Work machine

Abstract

To prevent backflow from a hydraulic actuator to a delivery line of a hydraulic pump.SOLUTION: A working machine comprises: a plurality of direction control valves connected to a delivery line in parallel with one another; a plurality of flow volume control valves controlling flow volume of pressure oil supplied to a plurality of hydraulic actuators; a plurality of electromagnetic valves outputting command pressure to the plurality of flow volume control valves; and a controller unit controlling the electromagnetic valves. Each of the flow volume control valves includes a poppet valve which can adjust an area of a first opening between a pump passage and an actuator passage, a check valve arranged at a passage which causes the pump passage and a backpressure chamber of the poppet valve to be communicated with each other, and a spool valve which can adjust an area of a second opening between the backpressure chamber of the poppet valve and the actuator passage. The controller unit controls the electromagnetic valves in such a manner that the second opening is opened when actuator pressure is transited to a high state from a low state lower than pump pressure (or backpressure) on the basis of a fore-and-aft pressure difference of the spool valve.SELECTED DRAWING: Figure 10C

Description

Technical Field

[0001] The present invention relates to a work machine provided with a flow control valve for controlling the flow rate of hydraulic oil to a hydraulic actuator.

Background Art

[0002] Work machines such as hydraulic excavators are provided with a plurality of hydraulic actuators. As a control method for the hydraulic actuators of a work machine, there are direction switching control for switching the supply and discharge directions of hydraulic oil to the hydraulic actuator, meter-in opening control for controlling the supply flow rate of hydraulic oil from a hydraulic pump to the hydraulic actuator, and meter-out opening control for controlling the discharge flow rate from the hydraulic actuator to an oil tank, and a control method performed by a single spool valve is known.

[0003] When performing meter-in opening control and meter-out opening control with a single spool valve, the relationship between the opening area on the meter-in side and the opening area on the meter-out side with respect to an operation command (operation pressure) to the spool valve is uniquely determined.

[0004] Therefore, when performing a combined operation of operating a plurality of hydraulic actuators, due to differences in the loads of the plurality of hydraulic actuators, the operation of the hydraulic actuators may not be the operation intended by the operator. For example, even if the operation command is maintained during a combined operation, so-called inflow occurs in which the meter-in flow rate increases as the pressure difference between the load pressure and the pump pressure of the hydraulic actuator on the low-load side increases, and the speed of the hydraulic actuator on the low-load side may become greater than the speed intended by the operator. Also, the speed of the hydraulic actuator on the high-load side may become smaller than the speed intended by the operator due to a decrease in the meter-in flow rate to the hydraulic actuator on the high-load side. Thus, when performing meter-in opening control and meter-out opening control with a single spool valve, there is a possibility that the operability may deteriorate.

[0005] Therefore, in order to operate the hydraulic actuator at the speed intended by the operator, a hydraulic circuit has been proposed in which an auxiliary flow control valve capable of controlling the supply flow rate to the direction control valve is arranged upstream of a direction control valve (spool valve) that changes the meter-in opening according to an operation command (see Patent Document 1 and Patent Document 2).

[0006] In the hydraulic circuit described in Patent Document 1, when boom raising is detected, the supply flow rate of pressure oil to the direction control valve for the bucket is restricted by an auxiliary flow control valve provided upstream of the direction control valve for the bucket.

[0007] Patent Document 1 discloses an auxiliary flow control valve (FIGS. 7 to 9 of Patent Document 1) having a pilot spool valve (pilot variable throttle valve) and a poppet valve (seat valve). The pilot spool valve is driven by a command pressure. When the pilot spool valve opens, a flow occurs in the pilot spool valve. The poppet valve is driven by the pressure difference between the pump passage and the back pressure chamber of the poppet valve generated according to the flow rate of the pilot spool valve. The valve body (poppet) of the poppet valve is displaced to a position where the forces acting on the valve body are balanced, and the opening area of the poppet valve is maintained.

[0008] According to this configuration, by miniaturizing the pilot spool valve driven by a command pressure lower than the pump pressure, the inertial force and sliding force acting on the valve body (spool) of the pilot spool valve can be reduced. Also, the poppet valve can be driven by a pump pressure higher than the command pressure. As a result, the auxiliary flow control valve has excellent responsiveness. Further, a check valve is built into the valve body of the poppet valve. For this reason, when the pressures of the pump passage and the actuator passage are reversed and the pressure of the actuator passage becomes higher than the pressure of the pump passage, backflow of the hydraulic oil can be prevented.

[0009] Patent Document 2 discloses a hydraulic circuit including a flow control valve that controls the supply flow rate from a hydraulic pump to a hydraulic actuator, and a direction control valve that is disposed downstream of the flow control valve, switches the supply / discharge direction of the hydraulic oil to the hydraulic actuator, and controls the discharge flow rate from the hydraulic actuator.

Prior Art Documents

Patent Documents

[0010]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0011] The meter-in flow rate is desired to be controlled with high responsiveness. However, when a pilot spool valve and a poppet valve described in Patent Document 1 are adopted for the flow control valve described in Patent Document 2 in order to control the meter-in flow rate with high responsiveness, the following problems occur.

[0012] When the supply flow rate from the hydraulic pump to the hydraulic actuator is controlled from 0 (zero) to the maximum value by the flow control valve, the opening of the pilot spool valve needs to be controlled between fully closed and fully open. In a state where the opening of the pilot spool valve is fully closed, the pressure in the back pressure chamber of the poppet valve becomes equal to the pressure in the pump passage. For this reason, if the pressure on the hydraulic actuator side of the pilot spool valve becomes higher than the pressure on the hydraulic pump side of the pilot spool valve, the poppet valve may open. As a result, due to the occurrence of backflow from the hydraulic actuator to the discharge line of the hydraulic pump, the operation of other hydraulic actuators connected to the discharge line may become unstable.

[0013] An object of the present invention is to provide a working machine capable of controlling the meter-in flow rate with high responsiveness and preventing backflow from a hydraulic actuator to a discharge line of a hydraulic pump.

Means for Solving the Problems

[0014] A working machine according to one aspect of the present invention includes a machine body, a working device attached to the machine body, a prime mover, a hydraulic pump driven by the prime mover, a plurality of hydraulic actuators that operate by the discharge pressure of the hydraulic pump and drive the working device, a plurality of direction control valves provided between the hydraulic actuators and the hydraulic pump, connected in parallel to the discharge line of the hydraulic pump, and switching the flow direction of the pressure oil supplied from the hydraulic pump to the plurality of hydraulic actuators, a plurality of flow control valves provided upstream of the direction control valves and controlling the flow rate of the pressure oil supplied to the plurality of hydraulic actuators, a plurality of solenoid valves that output a command pressure to the plurality of flow control valves, an operating device that outputs an operation signal for operating the working device, and a controller unit that controls the solenoid valves based on the operation signal from the operating device. The flow control valve includes a pump passage connected to the discharge line, an actuator passage connected to the hydraulic actuator via the direction control valve, a poppet provided between the pump passage and the actuator passage, capable of blocking a first opening between the pump passage and the actuator passage, and capable of adjusting the area of the first opening, a poppet valve having a back pressure chamber formed on the back surface of the poppet and communicating with the pump passage, a check valve provided in a passage communicating the pump passage and the back pressure chamber, allowing the flow from the pump passage to the back pressure chamber and prohibiting the flow from the back pressure chamber to the pump passage, a spool provided between the back pressure chamber and the actuator passage, capable of blocking a second opening between the back pressure chamber and the actuator passage, and capable of adjusting the area of the second opening, and a spool valve having a command pressure chamber into which the command pressure from the solenoid valve is input. Further, the working machine includes a differential pressure detection device that detects the differential pressure across the spool valve.The controller unit monitors whether the pressure on the hydraulic actuator side of the spool valve has transitioned from a state lower than the pressure on the hydraulic pump side of the spool valve to a higher state based on the detection result of the differential pressure detection device, and when the pressure on the hydraulic actuator side of the spool valve has transitioned from a state lower than the pressure on the hydraulic pump side of the spool valve to a higher state, controls the solenoid valve so that the second opening opens.

Advantages of the Invention

[0015] According to the present invention, it is possible to provide a working machine that can control the meter-in flow rate with high responsiveness and prevent backflow from the hydraulic actuator to the discharge line of the hydraulic pump.

Brief Description of the Drawings

[0016]

Figure 1

Figure 2A

Figure 2B

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Figure 9

Figure 10A

Figure 10B

Figure 10C

Figure 10D

Figure 11

Figure 12

Figure 13

Figure 14

Figure 15

Figure 16

Figure 17

[0017] With reference to the drawings, a working machine according to an embodiment of the present invention will be described.

[0018] <First Embodiment> FIG. 1 is a side view of a hydraulic excavator 901 shown as an example of a work machine according to the first embodiment of the present invention. As shown in FIG. 1, the hydraulic excavator 901 includes a machine body 220 and a front work device (hereinafter referred to as a work device) 203 attached to the machine body 220. The machine body 220 includes a crawler-type traveling body 201 and a revolving body 202 rotatably provided with respect to the traveling body 201.

[0019] A pair of left and right hydraulic motors for traveling (hereinafter referred to as traveling motors) are provided on the traveling body 201. The left crawler is driven by a traveling motor (also referred to as a left traveling motor) 201L, and the right crawler (not shown) is driven by a traveling motor (also referred to as a right traveling motor), so that the left and right crawlers are independently rotationally driven. Thereby, the traveling body 201 travels forward or backward.

[0020] The revolving body 202 includes a revolving frame 202a, an operator's cab 207 provided on the front side of the revolving frame 202a, a counterweight 209 provided on the rear side of the revolving frame 202a, and a machine room 208 provided between the operator's cab 207 and the counterweight 209. In the operator's cab 207, an operation device (including the operation devices 95a and 95b in FIG. 2B) that outputs an operation signal for operating the work device 203, the traveling body 201, and the revolving body 202, an operator's seat on which the operator sits, and a controller unit 94 that controls each part of the hydraulic excavator 901 are arranged. The operation device includes operation members such as levers and pedals operated by an operator, and an operation amount sensor that detects the operation amount of the operation member. The operation amount sensor outputs a signal representing the detection result as an operation signal to the controller unit 94.

[0021] In the machinery room 208, there are mounted an engine 217 which is a prime mover, a hydraulic pump driven by the engine 217, and a hydraulic motor for slewing (hereinafter referred to as a slewing motor) 211, etc. The counterweight 209 is provided to ensure the weight balance of the hydraulic excavator 901. The slewing body 202 is slewed rightward or leftward with respect to the traveling body 201 by the slewing motor 211.

[0022] The working device 203 is an articulated working device attached to the slewing body 202, and has a plurality of hydraulic actuators (hydraulic cylinders) and a plurality (three in this embodiment) of drive target members driven by the plurality of hydraulic actuators. The boom 204, the arm 205, and the bucket 206 which are drive target members are connected in series. The plurality of hydraulic actuators (boom cylinder 204a, arm cylinder 205a, and bucket cylinder 206a) operate by the discharge pressure of hydraulic pumps 1, 2, 3 (see FIG. 2A) described later to drive the working device 203. By driving the working device 203 by the plurality of hydraulic actuators, operations such as excavation are performed.

[0023] The base end portion of the boom 204 is rotatably connected to the front portion of the slewing body 202 via a boom pin. The base end portion of the arm 205 is rotatably connected to the tip end portion of the boom 204 via an arm pin. The bucket 206 is rotatably connected to the tip end portion of the arm 205 via a bucket pin.

[0024] The boom 204 is rotationally driven by the telescopic movement of the boom cylinder 204a, which is a hydraulic cylinder. The arm 205 is rotationally driven by the telescopic movement of the arm cylinder 205a, which is a hydraulic cylinder. The bucket 206 is rotationally driven by the telescopic movement of the bucket cylinder 206a, which is a hydraulic cylinder. One end of the boom cylinder 204a is connected to the boom 204, and the other end is connected to the slewing frame 202a of the slewing body 202. One end of the arm cylinder 205a is connected to the arm 205, and the other end is connected to the boom 204. One end of the bucket cylinder 206a is connected to the bucket 206 via a bucket link, and the other end is connected to the arm 205.

[0025] The hydraulic excavator 901 is equipped with a plurality of attitude sensors for detecting the attitude and operating state of the hydraulic excavator 901. The plurality of attitude sensors include IMUs (Inertial Measurement Units) 212, 213, 214 for detecting the attitude and operating state of the working device 203, and IMUs 215, 216 for detecting the attitude of the machine body 220 and the rotational speed of the slewing body 202.

[0026] The IMU 212 is attached to the boom 204, the IMU 213 is attached to the arm 205, the IMU 214 is attached to the bucket link, and the IMUs 215, 216 are attached to the slewing body 202. The IMUs 212 to 216 acquire the angular velocity and acceleration of the three orthogonal axes of the boom 204, the arm 205, the bucket 206, and the slewing body 202, and output them to the controller unit 94. The controller unit 94 calculates parameters related to the attitude, such as the angle and angular velocity around the boom pin of the boom 204, the angle and angular velocity around the arm pin of the arm 205, the angle and angular velocity around the bucket pin of the bucket 206, and the pitch angle, roll angle, slewing angle, and slewing speed of the slewing body 202. Note that an IMU controller may be provided separately from the controller unit 94, and the IMU controller may calculate parameters related to the attitude based on signals from the plurality of IMUs 212 to 216 and output the calculation results to the controller unit 94.

