and controls the opening degree of the third unload valve in accordance with the third difference, which is the difference between the required regenerative flow rate and the required discharge flow rate for the third hydraulic pump motor, as described in claim 4.

9. Equipped with an additional merging mechanism, The merging mechanism merges the working fluid discharged from the respective discharge ports of the second hydraulic pump motor and the third hydraulic pump motor and supplies it to the second hydraulic actuator or the third hydraulic actuator. The hydraulic drive device according to claim 8, wherein the control device operates the directional control valve in response to an input signal to connect the first hydraulic actuator to the meter-out passage and combines the working fluid discharged from the respective discharge ports of the second hydraulic pump motor and the third hydraulic pump motor by the confluence mechanism, controlling the opening degree of the second unload valve according to the second difference and the opening degree of the third unload valve according to the third difference.

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