JP7572280B2 - Hydraulic drive systems for construction machinery - Google Patents

Description

The present invention relates to a hydraulic drive system for construction machinery such as a hydraulic excavator, and in particular to a hydraulic drive system for construction machinery in which multiple hydraulic actuators and multiple dual-discharge, fixed-displacement hydraulic pumps are connected to form multiple closed circuits.

As a hydraulic drive system for construction machinery such as a hydraulic excavator, a closed circuit type hydraulic drive system in which multiple hydraulic actuators and multiple dual-discharge fixed displacement hydraulic pumps are connected to form multiple closed circuits, and the multiple hydraulic pumps are each driven by multiple electric motors, is described in, for example, Figures 1 and 6 of Patent Document 1.

For example, Patent Document 2 describes an open-circuit three-pump system that includes three pumps, two variable-displacement first and second hydraulic pumps and one fixed-displacement third hydraulic pump, and that is connected to a number of different hydraulic actuators via a number of open-center directional control valves to drive the respective actuators.

In the three-pump system described in Patent Document 2, the first and second hydraulic pumps are equipped with a common regulator, which induces the discharge pressure of the third hydraulic pump in addition to the discharge pressures of the first and second hydraulic pumps. Even if the discharge pressure of any of the first to third hydraulic pumps increases, horsepower control is performed to reduce the flow rate of the first and second hydraulic pumps and reduce the absorption horsepower of each of the first and second hydraulic pumps, thereby preventing overload on the engine.
WO2013-105357 publication Patent No. 6619314

Construction machinery such as hydraulic excavators have traditionally been equipped with an open-circuit three-pump system as described in Patent Document 2 as a hydraulic drive system.

In response to this, in recent years, with a view to saving energy, development of closed circuit hydraulic drive systems such as those described in Patent Document 1 has been progressing. In closed circuit hydraulic systems, a hydraulic pump is directly connected to a hydraulic actuator to form a closed circuit, and the hydraulic actuator is directly driven by the hydraulic pump. This eliminates pressure loss and shunt leaks caused by open center directional control valves, and can achieve energy savings.

However, in the closed circuit hydraulic drive system described in Patent Document 1, when multiple hydraulic actuators are driven simultaneously, if the load on the multiple hydraulic actuators increases, the discharge pressure of the multiple hydraulic pumps increases, and the power of each pump increases, resulting in increased power consumption.

In addition, in the open circuit type three-pump system described in Patent Document 2, when multiple hydraulic actuators are driven simultaneously, if the load on any of the multiple hydraulic actuators increases and the discharge pressure of the hydraulic pump rises, the discharge flow rate of each of the multiple hydraulic pumps is reduced by horsepower control, and the reduced flow rate of pressurized oil is supplied to the multiple hydraulic actuators. This reduces the drive speed of the multiple hydraulic actuators together, ensuring a speed balance between the multiple hydraulic actuators and providing good combined operability.

In contrast, in the closed circuit hydraulic drive system described in Patent Document 1, even if horsepower control is applied to control the hydraulic pump, when multiple hydraulic actuators are driven simultaneously, if the load on one of the hydraulic actuators increases and the discharge pressure of the hydraulic pump rises, only the discharge flow rate of the hydraulic pump of the hydraulic actuator with the increased load decreases, causing the speed balance between the multiple hydraulic actuators to be lost and the combined operability to deteriorate.

The object of the present invention is to provide a closed-circuit hydraulic drive system for construction machinery that reduces the power consumption of the hydraulic pump when multiple hydraulic actuators are driven simultaneously, ensures a good speed balance between the multiple hydraulic actuators, and provides good combined operability.

In order to solve the above-mentioned problems, the present invention provides a hydraulic drive system for a construction machine including a plurality of fixed displacement dual discharge type hydraulic pumps, a plurality of hydraulic actuators connected in a closed circuit to each of the plurality of hydraulic pumps, a plurality of electric motors for driving each of the plurality of hydraulic pumps, and a plurality of operating devices for instructing the operation of each of a plurality of driven bodies driven by the plurality of hydraulic actuators, the system further comprising a plurality of pressure sensors for detecting the discharge pressures of each of the plurality of hydraulic pumps, a plurality of operation sensors for detecting the operation amounts of each of the plurality of operating devices, and a controller for controlling the plurality of electric motors, the controller controlling the plurality of electric motors, when an operating device corresponding to at least two specific hydraulic actuators among the plurality of hydraulic actuators is operated so that at least two specific hydraulic actuators among the plurality of hydraulic actuators are simultaneously driven, based on the discharge pressures of each of the plurality of hydraulic pumps detected by the plurality of pressure sensors and the operation amounts of each of the plurality of operating devices detected by the plurality of operation sensors, so that the power consumption of the hydraulic pumps corresponding to the at least two specific hydraulic actuators among the plurality of hydraulic pumps does not exceed a preset pump power. The controller controls the rotation speed of the electric motors corresponding to the at least two specific hydraulic actuators among the electric motors , and the controller presets, in addition to the pump power, a pump set capacity equal to the capacity of the hydraulic pump corresponding to the at least two specific hydraulic actuators, calculates a rotation speed limit value of the electric motor corresponding to the at least two specific hydraulic actuators based on the discharge pressures of the hydraulic pumps corresponding to the at least two specific hydraulic actuators detected by the multiple pressure sensors, the pump power, and the pump set capacity, calculates a first target rotation speed of the electric motor corresponding to the at least two specific hydraulic actuators based on the operation amount of the operating device corresponding to the at least two specific hydraulic actuators detected by the multiple operation sensors, calculates a second target rotation speed of the electric motor corresponding to the at least two specific hydraulic actuators by correcting the first target rotation speed of the electric motor corresponding to the at least two specific hydraulic actuators so as not to exceed the rotation speed limit value, and controls the rotation speed of the electric motor corresponding to the at least two specific hydraulic actuators based on the second target rotation speed .

This makes it possible to perform control that simulates the horsepower control of an open-circuit three-pump system, reducing the power consumption of the hydraulic pump and ensuring a good speed balance between multiple hydraulic actuators, resulting in good combined operability.

According to the present invention, it is possible to perform control that simulates the horsepower control of an open-circuit three-pump system, reducing the power consumption of the hydraulic pump and ensuring a good speed balance between multiple hydraulic actuators, thereby achieving good combined operability.

1 is a diagram showing a hydraulic excavator as a representative example of a construction machine on which the hydraulic drive system of the present invention is mounted. 1 is a diagram showing a hydraulic drive system of a construction machine according to an embodiment of the present invention. FIG. 4 is a functional block diagram showing the calculation contents of a controller. 4 is a functional block diagram showing details of the calculation contents of a limit value calculation unit. FIG. 4 is a functional block diagram showing details of calculation contents of a composite operation determination unit. FIG. FIG. 4 is a functional block diagram showing details of calculation contents of a rotation speed calculation unit. FIG. 13 is a diagram showing a rotation speed reduction rate characteristic set in a table. FIG. 13 is a diagram showing a target rotation speed characteristic set in a table. FIG. 1 is a diagram showing a three-pump system that is an example of an open-circuit hydraulic drive system. FIG. 11 is a diagram showing torque control (horsepower control) of a regulator and torque control characteristics (horsepower control characteristics) obtained by a spring.

The following describes an embodiment of the present invention with reference to the drawings.

~Construction machinery (hydraulic excavators)~
FIG. 1 is a diagram showing a hydraulic excavator, which is a typical example of a construction machine on which the hydraulic drive system of the present invention is mounted.

In FIG. 1, the hydraulic excavator includes a revolving body 300, a traveling body 301, and a front work machine 302, and the front work machine 302 has a boom 306, an arm 307, and a bucket 308. The revolving body 300 is mounted on the upper center of the traveling body 301 so as to be able to rotate, and rotates on the traveling body 301 by the rotation of the revolving motor 22. A swing post 303 is attached to the front of the revolving body 300, and the front work machine 302 is attached to the swing post 303 so as to be able to move up and down. The swing post 303 can rotate horizontally relative to the revolving body 300 by the extension and contraction of the swing cylinder 20 (see FIG. 2), and the boom 306, arm 307, and bucket 308 of the front work machine 302 can rotate up and down by the extension and contraction of the boom cylinder 17, arm cylinder 18, and bucket cylinder 19.

Crawler-type left and right running devices 301a, 301b and a blade 304 are attached to the central frame of the running body 301. The left and right running devices 301a, 301b are driven by left and right running motors 23, 24, respectively, to run. The blade 304 moves up and down by extending and retracting the blade cylinder 21.

The rotating body 300 is formed with a cab 350, which is provided with a driver's seat 351 and left and right lever-type operating devices 309, 310 that control the operation of the boom 306, arm 307, bucket 308, and rotating body 300.

In addition, inside the cab 350, there are provided left and right travel operation devices 311, 312 of the lever/pedal type that instruct the operation of the left and right travel devices 301a, 301b, a pedal type swing operation device 313 (see Figure 2) that instructs the operation of the swing post 303, and a lever type blade operation device 314 (see Figure 2) that instructs the operation of the blade 304.

The operation levers of the left and right operation devices 309, 310 can be operated in all directions based on the cross directions of left and right and front and rear, respectively. When the operation lever of the left operation device 309 is operated in the left and right direction, the left operation device 309 functions as an arm operation device 309-1 (see FIG. 2), and when the operation lever of the left operation device 309 is operated in the front and rear direction, the left operation device 309 functions as a swing operation device 309-2 (see FIG. 2). When the operation lever of the right operation device 310 is operated in the front and rear direction, the right operation device 310 functions as a boom operation device 310-1 (see FIG. 2), and when the operation lever of the right operation device 310 is operated in the left and right direction, the right operation device 310 functions as a bucket operation device 310-2 (see FIG. 2).

Here, "left direction" and "right direction" refer to the left and right directions as seen by the operator seated in the driver's seat 351, and "forward direction" and "rearward direction" refer to the forward and rearward directions as seen by the operator seated in the driver's seat 351.

~Hydraulic drive system 1~
FIG. 2 is a diagram showing a hydraulic drive system for a construction machine according to one embodiment of the present invention.

In FIG. 2, the hydraulic drive system according to this embodiment includes a plurality of fixed displacement, dual discharge hydraulic pumps 9-16 including a boom pump 9, an arm pump 10, a bucket pump 11, a swing pump 12, a blade pump 13, a slewing pump 14, a left traveling pump 15, and a right traveling pump 16; a plurality of hydraulic actuators 17-24 including the boom cylinder 17, an arm cylinder 18, a bucket cylinder 19, a swing cylinder 20, a blade cylinder 21, a slewing motor 22, a left traveling motor 23, and a right traveling motor 24, each connected to the plurality of hydraulic pumps 9-16 by a closed circuit A-H; and a plurality of electric motors 1-8 including a boom electric motor 1, an arm electric motor 2, a bucket electric motor 3, a swing electric motor 4, a blade electric motor 5, a slewing electric motor 6, a left traveling electric motor 7, and a right traveling electric motor 8, which drive the plurality of hydraulic pumps 9-16, respectively.

The closed circuit A includes a first supply line (bottom-side pipeline line) 41 and a second supply line (rod-side pipeline line) 42 that connect the two discharge ports of the boom pump 9 to the rod-side chamber 79 and the bottom-side chamber 80 of the boom cylinder 17. Similarly, the closed circuits B to E include first supply lines (bottom-side pipeline lines) 43, 45, 47, 49 and second supply lines (rod-side pipeline lines) 44, 46, 48, 50 that connect the two discharge ports of the arm pump 10, the bucket pump 11, the swing pump 12, and the blade pump 13 to the rod-side chambers 81, 83, 85, 87 and the bottom-side chambers 82, 84, 86, 88 of the arm cylinder 18, the bucket cylinder 19, the swing cylinder 20, and the blade cylinder 21.

The closed circuit F includes a first supply line 51 and a second supply line 52 that connect the two discharge ports of the swivel pump 14 to the first port 89 and the second port 90 of the swivel motor 22, and the closed circuits G and H similarly include first supply lines 53 and 55 and second supply lines 54 and 56 that connect the two discharge ports of the left traveling pump 15 and the right traveling pump 16 to the first ports 91 and 93 and the second ports 92 and 94 of the left traveling motor 23 and the right traveling motor 24.

The closed circuit A also includes relief valves 25, 26 and a shuttle valve 95 connected between the first supply line 41 and the second supply line 42. Similarly, the closed circuits B to H also include relief valves 27, 28; 29, 30; 31, 32; 33, 34; 35, 36; 37, 38; 39, 40 and shuttle valves 96, 97, 98, 99, 100, 101, 102 connected between the first supply lines 43, 45, 47, 49, 51, 53, 55 and the second supply lines 44, 46, 48, 50, 52, 54, 56, respectively.