[0027] As the attitude sensor of the working device 203, instead of the above IMU 212 to 214, a potentiometer that outputs a voltage signal according to the rotation angles of the boom 204, the arm 205, and the bucket 206 may be adopted. Further, as the attitude sensor of the working device 203, a stroke sensor that detects the strokes of the boom cylinder 204a, the arm cylinder 205a, and the bucket cylinder 206a may be adopted. As the attitude sensor of the aircraft body 220, instead of the above IMU 215 and 216, an inclination angle sensor or a rotary encoder may be provided to detect the inclination angle (pitch angle and roll angle) of the aircraft body 220, the turning angle and the turning speed of the slewing body 202.

[0028] With reference to FIGS. 2A and 2B, the hydraulic drive device 902 of the hydraulic excavator 901 will be described. FIGS. 2A and 2B are circuit diagrams of the hydraulic drive device 902 according to the first embodiment of the present invention. FIG. 2A shows the hydraulic equipment connected to the first to third hydraulic pumps, and FIG. 2B shows the solenoid valves connected to the pilot pump, the controller unit, and the equipment connected to the controller unit.

[0029] As shown in FIGS. 2A and 2B, the hydraulic drive device 902 includes a first hydraulic pump 1, a second hydraulic pump 2, a third hydraulic pump 3, a pilot pump 4, a hydraulic oil tank 5, a plurality of control valves (direction control valves 6 to 16, flow control valves 21 to 31, bleed-off valves 35 to 37, and a merging valve 17), and a controller unit 94 that controls the operations of the plurality of control valves. The controller unit 94 controls the plurality of control valves shown in FIG. 2A by controlling the solenoid valves shown in FIG. 2B. Hydraulic oil is stored in the hydraulic oil tank 5.

[0030] The first to third hydraulic pumps 1 to 3 shown in FIG. 2A are driven by the engine 217, suck the hydraulic oil in the hydraulic oil tank 5, and discharge it to the discharge lines 41, 51, 61. The first to third hydraulic pumps 1 to 3 are variable displacement hydraulic pumps whose discharge capacity (displacement volume per revolution) can be changed. The first to third hydraulic pumps 1 to 3 are, for example, swash plate type or swash shaft type piston pumps. The pilot pump 4 shown in FIG. 2B is driven by the engine 217, sucks the hydraulic oil in the hydraulic oil tank 5, and discharges it to the pilot line 96. The pilot pump 4 is a fixed displacement hydraulic pump with a constant discharge capacity.

[0031] As shown in FIG. 2A, the discharge capacity (tilt angle) of the first hydraulic pump 1 is controlled by a regulator attached to the first hydraulic pump 1. The regulator of the first hydraulic pump 1 includes a command pressure chamber 1a. The discharge capacity (tilt angle) of the second hydraulic pump 2 is controlled by a regulator attached to the second hydraulic pump 2. The regulator of the second hydraulic pump 2 includes a command pressure chamber 2a. The discharge capacity (tilt angle) of the third hydraulic pump 3 is controlled by a regulator attached to the third hydraulic pump 3. The regulator of the third hydraulic pump 3 includes a command pressure chamber 3a.

[0032] In the discharge line 41 of the first hydraulic pump 1, there are provided in parallel a direction control valve 6 (hereinafter also referred to as the right travel direction control valve) which is provided between the first hydraulic pump 1 and a right travel motor (not shown) and switches the flow direction of the pressure oil supplied from the first hydraulic pump 1 to the right travel motor (not shown), a direction control valve 7 (hereinafter also referred to as the bucket direction control valve) which is provided between the first hydraulic pump 1 and the bucket cylinder 206a and switches the flow direction of the pressure oil supplied from the first hydraulic pump 1 to the bucket cylinder 206a, a direction control valve 8 (hereinafter also referred to as the second arm direction control valve) which is provided between the first hydraulic pump 1 and the arm cylinder 205a and switches the flow direction of the pressure oil supplied from the first hydraulic pump 1 to the arm cylinder 205a, and a direction control valve 9 (hereinafter also referred to as the first boom direction control valve) which is provided between the first hydraulic pump 1 and the boom cylinder 204a and switches the flow direction of the pressure oil supplied from the first hydraulic pump 1 to the boom cylinder 204a.

[0033] The right travel direction control valve 6 is connected to the first hydraulic pump 1 via an oil passage 42 branched from the discharge line 41. The bucket direction control valve 7 is connected to the first hydraulic pump 1 via an oil passage 44 branched from the discharge line 41. The second arm direction control valve 8 is connected to the first hydraulic pump 1 via an oil passage 46 branched from the discharge line 41. The first boom direction control valve 9 is connected to the first hydraulic pump 1 via an oil passage 48 branched from the discharge line 41.

[0034] In the discharge line 41, a first main relief valve 38 for defining the maximum pressure of the discharge line 41 is provided to protect the hydraulic circuit from excessive pressure rise. The first hydraulic pump 1 is connected to the hydraulic oil tank 5 via the first main relief valve 38. In the discharge line 41, a first bleed-off valve 35 is provided. The first hydraulic pump 1 is connected to the hydraulic oil tank 5 via the first bleed-off valve 35.

[0035] In the discharge line 51 of the second hydraulic pump 2, there are a direction control valve (hereinafter also referred to as the second boom direction control valve) 10 provided between the second hydraulic pump 2 and the boom cylinder 204a for switching the flow direction of the pressure oil supplied from the second hydraulic pump 2 to the boom cylinder 204a, a direction control valve (hereinafter also referred to as the first arm direction control valve) 11 provided between the second hydraulic pump 2 and the arm cylinder 205a for switching the flow direction of the pressure oil supplied from the second hydraulic pump 2 to the arm cylinder 205a, a direction control valve (hereinafter also referred to as the first attachment direction control valve) 12 provided between the second hydraulic pump 2 and a first actuator (not shown) for driving a first special attachment (not shown), and a direction control valve (hereinafter also referred to as the left travel direction control valve) 13 provided between the second hydraulic pump 2 and the left travel motor 201L for switching the flow direction of the pressure oil supplied from the second hydraulic pump 2 to the left travel motor 201L, which are connected in parallel. The first special attachment is, for example, a small mower provided in place of the bucket 206. The first attachment direction control valve 12 is used when a small mower is attached to the arm 205 in place of the bucket 206.

[0036] The second boom direction control valve 10 is connected to the second hydraulic pump 2 via an oil passage 52 branched from the discharge line 51. The first arm direction control valve 11 is connected to the second hydraulic pump 2 via an oil passage 54 branched from the discharge line 51. The first attachment direction control valve 12 is connected to the second hydraulic pump 2 via an oil passage 56 branched from the discharge line 51. The left travel direction control valve 13 is connected to the second hydraulic pump 2 via an oil passage 58 branched from the discharge line 51.

[0037] The discharge line 51 is provided with a second main relief valve 39 that defines the maximum pressure of the discharge line 51 in order to protect the hydraulic circuit from excessive pressure rise. The second hydraulic pump 2 is connected to the hydraulic oil tank 5 via the second main relief valve 39. The discharge line 51 is provided with a second bleed-off valve 36. The second hydraulic pump 2 is connected to the hydraulic oil tank 5 via the second bleed-off valve 36.

[0038] The discharge line 41 of the first hydraulic pump 1 and the discharge line 51 of the second hydraulic pump 2 are connected via a confluence valve 17.

[0039] The discharge line 61 of the third hydraulic pump 3 is provided, between the third hydraulic pump 3 and the swing motor 211, with a direction control valve (hereinafter also referred to as the swing direction control valve) 14 that switches the flow direction of the pressure oil supplied from the third hydraulic pump 3 to the swing motor 211, and, between the third hydraulic pump 3 and the boom cylinder 204a, with a direction control valve (hereinafter also referred to as the third boom direction control valve) 15 that switches the flow direction of the pressure oil supplied from the third hydraulic pump 3 to the boom cylinder 204a, and, between the third hydraulic pump 3 and a second actuator (not shown) that drives a second special attachment (not shown), with a direction control valve (hereinafter also referred to as the second attachment direction control valve) 16 that switches the flow direction of the pressure oil supplied from the third hydraulic pump 3 to the second actuator (not shown), and these are connected in parallel.

[0040] Note that the second attachment direction control valve 16 is used when a second special attachment having a second actuator in addition to the first special attachment is attached to the working device 203, or when a second special attachment having two actuators, namely a first actuator and a second actuator, in place of the first special actuator is attached.

[0041] The swing direction control valve 14 is connected to the third hydraulic pump 3 via an oil passage 62 branching from the discharge line 61. The third boom direction control valve 15 is connected to the third hydraulic pump 3 via an oil passage 64 branching from the discharge line 61. The second attachment direction control valve 16 is connected to the third hydraulic pump 3 via an oil passage 66 branching from the discharge line 61.

[0042] A third main relief valve 40 that defines the maximum pressure of the discharge line 61 is provided in the discharge line 61 to protect the hydraulic circuit from excessive pressure rise. The third hydraulic pump 3 is connected to the hydraulic oil tank 5 via the third main relief valve 40. A third bleed-off valve 37 is provided in the discharge line 61. The third hydraulic pump 3 is connected to the hydraulic oil tank 5 via the third bleed-off valve 37.

[0043] A flow control valve (hereinafter also referred to as the right travel flow control valve) 21 that adjusts the flow rate of the pressure oil supplied to the right travel motor is provided in the oil passage 42 upstream of the right travel direction control valve 6. A flow control valve (hereinafter also referred to as the bucket flow control valve) 22 that adjusts the flow rate of the pressure oil supplied to the bucket cylinder 206a is provided in the oil passage 44 upstream of the bucket direction control valve 7. A flow control valve (hereinafter also referred to as the second arm flow control valve) 23 that adjusts the flow rate of the pressure oil supplied to the arm cylinder 205a is provided in the oil passage 46 upstream of the second arm direction control valve 8. A flow control valve (hereinafter also referred to as the first boom flow control valve) 24 that adjusts the flow rate of the pressure oil supplied to the boom cylinder 204a is provided in the oil passage 48 upstream of the first boom direction control valve 9.

[0044] In the oil passage 52 upstream of the direction control valve 10 for the second boom, a flow control valve (hereinafter also referred to as the flow control valve for the second boom) 25 for adjusting the flow rate of the pressure oil supplied to the boom cylinder 204a is provided. In the oil passage 54 upstream of the direction control valve 11 for the first arm, a flow control valve (hereinafter also referred to as the flow control valve for the first arm) 26 for adjusting the flow rate of the pressure oil supplied to the arm cylinder 205a is provided. In the oil passage 56 upstream of the direction control valve 12 for the first attachment, a flow control valve (hereinafter also referred to as the flow control valve for the first attachment) 27 for adjusting the flow rate of the pressure oil supplied to the first attachment is provided. In the oil passage 58 upstream of the direction control valve 13 for left travel, a flow control valve (hereinafter also referred to as the flow control valve for left travel) 28 for adjusting the flow rate of the pressure oil supplied to the left travel motor 201L is provided.

[0045] In the oil passage 62 upstream of the slewing direction control valve 14, a flow control valve (hereinafter also referred to as the flow control valve for slewing) 29 for adjusting the flow rate of the pressure oil supplied to the slewing motor 211 is provided. In the oil passage 64 upstream of the direction control valve 15 for the third boom, a flow control valve (hereinafter also referred to as the flow control valve for the third boom) 30 for adjusting the flow rate of the pressure oil supplied to the boom cylinder 204a is provided. In the oil passage 66 upstream of the direction control valve 16 for the second attachment, a flow control valve (hereinafter also referred to as the flow control valve for the second attachment) 31 for adjusting the flow rate of the pressure oil supplied to the second attachment is provided.

[0046] Thus, the hydraulic drive device 902 includes a plurality of direction control valves 6 to 16 for controlling the flow direction of the pressure oil supplied to the plurality of hydraulic actuators, and a plurality of flow control valves 21 to 31 provided upstream of each of the plurality of direction control valves 6 to 16 for controlling the flow rate (i.e., the meter-in flow rate) of the pressure oil supplied to the plurality of hydraulic actuators.

[0047] The plurality of flow control valves 21 to 31 have the same configuration. Therefore, in FIG. 2A, the configuration of the flow control valve 26 is shown as a representative, and the diagrams showing the configurations of the other flow control valves 21 to 25, 27 to 31 are omitted. The flow control valve 26 includes a sheet-shaped poppet valve 32 and a pilot spool valve 33 that controls the opening area of the poppet valve 32. The pilot spool valve 33 operates in response to a command pressure output from the solenoid valve unit 93 (see FIG. 2B). Details of the structure and function of the flow control valve 26 will be described later.

[0048] As shown in FIG. 2B, the pilot pump 4 is connected to the hydraulic oil tank 5 via a pilot relief valve 92 for generating a pilot primary pressure. The pilot pump 4 is also connected to the solenoid valve unit 93 via a pilot line 96. The solenoid valve unit 93 includes a plurality of solenoid valves that output a command pressure to the regulators of the hydraulic pumps 1 to 3, the direction control valves 6 to 16, the flow control valves 21 to 31, the bleed-off valves 35 to 37, and the confluence valve 17. The plurality of solenoid valves are electromagnetic proportional pressure reducing valves that output, as a command pressure, a secondary pressure generated by reducing the primary pressure of the pilot pump 4 in accordance with a control signal from the controller unit 94.

