Hydraulic drive system

Abstract

The hydraulic drive system includes a first circuit system, a first hydraulic pump, a second circuit system, a second hydraulic pump, a confluence valve for opening and closing the confluence path connecting the first and second hydraulic pumps, an operating device for outputting operating commands corresponding to the operating quantities indicating the working quantities of the first and second hydraulic actuators, and a control device for controlling the action of the confluence valve according to the operating commands from the operating device. The first circuit system has a first inlet control valve for controlling the inlet flow rate of the working fluid flowing to the first hydraulic actuator and a first outlet control valve for controlling the outlet flow rate of the working fluid discharged from the first hydraulic actuator to the storage tank. The control device controls the opening degree of the first inlet control valve and the first outlet control valve respectively.

Description

Technical Field

[0001] This invention relates to a hydraulic drive system for driving hydraulic actuators. Background Technology

[0002] As a hydraulic drive system, a hydraulic control device, such as that described in Patent Document 1, is known. This hydraulic control device has two circuit systems. Each circuit system is connected to a separate hydraulic pump. Furthermore, the two hydraulic pumps are interconnected via a confluence valve. Thus, the working fluid discharged from the two hydraulic pumps can be combined through the confluence valve and flow into either of the two circuit systems or either one.

[0003] Existing technical documents:

[0004] Patent documents:

[0005] Patent document 1: Japanese Patent Application Publication No. 6-123302. Summary of the Invention

[0006] The problem the invention aims to solve:

[0007] In the hydraulic control device of Patent Document 1, each hydraulic actuator is equipped with a pressure compensation valve. This prevents flow bias towards the actuator with the lower load when multiple hydraulic actuators operate simultaneously. However, pressure loss occurs due to the pressure compensation valves. Consequently, energy consumption of the hydraulic control device, i.e., the hydraulic drive system, cannot be suppressed.

[0008] Therefore, the purpose of this invention is to provide a hydraulic drive system that can suppress energy consumption.

[0009] Solution methods:

[0010] The hydraulic drive system of the present invention comprises: a first circuit system for controlling the supply and discharge of working fluid to a first hydraulic actuator; a first hydraulic pump for supplying working fluid to the first circuit system; a second circuit system for controlling the supply and discharge of working fluid to a second hydraulic actuator; a second hydraulic pump for supplying working fluid to the second circuit system; a confluence valve for opening and closing a confluence path connecting the first hydraulic pump and the second hydraulic pump; an operating device for outputting an operating command corresponding to an operating amount indicating the working quantity of the first hydraulic actuator and the second hydraulic actuator; and a control device for controlling the operation of the confluence valve according to the operating command from the operating device; the first circuit system comprises: a first inlet control valve for controlling the inlet flow rate of working fluid flowing to the first hydraulic actuator; and a first outlet control valve for controlling the outlet flow rate of working fluid discharged from the first hydraulic actuator to a storage tank; the control device controls the opening degree of the first inlet control valve and the first outlet control valve respectively.

[0011] According to the present invention, when the first hydraulic actuator and the second hydraulic actuator operate simultaneously, and the load on the first hydraulic actuator is smaller than that on the second hydraulic actuator, the control device can ensure the flow rate of the first hydraulic actuator by controlling the opening of the first inlet control valve. Therefore, the pressure compensation valve designed for the first hydraulic actuator can be eliminated, thus suppressing energy consumption when the first and second hydraulic actuators operate simultaneously.

[0012] Invention effects:

[0013] According to the present invention, energy consumption can be suppressed.

[0014] The above-mentioned objects, other objects, features and advantages of the present invention will become clear from the following detailed description of preferred embodiments, based on the accompanying drawings. Attached Figure Description

[0015] Figure 1 This is a hydraulic circuit diagram illustrating the hydraulic drive system according to the first embodiment of the present invention;

[0016] Figure 2 yes Figure 1 A block diagram of the control device for controlling the opening degree of the merging valve in the hydraulic drive system;

[0017] Figure 3 yes Figure 1 A block diagram of the control valve opening control in the control device of the hydraulic drive system;

[0018] Figure 4 This is a block diagram of the control device for the hydraulic drive system of the second embodiment of the present invention regarding the control of the opening degree of the confluence valve. Detailed Implementation

[0019] Hereinafter, the hydraulic drive systems 1 and 1A of the first and second embodiments of the present invention will be described with reference to the accompanying drawings in the foregoing specification. Furthermore, the directional concepts used in the following description are for ease of explanation only and are not intended to limit the structural orientation of the invention to these directions. Also, the hydraulic drive systems 1 and 1A described below are only one embodiment of the present invention. Therefore, the present invention is not limited to any particular embodiment, and additions, deletions, and modifications can be made without departing from the spirit of the invention.

[0020] [First Implementation Method]

[0021] <Hydraulic Driven Machinery>

[0022] Hydraulically driven machinery, such as construction machinery, industrial machinery, and industrial vehicles, includes multiple hydraulic actuators 2-5 and a hydraulic drive system 1. Furthermore, the hydraulically driven machinery causes various structural movements by operating the hydraulic actuators 2-5. The hydraulic actuators 2-5 are, for example, hydraulic cylinders and hydraulic motors. In this embodiment, the hydraulically driven machinery is, for example, a hydraulic excavator. Moreover, the multiple hydraulic actuators 2-5 are, for example, a boom cylinder 2, a boom cylinder 3, a bucket cylinder 4, and a swing motor 5.

[0023] Hydraulic cylinders 2-4 can respectively actuate the stick, boom, and bucket (none shown) which are of various structures by extending and retracting. More specifically, hydraulic cylinders 2-4 are, for example, the stick cylinder 2 (a first hydraulic actuator), the boom cylinder 3 (a second hydraulic actuator), and the bucket cylinder 4. Furthermore, in hydraulic cylinders 2-4, rods 2b-4b are retractably inserted into the cylinder tubes 2a-4a. Rod-side ports 2c-4c and head-side ports 2d-4d are formed on the cylinder tubes 2a-4a, respectively. Moreover, by supplying or discharging working fluid to each port 2c-4c and 2d-4d, the rods 2b-4b move forward and backward relative to the cylinder tubes 2a-4a, that is, hydraulic cylinders 2-4 extend and retract.

[0024] The rotary motor 5 can rotate a rotating body (not shown) to return to its original position. More specifically, the rotary motor 5 is a hydraulic motor. That is, the rotary motor 5 has two suction and discharge ports 5c and 5d. Furthermore, if working fluid is supplied to one suction / discharge port 5c, the rotary motor 5 rotates the rotating body in a predetermined direction of rotation. Conversely, if working fluid is supplied to the other suction / discharge port 5d, the rotary motor 5 rotates the rotating body in the other predetermined direction of rotation.

[0025] <Hydraulic Drive System>

[0026] The hydraulic drive system 1 operates the hydraulic actuators 2-5 by supplying or discharging working fluid to them. More specifically, the hydraulic drive system 1 is connected in parallel with the hydraulic actuators 2-5. That is, the hydraulic drive system 1 is connected separately to each of the ports 2c-5c and 2d-5d of the hydraulic actuators 2-5. Furthermore, the hydraulic drive system 1 can draw in or discharge working fluid relative to each of the ports 2c-5c and 2d-5d of the hydraulic actuators 2-5. This enables the hydraulic actuators 2-5 to operate.