The relief valves 25, 26-39, 40 open when the pressure in the high-pressure supply line of the first supply line 41, 43, 45, 47, 49, 51, 53, 55 and the second supply line 42, 44, 46, 48, 50, 52, 54, 56 exceeds the set pressure, and regulate the circuit pressure so that the maximum load pressure of the closed circuits A-H does not exceed the set pressure. The shuttle valves 95-102 select and output the higher pressure of the first supply line 41, 43, 45, 47, 49, 51, 53, 55 and the second supply line 42, 44, 46, 48, 50, 52, 54, 56. This output pressure is detected by pressure sensors 103-110 (described later) as the discharge pressure of the hydraulic pumps 9-16.

The closed circuit A further includes a first tank line 67 that branches off from the first supply line 41 and leads to the tank 77, a check valve 57 that is provided in the first tank line 67 and allows flow from the tank 77 to the first supply line 41 but prohibits flow in the opposite direction, a second tank line 68 that branches off from the second supply line 42 and leads to the tank 77, and an operated check valve 58 that is provided in the second tank line 68 and allows flow from the tank 77 to the second supply line 42, but prohibits flow from the second supply line 42 to the tank 77 when the pressure of the first supply line 41 is lower than a set pressure and allows flow when the pressure is higher than the set pressure.

Similarly, closed circuits B, C, D, and E each have a first tank line 69, 71, 73, and 75, check valves 59, 61, 63, and 65, a second tank line 70, 72, 74, and 76, and operated check valves 60, 62, 64, and 66, respectively.

The boom cylinder 17, arm cylinder 18, bucket cylinder 19, swing cylinder 20, and blade cylinder 21 are each a single-rod hydraulic cylinder. In a single-rod hydraulic cylinder, the pressure-receiving area is different between the rod side chamber and the bottom side chamber (rod side < bottom side). When the hydraulic cylinder is driven by the supply of pressure oil from the hydraulic pump, the difference in pressure-receiving area causes a flow rate difference between the pressure oil flowing into the rod side chamber and the pressure oil flowing out of the bottom side chamber, or between the pressure oil flowing into the bottom side chamber and the pressure oil flowing out of the rod side chamber. The first tank lines 67, 69, 71, 73, 75, check valves 57, 59, 61, 63, 65, second tank lines 68, 70, 72, 74, 76, and operate check valves 58, 60, 62, 64, 66 discharge the excess pressure oil due to the flow rate difference into the tank 77 and absorb the shortage of pressure oil by drawing it from the tank.

The boom cylinder 17, arm cylinder 18 and bucket cylinder 19 may extend or contract due to the weight of the front work machine 302, and even in this case, it is necessary to open the operate check valves 58, 60 and 62 to drain the excess pressurized oil caused by the difference in pressure-receiving area between the rod side chamber and the bottom side chamber into the tank 77. For this purpose, the first supply lines 41, 43, 45 and the second supply lines 42, 44, 46 are provided with a pressure adjustment mechanism including a throttle and an operated check valve which ensures a predetermined pressure in the first supply lines 41, 43, 45 (or the second supply lines 42, 44, 46) and keeps the pressure in the second supply lines 42, 44, 46 (or the first supply lines 41, 43, 45) from becoming higher than the pressure in the first supply lines 41, 43, 45 (or the second supply lines 42, 44, 46) when the boom cylinder 17, the arm cylinder 18 and the bucket cylinder 19 contract (or extend) due to the weight of the front work machine 302. Furthermore, by providing this pressure adjustment mechanism, even if the boom cylinder 17, arm cylinder 18, and bucket cylinder 19 are contracted (or extended) by the weight of the front work machine 302, the shuttle valves 95-97 can detect the discharge pressure of the hydraulic pumps 9-11, and the pressure sensors 103-105 can detect the discharge pressure of the hydraulic pumps 9-11. This pressure adjustment mechanism is described in detail in the applicant's Japanese patent application "Patent Application No. 2020-053376".

As described above, the hydraulic drive system of this embodiment is configured as a closed circuit type hydraulic drive system including a closed circuit A for the boom that drives the boom cylinder 17, a closed circuit B for the arm that drives the arm cylinder 18, a closed circuit C for the bucket that drives the bucket cylinder 19, a closed circuit D for the swing that drives the swing cylinder 20, a closed circuit E for the blade that drives the blade cylinder 21, a closed circuit F for rotation that drives the rotation motor 22, a closed circuit G for left travel that drives the left travel motor 23, and a closed circuit H for right travel that drives the right travel motor.

~Hydraulic drive system 2~
In addition, the hydraulic drive system of this embodiment includes a plurality of operating devices 309-1 to 314 that instruct the operation of each of a plurality of driven bodies driven by a plurality of hydraulic actuators 19 to 24, a plurality of pressure sensors 103 to 110 that detect the discharge pressure of each of the plurality of hydraulic pumps 9 to 16, a plurality of operation sensors 209-1 to 214 that detect the operation amounts of each of the plurality of operating devices 309 to 314, and a controller 78.

The multiple driven bodies include a boom 306, an arm 307, a bucket 308, a swing post 303, a blade 304, a rotating body 300, and left and right traveling devices 301a, 301b, and the multiple operating devices 309-1 to 314 include a boom operating device 310-1, an arm operating device 309-1, a bucket operating device 310-2, a swing operating device 313, a blade operating device 314, a swing operating device 309-2, a left traveling operating device 311, and a right traveling operating device 312.

The multiple pressure sensors 103-110 also include a boom pressure sensor 103, an arm pressure sensor 104, a bucket pressure sensor 105, a swing pressure sensor 106, a blade pressure sensor 107, a rotation pressure sensor 108, a left traveling pressure sensor 109, and a right traveling pressure sensor 110, which detect the discharge pressure of the hydraulic pumps 9-16 output from the shuttle valves 95-102 and generate pressure signals.

The multiple operating devices 309-1 to 314 are electric lever type devices that generate an electric signal according to the amount of operation of the operating lever/pedal, and the multiple operation sensors 209-1 to 214 include operation sensors 209-1, 209-2, 210-1, 210-2, 211 to 214 that detect the electric signal and generate an operation signal.

Operating devices 309-1 to 314 may be hydraulic pilot systems that generate conventional operating pilot pressure. In that case, a pressure sensor that detects the operating pilot pressure is provided as an operating sensor, and an operating signal is generated by this pressure sensor.

The controller 78 inputs pressure signals from the pressure sensors 103 to 110 and operation signals from the operation sensors 209-1 to 214, performs a predetermined calculation process, calculates the target rotation speeds of the electric motors 1 to 8, and controls the rotation direction and rotation speeds of the electric motors 1 to 8.

In this embodiment, electric motors 1 to 8 are servo motors. Hereinafter, electric motors 1 to 8 may be referred to as servo motors.

~Controller 78~
FIG. 3 is a functional block diagram showing the calculation contents of the controller 78.

In FIG. 3, pressure signals from pressure sensors 103-110 and operation signals from operation devices 309-314 are fed to controller 78.

The controller 78 includes a limit value calculation unit 78-1 that calculates the rotation speed limit values Nlimita and Nlimitb of the servo motors 1 to 3, 7, and 8, which are electric motors corresponding to the boom cylinder 17, arm cylinder 18, bucket cylinder 19, left traveling motor 23, and right traveling motor 24 (at least two specific actuators) among the electric motors 1 to 8, from the pressure signals from the pressure sensors 103 to 110; a composite operation determination unit 78-2 that determines a composite operation from the pressure signals from the pressure sensors 103, 105 to 108; and a rotation speed calculation unit 78-3 that calculates the target rotation speeds of the servo motors 1 to 8 based on the operation signals from the operation devices 309 to 314.

Figure 3A is a functional block diagram showing the details of the calculation content of the limit value calculation unit 78-1.

3A, limit value calculation unit 78-1 selects in a maximum value selection unit Ma the higher of the pressure signals from pressure sensor 103 (boom pressure sensor) that detects the discharge pressure of boom pump 9 and pressure sensor 105 (bucket pressure sensor) that detects the discharge pressure of bucket pump 11, calculates in an average value calculation unit Aa the average value of this selected pressure and the pressure signal from pressure sensor 104 (arm pressure sensor) that detects the discharge pressure of arm pump 10, and calculates the pump flow rate Qa (m3/min) of a virtual hydraulic pump that discharges pressure oil at the calculated pressure and consumes the pump power Hset using this average pressure (N/ ^m2 ), a preset pump power Hset (N·m/sec), and the numerical value "60" according to the following equation ( ¹ ). Next, using the pump flow rate Qa, a preset pump set capacity Dset (L (liters)/revolution (rev)), and the numerical value "1000", the pump speed Na (rev/min) of a virtual hydraulic pump having a pump capacity equal to the pump set capacity Dset is calculated according to the following formula (2).

Pump flow rate = (pump power Hset × 60) ÷ pressure (1)
Pump speed = (pump flow rate × 1000) ÷ pump set capacity Dset (2)
Here, the present invention operates a closed circuit system to simulate the horsepower control (described later) of a conventional three-pump system, and the "pump power Hset" is set to a value equal to the maximum horsepower H12max (HP) (described later) of the horsepower control performed by the pump regulator of the three-pump system. Also, the "pump set capacity Dset" is set to a value equal to the capacity of the hydraulic pumps 9, 10, and 11 of the boom/arm/bucket.

The limit value calculation unit 78-1 also selects the maximum pressure from among the pressure signals of the pressure sensor 106 (swing pressure sensor) that detects the discharge pressure of the swing pump 12, the pressure sensor 107 (blade pressure sensor) that detects the discharge pressure of the blade pump 13, and the pressure sensor 108 (swirl pressure sensor) that detects the discharge pressure of the swirl pump 14 in a maximum value selection unit Mab, calculates a first rotation speed reduction rate Ra using this selected pressure (pump discharge pressure) and table 124, calculates a first rotation speed limit value Nlimita by multiplying this first rotation speed reduction rate Ra by the pump rotation speed Na calculated by the above formula (2), and outputs this first rotation speed limit value Nlimita to the servo motors 1 to 3.

Figure 4 is a diagram showing the rotation speed reduction rate characteristic set in table 124. In table 124, the rotation speed reduction rate Ra is 1 when the pump discharge pressure selected in the maximum value selection section Mab is equal to or lower than a predetermined pressure P0, and when the pump discharge pressure rises to the maximum pressure Pmax, the rotation speed reduction rate Ra is 0.5. The rotation speed reduction rate characteristic is set so that the rotation speed reduction rate Ra decreases proportionally from 1 to 0.5 as the pump discharge pressure increases from P0 to Pmax.

The specified pressure P0 is set to a pressure equal to or slightly higher than the minimum pressure in the pump discharge pressure range when the operating device is operated, and the maximum pressure Pmax is set to a pressure equal to or slightly lower than the relief setting pressure of the relief valve provided in the closed circuit (e.g., relief valves 35, 36 of the closed swing circuit F).

The limit value calculation unit 78-1 further calculates the average value of the pressure signals from the pressure sensor 109 (traveling left pressure sensor) that detects the discharge pressure of the traveling left pump 15 and the pressure sensor 110 (traveling right pressure sensor) that detects the discharge pressure of the traveling right pump 16 in the average value calculation unit Ab, and uses this calculated pressure, the pump power Hset, the pump set capacity Dset, and the numerical values "60" and "1000" to calculate the pump flow rate Qb of a virtual hydraulic pump that discharges pressure oil at the calculated pressure and consumes the pump power Hset using the above formula (1), in the same way as when the pump flow rate Qa and the pump speed Na are calculated to calculate the first speed limit value Nlimita, and calculates the pump speed Nb of a virtual hydraulic pump that has a pump capacity equal to the pump set capacity Dset using the above formula (2).

Here, the pump power Hset for calculating the pump flow rate Qb is set to the same value as the pump power Hset for calculating the pump flow rate Qa, and the pump set capacity Dset for calculating the pump speed Nb is set to the same value as the capacity Dset of the left and right traveling hydraulic pumps 15, 16.

The limit value calculation unit 78-1 also selects the maximum pressure from among the pressure signals of the boom pressure sensor 103, arm pressure sensor 104, bucket pressure sensor 105, swing pressure sensor 106, blade pressure sensor 107, and rotation pressure sensor 108 in a maximum value selection unit Mb, calculates a second rotation speed reduction rate Rb using this selected pressure and table 125, calculates a second rotation speed limit value Nlimitb by multiplying this rotation speed reduction rate Rb by the pump rotation speed Nb calculated by the above formula (2), and outputs this second rotation speed limit value Nlimitb to the servo motors 7 and 8.

Table 125 also has the same rotation speed reduction ratio characteristics as table 124 shown in Figure 4.

Figure 3B is a functional block diagram showing the details of the calculations performed by the composite operation determination unit 78-2.

In FIG. 3B, the composite operation determination unit 78-2 determines in pressure determination units Ja and Jb whether the pressure of the pressure signals from the pressure sensors 103 and 105 is equal to or greater than a preset determination pressure, and if the pressure is equal to or greater than the determination pressure, determines that the operating devices 310-1 and 310-2 of the hydraulic actuators (boom cylinder 17 and bucket cylinder 19) of the closed circuits A and C corresponding to the pressure signals from the pressure sensors 103 and 105 are being operated, and calculates the number of actuators whose operating devices are being operated as the boom/bucket composite operation determination value Jna in the adder unit 126.