[0049] In FIG. 2B, among the plurality of solenoid valves, a solenoid valve 93a that outputs a command pressure to the command pressure chamber 2a of the regulator of the second hydraulic pump 2, a solenoid valve 93b that outputs a command pressure to the command pressure chamber 11a of the direction control valve 11 for the first arm, a solenoid valve 93c that outputs a command pressure to the command pressure chamber 11b of the direction control valve 11 for the first arm, a solenoid valve 93d that outputs a command pressure to the command pressure chamber 33a of the flow control valve 26 for the first arm, and a solenoid valve 93e that outputs a command pressure to the command pressure chamber 36a of the second bleed-off valve 36 are shown, and the illustration of the other solenoid valves is omitted.

[0050] Among the plurality of solenoid valves for which illustration is omitted, there are solenoid valves that output a command pressure to the command pressure chambers 1a and 3a of the regulators of the hydraulic pumps 1 and 3, solenoid valves that output a command pressure to the command pressure chambers of the direction control valves 6 to 10 and 12 to 16, solenoid valves that output a command pressure to the command pressure chambers of the flow control valves 21 to 25 and 27 to 31, and solenoid valves that output a command pressure to the command pressure chambers 35a and 37a of the regulators of the bleed-off valves 35 and 37.

[0051] The hydraulic drive device 902 includes an operating device 95a that can switch the first boom direction control valve 9, the second boom direction control valve 10, and the third boom direction control valve 15, and an operating device 95b that can switch the first arm direction control valve 11 and the second arm direction control valve 8. For the sake of simplicity of explanation, the right travel operation lever for switching the right travel direction control valve 6, the bucket operation lever for switching the bucket direction control valve 7, the first attachment operation lever for switching the first attachment direction control valve 12, the left travel operation lever for switching the left travel direction control valve 13, the swing operation lever for switching the swing direction control valve 14, and the second attachment operation lever for switching the second attachment direction control valve 16 are not shown in the figure.

[0052] As shown in FIG. 2A, a pressure sensor (hereinafter, also referred to as a pump pressure sensor) 81 that detects the pump pressure, which is the discharge pressure of the second hydraulic pump 2, and outputs a detection signal, which is a signal representing the detection result, to the controller unit 94 is provided in the discharge line 51 of the second hydraulic pump 2. A pressure sensor (hereinafter, also referred to as an actuator pressure sensor) 82 that detects the actuator pressure, which is the pressure of the hydraulic actuator (arm cylinder 205a), and outputs a detection signal, which is a signal representing the detection result, to the controller unit 94 is provided in the actuator passage 54A, which is an oil passage connecting the first arm direction control valve 11 and the first arm flow control valve 26.

[0053] As shown in FIG. 2B, the pump pressure sensor 81 and the actuator pressure sensor 82 constitute a differential pressure detection device 80 that detects the differential pressure ΔP across the pilot spool valve 33 of the first arm flow control valve 26. Although not shown, the differential pressure detection device 80 is similarly provided for the flow control valves 21-25, 27-31. That is, although not shown, the actuator pressure sensor 82 that constitutes the differential pressure detection device 80 is provided for each of the plurality of flow control valves 21-25, 27-31. Also, although not shown, the pump pressure sensor 81 that constitutes the differential pressure detection device 80 for detecting the differential pressure ΔP across the pilot spool valve 33 of the flow control valves 21-24 is provided in the discharge line 41 of the first hydraulic pump 1. Further, although not shown, the pump pressure sensor 81 that constitutes the differential pressure detection device 80 for detecting the differential pressure ΔP across the pilot spool valve 33 of the flow control valves 29-31 is provided in the discharge line 61 of the third hydraulic pump 3.

[0054] Signals output from the operating devices 95a, 95b (including operating devices not shown), signals output from the pressure sensors 81, 82 (including pressure sensors 81, 82 not shown), and signals output from the IMUs 212-216 are input to the controller unit 94. The controller unit 94 outputs control signals to the solenoid valves 93a-93e (including solenoid valves not shown) of the solenoid valve unit 93.

[0055] The controller unit 94 controls the solenoid valves 93a-93e (including solenoid valves not shown) based on the operation signals from the operating devices 95a, 95b (including operating devices not shown) and the detection signals from the pressure sensors 81, 82 (including pressure sensors 81, 82 not shown).

[0056] The controller unit 94 is composed of a computer including a processing device 94v such as a CPU (Central Processing Unit), MPU (Micro Processing Unit), DSP (Digital Signal Processor), a non-volatile memory 94w such as a ROM (Read Only Memory), a flash memory, a hard disk drive, a volatile memory 94x called a so-called RAM (Random Access Memory), an input interface 94y, an output interface 94z, and other peripheral circuits. Note that the controller unit 94 may be composed of one computer or a plurality of computers. Further, as the processing device 94v, an ASIC (application specific integrated circuit), an FPGA (Field Programmable Gate Array), etc. can be used.

[0057] The non-volatile memory 94w stores programs capable of executing various operations, threshold values, data tables, etc. That is, the non-volatile memory 94w is a storage medium (storage device) capable of reading a program for realizing the functions of the present embodiment. The processing device 94v is an arithmetic device that expands the program stored in the non-volatile memory 94w into the volatile memory 94x and executes arithmetic operations, and performs predetermined arithmetic processing on the signals taken in from the input interface 94y, the non-volatile memory 94w, and the volatile memory 94x according to the program.

[0058] The input interface 94y converts the signals input from various devices (operation devices 95a, 95b, pressure sensors 81, 82, IMU 212 to 216, etc.) so that they can be arithmetically operated by the processing device 94v. Further, the output interface 94z generates an output signal corresponding to the arithmetic result in the processing device 94v and outputs the signal to various devices (solenoid valves 93a to 93e, etc.).

[0059] Referring to FIG. 3, the structure of the flow control valve 26 will be described in detail. FIG. 3 is a schematic cross-sectional view showing the structure of the flow control valve 26. As described above, since the other flow control valves 21 to 25, 27 to 31 have the same configuration as the flow control valve 26, the description thereof will be omitted. As shown in FIG. 3, the flow control valve 26 includes a pump passage 54P connected to the discharge line 51 of the second hydraulic pump 2, an actuator passage 54A connected to the arm cylinder 205a (see FIG. 2A) via the first arm direction control valve 11 (see FIG. 2A), a seat-shaped poppet valve 32 provided between the pump passage 54P and the actuator passage 54A, and a pilot spool valve 33 provided between the back pressure chamber 32e of the poppet valve 32 and the actuator passage 54A.

[0060] The poppet valve 32 can block the opening (hereinafter referred to as the first opening) 121 between the pump passage 54P and the actuator passage 54A, and includes a poppet (valve body) 32a capable of adjusting the area of the first opening 121, and a back pressure chamber (pressure chamber) 32e formed on the back surface of the poppet 32a and communicating with the pump passage 54P.

[0061] The poppet 32a is slidably installed in the main housing 110. The main housing 110 is formed with a housing hole 32f for accommodating the poppet 32a, a pump passage 54P, a pump pressure chamber 32c, an actuator passage 54A, an actuator pressure chamber 32d, and an oil passage 78b. The pump pressure chamber 32c is continuously formed with the pump passage 54P. The actuator pressure chamber 32d is continuously formed with the actuator passage 54A. The oil passage 78b is continuously formed with the actuator pressure chamber 32d. The pump passage 54P and the actuator passage 54A constitute an oil passage 54 branched from the discharge line 51.

[0062] The poppet 32a has a pressure-receiving portion facing the pump pressure chamber 32c and receiving the pressure of the pump pressure chamber 32c, a pressure-receiving portion facing the actuator pressure chamber 32d and receiving the pressure of the actuator pressure chamber 32d, and a pressure-receiving portion facing the back pressure chamber 32e and receiving the pressure of the back pressure chamber 32e.

[0063] A spring 101 for biasing the poppet 32a against the pressures in the pump pressure chamber 32c and the actuator pressure chamber 32d is provided in the back pressure chamber 32e. Due to the biasing force of the spring 101, the poppet 32a seats on the seat portion 110a. When the poppet 32a is seated on the seat portion 110a, the communication between the pump pressure chamber 32c and the actuator pressure chamber 32d is blocked.

[0064] An internal passage 113 for communicating the pump pressure chamber 32c and the back pressure chamber 32e is provided in the poppet 32a. A check valve 114 that allows the flow from the pump pressure chamber 32c to the back pressure chamber 32e and prohibits the flow from the back pressure chamber 32e to the pump pressure chamber 32c is provided in the internal passage 113.

[0065] The check valve 114 has a plug 114p that closes the opening on the back pressure chamber 32e side of the internal passage 113, a ball 114b that can block the internal passage 113, and a spring 114s provided between the plug 114p and the ball 114b for biasing the ball 114b against the pressure in the pump pressure chamber 32c. The internal passage 113 has a large-diameter portion where the ball 114b is disposed and a small-diameter portion smaller than the large-diameter portion, and due to the biasing force of the spring 114s, the ball 114b closes the small-diameter portion of the internal passage 113.

[0066] A communication groove 32b that opens into the back pressure chamber 32e is provided on the outer peripheral surface of the end portion (the upper end portion shown in the figure) on the back pressure chamber 32e side of the poppet 32a. A communication passage that communicates the internal passage 113 and the communication groove 32b is formed in the poppet 32a. The hydraulic oil in the pump pressure chamber 32c is guided to the back pressure chamber 32e through the check valve 114 and the communication groove 32b. An opening (hereinafter referred to as the third opening) 123 between the poppet 32a and the accommodation hole 32f constitutes a controllable variable throttle for communicating the back pressure chamber 32e and the pump pressure chamber 32c. The opening area of this controllable variable throttle changes according to the movement amount of the poppet 32a. The opening characteristics of the controllable variable throttle are determined by the shape, size, and number of the communication grooves 32b.

[0067] On the outer peripheral surface of the end portion (the lower end portion shown in the figure) of the poppet 32a on the pump pressure chamber 32c side, a plurality of notches 102 that open into the pump pressure chamber 32c are formed. The plurality of notches 102 are provided at intervals in the circumferential direction of the poppet 32a. When the poppet 32a is seated on the seat portion 110a, the communication between the pump pressure chamber 32c and the actuator pressure chamber 32d is blocked. When the poppet 32a is separated from the seat portion 110a, the pump pressure chamber 32c and the actuator pressure chamber 32d communicate with each other through the notch 102. The notch 102 has a first notch portion 102a and a second notch portion 102b that is continuously formed with the first notch portion 102a. The seat portion 110a and the lower end portion of the poppet 32a where the notch 102 is formed form a first opening 121. The first opening 121 constitutes a variable throttle that communicates the pump pressure chamber 32c and the actuator pressure chamber 32d. The opening area of this variable throttle changes according to the movement amount of the poppet 32a. The opening characteristics of the variable throttle are determined by the shape, size, and number of the notches 102.

[0068] The pilot spool valve 33 can block an opening (hereinafter referred to as a second opening) 122 between the back pressure chamber 32e and the actuator pressure chamber 32d, and has a spool (valve body) 112 that can adjust the area of the second opening 122, and a command pressure chamber 33a into which a command pressure from the solenoid valve 93d is input.

[0069] The spool 112 is slidably installed in the pilot housing 111. The pilot housing 111 is attached to the main housing 110. The pilot housing 111 is formed with a housing hole 111a for housing the spool 112, a command pressure chamber 33a facing one end (the right end shown in the figure) of the spool 112, and a spring chamber 33b facing the other end (the left end shown in the figure) of the spool 112.

[0070] One end (the right end in the figure) of the spool 112 is connected to a rod 109 extending into the command pressure chamber 33a. When the rod 109 abuts against the wall surface of the command pressure chamber 33a, the movement of the spool 112 in the right direction in the figure is restricted. A spring 107 is provided in the spring chamber 33b to bias the spool 112 against the command pressure in the command pressure chamber 33a. The spring chamber 33b communicates with the hydraulic oil tank 5 maintained at atmospheric pressure.

[0071] The accommodation hole 111a of the pilot housing 111 is a non-through hole extending from the left end in the figure of the pilot housing 111 toward the right in the figure. The opening of the accommodation hole 111a is closed by a plug 106. The spring chamber 33b is formed by the plug 106 and the left end of the spool 112. In the accommodation hole 111a of the pilot housing 111, a first oil chamber 104 and a second oil chamber 105 are formed at a predetermined interval in the axial direction. The first oil chamber 104 is connected to an oil passage 77 communicating with the back pressure chamber 32e, and the second oil chamber 105 is connected to an oil passage 78a communicating with the actuator pressure chamber 32d via an oil passage 78b. The oil passage 78a and the oil passage 78b constitute an oil passage 78 communicating the accommodation hole 111a and the actuator pressure chamber 32d.

[0072] The spool 112 has a columnar first land portion 112a and a second land portion 112b that are in sliding contact with the inner peripheral surface of the accommodation hole 111a. The first land portion 112a is configured to be able to block the first oil chamber 104 and the second oil chamber 105 by its outer peripheral surface. The second land portion 112b forms the spring chamber 33b with its end face and the plug 106.

[0073] A plurality of notches 108 are formed on the outer peripheral surface of the first land portion 112a. The plurality of notches 108 are provided at intervals in the circumferential direction of the first land portion 112a. The notches 108 extend in the axial direction of the spool 112 from the end face of the first land portion 112a on the side of the second land portion 112b.

[0074] The second opening 122 is formed by the inner peripheral surface of the accommodation hole 111a and the first land portion 112a in which the notch 108 is formed. The second opening 122 constitutes a throttle portion that communicates the first oil chamber 104 and the second oil chamber 105. The opening area of this throttle portion changes according to the movement amount of the spool 112. The opening characteristics of the throttle portion are determined by the shape, size, and number of the notches 108.