[0027] The hydraulic drive system 1 includes a first hydraulic pump 11, a first circuit system 12, a second hydraulic pump 13, a second circuit system 14, a confluence valve 15, multiple pressure sensors 17, 18, 19R to 21R, 19H to 21H, 22L, 22R, an operating device 23, and a control device 24.

[0028] The first hydraulic pump 11 is connected to a drive source. The drive source is an engine E or an electric motor. In this embodiment, the drive source is an engine E. The first hydraulic pump 11 is driven to rotate by the drive source to discharge working fluid. The discharged working fluid is primarily supplied to the first circuit system 12. The first hydraulic pump 11 can vary its discharge capacity. In this embodiment, the first hydraulic pump 11 is a swashplate pump or a swashplate pump.

[0029] The first circuit system 12 is connected to the first hydraulic pump 11. Furthermore, the first circuit system 12 is connected in parallel with the boom cylinder 2 and the gyratory motor 5, respectively. Moreover, the first circuit system 12 controls the supply and discharge of working fluid to the boom cylinder 2 and the gyratory motor 5. More specifically, the first circuit system 12 includes a boom inlet control valve 31, a boom outlet control valve 32, a gyratory inlet control valve 33, and a gyratory outlet control valve 34.

[0030] As an example of a first inlet control valve, the boom inlet control valve 31 is connected to the first hydraulic pump 11 and the boom cylinder 2. Furthermore, the boom inlet control valve 31 controls the flow rate of the working fluid from the first hydraulic pump 11 to the boom cylinder 2. More specifically, the boom inlet control valve 31 is connected to the first hydraulic pump 11 via the first pump passage 11a. Moreover, the boom inlet control valve 31 is connected to the rod-side port 2c of the boom cylinder 2 via the rod-side passage 2e, and also to the head-side port 2d of the boom cylinder 2 via the head-side passage 2f. Furthermore, the boom inlet control valve 31 can control the direction and flow rate of the working fluid supplied from the first hydraulic pump 11 to the boom cylinder 2 according to the input boom inlet command. That is, the boom inlet control valve 31 can supply the working fluid from the first hydraulic pump 11 to either port 2c or 2d of the boom cylinder 2, and control the flow rate. In this embodiment, the boom inlet control valve 31 is an electronically controlled spool valve that drives the valve core via an electromagnetic proportional control valve and an electric actuator. That is, the boom inlet control valve 31 moves the valve core 31a based on a boom inlet command, thereby switching the flow direction of the working fluid, and also controls the opening degree of the boom inlet control valve 31.

[0031] As an example of a first discharge control valve, the boom discharge control valve 32 is connected to the boom cylinder 2 and the storage tank 10. Furthermore, the boom discharge control valve 32 controls the discharge flow rate of the working fluid from the boom cylinder 2 to the storage tank 10. More specifically, the boom discharge control valve 32 and the boom inlet control valve 31 are arranged in pairs. Moreover, the boom discharge control valve 32 is connected to the boom-side passage 2e and the head-side passage 2f, respectively, in parallel with the corresponding boom inlet control valve 31. Furthermore, the boom discharge control valve 32 can control the direction and flow rate of the working fluid discharged from the boom cylinder 2 to the storage tank 10 according to the input boom discharge command. That is, the boom discharge control valve 32 connects ports 2d and 2c, different from those connected to the boom inlet control valve 31, to the storage tank 10 and controls the discharge flow rate. Furthermore, the discharge control valve 32 for the boom can independently control the discharge flow rate passing through it, separate from the inlet flow rate supplied to the boom cylinder 2 via the inlet control valve 31 for the boom. More specifically, the discharge control valve 32 and the inlet control valve 31 for the boom are configured such that their respective valve cores operate independently. Therefore, the discharge control valve 32 and the inlet control valve 31 can be controlled separately. In this embodiment, the discharge control valve 32 for the boom is an electronically controlled spool valve. That is, the discharge control valve 32 for the boom moves its valve core 32a based on the boom discharge command. Moreover, by moving the valve core 32a, the discharge control valve 32 for the boom can switch the flow direction of the working fluid and also control the opening degree of the discharge control valve 32.

[0032] The rotary inlet control valve 33 is connected to the first hydraulic pump 11 in parallel with the boom inlet control valve 31, and is also connected to the rotary motor 5. Furthermore, the rotary inlet control valve 33 controls the flow rate of the working fluid from the first hydraulic pump 11 to the rotary motor 5. More specifically, the rotary inlet control valve 33 is connected to the first pump passage 11a in parallel with the boom inlet control valve 31. The rotary inlet control valve 33 is connected to the first suction / discharge port 5c of the rotary motor 5 via the first rotary passage 5e, and also to the second suction / discharge port 5d of the rotary motor 5 via the second rotary passage 5f. Moreover, the rotary inlet control valve 33 can control the direction and flow rate of the working fluid supplied from the first hydraulic pump 11 to the rotary motor 5 according to the input rotary inlet command. In this embodiment, the rotary inlet control valve 33 is an electronically controlled spool valve. That is, the rotary inlet control valve 33 moves the valve core 33a based on the inlet command of the boom, thereby switching the flow direction of the working fluid, and also controls the opening degree of the rotary inlet control valve 33.

[0033] The rotary discharge control valve 34 is connected to the rotary motor 5 and the storage tank 10. Furthermore, the rotary discharge control valve 34 controls the discharge flow rate of the working fluid from the rotary motor 5 to the storage tank 10. More specifically, the rotary discharge control valve 34 and the rotary inlet control valve 33 are arranged in pairs. Moreover, the rotary discharge control valve 34 is connected to the first rotary passage 5e and the second rotary passage 5f, respectively, in parallel with the corresponding rotary inlet control valve 33. Furthermore, the rotary discharge control valve 34 can control the direction and flow rate (discharge flow rate) of the working fluid discharged from the rotary motor 5 to the storage tank 10 according to the input rotary discharge command. Additionally, the rotary discharge control valve 34 can independently control the discharge flow rate flowing through it, in addition to the inlet flow rate supplied to the rotary motor 5 via the rotary inlet control valve 33. In more detail, the gyratory discharge control valve 34 and the gyratory inlet control valve 33 are configured such that their respective valve cores operate independently. Therefore, the gyratory discharge control valve 34 and the gyratory inlet control valve 33 can be controlled separately. In this embodiment, the gyratory discharge control valve 34 is an electronically controlled spool valve. That is, the gyratory discharge control valve 34 moves its valve core 34a based on a gyratory discharge command to switch the flow direction of the working fluid, and can also control the opening degree of the gyratory discharge control valve 34.

[0034] The second hydraulic pump 13 is connected to the drive source in the same way as the first hydraulic pump 11. That is, the second hydraulic pump 13 is driven to rotate by the drive source to discharge working fluid. Moreover, the discharged working fluid is mainly supplied to the second circuit system 14. The discharge capacity of the second hydraulic pump 13 can also be changed. In this embodiment, the second hydraulic pump 13 is a swashplate pump or a swashplate pump. Furthermore, the drive source of the second hydraulic pump 13 can be the same as or separate from the drive source of the first hydraulic pump 11.

[0035] The second circuit system 14 is connected to the second hydraulic pump 13. Furthermore, the second circuit system 14 is connected in parallel with both the boom cylinder 3 and the bucket cylinder 4. Moreover, the second circuit system 14 controls the supply and discharge of working fluid to the boom cylinder 3 and the bucket cylinder 4. More specifically, the second circuit system 14 includes a boom inlet control valve 35, a boom outlet control valve 36, a bucket inlet control valve 37, and a bucket outlet control valve 38.

