Work machine

Abstract

A work machine is provided with: a cylinder control valve for controlling the flow of hydraulic oil from a hydraulic pump to a hydraulic cylinder; a first pressure reducing valve that reduces the pressure of the hydraulic oil discharged from the hydraulic pump and generates a pilot primary pressure; a second pressure reducing valve that generates a secondary pressure acting on a pressure receiving portion of the cylinder control valve; a bypass stop valve; a third pressure reducing valve for generating a secondary pressure acting on the pressure receiving portion of the bypass stop valve; a regeneration passage connecting the inlet throttle passage and the outlet throttle passage; an outlet throttle; and a control device. When the pressure of the hydraulic pump detected by the pressure sensor becomes low, the control device controls the third pressure reducing valve so that the opening area of the bypass shut-off valve becomes smaller, and the control device reduces the opening area of the outlet throttle as the amount of operation of the work device in the gravitational direction becomes larger.

Description

Technical Field

[0001] The present invention relates to a working machine. Background Art

[0002] A working machine is known, which has: a main circuit, which uses a cylinder control valve to control the working oil ejected from the hydraulic pump and supply it to the hydraulic cylinder; a pilot circuit, which uses a pilot pressure reducing valve to reduce the pressure of a part of the working oil ejected from the above-mentioned hydraulic pump, supplies it to the electromagnetic proportional pressure reducing valve as a pilot primary pressure, and guides the secondary pressure generated by the electromagnetic proportional pressure reducing valve to the cylinder control valve (refer to patent document 1). In the working machine described in patent document 1, a bypass sequence valve is provided in the bypass passage connecting the hydraulic pump and the oil tank. The bypass sequence valve is controlled to be in a connected state when there is no manual operation signal from the operating device, and is controlled to be a pressure at the inlet of the bypass sequence valve (i.e., the discharge pressure of the hydraulic pump) to be a pressure greater than the pilot primary pressure when there is a manual operation signal from the operating device.

[0003] Prior art literature

[0004] Patent Literature

[0005] Patent Document 1: Japanese Patent Application Publication No. 2001-263304 Summary of the invention

[0006] Problems to be solved by the invention

[0007] The working device includes a boom, an arm, and a bucket. In a working machine having the working device, when the working device is moved in a direction in which gravity acts on the working device (hereinafter referred to as the gravity direction), such as a boom lowering operation in a state where the bucket is in the air, an arm loading operation in which the working device is pulled toward the front side from an extended state of the working device, etc., the discharge pressure of the hydraulic pump decreases. In the technology described in Patent Document 1, as described above, the bypass sequence valve is controlled so that the discharge pressure of the hydraulic pump becomes a pressure greater than the pilot primary pressure.

[0008] However, when the weight and center of gravity of the working device are changed and the inertia moment of the working device is increased by replacing the bucket installed at the front end of the working device with a heavier bucket, the discharge pressure of the hydraulic pump may be lower than the pilot primary pressure only by controlling the bypass sequence valve when the working device is operated in the direction of gravity. That is, in the technology described in Patent Document 1, it is sometimes difficult to ensure a stable pilot primary pressure when the specifications of the working device are changed.

[0009] An object of the present invention is to provide a working machine capable of ensuring a stable pilot primary pressure when an operation is performed to cause a working device to operate in a gravity direction.

[0010] Means for solving problems

[0011] A working machine according to one embodiment of the present invention comprises: a working device having a plurality of hydraulic cylinders and a plurality of driven object parts driven by the plurality of hydraulic cylinders; an operating device for operating the hydraulic cylinders; a main circuit for supplying working oil ejected from a hydraulic pump to the hydraulic cylinders; a cylinder control valve provided in the main circuit for controlling the flow of working oil supplied from the hydraulic pump to the hydraulic cylinders; a pilot circuit for guiding a part of the working oil ejected from the hydraulic pump to a pilot pressure receiving part of the cylinder control valve; a first pressure reducing valve provided in the pilot circuit for The pressure of the working oil ejected from the hydraulic pump is reduced to generate a pilot primary pressure; a second pressure reducing valve is provided in the pilot circuit and reduces the pressure of the pilot primary pressure to generate a pilot secondary pressure acting on the pilot pressure receiving part of the cylinder control valve; a central bypass passage connects the hydraulic pump and the oil tank and is provided with the cylinder control valve; a bypass stop valve is provided in the central bypass passage; a third pressure reducing valve is provided in the pilot circuit and reduces the pressure of the pilot primary pressure to generate a pilot secondary pressure acting on the pilot pressure receiving part of the bypass stop valve a regeneration passage connecting an inlet throttle passage and an outlet throttle passage, wherein the inlet throttle passage guides the working oil discharged from the hydraulic pump to the hydraulic cylinder, and the outlet throttle passage guides the return oil from the hydraulic cylinder to the oil tank; a check valve, which is provided in the regeneration passage and allows the working oil to flow from the outlet throttle passage to the inlet throttle passage and prohibits the working oil from flowing from the inlet throttle passage to the outlet throttle passage; an outlet throttle portion, which is provided in the outlet throttle passage; a pressure sensor, which detects the pressure of the working oil on the discharge side of the hydraulic pump; and a control device, which controls the second pressure reducing valve according to the operation amount of the operating device, wherein the control device controls the third pressure reducing valve according to the pressure detected by the pressure sensor, and when the pressure detected by the pressure sensor becomes lower, the control device controls the third pressure reducing valve so that the opening area of ​​the bypass stop valve becomes smaller, and the larger the operation amount of the operation performed by the operating device to operate the working device in the gravity direction, the larger the opening area of ​​the outlet throttle portion is, the more the control device reduces the opening area of ​​the outlet throttle portion.

[0012] Effects of the Invention

[0013] According to the present invention, when an operation is performed to operate the working device in the direction of gravity, a stable pilot primary pressure can be ensured. BRIEF DESCRIPTION OF THE DRAWINGS

[0014] Figure 1 It is a side view of the hydraulic excavator according to the first embodiment of the present invention.

[0015] Figure 2 It is a diagram showing a hydraulic system mounted on a hydraulic excavator according to a first embodiment of the present invention.

[0016] Figure 3 This is a flowchart showing an example of a flow of valve control processing executed by the main controller according to the first embodiment of the present invention.

[0017] Figure 4 It is a graph showing the time series changes of the operating position of the door lock rod device, the boom lowering operation amount of the boom operating device, the discharge pressure of the hydraulic pump, the discharge capacity of the hydraulic pump, the opening area of ​​the bypass stop valve, and the opening area of ​​the outlet throttling part of the CT opening control valve.

[0018] Figure 5 This is a functional block diagram of a main controller according to a second embodiment of the present invention, and shows functions related to control of a bypass stop valve.

[0019] Figure 6 It is a diagram showing a hydraulic system according to a modified example of the embodiment of the present invention. DETAILED DESCRIPTION

[0020] A working machine according to an embodiment of the present invention will be described with reference to the drawings. In this embodiment, an example in which the working machine is a crawler-type hydraulic excavator will be described.

[0021] <First embodiment>

[0022] Figure 1 FIG. 1 is a side view of a hydraulic excavator 1 according to a first embodiment of the present invention. Figure 1 The front-rear and the up-down directions of the hydraulic excavator 1 are defined as shown. In the present embodiment, the front of the operator's seat (left direction in the figure) is defined as the front of the hydraulic excavator 1 unless otherwise specified.

[0023] The hydraulic excavator 1 includes a machine body (vehicle body) 20 and a working device 10 mounted on the machine body 20. The machine body 20 includes a traveling body 2 and a revolving body 3 mounted on the traveling body 2 in a revolvable manner. The traveling body 2 includes a pair of left and right crawlers and a traveling hydraulic motor 2a as an actuator. The traveling body 2 travels by driving the crawlers by the traveling hydraulic motor 2a. The revolving body 3 includes a revolving frame 30, a revolving hydraulic motor 3a as an actuator, and a speed reduction mechanism that reduces the rotation of the revolving hydraulic motor 3a and transmits it to the revolving frame 30. The revolving body 3 rotates relative to the traveling body 2 by the revolving hydraulic motor 3a.

[0024] The revolving body 3 has a cab 31 provided on the left side of the front part of the revolving frame 30, a counterweight 32 provided on the rear part of the revolving frame 30, and an engine room 33 provided on the rear side of the cab 31 in the revolving frame 30. An engine as a prime mover and hydraulic equipment such as a hydraulic pump, a valve, and an accumulator are accommodated in the engine room 33. The working device 10 is rotatably connected to the front center of the revolving frame 30.

[0025] The working device 10 is a multi-joint working device, which has: a plurality of drive target parts that are rotatably connected, and a plurality of hydraulic cylinders that drive the drive target parts. In this embodiment, three drive target parts, namely, a boom 11, a dipper arm 12, and a bucket 13, are connected in series. The base end of the boom 11 is rotatably connected to the front part of the revolving frame 30. The base end of the dipper arm 12 is rotatably connected to the front end of the boom 11. The bucket 13 is rotatably connected to the front end of the dipper arm 12.