[0075] FIG. 4 is a diagram showing the opening characteristics of the flow control valves 21 to 31 according to the first embodiment of the present invention. The horizontal axis indicates the command pressure input to the command pressure chamber 33a of the pilot spool valve 33, and the vertical axis indicates the opening area size of the poppet valve 32 and the pilot spool valve 33. As shown in FIG. 4, the opening area aMP of the first opening 121 of the poppet valve 32 decreases as the command pressure increases, and becomes fully closed when the command pressure becomes a predetermined value P0 or more. The opening area aPS of the second opening 122 of the pilot spool valve 33 decreases as the command pressure increases, and becomes fully closed when the command pressure becomes a predetermined value P0 or more.

[0076] Note that the opening characteristics of the poppet valve 32 and the opening characteristics of the pilot spool valve 33 are set by the shape, size, and number of the notch 102, the communication groove 32b, and the notch 108. The opening characteristics of the poppet valve 32 and the opening characteristics of the pilot spool valve 33 shown in FIG. 4 are examples, and various opening characteristics can be obtained. For example, in the example shown in FIG. 4, an example in which the opening areas of the poppet valve 32 and the pilot spool valve 33 become 0 (zero) at the same command pressure P0 is shown, but the command pressure at which the opening area aMP of the poppet valve 32 becomes 0 (zero) and the command pressure at which the opening area aPS of the pilot spool valve 33 becomes 0 (zero) may be different.

[0077] The state of the force acting on the poppet valve 32 will be described with reference to FIG. 5. FIG. 5 is a diagram showing the relationship of each pressure receiving area of the poppet valve 32. As shown in FIG. 5, the sum of the pressure receiving area Ap of the poppet 32a in the pump pressure chamber 32c and the pressure receiving area Aa of the poppet 32a in the actuator pressure chamber 32d is equal to the pressure receiving area Ac of the poppet 32a in the back pressure chamber 32e.

[0078] The state of the force acting on the poppet 32a is organized from the relationship between the pump pressure Pp which is the pressure in the pump pressure chamber 32c, the back pressure Pc which is the pressure in the back pressure chamber 32e, the actuator pressure Pa which is the pressure in the actuator pressure chamber 32d, and the pressure receiving areas Ap, Ac, Aa of each of the poppet 32a of the poppet valve 32 as follows.

[0079] - First state - When the pilot spool valve 33 is in the open state and the pump pressure Pp is higher than the actuator pressure Pa, the magnitude relationship of the respective pressures Pp, Pc, Pa is as shown in the following formula (1), and the relationship of the forces acting on the poppet 32a is as shown in the following formula (2). Pp > Pc > Pa ···(1) Ap × Pp + Aa × Pa = Ac × Pc ···(2) In formula (2), the left side is the force in the opening direction of the poppet 32a, and the right side is the force in the closing direction of the poppet 32a.

[0080] When the pilot spool valve 33 is in the open state and, as in formula (1), the pressures are low in the order of the pump pressure Pp, the back pressure Pc, and the actuator pressure Pa, the poppet 32a is at a position where the forces are balanced and the opening area aMP of the first opening 121 is maintained, and the hydraulic oil flows from the pump pressure chamber 32c to the actuator pressure chamber 32d.

[0081] - Second state - When the pilot spool valve 33 is in the open state and the actuator pressure Pa is higher than the pump pressure Pp, the magnitude relationship of the respective pressures Pp, Pc, Pa is as shown in the following formula (3), and the relationship of the forces acting on the poppet 32a is as shown in the following formula (4). Pp < Pc = Pa ···(3) Ap × Pp + Aa × Pa < Ac × Pc ···(4) In formula (4), the left side is the force in the opening direction of the poppet 32a, and the right side is the force in the closing direction of the poppet 32a.

[0082] When the pilot spool valve 33 is open and the actuator pressure Pa is greater than the pump pressure Pp, as shown in Equation (3), the back pressure Pc becomes equal to the actuator pressure Pa, and the force in the closing direction of the poppet 32a becomes greater than the force in the opening direction. Therefore, the poppet 32a fully closes, preventing backflow from the actuator pressure chamber 32d to the pump pressure chamber 32c.

[0083] -Third state- When the pilot spool valve 33 is closed and the actuator pressure Pa is higher than the pump pressure Pp, the magnitude relationship of the pressures Pp, Pc, and Pa is as shown in the following Equation (5), and the relationship of the forces acting on the poppet 32a is as shown in the following Equation (6). Pp = Pc < Pa ···(5) Ap × Pp + Aa × Pa > Ac × Pc ···(6) In Equation (6), the left side is the force in the opening direction of the poppet 32a, and the right side is the force in the closing direction of the poppet 32a.

[0084] When the pilot spool valve 33 closes, as shown in Equation (5), the back pressure Pc becomes equal to the pump pressure Pp, and as shown in Equation (6), the force in the opening direction of the poppet 32a becomes greater than the force in the closing direction. Therefore, the poppet 32a may be displaced in the opening direction, and backflow from the actuator pressure chamber 32d to the pump pressure chamber 32c may occur.

[0085] If backflow occurs from the actuator pressure chamber 32d to the pump pressure chamber 32c, an unintended flow of hydraulic oil may occur in the hydraulic circuit, potentially impairing the controllability and operability of the hydraulic actuator.

[0086] The flow control valve 26 according to this embodiment controls the supply flow rate from the second hydraulic pump 2 to the arm cylinder 205a from 0 (zero) to the maximum value. For this reason, the pilot spool valve 33 is controlled between fully closed and fully open. However, when the pilot spool valve 33 is fully closed, there is a possibility of the above-described third state occurring, and due to the reverse flow from the arm cylinder 205a to the discharge line 51 of the second hydraulic pump 2, the operations of other hydraulic actuators (left travel motor 201L, boom cylinder 204a, etc.) connected to the discharge line 51 may become unstable.

[0087] Therefore, based on the detection result of the differential pressure detection device 80, the controller unit 94 according to this embodiment determines whether or not the actuator pressure Pa, which is the pressure on the hydraulic actuator side of the pilot spool valve 33, has transitioned from a state lower than the pump pressure Pp, which is the pressure on the hydraulic pump side of the pilot spool valve 33, to a higher state. When the actuator pressure Pa has transitioned from a state lower than the pump pressure Pp to a higher state, the controller unit 94 controls the solenoid valve so that the second opening 122 of the pilot spool valve 33 opens.

[0088] Referring to FIG. 6, the functions of the controller unit 94 will be described in detail. FIG. 6 is a functional block diagram of the controller unit 94. As shown in FIG. 6, the controller unit 94 functions as an actuator target flow rate calculation unit 94a, a pump target flow rate calculation unit 94b, a pump control command unit 94c, a direction control valve target opening calculation unit 94d, a direction control valve control command unit 94e, a reference opening calculation unit 94f, a pressure state determination unit 94g, an auxiliary opening calculation unit 94h, a flow control valve target opening determination unit 94i, a flow control valve control command unit 94j, a bleed-off valve target opening calculation unit 94k, and a bleed-off valve control command unit 94l by executing a program stored in the nonvolatile memory 94w.

[0089] The actuator target flow rate calculation unit 94a calculates a target supply flow rate, which is the target value of the flow rate of the hydraulic oil supplied to the hydraulic actuator, based on the operation amount output from the operation device and the target flow rate characteristics determined in advance for each hydraulic actuator. The target flow rate characteristics of the hydraulic actuator are characteristics that define the relationship between the operation amount and the target supply flow rate, and are stored in the non-volatile memory 94w in a table format. The target flow rate characteristics of the hydraulic actuator are such that the target supply flow rate increases as the operation amount increases. The pump target flow rate calculation unit 94b calculates a target discharge flow rate, which is the target value of the discharge flow rate of the hydraulic pump, based on the target supply flow rates of the respective hydraulic actuators calculated by the actuator target flow rate calculation unit 94a.

[0090] The pump control command unit 94c calculates a pump control command value based on the target discharge flow rate calculated by the pump target flow rate calculation unit 94b and the predetermined pump command characteristics. The pump control command unit 94c outputs a pump control command, which is an electrical signal corresponding to the calculation result, to the electromagnetic valve for pump flow rate control (for example, the electromagnetic valve 93a shown in FIG. 2B). The pump command characteristics are characteristics that define the relationship between the target discharge flow rate and the pump control command value for the electromagnetic valve for pump flow rate control, and are stored in the non-volatile memory 94w in a table format.

[0091] The directional control valve target opening calculation unit 94d calculates the target opening area of the directional control valve based on the operation amount output from the operation device and the target opening characteristics of the directional control valve determined in advance. As shown in FIG. 7, the target opening characteristics of the directional control valve are characteristics that define the relationship between the operation amount and the target opening area of the directional control valve, and are stored in the non-volatile memory 94w in a table format. The target opening characteristics of the directional control valve are such that the target opening area increases as the operation amount increases. Note that the target opening characteristics of the directional control valve are not the opening characteristics for the purpose of controlling the meter-in flow rate.

[0092] The direction control valve control command unit 94e shown in FIG. 6 calculates a direction control valve control command value based on the target opening area of the direction control valve calculated by the direction control valve target opening calculation unit 94d and a predetermined direction control valve command characteristic. The direction control valve control command unit 94e outputs a direction control valve control command, which is an electrical signal corresponding to the calculation result, to the electromagnetic valves for the direction control valve (for example, the electromagnetic valves 93b and 93c shown in FIG. 2B). The direction control valve command characteristic is a characteristic that defines the relationship between the target opening area of the direction control valve and the direction control valve control command value for the electromagnetic valves for the direction control valve, and is stored in the non-volatile memory 94w in a table format.

[0093] The reference opening calculation unit 94f calculates the reference opening area of the flow control valve based on the target supply flow rate calculated by the actuator target flow rate calculation unit 94a, the pump pressure detected by the pump pressure sensor 81, and the actuator pressure detected by the actuator pressure sensor 82.

[0094] The reference opening calculation unit 94f calculates the reference opening area a_BaseFcv of the flow control valve according to the following formula (7). a_BaseFcv = Q_TgtAct / (Cd × √(2(Pp - Pa) / ρ)) ···(7) Q_TgtAct is the target supply flow rate of the hydraulic actuator calculated by the actuator target flow rate calculation unit 94a. Pp is the pump pressure detected by the pump pressure sensor 81. Pa is the actuator pressure detected by the actuator pressure sensor 82. Cd is the flow coefficient of the flow control valve, and ρ is the density of the hydraulic oil. The flow coefficient Cd and ρ are stored in the non-volatile memory 94w.

[0095] The pressure state determination unit 94g determines the state of the differential pressure ΔP across the pilot spool valve 33 based on the pump pressure Pp detected by the pump pressure sensor 81 and the actuator pressure Pa detected by the actuator pressure sensor 82. The pressure state determination unit 94g calculates the differential pressure ΔP across the pilot spool valve 33 by subtracting the actuator pressure Pa detected by the actuator pressure sensor 82 from the pump pressure Pp detected by the pump pressure sensor 81 (ΔP = Pp - Pa). When the pump pressure Pp is higher than the actuator pressure Pa, the pressure state determination unit 94g determines that the pressure state of the flow control valve 26 is the normal pressure state. When the pump pressure Pp is lower than the actuator pressure Pa, the pressure state determination unit 94g determines that the pressure state of the flow control valve 26 is the differential pressure reversal state.

[0096] Based on the detection result of the differential pressure detection device 80, the pressure state determination unit 94g monitors the differential pressure between the pump pressure Pp and the actuator pressure Pa. Further, based on the detection result of the differential pressure detection device 80, the pressure state determination unit 94g monitors whether a transition has occurred from the normal pressure state to the differential pressure reversal state, and whether a transition has occurred from the differential pressure reversal state to the normal pressure state.

[0097] The auxiliary opening calculation unit 94h calculates the auxiliary opening area of the flow control valve based on the pressure state determination result by the pressure state determination unit 94g and a predetermined auxiliary opening characteristic. As shown in FIG. 8, the auxiliary opening characteristic is a characteristic that defines the relationship between the differential pressure ΔP across the pilot spool valve 33 and the auxiliary opening area, and is stored in the non-volatile memory 94w in a table format. For example, when the pressure state determination unit 94g determines that the pressure state of the flow control valve is the normal pressure state, that is, when the differential pressure ΔP is 0 or more, the auxiliary opening calculation unit 94h calculates the auxiliary opening area as 0 (zero). When the pressure state determination unit 94g determines that the pressure state of the flow control valve 26 is the differential pressure reversal state, that is, when the differential pressure ΔP is a negative value, the auxiliary opening calculation unit 94h calculates the auxiliary opening area as a predetermined value aPS1.

[0098] The predetermined value aPS1 may be set to a magnitude that enables the poppet valve 32 to be fully closed. If the predetermined value aPS1 is too large, when returning from the differential pressure reversal state to the normal pressure state, the poppet valve 32 may suddenly open, potentially causing a shock. Therefore, it is preferable that the predetermined value aPS1 be as small as possible.

[0099] The flow control valve target opening determination unit 94i shown in FIG. 6 determines the target opening area of the flow control valve based on the reference opening area of the flow control valve calculated by the reference opening calculation unit 94f and the auxiliary opening area of the flow control valve calculated by the auxiliary opening calculation unit 94h. The flow control valve target opening determination unit 94i determines the larger of the reference opening area of the flow control valve and the auxiliary opening area of the flow control valve as the target opening area of the flow control valve. Note that the target opening area of the flow control valve refers to the target value of the combined opening area of the poppet valve 32 and the pilot spool valve 33.