Similarly, the composite operation determination unit 78-2 determines whether the pressure of the pressure signal from the pressure sensors 106, 107, 108 is equal to or greater than a preset determination pressure in the pressure determination units Jc, Jd, Je, and if the pressure is equal to or greater than the determination pressure, it determines that the operating devices 314, 315, 309-2 of the hydraulic actuators (swing cylinder 20, blade cylinder 21, and rotation motor 22) of the closed circuits D, E, F corresponding to the pressure signals from the pressure sensors 106, 107, 108 are being operated, and the adder 127 calculates the number of actuators whose operating devices are being operated as the composite operation determination value Jnb for rotation/swing/blade.

The preset judgment pressure is set, for example, to a predetermined pressure P0 (a pressure equal to or slightly higher than the minimum pressure in the pump discharge pressure range when the operating device is operated) as described in FIG. 4.

In addition, instead of a pressure sensor, an operation signal from the operating device may be used to determine whether the operating device is being operated.

Figure 3C is a functional block diagram showing the details of the calculations performed by the rotation speed calculation unit 78-3.

In FIG. 3C, the rotation speed calculation unit 78-3 calculates the first target rotation speeds Nta1 to Nth1 of the servo motors 1 to 8 using the operation signals of the operation devices 309-1 to 314 and tables 116 to 123.

Figure 5 shows the target rotation speed characteristics set in tables 116 to 123. The horizontal axis indicates the amount of operation of the control lever/pedal of the control device, and the vertical axis indicates the first target rotation speed of servo motors 1 to 8. Of the four plane coordinates created by the horizontal and vertical axes, the first quadrant indicates the target rotation speed characteristics when the control lever/pedal is operated in one direction, and the third quadrant indicates the target rotation speed characteristics when the control lever/pedal is operated in the other direction.

Operation devices 309-314 generate a positive operation signal when the operation lever/pedal is operated in one direction, and in the first quadrant of tables 116-123, target rotation speed characteristics are set so that when the operation signal is a positive value, the positive first target rotation speeds Nta1-Nth1 increase as the operation amount increases. The positive first target rotation speeds Nta1-Nth1 are target rotation speeds at which the hydraulic pumps 9-16 rotate the servo motors 1-8 in the direction in which they discharge pressure oil to the first supply lines 41, 43, 45, 47, 49, 51, 53, 55.

In addition, the operating devices 309-314 generate a negative operating signal when the operating lever/pedal is operated in the other direction (the opposite direction to the one direction described above), and in the third quadrant of the tables 116-123, target rotation speed characteristics are set so that when the operating signal is negative, the absolute value of the negative first target rotation speeds Nta1-Nth1 increases as the absolute value of the operating amount increases. The negative first target rotation speeds Nta1-Nth1 are the target rotation speeds at which the servo motors 1-8 rotate in the direction in which the hydraulic pumps 9-16 discharge pressure oil to the second supply lines 42, 44, 46, 48, 50, 52, 54, 56.

The rotation speed calculation unit 78-3 uses limiters 111-115 to restrict the upper and lower limits of the first target rotation speeds Nta1-Nte1 calculated in tables 116-120, and generates second target rotation speeds Nta2-Nte2.

The first rotation speed limit value Nlimita of the boom/arm/bucket servo motors 1-3 calculated by the limit value calculation unit 78-1 described above is input to the boom, arm, and bucket limiters 111-113 as an upper limit value, and the first rotation speed limit value Nlimita is converted to a negative value and input as a lower limit value. The second rotation speed limit value Nlimitb of the left and right traveling servo motors 7 and 8 calculated by the limit value calculation unit 78-1 described above is input to the left and right traveling limiters 114, 115 as an upper limit value, and the second rotation speed limit value Nlimitb is converted to a negative value and input as a lower limit value.

The rotation speed calculation unit 78-3 then divides the second target rotation speeds Nta2, Ntc2 generated by the boom and bucket limiters 111, 113 by the boom/bucket composite operation judgment value (actuator number) calculated by the composite operation judgment unit 78-2 described above in division units Da, Dc to calculate third target rotation speeds Nta3, Ntc3, and outputs the third target rotation speeds Nta3, Ntc3 as the target rotation speeds of servo motors 1, 3. On the other hand, the second target rotation speed Ntb2 generated by the arm limiter 112 and the left and right travel limiters 114, 115 is output as is as the target rotation speeds of servo motors 2, 7, and 8.

The rotation speed calculation unit 78-3 also divides the first target rotation speeds Ntf1 to Nth1 of the servo motors 6, 4, and 5 calculated in tables 121 to 123 by the rotation/swing/blade composite operation determination value (number of actuators) Jnb calculated in the composite operation determination unit 78-2 described above in the division units Df to Dh to calculate second target rotation speeds Ntf2 to Nth2, and outputs the second target rotation speeds Ntf2 to Nth2 as the target rotation speeds of the servo motors 6, 4, and 5.

~Open circuit type hydraulic drive system (comparison example)~
Fig. 6 is a diagram showing an example of an open circuit type hydraulic drive system called a three-pump system. In Fig. 6, the hydraulic actuators are given the same reference numerals as the hydraulic actuators of this embodiment shown in Fig. 2. In addition, although the operating device is of a hydraulic pilot type, for convenience, it is given the same reference numerals as the operating device of this embodiment shown in Fig. 2.

In FIG. 6, the open circuit type three-pump system includes a prime mover (e.g., a diesel engine, hereinafter referred to as the engine) E, a first hydraulic pump P1, a second hydraulic pump P2, and a third hydraulic pump P3, which are main pumps driven by the prime mover E, a pilot pump P4 driven by the engine E in conjunction with the first, second, and third hydraulic pumps P1, P2, and P3, hydraulic actuators 17, 19, and 23 driven by pressure oil discharged from the first hydraulic pump P1, hydraulic actuators 18 and 24 driven by pressure oil discharged from the second hydraulic pump P2, hydraulic actuators 20, 21, and 22 driven by pressure oil discharged from the third hydraulic pump P3, and a control valve V.

The first and second hydraulic pumps P1 and P2 are variable displacement hydraulic pumps. The first and second hydraulic pumps P1 and P2 are composed of a split-flow type hydraulic pump PW equipped with a common regulator PR, and the two discharge ports of the hydraulic pump PW constitute the first and second hydraulic pumps P1 and P2. The third hydraulic pump P3 is a fixed displacement hydraulic pump. The regulator PR is equipped with torque control (horsepower control) pistons Pp1, Pp2, and Pp3 that guide the discharge pressures of the first, second, and third hydraulic pumps P1, P2, and P3, and reduce the capacity (tilt angle of the swash plate) of the first and second hydraulic pumps P1 and P2 as the pressures increase, and a spring Ps that sets the maximum torque available to the first, second, and third hydraulic pumps P1, P2, and P3.

Actuator 21 is a blade cylinder, actuator 22 is a rotation motor, actuator 20 is a swing cylinder, actuator 17 is a boom cylinder, actuator 18 is an arm cylinder, actuator 19 is a bucket cylinder, and actuators 23 and 24 are left and right travel motors.

The control valve V is connected to the pressure oil supply passage of the first hydraulic pump P1 and includes a plurality of open center type directional control valves V9, V10, V11 that respectively control the direction of the pressure oil supplied from the first hydraulic pump P1 to the actuators 23, 17, 19, a plurality of open center type directional control valves V7, V8 that respectively control the direction of the pressure oil supplied from the second hydraulic pump P2 to the actuators 24, 18, a plurality of open center type directional control valves V3, V4, V5 that respectively control the direction of the pressure oil supplied from the third hydraulic pump P3 to the actuators 21, 22, 20, a main relief valve V26 that is provided in the pressure oil supply passage of the first, second and third hydraulic pumps P1, P2, P3 and limits the discharge pressure of the first hydraulic pump P1, a main relief valve V27 that limits the discharge pressure of the second hydraulic pump P2, and a main relief valve V28 that limits the discharge pressure of the third hydraulic pump P3. In this way, the hydraulic drive system in Figure 6 is configured as an open circuit type three-pump system equipped with open center type directional control valves V3 to V11.

When the operating levers/pedals of the operating devices 310-1, 310-2, 311 are in neutral positions, the directional control valves V9, V10, V11 are in neutral positions, and the oil discharged from the first hydraulic pump P1 is returned to the tank T via the directional control valves V9, V10, V11. When any of the operating levers/pedals of the operating devices 310-1, 310-2, 311 is operated, any of the directional control valves V9, V10, V11 is switched, and pressure oil is supplied from the first hydraulic pump P1 to either the travel motor 23, the boom cylinder 17, or the bucket cylinder 19, and either the travel motor 23, the boom cylinder 17, or the bucket cylinder 19 is driven.

When the operating lever/pedal of the operating device 309-1, 312 is in neutral, the directional control valves V7, V8 are in the neutral position, and the oil discharged from the second hydraulic pump P2 is returned to the tank T via the directional control valves V7, V8. When either the operating lever/pedal of the operating device 309-1, 312 is operated, the directional control valves V7, V8 are switched, and pressure oil is supplied from the second hydraulic pump P2 to either the travel motor 24 or the arm cylinder 18, driving either the travel motor 24 or the arm cylinder 18.

When the operating lever/pedal of the operating device 314, 309-2, 313 is in neutral, the oil discharged from the third hydraulic pump P3 is returned to the tank T via the directional control valves V3, V4, V5. When any of the operating levers/pedals of the operating devices 314, 309-2, 313 is operated, the directional control valves V3, V4, V5 are switched, and pressure oil is supplied from the third hydraulic pump P3 to either the blade cylinder 21, the rotation motor 22, or the swing cylinder 20, and either the blade cylinder 21, the rotation motor 22, or the swing cylinder 20 is driven.

When the operating levers/pedals of two or more of the operating devices 309-1 to 314 are operated, the corresponding multiple directional control valves are switched, and pressure oil is supplied from the hydraulic pumps corresponding to the first to third hydraulic pumps P1 to P3 to the corresponding multiple hydraulic actuators, driving those hydraulic actuators.

Figure 7 is a diagram showing the torque control characteristics (horsepower control characteristics) obtained by the torque control (horsepower control) pistons Pp1, Pp2, Pp3 of the regulator PR and the spring Ps. In Figure 7, the horizontal axis is the average value Pd12 (= (Pd1 + Pd2) / 2) of the discharge pressures Pd1, Pd2 of the hydraulic pumps P1, P2, the vertical axis is the capacity of the hydraulic pumps P1, P2 (capacity of the split flow pump PW (tilt angle of the swash plate)) q12, P12max on the horizontal axis is the average value of the maximum discharge pressures of the hydraulic pumps P1, P2 obtained by the main relief valves V26, V27, and q12max on the vertical axis is the maximum capacity (maximum tilt angle) of the hydraulic pumps P1, P2 determined by the structure of the split flow pump PW.

In addition, in FIG. 7, C1 and C2 are characteristic lines C1 and C2 of the maximum torque set by the spring 112u, and the curve (hyperbola) tangent to these characteristic lines C1 and C2 is the maximum torque T12max that can be used by the hydraulic pumps P1 and P2.

By operating the operating lever/pedal of the operating device described above, the actuator is driven by the pressurized oil discharged from the hydraulic pumps P1, P2, and when the total absorption torque of the hydraulic pumps P1, P2 increases to a value on the characteristic lines C1, C2, the capacity q12 of the hydraulic pumps P1, P2 is limited by the torque control pistons Pp1, Pp2 of the regulator PR so that the total absorption torque of the hydraulic pumps P1, P2 does not increase any further. As a result, the total absorption torque of the hydraulic pumps P1, P2 is controlled so as not to exceed the maximum torque T12max.

In Figure 7, the curve indicated by the symbol TE is the rated torque of the prime mover E, and the maximum torque T12max is set to a value smaller than the rated torque TE.

In addition, in FIG. 7, arrows AR1 and AR2 indicate the effect of the torque control piston Pp3. When the discharge pressure or capacity of the third hydraulic pump P3 increases and the absorption torque of the third hydraulic pump P3 increases, the torque control piston Pp3 shifts the characteristic lines C1 and C2 of the maximum torque set by the spring Ps as shown by arrows AR1 and AR2 in FIG. 7, and reduces the maximum torque T12max available to the hydraulic pumps P1 and P2 by the absorption torque of the third hydraulic pump P3. As a result, even during combined operation in which the actuators related to the first and second hydraulic pumps P1 and P2 and the actuators related to the third hydraulic pump P3 are driven simultaneously, the total absorption torque of the first and second hydraulic pumps P1 and P2 and the third hydraulic pump P3 is controlled so as not to exceed the maximum torque T12max (three-pump total torque control).