[0026] The boom 11 is driven by a hydraulic cylinder (hereinafter, also referred to as the boom cylinder 11a) as an actuator, and rotates relative to the revolving frame 30. The arm 12 is driven by a hydraulic cylinder (hereinafter, also referred to as the arm cylinder 12a) as an actuator, and rotates relative to the boom 11. The bucket 13 is driven by a hydraulic cylinder (hereinafter, also referred to as the bucket cylinder 13a) as an actuator, and rotates relative to the arm 12.

[0027] Figure 2 1 is a diagram showing a hydraulic system 90 mounted on the hydraulic excavator 1. The hydraulic system 90 includes hydraulic devices for driving a plurality of hydraulic actuators (2a, 3a, 11a, 12a, 13a). Figure 2 In the figure, only the hydraulic equipment for driving the boom cylinder 11a and the arm cylinder 12a is illustrated, and the hydraulic equipment for driving other hydraulic actuators (2a, 3a, 13a) is omitted. In addition, in most cases, multiple hydraulic pumps 81 are used to drive the actuator, but in the following description, the case where only one hydraulic pump 81 is used to drive the actuator is used as an example.

[0028] exist Figure 2 In the figure, a main controller 100 as a control device for controlling the hydraulic system 90 and a device for outputting a signal to the main controller 100 are also shown. Figure 2 As shown, the hydraulic excavator 1 includes an engine control dial 21 for setting a target speed of the engine 80, an operating device (also referred to as a boom operating device) 23 for operating the boom cylinder 11a (boom 11), an operating device (also referred to as an arm operating device) 24 for operating the arm cylinder 12a (arm 12), and a door lock lever device 22. These devices (21 to 24) are provided in the cab 31.

[0029] The boom operating device 23 includes an operating lever 23a that can be tilted from a neutral position to a boom raising side and a boom lowering side, and an operating sensor that detects the operating direction and the operating amount of the operating lever 23a, and outputs an operating signal indicating the operating direction and the operating amount of the operating lever 23a to the main controller 100. The arm operating device 24 includes an operating lever 24a that can be tilted from a neutral position to an arm shoveling side and an arm dumping side, and an operating sensor that detects the operating direction and the operating amount of the operating lever 24a, and outputs an operating signal indicating the operating direction and the operating amount of the operating lever 24a to the main controller 100. The operating amount (operating angle) of the operating levers 23a and 24a detected by the operating sensors of the operating devices 23 and 24 is 0 [%] (0°) at the neutral position, and the absolute value thereof increases as the tilting is further from the neutral position.

[0030] The door lock rod device 22 includes a rod 22a that is selectively operated to a locking position (upward position) that allows access to the cab 31 and prohibits the operation of the actuator (11a, 12a, 13a) and an unlocking position (downward position) that prohibits access to the cab 31 and permits the operation of the actuator (11a, 12a, 13a). In addition, the door lock rod device 22 includes an operation position sensor that detects the operation position of the rod 22a and outputs a door lock rod signal indicating the operation position of the rod 22a to the main controller 100.

[0031] The engine control dial 21 is an operating device for setting the target speed of the engine 80, and outputs an operating signal to the main controller 100. The main controller 100 determines the target speed based on the operating signal from the engine control dial 21, and outputs a signal of the determined target speed to the engine controller 105. The engine 80 is provided with a speed sensor 80a for detecting the actual speed of the engine 80 and a fuel injection device 80b for adjusting the amount of fuel injected into the cylinder of the engine 80. The engine controller 105 controls the fuel injection device 80b so that the actual speed of the engine 80 detected by the speed sensor 80a becomes the target speed output from the main controller 100.

[0032] The hydraulic system 90 includes a hydraulic pump 81, a main circuit HC1 that supplies the hydraulic oil as a working fluid ejected from the hydraulic pump 81 to the boom cylinder 11a and the arm cylinder 12a, a pilot circuit HC2 that is connected to the main circuit HC1, and a center bypass passage Lb that connects the hydraulic pump 81 to the oil tank 19 storing the hydraulic oil. The pilot circuit HC2 is a circuit that guides a part of the hydraulic oil ejected from the hydraulic pump 81 to the pilot pressure receiving parts 45a, 45b, 46a, 46b of the cylinder control valves 45 and 46 described later, the pilot pressure receiving part 17a of the bypass cut valve 17 described later, and the pilot pressure receiving parts of the CT opening control valves 26A and 26B described later.

[0033] The hydraulic pump 81 is connected to the engine 80 and driven by the engine 80 to suck and discharge working oil from the oil tank 19. The hydraulic pump 81 is a variable capacity piston type hydraulic pump. The tilt angle of the swash plate is changed by the regulator 81a, thereby changing the discharge capacity (displacement). The regulator 81a has: a tilt actuator that controls the tilt angle of the swash plate of the hydraulic pump 81, and an electromagnetic proportional valve that uses the discharge pressure of the hydraulic pump 81 as the initial pressure to generate the control pressure of the tilt actuator. The engine 80 is a power source of the hydraulic excavator 1, and is composed of an internal combustion engine such as a diesel engine.

[0034] The main circuit HC1 is provided with: a cylinder control valve (hereinafter also referred to as a boom control valve) 45 for controlling the flow (flow rate and direction) of the working oil supplied from the hydraulic pump 81 to the boom cylinder 11a, and a cylinder control valve (hereinafter also referred to as a boom control valve) 46 for controlling the flow (flow rate and direction) of the working oil supplied from the hydraulic pump 81 to the boom cylinder 12a.

[0035] The main circuit HC1 is provided with a relief valve 47. If the discharge pressure (circuit pressure) of the hydraulic pump 81 exceeds a preset set pressure, the relief valve 47 discharges the working oil discharged from the hydraulic pump 81 to the oil tank 19, thereby regulating the maximum pressure of the discharge pressure of the hydraulic pump 81.

[0036] The main circuit HC1 includes a pump discharge passage Ld connected to a discharge port of the hydraulic pump 81 and a parallel passage Lp connected to the pump discharge passage Ld.

[0037] The parallel passage Lp is a passage that guides the working oil from the pump discharge passage Ld to the pump ports of the boom control valve 45 and the boom control valve 46. That is, the parallel passage Lp constitutes a part of the inlet throttle passage that guides the working oil discharged from the hydraulic pump 81 to the hydraulic cylinder. A check valve 41 for maintaining the load pressure of the boom cylinder 11a is provided in the parallel passage Lp connected to the pump port of the boom control valve 45. The check valve 41 becomes fully closed when the pump discharge pressure is lower than the cylinder pressure. The check valve 42 for maintaining the load pressure of the boom cylinder 12a is provided in the parallel passage Lp connected to the pump port of the boom control valve 46. The check valve 42 becomes fully closed when the pump discharge pressure is lower than the cylinder pressure.

[0038] The tank port of the boom control valve 45 is connected to the tank 19 via a return oil passage 45r. The return oil passage 45r constitutes a part of the outlet throttle passage for guiding the return oil of the boom cylinder 11a to the tank 19 in the future. A CT opening control valve (outlet throttle control valve) 26A is provided in the return oil passage 45r. The CT opening control valve 26A has an outlet throttle portion 28A that applies resistance to the flow of the working oil passing through, and discharges the return oil of the boom cylinder 11a to the tank 19 through the outlet throttle portion 28A. The CT opening control valve 26A is operated according to the pilot secondary pressure output from the solenoid valve 35A described later, and the opening area (opening degree) of the outlet throttle portion 28A changes. The return oil passage (outlet throttle passage) 45r of the boom control valve 45 is connected to the parallel passage (inlet throttle passage) Lp through a regeneration passage provided with a check valve 27A for regeneration. The check valve 27A is a check valve that allows the flow of hydraulic oil from the return oil passage 45r to the parallel passage Lp and prohibits the flow of hydraulic oil from the parallel passage Lp to the return oil passage 45r.

[0039] For example, when the working device 10 is held in the air while the bucket 13 is not in contact with the ground, and the boom lowering operation is performed to lower the working device 10, the rod pressure becomes lower and the bottom pressure becomes higher as the boom cylinder 11a contracts. The regeneration check valve 27A opens when the bottom pressure exceeds the rod pressure. As a result, a portion of the return oil from the bottom chamber is regenerated and supplied to the rod chamber through the check valve 27A, and the remaining portion is returned to the oil tank 19 through the outlet throttle portion 28A of the CT opening control valve 26A. In addition, when the boom lowering operation is performed in the state where the bucket 13 is grounded, and the rod pressure exceeds the bottom pressure by performing a lifting action to float the machine body 20 by the working device 10, the regeneration check valve 27A is fully closed.

[0040] The same regeneration passage is also provided in the boom control valve 46. The oil tank port of the boom control valve 46 is connected to the oil tank 19 via the return oil passage 46r. The return oil passage 46r constitutes a part of the outlet throttling passage that guides the return oil from the boom cylinder 12a to the oil tank 19. A CT opening control valve (outlet throttling control valve) 26B is provided in the return oil passage 46r. The CT opening control valve 26B has an outlet throttling portion 28B that applies resistance to the flow of the working oil passing through, and the return oil from the boom cylinder 12a is discharged to the oil tank 19 through the outlet throttling portion 28B. The CT opening control valve 26B operates according to the pilot secondary pressure output from the solenoid valve 35B described later, and the opening area (opening degree) of the outlet throttling portion 28B changes.

