Hydraulic drive device

Abstract

To provide a hydraulic driving device capable of downsizing a hydraulic pump motor.SOLUTION: The hydraulic driving device for supplying working liquid to a plurality of hydraulic cylinders including a first hydraulic cylinder includes a plurality of hydraulic driving systems associated with the plurality of hydraulic cylinders, respectively, for supplying the working liquid to the associated hydraulic cylinders, and at least one communication valve for communicating the plurality of hydraulic driving systems with each other in response to an input communication command. Each of the plurality of hydraulic driving systems includes a hydraulic pump motor, an electric motor, and a direction control valve. A first hydraulic driving system as the hydraulic driving system associated with the first hydraulic cylinder includes a first direction control valve as the direction control valve. The first direction control valve allows the working liquid to flow from the first hydraulic cylinder to the hydraulic pump motor in response to an input first operation command.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

[0002] A hydraulic drive device drives a hydraulic cylinder by supplying hydraulic fluid to the hydraulic cylinder. As a hydraulic drive device, for example, a drive device as disclosed in Patent Document 1 is known. The drive device of Patent Document 1 includes a plurality of drive circuits. One of the plurality of drive circuits includes a pump motor that generates electricity by the return fluid from the hydraulic cylinder. On the other hand, the other drive circuit operates by the electric power generated by the pump motor. More specifically, the other drive circuit includes an electric pump. Then, the other drive circuit operates the electric pump by the generated electric power.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] In the drive device of Patent Document 1, a pump motor having a capacity corresponding to the flow rate of the fluid returning from the fluid pressure actuator, that is, the return flow rate, is adopted. Therefore, it is necessary to adopt a pump motor having a capacity corresponding to the size of the hydraulic cylinder. Therefore, it is difficult to miniaturize the pump motor.

[0005] Therefore, an object of the present invention is to provide a hydraulic drive device capable of miniaturizing a hydraulic pump motor.

Means for Solving the Problems

[0006] The hydraulic drive device of the present invention is a hydraulic drive device that supplies working fluid to a plurality of hydraulic cylinders including a first hydraulic cylinder, comprising: a plurality of hydraulic drive systems associated with each of the plurality of hydraulic cylinders and supplying working fluid to the corresponding hydraulic cylinders; and at least one communication valve that connects the plurality of hydraulic drive systems to each other in response to an input communication command, wherein each of the plurality of hydraulic drive systems includes a hydraulic pump motor that discharges working fluid and rotates when working fluid is supplied, and the hydraulic pump motor rotates to drive the hydraulic pump motor The first hydraulic drive system, which is the hydraulic drive system associated with the first hydraulic cylinder, includes an electric motor that discharges working fluid from a source and generates electricity by being rotationally driven by the hydraulic pump motor, and a directional control valve that switches the direction of flow of working fluid between the hydraulic pump motor and the corresponding hydraulic cylinder according to an operation command, and the first hydraulic drive system, which is the hydraulic drive system associated with the first hydraulic cylinder, includes the first directional control valve, which is the directional control valve, and the first directional control valve flows working fluid from the first hydraulic cylinder to the hydraulic pump motor according to a first operation command that is input.

[0007] According to the present invention, at least one communication valve is provided to connect multiple hydraulic drive systems to each other in response to an input communication command. Therefore, when a communication command is output to the communication valve when the working fluid is flowed from the first hydraulic cylinder to the hydraulic pump motor by the first directional control valve, the working fluid returned from the first hydraulic cylinder can be distributed to the hydraulic pump motors of the multiple hydraulic drive systems. Therefore, the working fluid returned from the first hydraulic cylinder can be regenerated by the multiple hydraulic pump motors. Therefore, the capacity of the first hydraulic pump motor can be reduced, and thus the first hydraulic pump motor can be miniaturized. [Effects of the Invention]

[0008] According to the present invention, the hydraulic pump motor can be miniaturized. [Brief explanation of the drawing]

[0009] [Figure 1] This is a circuit diagram showing the configuration of the hydraulic drive device of this embodiment. [Figure 2] Figure 1 is a flowchart showing the procedure for boom regeneration of the hydraulically driven device. [Modes for carrying out the invention]

[0010] 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.

[0011] 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 cylinders 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 cylinder, a bucket cylinder 4 which is the second hydraulic cylinder, and an arm cylinder 5 which is the third hydraulic cylinder. Each of the hydraulic cylinders 3 to 5 is provided on the boom, bucket, and arm, respectively. The hydraulic excavator moves the bucket by extending and retracting the three hydraulic cylinders 3 to 5. As a result, the hydraulic excavator can perform various tasks.

[0012] <Hydraulic drive device> The hydraulic drive unit 1 drives the hydraulic cylinders 3 to 5. In this embodiment, the hydraulic drive unit 1 drives at least the boom cylinder 3, bucket cylinder 4, and arm cylinder 5 described above. The hydraulic drive unit 1 comprises first to third hydraulic drive systems 11 to 13 and two communication valves 14 and 15. Furthermore, the hydraulic drive unit 1 comprises an operating device 16 and a control device 17.

[0013] <Multiple hydraulic drive systems> Each of the hydraulic drive systems 11 to 13 corresponds to each of the hydraulic cylinders 3 to 5. In this embodiment, the first hydraulic drive system 11 corresponds to the boom cylinder 3, the second hydraulic drive system 12 corresponds to the bucket cylinder 4, and the third hydraulic drive system 13 corresponds to the arm cylinder 5. Each of the hydraulic drive systems 11 to 13 supplies working fluid (for example, oil and water) to the corresponding hydraulic cylinders 3 to 5. Each of the first to third hydraulic drive systems 11 to 13 includes hydraulic pump motors 21, 31, and 41, electric motors 22, 32, and 42, and directional control valves 23, 33, and 43, respectively. The first and third hydraulic drive systems 11 and 13 also further include regeneration valves 24 and 44. The configurations of the first to third hydraulic drive systems 11 to 13 will be described in detail below.

[0014] <First hydraulic drive system> The first hydraulic drive system 11 supplies working fluid to the boom cylinder 3. The first hydraulic drive system 11 also regenerates the fluid energy of the working fluid discharged from the boom cylinder 3 into electrical energy. Furthermore, the first hydraulic drive system 11 regenerates the working fluid discharged from the head-side port 3a of the boom cylinder 3 to the rod-side port 3b. As described above, the first hydraulic drive system 11 includes a first hydraulic pump motor 21, a first electric motor 22, and a first directional control valve 23. The first hydraulic drive system 11 also includes a first regeneration valve 24.

[0015] [First hydraulic pump motor] The first hydraulic pump motor 21 discharges working fluid. Furthermore, the first hydraulic pump motor 21 rotates when working fluid is supplied. More specifically, the first hydraulic pump motor 21 has a shaft 21a and a pump port 21b. When the shaft 21a is rotationally driven, the first hydraulic pump motor 21 discharges working fluid from the pump port 21b. On the other hand, when working fluid is supplied to the pump port 21b, the first hydraulic pump motor 21 rotates the shaft 21a. In this embodiment, the first hydraulic pump motor 21 is a variable displacement swashplate pump and has a regulator 21c. The regulator 21c changes the pump capacity of the first hydraulic pump motor 21 based on a first displacement command that is input.