[0100] The flow control valve control command unit 94j calculates a flow control valve control command value based on the target opening area of the flow control valve determined by the flow control valve target opening determination unit 94i and a predetermined flow control valve command characteristic. The flow control valve control command unit 94j outputs a flow control valve control command, which is an electrical signal corresponding to the calculation result, to an electromagnetic valve for the flow control valve (for example, the electromagnetic valve 93d shown in FIG. 2B). The flow control valve command characteristic is a characteristic that defines the relationship between the target opening area of the flow control valve and the flow control valve control command value for the electromagnetic valve for the flow control valve, and is stored in the non-volatile memory 94w in a table format.

[0101] The bleed-off valve target opening calculation unit 94k calculates the target opening area of the bleed-off valve based on the operation amount output from the operation device and a predetermined bleed-off valve target opening characteristic. As shown in FIG. 9, the bleed-off valve target opening characteristic is a characteristic that defines the relationship between the operation amount and the target opening area of the bleed-off valve, and is stored in the non-volatile memory 94w in a table format. The bleed-off target opening characteristic is such that the target opening area decreases as the operation amount increases, and becomes 0 (zero) when the operation amount is equal to or greater than a predetermined value.

[0102] The bleed-off valve control command unit 94l calculates a bleed-off valve control command value based on the bleed-off valve target opening area calculated by the bleed-off valve target opening calculation unit 94k and a predetermined bleed-off valve command characteristic. The bleed-off valve control command unit 94l outputs a bleed-off valve control command, which is an electrical signal corresponding to the calculation result, to the solenoid valve of the bleed-off valve (for example, the solenoid valve 93e shown in FIG. 2B). The bleed-off valve command characteristic is a characteristic that defines the relationship between the target opening area of the bleed-off valve and the bleed-off valve control command value for the solenoid valve for the bleed-off valve, and is stored in the non-volatile memory 94w in a table format. With reference to FIG. 10A, an example of the control of the hydraulic pump executed by the controller unit 94 will be described. The process shown in the flowchart of FIG. 10A is started when an ignition switch (not shown) is turned on, and after initial settings (not shown) are made, it is repeatedly executed at a predetermined control cycle.

[0103] As shown in FIG. 10A, in step S101, the controller unit 94 determines whether an operating device is being operated. If it is determined in step S101 that at least one of the plurality of operating devices is being operated, the process proceeds to step S102. If it is determined in step S101 that none of the plurality of operating devices is being operated, the process shown in the flowchart of FIG. 10A for this control cycle ends.

[0104] In step S102, the controller unit 94 calculates the target supply flow rate Q_TgtAct(i) of each hydraulic actuator based on the operation amount output from the operating device and the target flow rate characteristic of the hydraulic actuator, and proceeds to step S103. i is a symbol for identifying the hydraulic actuator.

[0105] For example, the controller unit 94 calculates the target supply flow rate Q_TgtAct(1) of the boom cylinder 204a based on the operation amount output from the operation device 95a of the boom 204 and the target flow rate characteristics of the boom cylinder 204a. Further, the controller unit 94 calculates the target supply flow rate Q_TgtAct(2) of the arm cylinder 205a based on the operation amount output from the operation device 95b of the arm 205 and the target flow rate characteristics of the arm cylinder 205a.

[0106] In step S103, the controller unit 94 calculates the target discharge flow rate Q_TgtPmp of each hydraulic pump based on the target supply flow rate Q_TgtAct(i) of the hydraulic actuator calculated in step S102, and proceeds to step S104. For example, the controller unit 94 calculates the target discharge flow rate of the first hydraulic pump 1 based on the sum of the target supply flow rates of the hydraulic actuators connected to the discharge line 41 of the first hydraulic pump 1. The controller unit 94 calculates the target discharge flow rate of the second hydraulic pump 2 based on the sum of the target supply flow rates of the hydraulic actuators connected to the discharge line 51 of the second hydraulic pump 2. The controller unit 94 calculates the target discharge flow rate of the third hydraulic pump 3 based on the sum of the target supply flow rates of the hydraulic actuators connected to the discharge line 61 of the third hydraulic pump 3.

[0107] Note that the target discharge flow rate Q_TgtPmp of the hydraulic pump is preferably calculated in consideration of bleed-off flow rate, drain flow rate, and the like.

[0108] In step S104, the controller unit 94 generates a pump control command based on the target discharge flow rate Q_TgtPmp of the hydraulic pump calculated in step S103, outputs it to the electromagnetic valve for pump flow rate control, and ends the process shown in the flowchart of FIG. 10A in this control cycle.

[0109] For example, when a pump control command is output from the controller unit 94 to the solenoid valve 93a for controlling the flow rate of the second hydraulic pump 2, the solenoid valve 93a generates a pump control command pressure and outputs it to the command pressure chamber 2a of the regulator of the second hydraulic pump 2. When the pump control command pressure is input to the command pressure chamber 2a, the discharge capacity (tilt angle) of the second hydraulic pump 2 changes, and the discharge flow rate of the second hydraulic pump 2 is controlled to be the target discharge flow rate Q_TgtPmp.

[0110] With reference to FIG. 10B, an example of the control of the direction control valve executed by the controller unit 94 will be described. Since the control contents of each of the direction control valves 6 to 16 are the same, the control contents of the direction control valve 11 that controls the flow direction of the hydraulic oil to the arm cylinder 205a will be described as a representative below. The process shown in the flowchart of FIG. 10B is started when an ignition switch (not shown) is turned on, and after initial settings (not shown) are made, it is repeatedly executed at a predetermined control cycle.

[0111] As shown in FIG. 10B, in step S201, the controller unit 94 determines whether or not the operating device 95b is being operated. If it is determined in step S201 that the operating device 95b is being operated, the process proceeds to step S202. If it is determined in step S201 that the operating device 95b is not being operated, the process shown in the flowchart of FIG. 10B in this control cycle ends.

[0112] In step S202, the controller unit 94 calculates the target opening area a_TgtMS of the direction control valve 11 based on the operation amount output from the operating device 95b and the target opening characteristic of the direction control valve 11 (see FIG. 7), and proceeds to step S203.

[0113] In step S203, the controller unit 94 generates a direction control valve control command based on the target opening area a_TgtMS calculated in step S202 and the direction control valve command characteristic, and outputs it to the solenoid valves 93b and 93c for the direction control valve 11, and ends the process shown in the flowchart of FIG. 10B in this control cycle.

[0114] For example, when a direction control valve control command is output from the controller unit 94 to the solenoid valve 93b for the direction control valve 11, the solenoid valve 93b generates a direction control valve command pressure and outputs it to the command pressure chamber 11a of the direction control valve 11. When the direction control valve command pressure is input to the command pressure chamber 11a, the direction control valve 11 operates and is controlled so that the opening area of the direction control valve 11 becomes the target opening area a_TgtMS.

[0115] With reference to FIG. 10C, an example of the control of the flow control valve executed by the controller unit 94 will be described. Since the control contents of each of the flow control valves 21 to 31 are the same, hereinafter, the control contents of the flow control valve 26 that controls the meter-in flow rate of the hydraulic oil for the arm cylinder 205a will be described as a representative. The process shown in the flowchart of FIG. 10C is started when an ignition switch (not shown) is turned on, and after initial settings (not shown) are made, it is repeatedly executed at a predetermined control cycle.

[0116] As shown in FIG. 10C, in step S301, the controller unit 94 determines whether or not the operating device 95b is being operated. If it is determined in step S301 that the operating device 95b is being operated, the process proceeds to step S302. If it is determined in step S301 that the operating device 95b is not being operated, the process shown in the flowchart of FIG. 10C for the present control cycle ends.

[0117] In step S302, the controller unit 94 calculates the target supply flow rate Q_TgtAct of the arm cylinder 205a based on the operation amount output from the operating device 95b and the target flow rate characteristics of the arm cylinder 205a, and proceeds to step S303 and step S304.

[0118] In step S303, based on the target supply flow rate Q_TgtAct calculated in step S302, the pump pressure Pp detected by the pump pressure sensor 81, and the actuator pressure Pa detected by the actuator pressure sensor 82, the controller unit 94 calculates the reference opening area a_BaseFcv of the flow control valve 26 according to Equation (7), and proceeds to step S306.

[0119] In step S304, based on the pump pressure Pp detected by the pump pressure sensor 81 and the actuator pressure Pa detected by the actuator pressure sensor 82, the controller unit 94 calculates the differential pressure ΔP (= Pp - Pa) across the pilot spool valve 33 of the flow control valve 26, and proceeds to step S305.

[0120] In step S305, based on the differential pressure ΔP calculated in step S304 and the auxiliary opening characteristic (see FIG. 8), the controller unit 94 calculates the auxiliary opening area a_AuxFcv of the flow control valve 26, and proceeds to step S306.

[0121] When the processes of both step S303 and step S305 are completed, the maximum value selection process of step S306 is executed. In step S306, the controller unit 94 selects the larger one between the reference opening area a_BaseFcv calculated in step S303 and the auxiliary opening area a_AuxFcv calculated in step S305, and determines the selected one as the target opening area a_TgtFcv of the flow control valve 26. When the maximum value selection process of step S306 is completed, the process proceeds to step S307.

[0122] In step S307, based on the target opening area a_TgtFcv determined in step S306 and the flow control valve command characteristic, the controller unit 94 generates a flow control valve control command, outputs it to the solenoid valve 93d for the flow control valve 26, and ends the process shown in the flowchart of FIG. 10C in this control cycle.

[0123] When a flow control valve control command is output from the controller unit 94 to the solenoid valve 93d for the flow control valve 26, the solenoid valve 93d generates a flow control valve command pressure and outputs it to the command pressure chamber 33a of the flow control valve 26. When the flow control valve command pressure is input to the command pressure chamber 33a, the pilot spool valve 33 of the flow control valve 26 operates, and the opening area of the flow control valve 26 (the combined opening area of the poppet valve 32 and the pilot spool valve 33) is controlled to be the target opening area a_TgtFcv.

[0124] Referring to FIG. 10D, an example of the control of the bleed-off valve executed by the controller unit 94 will be described. Since the control contents of each of the bleed-off valves 35 to 37 are the same, the control contents of the bleed-off valve 36 provided in the discharge line 51 of the second hydraulic pump 2 will be described as representative below. The process shown in the flowchart of FIG. 10D is started when an ignition switch (not shown) is turned on, and after initial settings (not shown) are made, it is repeatedly executed at a predetermined control cycle.

[0125] As shown in FIG. 10D, in step S401, the controller unit 94 determines whether the operating device of the hydraulic actuator provided in the discharge line 51 of the second hydraulic pump 2 is being operated. If it is determined in step S401 that at least one of the operating devices is being operated, the process proceeds to step S402. If it is determined in step S401 that none of the operating devices is being operated, the process shown in the flowchart of FIG. 10D in this control cycle ends.

[0126] In step S402, the controller unit 94 calculates the target opening area a_TgtBov of the bleed-off valve 36 based on the operation amount output from the operating device and the target opening characteristic (see FIG. 9) of the bleed-off valve 36, and proceeds to step S403.

[0127] In step S403, the controller unit 94 generates a bleed-off valve control command based on the target opening area a_TgtBov calculated in step S402 and the bleed-off valve command characteristics, outputs it to the electromagnetic valve 93e for the bleed-off valve 36, and ends the process shown in the flowchart of FIG. 10B in the present control cycle.

[0128] When the bleed-off valve control command is output from the controller unit 94 to the electromagnetic valve 93e for the bleed-off valve 36, the electromagnetic valve 93e generates a bleed-off valve command pressure and outputs it to the command pressure chamber 36a of the bleed-off valve 36. When the bleed-off valve command pressure is input to the command pressure chamber 36a, the bleed-off valve 36 operates and is controlled so that the opening area of the bleed-off valve 36 becomes the target opening area a_TgtBov.

[0129] Referring to FIG. 11, the main operations and effects of the hydraulic excavator 901 according to the present embodiment will be described. FIG. 11 is a diagram showing the time-series changes of each parameter (operation amount, target supply flow rate to the hydraulic actuator, pressure, differential pressure ΔP between the front and rear of the pilot spool valve 33, opening area of the pilot spool valve 33, and opening area of the poppet valve 32) of the hydraulic excavator 901 according to the present embodiment. Hereinafter, an example of the operations of the third boom flow control valve 30, the second boom flow control valve 25, and the first arm flow control valve 26 when the combined operation of the boom 204 and the arm 205 is performed will be described.

[0130] The horizontal axis in FIGS. 11(a) to (f) indicates the time from the start of the operation (time point T1). The vertical axis in FIG. 11(a) indicates the operation amount of the operation device. In FIG. 11(a), the solid line indicates the operation amount LBm of the operation device 95a of the boom 204, and the broken line indicates the operation amount LAm of the operation device 95b of the arm 205.

[0131] The vertical axis of Fig. 11(b) indicates the target supply flow rate calculated by the controller unit 94. In Fig. 11(b), the solid line indicates the target value QtBm3 of the flow rate of the hydraulic oil supplied to the boom cylinder 204a through the flow control valve 30 for the third boom and the direction control valve 15 for the third boom. In Fig. 11(b), the dashed-dotted line indicates the target value QtBm2 of the flow rate of the hydraulic oil supplied to the boom cylinder 204a through the flow control valve 25 for the second boom and the direction control valve 10 for the second boom. In Fig. 11(b), the broken line indicates the target value QtAm1 of the flow rate of the hydraulic oil supplied to the arm cylinder 205a through the flow control valve 26 for the first arm and the direction control valve 11 for the first arm.