[0041] The return oil passage (outlet throttle passage) 46r of the boom control valve 46 is connected to the parallel passage (inlet throttle passage) Lp through a regeneration passage provided with a regeneration check valve 27B. The check valve 27B is a check valve that allows the flow of working oil from the return oil passage 46r to the parallel passage Lp and prohibits the flow of working oil from the parallel passage Lp to the return oil passage 46r. The regeneration check valve 27B opens when the bottom pressure exceeds the rod pressure as the boom cylinder 12a contracts. As a result, a portion of the return oil from the bottom chamber is regenerated and supplied to the rod chamber through the check valve 27B, and the remaining portion is returned to the oil tank 19 through the outlet throttle portion 28B of the CT opening control valve 26B. In addition, when the rod pressure exceeds the bottom pressure, the regeneration check valve 27B is fully closed.

[0042] The center bypass passage Lb branches from the pump discharge passage Ld and is connected to the oil tank 19. In the center bypass passage Lb, a boom control valve 45, an arm control valve 46, and a bypass shutoff valve 17 are sequentially arranged in series from the upstream side toward the downstream side. The bypass shutoff valve 17 has a throttle portion that applies resistance to the flow of the working oil passing therethrough, and the working oil ejected from the hydraulic pump 81 is discharged to the oil tank 19 through the throttle portion. The bypass shutoff valve 17 can adjust the pump discharge pressure by changing the opening area (opening degree) of the throttle portion.

[0043] The pilot circuit HC2 is provided with a pilot pressure reducing valve (first pressure reducing valve) 71 that reduces the pressure of the hydraulic oil discharged from the hydraulic pump 81 (i.e., the pump discharge pressure) to generate a pilot primary pressure, a check valve 72 that is used to maintain the pilot primary pressure, an accumulator 73 that is used to smooth the pilot primary pressure, and a lock valve 74 that can block the pilot primary pressure. In addition, the pilot circuit HC2 is provided with electromagnetic valves (second pressure reducing valves) 61A and 61B that reduce the pilot primary pressure to generate a pilot secondary pressure that acts on the pilot pressure receiving parts 45a and 45b of the boom control valve 45, and electromagnetic valves (second pressure reducing valves) 62A and 62B that reduce the pilot primary pressure to generate a pilot secondary pressure that acts on the pilot pressure receiving parts 46a and 46b of the boom control valve 46. Furthermore, the pilot circuit HC2 is provided with a solenoid valve (third pressure reducing valve) 63 that reduces the pilot primary pressure to generate a pilot secondary pressure that acts on the pilot pressure receiving portion 17 a of the bypass cut valve 17 .

[0044] In addition, the pilot circuit HC2 is provided with a solenoid valve (fourth pressure reducing valve) 35A that reduces the pilot primary pressure to generate a pilot secondary pressure acting on the pilot pressure receiving portion of the CT opening control valve 26A, and a solenoid valve (fourth pressure reducing valve) 35B that reduces the pilot primary pressure to generate a pilot secondary pressure acting on the pilot pressure receiving portion of the CT opening control valve 26B. The solenoid valves 35A, 35B, 61A, 61B, 62A, 62B, and 63 are solenoid proportional valves driven by solenoid thrust generated according to the control current supplied to the solenoid.

[0045] The solenoid valves 61A and 61B use the pilot primary pressure generated by the pilot pressure reducing valve 71 as the initial pressure to generate the pilot secondary pressure output to the pilot pressure receiving parts 45a and 45b of the boom control valve 45. The solenoid valves 61A and 61B are controlled by a signal (control current) output from the main controller 100. The main controller 100 controls the solenoid valves 61A and 61B according to the operation signal output from the boom operating device 23.

[0046] When the pilot secondary pressure generated by the solenoid valve 61A acts on the pilot pressure receiving portion 45a of the boom control valve 45, the boom control valve 45 is switched to the extension position. As a result, the hydraulic oil ejected from the hydraulic pump 81 is guided to the bottom chamber of the boom cylinder 11a, and the hydraulic oil is discharged from the rod chamber to the oil tank 19, and the boom cylinder 11a is extended. As a result, the boom 11 is rotated upward (that is, the boom 11 is erected).

[0047] When the pilot secondary pressure generated by the solenoid valve 61B acts on the pilot pressure receiving portion 45b of the boom control valve 45, the boom control valve 45 is switched to the retracted position. As a result, the hydraulic oil ejected from the hydraulic pump 81 is guided to the rod chamber of the boom cylinder 11a, and the hydraulic oil is discharged from the bottom chamber to the oil tank 19, and the boom cylinder 11a is retracted. As a result, the boom 11 is rotated downward (that is, the boom 11 is lowered).

[0048] The solenoid valves 62A and 62B use the pilot primary pressure generated by the pilot pressure reducing valve 71 as the initial pressure to generate the pilot secondary pressure output to the pilot pressure receiving parts 46a and 46b of the boom control valve 46. The solenoid valves 62A and 62B are controlled by a signal (control current) output from the main controller 100. The main controller 100 controls the solenoid valves 62A and 62B according to the operation signal output from the boom operating device 24.

[0049] When the pilot secondary pressure generated by the solenoid valve 62A acts on the pilot pressure receiving portion 46a of the boom control valve 46, the boom control valve 46 is switched to the extension position. As a result, the hydraulic oil ejected from the hydraulic pump 81 is guided to the bottom chamber of the boom cylinder 12a, and the hydraulic oil is discharged from the rod chamber to the oil tank 19, and the boom cylinder 12a is extended. As a result, the boom 12 rotates downward (that is, the boom 12 performs a shoveling action).

[0050] When the pilot secondary pressure generated by the solenoid valve 62B acts on the pilot pressure receiving portion 46b of the boom control valve 46, the boom control valve 46 is switched to the retracted position. As a result, the hydraulic oil ejected from the hydraulic pump 81 is guided to the rod chamber of the boom cylinder 12a, and the hydraulic oil is discharged from the bottom chamber to the oil tank 19, and the boom cylinder 12a is retracted. As a result, the boom 12 rotates upward (that is, the boom 12 performs a dumping action).

[0051] The solenoid valve 63 uses the pilot primary pressure generated by the pilot pressure reducing valve 71 as the initial pressure to generate the pilot secondary pressure output to the pilot pressure receiving portion 17a of the bypass stop valve 17. The solenoid valve 63 is controlled according to the signal (control current) output from the main controller 100. The main controller 100 controls the solenoid valve 63 according to the door lock rod signal output from the door lock rod device 22, the operation signal output from the operation devices 23 and 24, and the pressure detected by the pressure sensor 25 described later.

[0052] The bypass cut-off valve 17 controls the position of the valve core according to the pilot secondary pressure acting on the pilot pressure receiving part 17a. When the pilot secondary pressure is equal to the tank pressure, the valve core is kept in the neutral position by the spring force of the return spring. At this time, the opening area of ​​the throttle part becomes the maximum opening area Abmax.

[0053] If the pilot secondary pressure acting on the pilot pressure receiving part 17a increases, the valve core moves against the spring force of the return spring, and the opening area of ​​the throttle portion becomes smaller. If the pilot secondary pressure acting on the pilot pressure receiving part 17a further increases, the valve core moves to the blocking position, and the communication between the hydraulic pump 81 and the oil tank 19 is blocked by the bypass stop valve 17. At this time, the opening area of ​​the throttle portion becomes the minimum opening area Abmin (for example, 0).

[0054] A locking valve 74 is provided between the pilot pressure reducing valve 71 and the solenoid valves 35A, 35B, 61A, 61B, 62A, 62B, and 63. The locking valve 74 is an electromagnetic switching valve that is switched to one of a blocking position and a connecting position by a control signal output from the main controller 100 according to the operating position of the door lock rod device 22.

[0055] When the door lock rod device 22 is operated to the lock position, the lock valve 74 is switched to the blocking position. As a result, the pilot primary pressure to the solenoid valves 61A, 61B, 62A, 62B is blocked, and the operation of the operating rods 23a, 24a is invalidated. In addition, the pilot primary pressure to the solenoid valve 63 is also blocked, so that the bypass stop valve 17 is maintained in the neutral position regardless of the operation of the operating devices 23, 24.

[0056] When the door lock rod device 22 is operated to the unlocked position, the lock valve 74 is switched to the connected position. Therefore, when the door lock rod device 22 is operated to the unlocked position, the solenoid valves 61A, 61B, 62A, 62B generate pilot secondary pressures corresponding to the operation direction and operation amount of the operating rods 23a, 24a, and the actuators (11a, 12a) corresponding to the operated operating rods 23a, 24a are actuated.

[0057] Furthermore, as described above, the pilot circuit HC2 is provided with the check valve 72 and the accumulator 73 . Therefore, even when the discharge pressure of the hydraulic pump 81 temporarily falls below the set pressure of the pilot pressure reducing valve 71 , the pilot primary pressure can be maintained.

[0058] The main controller 100 is composed of a microcomputer having a CPU (Central Processing Unit) 101 as an action circuit, a ROM (Read Only Memory) 102 as a storage device, a RAM (Random Access Memory) 103 as a storage device, an input / output interface 104, and other peripheral circuits. The main controller 100 can be composed of a single microcomputer or a plurality of microcomputers. The engine controller 105 also has the same structure as the main controller 100, and is connected to the main controller 100 to exchange information (data).