[0016] [1st electric motor] The first electric motor 22 rotates the first hydraulic pump motor 21, thereby discharging working fluid from the first hydraulic pump motor 21. Furthermore, the first electric motor 22 generates electricity when rotated by the first hydraulic pump motor 21. In other words, the first electric motor 22, in cooperation with the first hydraulic pump motor 21, regenerates the fluid energy of the working fluid into electrical energy. More specifically, the first electric motor 22 is connected to the shaft 21a. The first electric motor 22 rotates the shaft 21a, thereby discharging working fluid from the pump port 21b. Also, the first electric motor 22 generates electricity when the first hydraulic pump motor 21 rotates the shaft 21a. Furthermore, the first electric motor 22 changes its rotational speed in response to a first rotational speed command.

[0017] [First Directional Control Valve] The first directional control valve 23 is connected to the first hydraulic pump motor 21 via the pump passage 25. The first directional control valve 23 is also connected to the boom cylinder 3. More specifically, the first directional control valve 23 is connected to the head-side port 3a and the rod-side port 3b of the boom cylinder 3. Furthermore, the first directional control valve 23 is connected to the tank 18.

[0018] The first direction control valve 23 switches the flow direction of the hydraulic fluid flowing between the first hydraulic pump motor 21 and the boom cylinder 3 according to the input first operation command. More specifically, the first direction control valve 23 causes the hydraulic fluid to flow from the boom cylinder 3 to the first hydraulic pump motor 21 according to the input first operation command. Also, the first direction control valve 23 causes the hydraulic fluid to flow from the first hydraulic pump motor 21 to the boom cylinder 3 (in this embodiment, the head side port 3a of the boom cylinder 3) according to the first operation command. Further, in this embodiment, the first direction control valve 23 causes the hydraulic fluid to flow in either the head side supply direction or the rod side supply direction according to the input first operation command. The head side supply direction is the direction in which the hydraulic fluid flows from the first hydraulic pump motor 21 to the head side port 3a, and the rod side supply direction is the direction in which the hydraulic fluid flows from the first hydraulic pump motor 21 to the rod side port 3b. Furthermore, the first direction control valve 23 can block the passage between the first hydraulic pump motor 21 and the boom cylinder 3. Additionally, the first direction control valve 23 controls the opening degree according to the first operation command during regeneration when the hydraulic fluid flows from the boom cylinder 3 to the first hydraulic pump motor 21.

[0019] [First regeneration valve] The first regeneration valve 24 is connected to the head side port 3a and the rod side port 3b of the boom cylinder 3. The first regeneration valve 24 communicates the head side port 3a and the rod side port 3b according to the first regeneration command. Also, the first regeneration valve 24 allows the flow of the hydraulic fluid in the first regeneration direction in a state where the head side port 3a and the rod side port 3b are in communication, and blocks the reverse flow. The first regeneration direction is the flow from the head side port 3a to the rod side port 3b. Thereby, when supplying the hydraulic fluid to the rod side port 3b, the first regeneration valve 24 regenerates the hydraulic fluid discharged from the head side port 3a to the rod side port 3b.

[0020] <Second hydraulic drive system> The second hydraulic drive system 12 supplies hydraulic fluid to the bucket cylinder 4. As described above, the second hydraulic drive system 12 includes a second hydraulic pump motor 31, a second electric motor 32, and a second direction control valve 33. The second hydraulic pump motor 31 and the second electric motor 32 have the same configuration as the first hydraulic pump motor 21 and the first electric motor 22 described above. Therefore, for the configuration of the second hydraulic pump motor 31 and the second electric motor 32, the description of the first hydraulic pump motor 21 and the first electric motor 22 described above is referred to, and their detailed description is omitted. The regulator 31c of the second hydraulic pump motor 31 changes the discharge capacity according to the second capacity command, and the second electric motor 32 changes the rotational speed according to the second rotational speed command.

[0021] [Second Direction Control Valve] The second direction control valve 33 is connected to the second hydraulic pump motor 31 via a pump passage 35 and is also connected to the bucket cylinder 4. The second direction control valve 33 switches the flow direction of the hydraulic fluid flowing between the second hydraulic pump motor 31 and the bucket cylinder 4 according to the second operation command. More specifically, the second direction control valve 33 connects the second hydraulic pump motor 31 to one of the rod side port 4a and the head side port 4b of the bucket cylinder 4 according to the second operation command. Also, the second direction control valve 33 connects the other of the rod side port 4a and the head side port 4b to the tank 18 according to the second operation command. Thereby, the second direction control valve 33 causes the hydraulic fluid discharged from the second hydraulic pump motor 31 to flow to one of the rod side port 4a and the head side port 4b. Also, the second direction control valve 33 can block the connection between the second hydraulic pump motor 31 and the bucket cylinder 4.

[0022] [Third Hydraulic Drive System]< The third hydraulic drive system 13 supplies working fluid to the arm cylinder 5. The third hydraulic drive system 13 also regenerates the working fluid discharged from the rod-side port 5a of the arm cylinder 5 to the head-side port 5b. As described above, the third hydraulic drive system 13 includes a third hydraulic pump motor 41, a third electric motor 42, and a third directional control valve 43. Furthermore, the third hydraulic drive system 13 also includes a second regeneration valve 44. The third hydraulic pump motor 41 and the third electric motor 42 also have the same configuration as the first hydraulic pump motor 21 and the first electric motor 22 described above. Therefore, the configurations of the third hydraulic pump motor 41 and the third electric motor 42 are described in the same way as the first hydraulic pump motor 21 and the first electric motor 22 described above, and their detailed descriptions are omitted. Furthermore, the regulator 41c of the third hydraulic pump motor 41 changes the discharge capacity in accordance with the third capacity command, and the third electric motor 42 changes its rotational speed in accordance with the third rotational speed command.

[0023] [Third Directional Control Valve] The third directional control valve 43 is connected to the third hydraulic pump motor 41 via the pump passage 45, and is also connected to the arm cylinder 5. The third directional control valve 43 switches the direction of the hydraulic fluid flow between the third hydraulic pump motor 41 and the arm cylinder 5 in response to the third operation command. Specifically, the third directional control valve 43 switches the direction of the hydraulic fluid flow from the third hydraulic pump motor 41 to one of the rod-side port 5a and head-side port 5b of the arm cylinder 5 in response to the third operation command. The other of the rod-side port 5a and head-side port 5b of the third directional control valve 43 is connected to the tank 18. Furthermore, the third directional control valve 43 can shut off the connection between the third hydraulic pump motor 41 and the arm cylinder 5 in response to the third operation command.

[0024] [Second regeneration valve] The second regeneration valve 44 is connected to the rod-side port 5a and the head-side port 5b of the arm cylinder 5. The second regeneration valve 44 connects the rod-side port 5a and the head-side port 5b in response to the second regeneration command. The second regeneration valve 44 also allows the flow of working fluid in the second regeneration direction and prevents flow in the reverse direction while maintaining communication between the rod-side port 5a and the head-side port 5b. The second regeneration direction is the flow from the rod-side port 5a to the head-side port 5b. As a result, when the second regeneration valve 44 supplies working fluid to the head-side port 5b, it regenerates the working fluid discharged from the rod-side port 5a into the head-side port 5b.

