Hydraulic drive system

Abstract

The hydraulic drive system includes: a hydraulic pump capable of changing the discharge flow rate of the working fluid; an inlet control valve for controlling the inlet flow rate of the working fluid flowing from the hydraulic pump to the hydraulic actuator; an outlet control valve independently provided with the inlet control valve for controlling the outlet flow rate of the working fluid discharged from the hydraulic actuator to the tank; an operating device for outputting an operating instruction; a first pressure sensor for detecting the discharge pressure of the hydraulic actuator; and a control device for setting a target outlet flow rate according to the operating instruction from the operating device and controlling the opening of the outlet control valve based on the discharge pressure detected by the first pressure sensor and the target outlet flow rate.

Description

Technical Field

[0001] The present invention relates to a hydraulic drive system for supplying working fluid to a hydraulic actuator. Background Art

[0002] Among hydraulic drive systems, there are those that can independently control the inlet (meter-in) flow rate and outlet (meter-in) flow rate of a hydraulic actuator. As such a hydraulic drive system, for example, a hydraulic supply device disclosed in Patent Document 1 is known.

[0003] Prior art literature:

[0004] Patent Literature:

[0005] Patent Document 1: Japanese Patent Application Laid-Open No. 11-303814. Summary of the Invention

[0006] Problems to be solved by the invention:

[0007] In the hydraulic supply device of Patent Document 1, the operation of the hydraulic actuator is controlled by controlling the inlet flow rate. However, compared with the case where the operation of the hydraulic actuator is controlled by the inlet flow rate, it is necessary to improve the operability of the hydraulic actuator.

[0008] Therefore, an object of the present invention is to provide a hydraulic drive system capable of improving the operability of a hydraulic actuator.

[0009] Means of solving the problem:

[0010] The hydraulic drive system of the present invention comprises: a hydraulic pump capable of changing the discharge flow rate of the working fluid; an inlet control valve for controlling the inlet flow rate of the working fluid flowing from the hydraulic pump to the hydraulic actuator; an outlet control valve independently provided with the inlet control valve for controlling the outlet flow rate of the working fluid discharged from the hydraulic actuator to the tank; an operating device for outputting an operating instruction; a first pressure sensor for detecting the discharge pressure of the hydraulic actuator; and a control device for setting a target outlet flow rate according to the operating instruction from the operating device and controlling the opening of the outlet control valve based on the discharge pressure detected by the first pressure sensor and the target outlet flow rate.

[0011] According to the present invention, by controlling the outflow rate of the hydraulic actuator, the hydraulic actuator can be accelerated or decelerated, particularly decelerated, at a speed corresponding to an operation instruction, thereby improving the operability of the hydraulic actuator.

[0012] Effects of the invention:

[0013] According to the present invention, the operability of the hydraulic actuator can be improved.

[0014] The above objects, other objects, features and advantages of the present invention will become apparent from the following detailed description of preferred embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 is a hydraulic circuit diagram showing a hydraulic system according to an embodiment of the present invention;

[0016] Figure 2 yes Figure 1 A block diagram of the opening control of each control valve in the control device of the hydraulic system;

[0017] Figure 3 It involves Figure 2 A block diagram of flow rate setting in the target flow rate setting unit. DETAILED DESCRIPTION

[0018] The following describes a hydraulic drive system 1 according to an embodiment of the present invention, with reference to the accompanying drawings. The directional concepts used in the following description are for convenience only and do not limit the orientation of the structure of the invention to these directional concepts. Furthermore, the hydraulic drive system 1 described below is merely one embodiment of the present invention. Therefore, the present invention is not limited by the embodiment and may be added, deleted, or modified without departing from the spirit of the invention.

[0019] <Hydraulic Drive Machinery>

[0020] Hydraulic drive machinery such as construction machinery, industrial machinery, and industrial vehicles is provided with a plurality of hydraulic actuators 2, 3 and a hydraulic drive system 1. The hydraulic drive machinery can operate various structures by operating the hydraulic actuators 2, 3. In the present embodiment, the hydraulic drive machinery is, for example, a hydraulic excavator. Furthermore, the hydraulic drive machinery has at least two hydraulic actuators 2, 3. The two hydraulic actuators 2, 3 are hydraulic cylinders, and are boom cylinders and bucket cylinders. In addition, the hydraulic drive machinery may also have three or more hydraulic actuators. In addition, the hydraulic actuator is not limited to the boom cylinder and the bucket cylinder, but may also be an arm cylinder, or a hydraulic motor such as a swing motor.

[0021] Hydraulic cylinders 2 and 3 can each operate various structures by extending and retracting. Specifically, rods 2b and 3b are inserted into cylinder tubes 2a and 3a, respectively, so they can advance and retract. Furthermore, rod-side ports 2c and 3c, as well as head-side ports 2d and 3d, are formed in cylinder tubes 2a and 3a, respectively. By supplying and discharging hydraulic fluid to and from ports 2c, 2d, 3c, and 3d, rods 2b and 3b advance and retract relative to cylinder tubes 2a and 3a, respectively, thereby extending and retracting hydraulic cylinders 2 and 3.

[0022] To explain in more detail, the rods 2b and 3b have pressure-receiving portions 2g and 3g. Furthermore, the pressure-receiving portions 2g and 3g partition the interior of the cylinders 2a and 3a into rod-side chambers 2i and 3i and head-side chambers 2h and 3h. The rod-side chambers 2i and 3i are connected to the rod-side ports 2c and 3c, while the head-side chambers 2h and 3h are connected to the head-side ports 2d and 3d. Furthermore, when hydraulic fluid flows into the rod-side chambers 2i and 3i, the pressure-receiving portions 2g and 3g push against the head-side chambers 2h and 3h through the head-side ports 2d and 3d. On the other hand, when hydraulic fluid flows into the head-side chambers 2h and 3h, the pressure-receiving portions 2g and 3g push against the rod-side chambers 2i and 3i through the rod-side ports 2c and 3c.

[0023] <Hydraulic drive system>

[0024] The hydraulic drive system 1 operates the hydraulic actuators 2 and 3 by supplying and discharging working fluid to and from the hydraulic actuators 2 and 3. More specifically, the hydraulic cylinders 2 and 3 are connected in parallel to the hydraulic drive system 1. Specifically, the ports 2c, 2d, 3c, and 3d of the hydraulic actuators 2 and 3 are connected to the hydraulic drive system 1, respectively. Furthermore, the hydraulic drive system 1 is capable of supplying and discharging working fluid to and from the ports 2c, 2d, 3c, and 3d of the hydraulic actuators 2 and 3, thereby operating the hydraulic actuators 2 and 3. The hydraulic drive system 1, which has such functions, includes: a hydraulic pump 11; a variable displacement device 12; multiple inlet control valves 13 and 15; multiple outlet control valves 14 and 16; multiple pressure sensors 17, 18R, 18H, 19R, and 19H; an operating device 20; and a control device 21.

[0025] The hydraulic pump 11 is connected to a driving source. The driving source is an engine E or an electric motor. In addition, the driving source is an engine E in this embodiment. Moreover, the hydraulic pump 11 discharges the working fluid by being rotationally driven by the driving source. In addition, the hydraulic pump 11 is a variable capacity hydraulic pump. That is, the hydraulic pump 11 can change the discharge flow rate by changing the discharge capacity. In this embodiment, the hydraulic pump 11 is a variable capacity inclined plate pump. That is, the hydraulic pump 11 can change the discharge flow rate by changing the inclination angle of the inclined plate 11a. In addition, the hydraulic pump 11 can also be a variable capacity inclined axis pump.