[0059] ROM102 is a non-volatile memory such as EEPROM, which stores programs that can perform various operations. That is, ROM102 is a storage medium that can read programs that implement the functions of this embodiment. RAM103 is a volatile memory, which is a working memory that directly inputs and outputs data with CPU101. RAM103 temporarily stores necessary data while CPU101 is executing the program. In addition, the main controller 100 may also have a storage device such as a flash memory and a hard disk drive.

[0060] The CPU 101 is a processing device that expands the program stored in the ROM 102 in the RAM 103 and executes the calculation. The CPU 101 performs a predetermined calculation process on the signals taken from the input / output interface 104, the ROM 102, and the RAM 103 according to the program. The input / output interface 104 receives signals from the engine control dial 21, the door lock lever device 22, the operating devices 23 and 24, the pressure sensor 25, the engine controller 105, and the like. The input unit of the input / output interface 104 converts the input signal into a signal that can be calculated by the CPU 101. In addition, the output unit of the input / output interface 104 generates an output signal corresponding to the calculation result in the CPU 101, and outputs the signal to the lock valve 74, the solenoid valves 35A, 35B, 61A, 61B, 62A, 62B, 63, and the regulator 81a, and the like.

[0061] The pressure sensor 25 detects the pressure of the working oil on the discharge side of the hydraulic pump 81. The pressure sensor 25 of this embodiment detects the discharge pressure of the hydraulic pump 81 (circuit pressure of the main circuit HC1), and outputs a signal indicating the detection result (pump discharge pressure) to the main controller 100. The main controller 100 controls the discharge capacity of the hydraulic pump 81 through the regulator 81a based on the pump discharge pressure and the actual engine speed detected by the sensors 25 and 80a, and the operation signal from the operating device 23 and 24.

[0062] The hydraulic system 90 of this embodiment comprises: a control valve block 4, which has a boom control valve 45, a boom control valve 46, a bypass stop valve 17, a CT opening control valve 26A, 26B, check valves 27A, 27B, 41, 42 and a relief valve 47; a first solenoid valve block 5, which has solenoid valves 61A, 62A; a second solenoid valve block 6, which has solenoid valves 61B, 62B, 63; a third solenoid valve block 8, which has solenoid valves 35A, 35B; a pilot primary pressure generating block 7, which has a pilot pressure reducing valve 71, a check valve 72 and a locking valve 74.

[0063] The control valve block 4 distributes the hydraulic oil discharged from the hydraulic pump 81 to the hydraulic cylinders such as the boom cylinder 11a and the arm cylinder 12a. The pilot primary pressure generating block 7 reduces the pressure of the hydraulic oil discharged from the hydraulic pump 81 to an appropriate set pressure (for example, 4 MPa) by using the pilot pressure reducing valve 71. When the lock valve 74 is switched to the connecting position, the pilot primary pressure generated by the pilot pressure reducing valve 71 is guided to the first to third solenoid valve blocks 5, 6, and 8. When the lock valve 74 is switched to the blocking position, the pilot primary pressure circuits of the first to third solenoid valve blocks 5, 6, and 8 are connected to the oil tank 19. As a result, the primary pressures of the solenoid valves 35A, 35B, 61A, 61B, 62A, 62B, and 63 are opened to near 0 (zero), so that each valve 17, 26A, 26B, 45, and 46 is maintained in a neutral position. Furthermore, since the pilot primary pressure generating block 7 includes the check valve 72 and the accumulator 73 , even when the pump discharge pressure is lower than the set pressure of the pilot pressure reducing valve 71 , the pilot primary pressure is temporarily maintained.

[0064] If the working device 10 is operated in the direction in which gravity acts (gravity direction) such as the boom lowering operation with the bucket 13 in the air, the arm shoveling operation in which the dipper arm 12 is vertical relative to the ground, etc., the pump discharge pressure decreases. When the pump discharge pressure decreases, the main controller 100 increases the pump discharge pressure by reducing the opening area of ​​the throttling part of the bypass shut-off valve 17 to ensure the pilot primary pressure. Here, if the working device 10 becomes a specification different from the standard specification due to the replacement of the bucket 13, the weight of the working device 10 may increase, or the center of gravity of the working device 10 may be far away from the center of rotation. In this case, the inertia moment of the working device 10 increases. In a state where the inertia moment is increased compared to the standard specification, when an operation is performed to make the working device 10 work in the gravity direction, the pump discharge pressure may be lower than the pilot primary pressure maintained by the check valve 72 only by the control of the bypass shut-off valve 17.

[0065] Therefore, in the present embodiment, when the operation of making the working device 10 work in the gravity direction is performed, in addition to controlling the bypass stop valve 17, the CT opening control valves 26A and 26B are controlled to reduce the opening of the meter-out portions 28A and 28B, thereby increasing the regeneration flow rate to the hydraulic cylinders 11a and 12a. In this way, the pump discharge flow rate is not consumed as much as possible, and the hydraulic cylinders 11a and 12a can be driven at a speed corresponding to the operation amount, and the discharge pressure of the hydraulic pump 81 is prevented from being lower than the set pressure of the pilot pressure reducing valve 71, and the pilot primary pressure is maintained.

[0066] Reference Figure 3 , an example of a processing flow of valve control executed by the main controller 100 is described. Figure 3 The process shown in the flowchart is started by turning on an ignition switch (not shown), and is repeatedly executed in a predetermined control cycle.

[0067] like Figure 3 As shown, in step S100, the main controller 100 obtains a door lock rod signal from the door lock rod device 22, an operation signal from the operation devices 23 and 24, and a pressure signal from the pressure sensor 25, and the process proceeds to step S105.

[0068] In step S105, the main controller 100 determines whether the door lock rod device 22 is operated to the unlocked position (lowered position) based on the door lock rod signal obtained in step S100. In step S105, if it is determined that the door lock rod device 22 is operated to the unlocked position (i.e., the state in which the actuator can be activated), the process proceeds to step S110. In step S105, if it is determined that the door lock rod device 22 is operated to the locked position (upward position) (i.e., the state in which the actuator cannot be activated), the process proceeds to step S115.

[0069] In step S115 , the main controller 100 sets the target opening area Abt of the bypass cut valve 17 to the maximum opening area Abmax, and sets the target opening area Act of the CT opening control valves 26A, 26B to the maximum opening area Acmax, and proceeds to step S180 .

[0070] In step S110, the main controller 100 determines whether at least one of the operating devices 23 and 24 is operated based on the operation signal obtained in step S100. When the operation amount of the operating devices 23 and 24 is greater than the specified value, the main controller 100 determines that the operating devices 23 and 24 are operated. When the operation amount of the operating devices 23 and 24 is less than the above-mentioned specified value, the main controller 100 determines that the operating devices 23 and 24 are not operated. In step S110, if it is determined that at least one of the operating devices 23 and 24 is operated, the process proceeds to step S120. In step S110, if it is determined that neither of the operating devices 23 and 24 is operated, the process proceeds to step S125.

[0071] In step S125, the main controller 100 sets the opening area Abn for non-operation as the target opening area Abt of the bypass stop valve 17, and sets the maximum opening area Acmax as the target opening area Act of the CT opening control valves 26A and 26B. Here, the opening area Abn for non-operation is a value larger than the minimum opening area Abmin and smaller than the maximum opening area Abmax (Abmin<Abn<Abmax). The opening area Abn for non-operation is set so that even if a slight pressure drop occurs, a pilot primary pressure that can displace the valve core of the control valve 45 and 46 to the maximum stroke can be generated. For example, when the pilot primary pressure that can displace the valve core to the maximum stroke is 3.0 [MPa], the opening area Abn for non-operation is an opening area that can generate a pilot primary pressure of 3.3 [MPa], which is the lower limit pressure Pimin of the pilot primary pressure.

[0072] The opening area Abn for non-operation can be any opening area that can generate a pilot pressure that can move the valve core to a certain range of the maximum stroke (above the lower limit pressure Pimin and below the upper limit pressure Pimax). In this embodiment, when the door lock rod device 22 is operated to the unlocking position and the operating devices 23 and 24 are not operated (standby state), the opening area Abn for non-operation is set so that the pump discharge pressure Pp becomes the upper limit pressure Pimax of the pilot pressure (for example, about 4 MPa).

[0073] In addition, the main controller 100 can also detect the pump discharge flow rate that changes according to the temperature of the working oil and the engine speed, and calculate the opening area Abn used during non-operation, so that the discharge pressure of the hydraulic pump 81 detected by the pressure sensor 25 converges within a certain range (above the lower limit pressure Pimin and below the upper limit pressure Pimax).

[0074] In step S120, the main controller 100 determines whether the pump discharge pressure Pp is within a certain range (above the lower limit pressure Pimin and below the upper limit pressure Pimax) based on the pressure signal obtained in step S100. In step S120, if it is determined that the pump discharge pressure Pp is within the certain range, the process proceeds to step S130. In step S120, if it is determined that the pump discharge pressure Pp is not within the certain range, the process proceeds to step S135.