[0025] <Communicating valve> The two communication valves 14 and 15 connect the first to third hydraulic drive systems 11 to 13 to each other in response to the input communication command. More specifically, the first communication valve 14 is connected to the pump passage 25 of the first hydraulic drive system 11 and the pump passage 35 of the second hydraulic drive system 12. The first communication valve 14 opens in response to the input first communication command. This connects the two pump passages 25 and 35, allowing the hydraulic fluid to flow between them. The second communication valve 15 is connected to the pump passage 35 of the second hydraulic drive system 12 and the pump passage 45 of the third hydraulic drive system 13. The second communication valve 15 connects the two pump passages 35 and 45 in response to the input second communication command. This allows the hydraulic fluid to flow between the pump passages 35 and 45.

[0026] <Operating device> The operating device 16 is operated by an operator or the like to move the boom cylinder 3, bucket cylinder 4, and arm cylinder 5. More specifically, the operating device 16 can operate each of the cylinders 3 to 5. The operating device 16 outputs an operation signal corresponding to the direction of operation and the amount of operation (hereinafter referred to as the "operation state") for each of the cylinders 3 to 5 (hereinafter referred to as "each operation"). The operating device 16 includes, for example, a plurality of operating levers 16a, 16b. In this embodiment, the operating device 16 includes two operating levers 16a, 16b. The operating levers 16a, 16b can be operated in various directions (e.g., tilting). The operating device 16 outputs an operation signal as the operation state for each operation, with the respective operating direction (e.g., tilting direction) and amount of operation (e.g., tilting amount) of the operating levers 16a, 16b. The operating device 16 may also take other forms, such as an operation panel, and may output operation signals according to operations on the operation panel or pre-stored programs.

[0027] <Control device> The control device 17 receives operation signals from the operating device 16. The control device 17 then controls the operation of the directional control valves 23, 33, and 43 by outputting operation commands to each of the first to third hydraulic drive systems 11 to 13 according to the operating state of each operation. More specifically, the control device 17 activates the first directional control valve 23 by outputting a first operation command according to the operating state of the first operation, which is an operation on the boom cylinder 3. The control device 17 also activates the second directional control valve 33 by outputting a second operation command according to the operating state of the second operation, which is an operation on the bucket cylinder 4. Furthermore, the control device 17 activates the third directional control valve 43 by outputting a third operation command according to the operating state of the third operation, which is an operation on the arm cylinder 5.

[0028] The control device 17 activates the first regeneration valve 24 by outputting a first regeneration command. The control device 17 activates the second regeneration valve 44 by outputting a second regeneration command. The control device 17 outputs first and second communication commands according to the operating status of the first to third operations. As a result, the control device 17 opens and closes the first and second communication valves 14 and 15.

[0029] The control device 17 controls the discharge flow rate or suction flow rate of each hydraulic pump motor 21, 31, and 41 by controlling the movement of the electric motors 22, 32, and 42 and the regulators 21c, 31c, and 41c. For example, the control device 17 calculates the discharge flow rate or suction flow rate of each hydraulic pump motor 21, 31, and 41 according to the operating state of each operation. Based on the calculated discharge flow rate or suction flow rate, the control device 17 calculates the rotational speed of each electric motor 22, 32, and 42 and the pump capacity of each hydraulic pump motor 21, 31, and 41, respectively. The control device 17 then outputs first to third rotational speed commands to each electric motor 22, 32, and 42 according to the rotational speed, and outputs first to third capacity commands to each hydraulic pump motor 21, 31, and 41 according to the pump capacity. In this way, the control device 17 controls the discharge flow rate or suction flow rate of each hydraulic pump motor 21, 31, and 41 according to the operating state of each operation.

[0030] <Operation of the hydraulic drive device> In the hydraulic drive device 1, when the operating device 16 is operated (in this embodiment, the operating levers 16a and 16b are operated), an operation signal corresponding to the operating state of each operation is output from the operating device 16. When an operation signal is output, the control device 17 extends and retracts each 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.

[0031] More specifically, the control device 17 outputs rotational speed commands to the electric motors 22, 32, and 42 according to the operating state of each operation. The control device 17 also outputs capacity commands to the hydraulic pump motors 21, 31, and 41 according to the operating state of each operation. As a result, the control device 17 causes the electric motors 22, 32, and 42 and the hydraulic pump motors 21, 31, and 41 to discharge or draw in working fluid at a flow rate corresponding to the amount of operation for each operation, according to the direction of operation for each operation. Furthermore, the control device 17 outputs operation commands to the hydraulic drive systems 11-13 according to the operating state of each operation. Then, the directional control valves 23, 33, and 43 connect the hydraulic pump motors 21, 31, and 41 to the corresponding hydraulic cylinders 3-5. This causes each cylinder 3-5 to extend and retract in the direction corresponding to the direction of operation and at a speed corresponding to the amount of operation. The extension and retraction operation of each cylinder due to each operation will be described below.

[0032] [Extending motion of each cylinder] For example, when a first operation (specifically, a boom-raising operation) is performed on the operating device 16 to extend the boom cylinder 3, the control device 17 outputs a first rotation speed command and a first volume command corresponding to the operation state of the first operation. As a result, a flow rate of working fluid corresponding to the amount of the operation in the first operation is discharged from the first hydraulic pump motor 21. The control device 17 also outputs a first operation command to the first hydraulic drive system 11 according to the operation state of the first operation. As a result, the first hydraulic pump motor 21 is connected to the head-side port 3a of the boom cylinder 3 by the first directional control valve 23. This switches the direction of flow of the working fluid to the head-side supply direction. In this embodiment, the opening between the first hydraulic pump motor 21 and the head-side port 3a is fully open during the boom-raising operation. Therefore, a flow rate of working fluid corresponding to the amount of the operation in the first operation flows in the head-side supply direction. Consequently, the boom cylinder 3 extends at a speed corresponding to the amount of the operation in the first operation.

[0033] Furthermore, when the amount of operation in the first operation exceeds a predetermined boom confluence threshold, the control device 17 opens the first communication valve 14. In addition, the control device 17 outputs a second rotation speed command and a second capacity command corresponding to the operation state of the first operation. As a result, working fluid is discharged from the second hydraulic pump motor 31 in addition to the first hydraulic pump motor 21. The working fluid discharged from each of the hydraulic pump motors 21 and 31 is combined by the first communication valve 14 and supplied to the boom cylinder 3 (more specifically, the head-side port 3a). This allows the boom cylinder 3 to be extended at a faster speed. Therefore, the first hydraulic pump motor 21 can be made smaller.

[0034] Furthermore, when a second operation (specifically, a bucket-in operation) is performed in the operating device 16 to extend the bucket cylinder 4 in the hydraulic drive device 1, the control device 17 outputs a second rotation speed command and a second capacity command according to the operating state of the second operation. The control device 17 also outputs a second operation command to the second hydraulic drive system 12 according to the operating state of the second operation. As a result, the bucket cylinder 4 extends at a speed corresponding to the amount of operation of the second operation.

[0035] Furthermore, when a third operation (specifically, an arm-in operation) is performed on the operating device 16 to extend the arm cylinder 5, the control device 17 operates as follows. That is, the control device 17 calculates the posture of the arm based on the respective angles of the boom and the arm. For example, angle sensors are provided on both the boom and the arm. The control device 17 calculates the posture of the arm based on the detection results obtained from each of the angle sensors. Then, based on the calculation results, the control device 17 determines whether or not the weight of the arm is acting in the direction of extension, that is, it performs a self-weight extension determination. The control device 17 may also perform the self-weight extension determination based on the hydraulic pressure of the rod-side port 5a and the head-side port 5b.