[0036] As an example of a second inlet control valve, the boom inlet control valve 35 is connected to the second hydraulic pump 13 and the boom cylinder 3. Furthermore, the boom inlet control valve 35 controls the flow rate of the working fluid from the second hydraulic pump 13 to the boom cylinder 3. More specifically, the boom inlet control valve 35 is connected to the second hydraulic pump 13 via the second pump passage 13a. Moreover, the boom inlet control valve 35 is connected to the rod-side port 3c of the boom cylinder 3 via the rod-side passage 3e, and also to the head-side port 3d of the boom cylinder 3 via the head-side passage 3f. Furthermore, the boom inlet control valve 35 can control the direction and flow rate of the working fluid supplied from the second hydraulic pump 13 to the boom cylinder 3 according to the input boom inlet command. That is, the boom inlet control valve 35 can supply working fluid from the second hydraulic pump 13 to either port 3c or 3d of the boom cylinder 3, and control the flow rate. In this embodiment, the boom fluid inlet control valve 35 is an electronically controlled spool valve. That is, the boom fluid inlet control valve 35 moves the valve core 35a based on the boom fluid inlet command, thereby switching the flow direction of the working fluid, and also controls the opening degree of the boom fluid inlet control valve 35.

[0037] As an example of a second discharge control valve, the boom discharge control valve 36 is connected to the boom cylinder 3 and the storage tank 10. Furthermore, the boom discharge control valve 36 controls the discharge flow rate of the working fluid from the boom cylinder 3 to the storage tank 10. More specifically, the boom discharge control valve 36 and the boom inlet control valve 35 are arranged in pairs. Moreover, the boom discharge control valve 36 is connected to the rod-side passage 3e and the head-side passage 3f, respectively, in parallel with the corresponding boom inlet control valve 35. Furthermore, the boom discharge control valve 36 can control the direction and flow rate of the working fluid discharged from the boom cylinder 3 to the storage tank 10 according to the input boom discharge command. That is, the boom discharge control valve 36 connects ports 3d and 3c, different from those connected to the boom inlet control valve 35, to the storage tank 10 and controls the discharge flow rate. Furthermore, the boom discharge control valve 36 can independently control the discharge flow rate passing through it, separate from the inlet flow rate supplied to the boom cylinder 3 via the boom inlet control valve 35. More specifically, the boom discharge control valve 36 and the boom inlet control valve 35 are configured such that their respective valve cores operate independently. Therefore, the boom discharge control valve 36 and the boom inlet control valve 35 can be controlled separately. In this embodiment, the boom discharge control valve 36 is an electronically controlled spool valve. That is, the boom discharge control valve 36 moves its valve core 36a based on a boom discharge command to switch the flow direction of the working fluid, and can also control the opening degree of the boom discharge control valve 36.

[0038] The bucket inlet control valve 37 is connected to the second hydraulic pump 13 in parallel with the boom inlet control valve 35, and is also connected to the bucket cylinder 4. Furthermore, the bucket inlet control valve 37 controls the flow rate of the working fluid from the second hydraulic pump 13 to the bucket cylinder 4. More specifically, the bucket inlet control valve 37 is connected to the second pump passage 13a in parallel with the boom inlet control valve 35. The bucket inlet control valve 37 is connected to the rod-side port 4c of the bucket cylinder 4 via the rod-side passage 4e, and also to the head-side port 4d of the bucket cylinder 4 via the head-side passage 4f. Moreover, the bucket inlet control valve 37 can control the direction and flow rate of the working fluid supplied from the second hydraulic pump 13 to the bucket cylinder 4 according to the input bucket inlet command. In this embodiment, the bucket inlet control valve 37 is an electronically controlled spool valve. That is, the bucket inlet control valve 37 moves the valve core 37a based on the bucket inlet command, thereby switching the flow direction of the working fluid, and also controls the opening degree of the bucket inlet control valve 37.

[0039] The bucket discharge control valve 38 is connected to the bucket cylinder 4 and the storage tank 10. Furthermore, the bucket discharge control valve 38 controls the discharge flow rate of the working fluid from the bucket cylinder 4 to the storage tank 10. More specifically, the bucket discharge control valve 38 and the bucket inlet control valve 37 are arranged in pairs. Moreover, the bucket discharge control valve 38 is connected to the boom-side passage 4e and the head-side passage 4f, respectively, in parallel with the corresponding bucket inlet control valve 37. Furthermore, the bucket discharge control valve 38 can control the direction and flow rate of the working fluid discharged from the bucket cylinder 4 to the storage tank 10 according to the input bucket discharge command. Additionally, the bucket discharge control valve 38 can independently control the discharge flow rate passing through it, in addition to the inlet flow rate supplied to the bucket cylinder 4 via the bucket inlet control valve 37. In more detail, the bucket discharge control valve 38 and the bucket inlet control valve 37 are configured such that their respective valve cores operate independently. Therefore, the bucket discharge control valve 38 and the bucket inlet control valve 37 can be controlled separately. In this embodiment, the bucket discharge control valve 38 is an electronically controlled spool valve. That is, the bucket discharge control valve 38 moves its valve core 38a based on the bucket discharge command, thereby switching the flow direction of the working fluid, and can also control the opening degree of the bucket discharge control valve 38.

[0040] The confluence valve 15 opens and closes the flow path 15a. The confluence path 15a connects the first hydraulic pump 11 and the second hydraulic pump 13. More specifically, the confluence path 15a is connected to the first and second pump passages 11a and 13a. In this embodiment, the confluence path 15a is connected in the first pump passage 11a to the portion of the hydraulic actuators 2 and 5 closer to the upstream side, and in the second pump passage 13a to the portion of the hydraulic actuators 3 and 4 closer to the upstream side. Moreover, the confluence path 15a allows the working fluid discharged from the first hydraulic pump 11 to flow into the second pump passage 13a, and also allows the working fluid discharged from the second hydraulic pump 13 to flow into the first pump passage 11a. The confluence valve 15 is disposed in the confluence path 15a. Moreover, the confluence valve 15 opens and closes the flow path 15a based on the input confluence command. Furthermore, the opening degree of the confluence valve 15 can be controlled based on the input confluence command. In this embodiment, the confluence valve 15 is an electromagnetic proportional control valve.

[0041] Multiple pressure sensors 17, 18, 19R-21R, 19H-21H, 22L, and 22R detect the pressure of the working fluid flowing through various points. Furthermore, these pressure sensors 17, 18, 19R-21R, 19H-21H, 22L, and 22R output the detected pressure to the control device 24. More specifically, the first discharge pressure sensor 17 and the second discharge pressure sensor 18 are connected to the first pump passage 11a and the second pump passage 13a, respectively. They also detect the discharge pressure of the first hydraulic pump 11 and the second hydraulic pump 13, respectively. Additionally, the lever-side pressure sensors 19R-21R are connected to lever-side passages 2e-4e, respectively. These sensors detect the pressure (lever pressure) at the lever-side ports 2c-4c of the boom cylinder 2, boom cylinder 3, and bucket cylinder 4. Furthermore, head-side pressure sensors 19H to 21H are connected to head-side passages 2f to 4f, respectively. These sensors detect the pressure (head pressure) at the head-side ports 2d to 4d of the boom cylinder 2, boom cylinder 3, and bucket cylinder 4. The first rotation pressure sensor 22L and the second rotation pressure sensor 22R are connected to the first rotation passage 5e and the second rotation passage 5f, respectively. These sensors also detect the pressure (port pressure) at the two suction and discharge ports 5c and 5d.