The total absorption torque of the hydraulic pumps P1, P2 (absorption torque of the split flow pump PW) is expressed as the product of the average value P12 of the discharge pressures of the hydraulic pumps P1, P2 and the capacity q12 of the hydraulic pumps P1, P2, and the total absorption horsepower of the hydraulic pumps P1, P2 (absorption horsepower of the split flow pump PW) is the absorption torque multiplied by the rotation speed of the split flow pump PW. In other words, by replacing the parameters on the vertical axis of Figure 7 with the total discharge flow rate of the hydraulic pumps P1, P2, Figure 7 becomes a diagram showing the horsepower control characteristics.

In this case, the curve (hyperbola) tangent to characteristic lines C1, C2 is the characteristic line of the maximum horsepower H12max available to hydraulic pumps P1, P2, and the maximum horsepower H12max is set to a value smaller than the rated horsepower HE of prime mover E. The hydraulic drive system of the construction machinery is provided with an engine control dial for indicating the target rotation speed of prime mover E, and during normal work, the target rotation speed of prime mover E is set to the maximum. The maximum horsepower H12max is the value obtained by multiplying the rated torque TE of prime mover E by its maximum rotation speed.

In this way, when FIG. 7 is replaced with a diagram showing horsepower control characteristics, by performing torque control as described above, horsepower control or total horsepower control of the three pumps can be performed so that the total absorption horsepower of the first and second hydraulic pumps P1, P2 or the total absorption horsepower of the first and second hydraulic pumps P1, P2 and the third hydraulic pump P3 does not exceed the maximum horsepower H12max.

In addition, during combined operations that drive multiple actuators, such as when driving a boom and arm simultaneously, if the discharge pressure of one of the hydraulic pumps rises as described above, the horsepower control reduces the discharge flow rate of both hydraulic pumps P1 and P2 along characteristic lines C1 and C2, and this reduced flow rate of pressurized oil is supplied to the multiple actuators. This reduces the drive speeds of the multiple actuators together, ensuring a speed balance between the multiple actuators and providing good combined operability.

Furthermore, when two or more of the multiple actuators associated with the third pump P3 are driven simultaneously, such as when turning and front swinging are performed simultaneously, the output horsepower of the third pump P3 is distributed to the multiple hydraulic actuators, and the horsepower consumed by the third pump P3 is controlled so as not to exceed a preset pump power.

～Operation～
Next, the operation of the hydraulic drive system of this embodiment will be described.

<Boom raising operation alone>
When the operating lever of the boom operating device 310 - 1 is operated with the intention of raising the boom, an operation signal from the boom operating device 310 - 1 and a pressure signal from the boom pressure sensor 103 are input to the controller 78 .

The operation signal of the boom operation device 310-1 input to the controller 78 is input to the rotation speed calculation unit 78-3, and the pressure signal of the boom pressure sensor 103 is input to the limit value calculation unit 78-1 and the composite operation determination unit 78-2.

In the limit value calculation unit 78-1, the maximum value selection unit Ma selects the higher pressure of the pressure signal value (boom pressure) of the boom pressure sensor 103 and the pressure signal value (bucket pressure) of the bucket pressure sensor 105. At this time, the operation lever of the bucket operation device 310-2 is not operated, so the maximum value selection unit Ma selects the boom pressure. Next, the average value calculation unit Aa calculates the average value of the boom pressure and the pressure signal value (arm pressure) of the arm pressure sensor, but since the operation lever of the arm operation device 309-1 is not operated, the average value calculation unit Aa calculates 1/2 the boom pressure as the average value, and the pump rotation speed Na is calculated using this average value, the pump power Hset, and the pump set capacity Dset according to the above-mentioned formulas (1) and (2).

At this time, no operating devices other than the boom operating device 310-1 are being operated, and the pressure signal value of the swing pressure sensor (swing pressure), the pressure signal value of the swing pressure sensor (swing pressure), and the pressure signal value of the blade pressure sensor (blade pressure) are approximately 0 MPa. Therefore, the rotation speed reduction rate Ra is calculated as 1 in table 124, this calculated value is multiplied by the pump rotation speed Na, and the first rotation speed limit value Nlimita is output.

In the composite operation determination unit 78-2, the pressure determination unit Ja determines that the boom pressure is equal to or greater than the determination pressure, and the adder 126 calculates 1 as the number of actuators whose operating devices are being operated, and outputs 1 as the boom/bucket composite operation determination value Jna.

In the rotation speed calculation unit 78-3, the first target rotation speed Nta1 corresponding to the value of the operation signal of the boom operation device 310-1 (boom operation amount) is calculated as a positive value in the table 116, and the first rotation speed limit value Nlimita calculated in the limit value calculation unit 78-1 is set as the upper limit value in the limiter 111, and a second target rotation speed Nta2 is calculated in which the first target rotation speed Nta1 is limited to or less than the first rotation speed limit value Nlimita. Furthermore, in the division unit Da, the second target rotation speed Nta2 is divided by the actuator number "1" of the composite operation determination value Jna calculated in the composite operation determination unit 78-2, and a third target rotation speed Nta3 is calculated. This third target rotation speed Nta3 is output as the target rotation speed of the servo motor 1, and the servo motor 1 rotates in the right direction.

When the servo motor 1 rotates to the right, the pressurized oil discharged from the boom pump 9 flows through the second supply line 42 into the bottom side chamber 80 of the boom cylinder 17, and the pressurized oil is discharged from the rod side chamber 79, causing the boom cylinder 17 to extend.

Pressurized oil discharged from the rod side chamber 79 of the boom cylinder 17 passes through the first supply line 41 and is returned to the boom pump 9. The pressure oil that is insufficient due to the area difference between the rod side chamber 79 and the bottom side chamber 80 of the boom cylinder 17 is supplied to the boom pump 9 from the tank 77 through the first tank line 67 and the check valve 57.

<Independent boom lowering operation>
When the operating lever of the boom operation device 310-1 is operated with the intention of lowering the boom, the operation signal of the boom operation device 310-1 and the pressure signal of the boom pressure sensor 103 are input to the controller 78, just as in the case of boom raising, and the limit value calculation unit 78-1 and the composite operation determination unit 78-2 perform calculations similar to those in the case of boom raising.

In addition, in the rotation speed calculation unit 78-3, the first target rotation speed Nta1 is calculated as a negative value in the table 116,
In the limiter 111, in which the negative value of the first rotation speed limit value Nlimita calculated by the limit value calculation unit 78-1 is set as the lower limit value, the first target rotation speed Nta1 is limited to the first rotation speed limit value Nlimita or more to calculate a second target rotation speed Nta2 of a negative value, and further, in the division unit Da, a third target rotation speed Nta3 of a negative value is calculated. This third target rotation speed Nta3 of a negative value is output as the target rotation speed of the servo motor 1, and the servo motor 1 rotates in the left direction.

When the servo motor 1 rotates to the left, the pressurized oil discharged from the boom pump 9 flows through the first supply line 41 into the rod side chamber 79 of the boom cylinder 17, and the pressurized oil is discharged from the bottom side chamber 80, causing the boom cylinder 17 to contract.

The pressurized oil discharged from the bottom side chamber 80 of the boom cylinder 17 passes through the second supply line 42 and is returned to the boom pump 9.

The excess pressure oil due to the area difference between the rod side chamber 79 and the bottom side chamber 80 of the boom cylinder 17 flows back to the tank 77 through the second tank line 68 and the operated check valve 58.

< Bucket Cloud Independent Operation >
When the operation lever of the bucket operation device 310 - 2 is operated with the intention of bucket crowding, an operation signal of the bucket operation device 310 - 2 and a pressure signal of the bucket pressure sensor 105 are input to the controller 78 .

In the limit value calculation section 78-1 of the controller 78, a calculation similar to that for boom raising is performed, except that the bucket pressure is selected as the maximum value in the maximum value selection section Ma, and the first rotation speed limit value Nlimita is output.

In the composite operation determination unit 78-2, the pressure determination unit Jb determines that the bucket pressure is equal to or greater than the determination pressure, and the adder 126 calculates 1 as the number of actuators whose control devices are being operated, just as in the case of boom raising, and outputs 1 as the boom/bucket composite operation determination value Jna.

In addition, in the rotation speed calculation unit 78-3, the third target rotation speed Ntc3 is calculated in the same manner as in the case of boom raising, using the table 118, limiter 113, and division unit Dc. This third target rotation speed Ntc3 is output as the target rotation speed of the servo motor 3, and the servo motor 3 rotates in the right direction.

When the servo motor 3 rotates to the right, the pressurized oil discharged from the bucket pump 11 flows through the second supply line 46 into the bottom side chamber 84 of the bucket cylinder 19, and the pressurized oil is discharged from the rod side chamber 83, causing the bucket cylinder 19 to extend.

Pressurized oil discharged from the rod side chamber 83 of the bucket cylinder 19 passes through the first supply line 45 and is returned to the bucket pump 11. The pressure oil that is insufficient due to the area difference between the rod side chamber 83 and the bottom side chamber 84 of the bucket cylinder 19 is replenished from the tank 77 to the bucket pump 11 through the first tank line 71 and the check valve 61.

<Independent operation of bucket dump>
When the operating lever of bucket operating device 310-2 is operated with the intention of bucket dumping, an operation signal from bucket operating device 310-2 and a pressure signal from bucket pressure sensor 105 are input to controller 78, and limit value calculation unit 78-1 and composite operation determination unit 78-2 perform calculations similar to those in the case of boom raising.

In addition, in the rotation speed calculation unit 78-3, the first target rotation speed Ntc1 is calculated as a negative value in the table 118, the second target rotation speed Ntc2, which is a negative value, is calculated in the limiter 113, and the third target rotation speed Ntc3, which is a negative value, is calculated in the division unit Dc. This third target rotation speed Ntc3, which is a negative value, is output as the target rotation speed of the servo motor 3, and the servo motor 3 rotates in the left direction.

When the servo motor 3 rotates to the left, the pressurized oil discharged from the bucket pump 11 flows through the first supply line 45 into the rod side chamber 83 of the bucket cylinder 19, and the bucket cylinder 19 contracts as the pressurized oil is discharged from the bottom side chamber 84.

The pressurized oil discharged from the bottom side chamber 84 of the bucket cylinder 19 passes through the second supply line 46 and is returned to the bucket pump 11. The excess pressurized oil due to the area difference between the rod side chamber 83 and the bottom side chamber 84 of the bucket cylinder 19 flows back to the tank 77 through the second tank line 72 and the operated check valve 62.

<Independent operation of Arm Cloud>
When the operation lever of the arm operation device 309 - 1 is operated with the intention of arm crowding, an operation signal from the arm operation device 309 - 1 and a pressure signal from the arm pressure sensor 104 are input to the controller 78 .

The operation signal of the operating device 319-1 input to the controller 78 is input to the rotation speed calculation unit 78-3, and the pressure signal of the arm pressure sensor 104 is input to the limit value calculation unit 78-1.

In the limit value calculation unit 78-1, the average value calculation unit Aa calculates the average value of the boom pressure, the maximum value of the bucket pressure, and the arm pressure selected in the maximum value selection unit Aa, but because the operation levers of the boom operation device 310-1 and the bucket operation device 310-2 are not being operated, the average value calculation unit Aa calculates 1/2 the value of the arm pressure as the average value, and uses this calculated value, the pump power Hset, and the pump set capacity Dset to calculate the pump speed Na according to the above-mentioned equations (1) and (2). Except for the fact that the pump speed Na is calculated in this way, the limit value calculation unit 78-1 calculates the first speed limit value Nlimita in the same way as in the case of boom raising, and outputs it to the speed calculation unit 78-3.

In the rotation speed calculation unit 78-3, the first target rotation speed Ntb1 and the second target rotation speed Ntb2 are calculated using the table 117 and the limiter 112 in the same manner as in the boom raising case described above. The second target rotation speed Ntb2 is output as the target rotation speed of the servo motor 2, and the servo motor 2 rotates in the right direction.

When the servo motor 2 rotates to the right, the pressurized oil discharged from the arm pump 10 flows through the second supply line 44 into the bottom side chamber 82 of the arm cylinder 18, and the pressurized oil is discharged from the rod side chamber 81, causing the arm cylinder 18 to extend.

The pressurized oil discharged from the rod side chamber 81 of the arm cylinder 18 passes through the first supply line 43 and is returned to the arm pump 10. The pressure oil that is insufficient due to the area difference between the rod side chamber 81 and the bottom side chamber 82 of the arm cylinder 18 is replenished from the tank 77 to the arm pump 10 through the first tank line 69 and the check valve 59.

<Independent operation of arm dump>
When the operating lever of the arm operating device 309-1 is operated with the intention of arm dumping, the operation signal of the arm operating device 309-1 and the pressure signal of the arm pressure sensor 104 are input to the controller 78, and the limit value calculation unit 78-1 and the composite operation determination unit 78-2 perform calculations similar to those in the case of arm crowding.

In addition, in the rotation speed calculation unit 78-3, the first target rotation speed Ntb1 is calculated as a negative value in the table 117, and a negative second target rotation speed Ntb2 is calculated in the limiter 112. This negative second target rotation speed Ntb2 is output as the target rotation speed of the servo motor 2, and the servo motor 2 rotates in the left direction.