[0026] The variable displacement device 12 changes the discharge displacement of the hydraulic pump 11 in response to an input pump command. Specifically, the variable displacement device 12 is provided on the swash plate 11a of the hydraulic pump 11. The variable displacement device 12 changes the discharge flow rate of the hydraulic pump 11 by changing the inclination angle of the swash plate 11a.

[0027] The first inlet control valve 13, one of the multiple inlet control valves, is connected to the hydraulic pump 11 and the first hydraulic cylinder 2. Furthermore, the first inlet control valve 13 controls the inlet flow rate of the working fluid from the hydraulic pump 11 to the first hydraulic cylinder 2. Specifically, the first inlet control valve 13 is connected to the hydraulic pump 11 via a pump passage 11b. Furthermore, the first inlet control valve 13 is connected to the rod-side port 2c of the first hydraulic cylinder 2 via a rod-side passage 2e and to the head-side port 2d of the first hydraulic cylinder 2 via a head-side passage 2f. Furthermore, the first inlet control valve 13 can control the direction and inlet flow rate of the working fluid supplied from the hydraulic pump 11 to the first hydraulic cylinder 2 based on an input first inlet command. In other words, the first inlet control valve 13 can supply working fluid from the hydraulic pump 11 to either port 2c or port 2d of the first hydraulic cylinder 2 and control the inlet flow rate. In this embodiment, the first inlet control valve 13 is an electronically controlled spool valve. That is, the first inlet control valve 13 moves the valve element 13 a based on the first inlet command to switch the flow direction of the hydraulic oil and control the opening degree of the first inlet control valve 13 .

[0028] The first discharge control valve 14, one of the multiple discharge control valves, is connected to the first hydraulic cylinder 2 and the tank 10. Furthermore, the first discharge control valve 14 controls the discharge flow rate of the hydraulic fluid discharged from the first hydraulic cylinder 2 to the tank 10. Specifically, the first discharge control valve 14 is provided corresponding to the first inlet control valve 13. Furthermore, the first discharge control valve 14 is connected to the rod-side passage 2e and the head-side passage 2f, respectively, in parallel with the corresponding first inlet control valve 13. Furthermore, the first discharge control valve 14 can control the direction and discharge flow rate of the hydraulic fluid discharged from the first hydraulic cylinder 2 to the tank 10 based on an input first discharge command. Specifically, the first discharge control valve 14 connects ports 2d and 2c, which are different from the ports 2c and 2d connected to the first inlet control valve 13, to the tank 10 to control the discharge flow rate. Furthermore, the first discharge control valve 14 can control the discharge flow rate of the hydraulic fluid flowing through the first discharge control valve 14 independently of the inlet flow rate of the fluid supplied to the first hydraulic cylinder 2 via the first inlet control valve 13. In this embodiment, the first liquid discharge control valve 14 is an electronically controlled spool valve. Specifically, the first liquid discharge control valve 14 moves a valve element 14a based on a first liquid discharge command. Furthermore, the movement of the valve element 14a switches the flow direction of the hydraulic oil and controls the opening of the first liquid discharge control valve 14.

[0029] The second inlet control valve 15, one of the multiple inlet control valves, is connected to the hydraulic pump 11 and to the second hydraulic cylinder 3 in parallel with the first inlet control valve 13. Furthermore, the second inlet control valve 15 controls the inlet flow rate of the hydraulic fluid from the hydraulic pump 11 to the second hydraulic cylinder 3. Specifically, the second inlet control valve 15 is connected to the pump passage 11b in parallel with the first inlet control valve 13. The second inlet control valve 15 is connected to the rod-side port 3c of the second hydraulic cylinder 3 via the rod-side passage 3e and to the head-side port 3d of the second hydraulic cylinder 3 via the head-side passage 3f. Furthermore, the second inlet control valve 15 controls the direction and inlet flow rate of the hydraulic fluid supplied from the hydraulic pump 11 to the second hydraulic cylinder 3 in response to a second inlet command. In this embodiment, the second inlet control valve 15 is an electronically controlled spool valve. Specifically, the second inlet control valve 15 switches the flow direction of the hydraulic fluid by moving the valve spool 15a in response to the second inlet command, thereby controlling the opening of the second inlet control valve 15.

[0030] The second discharge control valve 16, one of the multiple discharge control valves, is connected to the second hydraulic cylinder 3 and the tank 10. Furthermore, the second discharge control valve 16 controls the discharge flow rate of the hydraulic fluid discharged from the second hydraulic cylinder 3 to the tank 10. Specifically, the second discharge control valve 16 is provided corresponding to the second inlet control valve 15. Furthermore, the second discharge control valve 16 is connected to the rod-side passage 3e and the head-side passage 3f, respectively, in parallel with the corresponding second inlet control valve 15. Furthermore, the second discharge control valve 16 can control the direction and discharge flow rate of the hydraulic fluid discharged from the second hydraulic cylinder 3 to the tank 10 based on an input second discharge command. Furthermore, the second discharge control valve 16 can also control the discharge flow rate of the hydraulic fluid flowing through the second discharge control valve 16 independently of the inlet flow rate supplied to the second hydraulic cylinder 3 via the second inlet control valve 15. In this embodiment, the second discharge control valve 16 is an electronically controlled spool valve. That is, the second discharge control valve 16 can switch the flow direction of the hydraulic oil by moving the valve element 16 a based on the second discharge command, thereby controlling the opening degree of the second discharge control valve 16 .

[0031] Multiple pressure sensors 17, 18R, 18H, 19R, and 19H detect the pressure of the working fluid flowing through each location. Furthermore, the multiple pressure sensors 17, 18R, 18H, 19R, and 19H output the detected pressures to the control device 21. To explain in more detail, the discharge pressure sensor 17 is connected to the pump passage 11b. Furthermore, the discharge pressure sensor 17 detects the discharge pressure of the hydraulic pump 11. Furthermore, the rod-side pressure sensors 18R and 19R are connected to the rod-side passages 2e and 3e, respectively. Furthermore, the rod-side pressure sensors 18R and 19R detect the pressure (rod pressure) at the rod-side ports 2c and 3c of the first hydraulic cylinder 2 and the second hydraulic cylinder 3. Furthermore, the head-side pressure sensors 18H and 19H are connected to the head-side passages 2f and 3f, respectively. Furthermore, the head-side pressure sensors 18H and 19H detect the pressure (head pressure) at the head-side ports 2d and 3d of the first hydraulic cylinder 2 and the second hydraulic cylinder 3. In addition, the plurality of first pressure sensors and the plurality of second pressure sensors correspond to the plurality of pressure sensors 17 , 18R, 18H, 19R, and 19H in the present embodiment.

[0032] The operating device 20 outputs operating commands for operating the hydraulic actuators 2 and 3 to the control device 21. In this embodiment, the operating device 20 is, for example, an operating valve or an electric joystick. Furthermore, the operating device 20 includes multiple operating levers (two operating levers in this embodiment) 20a and 20b. The operating levers 20a and 20b, as an example of multiple operating tools, are operable by an operator. Furthermore, the operating device 20 outputs operating commands corresponding to the amount of operation of the operating levers 20a and 20b to the control device 21. In this embodiment, the two operating levers 20a and 20b can each be pivoted in a predetermined operating direction. Furthermore, the operating device 20 outputs operating commands corresponding to the operation of the operating levers 20a and 20b (in this embodiment, the operation direction and the amount of operation) to the control device 21. More specifically, when the first operating lever 20a is operated, the operating device 20 outputs a first operating command corresponding to the amount of operation. Furthermore, when the second operating lever 20b is operated, the operating device 20 outputs a second operating command corresponding to the amount of operation. The first operating command is an operating command for operating the first hydraulic cylinder 2. The second operating command is an operating command for operating the second hydraulic cylinder 3. Alternatively, the operating lever may be configured to be omnidirectionally movable when viewed from a plane encompassing two intersecting directions (e.g., the front-to-back direction and the left-to-right direction). In this case, the operating device 20 decomposes the operating amount of the operating lever into a front-to-back component and a left-to-right component, and outputs the first and second operating commands corresponding to each component.