[0042] The operating device 23 outputs an operating command to the control device 24 corresponding to the operating amount indicating the workload of the hydraulic actuators 2-5. In this embodiment, the operating device 23 may be, for example, an operating valve or an electric joystick. Furthermore, the operating device 23 has two levers 23a and 23b. The levers 23a and 23b are configured to be operable by an operator. The levers 23a and 23b are operating tools used to indicate the workload of the hydraulic actuators 2-5 according to their operating amount. That is, the operating device 23 outputs an operating command to the control device 24 corresponding to the operating amount of the levers 23a and 23b. In this embodiment, each of the two levers 23a and 23b is configured to swing in all 360 degrees, including two intersecting directions (e.g., the front-back direction and the left-right direction). Furthermore, the operating device 23 outputs an operating command to the control device 24 corresponding to the operating direction and operating amount of the levers 23a and 23b. In this embodiment, when the first operating lever 23a is operated in the first direction from a top-down view, it outputs a stick operation command corresponding to the operation amount. When operated in the second direction from a top-down view, it outputs a rotation operation command corresponding to the operation amount. Furthermore, when the operating lever 23a is operated in an oblique direction from a top-down view (e.g., a direction at an angle α to the first direction from a top-down view), it outputs both a stick operation command and a rotation operation command. Moreover, it outputs a stick operation command corresponding to the first directional component (i.e., the operation amount in the first direction) of the operation amount of the operating lever 23a, and also outputs a rotation operation command corresponding to the second directional component. Similarly, when the second operating lever 23b is operated in a third direction, it outputs a boom operation command corresponding to the operation amount, and when operated in a fourth direction, it outputs a bucket operation command corresponding to the operation amount. Furthermore, when the operating lever 23b is operated in an oblique direction from a top-down view (e.g., a direction at an angle β to the third direction from a top-down view), it outputs both a boom operation command and a bucket operation command. Furthermore, the system outputs boom operation commands corresponding to the third-direction component (i.e., the third-direction operation) of the operating amount of the control lever 23b, and also outputs bucket operation commands corresponding to the fourth-direction component. The stick operation command is the operation command that activates the stick cylinder 2. The swivel operation command is the operation command that activates the swivel motor 5. The boom operation command is the operation command that activates the boom cylinder 3. The bucket operation command is the operation command that activates the bucket cylinder 4.

[0043] The control device 24 is connected to each hydraulic pump 11, 13, each control valve 31-38, the confluence valve 15, each pressure sensor 17, 18, 19R-21R, 19H-21H, 22L, 22R, and the operating device 23. Furthermore, the control device 24 controls the output flow rate of each hydraulic pump 11, 13. In this embodiment, the control device 24 controls the output flow rate of the hydraulic pumps 11, 13 based on the pressure detected by the output pressure sensors 17, 18. However, the control method for the output flow rate of the hydraulic pumps 11, 13 is not limited to power control; it can also be load-sensing control. Moreover, the control device 24 controls the opening degree of the confluence valve 15 and each control valve 31-38 based on the operating commands from the operating device 23 and the pressure detected by the pressure sensors 17, 18, 19R-21R, 19H-21H, 22L, 22R. In more detail, the control device 24 controls the operation of the confluence valve 15 according to the operation commands from the operating device 23 and the load of the hydraulic actuators 2-5. That is, the control device 24 opens and closes the flow path 15a of the confluence valve 15 according to the operation commands from the operating device 23 and the load of the hydraulic actuators 2-5. As a result, the working fluid discharged from one of the first hydraulic pump 11 and the second hydraulic pump 13 can be combined with the working fluid discharged from the other. In addition, the control device 24 controls the opening degree of the confluence valve 15 according to the operation commands from the operating device 23 and the load of the hydraulic actuators 2-5. By controlling the opening degree of the confluence valve 15, the control device 24 can combine the working fluid flow rates corresponding to the operation amounts of the operating levers 23a and 23b. Furthermore, the control device 24 controls the inlet flow rate of the working fluid supplied to each of the hydraulic actuators 2-5 by controlling the opening degree of the inlet control valves 31, 33, 35, and 37. Furthermore, the control device 24 controls the flow rate of the working fluid discharged from the hydraulic actuators 2 to 5 by controlling the opening degree of the discharge control valves 32, 34, 36, and 38.

[0044] In more detail, the control device 24 has the following functions to control the operation of the confluence valve 15. That is, the control device 24, as... Figure 2 The device shown includes a merging determination unit 41, a merging valve opening calculation unit 42, a merging switching unit 43, and a multiplier 44. Furthermore, the control device 24 has the following structure to adjust the inlet flow rate and the outlet flow rate. That is, the control device 24 is as follows: Figure 3 The device shown includes an inlet control valve opening calculation unit (M / I control valve opening calculation unit) 45, an M / I control valve opening calculation unit 46 with pressure compensation, and an outlet control valve opening calculation unit (M / O control valve opening calculation unit) 47.

[0045] Figure 2The shown merging determination unit 41 determines whether the working fluid discharged from one of the first hydraulic pump 11 and the second hydraulic pump 13 merges with the working fluid discharged from the other (i.e., whether merging occurs). More specifically, the control device 24 determines whether the merging condition is met based on the various operating commands from the operating device 23 and the load of the hydraulic actuators 2-5. In this embodiment, multiple merging conditions corresponding to the operating states of the hydraulic actuators 2-5 are set in the control device 24. For example, a first merging condition and a second merging condition are set in the control device 24. The first merging condition (simultaneous operation of the stick and boom) refers to a condition where the operating amount of the first operating lever 23a in the first direction and the operating amount of the second operating lever 23b in the third direction are respectively a first and a second predetermined amount or more, and the load of the stick cylinder 2 is a predetermined value or more. Here, the load of the stick cylinder 2 refers to the value obtained by multiplying the inflow pressure area of ​​the stick cylinder 2 by the inflow pressure and subtracting the value obtained by multiplying the outflow pressure area of ​​the stick cylinder 2 by the outflow pressure. Furthermore, the second confluence condition (single boom operation) refers to a condition where the operation amount of the first operating lever 23a in the first direction is at least a third predetermined amount and the load on the boom cylinder 2 is at least a predetermined value. That is, the control device 24 determines the confluence when the boom cylinder 2 and the boom cylinder 3 operate simultaneously based on the first confluence condition, and also determines the confluence when the boom cylinder 2 operates alone based on the second confluence condition. Additionally, the control device 24 is equipped with multiple confluence conditions that can be determined based on the various operating commands from the operating device 23 and the loads of the hydraulic actuators 2-5. Moreover, the control device 24 determines whether multiple confluence conditions, including the first and second confluence conditions, are satisfied. Furthermore, the confluence conditions are not limited to the aforementioned and can be set based on the individual operation and combined operation of each operating lever 23a, 23b. Furthermore, while the control device 24 determines whether multiple confluence conditions exist based on the operation amount of each operating lever 23a, 23b, the pilot pressure applied to the valve cores 31a-38a of each control valve 31-38 can also be used as the operation amount.