When the servo motor 2 rotates to the left, the pressurized oil discharged from the arm pump 10 flows through the first supply line 43 into the rod side chamber 81 of the arm cylinder 18, and the arm cylinder 18 contracts as the pressurized oil is discharged from the bottom side chamber 82.

The pressure oil discharged from the bottom side chamber 82 of the arm cylinder 18 passes through the second supply line 44 and is returned to the arm pump 10. The excess pressure oil due to the area difference between the rod side chamber 81 and the bottom side chamber 82 of the arm cylinder 18 flows back to the tank 77 through the second tank line 70 and the operated check valve 60.

<Independent operation of forward travel>
When the operation pedals of the left traveling operation device 311 and the right traveling operation device 312 are operated with the intention of traveling forward, operation signals from the operation devices 311, 312 and pressure signals from the left traveling pressure sensor 109 and the right traveling pressure sensor 110 are input to the controller 78.

The operation signals of the operating devices 311, 312 input to the controller 78 are input to the rotation speed calculation unit 78-3, and the pressure signals of the pressure sensors 109, 110 are input to the limit value calculation unit 78-1.

In the limit value calculation unit 78-1, the average value calculation unit Aa calculates the average value of the pressure signal value (left driving pressure) of the left driving pressure sensor 109 and the pressure signal value (right driving pressure) of the right driving pressure sensor 110, and uses this average value, the pump power Hset, and the pump set capacity Dset to calculate the pump rotation speed Nb according to the above-mentioned formulas (1) and (2).

At this time, the operating levers/pedals of the boom operating device 310-1, arm operating device 309-1, bucket operating device 310-2, rotation operating device 309-2, swing operating device 313 and blade operating device 314 are not being operated, and the boom pressure, arm pressure, bucket pressure, rotation pressure, swing pressure and blade pressure are approximately 0 MPa, so that the rotation speed reduction rate Rb is calculated as 1 in table 125, this calculated value is multiplied by the pump rotation speed Nb, and the second rotation speed limit value Nlimitb is output.

In the rotation speed calculation unit 78-3, the first target rotation speeds Ntd1, Nte1 are calculated as positive values in tables 119, 120 according to the values of the operation signals (traveling left operation amount and traveling right operation amount) of the traveling left operation device 311 and the traveling right operation device 312, and the second target rotation speeds Ntd2, Nte2 are calculated by limiters 114, 115, to which the second rotation speed limit value Nlimitb calculated in the limit value calculation unit 78-1 is set as the upper limit value, and the first target rotation speeds Ntd1, Nte1 are limited to or less than the second rotation speed limit value Nlimitb. These second target rotation speeds Ntd2, Nte2 are output as target rotation speeds for the servo motors 7, 8, and the servo motors 7, 8 rotate in the right direction.

When the servo motors 7 and 8 rotate to the right, the pressurized oil discharged from the left traveling pump 15 and the right traveling pump 16 flows through the second supply lines 54 and 56 into the second port 94 of the left traveling motor 23 and the right traveling motor 24, and the pressurized oil is discharged from the first port 91 of the left traveling motor 23 and the right traveling motor 24, causing the left traveling motor 23 and the right traveling motor 24 to rotate in the forward direction.

The pressurized oil discharged from the left traveling motor 23 and the right traveling motor 24 passes through the first supply lines 53, 55 and is returned to the left traveling pump 15 and the right traveling pump 16.

<Independent operation of driving in reverse>
When the operating pedals of the left traveling operation device 311 and the right traveling operation device 312 are operated with the intention of traveling backwards, the operation signals of the operation devices 311, 312 and the pressure signals of the left traveling pressure sensor 109 and the right traveling pressure sensor 110 are input to the controller 78, and the limit value calculation unit 78-1 performs calculations similar to those in the case of operating forward traveling alone.

In addition, in the rotation speed calculation unit 78-3, the first target rotation speeds Ntd1, Nte1 are calculated as negative values in tables 119, 120, and the second target rotation speeds Ntd2, Nte2, which are negative values, are calculated in limiter 111. These second target rotation speeds Ntd2, Nte2, which are negative values, are output as the target rotation speeds of the servo motors 7, 8, and the servo motors 7, 8 rotate in the left direction.

When the servo motors 7 and 8 rotate to the left, the pressurized oil discharged from the left traveling pump 15 and the right traveling pump 16 flows through the first supply lines 53 and 55 into the first ports 91 and 92 of the left traveling motor 23 and the right traveling motor 24, and the pressurized oil is discharged from the second ports 92 and 94 of the left traveling motor 23 and the right traveling motor 24, causing the left traveling motor 23 and the right traveling motor 24 to rotate in the reverse direction.

The pressurized oil discharged from the left traveling motor 23 and the right traveling motor 24 passes through the second supply lines 54, 56 and is returned to the left traveling pump 15 and the right traveling pump 16.

<Independent left turn operation>
When the operation lever of the swing operation device 309 - 2 is operated with the intention of turning left, an operation signal of the swing operation device 309 - 2 and a pressure signal of the swing pressure sensor 108 are input to the controller 78 .

The operation signal of the rotation operation device 319-2 input to the controller 78 is input to the rotation speed calculation unit 78-3, and the pressure signal of the rotation pressure sensor 108 is input to the limit value calculation unit 78-1 and the composite operation determination unit 78-2.

In the limit value calculation unit 78-1, the rotation pressure is selected in the maximum value selection unit Mab, and the first rotation speed reduction rate Ra corresponding to the rotation pressure is calculated in table 124. In addition, the rotation pressure is selected again in the maximum value selection unit Mb, and the second rotation speed reduction rate Rb corresponding to the rotation pressure is calculated in table 125. However, these values do not affect the calculation of the target rotation speed of the rotation servo motor 6 in the rotation speed calculation unit 78-3.

In the composite operation determination unit 78-2, the pressure determination unit Jc determines that the rotation pressure is equal to or greater than the determination pressure, and the adder 127 calculates 1 as the number of actuators whose control devices are being operated, and outputs 1 as the composite operation determination value Jnb for rotation/swing/blade.

In the rotation speed calculation unit 78-3, a first target rotation speed Ntf1 corresponding to the turning operation amount is calculated as a positive value in the table 121, and in the division unit Df, the first target rotation speed Ntf1 is divided by the actuator number "1" of the composite operation determination value Jnb calculated in the composite operation determination unit 78-2 to calculate a second target rotation speed Ntf2. This second target rotation speed Ntf2 is output as the target rotation speed of the servo motor 6, and the servo motor 6 rotates in the right direction.
When the servo motor 6 rotates in the right direction, the pressurized oil discharged from the slewing pump 14 flows through the second supply line 52 into the second port 90 of the slewing motor 22, and the pressurized oil is discharged from the first port 89 of the slewing motor 22, causing the slewing motor 22 to rotate in the left direction.

The pressurized oil discharged from the first port 89 of the slewing motor 22 passes through the first supply line 51 and is returned to the slewing pump 14.

<Independent operation of turning right>
When the operating lever of the turning operation device 309-2 is operated with the intention of turning right, the operation signal of the turning operation device 309-2 and the pressure signal of the turning pressure sensor 108 are input to the controller 78, and the limit value calculation unit 78-1 and the composite operation judgment unit 78-2 perform calculations similar to those in the case of turning left.

In addition, in the rotation speed calculation unit 78-3, the first target rotation speed Ntf1 is calculated as a negative value in the table 121, and a negative second target rotation speed Ntf2 is calculated in the division unit Df. This negative second target rotation speed Ntf2 is output as the target rotation speed of the servo motor 6, and the servo motor 6 rotates in the left direction.

When the servo motor 6 rotates to the left, the pressurized oil discharged from the slewing pump 14 flows through the first supply line 51 into the first port 89 of the slewing motor 22, and the pressurized oil is discharged from the second port 90 of the slewing motor 22, causing the slewing motor 22 to rotate to the right.

The pressurized oil discharged from the second port 90 of the slewing motor 22 passes through the second supply line 52 and is returned to the slewing pump 14.

<Swing and blade operation alone>
When the operation pedal of the swing operation device 313 is operated with the intention of swinging left or right, the operation signal of the swing operation device 313 and the pressure signal of the swing pressure sensor 106 are input to the controller 78, and the first target rotation speed Ntg1 and the second target rotation speed Ntg2 are calculated in the table 122 and the division unit Dg in the same manner as in the case of the left swing alone operation or the right swing alone operation, and the servo motor 4 rotates rightward or leftward based on the second target rotation speed Ntg2. This rotation of the servo motor 4 discharges pressure oil from the swing pump 12, and the swing cylinder 20 extends or contracts in the same manner as in the case of boom raising or boom raising alone operation. The pressure oil discharged from the swing cylinder 20 is returned to the swing pump 12, and the pressure oil insufficient due to the area difference of the swing cylinder 20 is supplied to the swing pump 12 from the tank 77 through the check valve 63, and the surplus pressure oil flows back to the tank 77 through the operate check valve 64.

When the operating lever of the blade operating device 314 is operated to lower or raise the blade, similarly to when the operating pedal of the swing operating device 313 is operated to swing left or right, the first target rotation speed Nth1 and the second target rotation speed Nth2 are calculated in the table 123 and the division unit Dh, and the servo motor 5 rotates to the right or left based on the second target rotation speed Nth2, and the blade cylinder 21 extends or contracts. In addition, the pressure oil discharged from the blade cylinder 21 is returned to the blade pump 13, and the pressure oil that is insufficient due to the area difference of the blade cylinder 21 is replenished from the tank 77 to the blade pump 13 through the check valve 65, and the excess pressure oil is returned to the tank 77 through the operated check valve 66.

<Combined operation of boom raising and arm crowding>
When the operating levers of the boom operating device 310-1 and the arm operating device 309-1 are operated with the intention of performing a combined operation of boom raising and arm crowding, operation signals of the boom operating device 310-1 and the arm operating device 309-1 and pressure signals of the boom pressure sensor 103 and the arm pressure sensor 104 are input to the controller 78.

The operation signals of the operation devices 310-1, 309-1 input to the controller 78 are input to the rotation speed calculation unit 78-3, the pressure signals of the boom pressure sensor 103 and the arm pressure sensor 104 are input to the limit value calculation unit 78-1, and the pressure signal of the boom pressure sensor 103 is further input to the composite operation determination unit 78-2.

In the limit value calculation unit 78-1, because the operating lever of the bucket operation device 310-2 is not being operated, the maximum value selection unit Ma selects the boom pressure, and the average value calculation unit Aa calculates the average value of the boom pressure and arm pressure. Using this average value, the pump power Hset, and the pump set capacity Dset, the pump rotation speed Na is calculated according to the above-mentioned formulas (1) and (2).

At this time, no operating devices other than the boom operating device 310-1 and arm operating device 309-1 are being operated, and the rotation pressure, swing pressure, and blade pressure are approximately 0 MPa, so the rotation speed reduction rate Ra is calculated as 1 in table 124, this calculated value is multiplied by the pump rotation speed Na, and the first rotation speed limit value Nlimita is output.

In the composite operation determination unit 78-2, the pressure determination unit Ja determines that the boom pressure is equal to or greater than the determination pressure, and the adder 126 calculates 1 as the number of actuators whose operating devices are being operated, and outputs 1 as the boom/bucket composite operation determination value Jna.

In the rotation speed calculation unit 78-3, the third target rotation speed Nta3 is calculated using the table 116, the limiter 111, and the division unit Da in the same manner as in the case of the sole operation of the boom raising, and the second target rotation speed Ntb2 is calculated using the table 117 and the limiter 112 in the same manner as in the case of the sole operation of the arm crowd. The third target rotation speed Nta3 and the second target rotation speed Ntb2 are output as the target rotation speeds of the servo motors 1 and 2, the servo motors 1 and 2 rotate to the right, and the boom cylinder 17 and the arm cylinder 18 extend. In addition, the pressure oil discharged from the boom cylinder 17 and the arm cylinder 18 is returned to the boom pump 9 and the arm pump 10, and the pressure oil that is insufficient due to the area difference between the boom cylinder 17 and the arm cylinder 18 is supplied from the tank 77 to the boom pump 9 and the arm pump 10 through the check valves 57 and 59.

<Combined operation of boom raising and bucket crowding>
When the operating levers of the boom operating device 310-1 and the bucket operating device 310-2 are operated with the intention of performing a combined operation of boom raising and bucket crowding, operation signals of the boom operating device 310-1 and the bucket operating device 310-2 and pressure signals of the boom pressure sensor 103 and the bucket pressure sensor 105 are input to the controller 78.

The operation signals of the operating devices 310-1, 310-2 input to the controller 78 are input to the rotation speed calculation unit 78-3, the pressure signals of the boom pressure sensor 103 and the bucket pressure sensor 105 are input to the limit value calculation unit 78-1, and the pressure signal of the bucket pressure sensor 105 is further input to the composite operation determination unit 78-2.