[0132] The vertical axis of Fig. 11(c) indicates pressure. In Fig. 11(c), the solid line indicates the actuator pressure PaBm of the boom cylinder 204a, and the broken line indicates the actuator pressure PaAm of the arm cylinder 205a. In Fig. 11(c), the dashed-dotted line indicates the pump pressure Pp3 of the third hydraulic pump 3, and the dotted line indicates the pump pressure Pp2 of the second hydraulic pump 2.

[0133] The vertical axis of Fig. 11(d) indicates the differential pressure ΔP across the pilot spool valve 33. In Fig. 11(d), the solid line indicates the differential pressure ΔPBm3 across the pilot spool valve 33 of the flow control valve 30 for the third boom, the dashed-dotted line indicates the differential pressure ΔPBm2 across the pilot spool valve 33 of the flow control valve 25 for the second boom, and the broken line indicates the differential pressure ΔPAm1 across the pilot spool valve 33 of the flow control valve 26 for the first arm.

[0134] The vertical axis of Fig. 11(e) indicates the opening area aPs of the pilot spool valve 33. In Fig. 11(e), the solid line indicates the opening area aPSBm3 of the pilot spool valve 33 of the flow control valve 30 for the third boom, the dashed-dotted line indicates the opening area aPSBm2 of the pilot spool valve 33 of the flow control valve 25 for the second boom, and the broken line indicates the opening area aPSAm1 of the pilot spool valve 33 of the flow control valve 26 for the first arm.

[0135] The vertical axis in Fig. 11(f) indicates the opening area aMP of the poppet valve 32. In Fig. 11(e), the solid line indicates the opening area aMPBm3 of the poppet valve 32 of the flow control valve 30 for the third boom, the dashed-dotted line indicates the opening area aMPBm2 of the poppet valve 32 of the flow control valve 25 for the second boom, and the dashed line indicates the opening area aMPAm1 of the poppet valve 32 of the flow control valve 26 for the first arm.

[0136] At time point T1, the operator starts operating the boom operating device 95a. As shown in Fig. 11(a), the operation amount LBm of the boom operating device 95a increases from time point T1 to time point T2 and is maintained at the maximum value after time point T2. The controller unit 94 calculates the target supply flow rate according to the operation amount LBm of the operating device 95a. The controller unit 94 outputs a pump control command corresponding to the target supply flow rate to the electromagnetic valves corresponding to the second hydraulic pump 2 and the third hydraulic pump 3, and outputs a flow control valve control command corresponding to the target supply flow rate to the electromagnetic valves corresponding to the flow control valve 25 for the second boom and the flow control valve 30 for the third boom. As a result, the pump control command pressure is input to the command pressure chamber 2a of the second hydraulic pump 2 and the command pressure chamber 3a of the third hydraulic pump 3, and the flow control valve command pressure is input to the command pressure chamber 33a of the flow control valve 25 for the second boom and the command pressure chamber 33a of the flow control valve 30 for the third boom.

[0137] As shown in Fig. 11(b), Fig. 11(e) and Fig. 11(f), the target supply flow rates QtBm3, QtBm2, the opening areas aPSBm3, aPSBm2 of the pilot spool valve 33 and the opening areas aMPBm3, aMPBm2 of the poppet valve 32 increase from time point T1 to time point T2 and are maintained at the maximum value from time point T2 to time point T3.

[0138] Although not shown in the drawings, the controller unit 94 outputs bleed-off valve control commands to solenoid valves corresponding to the bleed-off valve 36 provided in the discharge line 51 of the second hydraulic pump 2 and the bleed-off valve 37 provided in the discharge line 61 of the third hydraulic pump 3. The bleed-off valves 36 and 37 have an opening area that decreases as the operation amount increases and fully closes between time point T1 and time point T2. Further, the controller unit 94 outputs direction control valve control commands to solenoid valves corresponding to the second boom direction control valve 10 and the third boom direction control valve 15. The direction control valves 10 and 15 have an opening area that increases as the operation amount increases and fully opens between time point T1 and time point T2.

[0139] As shown in FIG. 11(c), since the pressurized oil discharged from the second hydraulic pump 2 and the third hydraulic pump 3 flows into the boom cylinder 204a, the pump pressures Pp2 and Pp3 and the actuator pressure PaBm of the boom cylinder 204a increase from time point T1 to time point T2. Further, as shown in FIG. 11(d), the differential pressure ΔPAm1 across the pilot spool valve 33 of the first arm flow control valve 26 also increases from time point T1 to time point T2.

[0140] From time point T2 to time point T3, the pump pressures Pp3, Pp2, and the actuator pressure PaBm are maintained at the maximum values.

[0141] At time point T3, the operator starts operating the arm operating device 95b. As shown in FIG. 11(a), the operation amount of the arm operating device 95b increases from time point T3 to time point T4 and is maintained at the maximum value after time point T4. The controller unit 94 calculates the target supply flow rate according to the operation amount Lam of the operating device 95b.

[0142] When shifting from the single operation of the boom 204 to the combined operation of the boom 204 and the arm 205, the controller unit 94 switches the supply destination of the hydraulic oil discharged from the second hydraulic pump 2 from the boom cylinder 204a to the arm cylinder 205a in order to prioritize the operation of the arm 205 connected to the discharge line 51 of the second hydraulic pump 2.

[0143] Specifically, from time point T3 to time point T4, the controller unit 94 decreases the target value (target supply flow rate) QtBm2 of the flow rate of the hydraulic oil supplied to the boom cylinder 204a through the boom second flow control valve 25 in response to an increase in the operation amount Lam of the operation device 95b. Further, from time point T3 to time point T4, the controller unit 94 increases the flow rate (target supply flow rate) QtAm1 of the hydraulic oil supplied to the arm cylinder 205a through the arm first flow control valve 26 in response to an increase in the operation amount Lam of the operation device 95b.

[0144] Therefore, the controller unit 94 increases the reference opening area of the arm first flow control valve 26 and decreases the reference opening area of the boom second flow control valve 25 in response to an increase in the operation amount Lam of the operation device 95b.

[0145] The controller unit 94 outputs a flow control valve control command corresponding to the target supply flow rate to the solenoid valves corresponding to the boom second flow control valve 25 and the arm first flow control valve 26. Thereby, the flow control valve command pressure is input to the command pressure chamber 33a of the boom second flow control valve 25 and the command pressure chamber 33a of the arm first flow control valve 26.

[0146] As shown in FIGS. 11(b), 11(e), and 11(f), the target supply flow rate QtAm1, the opening area aPSAm1 of the pilot spool valve 33, and the opening area aMPAm1 of the poppet valve 32 increase from time point T3 to time point T4 and are maintained at the maximum value after time point T4. On the other hand, the target supply flow rate QtBm2, the opening area aPsBm2 of the pilot spool valve 33, and the opening area aMPBm2 of the poppet valve 32 decrease from time point T3 to time point T4 and are maintained at 0 (zero) from time point T4 to time point T5.

[0147] As shown in FIG. 11(c), at time point T3, the supply of hydraulic oil to the arm cylinder 205a is started through the flow control valve 26 for the first arm and the direction control valve 11 for the first arm. At time point T3, since the arm cylinder 205a is in a stopped state, immediately after the discharge line 51 of the second hydraulic pump 2 and the arm cylinder 205a are communicated, due to the inertial load, the actuator pressure PaAm of the arm cylinder 205a temporarily rises to near the pump pressures Pp2, P3 and the actuator pressure PaBm of the boom cylinder 204a.

[0148] After that, when the arm cylinder 205a starts to move, the actuator pressure PaAm of the arm cylinder 205a approaches the load pressure of the arm cylinder 205a. At this time, the load pressure of the arm cylinder 205a is smaller than the load pressure of the boom cylinder 204a. Also, since the discharge line 51 of the second hydraulic pump 2 is still in communication with the boom cylinder 204a via the flow control valve 25 for the second boom, the pump pressure Pp2 becomes a value close to the pump pressure Pp3 and the actuator pressure PaBm of the boom cylinder 204a.

[0149] As shown in FIG. 11(d), from time point T3 to time point T4, the differential pressure ΔPBm2 between the front and rear of the pilot spool valve 33 of the flow control valve 25 for the second boom is maintained at a predetermined value (substantially zero). Also, although the differential pressure ΔPAm1 between the front and rear of the flow control valve 26 for the first arm temporarily decreases from time point T3, since the pump pressure Pp2 is maintained at a state higher than the actuator pressure PaAm of the arm cylinder 205a, the differential pressure ΔPAm1 is maintained at a positive value.

[0150] As shown in FIG. 11(b), at time point T4, when the target value QtBm2 of the flow rate of the hydraulic oil supplied to the boom cylinder 204a through the flow control valve 25 for the second boom and the direction control valve 10 for the second boom becomes 0 (zero), as shown in FIGS. 11(e) and 11(f), the opening area aPSBm2 of the pilot spool valve 33 and the opening area aMPBm2 of the poppet valve 32 of the flow control valve 25 for the second boom become 0 (zero).

[0151] At time T4, since the flow control valve 25 for the second boom is fully closed, the communication between the discharge line 61 of the second hydraulic pump 2 and the boom cylinder 204a is blocked. As a result, as shown in FIG. 11(c), the pump pressure Pp2 of the second hydraulic pump 2 decreases from time T4. Since the pump pressure P2 starts to decrease, the positive / negative of the differential pressure ΔPBm2 across the pilot spool valve 33 of the flow control valve 25 for the second boom is reversed. That is, after time T4, the differential pressure ΔPBm2 across the pilot spool valve 33 of the flow control valve 25 for the second boom is a negative value.

[0152] The pump pressure Pp2 becomes lower than the actuator pressure PaAm of the arm cylinder 205a at time T5. Therefore, after time T5, the differential pressure ΔPAm1 across the pilot spool valve 33 of the flow control valve 26 for the first arm is a negative value.

[0153] At time T4, the controller unit 94 detects the reversal of the positive / negative of the differential pressure ΔPBm2 across the pilot spool valve 33 of the flow control valve 25 for the second boom. At time T4, the controller unit 94 calculates the auxiliary opening area as a predetermined value aPS1. At time T4, the reference opening area is 0 (zero).

[0154] The controller unit 94 determines the auxiliary opening area as the target opening area and outputs a flow control valve control command corresponding to the target opening area to the electromagnetic valve corresponding to the flow control valve 25 for the second boom. As a result, the flow control valve command pressure is input to the command pressure chamber 33a of the flow control valve 25 for the second boom, and the opening area of the pilot spool valve 33 of the flow control valve 25 for the second boom is controlled to be the target opening area (auxiliary opening area aPS1). After time T4, the opening area of the pilot spool valve 33 of the flow control valve 25 for the second boom is the auxiliary opening area aPS1.

[0155] The back pressure chamber 32e of the flow control valve 25 for the second boom and the actuator pressure chamber 32d communicate with each other via the pilot spool valve 33. When the actuator pressure PaBm is greater than the pump pressure Pp2, the pressure in the back pressure chamber 32e becomes the same as the pressure in the actuator pressure chamber 32d. That is, the flow control valve 25 for the second boom assumes the above-described second state, and a closing force acts on the poppet valve 32 of the flow control valve 25 for the second boom, causing the opening of the poppet valve 32 to fully close.

[0156] At time point T6 when a predetermined time has elapsed since time point T5, the pilot spool valve 33 of the flow control valve 25 for the second boom remains in the open state. That is, at time point T6, the second state is maintained. For this reason, even when the magnitude relationship of the differential pressure across the pilot spool valve 33 of the flow control valve 25 for the second boom is reversed (PaBm > Pp2), the opening of the poppet valve 32 remains fully closed.

[0157] Although not shown in the drawings, after time point T6, when the operator stops operating the arm 205, the controller unit 94 increases the reference opening area of the flow control valve 25 for the second boom. As a result, the hydraulic oil discharged from the second hydraulic pump 2 is again supplied to the boom cylinder 204a through the flow control valve 25 for the second boom. Consequently, the pump pressure Pp2 of the second hydraulic pump 2 increases, and the pressure state of the flow control valve 25 for the second boom transitions from the reverse differential pressure state to the normal pressure state.

[0158] Also, although not shown in the drawings, after time point T6, during the combined operation of the boom 204 and the arm 205, if the load pressure of the arm cylinder 205a increases, the pump pressure Pp2 of the second hydraulic pump 2 increases. Therefore, the pressure state of the flow control valve 25 for the second boom transitions from the reverse differential pressure state to the normal pressure state. In this case, the pilot spool valve 33 of the flow control valve 25 for the second boom fully closes.

[0159] According to the above-described embodiment, the following operational effects are achieved. The reference numerals in parentheses indicate an example of the configuration.

[0160] (1) The controller unit 94 controls the flow control valves (25, 26, 30) by controlling the solenoid valve (93d) based on the operation signals from the operation devices (95a, 95b). The controller unit 94 controls the solenoid valve (93d) so that the opening area of the second opening 122 of the pilot spool valve 33 changes from 0 (zero) to the maximum value according to the operation amount of the operation devices (95a, 95b).