[0036] If the arm's own weight is not acting on the arm cylinder 5 in the direction of extension, the control device 17 outputs a third operation command to the third hydraulic drive system 13 according to the operation state of the third operation. As a result, the rod-side port 5a and the tank 18 are connected by the third directional control valve 43. The control device 17 also controls the opening degree between the rod-side port 5a and the tank 18 according to the amount of operation of the third operation. Furthermore, the control device 17 outputs a third rotation speed command and a third volume command according to the operation state of the third operation. As a result, a flow rate of hydraulic fluid corresponding to the amount of operation of the third operation is supplied from the third hydraulic pump motor 41 to the head-side port 5b and discharged from the rod-side port 5a to the tank 18 via the third directional control valve 43. Therefore, the arm cylinder 5 extends at a speed corresponding to the amount of operation of the third operation. When the amount of operation of the third operation increases, the control device 17 opens the second communication valve 15 to combine the hydraulic fluid of the second hydraulic pump motor 31 with the hydraulic fluid of the third hydraulic pump motor 41. This allows the arm cylinder 5 to extend more quickly. Furthermore, when the amount of operation in the third operation increases further, the control device 17 opens the first communication valve 14 to allow the working fluid from the first hydraulic pump motor 21 to merge with the working fluid from the second hydraulic pump motor 31. This allows the arm cylinder 5 to extend even faster.

[0037] On the other hand, if the weight of the arm is acting on the arm cylinder 5 in a direction that extends it, the control device 17 performs arm regeneration processing. That is, the control device 17 opens the second regeneration valve 44 by outputting a second regeneration command to the second regeneration valve 44. This connects the rod-side port 5a and the head-side port 5b. The control device 17 then uses the third directional control valve 43 to shut off the connection between the third hydraulic pump motor 41 and the arm cylinder 5. That is, the rod-side port 5a, the head-side port 5b, the third hydraulic pump motor 41, and the tank 18 are all shut off from each other by the third directional control valve 43. This allows the working fluid discharged from the rod-side port 5a to be regenerated at the head-side port 5b. Any insufficient working fluid is drawn up to the head-side port 5b from a makeup circuit (not shown). This causes the arm cylinder 5 to extend at a speed corresponding to the amount of operation of the third operation.

[0038] [Retraction action of each cylinder] When a second operation (specifically, a bucket-out operation) is performed in the operating device 16 to retract the bucket cylinder 4, the control device 17 outputs a second rotation speed command and a second capacity command corresponding to the operating state of the second operation. The control device 17 also outputs a second operation command corresponding to the operating state of the second operation to the second hydraulic drive system 12. As a result, the second hydraulic pump motor 31 is connected to the rod-side port 4a of the bucket cylinder 4 by the second directional control valve 33. This causes the bucket cylinder 4 to retract at a speed corresponding to the amount of the second operation.

[0039] Furthermore, when a third operation (specifically, an arm-out operation) is performed in the operating device 16 to retract the arm cylinder 5, the control device 17 outputs a third rotation speed command and a third capacity command according to the operating state of the third operation. The control device 17 also outputs a third operation command to the third hydraulic drive system 13 according to the operating state of the third operation. As a result, the third hydraulic pump motor 41 is connected to the rod-side port 5a of the arm cylinder 5 by the third directional control valve 43. This causes the arm cylinder 5 to retract at a speed corresponding to the amount of the third operation.

[0040] Furthermore, when the amount of operation in the third operation exceeds a predetermined arm confluence threshold, the control device 17 opens the second communication valve 15. In addition, the control device 17 outputs a second rotation speed command and a second capacity command corresponding to the operation state of the third operation. As a result, working fluid is discharged from the second hydraulic pump motor 31 in addition to the third hydraulic pump motor 41. The working fluid discharged from each of the hydraulic pump motors 31 and 41 is combined by the second communication valve 15 and supplied to the arm cylinder 5. This allows the arm cylinder 5 to be retracted at a faster speed.

[0041] [Boom cylinder retraction operation] Furthermore, when the first operation (specifically, the boom lowering operation) is performed in the operating device 16 to retract the boom cylinder 3, the control device 17 performs regenerative control. That is, in the hydraulic drive device 1, when the boom cylinder 3 is retracted to lower the boom, the fluid energy of the working fluid is regenerated into electrical energy. In addition, the control device 17 performs regeneration control along with regenerative control. That is, in the hydraulic drive device 1, the working fluid discharged from the head-side port 3a is regenerated into the rod-side port 3b. Furthermore, in the hydraulic drive device 1, the number of hydraulic pump motors 21, 31, and 41 used for regeneration changes depending on the operating state (mainly the amount of operation) of the first to third operations. The regenerative control of the control device 17 will be explained below with reference to the flow shown in Figure 2. If the first operation is the boom lowering operation, the control device 17 proceeds to step S1.

[0042] In step S1, which is a regeneration determination process, it is determined whether the manipulated variable BO of the first operation is greater than or equal to a predetermined regeneration start threshold BO1 (i.e., BO≧BO1). If the manipulated variable BO of the first operation is less than the regeneration start threshold BO1 (for example, if the manipulated variable is zero), it is determined that energy regeneration is unnecessary. In this case, regeneration control ends. On the other hand, if the manipulated variable BO of the first operation is greater than or equal to the regeneration start threshold BO1, the process proceeds to step S2.

[0043] In step S2, which is the regeneration initiation process, energy regeneration is performed using the first hydraulic pump motor 21. Specifically, the control device 17 outputs a first drive command to the first hydraulic drive system 11 according to the operating state of the first operation. As a result, the first directional control valve 23 connects the head-side port 3a of the boom cylinder 3 to the first hydraulic pump motor 21. At this time, the control device 17 keeps the communication valves 14 and 15 closed. This allows the working fluid to be returned from the head-side port 3a of the boom cylinder 3 to the first hydraulic pump motor 21. The first hydraulic pump motor 21 is rotated by the flowing working fluid. This causes the electric motor 22 to generate electricity. Therefore, the fluid energy of the working fluid is regenerated into electrical energy using the first hydraulic pump motor 21.

[0044] Furthermore, the control device 17 outputs a first operation command during regeneration and also outputs a first regeneration command to the first regeneration valve 24. As a result, the first regeneration valve 24 opens, and the rod-side port 3b and the head-side port 3a communicate with each other. In addition, the control device 17 controls the opening degree of the first directional control valve 23 to the opening degree corresponding to the first operation command by outputting a first operation command corresponding to the amount of the first operation. This limits the flow rate of the working fluid returned from the head-side port 3a to the first hydraulic pump motor 21, and allows a portion of the working fluid discharged from the head-side port 3a to be regenerated to the rod-side port 3b. Furthermore, the control device 17 controls the suction flow rate of the working fluid drawn into the first hydraulic pump motor 21 to the flow rate corresponding to the amount of the first operation by outputting a first rotation speed command and a first capacity command according to the amount of the first operation. As a result, the first electric motor 22 generates power corresponding to the amount of the first operation. When the fluid energy of the working fluid is recovered as electrical energy using the first hydraulic pump motor 21, the process proceeds to step S3.