[0075] In step S130, the main controller 100 sets the target opening area Abt (last value) set before a control cycle as the target opening area Abt of the bypass shut-off valve 17, and sets the target opening area Act (last value) set before a control cycle as the target opening area Act of the CT opening control valves 26A and 26B, and the processing enters step S180.

[0076] In step S135, the main controller 100 determines whether the pump discharge pressure Pp is higher than the upper limit pressure Pimax based on the pressure signal obtained in step S100. In step S135, if it is determined that the pump discharge pressure Pp is higher than the upper limit pressure Pimax, the process proceeds to step S140. In step S135, if it is determined that the pump discharge pressure Pp is lower than the upper limit pressure Pimax, the process proceeds to step S150.

[0077] In step S140, the main controller 100 determines whether the target opening area Abt of the bypass cut valve 17 is greater than or equal to the maximum opening area Abmax. In step S140, if it is determined that the target opening area Abt of the bypass cut valve 17 is greater than or equal to the maximum opening area Abmax, the process proceeds to step S130. In step S140, if it is determined that the target opening area Abt of the bypass cut valve 17 is less than the maximum opening area Abmax, the process proceeds to step S145.

[0078] In step S145, the main controller 100 sets the value obtained by adding the specified value ΔAb to the target opening area Abt (previous value) of the bypass cut valve 17 as the new target opening area Abt (this time value). In addition, the main controller 100 sets the target opening area Act (previous value) set one control cycle ago as the target opening area Act of the CT opening control valves 26A and 26B, and proceeds to step S180.

[0079] In step S150, the main controller 100 determines whether the pump discharge pressure Pp is lower than the lower limit pressure Pimin based on the pressure signal obtained in step S100. In step S150, if it is determined that the pump discharge pressure Pp is lower than the lower limit pressure Pimin, the process proceeds to step S160. In step S150, if it is determined that the pump discharge pressure Pp is higher than the lower limit pressure Pimin, the process returns to step S120.

[0080] In step S160, the main controller 100 determines whether the target opening area Abt of the bypass cut valve 17 is less than the minimum opening area Abmin. In step S160, if it is determined that the target opening area Abt of the bypass cut valve 17 is less than the minimum opening area Abmin, the process proceeds to step S170. In step S160, if it is determined that the target opening area Abt of the bypass cut valve 17 is larger than the minimum opening area Abmin, the process proceeds to step S175.

[0081] In step S170, the main controller 100 sets the minimum opening area (e.g., 0) Acmin as the target opening area Act of the CT opening control valves 26A and 26B. In addition, the main controller 100 sets the target opening area Abt (previous value) set one control cycle ago as the target opening area Abt of the bypass cut valve 17, and the process proceeds to step S180.

[0082] In step S175, the main controller 100 sets the value obtained by subtracting the specified value ΔAb from the target opening area Abt (previous value) of the bypass cut valve 17 as the new target opening area Abt (this time value). In addition, the main controller 100 sets the target opening area Act (previous value) set one control cycle ago as the target opening area Act of the CT opening control valves 26A and 26B, and proceeds to step S180.

[0083] In step S180, the main controller 100 outputs a control current corresponding to the target opening area Abt of the bypass cutoff valve 17 to the solenoid valve 63, and the process proceeds to step S190. In step S190, the main controller 100 outputs a control current corresponding to the target opening area Act of the CT opening control valves 26A and 26B to the solenoid valves 61A and 61B, and the process ends. Figure 3 The process is shown in the flowchart.

[0084] Reference Figure 4 , main operations of the hydraulic system 90 when the boom lowering operation is performed will be described. Figure 4 It is a diagram showing the time series changes of the operation position Pg of the door lock lever device 22, the boom lowering operation amount L of the boom operating device 23, the discharge pressure Pp of the hydraulic pump 81, the discharge capacity (tilt angle of the swash plate) q of the hydraulic pump 81, the opening area Ab of the bypass cut-off valve 17, and the opening area Ac of the outlet throttle portion 28A of the CT opening control valve 26A. Figure 4In the figure, the horizontal axis represents time (elapsed time). At time t0, the door lock lever device 22 is in the locked position, and the bucket 13 is sufficiently away from the ground. At time t1, the operator operates the door lock lever device 22 to the unlocked position. As a result, the state (standby state) in which the operation of the working device 10 based on the operating devices 23 and 24 can be realized is achieved. The opening area of ​​the bypass stop valve 17 is reduced from the maximum opening area Abmax to the opening area Abn for non-operation (refer to Figure 3 As the opening area of ​​the bypass cutoff valve 17 decreases, the discharge pressure Pp of the hydraulic pump 81 increases to the upper limit pressure Pimax. Thus, the required pilot primary pressure is ensured, and when the operating devices 23 and 24 are operated, the solenoid valves 61A, 61B, 62A, and 62B are in a state where the pilot secondary pressure corresponding to the operation amount can be appropriately generated.

[0085] From time t2, the operator performs a boom lowering operation through the boom operating device 23. From time t2 to time t3, the operation amount L of the boom operating device 23 gradually increases. From time t3 to time t4, the operation amount L is maintained at the operation amount L1 for micro-operation. As the operation amount L increases from time t2, the discharge capacity q of the hydraulic pump 81 increases. The valve core of the boom control valve 45 is displaced to a position corresponding to the operation amount L, and the boom 11 is lowered. As the operation amount L of the boom lowering operation increases, the discharge pressure Pp of the hydraulic pump 81 decreases.

[0086] When the discharge pressure Pp of the hydraulic pump 81 decreases to the lower limit pressure Pimin at time t3, the opening area Ab of the bypass cut valve 17 decreases by a predetermined value ΔAb (see Figure 3 As a result, the discharge pressure Pp of the hydraulic pump 81 rises to the upper limit pressure Pimax.

[0087] From time t4 to time t5, the operation amount L of the boom operating device 23 gradually increases. From time t5 to time t6, the operation amount L is maintained at the operation amount L2 for semi-operation. As the operation amount L increases from time t4, the discharge capacity q of the hydraulic pump 81 increases. The valve core of the boom control valve 45 is displaced to a position corresponding to the operation amount L, and the lowering speed of the boom 11 increases. As the operation amount L of the boom lowering operation increases, the discharge pressure Pp of the hydraulic pump 81 decreases.

[0088] When the discharge pressure Pp of the hydraulic pump 81 drops to the lower limit pressure Pimin at time t5, the opening area Ab of the bypass cut valve 17 decreases by a predetermined value ΔAb (see Figure 3 As a result, the discharge pressure Pp of the hydraulic pump 81 rises to the upper limit pressure Pimax.

[0089] From time t6 to time t7, the operation amount L of the boom operating device 23 gradually increases. From time t7 to time t8, the operation amount L is maintained at the operation amount L3 between the half operation and the full operation. As the operation amount L increases from time t6, the discharge capacity q of the hydraulic pump 81 increases. The valve core of the boom control valve 45 is displaced to a position corresponding to the operation amount L, and the lowering speed of the boom 11 increases. As the operation amount L of the boom lowering operation increases, the discharge pressure Pp of the hydraulic pump 81 decreases.

[0090] When the discharge pressure Pp of the hydraulic pump 81 decreases to the lower limit pressure Pimin at time t7, the opening area Ab of the bypass cut valve 17 decreases to the minimum opening area Abmin (for example, 0) (see Figure 3 As a result, the discharge pressure Pp of the hydraulic pump 81 rises to the upper limit pressure Pimax.

[0091] From time t8 to time t9, the operation amount L of the boom operating device 23 gradually increases. From time t9 to time t10, the operation amount L is maintained at the maximum operation amount Lmax for full operation. As the operation amount L increases to the maximum operation amount Lmax from time t8, the discharge capacity q of the hydraulic pump 81 increases to the maximum discharge capacity (maximum tilt angle) qmax. The valve core of the boom control valve 45 is displaced to the maximum stroke position, and the lowering speed of the boom 11 increases. As the operation amount L of the boom lowering operation increases, the discharge pressure Pp of the hydraulic pump 81 decreases.

[0092] When the discharge pressure Pp of the hydraulic pump 81 decreases to the lower limit pressure Pimin at time t9, the opening area Ac of the CT opening control valve 26A decreases from the maximum opening area Acmax to the minimum opening area Acmin (for example, 0) (see Figure 3 As a result, the discharge pressure Pp of the hydraulic pump 81 rises to the upper limit pressure Pimax.

[0093] As described above, in the present embodiment, when the bucket 13 is sufficiently away from the ground, when the boom lowering operation is performed, for example, when the operation amount L is lower than the operation amount L3, the opening area of ​​the bypass cutoff valve 17 is reduced, thereby increasing the discharge pressure Pp of the hydraulic pump 81, and preventing the discharge pressure Pp from being lower than the lower limit pressure Pimin of the set pressure of the pilot pressure reducing valve 71. In addition, when the boom lowering operation is performed, for example, when the operation amount L is the maximum operation amount Lmax, in addition to the bypass cutoff valve 17, the opening area of ​​the meter-out portion 28A of the CT opening control valve 26A is also reduced. As a result, the flow rate (regeneration flow rate) of the working oil discharged from the bottom chamber of the boom cylinder 11a and regeneratively supplied to the rod chamber increases. That is, it is possible to ensure a sufficient flow rate on the meter-in side without consuming the discharge flow rate of the hydraulic pump 81 as much as possible. As a result, the discharge pressure (circuit pressure on the meter-in side) Pp of the hydraulic pump 81 increases, and the discharge pressure Pp is prevented from being lower than the set pressure of the pilot pressure reducing valve 71. That is, according to the present embodiment, when the boom lowering operation is performed while the bucket 13 is away from the ground, a stable pilot primary pressure can be ensured, and as a result, a decrease in the cylinder speed can be prevented.