[0046] The merging valve opening calculation unit 42 calculates the opening of the merging valve 15. More specifically, the merging valve opening calculation unit 42 is equipped with multiple merging opening maps or multiple calculation formulas corresponding to each of the aforementioned multiple merging conditions. Furthermore, in the merging opening map or calculation formula, the operating quantity corresponds to the opening of the merging valve 15. The merging valve opening calculation unit 42 calculates the opening of the merging valve 15 based on the operating quantity and the merging opening map or calculation formula. The merging valve opening calculation unit 42 calculates the opening of the merging valve 15 relative to all satisfied merging conditions. Moreover, the merging valve opening calculation unit 42 selects the largest opening among the calculated multiple openings as the merging opening of the merging valve 15.

[0047] The merging switching unit 43 switches the output of the merging command based on the determination result of the merging determination unit 41. More specifically, the merging switching unit 43 outputs a switching coefficient based on the determination result of the merging determination unit 41. In this embodiment, the control device 24 switches the merging status based on whether multiple merging conditions are met. That is, when the merging is set to a non-merging state, the merging switching unit 43 outputs a value of 0. On the other hand, when the merging is set to a merging-allowed state by a switching command, the merging switching unit 43 outputs a value of 1.

[0048] The multiplier 44 generates a merging command by multiplying the merging opening selected in the merging valve opening calculation unit 42 by a switching coefficient output from the merging switching unit 43. Furthermore, the multiplier 44 outputs the generated merging command to the merging valve 15. Thus, in a merging-possible state, the opening of the merging valve 15 is controlled based on the result of the merging determination unit 41. On the other hand, in a non-merging-possible state, the merging passage 15a is kept closed by the merging valve 15.

[0049] Figure 3 The M / I control valve opening calculation unit 45 shown calculates the opening degree of each of the inlet control valves 33, 35, and 37 based on each operation command received from the operating device 23. More specifically, the M / I control valve opening calculation unit 45 has an opening degree mapping diagram or formula representing the relationship between each operation command and the opening degree of its corresponding inlet control valves 33, 35, and 37. Furthermore, the M / I control valve opening degree calculation unit 45 calculates the opening degree of the inlet control valves 33, 35, and 37 based on the received operation commands and the opening degree mapping diagram or formula. The M / I control valve opening degree calculation unit 45 outputs an inlet command corresponding to the calculated opening degree to the corresponding inlet control valves 33, 35, and 37. Thus, the M / I control valve opening degree calculation unit 45 controls the opening degree of the inlet control valves 33, 35, and 37, supplying an inlet flow rate corresponding to the operation command received from the operating device 23 to the corresponding hydraulic actuators 3 to 5.

[0050] The pressure-compensated M / I control valve opening calculation unit (hereinafter referred to as the "pressure compensation calculation unit") 46 calculates the opening degree of the boom inlet control valve 31 based on the boom operation command from the operating device 23 and the pressure before and after the boom inlet control valve 31. The pressure before and after the boom inlet control valve 31 is the pressure difference between the discharge pressure detected by the first discharge pressure sensor 17 and the inlet pressure of the boom cylinder 2 detected by the boom-side pressure sensor 19R or the head-side pressure sensor 19H (inlet pressure sensor). More specifically, the pressure compensation calculation unit 46 has a flow map or formula representing the relationship between the boom operation command and the inlet flow rate. Moreover, the pressure compensation calculation unit 46 calculates the target boom inlet flow rate based on the acquired boom operation command and the flow map or formula. Here, the target boom inlet flow rate is the target value of the inlet flow rate of the boom cylinder 2. Next, the pressure compensation calculation unit 46 calculates the front and rear pressures of the boom inlet control valve 31 based on the first discharge pressure sensor 17, the boom-side pressure sensor 19R, and the head-side pressure sensor 19H. Furthermore, the pressure compensation calculation unit 46 calculates the opening degree of the boom inlet control valve 31 based on the calculated front and rear pressures, the target inlet flow rate, and a calculation formula (e.g., Bernoulli's theorem). The pressure compensation calculation unit 46 outputs a boom inlet command corresponding to the calculated opening degree to the boom inlet control valve 31. Thus, the pressure compensation calculation unit 46 can perform pressure compensation relative to the inlet flow rate of the boom cylinder 2. Therefore, working fluid with a target inlet flow rate corresponding to the boom operation command can be supplied to the boom cylinder 2. Furthermore, by performing pressure compensation, the inlet flow rate of the working fluid flowing in other hydraulic actuators 3-5 operating simultaneously can be ensured.

[0051] The M / O control valve opening calculation unit 47 calculates the opening degree of each of the discharge control valves 32, 34, 36, and 38 based on the operation commands from the operating device 23. Furthermore, the M / O control valve opening calculation unit 47 outputs a discharge command corresponding to the calculated opening degree to the corresponding discharge control valves 32, 34, 36, and 38. Thus, the opening degree of the discharge control valves 32, 34, 36, and 38 is controlled, and the discharge flow rate corresponding to the operation command from the operating device 23 is discharged from the hydraulic actuators 2 to 5, respectively.

[0052] <Action of the hydraulic drive system>

[0053] When the operating levers 23a and 23b are operated, the hydraulic drive system 1 outputs an operation command corresponding to the operation direction and amount from the operating device 23 to the control device 24. Furthermore, the M / I control valve opening calculation unit 45 and the pressure compensation calculation unit 46 output inlet commands to the inlet control valves 31, 33, 35, and 37 based on the operation commands. Also, the M / O control valve opening calculation unit 47 outputs outlet commands to the outlet control valves 32, 34, 36, and 38 based on the operation commands. Thus, working fluid with an inlet flow rate corresponding to the operation commands is supplied to one of the ports 2c-5c and 2d-5d of the hydraulic actuators 2-5, and working fluid with an outlet flow rate corresponding to the operation commands is discharged from the other ports 2d-5d and 2c-5c. Therefore, the hydraulic actuators 2-5 operate at a speed corresponding to the operation commands.

[0054] Furthermore, when any of the aforementioned merging conditions is met, the hydraulic drive system 1 causes the working fluids of the two hydraulic pumps 11 and 13 to merge. More specifically, the control device 24 determines whether any merging condition is met based on the operating command output from the operating device 23. For example, the following describes the case where, in order to operate the boom cylinder 2 and the boom cylinder 3 simultaneously, the first operating lever 23a is moved in a first direction and the second operating lever 23b is moved in a third direction.

[0055] First, the merging determination unit 41 of the control device 24 determines whether the first merging condition is met based on the stick operation command and the boom operation command. Furthermore, if the operation amount in the first direction of the first operating lever 23a is greater than or equal to the first operating amount, and the operation amount in the third direction of the second operating lever 23b is greater than or equal to the second operating amount, and the pressures of sensors 19H and 19R are both above a specified value, the merging determination unit 41 determines that the first merging condition is met. Next, the merging determination unit 41 determines whether the second merging condition is met based on the stick operation command. Furthermore, if the operation amount in the third direction of the second operating lever 23b is greater than or equal to the third operating amount, and the load on the stick cylinder 2 is greater than or equal to a specified value, the merging determination unit 41 determines that the second merging condition is met. Moreover, when at least one merging condition is met, the merging switching unit 43 outputs a value switching coefficient of 1 to the multiplier 44.