[0033] The control device 21 is connected to the four control valves 13-16, the pressure sensors 17, 18R, 18H, 19R, and 19H, and the operating device 20. The control device 21 controls the openings of the control valves 13-16 based on the operating commands from the operating device 20 and the pressures detected by the pressure sensors 17, 18R, 18H, 19R, and 19H. More specifically, the control device 21 sets a target discharge flow rate (hereinafter referred to as the "target M / O flow rate") based on the operating commands from the operating device 20. Furthermore, the control device 21 controls the openings of the discharge control valves 14 and 16 based on the discharge pressure of the hydraulic actuators 2 and 3 detected by any of the pressure sensors 17, 18R, 18H, 19R, and 19H and the target M / O flow rate. This allows the control device 21 to operate the hydraulic actuators 2 and 3 at a speed corresponding to the operating commands, that is, the amount of operation of the operating levers 20a and 20b. In addition, the control device 21 sets a target inlet flow rate (hereinafter referred to as "target M / I flow rate") corresponding to the target M / O flow rate. Furthermore, the control device 21 controls the discharge flow rate of the hydraulic pump 11 and the opening degree of the inlet control valves 13 and 15 in such a manner that the target M / I flow rate is supplied to the hydraulic actuators 2 and 3. The control device 21 having such a function has the following structure. That is, the control device 21 is as follows. Figure 2 As shown, it has a target flow setting part 31, a first liquid outlet flow control part (hereinafter referred to as the "first M / O flow control part") 32, a second liquid outlet flow control part (hereinafter referred to as the "second M / O flow control part") 33, a first correction part 34, a first liquid inlet flow control part (hereinafter referred to as the "first M / I flow control part") 35, a second correction part 36, a second liquid inlet flow control part (hereinafter referred to as the "second M / I flow control part") 37, a total flow calculation part 38 and a correction calculation part 39.

[0034] The target flow rate setting unit 31 sets a target M / O flow rate and a target M / I flow rate for each hydraulic cylinder 2, 3 based on the operating command of the operating levers 20a, 20b. The target M / O flow rate is the target flow rate to be discharged from the hydraulic cylinders 2, 3 in order to operate the hydraulic cylinders 2, 3 at the target speed corresponding to the operating amount. The target M / I flow rate is the target flow rate to be discharged from the hydraulic cylinders 2, 3, neither too high nor too low relative to the target speed. This flow rate is set based on the target M / O flow rate. Furthermore, when the total flow rate of the inflow flow rates supplied to the two hydraulic cylinders 2, 3 exceeds a predetermined flow rate, the target flow rate setting unit 31 adjusts the target M / I flow rate so that the total flow rate converges to the predetermined flow rate. The total flow rate is the flow rate corrected by the correction calculation unit 39, described in detail later. However, the total flow rate may also be the flow rate obtained by simply summing the inflow flow rates. Furthermore, the target flow rate setting unit 31 adjusts the target M / O flow rate based on the adjusted target M / I flow rate. In this embodiment, the predetermined flow rate is the maximum discharge flow rate of the hydraulic pump 11. Furthermore, when regeneration and recovery of the hydraulic fluid are being performed in each hydraulic cylinder 2, 3, the flow rate obtained by adding the regeneration flow rate and recovery flow rate to the maximum discharge flow rate of the hydraulic pump 11 is set as the prescribed flow rate. Furthermore, if the hydraulic drive system includes an accumulator, the flow rate supplied from the accumulator to each hydraulic cylinder 2, 3 is also added to the prescribed flow rate.

[0035] If described in more detail, the target flow rate setting unit 31 is as follows: Figure 3 As shown, it has: a first speed calculation part 41, a first liquid outlet flow calculation part (hereinafter referred to as the "first M / O flow calculation part") 42, a first liquid inlet flow calculation part (hereinafter referred to as the "first M / I flow calculation part") 43, a second speed calculation part 44, a second liquid outlet flow calculation part (hereinafter referred to as the "second M / O flow calculation part") 45, a second liquid inlet flow calculation part (hereinafter referred to as the "second M / I flow calculation part") 46, a redistribution calculation part 47, a first selection part 48, a second selection part 49, a first flow adjustment part 50 and a second flow adjustment part 51.

[0036] The first speed calculation unit 41 calculates a first target speed, which is the target speed of the first hydraulic cylinder 2, based on the first operation command. Specifically, the first speed calculation unit 41 calculates the first target speed corresponding to the amount of operation of the first operating lever 20a. In this embodiment, the first speed calculation unit 41 includes a first map. The amount of operation of the first operating lever 20a in the first map corresponds to the first target speed. The first speed calculation unit 41 calculates the first target speed based on the first map and the amount of operation of the first operating lever 20a.

[0037] The first M / O flow rate calculation unit 42 calculates the first M / O flow rate based on the first target speed calculated by the first speed calculation unit 41 and the outlet-side pressure receiving area AO1 of the pressure-receiving portion 2g of the first hydraulic cylinder 2. Specifically, the first M / O flow rate calculation unit 42 obtains the operating direction of the rod 2b of the first hydraulic cylinder 2 based on the first operating command. Furthermore, the first M / O flow rate calculation unit 42 sets the outlet-side pressure receiving area AO1 of the pressure-receiving portion 2g based on the operating direction of the rod 2b. For example, when the first operating rod 20a is operated in one direction of the first operating direction, causing the rod 2b to extend, hydraulic fluid is discharged from the rod-side chamber 2i. Therefore, the area of ​​the portion of the pressure-receiving portion 2g facing the rod-side chamber 2i is set as the outlet-side pressure receiving area AO1. On the other hand, when the first operating rod 20a is operated in the other direction of the first operating direction, causing the rod 2b to retract, the area of ​​the portion of the pressure-receiving portion 2g facing the head-side chamber 2h is set as the outlet-side pressure receiving area AO1. Once set, the first M / O flow rate calculation unit 42 calculates the first M / O flow rate by multiplying the set liquid outlet side pressure receiving area AO1 by the first target speed.

[0038] The first M / I flow rate calculation unit 43 calculates the first M / I flow rate based on the first target speed calculated by the first speed calculation unit 41 and the inlet-side pressure receiving area AI1 of the pressure receiving portion 2g of the first hydraulic cylinder 2. More specifically, similar to the first M / O flow rate, the first M / I flow rate calculation unit 43 obtains the operating direction of the rod 2b of the first hydraulic cylinder 2 based on the first operating command. Furthermore, the first M / I flow rate calculation unit 43 sets the inlet-side pressure receiving area AI1 of the pressure receiving portion 2g based on the operating direction of the rod 2b. For example, when the first operating rod 20a is operated in one direction of the first operating direction, causing the rod 2b to extend, hydraulic fluid is supplied to the head-side chamber 2h. Therefore, the area of ​​the portion of the pressure receiving portion 2g facing the head-side chamber 2h is set as the inlet-side pressure receiving area AI1. On the other hand, when the first operating rod 20a is operated in the other direction of the first operating direction, causing the rod 2b to retract, the area of ​​the portion of the pressure receiving portion 2g facing the rod-side chamber 2i is set as the inlet-side pressure receiving area AI1. Once set, the first M / I flow rate calculation unit 43 calculates the first M / I flow rate by multiplying the set liquid inlet side pressure receiving area AI1 by the first target speed.