[0094] Furthermore, the operations of the bypass cutoff valve 17 and the CT opening control valve 26A when the boom lowering operation is performed have been described, but the operations of the bypass cutoff valve 17 and the CT opening control valve 26B when the arm loading operation is performed are also the same.

[0095] According to the above-mentioned first embodiment, the following effects are achieved.

[0096] (1) When the pressure (discharge pressure Pp) detected by the pressure sensor 25 is lower than the lower limit pressure (first pressure) Pimin and the opening area Ab of the bypass cutoff valve 17 is larger than the minimum opening area (first area) Abmin, the main controller (control device) 100 controls the solenoid valve (third pressure reducing valve) 63 so that the opening area Ab of the bypass cutoff valve 17 becomes smaller (see Figure 3Steps S150, S160, S175, and S180). That is, when the pressure Pp detected by the pressure sensor 25 becomes lower, the main controller 100 controls the solenoid valve (third pressure reducing valve) 63 so that the opening area Ab of the bypass stop valve 17 becomes smaller. Thus, when the boom lowering operation and the dipper arm shoveling operation cause the working device 10 to work in the direction of gravity and the discharge pressure of the hydraulic pump 81 decreases, the bypass stop valve 17 is controlled to the closed side and the discharge pressure of the hydraulic pump 81 increases. In addition, when the pressure Pp detected by the pressure sensor 25 is higher than the upper limit pressure (second pressure) Pimax that is higher than the lower limit pressure Pimin, and the opening area Ab of the bypass stop valve 17 is smaller than the maximum opening area (second area) Abmax that is larger than the minimum opening area Abmin, the main controller 100 controls the solenoid valve 63 so that the opening area Ab of the bypass stop valve 17 becomes larger (refer to Figure 3 Steps S135, S140, S145, and S180). As a result, when the discharge pressure of the hydraulic pump 81 increases, the bypass cut-off valve 17 is controlled to the open side, and the discharge pressure of the hydraulic pump 81 decreases. In this way, in the present embodiment, since feedback control based on the discharge pressure Pp of the hydraulic pump 81 is performed, the discharge pressure Pp of the hydraulic pump 81 can be maintained within a certain range (above the lower limit pressure Pimin and below the upper limit pressure Pimax) regardless of the flow rate of the hydraulic oil and the temperature of the hydraulic oil.

[0097] Here, as described above, when the weight and center of gravity position of the working device 10 are changed by replacing the bucket 13 installed at the front end of the working device 10 with a heavier bucket, when an operation is performed to make the working device 10 work in the direction of gravity, the discharge pressure of the hydraulic pump 81 may be lower than the pilot primary pressure only by controlling the opening of the bypass stop valve 17.

[0098] When the pressure Pp detected by the pressure sensor 25 is lower than the lower limit pressure Pimin and the opening area Ab of the bypass cutoff valve 17 is less than the minimum opening area, the main controller 100 of the present embodiment controls the solenoid valves (fourth pressure reducing valves) 35A and 35B so that the opening areas of the outlet throttle portions 28A and 28B become smaller (see Figure 3 That is, the hydraulic system 90 of the present embodiment is configured such that the greater the amount of operation (boom lowering operation, dipper arm shoveling operation) performed by the operating devices 23 and 24 to make the working device 10 work in the direction of gravity, the smaller the opening area of ​​the outlet throttle parts 28A and 28B.

[0099] According to this structure, when the specification of the working device 10 is changed so that the inertia moment of the working device 10 increases, when the operation of operating the working device 10 in the direction of gravity is performed, in addition to the opening area of ​​the bypass stop valve 17, the opening area of ​​the outlet meter-out parts 28A and 28B is also reduced, and the hydraulic oil of the flow rate required to maintain the speed of the hydraulic cylinders 11a and 12a is regenerated and supplied to the hydraulic cylinders through the regeneration passage. Therefore, according to this embodiment, when the operation of operating the working device 10 in the direction of gravity is performed, a stable pilot primary pressure can be ensured, and as a result, a decrease in the cylinder speed can be prevented.

[0100] (2) When the pressure Pp detected by the pressure sensor 25 is lower than the lower limit pressure Pimin and the opening area Ab of the bypass cut valve 17 is larger than the minimum opening area Abmin, the condition is satisfied (in Figure 3 In step S150, it is YES, and in step S160, it is NO), the main controller 100 controls the electromagnetic valve 63 so that the opening area Ab of the bypass cutoff valve 17 becomes an opening area smaller than the predetermined value ΔAb (refer to Figure 3 The main controller 100 controls the electromagnetic valve 63 whenever the above-mentioned condition is satisfied, thereby gradually reducing the opening area Ab of the bypass cutoff valve 17 (see Figure 4 ). Thus, it is possible to suppress rapid pressure fluctuations in the main circuit HC1.

[0101] <Second embodiment>

[0102] Reference Figure 5 A main controller 100 for controlling a hydraulic excavator 1 according to a second embodiment of the present invention will be described. Configurations identical or corresponding to those described in the first embodiment are denoted by the same reference numerals, and differences will be mainly described. Figure 5 It is a functional block diagram of the main controller 100 according to the second embodiment of the present invention, and shows functions related to the control of the bypass cut valve 17 .

[0103] In the first embodiment, an example is described in which the main controller 100 performs feedback control based on the discharge pressure Pp of the hydraulic pump 81. The main controller 100 of the first embodiment increases the discharge pressure Pp by reducing the opening area of ​​the bypass cut valve 17 when the discharge pressure Pp is lower than the lower limit pressure Pimin, and decreases the discharge pressure Pp by increasing the opening area of ​​the bypass cut valve 17 when the discharge pressure Pp is higher than the upper limit pressure Pimax.

[0104] The main controller 100 of the second embodiment has the functions described in the first embodiment, and further has a function of controlling the opening area of ​​the bypass cut-off valve 17 according to the rotation speed of the hydraulic pump 81 and the temperature of the working oil so that the discharge pressure Pp converges within a certain range (above the lower limit pressure Pimin and below the upper limit pressure Pimax). The control method (control mode) of the bypass cut-off valve 17 described in the first embodiment and the control method (control mode) of the bypass cut-off valve 17 to be described in the second embodiment can be switched, for example, by the operator performing a mode switching operation on the input device in the cab 31.

[0105] The main controller 100 of the second embodiment controls the opening area of ​​the bypass cutoff valve 17 in consideration of the influence of the flow rate change caused by the change in the rotation speed of the hydraulic pump 81 and the influence of the viscosity change caused by the temperature change of the hydraulic oil. For example, if the rotation speed of the hydraulic pump 81 increases while the opening area of ​​the bypass cutoff valve 17 is maintained at a predetermined area, the flow rate of the hydraulic oil passing through the bypass cutoff valve 17 increases, and the discharge pressure of the hydraulic pump 81 increases. Therefore, the opening area of ​​the bypass cutoff valve 17 is maintained at a predetermined area, and when the rotation speed of the hydraulic pump 81 is a predetermined speed, when the discharge pressure becomes a target pressure (for example, 4 [MPa]), when the rotation speed of the hydraulic pump 81 is greater than the predetermined speed, the opening area of ​​the bypass cutoff valve 17 needs to be larger than the predetermined area. Similarly, when the opening area of ​​the bypass cutoff valve 17 is maintained at a predetermined area and the temperature of the hydraulic oil is a predetermined temperature, when the discharge pressure becomes a target pressure (for example, 4 [MPa]), when the temperature of the hydraulic oil is lower than the predetermined temperature, the opening area of ​​the bypass cutoff valve 17 needs to be larger than the predetermined area.

[0106] Therefore, it is preferred that the characteristics of the opening area of ​​the bypass stop valve 17 relative to the rotational speed of the hydraulic pump 81 so that the discharge pressure becomes the target pressure and the characteristics of the opening area of ​​the bypass stop valve 17 relative to the temperature of the working oil are stored in a non-volatile memory in advance in a table or function form, and these characteristics are used to control the opening area of ​​the bypass stop valve 17.

[0107] like Figure 5 As shown, the main controller 100 of the second embodiment includes a first target area setting unit 111 , a second target area setting unit 112 , a minimum value selection unit 113 , a proportional valve pressure setting unit 114 , and a control current setting unit 118 .

[0108] The hydraulic pump 81 is mechanically connected to the engine 80. Therefore, the rotation speed sensor 80a functions as a sensor for detecting the rotation speed of the hydraulic pump 81. In addition, the sensor for detecting the rotation speed of the hydraulic pump 81 may be provided separately from the rotation speed sensor 80a of the engine 80. The temperature sensor 19a is provided in the oil tank 19 or the like (see Figure 2), detects the temperature of the working oil, and outputs a signal indicating the detection result to the main controller 100.