[0045] In step S3, which is the bucket drive determination process, it is determined whether the operating amount BU of the second operation is less than or equal to the first predetermined value BU1 (i.e., BU ≤ BU1). If the operating amount BU of the second operation is greater than the first predetermined value BU1 (for example, if the bucket cylinder 4 is being operated), the flow ends. Therefore, in regenerative control, energy regeneration is performed using only the first hydraulic pump motor 21. On the other hand, if the operating amount BU of the second operation is less than or equal to the first predetermined value BU1 (for example, if the operating amount is zero), the process proceeds to step S4.

[0046] In step S4, which is a confluence determination process, it is determined whether the manipulated amount AM of the third operation is less than or equal to the aforementioned arm confluence threshold AM1 (i.e., AM ≤ AM1). If the manipulated amount AM of the third operation is greater than the arm confluence threshold AM1 (for example, when the arm cylinder 5 is quickly extended), the flow ends. Therefore, in regenerative control, energy regeneration is performed using only the first hydraulic pump motor 21. On the other hand, if the manipulated amount AM of the third operation is less than or equal to the arm confluence threshold AM1, the process proceeds to step S5.

[0047] In step S5 which is the first operation amount determination process, it is determined whether or not the operation amount BO of the first operation is equal to or greater than a predetermined first communication threshold value BO2 (>BO1) (i.e., BO≧BO2). If the operation amount BO of the first operation is less than the first communication threshold value BO2, the flow ends. Therefore, in the regeneration control, energy regeneration is performed using only the first hydraulic pump motor 21. On the other hand, if the operation amount BO of the first operation is equal to or greater than the first communication threshold value BO2, the process proceeds to step S6.

[0048] In step S6 which is the first communication process, the control device 17 outputs a first communication command to the first communication valve 14. Then, since the first communication valve 14 is opened, the head side port 3a of the boom cylinder 3 is also connected to the second hydraulic pump motor 31. Also, the control device 17 keeps the second direction control valve 33 blocking the connection between the second hydraulic pump motor 31 and the bucket cylinder 4. Then, the hydraulic fluid discharged from the head side port 3a is also supplied to the second hydraulic pump motor 31. Further, the control device 17 outputs first and second rotation speed commands and first and second capacity commands according to the operation amount of the first operation. Then, the suction flow rate of the hydraulic fluid sucked into each of the first and second hydraulic pump motors 21, 31 is controlled to a flow rate corresponding to the operation amount of the first operation. As a result, electric power corresponding to the operation amount of the first operation is generated in the first and second electric motors 22, 32. When the fluid energy of the hydraulic fluid is regenerated into electric energy using the first and second hydraulic pump motors 21, 31, the process proceeds to step S7.

[0049] In step S7 which is the arm drive determination process, it is determined whether or not the operation amount AM of the third operation is less than or equal to a second predetermined value AM2 (<AM1) (i.e., AM≦AM2). If the operation amount AM of the third operation is greater than the second predetermined value AM2 (for example, when operating the arm cylinder 5), the process proceeds to step S8. On the other hand, if the operation amount AM of the third operation is less than or equal to the second predetermined value AM2 (for example, when the operation amount is zero), the process proceeds to step S10.

[0050] In step S8, which is the self-weight extension determination process, it is determined whether the arm cylinder 5 extends under load. More specifically, the control device 17 determines, similar to the self-weight extension determination described above, whether the self-weight of the arm is acting in a direction that extends the arm cylinder 5 during the arm-in operation. If the control device 17 determines that the third operation is not an arm-in operation, or that the self-weight of the arm is not acting in a direction that extends the arm cylinder 5, the flow ends. Therefore, in regenerative control, energy regeneration is performed using the first and second hydraulic pump motors 21 and 31. On the other hand, if the control device 17 determines that the third operation is an arm-in command and that the self-weight of the arm is acting in a direction that extends the arm cylinder 5, it proceeds to step S9.

[0051] In step S9, which is the arm cylinder regeneration process, the control device 17 executes the arm regeneration process described above. Specifically, the control device 17 opens the second regeneration valve 44 by outputting a second regeneration command to the second regeneration valve 44. As a result, the working fluid discharged from the rod-side port 5a to the tank 18 is regenerated to the head-side port 5b. Once regeneration is complete, the flow ends. Therefore, in regenerative control, energy regeneration is performed using the first and second hydraulic pump motors 21 and 31.

[0052] In step S10, which is the second manipulated amount determination step, it is determined whether the manipulated amount BO of the first operation is greater than or equal to a predetermined second communication threshold BO3 (>BO2) (i.e., BO≧BO3). If the manipulated amount BO of the first operation is less than the second communication threshold BO3, the flow ends. Therefore, in regenerative control, energy regeneration is performed using the first and second hydraulic pump motors 21 and 31. On the other hand, if the manipulated amount BO of the first operation is greater than or equal to the second communication threshold BO3, the process proceeds to step S11.

[0053] In the second connection process, the control device 17 outputs a second connection command to the second connection valve 15. This opens the second connection valve 15, connecting the head-side port 3a of the boom cylinder 3 to the third hydraulic pump motor 41. The control device 17 also keeps the connection between the third hydraulic pump motor 41 and the arm cylinder 5 blocked by the third directional control valve 43. This supplies the working fluid discharged from the head-side port 3a to the third hydraulic pump motor 41. The control device 17 also outputs first to third rotational speed commands and first to third capacity commands corresponding to the amount of operation in the first operation. This controls the suction flow rate of the working fluid drawn into each of the first to third hydraulic pump motors 21, 31, and 41 to a flow rate corresponding to the amount of operation in the first operation. As a result, the first to third electric motors 22, 32, and 42 generate power corresponding to the amount of operation in the first operation. In other words, in regenerative control, energy is recovered using the first to third hydraulic pump motors 21, 31, and 41. Then the flow ends.

[0054] In addition, powering operations may be performed when the boom is lowered. If powering operations are performed, the control device 17 performs powering control as described below. Whether or not powering operations are being performed is determined by the control device 17 based on, for example, the hydraulic pressure at the head-side port 3a and the rod-side port 3b of the boom cylinder 3. In powering control, the control device 17 outputs a first rotation speed command and a first volume command according to the operating state of the first operation. As a result, working fluid is discharged from the first hydraulic pump motor 21. Furthermore, the control device 17 connects the rod-side port 3b of the boom cylinder 3 to the first hydraulic pump motor 21 using the first directional control valve 23, and sets the opening between the rod-side port 3b and the first hydraulic pump motor 21 to an opening corresponding to the amount of operation of the first operation. As a result, working fluid flows in the rod-side supply direction at a flow rate corresponding to the amount of operation of the first operation. Therefore, the control device 17 can retract the boom cylinder 3 at a speed corresponding to the amount of operation of the first operation.

[0055] In the hydraulic drive device 1 of this embodiment, a first communication valve 14 is provided that connects the first and second hydraulic drive systems 11 and 12 to each other in response to a first communication command input. Therefore, when the first communication command is output to the first communication valve 14 when the working fluid is flowed from the boom cylinder 3 to the first hydraulic pump motor 21 by the first directional control valve 23, the working fluid returned from the boom cylinder 3 can be distributed to the first and second hydraulic pump motors 21 and 31. Therefore, the working fluid returned from the boom cylinder 3 can be regenerated by the first and second hydraulic pump motors 21 and 31. As a result, the capacity of the first hydraulic pump motor 21 can be reduced, and thus the first hydraulic pump motor 21 can be miniaturized.