In the limit value calculation unit 78-1, the maximum value selection unit Ma selects the high-pressure side pressure of the boom pressure and bucket pressure as the maximum value, and the average value calculation unit Aa calculates the average value of the high-pressure side pressure of the boom pressure and bucket pressure and the arm pressure. However, because the control lever of the arm operation device 309-1 is not being operated, the average value calculation unit Aa calculates 1/2 the high-pressure side pressure of the boom pressure and bucket pressure as the average value, and uses this average value, the pump power Hset, and the pump set capacity Dset to calculate the pump rotation speed Na according to the above-mentioned formulas (1) and (2).

At this time, too, no operating devices other than the boom operating device 310-1 and bucket operating device 310-2 are being operated, and the rotation pressure, swing pressure, and blade pressure are approximately 0 MPa, so the rotation speed reduction rate Ra is calculated as 1 in table 124, this calculated value is multiplied by the pump rotation speed Na, and the first rotation speed limit value Nlimita is output.

In the composite operation determination unit 78-2, the pressure determination unit Jb determines that the bucket pressure is equal to or greater than the determination pressure, and the adder 126 calculates 1 as the number of actuators whose operating devices are being operated, and outputs 1 as the boom/bucket composite operation determination value Jna.

In the rotation speed calculation unit 78-3, the third target rotation speeds Nta3 and Ntc3 are calculated using the tables 116 and 118, the limiters 111 and 113, and the division units Da and Dc, in the same manner as in the case of the independent operation of boom raising and bucket dumping. These third target rotation speeds Nta3 and Ntc3 are output as the target rotation speeds of the servo motors 1 and 3, which rotate in the right direction and extend the boom cylinder 17 and the bucket cylinder 19. In addition, the pressure oil discharged from the boom cylinder 17 and the bucket cylinder 19 is returned to the boom pump 9 and the bucket pump 11, and the pressure oil that is insufficient due to the area difference between the boom cylinder 17 and the bucket cylinder 19 is supplied from the tank 77 to the boom pump 9 and the bucket pump 11 through the check valves 57 and 61.

<Combined operation of arm cloud and bucket cloud>
When the operating levers of the arm operating device 309-1 and the bucket operating device 310-2 are operated with the intention of performing a combined operation of the arm crowding and bucket crowding, operation signals of the arm operating device 309-1 and the bucket operating device 310-2 and pressure signals of the arm pressure sensor 104 and the bucket pressure sensor 105 are input to the controller 78.

The operation signals of the operating devices 309-1, 310-2 input to the controller 78 are input to the rotation speed calculation unit 78-3, the pressure signals of the arm pressure sensor 104 and the bucket pressure sensor 105 are input to the limit value calculation unit 78-1, and the pressure signal of the bucket pressure sensor 105 is further input to the composite operation determination unit 78-2.

In the limit value calculation unit 78-1, because the control lever of the boom operation device 310-1 is not being operated, the maximum value selection unit Ma selects the bucket pressure, and the average value of the arm pressure and bucket pressure is calculated in the average value calculation unit Aa. Using this average value, the pump power Hset, and the pump set capacity Dset, the pump rotation speed Na is calculated according to the above-mentioned formulas (1) and (2).

In this case, the swirl pressure, swing pressure, and blade pressure are also approximately 0 MPa, so the rotation speed reduction rate Ra is calculated as 1 in table 124, and this calculated value is multiplied by the pump rotation speed Na to output the first rotation speed limit value Nlimita.

In the composite operation determination unit 78-2, the pressure determination unit Jb determines that the bucket pressure is equal to or greater than the determination pressure, and the adder 126 calculates 1 as the number of actuators whose operating devices are being operated, and outputs 1 as the boom/bucket composite operation determination value Jna.

In the rotation speed calculation unit 78-3, the second target rotation speed Ntb2 is calculated using the table 117 and the limiter 112 in the same manner as in the case of the arm cloud being operated alone, and the third target rotation speed Ntc3 is calculated using the table 118, the limiter 113, and the division unit Dc in the same manner as in the case of the bucket cloud being operated alone. The second target rotation speed Ntb2 and the third target rotation speed Ntc3 are output as the target rotation speeds of the servo motors 2 and 3, the servo motors 2 and 3 rotate in the right direction, and the arm cylinder 18 and the bucket cylinder 19 extend. In addition, the pressure oil discharged from the arm cylinder 18 and the bucket cylinder 19 is returned to the arm pump 10 and the bucket pump 11, and the pressure oil insufficient due to the area difference between the arm cylinder 18 and the bucket cylinder 19 is supplied from the tank 77 to the arm pump 10 and the bucket pump 11 through the check valves 59 and 61.

<Combined operation of boom raising and right rotation>
When the operating levers of the boom operation device 310-1 and the swing operation device 309-2 are operated with the intention of performing a combined operation of raising the boom and swinging right, the operation signals of the boom operation device 310-1 and the swing operation devices 310-1, 309-2 and the pressure signals of the boom pressure sensor 103 and the swing pressure sensor 108 are input to the controller 78.

The operation signals of the operating devices 310-1, 309-2 input to the controller 78 are input to the rotation speed calculation unit 78-3, the pressure signals of the boom pressure sensor 103 and the rotation pressure sensor 108 are input to the limit value calculation unit 78-1, and the pressure signals of the boom pressure sensor 103 and the rotation pressure sensor 108 are further input to the composite operation determination unit 78-2.

In the limit value calculation unit 78-1, the boom pressure is selected in the maximum value selection unit Ma because the control lever of the bucket operation device 310-2 is not being operated, and the control lever of the arm operation device 309-1 is not being operated, so the average value calculation unit Aa calculates 1/2 of the boom pressure as the average value, and this average value, the pump power Hset, and the pump set capacity Dset are used to calculate the pump rotation speed Na according to the above-mentioned formulas (1) and (2).

In addition, since the operating levers/pedals of the swing operating device 313 and the blade operating device 314 are not being operated and the swing pressure and blade pressure are approximately 0 MPa, the maximum value selection unit Mab selects the rotation pressure, and the first rotation speed reduction rate Ra according to the rotation pressure is calculated in table 124. This calculated value is multiplied by the pump rotation speed Na, and the first rotation speed limit value Nlimita is output.

In the composite operation determination unit 78-2, the pressure determination units Ja and Jc determine that the boom pressure and the rotation pressure are equal to or greater than the respective determination pressures, and the adders 126 and 127 calculate the number of actuators whose operating devices are being operated to 1, and output the combined boom/bucket operation determination value Jna and the combined rotation/swing/blade operation determination value Jnb of 1, respectively.

In the rotation speed calculation unit 78-3, the third target rotation speed Nta3 is calculated using the table 116, the limiter 111, and the division unit Da, and the second target rotation speed Ntf2 (negative value) is calculated using the table 121 and the division unit Df. The third target rotation speed Nta3 and the second target rotation speed Ntf2 are output as the target rotation speeds of the servo motors 1 and 6, the servo motor 1 rotates to the right, the servo motor 6 rotates to the left, the boom cylinder 17 extends, and the swing motor rotates to the right.

In addition, the pressurized oil discharged from the boom cylinder 17 is returned to the boom pump 9, and the pressure oil shortage due to the area difference of the boom cylinder 17 is replenished from the tank 77 through the check valves 57 and 59 to the boom pump 9 and arm pump 10.

<Combined operation of turning right and swinging left>
When the operating levers/pedals of the swing operation device 309-2 and the swing operation device 313 are operated with the intention of performing a combined operation of swinging right and swinging left, the operation signals of the swing operation device 309-2 and the swing operation device 313 and the pressure signals of the swing pressure sensor 108 and the swing pressure sensor 106 are input to the controller 78.

The operation signals of the operation devices 309-2 and 313 input to the controller 78 are input to the rotation speed calculation unit 78-3, and the pressure signals of the turning pressure sensor 108 and the swing pressure sensor 106 are input to the limit value calculation unit 78-1 and the composite operation determination unit 78-2.

In the limit value calculation unit 78-1, the maximum value selection unit Mab selects the high-pressure side of the rotation pressure and swing pressure, and the first and second rotation speed reduction rates Ra and Rb are calculated in tables 124 and 125 according to the high-pressure side of the rotation pressure and swing pressure, but these values do not affect the calculation of the target rotation speeds of the rotation and swing servo motors 6 and 5 in the rotation speed calculation unit 78-3.

In the composite operation determination unit 78-2, the pressure determination units Jc and Jd determine that the rotation pressure and swing pressure are equal to or greater than the determination pressure, and the adder unit 127 calculates 2 as the number of actuators whose control devices are being operated, and outputs 2 as the composite operation determination value Jnb for rotation/swing/blade.

In the rotation speed calculation unit 78-3, the first target rotation speed Ntf1 corresponding to the turning operation amount is calculated as a negative value in the table 121, and in the division unit Df, the first target rotation speed Ntf1 is divided by the number of actuators "2" of the composite operation determination value Jnb calculated in the composite operation determination unit 78-2, and a value of 1/2 of the first target rotation speed Ntf1 is calculated as the second target rotation speed Ntf2. This second target rotation speed Ntf2 is output as the target rotation speed of the servo motor 6, and the servo motor 6 rotates in the left direction.

This rotation of the servo motor 6 discharges pressure oil from the swing pump 14, and the swing motor 22 rotates in the right direction. The pressure oil discharged from the swing motor 22 is returned to the swing pump 14. Furthermore, in the table 122, a first target rotation speed Ntg1 corresponding to the swing operation amount is calculated, and in the division unit Dg, the first target rotation speed Ntg1 is divided by the number of actuators "2" of the composite operation determination value Jnb calculated in the composite operation determination unit 78-2, and a second target rotation speed Nt2 is calculated as 1/2 of the first target rotation speed Ntg1. This second target rotation speed Ntg2 is output as the target rotation speed of the servo motor 4, and the servo motor 4 rotates in the left direction.

This rotation of the servo motor 4 causes pressurized oil to be discharged from the swing pump 12, and the swing cylinder 20 contracts. The pressurized oil discharged from the swing cylinder 20 is returned to the swing pump 12, and the excess pressurized oil due to the area difference of the swing cylinder 20 flows back to the tank 77 through the operated check valve 64.

<Combined operation of boom raising, arm crowding and right rotation>
When the operating levers of the boom operation device 310-1, the arm operation device 309-1, and the swing operation device 309-2 are operated with the intention of performing the combined operation of boom raising, arm crowding, and right swing, operation signals from the boom operation device 310-1, the arm operation device 309-1, and the swing operation device 309-2 and pressure signals from the boom pressure sensor 103, the arm pressure sensor 104, and the swing pressure sensor 108 are input to the controller 78.

The operation signals of the operating devices 310-1, 309-1, and 309-2 input to the controller 78 are input to the rotation speed calculation unit 78-3, the pressure signals of the boom pressure sensor 103, arm pressure sensor 104, and rotation pressure sensor 108 are input to the limit value calculation unit 78-1, and the pressure signals of the boom pressure sensor 103 and rotation pressure sensor 108 are further input to the composite operation determination unit 78-2.

In the limit value calculation unit 78-1, because the operating lever of the bucket operation device 310-2 is not being operated, the maximum value selection unit Ma selects the boom pressure, and the average value calculation unit Aa calculates the average value of the boom pressure and arm pressure. Using this average value, the pump power Hset, and the pump set capacity Dset, the pump rotation speed Na is calculated according to the above-mentioned formulas (1) and (2).

In addition, since no operation devices other than the boom operation device 310-1, arm operation device 309-1, and rotation operation device 309-2 are being operated, the rotation pressure is selected in the maximum value selection section Mab, the first rotation speed reduction rate Ra corresponding to the rotation pressure is calculated in table 124, this calculated value is multiplied by the pump rotation speed Na, and the first rotation speed limit value Nlimita is output.

In the composite operation determination unit 78-2, the pressure determination units Ja and Jc determine that the boom pressure and the rotation pressure are equal to or greater than the respective determination pressures, and the adders 126 and 127 calculate the number of actuators whose operating devices are being operated to 1, and output the combined boom/bucket operation determination value Jna and the combined rotation/swing/blade operation determination value Jnb of 1, respectively.

In the rotation speed calculation unit 78-3, the third target rotation speed Nta3 is calculated using the table 116, the limiter 111, and the division unit Da, the second target rotation speed Ntb2 is calculated using the table 117 and the limiter 112, and the second target rotation speed Ntf2 (negative value) is calculated using the table 121 and the division unit Df. The third target rotation speed Nta3, the second target rotation speed Ntb2, and the second target rotation speed Ntf2 are output as the target rotation speeds of the servo motors 1, 2, and 6, the servo motors 1 and 2 rotate to the right, the servo motor 6 rotates to the left, the boom cylinder 17 and the arm cylinder 18 extend, and the swing motor 22 rotates to the right.

In addition, the pressurized oil discharged from the boom cylinder 17 and the arm cylinder 18 is returned to the boom pump 9 and the arm pump 10, and the pressure oil shortage due to the area difference between the boom cylinder 17 and the arm cylinder 18 is replenished from the tank 77 to the boom pump 9 and the arm pump 10 through the check valves 57 and 59.