[0161] The controller unit 94 monitors whether or not the actuator pressure Pa, which is the pressure on the hydraulic actuator side of the pilot spool valve 33, has transitioned from a state lower than the pump pressure Pp, which is the pressure on the hydraulic pump side of the pilot spool valve 33, to a higher state based on the detection result of the differential pressure detection device 80 (that is, the detection signals from the pressure sensors 81, 82). When the actuator pressure Pa detected by the actuator pressure sensor 82 of the flow control valve (25) has transitioned from a state lower than the pump pressure Pp detected by the pump pressure sensor 81 of the flow control valve (25) to a higher state, the controller unit 94 controls the solenoid valve (the solenoid valve that generates the flow control valve command pressure for the flow control valve 25) so that the second opening 122 of the pilot spool valve 33 of the flow control valve (25) opens.

[0162] According to this configuration, when the controller unit 94 detects the reversal of the forward and backward differential pressure ΔP and opens the pilot spool valve 33 of the flow control valve (25), a closing force in the closing direction for the poppet valve 32 can be ensured, and the poppet valve 32 can be surely seated on the seat portion 110a. Thereby, it is possible to accurately supply the flow rate to the hydraulic actuator to be driven without causing a reverse flow, and to ensure good controllability and operability.

[0163] As described above, according to the present embodiment, it is possible to provide a hydraulic excavator 901 that can control the meter-in flow rate with high responsiveness and can prevent reverse flow from the hydraulic actuators (such as the boom cylinder 204a, the arm cylinder 205a, and the bucket cylinder 206a) to the discharge lines 41, 51, 61 of the hydraulic pumps 1 to 3.

[0164] (2) The controller unit 94 calculates the reference opening area of the flow control valve (25) based on the operation amount of the operation device (95a) and the detection results of the pump pressure sensor 81 and the actuator pressure sensor 82. The controller unit 94 calculates the auxiliary opening area of the flow control valve (25) based on the differential pressure ΔP across the pilot spool valve 33 detected by the differential pressure detection device 80. The controller unit 94 determines the larger of the calculated reference opening area and the auxiliary opening area as the target opening area of the flow control valve (25). The controller unit 94 controls the solenoid valve (the solenoid valve that generates the flow control valve command pressure for the flow control valve 25) based on the determined target opening area.

[0165] When the reference opening area of the pilot spool valve 33 is 0 (zero) and the differential pressure ΔP becomes negative, the opening area of the second opening 122 of the pilot spool valve 33 is controlled to be the auxiliary opening area calculated based on the differential pressure ΔP. Therefore, in a state where the hydraulic pump (2) does not supply hydraulic oil to the hydraulic actuator (204a) through the flow control valve (25), and when the pressure state of the flow control valve (25) is in the differential pressure reversal state (the actuator pressure Pa is higher than the pump pressure Pp), the controller unit 94 can fully close the poppet valve 32 by opening the pilot spool valve 33 of the flow control valve (25). Thereby, it is possible to accurately supply the flow rate to the hydraulic actuator (205a) to be driven without causing the reverse flow of the hydraulic oil from the hydraulic actuator (204a) to the discharge line (51), and to ensure good controllability and operability.

[0166] (3) The controller unit 94 stores an auxiliary opening characteristic (see FIG. 8) that defines the relationship between the differential pressure ΔP across the pilot spool valve 33 and the auxiliary opening area. The controller unit 94 calculates the difference between the pump pressure Pp (the discharge pressure of the hydraulic pump) detected by the pump pressure sensor 81 and the actuator pressure Pa (the pressure of the hydraulic actuator) detected by the actuator pressure sensor 82 as the differential pressure ΔP across the pilot spool valve 33. The controller unit 94 calculates the auxiliary opening area based on the stored auxiliary opening characteristic and the differential pressure ΔP across the pilot spool valve 33.

[0167] According to this configuration, the pump pressure sensor 81 and the actuator pressure sensor 82 used for controlling the flow control valve (25) can be used as the differential pressure detection device 80. Therefore, there is no need to provide a sensor separate from the pump pressure sensor 81 and the actuator pressure sensor 82. As a result, an increase in the number of parts of the hydraulic excavator 901 can be prevented.

[0168] <Second Embodiment> With reference to FIGS. 12 and 13, the hydraulic excavator 901 according to the second embodiment of the present invention will be described. The same or corresponding components as those described in the first embodiment are denoted by the same reference numerals, and the differences will be mainly described. In the first embodiment, an example in which the controller unit 94 calculates the difference between the pump pressure Pp and the actuator pressure Pa as the differential pressure ΔP across the pilot spool valve 33 has been described. In contrast, in the second embodiment, the controller unit 94A calculates the difference between the back pressure Pc, which is the pressure in the back pressure chamber 32e of the poppet valve 32, and the actuator pressure Pa as the differential pressure ΔP across the pilot spool valve 33. Hereinafter, the configuration of the hydraulic excavator 901 according to the second embodiment and the functions of the controller unit 94A will be described in detail.

[0169] FIG. 12 is a diagram showing pressure sensors 82 and 83A provided in the flow control valve 26 according to the second embodiment. The hydraulic excavator 901 according to the second embodiment has the same configuration as that described in the first embodiment. The hydraulic excavator 901 according to the second embodiment includes, in addition to the configuration described in the first embodiment, a pressure sensor (hereinafter also referred to as a back pressure sensor) 83A that detects the back pressure Pc, which is the pressure in the back pressure chamber 32e of the poppet valve 32 of the flow control valve 26, and outputs a detection signal to the controller unit 94A. The back pressure sensor 83A is provided in an oil passage 77 that connects the back pressure chamber 32e and the pilot spool valve 33. Note that the back pressure sensor 83A is similarly provided in the flow control valves 21 to 25 and 27 to 31.

[0170] FIG. 13 is a functional block diagram of the controller unit 94A according to the second embodiment. As shown in FIG. 13, the controller unit 94A according to the second embodiment has functions as a pressure state determination unit 94gA and an auxiliary opening calculation unit 94hA instead of the pressure state determination unit 94g and the auxiliary opening calculation unit 94h described in the first embodiment. In the second embodiment, the differential pressure detection device 80A that detects the differential pressure ΔP across the pilot spool valve 33 is composed of an actuator pressure sensor 82 and a back pressure sensor 83A that detects the pressure in the back pressure chamber 32e, which is the pressure on the hydraulic pump side of the pilot spool valve 33.

[0171] The pressure state determination unit 94gA determines the state of the differential pressure ΔP across the pilot spool valve 33 based on the back pressure Pc detected by the back pressure sensor 83A and the actuator pressure Pa detected by the actuator pressure sensor 82. The pressure state determination unit 94gA calculates the differential pressure ΔP by subtracting the actuator pressure Pa detected by the actuator pressure sensor 82 from the back pressure Pc detected by the back pressure sensor 83A (ΔP = Pc - Pa). When the back pressure Pc is higher than the actuator pressure Pa, the pressure state determination unit 94gA determines that the pressure state of the flow control valve 26 is a normal pressure state. When the back pressure Pc is lower than the actuator pressure Pa, the pressure state determination unit 94g determines that the pressure state of the flow control valve 26 is a differential pressure reverse state.

[0172] The auxiliary opening calculation unit 94hA calculates the auxiliary opening area of the flow control valve based on the determination result of the pressure state by the pressure state determination unit 94gA and a predetermined auxiliary opening characteristic (see FIG. 8). The auxiliary opening characteristic is a characteristic that defines the relationship between the differential pressure ΔP across the pilot spool valve 33 and the auxiliary opening area, and is stored in the non-volatile memory 94w in tabular form. For example, when the pressure state determination unit 94g determines that the pressure state of the flow control valve is in the normal pressure state, that is, when the differential pressure ΔP is 0 or more, the auxiliary opening calculation unit 94hA calculates the auxiliary opening area as 0 (zero). When the pressure state determination unit 94g determines that the pressure state of the flow control valve 26 is in the differential pressure reversal state, that is, when the differential pressure ΔP is a negative value, the auxiliary opening calculation unit 94h calculates the auxiliary opening area as a predetermined value aPS1.

[0173] In the first embodiment, as shown in FIG. 11(e), after time point T4, the opening area of the pilot spool valve 33 is maintained at a predetermined value aPS1. On the other hand, in the second embodiment, at time point T4, when the pilot spool valve 33 is opened, the back pressure Pc and the actuator pressure Pa become the same and the poppet valve 32 is fully closed, which is the same as in the first embodiment. However, in the second embodiment, thereafter, since the differential pressure between the back pressure Pc and the actuator pressure Pa is 0 (zero), the controller unit 94 calculates the auxiliary opening area as 0 (zero), which is different from the first embodiment. In the second embodiment, after the poppet valve 32 is fully closed, the controller unit 94 determines the target opening area of the pilot spool valve 33 as 0 (zero). The controller unit 94 outputs a flow control valve control command corresponding to the determined target opening area. The solenoid valve to which the flow control valve control command is input outputs the flow control valve command pressure to the command pressure chamber 33a of the pilot spool valve 33. As a result, the opening of the pilot spool valve 33 becomes fully closed.

[0174] According to such a second embodiment, in addition to the same operational effects as those of the first embodiment, the following operational effects can be obtained.

[0175] (4) The differential pressure detection device 80A includes a back pressure sensor 83A that detects the pressure in the back pressure chamber 32e of the poppet valve 32, and an actuator pressure sensor 82. The controller unit 94A calculates the difference between the back pressure (the pressure in the back pressure chamber 32e) Pc detected by the back pressure sensor 83A and the actuator pressure (the pressure of the hydraulic actuator) detected by the actuator pressure sensor 82 as the differential pressure ΔP across the pilot spool valve 33. The controller unit 94 calculates the auxiliary opening area based on the stored auxiliary opening characteristics (see FIG. 8) and the differential pressure ΔP across the pilot spool valve 33.

[0176] According to this configuration, when the pressure state of the flow control valve reaches the differential pressure reversal state, after opening the pilot spool valve 33 and fully closing the poppet valve 32, the pilot spool valve 33 can be fully closed. That is, the flow control valve can be returned to its originally required state. As a result, when the flow rate supplied to the hydraulic actuator is controlled by the flow control valve again, the flow control valve can operate smoothly. Therefore, according to the second embodiment, better controllability and operability can be ensured than in the first embodiment.

[0177] <Third Embodiment> With reference to FIGS. 14 to 16, the hydraulic excavator 901 according to the third embodiment of the present invention will be described. Components that are the same as or corresponding to those described in the first embodiment are denoted by the same reference numerals, and the differences will be mainly described. The controller unit 94B according to the third embodiment controls the pilot spool valve 33 to be fully closed when a predetermined time has elapsed after the pressure state of the flow control valve transitions from the normal pressure state to the differential pressure reversal state. Hereinafter, the function of the controller unit 94B of the hydraulic excavator 901 according to the third embodiment will be described in detail.

[0178] FIG. 14 is a functional block diagram of the controller unit 94B according to the third embodiment. As shown in FIG. 14, the controller unit 94B according to the third embodiment further has functions as an opening time measurement unit 94mB and an auxiliary opening correction unit 94nB.

[0179] Similar to the first embodiment, the auxiliary opening calculation unit 94h calculates the auxiliary opening area of the flow control valve based on the determination result of the pressure state by the pressure state determination unit 94g.

[0180] The opening time measurement unit 94mB measures the time after the actuator pressure Pa transitions from the normal pressure state where it is lower than the pump pressure Pp to the high differential pressure reverse state. When the actuator pressure Pa transitions from the normal pressure state where it is lower than the pump pressure Pp to the high differential pressure reverse state, the pilot spool valve 33 opens. Therefore, hereinafter, the time measured by the opening time measurement unit 94mB is also referred to as the opening time To. In this embodiment, the opening time measurement unit 94mB starts measuring the opening time To at the timing when the auxiliary opening area calculated by the auxiliary opening calculation unit 94h changes from 0 (zero) to a value greater than 0 (zero) (predetermined value aPS1). Note that the opening time measurement unit 94mB may start measuring the opening time To at the timing when the differential pressure ΔP calculated by the pressure state determination unit 94g changes from a value of 0 (zero) or more to a value less than 0 (zero).

[0181] The auxiliary opening correction unit 94nB calculates a correction coefficient based on the opening time To measured by the opening time measurement unit 94mB and a predetermined correction characteristic. The correction characteristic is a characteristic that defines the relationship between the opening time To and the correction coefficient Cc, and is stored in the non-volatile memory 94w in a table format. The correction characteristic is such that the correction coefficient Cc is 1 when the opening time To is from 0 (zero) to the time threshold α, and the correction coefficient Cc becomes 0 (zero) when the opening time To is equal to or greater than the time threshold α. Note that the time threshold α is a value arbitrarily set by the designer.

[0182] The auxiliary opening correction unit 94nB corrects the auxiliary opening area by multiplying the calculated correction coefficient Cc by the auxiliary opening area calculated by the auxiliary opening calculation unit 94h.

[0183] Referring to FIG. 16, an example of the control of the flow control valve executed by the controller unit 94B will be described. Note that since the control contents of each of the flow control valves 21 to 31 are the same, the control contents of the flow control valve 26 that controls the meter-in flow rate of the hydraulic oil to the arm cylinder 205a will be described as a representative below.

[0184] FIG. 16 is a diagram similar to FIG. 10C and is a flowchart showing the flow of the process of controlling the flow control valve executed by the controller unit 94B according to the third embodiment. In the flowchart of FIG. 16, the processes of steps S310B, S311B, S312B, and S313B are added between the process of step S305 and the process of step S306 in the flowchart of FIG. 10C.

[0185] As shown in FIG. 16, in step S305, the controller unit 94B calculates the auxiliary opening area a_AuxFcv of the flow control valve 26 based on the differential pressure ΔP before and after calculated in step S304 and the auxiliary opening characteristic (see FIG. 8), and proceeds to step S310B.