[0056] Next, the merging valve opening calculation unit 42 calculates the opening of the merging valve 15 based on the merging opening mapping diagram or formula corresponding to the satisfied merging conditions. Furthermore, the merging valve opening calculation unit 42 selects the largest opening among the calculated openings as the merging opening. That is, the merging valve opening calculation unit 42 calculates two openings based on the merging opening mapping diagrams or formulas corresponding to the first and second merging conditions, respectively. Moreover, the merging valve opening calculation unit 42 selects the larger of the two openings as the merging opening. The multiplier 44 outputs a merging command obtained by multiplying the selected merging opening by the switching coefficient from the merging switching unit 43. When the merging state is set according to the switching command, the merging command is output to the merging valve 15. Thus, the merging flow path 15a is opened by the merging valve 15. Therefore, the working fluids of the first hydraulic pump 11 and the second hydraulic pump 13 can be merged. Therefore, working fluid with an inlet flow rate exceeding the maximum discharge flow rate of hydraulic pumps 11 and 13 is supplied to hydraulic cylinders 2 and 3 (boom cylinder 3 in this embodiment). In this embodiment, the maximum discharge flow rate refers to the maximum value that the horsepower-controlled hydraulic pumps 11 and 13 can discharge. That is, the maximum discharge flow rate of each hydraulic pump 11 and 13 is calculated based on the horsepower curves for each hydraulic pump 11 and 13 and the discharge pressure of each pump 11 and 13. However, the maximum discharge flow rate is not limited to the aforementioned maximum value, and may also be the maximum value of the discharge flow rate limited by other controls.

[0057] Furthermore, the M / I control valve opening calculation unit 45 controls the opening of the boom inlet control valve 35 based on the boom operation command and opening image or calculation formula from the operating device 23. This supplies working fluid to the boom cylinder 3 at an inlet flow rate corresponding to the boom operation command. That is, the boom cylinder 3 operates at a speed corresponding to the third-direction operation amount of the operating lever 23b. On the other hand, the pressure compensation calculation unit 46 controls the opening of the stick inlet control valve 31 based on the stick operation command from the operating device 23 and the front and rear pressure of the stick inlet control valve 31. That is, the pressure compensation calculation unit 46 supplies working fluid to the stick cylinder 2 at an inlet flow rate corresponding to the stick operation command while simultaneously compensating for pressure. In addition, the M / O control valve opening calculation unit 47 controls the opening of the outlet control valves 32 and 36 based on the stick operation command and boom operation command from the operating device 23. This allows the working fluid with the discharge flow rate corresponding to the stick operation command to be discharged from the stick cylinder 2, and the working fluid with the discharge flow rate corresponding to the boom operation command to be discharged from the boom cylinder 3.

[0058] In the hydraulic drive system 1, when the load on the stick cylinder 2 is less than the load on the boom cylinder 3, the control device 24 controls the opening of the stick inlet control valve 31 to limit the flow rate of working fluid into the stick cylinder 2. This eliminates the need for a pressure compensation valve relative to the stick cylinder 2, thus suppressing energy consumption when the stick cylinder 2 and boom cylinder 3 operate simultaneously. In this embodiment, fuel consumption of the engine E can be improved.

[0059] In more detail, the hydraulic drive system 1 can control the opening degree of the boom inlet control valve 31 and the boom outlet control valve 32 of the boom cylinder 2. That is, the control device 24 can maintain the opening degree of the boom outlet control valve 32 at the opening degree corresponding to the boom operation command, and control the opening degree of the boom inlet control valve 31 according to the opening and closing of the combined flow path 15a and the boom operation command. As a result, pressure compensation can be performed on the flow rate to the boom cylinder 2 by means of the boom inlet control valve 31. Therefore, even when the combined flow path 15a is open, the boom cylinder 2 can be operated at a speed corresponding to the operation amount in the first direction of the first operating lever 23a, and the boom cylinder 3 can be operated at a speed corresponding to the operation amount in the third direction of the second operating lever 23b.

[0060] Furthermore, in the hydraulic drive system 1, by merging the working fluids of each hydraulic pump 11 and 13, a working fluid flow rate exceeding the maximum discharge flow rate of any one hydraulic pump 11 or 13 can be supplied to the hydraulic cylinders 2 and 3. This allows for the miniaturization of the first hydraulic pump 11 and the second hydraulic pump 13.

[0061] In more detail, the control device 24 can ensure the flow rate of working fluid into the boom cylinder 3 by controlling the opening of the boom inlet control valve 35. That is, the hydraulic drive system 1 can also control the opening of the boom inlet control valve 35 and the boom outlet control valve 36 of the boom cylinder 3 respectively. In other words, the opening of the boom outlet control valve 36 can be maintained to ensure the outlet flow rate, while the opening of the boom inlet control valve 35 can be changed to adjust the inlet flow rate. Thus, even if the combined flow passage 15a is opened to supply a larger flow rate of working fluid to the second pump passage 13a, the boom cylinder 3 can be operated at a speed corresponding to the third-direction operation amount of the second operating lever 23b. That is, when the boom cylinder 2 and the boom cylinder 3 are operated simultaneously, both the boom cylinder 2 and the boom cylinder 3 can be operated at a speed corresponding to the corresponding operation amount.

[0062] Furthermore, in the hydraulic drive system 1, when the boom cylinder 2 and boom cylinder 3 operate simultaneously, the opening of the confluence valve 15 is controlled according to the respective operating amounts of the two operating levers 23a and 23b. This allows an appropriate amount of working fluid to flow from the first hydraulic pump 11 to the second circuit system 14 (or from the second hydraulic pump 13 to the first circuit system 12). Consequently, in the second circuit system 14 (or the first circuit system 12), the necessary introduction of more than the required amount of working fluid into the actuators 4 and 5 (or actuators 2 and 3) by throttling the flow rate can be suppressed. For example, when the boom cylinder 2 and boom cylinder 3 operate simultaneously, by introducing an appropriate amount of working oil into the second circuit system 14, the opening of the boom inlet control valve 35 can be set to a larger value. This suppresses energy consumption due to a reduction in the opening of the boom inlet control valve 35. In other words, it reduces the pressure loss of the boom inlet control valve 35 and suppresses energy consumption in the second circuit system 14.

[0063] Furthermore, in the hydraulic drive system 1, the pressure compensation calculation unit 46 controls the opening degree of the boom inlet control valve 31 based on the target inlet flow rate corresponding to the boom operation command and the front and rear pressures of the boom inlet control valve 31. That is, the pressure compensation calculation unit 46 performs pressure compensation on the inlet flow rate of the boom cylinder 2. Therefore, during simultaneous operation, working fluid with a flow rate corresponding to the operating amount of each of the two operating levers 23a and 23b can be supplied to the boom cylinder 2. As a result, the influence on the operability of the boom cylinder 2 during simultaneous operation can be suppressed. Furthermore, in the hydraulic drive system 1, when the difference between the load on the boom cylinder 2 and the load on the boom cylinder 3 is large, the flow rate of working fluid introduced into the boom cylinder 3 decreases. Therefore, the pressure compensation calculation unit 46 controls the opening degree of the boom inlet control valve 31 in the form of suppressing the inlet flow rate of the boom cylinder 2, which is particularly useful in the hydraulic drive system 1.

[0064] Furthermore, in the hydraulic drive system 1, when the output flow rate of the second hydraulic pump 13 is insufficient relative to the inlet flow rate corresponding to the boom operation command, the control device 24 opens the confluence valve 15, thereby allowing the working fluid of the first hydraulic pump 11 and the working fluid of the second hydraulic pump 13 to merge via the confluence valve 15. This ensures the inlet flow rate corresponding to the boom operation command relative to the boom cylinder 3. On the other hand, when sufficient flow rate is ensured by the second hydraulic pump 13 relative to the inlet flow rate corresponding to the boom operation command, closing the confluence path 15a via the confluence valve 15 suppresses energy consumption. In this embodiment, fuel consumption of the engine E can be improved.