～Effect～
1. Main Effects In the present invention, the boom cylinder 17, the arm cylinder 18, the bucket cylinder 19, the left traveling motor 23, and the right traveling motor 24 are defined as "at least two specific hydraulic actuators."

On this premise, when the operating devices corresponding to at least two specific hydraulic actuators among the multiple hydraulic actuators 19-24 are operated so that at least two specific hydraulic actuators are driven simultaneously, the controller 78 controls the rotation speeds of the electric motors 1-3, 7, and 8 corresponding to at least two specific hydraulic actuators among the multiple electric motors 1-8 based on the respective discharge pressures of the multiple hydraulic pumps 9-16 detected by the multiple pressure sensors 103-110 and the respective operation amounts of the multiple operation devices 309-314 detected by the multiple operation sensors 209-215 so that the power consumption of the hydraulic pumps corresponding to at least two specific hydraulic actuators among the multiple hydraulic pumps 9-16 does not exceed the pump power Hset.

The controller 78 also calculates the rotation speed limit value Nlimita or Nlimitb of the electric motors 1 to 3, 7, and 8 corresponding to the at least two specific hydraulic actuators based on the discharge pressure of the hydraulic pump corresponding to the at least two specific hydraulic actuators detected by the multiple pressure sensors 103 to 110, the pump power Hset, and the pump set capacity Dset, calculates a first target rotation speed of the electric motors 1 to 3, 7, and 8 corresponding to the at least two specific hydraulic actuators based on the operation amount of the operating device corresponding to the at least two specific hydraulic actuators, corrects the first target rotation speed of the electric motors 1 to 3, 7, and 8 corresponding to the at least two specific hydraulic actuators so as not to exceed the rotation speed limit value Nlimita or Nlimitb, calculates a second target rotation speed of the electric motors 1 to 3, 7, and 8 corresponding to the at least two specific hydraulic actuators, and controls the rotation speed of the electric motors 1 to 3, 7, and 8 corresponding to the at least two specific hydraulic actuators based on the second target rotation speed.

This makes it possible to perform control simulating the horsepower control shown in FIG. 7 in the open circuit type three pump system shown in FIG. 6, and reduces the power consumption of the hydraulic pump compared to when such control simulating control is not performed. Furthermore, when the "at least two specific hydraulic actuators" are the boom cylinder 17, arm cylinder 18, and bucket cylinder 19, it is possible to further ensure a good speed balance between the hydraulic actuators, and obtain good combined operability.

The details are explained below.

(1) "Combined operation of boom raising and arm crowding"
A limit value calculation unit 78-1 of the controller 78 calculates a first rotation speed limit value Nlimita corresponding to the average value of the boom pressure and the arm pressure based on the average value of the boom pressure and the arm pressure, the pump power Hset, and the pump set capacity Dset. The pump power Hset is set to a value equal to the maximum horsepower H12max shown in Fig. 7 of an open-circuit type three-pump system whose horsepower control is to be simulated. A rotation speed calculation unit 78-3 calculates a third target rotation speed Nta3 and a second target rotation speed Ntb2 limited to be equal to or less than the first rotation speed limit value Nlimita, and the servo motor 1 is driven with the third target rotation speed Nta3 as the target rotation speed, the servo motor 2 is driven with the second target rotation speed Ntb2 as the target rotation speed, and the boom pump 9 and the arm pump 10 are driven.

As a result, when the discharge pressure of the boom pump 9 and the arm pump 10 increases and the total horsepower consumption of the boom pump 9 and the arm pump 10 exceeds the pump power Hset, the discharge flow rate of the boom pump 9 and the arm pump 10 is reduced so that the horsepower consumption does not exceed the pump power Hset. This control is equivalent to the control in the open circuit type three pump system shown in FIG. 6, in which the discharge flow rate of the boom pump 9 and the arm pump 10 is reduced along the characteristic line of the maximum horsepower H12max shown in FIG. 7 when the total horsepower consumption of the boom pump 9 and the arm pump 10 exceeds the maximum horsepower H12max, so that the horsepower consumption does not exceed the maximum horsepower H12max. In this way, control simulating the horsepower control of the open circuit type three pump system shown in FIG. 6 is performed, and the power consumption of the boom pump 9 and the arm pump 10 can be reduced compared to the case where the control simulating the horsepower control is not performed.

In addition, when the load on either the boom cylinder 17 or the arm cylinder 18 increases during the combined operation of boom raising and arm crowding, causing the discharge pressure (boom pressure or arm pressure) of the boom pump 9 or arm pump 10 to rise, control simulating the horsepower control of the open circuit type three-pump system shown in FIG. 6 is similarly performed, and the drive speeds of both the boom cylinder 9 and the arm cylinder are reduced. This ensures a speed balance between the boom cylinder 17 and the arm cylinder 18, and good combined operability can be obtained.

(2) "Combined operation of arm cloud and bucket cloud"
As in the case of "combined operation of boom raising and arm crowding," control is performed that simulates the horsepower control of the open-circuit type three-pump system shown in Figure 6, and as in the case of "combined operation of boom raising and arm crowding," the effects of reducing power consumption and ensuring combined operability are obtained.

(3) "Combined operation of arm cloud and bucket cloud"
Except for the fact that "boom" is changed to "arm" and the third target rotation speed Nta3 is changed to the third target rotation speed Ntc3, the limit value calculation unit 78-1 and the rotation speed calculation unit 78-3 of the controller 78 perform control similar to that in the case of "combined operation of boom raising and arm crowding". As a result, similar to the case of "combined operation of boom raising and arm crowding", control simulating the horsepower control of the open circuit type three-pump system shown in Fig. 6 is performed, and similar to the case of "combined operation of boom raising and arm crowding", the effects of reducing power consumption and ensuring combined operability can be obtained.

(4) "Combined operation of boom raising, arm crowding and right rotation"
In the limit value calculation unit 78-1 of the controller 78, a first rotation speed reduction rate Ra corresponding to the swing pressure is calculated in the table 124, and this first rotation speed reduction rate Ra is multiplied by the pump rotation speed Na calculated from the formulas (1) and (2) using the average value of the boom pressure and the arm pressure, the pump power Hset, and the pump set capacity Dset, and a first rotation speed limit value Nlimita is output. As a result, the first rotation speed limit value Nlimita becomes a small value corresponding to the first rotation speed reduction rate Ra, and the second target rotation speeds Nta2 and Ntb2 calculated by the limiters 111 and 112 also become smaller than when the first rotation speed reduction rate Ra is 1, and the rotation speeds of the servo motors 1 and 2 are similarly reduced, and the discharge flow rates of the boom pump 9 and the arm pump 10 are also reduced. As a result, the total horsepower consumption of the boom pump 9, the arm pump 10, and the swing pump 14 is controlled so as not to exceed the pump power Hset. This control is equivalent to a control in which, when the discharge pressure of the third hydraulic pump P3 increases and the horsepower consumption of the third hydraulic pump P3 increases in the open circuit type three-pump system shown in Fig. 6, the maximum horsepower characteristic lines C1, C2 are shifted as shown by arrows AR1, AR2 in Fig. 7, and the maximum horsepower that can be consumed by the hydraulic pumps P1, P2 is reduced by the horsepower consumption of the third hydraulic pump P3 so that the total horsepower consumption of the first and second hydraulic pumps P1, P2 and the third hydraulic pump P3 does not exceed the maximum horsepower T12max. In this way, control simulating the total horsepower control of the open circuit type three-pump system shown in Fig. 6 is performed, and the power consumption of the boom pump 9, the arm pump 10 and the swing pump 14 can be reduced compared to the case where the total horsepower control is not performed.

In addition, for the combined operation of boom raising and arm crowding, the speed balance between the boom cylinder 17 and the arm cylinder 18 is ensured, as in the case of "combined operation of boom raising and arm crowding," and good combined operability can be obtained.

(5) "Independent operation of forward travel"
A limit value calculation unit 78-1 of the controller 78 calculates a second rotation speed limit value Nlimitb corresponding to the average value of the left and right traveling pressures based on the average value of the left and right traveling pressures, the pump power Hset, and the pump set capacity Dset. A rotation speed calculation unit 78-3 calculates second target rotation speeds Ntd2, Nte2 limited to the second rotation speed limit value Nlimitb or less, and the servo motors 7, 8 are driven with the second target rotation speeds Ntd2, Nte2 as the target rotation speeds, thereby driving the left traveling pump 15 and the right traveling pump 16.

As a result, if the discharge pressure of the traveling left pump 15 and the traveling right pump 16 rises and the total horsepower consumption of the traveling left pump 15 and the traveling right pump 16 exceeds the pump power Hset, the discharge flow rate of the traveling left pump 15 and the traveling right pump 16 is reduced so that the horsepower consumption does not exceed the pump power Hse, just as in the case of the combined operation of boom raising and arm crowding described above. In this way, even in this case, control simulating the horsepower control of the open circuit type three-pump system shown in Figure 6 is performed, and the power consumption of the traveling left pump 15 and the traveling right pump 16 can be reduced compared to when horsepower control is not performed.

(6) "Independent operation of driving and reversing"

As in the case of "solo operation of forward travel", control is performed simulating the horsepower control of the open circuit type three pump system shown in Figure 6, and as in the case of "solo operation of forward travel", the effects of reduced power consumption and ensured combined operability are obtained.

2. Other Effects (7) "Combined operation of boom raising and right rotation"
As in the case of "combined operation of boom raising, arm crowding, and right swing", in the limit value calculation unit 78-1 of the controller 78, the first rotation speed reduction rate Ra calculated in the table 124 according to the swing pressure is multiplied by the pump rotation speed Na calculated from the equations (1) and (2) using 1/2 the boom pressure (average value), the pump power Hset, and the pump set capacity Dset, and the first rotation speed limit value Nlimita is output. As a result, the first rotation speed limit value Nlimita becomes a small value according to the first rotation speed reduction rate Ra, and the second target rotation speed Nta2 calculated by the limiter 111 also becomes a smaller value than when the first rotation speed reduction rate Ra is 1, the rotation speed of the servo motor 1 is similarly reduced, and the discharge flow rate of the boom pump 9 is also reduced. As a result, similar to the case shown by arrows AR1 and AR2 in Fig. 7, the maximum horsepower that can be consumed by the boom pump 9 is reduced by the amount of horsepower consumed by the swing pump 14, and the total horsepower consumed by the boom pump 9 and the swing pump 14 is controlled so as not to exceed the pump power Hset. In this way, similar to the case of combined operation of the arm crowding and bucket crowding, control simulating the total horsepower control of the open circuit type three-pump system shown in Fig. 6 is performed, and the power consumption of the boom pump 9 and the swing pump 14 can be reduced compared to the case where total horsepower control is not performed.

(8) "Combined operation of turning right and swinging left"
In the composite operation judgment unit 78-2 of the controller 78, the pressure judgment units Jc and Jd judge that the rotation pressure and swing pressure are equal to or greater than the judgment pressure, and the adder unit 127 calculates 2 as the number of actuators for which the operating device is being operated, and the "number of actuators" of 2 is output as the rotation/swing/blade composite operation judgment value Jnb.

In the rotation speed calculation unit 78-3, the first target rotation speeds Ntf1, Ntg1 are divided by the actuator number "2" of the composite operation judgment value Jnb in the division units Df, Dg, and the second target rotation speeds Ntf2, Ntg2 are calculated as 1/2 of the first target rotation speeds Ntf1, Ntg1, and the rotation speeds of the servo motors 6 and 4 are also half of the values when the first target rotation speeds Ntf1, Ntg1 are not divided by the composite operation judgment value Jnb. As a result, the discharge flow rates of the swing pump 14 and the swing pump 12 are also reduced, and the swing motor 22 and the swing cylinder 20 are driven by the reduced discharge flow rates. As a result, as in the case where the combined operation of swing and swing is performed in the open circuit type three-pump system shown in FIG. 6, the total horsepower consumption of the swing pump 14 and the swing pump 12 is controlled so as not to exceed the pump power, and the total power consumption of the swing pump 14 and the swing pump 12 can be reduced compared to the case where such control is not performed.

＜Other＞
In this embodiment, the controller 78 is configured to control the rotation speeds of the electric motors 1 to 3 so as to perform control simulating the horsepower control of the open circuit type three-pump system shown in FIG. 6. However, the open circuit type three-pump system simulating the horsepower control is not limited to the system shown in FIG. 6, and the horsepower control of another open circuit type three-pump system may be simulated. For example, in the open circuit type three-pump system shown in FIG. 6, the first and second hydraulic pumps P1 and P2 are configured by two discharge ports of a split flow type hydraulic pump PW equipped with a common regulator PR, but they may be two independent variable displacement hydraulic pumps equipped with a common regulator. Even in this case, the controller 78 can perform control simulating the horsepower control in the same manner by using the calculation process of the functional block diagram shown in FIG. 3.

The combination of the first to third hydraulic pumps P1, P2, and P3 and the hydraulic actuators driven by the oil discharged from them is not limited to that shown in FIG. 6, but may be other combinations. In this case, the functional block diagram shown in FIG. 3 can be modified according to the differences in the combination to perform control that simulates the horsepower control of that combination.