[0056] Furthermore, the hydraulic drive device 1 of this embodiment is equipped with first and second communication valves 14 and 15 that connect the first to third hydraulic drive systems 11 to 13 to each other according to each of the communication commands that are input. Therefore, when the working fluid is returned from the boom cylinder 3 to the first hydraulic pump motor by the first directional control valve 23, and a communication command is output to each of the first and second communication valves 14 and 15, the working fluid returned from the boom cylinder 3 can be distributed to the first to third hydraulic pump motors 21, 31, and 41. Therefore, the working fluid returned from the boom cylinder 3 can be regenerated by the first to third hydraulic pump motors 21, 31, and 41. As a result, the capacity of the first hydraulic pump motor 21 can be further reduced, and thus the first hydraulic pump motor 21 can be made even smaller.

[0057] Furthermore, in the hydraulic drive device 1 of this embodiment, communication valves 14 and 15 are connected to the pump passages 25, 35, and 45 of the hydraulic drive systems 11 to 13 that are to be communicated. Therefore, by shutting off the second and third directional control valves 33 and 43 during regeneration, more working fluid can be supplied to each hydraulic pump motor 31 and 41. This improves the regeneration efficiency of the hydraulic drive device 1.

[0058] Furthermore, in the hydraulic drive device 1 of this embodiment, the working fluid discharged from the head-side port 3a can be regenerated to the rod-side port 3b by the first regeneration valve 24. This reduces the flow rate returning from the boom cylinder 3 to the first hydraulic pump motor 21, allowing the first hydraulic pump motor 21 to be further miniaturized.

[0059] Furthermore, in the hydraulic drive device 1 of this embodiment, the opening degree of the first directional control valve 23 is controlled according to a first operation command corresponding to the amount of operation of the first operation, and the communication valves 14 and 15 are operated according to the amount of operation of the first operation. Therefore, both the opening degree of the first directional control valve 23 and the communication by the communication valves 14 and 15 are controlled according to the amount of operation of the first operation. Consequently, when the opening degree of the first directional control valve 23 is opened according to the amount of operation of the first operation and the return flow rate of the working fluid increases, the hydraulic drive systems 11 to 13 can be connected to distribute and supply the working fluid to the first to third hydraulic pump motors 21, 31, and 41. This prevents the first hydraulic pump motor 21 from being unable to regenerate completely and thus prevents a decrease in regenerative efficiency.

[0060] Furthermore, in the hydraulic drive device 1 of this embodiment, the control device 17 outputs a first regeneration command to the first regeneration valve 24 during regeneration. A portion of the working fluid discharged from the head-side port 3a of the boom cylinder 3 can be regenerated to the rod-side port 3b while the remaining flow rate is regenerated. This reduces the return flow rate of the working fluid returning to the first hydraulic pump motor 21, making it possible to miniaturize the first hydraulic pump motor 21.

[0061] Furthermore, in the hydraulic drive device 1 of this embodiment, the first communication valve 14 is opened when, during regeneration, the operating amount of the first operation is greater than or equal to the first communication threshold and the operating amount of the second operation is less than the first predetermined value. Therefore, when the return flow rate from the boom cylinder 3 is large and the operating amount of the second operation is small, the working fluid returning from the boom cylinder 3 can be distributed to the first and second hydraulic drive systems 11 and 12. This makes it possible to suppress the flow rate of working fluid returned to the first hydraulic pump motor 21 during regeneration. Consequently, the first hydraulic pump motor 21 can be miniaturized. Also, since regeneration is performed by the first and second hydraulic pump motors 21 and 31, more fluid energy can be recovered as electrical energy.

[0062] Furthermore, in the hydraulic drive device 1 of this embodiment, if the operating amount of the first operation is greater than or equal to the second communication threshold and the operating amount of the third operation is less than the second predetermined value during regeneration, the second communication valve 15 is also opened. Therefore, when the return flow rate from the boom cylinder 3 is large and the operating amounts of the second and third operations are small, the working fluid returning from the boom cylinder 3 can be distributed to each of the first to third hydraulic pump motors 21, 31, and 41. This makes it possible to suppress the flow rate of working fluid returned to the first hydraulic pump motor 21 during regeneration. Consequently, the first hydraulic pump motor 21 can be miniaturized. Also, since regeneration is performed by the first to third hydraulic pump motors 21, 31, and 41, more fluid energy can be recovered as electrical energy.

[0063] Furthermore, in the hydraulic drive device 1 of this embodiment, the second regeneration valve 44 is opened when the arm cylinder 5 is extended under load. Therefore, a portion of the working fluid discharged from the rod-side port 5a of the arm cylinder 5 can be regenerated into the head-side port 5b.

[0064] Furthermore, the hydraulic drive device 1 of this embodiment can achieve the aforementioned functions in construction machinery and the like that equipped with a boom, bucket, and arm.

[0065] <Other Embodiments> The hydraulic drive device 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 device 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 device 1 may be two or four or more. In the case of two hydraulic cylinders, the number of communication valves will be one. Also, the number of hydraulic drive systems provided by the hydraulic drive device 1 does not necessarily have to be the same as the number of hydraulic cylinders. Moreover, hydraulic cylinders 3 to 5 are not limited to boom cylinder 3, bucket cylinder 4, and arm cylinder 5, but may be other hydraulic cylinders. Also, the configuration of hydraulic drive systems 11 to 13 is not limited to those described above, and may include other valves such as relief valves, check valves, and electromagnetic proportional valves.

[0066] In the hydraulic drive device 1 of this embodiment, the method for determining the number of hydraulic pump motors 21, 31, and 41 used for regenerative control is not limited to the flow described above. Also, each of the first and third hydraulic drive systems 11 and 13 does not necessarily need to be equipped with regeneration valves 24 and 44. The first hydraulic drive system 11 may supply working fluid to hydraulic cylinders other than the boom cylinder 3. The same applies to the second and third hydraulic drive systems 12 and 13. The amount of operation for each operation is not necessarily limited to the amount of operation for the operating levers 16a and 16b, but may be a value corresponding to the amount of operation for the operating levers 16a and 16b. The first to third hydraulic pump motors 21, 31, and 41 may be fixed-displacement pumps, or they may be oblique-shaft pumps and gear pumps, etc. When the first to third hydraulic pump motors 21, 31, and 41 are fixed-displacement pumps, the control device 17 controls the discharge flow rate and suction flow rate according to the rotational speed of the electric motors 22, 32, and 42.

[0067] <Exemplary Embodiment> The hydraulic drive device in the first phase is a hydraulic drive device that supplies working fluid to a plurality of hydraulic cylinders, including a first hydraulic cylinder, and comprises a plurality of hydraulic drive systems associated with each of the plurality of hydraulic cylinders and supplying working fluid to the corresponding hydraulic cylinder, and at least one communication valve that connects the plurality of hydraulic drive systems to each other in response to an input communication command, and each of the plurality of hydraulic drive systems comprises a hydraulic pump motor that discharges working fluid and rotates when working fluid is supplied, and the hydraulic pump motor rotates to power the hydraulic pump The first hydraulic drive system, which is the hydraulic drive system associated with the first hydraulic cylinder, includes an electric motor that discharges working fluid from a pump motor and generates electricity by being rotationally driven by the hydraulic pump motor, and a directional control valve that switches the direction of flow of working fluid flowing between the hydraulic pump motor and the hydraulic cylinder corresponding to the hydraulic pump motor according to an operation command, and the first hydraulic drive system, which is the hydraulic drive system associated with the first hydraulic cylinder, includes the first directional control valve, which is the directional control valve, and the first directional control valve flows working fluid from the first hydraulic cylinder to the hydraulic pump motor according to a first operation command that is input.