[0039] The second speed calculation unit 44 calculates a second target speed, which is the target speed of the second hydraulic cylinder 3, based on the second operation command. More specifically, the second speed calculation unit 44 calculates the first target speed corresponding to the amount of operation of the second operating lever 20b. In this embodiment, the second speed calculation unit 44 includes a second map. In the second map, the amount of operation of the second operating lever 20b corresponds to the second target speed. The second speed calculation unit 44 calculates the second target speed based on the second map and the amount of operation of the second operating lever 20b.

[0040] The second M / O flow rate calculation unit 45 calculates the second M / O flow rate based on the second target speed calculated by the second speed calculation unit 44 and the outlet-side pressure receiving area AO2 of the pressure receiving portion 3g of the second hydraulic cylinder 3. Specifically, the second M / O flow rate calculation unit 45 calculates the second M / O flow rate using the same method as the first M / O flow rate calculation unit 42. Specifically, the second M / O flow rate calculation unit 45 obtains the operating direction of the rod 3b of the second hydraulic cylinder 3 based on the second operating command. Furthermore, the second M / O flow rate calculation unit 45 sets the outlet-side pressure receiving area AO2 of the pressure receiving portion 3g based on the operating direction of the rod 3b. Specifically, similar to the outlet-side pressure receiving area AO1 of the pressure receiving portion 2g of the hydraulic cylinder 2, the outlet-side pressure receiving area AO2 of the pressure receiving portion 3g is set to either the area of ​​the portion of the pressure receiving portion 3g facing the rod-side chamber 3i or the area of ​​the portion facing the head-side chamber 3h based on the second operating direction of the second operating lever 20b. Furthermore, the second M / O flow rate calculation unit 45 calculates the second M / O flow rate by multiplying the set liquid outlet side pressure receiving area AO2 by the second target speed.

[0041] The second M / I flow rate calculation unit 46 calculates the second M / I flow rate based on the second target speed calculated by the second speed calculation unit 44 and the inlet-side pressure receiving area AI2 of the pressure receiving portion 3g of the second hydraulic cylinder 3. Specifically, the second M / I flow rate calculation unit 46 calculates the second M / I flow rate using the same method as the first target M / I flow rate. Specifically, the second M / I flow rate calculation unit 46 obtains the operating direction of the rod 3b of the second hydraulic cylinder 3 based on the second operating command. Furthermore, the second M / I flow rate calculation unit 46 sets the inlet-side pressure receiving area AI2 of the pressure receiving portion 3g based on the operating direction of the rod 3b. Specifically, the outlet-side pressure receiving area AO2 of the pressure receiving portion 3g is set to either the area of ​​the portion of the pressure receiving portion 3g facing the head-side chamber 3h or the area of ​​the portion facing the rod-side chamber 3i, similar to the inlet-side pressure receiving area AI1 of the pressure receiving portion 2g of the hydraulic cylinder 2, based on the second operating direction of the second operating lever 20b. Furthermore, the second M / I flow rate calculation unit 46 calculates the second M / I flow rate by multiplying the set liquid inlet side pressure receiving area AI2 by the second target speed.

[0042] The redistribution calculation unit 47 calculates the redistribution ratio to adjust the first and second M / I flows based on the total flow rate of the first and second M / I flows. Specifically, the redistribution calculation unit 47 calculates the redistribution ratio to adjust the flow rates of the first and second M / I flows so that the total flow rate converges below the aforementioned predetermined flow rate. The total flow rate is calculated by the total flow rate calculation unit 38, described in detail later. Specifically, the redistribution calculation unit 47 divides the predetermined flow rate by the total flow rate of the first and second M / I flows to calculate the ratio of the predetermined flow rate to the total flow rate. When the ratio of the predetermined flow rate is greater than 1, the total flow rate converges below the predetermined flow rate. Therefore, there is no need to adjust the first and second M / I flows, and the redistribution ratio is set to 1. On the other hand, when the ratio of the predetermined flow rate is less than 1, the total flow rate exceeds the predetermined flow rate. Thus, the redistribution calculation unit 47 sets the ratio of the predetermined flow rate as the redistribution ratio to ensure that the total flow rate converges below the predetermined flow rate.

[0043] The first selector 48 selects the smaller of the first M / I flow calculated by the first M / I flow calculation unit 43 and the first M / I flow redistributed by the redistribution calculation unit 47. For example, when the total flow rate is greater than or equal to a predetermined flow rate, the redistribution ratio is less than 1, so the redistributed first M / I flow rate is less than the first M / I flow rate before redistribution. Therefore, when the total flow rate is greater than or equal to the predetermined flow rate, the first selector 48 selects the redistributed first M / I flow rate as the first M / I flow rate. On the other hand, when the total flow rate is less than or equal to the predetermined flow rate, the redistribution ratio is 1, so the first M / I flow calculated by the first M / I flow calculation unit 43 and the first M / I flow redistributed by the redistribution calculation unit 47 are the same. Therefore, the first selector 48 selects the first M / I flow calculated by the first M / I flow calculation unit 43. The selected first M / I flow rate is then set as the first target M / I flow rate by the target flow setting unit 31.

[0044] Similar to the first selection unit 48, the second selection unit 49 selects the smaller of the second M / I flow rate calculated by the second M / I flow rate calculation unit 46 and the second M / I flow rate redistributed by the redistribution calculation unit 47. On the other hand, when the total flow rate is less than the predetermined flow rate, the redistribution ratio is 1, so the second M / I flow rate calculated by the second M / I flow rate calculation unit 46 and the first M / I flow rate redistributed by the redistribution calculation unit 47 are the same. Therefore, the second selection unit 49 selects the first M / I flow rate calculated by the second M / I flow rate calculation unit 46. The selected second M / I flow rate is then set as the second target M / I flow rate by the target flow rate setting unit 31.

[0045] The first flow rate regulator 50 adjusts the first target M / O flow rate based on the adjusted first M / I flow rate. More specifically, the first flow rate regulator 50 adjusts the first M / O flow rate based on the redistribution ratio calculated by the redistribution calculator 47. In this embodiment, the first flow rate regulator 50 multiplies the first M / O flow rate calculated by the first M / O flow rate calculator 42 by the redistribution ratio of the first M / I flow rate. The multiplied first M / O flow rate is then set as the first target M / O flow rate by the target flow rate setting unit 31.

[0046] Similar to the first flow rate regulator 50, the second flow rate regulator 51 adjusts the second target M / O flow rate based on the adjusted second M / I flow rate. More specifically, the second flow rate regulator 51 adjusts the second M / O flow rate based on the redistribution ratio calculated by the redistribution calculator 47. In this embodiment, the second flow rate regulator 51 multiplies the second target M / O flow rate calculated by the second M / O flow rate calculator 45 by the redistribution ratio of the second target M / I flow rate. The multiplied second M / O flow rate is then set as the second target M / O flow rate by the target flow rate setting unit 31.

[0047] The first M / O flow rate control unit 32 controls the opening of the first liquid discharge control valve 14 based on the first target M / O flow rate set by the target flow rate setting unit 31 and the pressures detected by the pressure sensors 18R and 18H. More specifically, the first M / O flow rate control unit 32 first calculates the pressure across the first liquid discharge control valve 14. The pressure across the first liquid discharge control valve 14 is the pressure difference between the discharge pressure of the first hydraulic cylinder 2, detected by the rod-side pressure sensor 18R or the head-side pressure sensor 18H (first pressure sensor), and the pressure (≈tank pressure) in the pipe connecting the first liquid discharge control valve 14 and the tank 10. In this embodiment, the pressure in the pipe is the tank pressure. The first M / O flow rate control unit 32 then calculates the opening of the first liquid discharge control valve 14 based on the first target M / O flow rate, the pressure across the first liquid discharge control valve 14, and a calculation formula (e.g., Bernoulli's theorem). The first M / O flow rate control unit 32 then outputs a first fluid discharge command (hereinafter referred to as the "first M / O command") corresponding to the calculated opening to the first fluid discharge control valve 14. This controls the opening of the first fluid discharge control valve 14 to an opening corresponding to the first target M / O flow rate. Furthermore, the hydraulic fluid at the first target M / O flow rate can be discharged from the first hydraulic cylinder 2 through the first fluid discharge control valve 14 to the tank 10. This allows the first hydraulic cylinder 2 to be operated at a speed corresponding to the amount of operation of the first operating lever 20a.