[0109] The first target area setting unit 111 sets the first target area Ab1 of the bypass cut-off valve 17 according to the rotation speed N of the hydraulic pump 81 detected by the rotation speed sensor 80a, with reference to the speed-opening table. The speed-opening table is a data table that specifies the relationship between the rotation speed N of the hydraulic pump 81 and the first target area Ab1, and is stored in a non-volatile memory. The speed-opening table specifies the characteristic that the first target area Ab1 increases from the minimum opening area Abmin to the opening area Abn used during non-operation as the rotation speed N of the hydraulic pump 81 increases. Therefore, the first target area setting unit 111 sets the first target area Ab1 of the bypass cut-off valve 17 to a larger value as the rotation speed N detected by the rotation speed sensor 80a increases. The rotation speed value of the speed-opening table uses a preset rotation speed value so as to obtain "a pressure that can ensure a stable pilot primary pressure".

[0110] The second target area setting unit 112 sets the second target area Ab2 of the bypass cut-off valve 17 according to the temperature To of the working oil detected by the temperature sensor 19a, with reference to the temperature-opening table. The temperature-opening table is a data table that specifies the relationship between the temperature To of the working oil and the second target area Ab2, and is stored in a non-volatile memory. The temperature-opening table specifies the characteristic that as the temperature To of the working oil rises, the second target area Ab2 decreases from the opening area Abn used during non-operation to the minimum opening area Abmin. Therefore, the higher the temperature To detected by the temperature sensor 19a, the smaller the value to which the second target area setting unit 112 sets the second target area Ab2 of the bypass cut-off valve 17. The temperature value of the temperature-opening table uses a pre-set temperature value so that a "pressure that can ensure a stable pilot primary pressure" can be obtained.

[0111] The minimum value selection unit 113 selects the smaller of the first target area Ab1 set by the first target area setting unit 111 and the second target area Ab2 set by the second target area setting unit 112, and sets it as the target opening area Abt of the bypass cut valve 17. In this way, the first target area setting unit 111, the second target area setting unit 112, and the minimum value selection unit 113 function as a target opening area setting unit that sets the target opening area of ​​the bypass cut valve 17.

[0112] The proportional valve pressure setting unit 114 sets the pilot secondary pressure generated by the solenoid valve 63, i.e., the proportional valve pressure po, according to the target opening area Abt set by the minimum value selection unit 113, with reference to the opening-proportional valve pressure table. The opening-proportional valve pressure table is a data table that specifies the relationship between the target opening area Abt and the proportional valve pressure po, and is stored in a non-volatile memory. The opening-proportional valve pressure table specifies the characteristic that the proportional valve pressure po decreases as the target opening area Abt increases. Therefore, the proportional valve pressure setting unit 114 sets the proportional valve pressure po to a smaller value as the target opening area Abt increases.

[0113] The control current setting unit 118 sets the control current I output to the solenoid valve 63 according to the proportional valve pressure po set by the proportional valve pressure setting unit 114. A data table defining the relationship between the set proportional valve pressure po and the control current I is stored in a non-volatile memory as a proportional valve pressure-control current table. The proportional valve pressure-control current table defines the characteristic that the control current I increases as the proportional valve pressure po increases. Therefore, the control current setting unit 118 sets the control current I to a larger value as the proportional valve pressure po increases. The control current setting unit 118 outputs the set control current I to the solenoid valve 63.

[0114] Thus, the main controller 100 of the second embodiment sets the first target area Ab1 of the bypass cutoff valve 17 to a larger value as the rotation speed N of the hydraulic pump 81 detected by the rotation speed sensor 80a increases, and the main controller 100 of the second embodiment sets the second target area Ab2 of the bypass cutoff valve 17 to a smaller value as the temperature To of the working oil detected by the temperature sensor 19a increases. The main controller 100 selects the smaller of the first target area Ab1 and the second target area Ab2 as the target opening area Abt. The main controller 100 sets the control current I according to the set target opening area Abt, and controls the solenoid valve (third pressure reducing valve) 63 by the set control current I.

[0115] According to this structure, the same effect as the first embodiment is achieved. Furthermore, according to the second embodiment, the risk of fluctuation based on feedback control can be avoided. In addition, the bypass cut-off valve 17 can be appropriately controlled according to the rotation speed N of the hydraulic pump 81 and the temperature To of the working oil. Therefore, according to the second embodiment, when an operation is performed to make the working device 10 work in the direction of gravity, the pump discharge pressure Pp can be appropriately maintained at the target value Ppt.

[0116] The following modified examples are also within the scope of the present invention. The structure shown in the modified example may be combined with the structure described in the above embodiment, or the structures described in the above different embodiments may be combined with each other, or the structures described in the following different modified examples may be combined with each other.

[0117] <Variation 1>

[0118] In the above-mentioned embodiment, the example in which the regeneration passage and the CT opening control valves 26A and 26B having the outlet throttle portions 28A and 28B are provided outside the cylinder control valves 45 and 46 (see Figure 2 ) is described, but the present invention is not limited thereto. Figure 6 As shown, the regeneration passage and the outlet throttle parts 28A, 28B may also be assembled inside the cylinder control valves 45, 46. The outlet throttle parts 28A, 28B are formed such that when the valve core of the cylinder control valve 45, 46 is displaced from the neutral position, after the opening area thereof becomes larger, the opening area gradually becomes smaller in accordance with the displacement of the valve core. In addition, the hydraulic system 90 of this modified example does not have the CT opening control valves 26A, 26B and the solenoid valves 35A, 35B described in the above embodiment.

[0119] According to this modification, the opening area of ​​the outlet throttling parts 28A and 28B is adjusted as the valve core of the cylinder control valves 45 and 46 is displaced, so that the same effect as the above-mentioned embodiment can be obtained. However, in this case, as the valve core of the cylinder control valves 45 and 46 is displaced, the opening area of ​​the outlet throttling parts 28A and 28B changes, thereby affecting the speed of the hydraulic cylinder during micro-operation and semi-operation. In addition, it is necessary to define the outlet throttling parts 28A and 28B according to the shape of the valve core and the hole that accommodates the valve core, so the formation of the cylinder control valves 45 and 46 takes effort. Therefore, it is preferred that, as in the above-mentioned embodiment, the CT opening control valves 26A and 26B and the cylinder control valves 45 and 46 are set to be independently controllable.

[0120] <Variation 2>

[0121] In the above embodiment, the pressure sensor 25 for detecting the discharge pressure of the hydraulic pump 81 is used as the pressure sensor for detecting the pressure of the working oil on the discharge side of the hydraulic pump 81, and the main controller 100 controls the solenoid valve 63 according to the detection result of the pressure sensor 25, but the present invention is not limited to this. The main controller 100 may also replace the detection result of the pressure sensor 25 with the pressure sensor 75 (refer to Figure 2 and Figure 6) to control the solenoid valve 63. The pressure sensor 25 is provided on the upstream side of the pilot pressure reducing valve 71 and is a pump pressure sensor that detects the discharge pressure of the hydraulic pump 81. In contrast, the pressure sensor 75 is provided on the downstream side of the pilot pressure reducing valve 71 and is an accumulator pressure sensor that detects the pressure of the accumulator 73. The structure in which the solenoid valve 63 is controlled based on the detection result of the pressure sensor 75 that detects the pressure of the accumulator 73 can reduce the frequency of throttling the bypass stop valve 17 compared to the structure in which the solenoid valve 63 is controlled based on the detection result of the pressure sensor 25 that detects the discharge pressure of the hydraulic pump 81.

[0122] <Variation 3>

[0123] In the first embodiment, the following example is described: when the boom lowering operation is performed and the bypass cut-off valve 17 is fully closed, the CT opening control valve 26A is controlled to be fully closed to prevent the discharge pressure Pp of the hydraulic pump 81 from decreasing, and when the boom loading operation is performed and the bypass cut-off valve 17 is fully closed, the CT opening control valve 26B is controlled to prevent the discharge pressure Pp of the hydraulic pump 81 from decreasing. However, the present invention is not limited to this. The control content of the CT opening control valve described in the first embodiment may also be applied to only one of the CT opening control valve 26A and the CT opening control valve 26B.

[0124] <Variation 4>

[0125] In the above embodiment, the structure in which the working oil ejected from the single hydraulic pump 81 is supplied to the boom cylinder 11a through the boom control valve 45 is described as an example, but the present invention is not limited to this. The present invention can also be applied to a structure in which the working oil ejected from two or more hydraulic pumps 81 is supplied to the boom cylinder 11a through a plurality of boom control valves 45. In this case, for one of the plurality of boom control valves 45, the outlet throttle portion 28A is assembled as in the second embodiment, and the boom control valve 45 provided with the outlet throttle portion 28A operates in the same manner as the CT opening control valve 26A described in the first embodiment, thereby achieving the same effects as those of the above-mentioned first embodiment.

[0126] <Variant 5>

[0127] In the second embodiment, an example is described in which the main controller 100 selects the smaller of the first target area Ab1 set according to the rotation speed N of the hydraulic pump 81 and the second target area Ab2 set according to the temperature To of the hydraulic oil to set as the target opening area Abt of the bypass cut valve 17. That is, the main controller 100 of the second embodiment is configured to set the target opening area Abt in consideration of both the rotation speed N of the hydraulic pump 81 and the temperature To of the hydraulic oil. However, the method of setting the target opening area Abt is not limited to this method.