[0068] According to the first phase, there is at least one communication valve that connects multiple hydraulic drive systems to each other in response to an input communication command. Therefore, when a communication command is output to the communication valve as the working fluid is flowed from the first hydraulic cylinder to the hydraulic pump motor by the first directional control valve, the working fluid returned from the first hydraulic cylinder can be distributed to the hydraulic pump motors of multiple hydraulic drive systems. Therefore, the working fluid returned from the first hydraulic cylinder can be regenerated by multiple hydraulic pump motors. Therefore, the capacity of the first hydraulic pump motor can be reduced, and thus the first hydraulic pump motor can be miniaturized.

[0069] In the second phase, the hydraulic drive device is such that, in the hydraulic drive device of the first phase, each of the directional control valves is connected to the hydraulic pump motor via a pump passage in each hydraulic drive system, and can block the connection between the hydraulic pump motor and the corresponding hydraulic cylinder, and the communication valves may be connected to the pump passages of the hydraulic drive systems to be communicated.

[0070] In the above scenario, a communication valve is connected to the pump passage of the hydraulic drive system to be connected. Therefore, by shutting off the directional control valves of the hydraulic drive systems other than the first hydraulic drive system during regeneration, more working fluid can be supplied to each hydraulic pump motor. This improves the regeneration efficiency of the hydraulic drive system.

[0071] The hydraulic drive device in the third phase is a hydraulic drive device in the first or second phase, in which the first hydraulic drive system may include a first regeneration valve connected to the rod-side port and the head-side port of the first hydraulic cylinder, which regenerates the working fluid by connecting the head-side port and the rod-side port in response to a first regeneration command.

[0072] Following the above procedure, the working fluid discharged from the head-side port can be regenerated to the rod-side port by the first regeneration valve. This reduces the flow rate returning from the first hydraulic cylinder to the first hydraulic pump motor, allowing the first hydraulic pump motor to be further miniaturized.

[0073] The hydraulic drive device in the fourth phase further includes a control device in any one of the first to third phases that outputs a first operation command to the first hydraulic drive system according to the amount of operation of the first operation, which is an operation on the first hydraulic cylinder, and the first directional control valve controls its opening degree according to the first operation command during regeneration when working fluid is flowed from the first hydraulic cylinder to the hydraulic pump motor, and the control device may output a communication command according to the amount of operation of the first operation.

[0074] In the above scenario, the opening degree of the first directional control valve is controlled according to the first operation command corresponding to the amount of the first operation, and the connecting valve is operated according to the amount of the first operation. Therefore, both the opening degree of the first directional control valve and the communication by the connecting valve are controlled according to the amount of the first operation. Consequently, when the opening degree of the first directional control valve is increased according to the amount of the first operation and the return flow rate increases, the hydraulic drive system can be connected to distribute the working fluid to each hydraulic pump motor. This prevents a decrease in regenerative efficiency that would occur if a single hydraulic pump motor could not fully regenerate the fluid.

[0075] The hydraulic drive device in the fifth phase is the hydraulic drive device in the fourth phase, wherein the first hydraulic drive system includes a first regeneration valve connected to the head-side port and the rod-side port of the first hydraulic cylinder, which regenerates the working fluid by connecting the head-side port and the rod-side port in response to a first regeneration command, and the control device may output a first regeneration command to the first regeneration valve during regeneration.

[0076] According to the above procedure, the control device outputs a first regeneration command to the first regeneration valve during regeneration. Therefore, a portion of the working fluid discharged from the head-side port of the hydraulic cylinder can be regenerated to the rod-side port while the remaining flow rate is regenerated. This reduces the return flow rate of the working fluid that returns to the hydraulic pump motor of the first hydraulic drive system, thus allowing the hydraulic pump motor to be miniaturized.

[0077] The hydraulic drive device in the sixth phase is a hydraulic drive device in the fourth or fifth phase, wherein the plurality of hydraulic drive systems further include a second hydraulic drive system provided in correspondence with a second hydraulic cylinder which is one of the plurality of hydraulic cylinders, and the at least one communication valve includes a first communication valve which is connected to the first hydraulic drive system and the second hydraulic drive system and operates in response to a first communication command, the second directional control valve which is the directional control valve of the second hydraulic drive system switches the direction of the flow of the hydraulic fluid in response to a second operation command and controls the degree of opening in response to the second operation command, the control device outputs a second operation command corresponding to the amount of operation of the second operation which is an operation on the second hydraulic cylinder, and the first communication valve may be opened when, during regeneration, the amount of operation of the first operation is equal to or greater than a first communication threshold and the amount of operation of the second operation is equal to or less than a first predetermined value.

[0078] According to the above procedure, during regeneration, if the amount of operation for the first operation is greater than or equal to the first communication threshold and the amount of operation for the second operation is less than the first predetermined value, the first communication valve is opened. Therefore, when the return flow rate from the first hydraulic cylinder is large and the amount of operation for the second operation is small, the working fluid returning from the first hydraulic cylinder can be distributed to the respective hydraulic pump motors of the first and second hydraulic drive systems. This makes it possible to reduce the flow rate of working fluid returned to the hydraulic pump motor of the first hydraulic drive system during regeneration. Consequently, the hydraulic pump motor of the first hydraulic drive system can be miniaturized. Furthermore, since regeneration is performed by multiple hydraulic pump motors, more fluid energy can be recovered as electrical energy.

[0079] The hydraulic drive device in the seventh phase is the hydraulic drive device in the sixth phase, wherein the plurality of hydraulic drive systems further include a third hydraulic drive system provided in correspondence with a third hydraulic cylinder which is one of the plurality of hydraulic cylinders, and the at least one communication valve further includes a second communication valve which is connected to the second hydraulic drive system and the third hydraulic drive system and operates in accordance with a second communication command, and the third directional control valve which is the directional control valve of the third hydraulic drive system switches the direction of flow of the hydraulic fluid in accordance with a third operation command and controls the degree of opening in accordance with a third operation command, and the control device outputs a third operation command corresponding to the amount of operation of the third operation which is an operation on the third hydraulic cylinder, and the second communication valve may be opened when, during regeneration, the amount of operation of the first operation is greater than or equal to a second communication threshold which is greater than the first communication threshold and the amount of operation of the third operation is less than or equal to a second predetermined value.

[0080] According to the above procedure, if the operating amount of the first operation is greater than or equal to the second communication threshold and the operating amount of the third operation is less than the second predetermined value during regeneration, the second communication valve is also opened. Therefore, when the return flow rate from the first hydraulic cylinder is large and the operating amounts of the second and third operations are small, the working fluid returning from the first hydraulic cylinder can be distributed to each of the hydraulic pump motors of the first to third hydraulic drive systems. This makes it possible to reduce the flow rate of working fluid returned to the hydraulic pump motor of the first hydraulic drive system during regeneration. Consequently, the hydraulic pump motor of the first hydraulic drive system can be miniaturized. Furthermore, since regeneration is performed by multiple hydraulic pump motors, more fluid energy can be recovered as electrical energy.