[0048] Similar to the first M / O flow rate control unit 32, the second M / O flow rate control unit 33 controls the opening of the second liquid discharge control valve 16 based on the second target M / O flow rate set by the target flow rate setting unit 31 and the pressures detected by the pressure sensors 19R and 19H. More specifically, the second M / O flow rate control unit 33 first calculates the pressure across the second liquid discharge control valve 16. The pressure across the second liquid discharge control valve 16 is the pressure difference between the discharge pressure of the second hydraulic cylinder 3, as detected by the rod-side pressure sensor 19R or the head-side pressure sensor 19H (first pressure sensor), and the pressure (≈tank pressure) in the pipe connecting the second liquid discharge control valve 16 and the tank 10. In this embodiment, the pressure in the pipe is the tank pressure. The second M / O flow rate control unit 33 then calculates the opening of the second liquid discharge control valve 16 based on the second target M / O flow rate, the pressure across the second liquid discharge control valve 16, and a calculation formula (e.g., Bernoulli's theorem). The second M / O flow rate control unit 33 then outputs a second fluid discharge command (hereinafter referred to as the "second M / O command") corresponding to the calculated opening to the second fluid discharge control valve 16. This controls the opening of the second fluid discharge control valve 16 to an opening corresponding to the second target M / O flow rate. Furthermore, the hydraulic fluid at the second target M / O flow rate can be discharged from the second hydraulic cylinder 3 through the second fluid discharge control valve 16 to the tank 10. This allows the second hydraulic cylinder 3 to be operated at a speed corresponding to the amount of operation of the second operating lever 20b.

[0049] The first correction unit 34 corrects the first target M / I flow rate set by the target flow rate setting unit 31 to calculate a first corrected M / I flow rate (corrected flow rate). More specifically, a predetermined coefficient K1 (>1) is set in the first correction unit 34. The first correction unit 34 then multiplies the first target M / I flow rate by the coefficient K1. This calculates the first corrected M / I flow rate, which is the corrected first target M / I flow rate.

[0050] The first M / I flow rate control unit 35 controls the opening of the first inlet control valve 13 based on the first corrected M / I flow rate corrected by the first correcting unit 34 and the pressure sensors 17, 18R, and 18H. More specifically, the first M / I flow rate control unit 35 first calculates the pressure across the first inlet control valve 13. The pressure across the first inlet control valve 13 is the difference between the inflow pressure of the first hydraulic cylinder 2, detected by the head-side pressure sensor 18H or the rod-side pressure sensor 18R (second pressure sensor), and the discharge pressure detected by the discharge pressure sensor 17 (third pressure sensor). The first M / I flow rate control unit 35 then calculates the target opening of the first inlet control valve 13 based on the first corrected M / I flow rate, the pressure across the first inlet control valve 13, and a calculation formula (e.g., Bernoulli's theorem).

[0051] Furthermore, the first M / I flow rate control unit 35 sets the first upper limit opening of the first inlet control valve 13 so that the discharge pressure detected by the discharge pressure sensor 17 is higher than the maximum pressure (maximum load pressure) of the inflow pressures (load pressures) of the hydraulic cylinders 2 and 3 by a predetermined pressure α. Specifically, the first M / I flow rate control unit 35 calculates the first upper limit opening so that the discharge pressure detected by the discharge pressure sensor 17 is higher than the maximum inflow pressure detected by the pressure sensors 18H, 18R, 19H, and 19R (hereinafter referred to as "maximum pressure of the hydraulic cylinders 2 and 3") by a predetermined pressure α. More specifically, the first M / I flow rate control unit 35 calculates the first upper limit opening based on the first target M / I flow rate, the maximum pressures of the hydraulic cylinders 2 and 3, the predetermined pressure α, and a calculation formula (e.g., Bernoulli's theorem). Specifically, the first M / I flow rate control unit 35 sets the maximum pressure of the hydraulic cylinders 2 and 3 to the downstream pressure of the first inlet control valve 13, and sets the upstream pressure (discharge pressure) of the first inlet control valve 13 to the pressure obtained by adding a predetermined pressure α to the maximum pressure of the hydraulic cylinders 2 and 3. Furthermore, the first M / I flow rate control unit 35 sets the pressure across the first inlet control valve 13 based on the downstream and upstream pressures of the first inlet control valve 13. Furthermore, the first M / I flow rate control unit 35 calculates a first upper limit opening degree based on the set pressure across the first inlet control valve 13, the first target M / I flow rate, and a calculation formula (e.g., Bernoulli's theorem).

[0052] Furthermore, when the target opening of the first inlet control valve 13 is less than the first upper limit opening, the first M / I flow rate control unit 35 sets the opening of the first inlet control valve 13 to the target opening. On the other hand, when the target opening of the first inlet control valve 13 is greater than the first upper limit opening, the first M / I flow rate control unit 35 sets the opening of the first inlet control valve 13 to the first upper limit opening. Furthermore, the first M / I flow rate control unit 35 outputs a first inlet command (hereinafter referred to as the "first M / I command") corresponding to the set opening to the first inlet control valve 13. This allows the first M / I flow rate control unit 35 to simultaneously control the opening of the first inlet control valve 13 while performing pressure compensation in the hydraulic cylinders 2 and 3. Furthermore, the first M / I flow rate control unit 35 sets the opening of the first inlet control valve 13 to the target opening when only the first operating lever 20a is operated.

[0053] The second correction unit 36 ​​corrects the second target M / I flow rate (corrected flow rate) set by the target flow rate setting unit 31. More specifically, the second correction unit 36 ​​is set with a predetermined coefficient K2 (>1). In this embodiment, the predetermined coefficient K2 is the same as the predetermined coefficient K1. Furthermore, the second correction unit 36 ​​multiplies the second target M / I flow rate by the coefficient K2. This calculates a second corrected M / I flow rate, which is the corrected second target M / I flow rate.

[0054] Similar to the first M / I flow rate control unit 35, the second M / I flow rate control unit 37 controls the opening of the second inlet control valve 15 based on the second corrected M / I flow rate corrected by the second corrector 36 and the pressure sensors 17, 19R, and 19H. More specifically, the second M / I flow rate control unit 37 first calculates the pressure across the second inlet control valve 15. The pressure across the second inlet control valve 15 is the difference between the discharge pressure detected by the discharge pressure sensor 17 and the inflow pressure into the second hydraulic cylinder 3 detected by the rod-side pressure sensor 19R or the head-side pressure sensor 19H (second pressure sensor). The second M / I flow rate control unit 37 then calculates the target opening of the second inlet control valve 15 based on the second corrected M / I flow rate, the pressure across the second inlet control valve 15, and a calculation formula (e.g., Bernoulli's theorem).