[0186] In step S310B, the controller unit 94B determines whether the auxiliary opening area a_AuxFcv calculated in step S305 is greater than 0 (zero). If it is determined in step S310B that the auxiliary opening area a_AuxFcv is greater than 0 (zero), the process proceeds to step S311B. If it is determined in step S310B that the auxiliary opening area a_AuxFcv is 0 or less, the process proceeds to step S306.

[0187] In step S311B, the controller unit 94B measures the opening time To and proceeds to step S312B. That is, the controller unit 94B starts measuring the opening time To from the timing when the auxiliary opening area a_AuxFcv calculated in step S305 becomes a value greater than 0 (zero) (Yes in step S310B → S311B). After that, when the state where the auxiliary opening area a_AuxFcv is greater than 0 (zero) is maintained, the opening time To is measured by adding the control cycle to the opening time To.

[0188] In step S312B, the controller unit 94B calculates a correction coefficient Cc based on the opening time To measured in step 311B and the correction characteristics (see FIG. 15), and proceeds to step S313B. In step S313B, the controller unit 94B corrects the auxiliary opening area a_AuxFcv by multiplying the auxiliary opening area a_AuxFcv calculated in step S305 by the correction coefficient Cc calculated in step S312B. As a result, when the opening time To reaches the time threshold α, the auxiliary opening area a_AuxFcv is corrected to 0 (zero). When the correction process in step S313B is completed, the process proceeds to step S306.

[0189] In the first embodiment, as shown in FIG. 11(e), after time point T4, the opening area of the pilot spool valve 33 is maintained at a predetermined value aPS1. In contrast, in the third embodiment, at time point T4, when the pilot spool valve 33 is opened, the back pressure Pc and the actuator pressure Pa become the same and the poppet valve 32 is fully closed, which is the same as in the first embodiment. However, in the third embodiment, when the time (opening time) To after the pilot spool valve 33 is opened reaches the time threshold α, the controller unit 94B calculates the auxiliary opening area as 0 (zero), which is different from the first embodiment. In the third embodiment, after the poppet valve 32 is fully closed, the controller unit 94 determines the target opening area of the pilot spool valve 33 as 0 (zero). The controller unit 94 outputs a flow control valve control command corresponding to the determined target opening area. The solenoid valve to which the flow control valve control command is input outputs the flow control valve command pressure to the command pressure chamber 33a of the pilot spool valve 33. As a result, the opening of the pilot spool valve 33 becomes fully closed.

[0190] According to such a third embodiment, in addition to the same operational effects as in the first embodiment, the following operational effects can be obtained.

[0191] (5) The controller unit 94 measures the time To after the actuator pressure Pa transitions from a state lower than the pump pressure Pp to a state higher than the pump pressure Pp. When the measured time To reaches a predetermined time threshold α, the controller unit 94 reduces the auxiliary opening area of the flow control valve. In this embodiment, an example in which the auxiliary opening area is set to 0 (zero) when the time To reaches the time threshold α has been described, but the auxiliary opening area may be set to a value larger than 0 (zero).

[0192] According to this configuration, similar to the second embodiment, when the pressure state of the flow control valve reaches the differential pressure reversal state, after opening the pilot spool valve 33 and fully closing the poppet valve 32, the pilot spool valve 33 can be fully closed. That is, the flow control valve can be returned to its originally required state. As a result, when the flow rate supplied to the hydraulic actuator is controlled by the flow control valve again, the flow control valve can operate smoothly. Therefore, according to the third embodiment, better controllability and operability than the first embodiment can be ensured. Furthermore, according to the third embodiment, it is not necessary to provide a back pressure sensor 83A as in the second embodiment. For this reason, in the third embodiment, the hydraulic drive device 902 can have a simpler configuration compared to the second embodiment.

[0193] The following variations are also within the scope of the present invention, and it is also possible to combine the configurations shown in the variations with the configurations described in the above embodiments, combine the configurations described in the different above embodiments with each other, or combine the configurations described in the following different variations with each other.

[0194] <Modification 1> In the third embodiment, an example has been described in which the controller unit 94 calculates the correction coefficient Cc and multiplies it by the auxiliary opening area a_AuxFcv. However, the present invention is not limited to this. As shown in FIG. 17, the controller unit 94 may monitor the pressure state of the flow control valve and calculate the auxiliary opening area according to the time To after the pressure state of the flow control valve transitions from the normal pressure state to the differential pressure reversal state.

[0195] <Modification 2> In the above embodiment, an example has been described in which when the pressure state of the second boom flow control valve 25 transitions from the normal pressure state to the differential pressure reversal state due to the transition from the single operation of the boom 204 to the combined operation of the boom 204 and the arm 205, the pilot spool valve 33 of the second boom flow control valve 25 is opened. However, the present invention is not limited to this. The same control is also performed when a plurality of hydraulic actuators connected to the discharge line of the same hydraulic pump are operated in combination.

[0196] For example, when shifting from the single operation of the boom 204 to the combined operation of the boom 204 and the slewing body 202, the controller unit 94 reduces the flow rate of the hydraulic oil supplied to the boom cylinder 204a through the flow control valve 30 for the third boom in order to prioritize the operation of the slewing motor 211 connected to the discharge line 61 of the third hydraulic pump 3. As a result, when the pressure state of the flow control valve 30 for the third boom transitions from the normal pressure state to the differential pressure reversal state, the controller unit 94 opens the pilot spool valve 33 of the flow control valve 30 for the third boom. Thereby, it is possible to prevent the hydraulic oil from flowing backward from the boom cylinder 204a to the discharge line 61 through the flow control valve 30 for the third boom.

[0197] <Modification Example 3> In the first and third embodiments, an example in which the differential pressure detection device 80 is constituted by the pump pressure sensor 81 and the actuator pressure sensor 82 has been described, and in the second embodiment, an example in which the differential pressure detection device 80A is constituted by the back pressure sensor 83A and the actuator pressure sensor 82 has been described. However, the present invention is not limited to this. For example, in the first and third embodiments, a single differential pressure detection device (differential pressure sensor) may be provided in a passage communicating the pump passage 54P and the actuator passage 54A. Further, in the second embodiment, a single differential pressure detection device (differential pressure sensor) may be provided in a passage communicating the back pressure chamber 32e and the actuator passage 54A.

[0198] <Modification Example 4> Also, in the above-described embodiments, the engine has been described as an example of the prime mover, but the prime mover is not limited to the engine, and an electric motor, a fuel cell, or the like may be used as the prime mover. Further, a combination of these may be used as the prime mover.

[0199] As described above, the embodiments of the present invention have been described. However, the above embodiments merely show a part of the application examples of the present invention, and are not intended to limit the technical scope of the present invention to the specific configurations of the above embodiments.

Description of Reference Numerals

[0200] 1…First hydraulic pump (hydraulic pump), 1a…Command pressure chamber, 2…Second hydraulic pump (hydraulic pump), 2a…Command pressure chamber, 3…Third hydraulic pump (hydraulic pump), 3a…Command pressure chamber, 6~16…Direction control valve, 21~31…Flow control valve, 32…Poppet valve, 32a…Poppet (valve body), 32b…Communication groove, 32c…Pump pressure chamber, 32d…Actuator pressure chamber, 32e…Back pressure chamber (pressure chamber), 32f…Accommodation hole, 33…Pilot spool valve, 33a…Command pressure chamber, 41…Discharge line, 42,44,46,48…Oil passage, 51…Discharge line, 52,54,56,58…Oil passage, 54A…Actuator passage, 54P…Pump passage, 61…Discharge line, 62,64,66…Oil passage, 77,78…Oil passage, 80,80A…Differential pressure detection device, 81…Pump pressure sensor (pressure sensor), 82…Actuator pressure sensor (pressure sensor), 83A…Back pressure sensor (pressure sensor), 93…Solenoid valve unit, 93a~93e…Solenoid valve, 94,94A,94B…Controller unit, 94a…Actuator target flow rate calculation unit, 94b…Pump target flow rate calculation unit, 94c…Pump control command unit, 94d…Direction control valve target opening calculation unit, 94e…Direction control valve control command unit, 94f…Reference opening calculation unit, 94g,94gA…Pressure state judgment unit, 94h,94hA…Auxiliary opening calculation unit, 94i…Flow control valve target opening determination unit, 94j…Flow control valve control command unit, 94k…Bleed-off valve target opening calculation unit, 94l…Bleed-off valve control command unit, 94mB…Opening time measurement unit, 94nB…Auxiliary opening correction unit, 94v…Processing device, 94w…Non-volatile memory (storage device), 95a,95b... operating device, 102... notch, 104... first oil chamber, 105... second oil chamber, 108... notch, 110... main housing, 110a... seat portion, 111... pilot housing, 111a... accommodation hole, 112... spool (valve body), 112a... first land portion, 112b... second land portion, 113... internal passage, 114... check valve, 121... first opening, 122... second opening, 123... third opening, 201... traveling body, 201L... left traveling motor (hydraulic actuator), 202... slewing body, 203... working device, 204... boom, 204a... boom cylinder (hydraulic actuator), 205... arm, 205a... arm cylinder (hydraulic actuator), 206... bucket, 206a... bucket cylinder (hydraulic actuator), 207... cab, 208... machine room, 211... slewing motor (hydraulic actuator), 217... engine (prime mover), 220... machine body, 901... hydraulic excavator (working machine),

Claims

1. a machine body, a working device attached to the machine body, a prime mover, a hydraulic pump driven by the prime mover, a plurality of hydraulic actuators that operate by the discharge pressure of the hydraulic pump and drive the working device, a plurality of direction control valves provided between the hydraulic actuator and the hydraulic pump, connected in parallel to the discharge line of the hydraulic pump, and switching the flow direction of the pressure oil supplied from the hydraulic pump to the plurality of hydraulic actuators, a plurality of flow control valves provided upstream of the direction control valve and controlling the flow rate of the pressure oil supplied to the plurality of hydraulic actuators, a plurality of solenoid valves that output a command pressure to the plurality of flow control valves, an operating device that outputs an operation signal for operating the working device, a controller unit that controls the solenoid valve based on the operation signal from the operating device, in a working machine comprising: the flow control valve includes a pump passage connected to the discharge line, an actuator passage connected to the hydraulic actuator via the direction control valve, a poppet valve provided between the pump passage and the actuator passage, capable of blocking a first opening between the pump passage and the actuator passage and capable of adjusting the area of the first opening, and a back pressure chamber formed on the back surface of the poppet and communicating with the pump passage, a check valve provided in a passage communicating the pump passage and the back pressure chamber, allowing the flow from the pump passage to the back pressure chamber and prohibiting the flow from the back pressure chamber to the pump passage, a spool valve provided between the back pressure chamber and the actuator passage, capable of blocking a second opening between the back pressure chamber and the actuator passage and capable of adjusting the area of the second opening, and a command pressure chamber into which the command pressure from the solenoid valve is input, comprising a differential pressure detection device for detecting the differential pressure before and after the spool valve, the controller unit monitors, based on the detection result of the differential pressure detection device, whether the pressure on the hydraulic actuator side of the spool valve has transitioned from a state lower than the pressure on the hydraulic pump side of the spool valve to a higher state, and controls the solenoid valve so that the second opening opens when the pressure on the hydraulic actuator side of the spool valve has transitioned from a state lower than the pressure on the hydraulic pump side of the spool valve to a higher state. A working machine characterized by the above.

2. In the working machine according to Claim 1, a pump pressure sensor for detecting the discharge pressure of the hydraulic pump, and an actuator pressure sensor for detecting the pressure of the hydraulic actuator, are provided, the controller unit calculates the reference opening area of the flow control valve based on the operation amount of the operation device and the detection results of the pump pressure sensor and the actuator pressure sensor, calculates the auxiliary opening area of the flow control valve based on the differential pressure before and after the spool valve detected by the differential pressure detection device, determines the larger of the calculated reference opening area and the auxiliary opening area as the target opening area of the flow control valve, and controls the solenoid valve based on the determined target opening area A working machine characterized by the above.

3. In the working machine according to Claim 2, the differential pressure detection device has the pump pressure sensor and the actuator pressure sensor, the opening characteristics defining the relationship between the differential pressure before and after the spool valve and the auxiliary opening area are stored in the controller unit, the controller unit calculates the difference between the discharge pressure of the hydraulic pump detected by the pump pressure sensor and the pressure of the hydraulic actuator detected by the actuator pressure sensor as the differential pressure before and after the spool valve, and calculates the auxiliary opening area based on the stored opening characteristics and the differential pressure before and after the spool valve A working machine characterized by the above.

4. In the working machine according to Claim 2, the differential pressure detection device has a back pressure sensor for detecting the pressure in the back pressure chamber of the poppet valve and the actuator pressure sensor, the opening characteristics defining the relationship between the differential pressure before and after the spool valve and the auxiliary opening area are stored in the controller unit, the controller unit calculates the difference between the pressure in the back pressure chamber detected by the back pressure sensor and the pressure of the hydraulic actuator detected by the actuator pressure sensor as the differential pressure before and after the spool valve, and calculates the auxiliary opening area based on the stored opening characteristics and the differential pressure before and after the spool valve A working machine characterized by the above.

5. In the working machine according to Claim 3, the controller unit Measure the time after the pressure on the hydraulic actuator side of the spool valve transitions from a state lower than the pressure on the hydraulic pump side of the spool valve to a higher state, When the measured time reaches a predetermined time threshold, reduce the auxiliary opening area of the flow control valve A work machine characterized by the above.

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