1-7 Servo motor (electric motor)
9 Boom pump (hydraulic pump)
10 Arm pump (hydraulic pump)
11 Bucket pump (hydraulic pump)
12 Swing pump (hydraulic pump)
13 Blade pump (hydraulic pump)
14 Swing pump (hydraulic pump)
15 Left travel pump (hydraulic pump)
16 Right travel pump (hydraulic pump)
17 Boom cylinder (specific hydraulic actuator)
18. Arm cylinder (specific hydraulic actuator)
19 Bucket cylinder (specific hydraulic actuator)
20 Swing cylinder (hydraulic actuator)
21 Blade cylinder (hydraulic actuator)
22 Swing motor (hydraulic actuator)
23 Left travel motor (specific hydraulic actuator)
24 Right travel motor (specific hydraulic actuator)
78 Controller 78-1 Limit value calculation unit 78-2 Composite operation determination unit 78-3 Rotation speed calculation unit 103 (Boom) pressure sensor 104 (Arm) pressure sensor 105 (Bucket) pressure sensor 106 (Swing) pressure sensor 107 (Blade) pressure sensor 108 (Turning) pressure sensor 109 (Traveling left) pressure sensor 110 (Traveling right) pressure sensor 209-1 (Arm) operation sensor 209-2 (Turning) operation sensor 210-1 (Boom) operation sensor 210-2 (Bucket) operation sensor 211 (Traveling left) operation sensor 212 (Traveling right) operation sensor 213 (Swing) operation sensor 214 (Blade) operation sensor 300 Swing body 301 Traveling body 301a, 301b Left and right traveling devices 302 Front working machine 303 Swing post 304 Blade 306 Boom 307 Arm 308 Bucket 309-1 Arm operating device 309-2 Swing operating device 310-1 Boom operating device 310-2 Bucket operating device 311 Travel left operating device 312 Travel right operating device 313 Swing operating device 314 Blade operating device Hset Pump power Dset Pump set capacity Nta1 to Nth1 First target rotation speed Nta2 to Nth2 Second target rotation speed Nta3, Ntc3 Third target rotation speed
Qa: flow rate of virtual hydraulic pump Na: revolution speed of virtual hydraulic pump Ra: first revolution speed reduction rate Rb: second revolution speed reduction rate Nlimita: first revolution speed limit value Nlimitb: second revolution speed limit value Jna, Jnb: composite operation judgment value

Claims (7)

A plurality of fixed displacement dual discharge hydraulic pumps;
A plurality of hydraulic actuators connected in a closed circuit to each of the plurality of hydraulic pumps;
a plurality of electric motors each driving the plurality of hydraulic pumps;
a plurality of operation devices for instructing the operation of each of a plurality of driven bodies driven by the plurality of hydraulic actuators,
A plurality of pressure sensors for detecting the discharge pressures of the respective hydraulic pumps;
A plurality of operation sensors for detecting the operation amounts of the plurality of operation devices;
A controller for controlling the plurality of electric motors,
The controller:
when operating devices corresponding to at least two specific hydraulic actuators among the plurality of hydraulic actuators are operated so that at least two specific hydraulic actuators are driven simultaneously, based on the discharge pressures of the plurality of hydraulic pumps detected by the plurality of pressure sensors and the operation amounts of the plurality of operation devices detected by the plurality of operation sensors, control the rotation speeds of electric motors among the plurality of electric motors corresponding to the at least two specific hydraulic actuators so that the power consumption of the hydraulic pumps corresponding to the at least two specific hydraulic actuators among the plurality of hydraulic pumps does not exceed a preset pump power;
The controller:
In addition to the pump power, a pump set displacement is preset equal to a displacement of a hydraulic pump corresponding to the at least two specific hydraulic actuators ;
calculating a rotation speed limit value of an electric motor corresponding to the at least two specific hydraulic actuators based on a discharge pressure of a hydraulic pump corresponding to the at least two specific hydraulic actuators detected by the plurality of pressure sensors, the pump power, and the pump set displacement;
calculating first target rotation speeds of electric motors corresponding to the at least two specific hydraulic actuators based on operation amounts of operation devices corresponding to the at least two specific hydraulic actuators detected by the plurality of operation sensors;
a first target rotation speed of an electric motor corresponding to the at least two specific hydraulic actuators is corrected so as not to exceed the rotation speed limit value, and a second target rotation speed of the electric motor corresponding to the at least two specific hydraulic actuators is calculated, and the rotation speed of the electric motor corresponding to the at least two specific hydraulic actuators is controlled based on the second target rotation speed. 2. The hydraulic drive system for a construction machine according to claim 1 ,
the at least two specific hydraulic actuators include a boom cylinder that drives a boom that is part of the plurality of driven bodies, an arm cylinder that drives an arm that is part of the plurality of driven bodies, and a bucket cylinder that drives a bucket that is part of the plurality of driven bodies;
the plurality of hydraulic pumps include a boom pump that supplies pressure oil to the boom cylinder, an arm pump that supplies pressure oil to the arm cylinder, and a bucket pump that supplies pressure oil to the bucket cylinder,
the plurality of electric motors include a boom electric motor that drives the boom pump, an arm electric motor that drives the arm pump, and a bucket electric motor that drives the bucket pump,
the plurality of operation devices include a boom operation device that instructs a movement of the boom, an arm operation device that instructs a movement of the arm, and a bucket operation device that instructs a movement of the bucket,
The controller:
calculating a rotation speed of a virtual pump having a pump capacity equal to the set pump capacity based on the discharge pressure of the boom pump, the discharge pressure of the arm pump, and the discharge pressure of the bucket pump, the pump power, and the set pump capacity, and further calculating a first rotation speed limit value as the rotation speed limit value based on the rotation speed of this virtual pump;
calculating, as the first target rotation speeds, a first target rotation speed of the boom electric motor, a first target rotation speed of the arm electric motor, and a first target rotation speed of the bucket electric motor based on an operation amount of the boom operation device, an operation amount of the arm operation device, and an operation amount of the bucket operation device;
a hydraulic drive system for a construction machine, characterized in that the first target rotation speed of the boom electric motor, the first target rotation speed of the arm electric motor, and the first target rotation speed of the bucket electric motor are corrected so as not to exceed the first rotation speed limit value, a second target rotation speed of the boom electric motor, a second target rotation speed of the arm electric motor, and a second target rotation speed of the bucket electric motor are calculated as the second target rotation speed, and the rotation speeds of the boom electric motor, the arm electric motor, and the bucket electric motor are controlled based on the second target rotation speed of the boom electric motor, the second target rotation speed of the arm electric motor, and the second target rotation speed of the bucket electric motor. 3. The hydraulic drive system for a construction machine according to claim 2 ,
the controller determines whether the boom cylinder and the bucket cylinder are being driven, based on the discharge pressure of the boom pump and the discharge pressure of the bucket pump, and the operation amount of the boom operation device and the operation amount of the bucket operation device, and calculates the number of actuators currently being driven based on the determination result;
a third target rotation speed of the boom electric motor and a third target rotation speed of the bucket electric motor are calculated by dividing the second target rotation speed of the boom electric motor and the second target rotation speed of the bucket electric motor by the number of actuators, and the rotation speeds of the boom electric motor and the bucket electric motor are controlled based on the third target rotation speed of the boom electric motor and the third target rotation speed of the bucket electric motor. 3. The hydraulic drive system for a construction machine according to claim 2 ,
The plurality of hydraulic actuators further includes a rotation motor that drives a rotation body that is one of the plurality of driven bodies,
The plurality of hydraulic pumps further includes a swing pump that supplies pressure oil to the swing motor,
The plurality of electric motors further includes a rotary electric motor that drives the rotary pump,
The plurality of operation devices further includes a rotation operation device that instructs the operation of the rotating body,
The controller:
calculating a first target rotation speed of the swing electric motor based on an operation amount of the swing operation device, and controlling the rotation speed of the swing electric motor based on the first target rotation speed of the swing electric motor;
calculating a first rotation speed reduction rate based on a discharge pressure of the rotary pump, the first rotation speed reduction rate being reduced as the discharge pressure increases;
A hydraulic drive system for a construction machine, comprising: a first rotation speed limit value calculating section that calculates the first rotation speed limit value by multiplying the virtual pump rotation speed by the first rotation speed reduction rate. 3. The hydraulic drive system for a construction machine according to claim 2 ,
The at least two specific hydraulic actuators further include a left traveling motor and a right traveling motor that drive crawler-type left traveling device and right traveling device that are part of the plurality of driven bodies,
the plurality of hydraulic pumps further include a left travel pump that supplies pressure oil to the left travel motor and a right travel pump that supplies pressure oil to the right travel motor,
the plurality of electric motors further include a left traveling electric motor that drives the left traveling pump and a right traveling electric motor that drives the right traveling pump,
The plurality of operation devices further includes a left traveling operation device that instructs the operation of the left traveling device and a right traveling operation device that instructs the operation of the right traveling device,
The controller:
Calculate a rotation speed of a virtual pump having a pump capacity equal to the set pump capacity based on the discharge pressure of the left traveling pump and the discharge pressure of the right traveling pump, the pump power, and the set pump capacity, and further calculate a second rotation speed limit value as the rotation speed limit value based on the rotation speed of this virtual pump;
calculating, as the first target rotation speed, a first target rotation speed of the left traveling electric motor and a first target rotation speed of the right traveling electric motor based on an operation amount of the left traveling operation device and an operation amount of the right traveling operation device;
a hydraulic drive system for a construction machine, characterized in that the first target rotation speed of the left traveling electric motor and the first target rotation speed of the right traveling electric motor are corrected so as not to exceed the second rotation speed limit value, a second target rotation speed of the left traveling electric motor and a second target rotation speed of the right traveling electric motor are calculated as the second target rotation speed, and the rotation speeds of the left traveling electric motor and the right traveling electric motor are controlled based on the second target rotation speed of the left traveling electric motor and the second target rotation speed of the right traveling electric motor. 6. The hydraulic drive system for a construction machine according to claim 5 ,
The plurality of hydraulic actuators further includes a rotation motor that drives a rotation body that is one of the plurality of driven bodies,
The plurality of hydraulic pumps further includes a swing pump that supplies pressure oil to the swing motor,
The plurality of electric motors further includes a rotary electric motor that drives the rotary pump,
The plurality of operation devices further includes a rotation operation device that instructs the operation of the rotating body,
The controller:
calculating a first target rotation speed of the swing electric motor based on an operation amount of the swing operation device, and controlling the rotation speed of the swing electric motor based on the first target rotation speed of the swing electric motor;
calculating a second rotation speed reduction rate that decreases as a maximum pressure among the discharge pressure of the boom pump, the discharge pressure of the arm pump, the discharge pressure of the bucket pump, and the discharge pressure of the swing pump increases;
A hydraulic drive system for a construction machine, comprising: a second rotation speed limit value calculating section for calculating the second rotation speed limit value by multiplying the virtual pump rotation speed by the second rotation speed reduction rate. 3. The hydraulic drive system for a construction machine according to claim 2 ,
The plurality of hydraulic actuators further include a rotation motor, a swing cylinder, and a blade cylinder that drive a rotation body, a swing post, and a blade that are part of the plurality of driven bodies,
The plurality of hydraulic pumps further include a swing pump that supplies pressure oil to the swing motor, a swing pump that supplies pressure oil to the swing cylinder, and a blade pump that supplies pressure oil to the blade cylinder,
the electric motors further include a swing electric motor that drives the swing pump, a swing electric motor that drives the swing pump, and a blade electric motor that drives the blade pump;
The plurality of operation devices further include a rotation operation device that instructs the operation of the rotating body, a swing operation device that instructs the operation of the swing post, and a blade operation device that instructs the operation of the blade,
The controller:
calculating a first target rotation speed of the swing electric motor, a first target rotation speed of the swing electric motor, and a first target rotation speed of the blade electric motor based on an operation amount of the swing operation device, an operation amount of the swing operation device, and an operation amount of the blade operation device, and controlling the rotation speeds of the swing electric motor, the swing electric motor, and the blade electric motor based on the first target rotation speed of the swing electric motor, the first target rotation speed of the swing electric motor, and the first target rotation speed of the blade electric motor;
determining whether the swing motor, the swing cylinder, and the blade cylinder are being driven based on the discharge pressure of the swing pump, the discharge pressure of the swing pump, and the discharge pressure of the blade pump, and the operation amount of the swing operation device, the operation amount of the swing operation device, and the operation amount of the blade operation device, and calculating the number of actuators currently being driven based on the determination result;
a second target rotation speed of the swing electric motor and a second target rotation speed of the blade electric motor are calculated by dividing the first target rotation speed of the swing electric motor and the first target rotation speed of the blade electric motor by the number of actuators, and the rotation speeds of the swing electric motor, the swing electric motor and the blade electric motor are controlled based on the second target rotation speed of the swing electric motor, the second target rotation speed of the swing electric motor and the second target rotation speed of the blade electric motor.

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