[0055] Furthermore, in this embodiment, the second upper limit opening of the second inlet control valve 15 is set such that the discharge pressure detected by the discharge pressure sensor 17 is higher than the maximum pressure (maximum load pressure) of the inflow pressures (load pressures) of the hydraulic cylinders 2 and 3 by a predetermined pressure α. Specifically, the second M / I flow rate control unit 37, similar to the first M / I flow rate control unit 35, calculates the second upper limit opening such that the discharge pressure detected by the discharge pressure sensor 17 is higher than the maximum pressure of the hydraulic cylinders 2 and 3 by the predetermined pressure α. More specifically, the second M / I flow rate control unit 37 calculates the second upper limit opening based on the second target M / I flow rate, the maximum pressures of the hydraulic cylinders 2 and 3, the predetermined pressure α, and a calculation formula (e.g., Bernoulli's theorem). Specifically, the maximum pressures of the hydraulic cylinders 2 and 3 are the downstream pressure of the second inlet control valve 15, and the pressure obtained by adding the predetermined pressure α to the maximum pressures of the hydraulic cylinders 2 and 3 is the upstream pressure (discharge pressure) of the second inlet control valve 15. The second M / I flow rate control unit 37 also sets the pressure across the second liquid inlet control valve 15 based on the downstream and upstream pressures of the second liquid inlet control valve 15. Furthermore, the second M / I flow rate control unit 37 calculates a second upper limit opening degree based on the set pressure across the second liquid inlet control valve 15, the second target M / I flow rate, and a calculation formula (e.g., Bernoulli's theorem).

[0056] Furthermore, when the target opening of the second inlet control valve 15 is less than the second upper limit opening, the second M / I flow rate control unit 37 sets the opening of the second inlet control valve 15 to the target opening. On the other hand, when the target opening of the second inlet control valve 15 is greater than the second upper limit opening, the second M / I flow rate control unit 37 sets the opening of the second inlet control valve 15 to the second upper limit opening. Furthermore, the second M / I flow rate control unit 37 outputs a second inlet command (hereinafter referred to as the "second M / I command") corresponding to the set opening to the second inlet control valve 15. This allows the second M / I flow rate control unit 37 to simultaneously control the opening of the second inlet control valve 15 while compensating for the pressures in the hydraulic cylinders 2 and 3. Furthermore, when only the operating lever 20b is operated, the second M / I flow rate control unit 37 sets the opening of the second inlet control valve 15 to its maximum opening.

[0057] The total flow rate calculation unit 38 calculates the total flow rate. More specifically, the total flow rate calculation unit 38 calculates the total of the target M / I flow rates set by the target flow rate setting unit 31, that is, the total flow rate that is the sum of the first target M / I flow rate and the second target M / I flow rate.

[0058] The correction calculation unit 39 corrects the total flow calculated by the total flow calculation unit 38. Furthermore, the correction calculation unit 39 sets the discharge flow of the hydraulic pump 11 based on the corrected total flow. To explain in more detail, the correction calculation unit 39 corrects the total flow by adding the bleed flow (not shown) and the leakage flow. Furthermore, when the total flow is less than the maximum discharge flow of the hydraulic pump 11, the correction calculation unit 39 sets the discharge flow of the hydraulic pump 11 to the total flow. On the other hand, when the total flow is greater than the maximum discharge flow of the hydraulic pump 11, the discharge flow of the hydraulic pump 11 is set to the maximum discharge flow. Furthermore, the correction calculation unit 39 outputs a pump instruction to the variable displacement device 12 based on the set discharge flow. Consequently, the variable displacement device 12 tilts the swash plate 11a at an inclination angle corresponding to the pump instruction. Furthermore, the hydraulic fluid at the set discharge flow is discharged from the hydraulic pump 11.

[0059] <Hydraulic drive system operation (single operation)>

[0060] In the hydraulic drive system 1, when only one of the operating levers 20a or 20b is operated, an operating instruction corresponding to the direction and amount of operation of the operated operating lever 20a or 20b is output from the operating device 20 to the control device 21. For example, when only the first operating lever 20a is operated, a first operating instruction is output from the operating device 20 to the control device 21. In this way, the target flow rate setting unit 31 of the control device 21 sets the first target M / O flow rate and the first target M / I flow rate based on the first operating instruction. More specifically, within the target flow rate setting unit 31, the first speed calculation unit 41 calculates the first target speed based on the first operating instruction. Furthermore, the first M / O flow rate calculation unit 42 calculates the first M / O flow rate based on the first target speed. Furthermore, the first M / I flow rate calculation unit 43 sets the first M / I flow rate based on the first target speed. The redistribution calculation unit 47 sets the redistribution ratio. For example, if the first M / I flow rate exceeds the maximum discharge flow rate due to the load on the first hydraulic cylinder 2, the redistribution calculation unit 47 sets the value obtained by dividing the specified flow rate by the first target M / I flow rate as the redistribution ratio. Furthermore, the redistribution calculation unit 47 sets the first M / I flow rate multiplied by the redistribution ratio as the first target M / I flow rate of the target flow rate setting unit 31. On the other hand, if the total flow rate is less than the maximum discharge flow rate, the value obtained by dividing the specified flow rate by the first target M / I flow rate exceeds 1. Therefore, the redistribution calculation unit 47 sets the redistribution ratio to 1. Thus, the redistribution calculation unit 47 sets the first M / I flow rate set by the first M / I flow rate calculation unit 43 as the first target M / I flow rate of the target flow rate setting unit 31.

[0061] The first M / O flow rate control unit 32 controls the opening of the first discharge control valve 14 based on the first target M / O flow rate set by the target flow rate setting unit 31 and the pressures detected by the pressure sensors 18R and 18H. This allows the first target M / O flow rate to be discharged from each hydraulic cylinder 2 in accordance with the amount of operation of the operating lever 20a. Consequently, the hydraulic cylinder 2 can be operated at a speed corresponding to the amount of operation of the operating lever 20a. Meanwhile, the first M / I flow rate control unit 35 controls the opening of the first inlet control valve 13 to its maximum opening. The opening of the first inlet control valve 13 is not limited to the maximum opening; it may be a predetermined opening relative to the maximum opening. Furthermore, the total flow rate calculation unit 38 calculates the total flow rate (= the first target M / I flow rate). The correction calculation unit 39 corrects the total flow rate calculated by the total flow rate calculation unit 38. The correction calculation unit 39 then sets the discharge flow rate of the hydraulic pump 11 based on the corrected total flow rate. Furthermore, the correction calculation unit 39 outputs a pump command to the variable displacement device 12 based on the set discharge flow rate. Thus, hydraulic fluid at the set discharge flow rate is discharged from the hydraulic pump 11. Thus, hydraulic fluid corresponding to the target M / O flow rate can be supplied to each hydraulic cylinder 2, 3.

[0062] Although not described in detail, when the second operating lever 20b is operated, the control device 21 sets the second M / O flow rate and the second M / I flow rate in the same manner. Furthermore, the control device 21 controls the operation of the hydraulic pump 11, the second inlet control valve 15, and the second outlet control valve 16 based on the set second M / O flow rate and the second M / I flow rate.

[0063] In the hydraulic drive system 1 thus configured, the outflow rate is controlled according to an operating command. This allows the hydraulic cylinders 2 and 3 to be accelerated or decelerated, particularly decelerated, at speeds corresponding to the operating command. This improves the operability of the hydraulic cylinders 2 and 3. Furthermore, by controlling the outflow rate, the speed of the hydraulic cylinders 2 and 3 can be accurately and stably controlled. Furthermore, by controlling the inflow rate according to the outflow rate, cavitation and excessive pressure buildup caused by excessive or insufficient inflow rate can be suppressed.

[0064] Furthermore, in the hydraulic drive system 1, the target M / O flow rate is set based on the target speed and the outlet-side pressure-receiving areas AO1 and AO2. Therefore, the hydraulic cylinders 2 and 3 can be operated at the target speed regardless of the size of the outlet-side pressure-receiving areas AO1 and AO2 in the pressure-receiving portions 2g and 3g of the hydraulic cylinders 2 and 3. This further improves the operability of the hydraulic cylinders 2 and 3.