[0128] <Variation 5-1>

[0129] For example, the main controller 100 may set the target opening area Abt of the bypass cut valve 17 to a larger value as the rotation speed N detected by the rotation speed sensor 80a increases, and control the solenoid valve 63. In this configuration, the bypass cut valve 17 can be appropriately controlled according to the rotation speed N of the hydraulic pump 81.

[0130] <Variation 5-2>

[0131] For another example, the higher the temperature To detected by the temperature sensor 19a, the main controller 100 may set the target opening area Abt of the bypass cut valve 17 to a smaller value and control the solenoid valve 63. In this configuration, the bypass cut valve 17 can be appropriately controlled according to the temperature To of the hydraulic oil.

[0132] <Variant 6>

[0133] In the above embodiment, the bypass cutoff valve 17 is provided downstream of the cylinder control valves 45 and 46 in the center bypass passage Lb, but the present invention is not limited thereto. The bypass cutoff valve 17 may be provided upstream of the cylinder control valves 45 and 46 in the center bypass passage Lb.

[0134] Although the embodiments of the present invention have been described above, the above embodiments merely represent a part of application examples of the present invention and are not intended to limit the technical scope of the present invention to the specific structures of the above embodiments.

[0135] Explanation of symbols

[0136] 1…Hydraulic excavator (working machine), 10…Working device, 11…Boom (driven component), 11a…Boom cylinder (hydraulic cylinder), 12…Arm (driven component), 12a…Arm cylinder (hydraulic cylinder), 13…Bucket (driven component), 13a…Bucket cylinder (hydraulic cylinder), 17…Bypass stop valve, 17a…Pilot pressure receiving part, 19…Oil tank, 19a…Temperature sensor, 20…Machine body (body), 22…Door lock lever device, 23…Boom operating device (operating device), 24…Arm operating device (operating device), 25…Pressure sensor, 26A, 26B…CT opening control valve (meter-out control valve), 27A, 27B…Check valve, 2 8A, 28B...throttle-out section, 35A, 35B...solenoid valve (fourth pressure reducing valve), 45...boom control valve (cylinder control valve), 45a, 45b...pilot pressure receiving section, 45r...return oil passage (throttle-out passage), 46...arm control valve (cylinder control valve), 46a, 46b...pilot pressure receiving section, 46r...return oil passage (throttle-out passage), 61A, 61B, 62A, 62B...solenoid valve (second pressure reducing valve), 63...solenoid valve (third pressure reducing valve), 71...pilot pressure reducing valve (first pressure reducing valve), 73...accumulator, 74...lock valve, 75...pressure sensor, 80...engine, 80a...speed sensor, 81...hydraulic pump, 81a...regulator, 90…Hydraulic system, 100…Main controller (control device), 111…First target area setting unit, 112…Second target area setting unit, 113…Minimum value selection unit, 114…Proportional valve pressure setting unit, 118…Control current setting unit, Ab…Opening area of ​​bypass cutoff valve, Ab1…First target area, Ab2…Second target area, Abmax…Maximum opening area (second area), Abmin…Minimum opening area (first area), Abn…Opening area for non-operation, Abt…Target opening area of ​​bypass cutoff valve, Ac…Opening area of ​​CT opening control valve, Acmax…Maximum opening area, Acmin…Minimum opening area, A ct…target opening area of ​​the CT opening control valve, HC1…main circuit, HC2…pilot circuit, I…control current, L…operation amount, Lb…center bypass passage, Ld…pump discharge passage, Lp…parallel passage (inlet throttle passage), N…speed of the hydraulic pump, Pimax…upper limit pressure (second pressure), Pimin…lower limit pressure (first pressure), po…proportional valve pressure, po'…corrected proportional valve pressure, Pp…discharge pressure of the hydraulic pump (actually measured value), Ppt…pressure target value of the working oil on the discharge side of the hydraulic pump, q…discharge capacity of the hydraulic pump, To…temperature of the working oil, ΔAb…specified value, Δpo…corrected value, ΔPp…pressure deviation (deviation).

Claims

1. A working machine having: A working device comprising a plurality of hydraulic cylinders and a plurality of driven components driven by the plurality of hydraulic cylinders; An operating device, used to operate the hydraulic cylinder; a main circuit for supplying the hydraulic oil ejected from the hydraulic pump to the hydraulic cylinder; a cylinder control valve provided in the main circuit and controlling the flow of the hydraulic oil supplied from the hydraulic pump to the hydraulic cylinder; a pilot circuit that guides a portion of the hydraulic oil discharged from the hydraulic pump to a pilot pressure receiving portion of the cylinder control valve; a first pressure reducing valve provided in the pilot circuit and reducing the pressure of the hydraulic oil discharged from the hydraulic pump to generate a pilot primary pressure; a second pressure reducing valve provided in the pilot circuit and reducing the pilot primary pressure to generate a pilot secondary pressure acting on a pilot pressure receiving portion of the cylinder control valve; a central bypass passage, which connects the hydraulic pump and the oil tank and is provided with the cylinder control valve; a bypass stop valve, which is arranged in the central bypass passage; a third pressure reducing valve provided in the pilot circuit and reducing the pilot primary pressure to generate a pilot secondary pressure acting on the pilot pressure receiving portion of the bypass stop valve; a regeneration passage connecting a throttle-in passage and a throttle-out passage, wherein the throttle-in passage guides the hydraulic oil ejected from the hydraulic pump to the hydraulic cylinder, and the throttle-out passage guides the return oil from the hydraulic cylinder to the oil tank; a check valve disposed in the regeneration passage and allowing the flow of the hydraulic oil from the outlet throttle passage to the inlet throttle passage and prohibiting the flow of the hydraulic oil from the inlet throttle passage to the outlet throttle passage; An outlet throttling portion, which is arranged in the outlet throttling passage; a pressure sensor that detects the pressure of the hydraulic oil on the discharge side of the hydraulic pump; and a control device for controlling the second pressure reducing valve according to the operation amount of the operating device, It is characterized in that The control device controls the third pressure reducing valve according to the pressure detected by the pressure sensor. When the pressure detected by the pressure sensor becomes low, the control device controls the third pressure reducing valve so that the opening area of ​​the bypass stop valve becomes smaller. The control device reduces the opening area of ​​the meter-out portion as the amount of operation of the operating device to operate the working device in the gravity direction increases.

2. The working machine according to claim 1, characterized in that: The working machine has: a meter-out control valve having the meter-out portion; and a fourth pressure reducing valve, which is provided in the pilot circuit and reduces the pilot primary pressure to generate a pilot secondary pressure acting on the pilot pressure receiving portion of the meter-out control valve, When the pressure detected by the pressure sensor is lower than the first pressure and the opening area of ​​the bypass stop valve is larger than the first area, the control device controls the third pressure reducing valve so that the opening area of ​​the bypass stop valve becomes smaller. When the pressure detected by the pressure sensor is higher than a second pressure higher than the first pressure and the opening area of ​​the bypass stop valve is smaller than a second area larger than the first area, the control device controls the third pressure reducing valve so that the opening area of ​​the bypass stop valve becomes larger. When the pressure detected by the pressure sensor is lower than the first pressure and the opening area of ​​the bypass cut valve is equal to or smaller than the first area, the control device controls the fourth pressure reducing valve so that the opening area of ​​the meter-out portion becomes smaller.

3. The working machine according to claim 2, characterized in that: When the pressure detected by the pressure sensor is lower than the first pressure and the opening area of ​​the bypass stop valve is larger than the first area, the control device controls the third pressure reducing valve so that the opening area of ​​the bypass stop valve becomes an opening area smaller than a predetermined value. The control device controls the third pressure reducing valve every time the condition is satisfied, thereby reducing the opening area of ​​the bypass cut valve in stages.

4. The working machine according to claim 1, characterized in that: The working machine has: a rotation speed sensor for detecting the rotation speed of the hydraulic pump; and A temperature sensor that detects the temperature of the working oil, The control device sets the first target area of ​​the bypass cut valve to a larger value as the rotation speed detected by the rotation speed sensor increases. The control device sets the second target area of ​​the bypass cutoff valve to a smaller value as the temperature detected by the temperature sensor is higher. The control device selects the smaller of the first target area and the second target area and sets the smaller one as the target opening area of ​​the bypass cutoff valve. The control device controls the third pressure reducing valve.

5. The working machine according to claim 1, characterized in that: The working machine includes: a rotation speed sensor for detecting the rotation speed of the hydraulic pump; The control device sets the target opening area of ​​the bypass cutoff valve to a larger value as the rotation speed detected by the rotation speed sensor increases. The control device controls the third pressure reducing valve.

6. The working machine according to claim 1, characterized in that: The working machine includes a temperature sensor for detecting the temperature of the working oil. The control device sets the target opening area of ​​the bypass cutoff valve to a smaller value as the temperature detected by the temperature sensor is higher. The control device controls the third pressure reducing valve.

7. The working machine according to claim 1, characterized in that: The pressure sensor is disposed on the downstream side of the first pressure reducing valve.

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