[0081] The hydraulic drive device in the eighth phase is a hydraulic drive device in the sixth or seventh phase, wherein the plurality of hydraulic drive systems further include a third hydraulic drive system provided in correspondence with a third hydraulic cylinder which is one of the plurality of hydraulic cylinders, and the third hydraulic drive system includes a second regeneration valve connected to the head-side port and the rod-side port of the third hydraulic cylinder, which regenerates the working fluid by communicating the head-side port and the rod-side port in response to a second regeneration command, and the control device may open the second regeneration valve when the third hydraulic cylinder is subjected to a load and extends.

[0082] According to the above procedure, when the third hydraulic cylinder is subjected to a load and contracts, the second regeneration valve opens. Therefore, a portion of the working fluid discharged from the rod-side port of the third hydraulic cylinder can be regenerated into the head-side port.

[0083] In the ninth phase, the hydraulic drive device may be a hydraulic drive device in the seventh or eighth phase in which the first hydraulic drive system supplies working fluid to the boom cylinder, which is the first hydraulic cylinder; the second hydraulic drive system supplies working fluid to the bucket cylinder, which is the second hydraulic cylinder; and the third hydraulic drive system supplies working fluid to the arm cylinder, which is the third hydraulic cylinder.

[0084] Following the above steps, the aforementioned functions can be achieved in construction machinery equipped with a boom, bucket, and arm. [Explanation of symbols]

[0085] 1. Hydraulic drive device 3. Boom Cylinder (First Hydraulic Cylinder) 3a Head-side port 3b Rod-side port 4. Bucket cylinder (second hydraulic cylinder) 5. Arm Cylinder (Third Hydraulic Cylinder) 5a Rod-side port 5b Head-side port 11. First hydraulic drive system 12. Second hydraulic drive system 13. Third hydraulic drive system 14. First connecting valve 15. Second connecting valve 17 Control device 18 tanks 21. First hydraulic pump motor 22 1st electric motor 23. First Directional Control Valve 24. First regeneration valve 25 Pump passage 31. Second hydraulic pump motor 32 2nd electric motor 33. Second Directional Control Valve 35 Pump passage 41. Third hydraulic pump motor 42 3rd motor 43. Third Directional Control Valve 44. Second regeneration valve 45 Pump passage

Claims

1. A hydraulic drive device that supplies working fluid to a plurality of hydraulic cylinders, including a first hydraulic cylinder, A plurality of hydraulic drive systems, each associated with one of the plurality of hydraulic cylinders, which supply working fluid to the corresponding hydraulic cylinder, It comprises at least one communication valve that connects the plurality of hydraulic drive systems to each other in response to an input communication command, Each of the plurality of hydraulic drive systems includes a hydraulic pump motor that discharges working fluid and rotates when working fluid is supplied, an electric motor that rotates to drive the hydraulic pump motor, thereby discharging working fluid from the hydraulic pump motor and generating electricity when rotated by the hydraulic pump motor, and a directional control valve that switches the direction of flow of the working fluid between the hydraulic pump motor and the corresponding hydraulic cylinder according to an operation command. The first hydraulic drive system, which is the hydraulic drive system associated with the first hydraulic cylinder, includes the first directional control valve, which is the directional control valve. The first directional control valve, in response to a first operational command input, flows the working fluid from the first hydraulic cylinder to the hydraulic pump motor of the corresponding hydraulic drive system, thereby regenerating electrical energy to the motor. The aforementioned communication valve is a hydraulic drive device that distributes a portion of the working fluid from the first hydraulic cylinder to the hydraulic pump motor of another hydraulic drive system communicating with the corresponding hydraulic drive system, thereby regenerating electrical energy to the electric motor which is rotationally driven by the hydraulic pump motor.

2. Each of the directional control valves is connected to the hydraulic pump motor in each hydraulic drive system via a pump passage, and can isolate the hydraulic pump motor from the corresponding hydraulic cylinder. The hydraulic drive device according to claim 1, wherein the communication valve is connected to the pump passage of the hydraulic drive system to be communicated with.

3. The hydraulic drive device according to claim 1, wherein the first hydraulic drive system is connected to the rod-side port and the head-side port of the first hydraulic cylinder and includes a first regeneration valve that regenerates the working fluid by connecting the head-side port and the rod-side port in response to a first regeneration command.

4. The system further includes a control device that outputs a first operation command to the first hydraulic drive system corresponding to the amount of operation of the first operation, which is an operation on the first hydraulic cylinder. The first directional control valve controls its opening degree in accordance with the first operation command during regeneration, when the working fluid is flowed from the first hydraulic cylinder to the hydraulic pump motor. The hydraulic drive device according to claim 1, wherein the control device outputs a communication command according to the amount of operation of the first operation.

5. The first hydraulic drive system includes a first regeneration valve connected to the head-side port and the rod-side port of the first hydraulic cylinder, which regenerates the working fluid by connecting the head-side port and the rod-side port in response to a first regeneration command. The hydraulic drive device according to claim 4, wherein the control device outputs a first regeneration command to the first regeneration valve during regeneration.

6. The plurality of hydraulic drive systems further include a second hydraulic drive system provided in correspondence with a second hydraulic cylinder, which is one of the plurality of hydraulic cylinders. The at least one communication valve includes a first communication valve that is connected to the first hydraulic drive system and the second hydraulic drive system and operates in response to a first communication command. The second directional control valve of the second hydraulic drive system switches the direction of the flow of the working fluid in accordance with the second operation command and controls the opening degree in accordance with the second operation command. The hydraulic drive device according to claim 4, wherein the control device outputs a second operation command corresponding to the amount of operation of the second operation, which is an operation on the second hydraulic cylinder, and when the amount of operation of the first operation is greater than or equal to a first communication threshold and the amount of operation of the second operation is less than or equal to a first predetermined value, the first communication valve is opened.

7. The plurality of hydraulic drive systems further include a third hydraulic drive system provided in correspondence with a third hydraulic cylinder, which is one of the plurality of hydraulic cylinders. The at least one communication valve further includes a second communication valve connected to the second hydraulic drive system and the third hydraulic drive system, and which operates in response to a second communication command. The third directional control valve of the third hydraulic drive system switches the direction of the flow of the working fluid in accordance with the third operation command and controls the opening degree in accordance with the third operation command. The hydraulic drive device according to claim 6, wherein the control device outputs a third operation command corresponding to the amount of operation of the third operation, which is an operation on the third hydraulic cylinder, and when the amount of operation of the first operation is greater than or equal to a second communication threshold which is greater than the first communication threshold and the amount of operation of the third operation is less than or equal to a second predetermined value, the second communication valve is opened.

8. The plurality of hydraulic drive systems further include a third hydraulic drive system provided in correspondence with a third hydraulic cylinder, which is one of the plurality of hydraulic cylinders. The third hydraulic drive system includes a second regeneration valve connected to the head-side port and the rod-side port of the third hydraulic cylinder, which regenerates the working fluid by connecting the head-side port and the rod-side port in response to a second regeneration command. The hydraulic drive device according to claim 6, wherein the control device opens the second regeneration valve when the third hydraulic cylinder is subjected to a load and extends.

9. The first hydraulic drive system supplies working fluid to the boom cylinder, which is the first hydraulic cylinder. The second hydraulic drive system supplies working fluid to the bucket cylinder, which is the second hydraulic cylinder. The hydraulic drive device according to claim 7 or 8, wherein the third hydraulic drive system supplies working fluid to the arm cylinder, which is the third hydraulic cylinder.

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