[0065] In the hydraulic drive system 1, similar to the target M / O flow rate, the target M / I flow rate is also set based on the amount of operation of the operating levers 20a and 20b. Specifically, the hydraulic drive system 1 controls the discharge flow rate of the hydraulic pump 11 and the openings of the inlet control valves 13 and 15 so that the target M / I flow rate corresponding to the target M / O flow rate is supplied to the hydraulic cylinders 2 and 3. By setting the target M / I flow rate to a flow rate corresponding to the target M / O flow rate, an excessive increase in the discharge pressure of the hydraulic pump 11 and the occurrence of cavitation can be suppressed. Furthermore, in the hydraulic drive system 1, the speeds of the hydraulic cylinders 2 and 3 are adjusted based on the discharge flow rate. This allows the M / I flow rate control units 35 and 37 to control the inlet control valves 13 and 15 based on a corrected M / I flow rate that is greater than the target M / I flow rate. This reduces pressure loss caused by excessive flow restriction of the opening of the inlet control valves 13 and 15 in response to fluctuations in the first and second M / O flow rates. In other words, pressure loss in the inlet control valves 13 and 15 can be reduced.

[0066] <Hydraulic drive system operation (compound operation)>

[0067] When the operating levers 20a and 20b are simultaneously operated in the hydraulic drive system 1, the operating device 20 outputs first and second operating commands corresponding to the operating direction and amount to be operated to the control device 21. In this manner, the target flow rate setting unit 31 sets the first and second target M / O flow rates and the first and second target M / I flow rates based on the operating commands. More specifically, in the target flow rate setting unit 31, the first and second speed calculation units 41 and 44 calculate the first and second target speeds, respectively, based on the operating commands, using the same method as when operating individually. Furthermore, the first M / O flow rate calculation unit 42 sets the first M / O flow rate based on the first target speed, and the first M / I flow rate calculation unit 43 sets the first M / I flow rate based on the first target speed. Furthermore, the second M / O flow rate calculation unit 45 sets the second M / O flow rate based on the second target speed, and the second M / I flow rate calculation unit 46 sets the second M / I flow rate based on the second target speed.

[0068] Furthermore, the redistribution calculation unit 47 sets a redistribution ratio. Specifically, when the total flow rate is less than the maximum discharge flow rate, the redistribution calculation unit 47 sets the redistribution ratio to 1. Thus, since the first and second M / I flow rates are not adjusted, the first and second M / I flow rates set by the first and second M / I flow rate calculation units 43 and 46 are set as the first and second target M / I flow rates of the target flow rate setting unit 31. Consequently, the first and second M / O flow rates set by the first and second M / O flow rate calculation units 42 and 45 are set as the first and second target M / O flow rates of the target flow rate setting unit 31.

[0069] On the other hand, when the total flow rate is greater than the maximum discharge flow rate, the redistribution calculation unit 47 sets the value obtained by dividing the specified flow rate by the first target M / I flow rate as the redistribution ratio. Furthermore, the first and second M / I flow rates are each multiplied by the redistribution ratio. Thus, the first and second selection units 48 and 49 select the first and second M / I flow rates divided by the redistribution ratio. Therefore, the first and second M / I flow rates divided by the redistribution ratio are set as the first and second target M / I flow rates of the target flow setting unit 31. Furthermore, the first and second flow rate adjustment units 50 and 51 adjust the first and second M / I flow rates based on the calculated redistribution ratio. Thus, the adjusted first and second M / I flow rates are set as the first and second target M / I flow rates of the target flow setting unit 31.

[0070] The first and second M / O flow rate control units 32 control the openings of the first and second liquid discharge control valves 14 and 16 based on the first and second target M / O flow rates set by the target flow rate setting unit 31 and the pressures detected by the pressure sensors 18R, 18H, 19R, and 19H. This allows the first and second target M / O flow rates to be discharged from the hydraulic cylinders 2 and 3 in accordance with the amount of operation of the operating levers 20a and 20b. Consequently, the hydraulic cylinders 2 and 3 can be operated at a speed corresponding to the amount of operation of the operating levers 20a and 20b.

[0071] Furthermore, the first and second correction units 34 and 36 correct the first and second target M / I flow rates set by the target flow rate setting unit 31. This causes the first corrected M / I flow rate to be set greater than the first target M / I flow rate, and the second corrected M / I flow rate to be set greater than the second target M / I flow rate. Furthermore, the first and second M / I flow rate control units 35 and 37 calculate the target openings of the first and second inlet control valves 13 and 15 based on the first and second corrected M / I flow rates and the pressures detected by the pressure sensors 17, 18R, 18H, 19R, and 19H. This controls the openings of the first and second inlet control valves 13 and 15 to openings corresponding to the corrected M / I flow rates. Furthermore, when the respective target openings are greater than the first and second upper limit openings, the openings of the first and second inlet control valves 13 and 15 are limited to the first and second upper limit openings. This allows pressure compensation in each hydraulic cylinder 2 and 3.

[0072] Furthermore, the total flow rate calculation unit 38 calculates the total flow rate. Furthermore, the correction calculation unit 39 corrects the total flow rate calculated by the total flow rate calculation unit 38. Furthermore, the correction calculation unit 39 sets the discharge flow rate of the hydraulic pump 11 based on the corrected total flow rate. Furthermore, the correction calculation unit 39 outputs a pump command to the variable displacement device 12 based on the set discharge flow rate. In this way, hydraulic fluid is discharged from the hydraulic pump 11 at the set discharge flow rate. This allows hydraulic fluid to be supplied to each hydraulic cylinder 2 and 3 at flow rates corresponding to the first and second target M / O flow rates, respectively.

[0073] In this manner, in the hydraulic drive system 1, when the combined flow rate exceeds a predetermined flow rate when the operating levers 20a and 20b are operated simultaneously, the target M / I flow rate is adjusted so that the combined flow rate falls within the maximum discharge flow rate. Furthermore, the control device 21 adjusts the target M / O flow rate based on the adjusted target M / I flow rate. This prevents concentrated supply of hydraulic fluid to any one hydraulic cylinder 2 or 3. This ensures operability of the hydraulic cylinders 2 and 3 when multiple operating levers 20a and 20b are operated simultaneously.

[0074] Furthermore, in the hydraulic drive system 1, the control device 21 resets the target M / I flow rate and the target M / O flow rate based on the redistribution ratio, which is the predetermined flow rate ratio. Therefore, when multiple hydraulic actuators 2 and 3 are operated simultaneously, any impact on the operability of each hydraulic cylinder 2 and 3 can be suppressed. Furthermore, in the hydraulic drive system 1, the control device 21 controls the opening of the inlet control valves 13 and 15 based on the upstream and downstream pressures of the inlet control valves 13 and 15 and the target M / I flow rate. Therefore, when multiple hydraulic actuators 2 and 3 are operated simultaneously, the target inlet flow rate of hydraulic fluid can be supplied to each hydraulic cylinder 2 and 3, even if the load pressures of each hydraulic cylinder 2 and 3 differ. Consequently, a decrease in the operability of the hydraulic cylinders 2 and 3 when multiple hydraulic actuators 2 and 3 are operated simultaneously can be suppressed.

[0075] Furthermore, in the hydraulic drive system 1, the control device 21 sets the upper limit openings of the inlet control valves 13 and 15 so that the discharge pressure of the hydraulic pump 11 is greater than the maximum load pressure among the load pressures of the hydraulic cylinders 2 and 3. This prevents a situation in which flow is not supplied to the hydraulic cylinders 2 and 3 with higher load pressures when multiple hydraulic actuators 2 and 3 are operated simultaneously.