[0065] [Second Implementation]

[0066] The hydraulic drive system 1A of the second embodiment is structurally similar to the hydraulic drive system 1 of the first embodiment. Therefore, regarding the structure of the hydraulic drive system 1A of the second embodiment, the differences from those of the hydraulic drive system 1 of the first embodiment will be mainly described, and identical structures will be marked with the same symbols and their descriptions will be omitted.

[0067] The hydraulic drive system 1A of the second embodiment is as follows: Figure 1 The device shown includes a first hydraulic pump 11, a first circuit system 12, a second hydraulic pump 13, a second circuit system 14, a confluence valve 15, multiple pressure sensors 17, 18, 19R to 21R, 19H to 21H, 22L, 22R, an operating device 23, and a control device 24A.

[0068] Control device 24A has the same functions as control device 24 in the first embodiment. Furthermore, control device 24A also controls the opening degree of the confluence valve 15 as follows: Control device 24A controls the opening degree of the confluence valve 15 based on either the difference between the first total flow rate and the maximum output flow rate of the first hydraulic pump 11 (i.e., the first flow rate difference), or the difference between the second total flow rate and the maximum output flow rate of the second hydraulic pump 13 (i.e., the second flow rate difference). The first total flow rate is the total flow rate of the target inlet flow rate (hereinafter referred to as the "target M / I flow rate") supplied from the first circuit system 12 to the hydraulic actuators 2 and 5. The second total flow rate is the total flow rate of the target M / I flow rate supplied from the second circuit system 14 to the hydraulic actuators 3 and 4. The target M / I flow rate of each hydraulic actuator 2-5 is the target value of the inlet flow rate of each hydraulic actuator 2-5.

[0069] In more detail, the control device 24A is as follows: Figure 4The device shown includes a first merging opening calculation unit 51, a second merging opening calculation unit 52, a merging opening selection unit 53, and a merging command output unit 54. The first merging opening calculation unit 51 calculates a first merging opening as the opening of the merging valve 15 based on a first flow differential. More specifically, the first merging opening calculation unit 51 calculates the target M / I flow rate of the stick (target M / I flow rate of the stick cylinder 2) based on a stick mapping diagram or formula and stick operation commands. Furthermore, the first merging opening calculation unit 51 calculates the target M / I flow rate of the gyration (target M / I flow rate of the gyration motor 5) based on a gyration mapping diagram or formula and gyration operation commands. Then, the first merging opening calculation unit 51 adds the calculated target M / I flow rate of the stick and the target M / I flow rate of the gyration to calculate a first total flow rate. Additionally, the first merging opening calculation unit 51 calculates the maximum discharge flow rate of the first hydraulic pump 11 based on the horsepower curve of the first hydraulic pump 11 and the discharge pressure detected by the first discharge pressure sensor 17. Furthermore, the first merging opening calculation unit 51 subtracts the first total flow rate from the maximum discharge flow rate of the first hydraulic pump 11 (i.e., calculates the first flow rate difference). Moreover, the first merging opening calculation unit 51 calculates the first merging opening based on the opening mapping diagram and the first flow rate difference.

[0070] The second merging opening calculation unit 52 also calculates the second merging opening as the opening of the merging valve 15 based on the second flow differential using the same method as the first merging opening calculation unit 51. More specifically, the second merging opening calculation unit 52 calculates the target M / I flow rate of the boom (target M / I flow rate of the boom cylinder 3) based on the boom mapping diagram or formula and the boom operation command. Furthermore, the second merging opening calculation unit 52 calculates the target M / I flow rate of the bucket (target M / I flow rate of the bucket cylinder 4) based on the bucket mapping diagram or formula and the bucket operation command. The second total flow calculation unit 73 adds the calculated target M / I flow rate of the boom and the target M / I flow rate of the bucket to calculate the second total flow rate. Additionally, the second merging opening calculation unit 52 calculates the maximum discharge flow rate of the second hydraulic pump 13 based on the horsepower curve of the second hydraulic pump 13 and the discharge pressure detected by the second discharge pressure sensor 18. Furthermore, the second merging opening calculation unit 52 subtracts the second total flow rate from the maximum discharge flow rate of the second hydraulic pump 13 (i.e., calculates the second flow rate difference). Moreover, the second merging opening calculation unit 52 calculates the second merging opening based on the opening mapping diagram and the second flow rate difference.

[0071] The merging opening selection unit 53 selects either the first merging opening calculated by the first merging opening calculation unit 51 or the second merging opening calculated by the second merging opening calculation unit 52. More specifically, the merging opening selection unit 53 selects either the first merging opening or the second merging opening, whichever is larger.

[0072] The merging command output unit 54 outputs a merging command based on the merging opening selected by the merging opening selection unit 53. More specifically, the merging command output unit 54 has a command mapping diagram showing the relationship between the merging opening and the merging command. The merging command output unit 54 generates a merging command based on the selected merging opening and the command mapping diagram. Furthermore, the merging command output unit 54 outputs the generated merging command to the merging valve 15. Thus, the opening of the merging valve 15 is controlled based on either the first flow differential or the second flow differential.

[0073] <Action of the hydraulic drive system>

[0074] When the operating levers 23a and 23b of the hydraulic drive system 1A are operated, the control device 24A controls the inlet control valves 31, 33, 35, and 37 and the opening degree of the merging valve 15 based on the operation command. Specifically, in the control device 24A, the first merging opening degree calculation unit 51 calculates the first merging opening degree, and the second merging opening degree calculation unit 52 calculates the second merging opening degree. Then, the merging opening degree selection unit 53 selects the larger of the calculated first and second merging opening degrees. Furthermore, the merging command output unit 54 outputs a merging command corresponding to the selected merging opening degree to the merging valve 15.

[0075] For example, when operating levers 23a and 23b are operated and the first total flow rate is greater than or equal to the maximum output flow rate of the first hydraulic pump 11, and the first merging opening is greater than the second merging opening, the merging opening selection unit 53 selects the first merging opening as the merging opening. The control device 24A outputs a merging command corresponding to the selected first merging opening to the merging valve 15. Thus, the opening of the merging valve 15 is controlled based on the first flow rate difference. Similarly, when the second total flow rate is greater than or equal to the maximum output flow rate of the second hydraulic pump 13, and the first merging opening is greater than the second merging opening, the merging opening selection unit 53 selects the second merging opening as the merging opening. The control device 24A outputs a merging command corresponding to the selected second merging opening to the merging valve 15. Thus, the opening of the merging valve 15 is controlled based on the second flow rate difference.

[0076] In this hydraulic drive system 1A, when the maximum output flow rate of the first hydraulic pump 11 is less than the first total flow rate, the working fluid of the second hydraulic pump 13 can be combined with that of the first hydraulic pump 11 via the confluence valve 15. This prevents insufficient flow of the working fluid in the hydraulic actuators 2 and 5. Similarly, when the maximum output flow rate of the second hydraulic pump 13 is less than the second total flow rate, the working fluid of the first hydraulic pump 11 can also be combined with that of the second hydraulic pump 13 via the confluence valve 15. This prevents insufficient flow of the working fluid in the hydraulic actuators 3 and 4.

[0077] Otherwise, the hydraulic drive system 1A of the second embodiment performs the same function as the hydraulic drive system 1 of the first embodiment.