[0076] <Other Implementation Methods>

[0077] In the hydraulic drive system 1 of this embodiment, inlet and outlet control valves are provided for all hydraulic actuators, but this configuration is not essential. Specifically, an inlet and outlet control valve may be provided for at least one of the multiple hydraulic actuators. Furthermore, directional control valves may be provided for the remaining hydraulic actuators to control the inlet and outlet flow rates on a one-to-one basis.

[0078] In the hydraulic drive system 1 of this embodiment, the pressure of the pipe connecting the first discharge control valve 14 and the tank 10 is close to the tank pressure. However, the pressure of the pipe may be detected by a pressure sensor or estimated from the target discharge flow rate.

[0079] In the hydraulic drive system 1 of this embodiment, when the operating levers 20a and 20b are individually operated, the openings of the inlet control valves 13 and 15 may be controlled to predetermined openings regardless of the operation amounts of the operating levers 20a and 20b.

[0080] Alternatively, the hydraulic drive system 1 of this embodiment may be provided with control valves 13 and 15 for controlling the inflow flow rate and control valves 14 and 16 for controlling the outflow flow rate, respectively, for the hydraulic actuators 2 and 3, but this configuration is not necessarily limited to this. For example, the hydraulic cylinders 2 and 3 may be provided with rod-side control valves for controlling the supply and discharge of working fluid to the rod-side ports 2c and 3c, and head-side control valves for controlling the supply and discharge of working fluid to the head-side ports 2d and 3d. Furthermore, when working fluid is supplied to the rod-side ports 2c and 3c, the rod-side control valves function as inflow control valves, while the head-side control valves function as outflow control valves. Conversely, when working fluid is supplied to the head-side ports 2d and 3d, the head-side control valves function as inflow control valves, while the rod-side control valves function as inflow control valves. A hydraulic drive system configured in this manner also achieves the same effects as the hydraulic drive system 1.

[0081] Furthermore, in the hydraulic drive system 1 of this embodiment, the hydraulic cylinders 2 and 3 may be operated based on operating instructions output from an operating device to achieve automatic operation. Specifically, the operating device determines the movement of the hydraulic cylinders 2 and 3 based on various sensors and programs. The operating device then outputs operating instructions corresponding to the determined movement to the control device 21. This enables automatic operation of the hydraulic cylinders 2 and 3. Furthermore, the operating device and the control device 21 may be integrally formed.

[0082] Based on the above description, many modifications and other embodiments of the present invention will be apparent to those skilled in the art. Therefore, the above description should be construed as merely illustrative and provided to inform those skilled in the art of the best mode for carrying out the present invention. The specific details of the structure and / or function may be substantially altered without departing from the spirit of the present invention.

[0083] Explanation of symbols:

[0084] 1. Hydraulic drive system

[0085] 2 First hydraulic cylinder

[0086] 2b rod

[0087] 2g pressure part

[0088] 3 Second hydraulic cylinder

[0089] 3b rod

[0090] 3g pressure part

[0091] 10 cans

[0092] 11 Hydraulic pump

[0093] 13 First liquid inlet control valve

[0094] 14 First liquid outlet control valve

[0095] 15 Second liquid inlet control valve

[0096] 16 Second liquid outlet control valve

[0097] 17 Discharge pressure sensor (third pressure sensor)

[0098] 18H Head side pressure sensor (first pressure sensor or second pressure sensor)

[0099] 18R Rod-side pressure sensor (first pressure sensor or second pressure sensor)

[0100] 19H Head side pressure sensor (first pressure sensor or second pressure sensor)

[0101] 19R Rod-side pressure sensor (first pressure sensor or second pressure sensor)

[0102] 20 Operating device

[0103] 21 Control device.

Claims

1. A hydraulic drive system comprising: A hydraulic pump capable of varying the discharge flow rate of the working fluid; an inlet control valve for controlling the inlet flow rate of the working fluid flowing from the hydraulic pump to the hydraulic actuator; A liquid outlet control valve is provided independently of the liquid inlet control valve and controls the outflow rate of the working fluid discharged from the hydraulic actuator to the tank; An operating device for outputting operating instructions; a first pressure sensor for detecting a discharge pressure of the hydraulic actuator; and a control device for setting a target liquid outflow rate according to an operation instruction from the operating device and controlling the opening of the liquid outflow control valve based on the discharge pressure detected by the first pressure sensor and the target liquid outflow rate; The liquid discharge control valve discharges the working fluid pressed out from the hydraulic actuator into the tank according to the instruction from the control device. The control device sets a target fluid discharge flow rate based on a fluid discharge side pressure receiving area of ​​a pressure receiving portion of the hydraulic actuator that presses out hydraulic fluid from the hydraulic actuator and a target speed corresponding to an operation command from the operating device.

2. The hydraulic drive system according to claim 1, characterized in that: The hydraulic actuator is a hydraulic cylinder with a rod, The control device sets a target liquid discharge flow rate based on a target speed and a pressure receiving area on a liquid discharge side of the pressure receiving portion of the rod.

3. The hydraulic drive system according to claim 1, characterized in that: The control device controls the discharge flow rate of the hydraulic pump and the opening degree of the fluid inlet control valve so that a target fluid inlet flow rate corresponding to a target fluid outlet flow rate is supplied to the hydraulic actuator.

4. The hydraulic drive system according to claim 1, characterized in that: A second pressure sensor is further provided to detect the inflow pressure of the hydraulic actuator. The control device controls the opening of the liquid inlet control valve based on the front and rear pressures of the liquid inlet control valve and a correction flow greater than the target liquid inlet flow. The front and rear pressures of the liquid inlet control valve are calculated based on the discharge pressure detected by the first pressure sensor and the inflow pressure detected by the second pressure sensor.

5. The hydraulic drive system according to claim 4, wherein: comprising: a plurality of liquid inlet control valves including the liquid inlet control valve; and including a plurality of liquid outlet control valves including the liquid outlet control valve, The operating device outputs operating instructions corresponding to a plurality of hydraulic actuators including the hydraulic actuator, Each of the plurality of liquid inlet control valves controls the liquid inlet flow from the hydraulic pump to the corresponding hydraulic actuator. Each of the plurality of liquid outlet control valves controls the liquid outlet flow rate discharged from the corresponding hydraulic actuator to the tank. When at least one operation instruction is output, the control device adjusts each target fluid inlet flow rate in such a way that the total fluid inlet flow rate converges to the prescribed flow rate, and adjusts the target fluid outlet flow rate according to the adjusted fluid inlet flow rate, when the total fluid inlet flow rate supplied to the hydraulic actuator corresponding to the output operation instruction is greater than the prescribed flow rate.

6. The hydraulic drive system according to claim 5, characterized in that: The control device adjusts the target liquid inlet flow rate and the target liquid outlet flow rate according to the ratio of each liquid inlet flow rate to the total flow rate.

7. The hydraulic drive system according to claim 5, wherein: comprising: a plurality of second pressure sensors for respectively detecting the inflow pressure of the hydraulic actuator; and a third pressure sensor for detecting the discharge pressure of the hydraulic pump, The control device controls the opening of the liquid inlet control valve based on the front and rear pressures of each liquid inlet control valve and the target liquid inlet flow rate. The front and rear pressures of each liquid inlet control valve are calculated based on the inflow pressure detected by each of the multiple second pressure sensors and the discharge pressure detected by the third pressure sensor.

8. The hydraulic drive system according to claim 7, characterized in that: The control device sets the upper limit opening of each of the plurality of liquid inlet control valves based on the inflow pressure detected by each of the plurality of second pressure sensors and the discharge pressure detected by the third pressure sensor so that the discharge pressure is greater than the maximum load pressure among the load pressures of the plurality of hydraulic actuators.

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