[0078] [Other Implementation Methods]

[0079] In the hydraulic drive systems 1 and 1A of this embodiment, the simultaneous operation of the stick cylinder 2 and the boom cylinder 3 is mainly described. However, when the third to fifth confluence conditions are met, the confluence valve 15 opens the confluence passage 15a in the same way as described above. Furthermore, the hydraulic drive system 1 may also include hydraulic actuators other than the stick cylinder 2, boom cylinder 3, bucket cylinder 4, and swing motor 5, and the simultaneous operation of these other hydraulic actuators is also applicable.

[0080] Furthermore, in the hydraulic drive systems 1 and 1A of this embodiment, the confluence valve 15 is an electromagnetic proportional control valve, but it can also be an on / off switching valve that only switches the opening and closing of the confluence path 15a. Also, the hydraulic drive system 1 can have three or more hydraulic pumps, as long as at least one hydraulic pump is present in each circuit system 12 and 14. Furthermore, the hydraulic drive system 1 can also have three or more circuit systems. In addition, the hydraulic drive system 1 can also include hydraulic actuators other than the stick cylinder 2, boom cylinder 3, bucket cylinder 4, and swing motor 5.

[0081] Furthermore, in the hydraulic drive systems 1 and 1A of this embodiment, the opening degrees of the outlet control valves 32, 34, 36, and 38 can also be controlled according to the opening degrees of the corresponding inlet control valves 31, 33, 35, and 37. That is, the outlet flow rate can also be controlled according to the inlet flow rate. Also, the opening degrees of the outlet control valves 32, 34, 36, and 38 can be controlled according to the various operating commands from the operating device 23 and the load of the hydraulic actuators 2 to 5. Other than these methods, the control methods for the opening degrees of the outlet control valves 32, 34, 36, and 38 are not limited to those described above.

[0082] Furthermore, in the hydraulic drive system 1 of this embodiment, only the stick cylinder 2 is pressure compensated, but the M / I control valve opening calculation unit 45 may also perform pressure compensation for each hydraulic actuator 3 to 5. Also, the pressure variation in the stick cylinder 2 is greater than that in the boom cylinder 3. Therefore, pressure compensation for the stick cylinder 2 is particularly useful. Furthermore, in the hydraulic drive system 1, pressure compensation valves are disabled for all actuators, but it is not necessary to disable pressure compensation valves for all actuators. For example, the bucket cylinder 4 may also be connected to a pressure compensation valve. In addition, the number of operating levers in the operating device 23 may be one or more, rather than two. For example, one operating lever may be provided on each of the hydraulic actuators 2 to 5.

[0083] Furthermore, in the hydraulic drive systems 1 and 1A of this embodiment, control valves 31, 33, 35, and 37 for controlling the inlet flow rate and control valves 32, 34, 36, and 38 for controlling the outlet flow rate are respectively provided for the hydraulic actuators 2 to 5, but this structure is not limited to this. For example, hydraulic cylinders 2 to 4 are provided with rod-side control valves for controlling the supply and discharge of working fluid to the rod-side ports 2c to 4c and head-side control valves for controlling the supply and discharge of working fluid to the head-side ports 2d to 4d. Moreover, when working fluid is supplied to the rod-side ports 2c to 4c, the rod-side control valve functions as an inlet control valve, and the head-side control valve functions as an outlet control valve. On the other hand, when working fluid is supplied to the head-side ports 2d to 4d, the head-side control valve functions as an inlet control valve, and the rod-side control valve functions as an inlet control valve. Even with such a configuration, the hydraulic drive system performs the same function as hydraulic drive system 1.

[0084] Furthermore, in the hydraulic drive systems 1 and 1A of this embodiment, the hydraulic actuators 2 to 5 can also operate automatically based on the operation commands output from the operating device 23. That is, the operating device determines the workload of the hydraulic actuators 2 to 5 based on various sensors or programs. In addition, the operating device sets the operation amount based on the determined workload and outputs the operation command corresponding to the operation amount to the control device 21. Thus, automatic operation of the hydraulic actuators 2 to 5 can be achieved. Alternatively, the aforementioned operating device can also be integrally configured with the control device 21.

[0085] Based on the foregoing description, numerous modifications or other embodiments of the present invention will become apparent to those skilled in the art. Therefore, the foregoing description is merely illustrative and provided for the purpose of teaching those skilled in the art the best mode of implementing the invention. Substantial changes to its specific structure and / or function may be made without departing from the spirit of the invention.

Claims

1. A hydraulic drive system, comprising: A first circuit system for controlling the supply and discharge of working fluid to at least one or more hydraulic actuators, including a first hydraulic actuator; A first hydraulic pump that supplies working fluid to the first circuit system; A second-circuit system that controls the supply and discharge of working fluid to the second hydraulic actuator; A second hydraulic pump that supplies working fluid to the second circuit system; A confluence valve that opens and closes the confluence path connecting the first hydraulic pump and the second hydraulic pump; An operating device that outputs operating commands corresponding to the operating quantities indicating the workload of the first hydraulic actuator and the second hydraulic actuator; as well as A control device that controls the action of the confluence valve according to the operation instructions from the operating device; The first loop system has: A first inlet control valve that controls the inlet flow rate of the working fluid to the first hydraulic actuator; and A first discharge control valve controls the discharge flow rate of the working fluid discharged from the first hydraulic actuator to the storage tank; The control device controls the opening degree of the first inlet control valve and the first outlet control valve respectively, and controls the opening degree of the confluence valve based on the difference between the first total flow rate and the maximum discharge flow rate of the first hydraulic pump, wherein the first total flow rate is the total flow rate of the flow supplied from the first circuit system to the at least one or more hydraulic actuators.

2. The hydraulic drive system according to claim 1, characterized in that, The second loop system has: A second inlet control valve that controls the flow rate of the working fluid to the second hydraulic actuator; and A second discharge control valve controls the discharge flow rate of the working fluid discharged from the second hydraulic actuator to the storage tank; The control device controls the opening degree of the second liquid inlet control valve and the second liquid outlet control valve respectively.

3. The hydraulic drive system according to claim 1 or 2, characterized in that, The control device controls the opening degree of the merging valve according to the operation amount.

4. The hydraulic drive system according to claim 1, characterized in that, It also includes: a discharge pressure sensor for detecting the discharge pressure of the first hydraulic pump; and An inflow pressure sensor that detects the inflow pressure of the first hydraulic actuator; The control device controls the opening degree of the first inlet control valve based on the target inlet flow rate and the pressure difference, wherein the target inlet flow rate is the flow rate corresponding to the operation command output from the first hydraulic actuator of the operating device, and the pressure difference is the pressure difference between the discharge pressure detected by the discharge pressure sensor and the inflow pressure detected by the inflow pressure sensor.

5. The hydraulic drive system according to claim 4, characterized in that, The control device controls the opening of the first inlet control valve, which suppresses the flow rate supplied to the first hydraulic actuator, which is under a small load relative to the second hydraulic actuator.

6. The hydraulic drive system according to claim 1, characterized in that, The second circuit system controls the supply and discharge of working fluid to at least one hydraulic actuator, including the second hydraulic actuator; The control device controls the opening of the confluence valve based on either the difference between the second total flow rate and the maximum output flow rate of the second hydraulic pump, or the difference between the first total flow rate and the maximum output flow rate of the first hydraulic pump, wherein the second total flow rate is the total flow rate of the flow supplied from the second circuit system to the at least one or more hydraulic actuators.

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