JP7263230B2 - work machine - Google Patents

Description

The present invention relates to working machines.

BACKGROUND ART Conventionally, a working machine disclosed in Patent Document 1 is known.
A work machine disclosed in Patent Document 1 includes a plurality of hydraulic actuators and a plurality of directional switching valves corresponding to the plurality of hydraulic actuators. Each directional valve switches the direction of hydraulic fluid to the corresponding hydraulic actuator.

JP 2017-115992 A

In the work machine disclosed in Patent Document 1, when a high-load hydraulic actuator with a high working pressure and a low-load hydraulic actuator with a lower working pressure than the high-load hydraulic actuator are operated in combination, the low-load hydraulic actuator is operated alone. The operating speed of the low-load hydraulic actuator may change depending on when it is operated.
SUMMARY OF THE INVENTION In view of the above problems, it is an object of the present invention to suppress changes in the operating speed of a low-load hydraulic actuator with a low operating pressure.

A work machine according to an aspect of the present invention includes a plurality of hydraulic actuators, a plurality of directional switching valves provided corresponding to the plurality of hydraulic actuators for switching a direction of hydraulic oil to the hydraulic actuators, and the plurality of hydraulic actuators. When a high-load hydraulic actuator with a high working pressure and a low-load hydraulic actuator with a lower working pressure than the high-load hydraulic actuator among the actuators are operated in combination, and when the low-load hydraulic actuator is operated alone, the low load hydraulic actuator is operated. a dummy load forming unit that forms a dummy load on a low load side directional switching valve that switches the direction of hydraulic fluid to the low load hydraulic actuator in order to suppress a change in the operating speed of the load hydraulic actuator ; The directional switching valve on the low load side includes an input port to which hydraulic fluid is input, an output port that communicates with the low load hydraulic actuator, and a low load hydraulic actuator that communicates with the input port and the output port. and a flow path through which hydraulic oil flows toward the high-load hydraulic actuator. The side directional switching valve has an input port to which hydraulic fluid is input, an output port communicating with the high-load hydraulic actuator, the input port of the high-load side directional switching valve, and the high-load side directional switching valve. and a flow passage, which is not provided with a throttle, and which communicates with the output port of to flow hydraulic oil toward the high-load hydraulic actuator.

According to the above-described work machine, the dummy load generator generates a dummy load in advance on the directional control valve on the low load side, and raises the operating pressure of the low load hydraulic actuator. It is possible to reduce the pressure difference when performing a combined operation with the hydraulic actuator. As a result, it is possible to suppress the change in the operating speed of the low-load hydraulic actuator between when the high-load hydraulic actuator and the low-load hydraulic actuator are operated in combination and when the low-load hydraulic actuator is operated singly.

It is a side view of a working machine. It is a top view of a working machine. 1 is a schematic diagram of a hydraulic system; FIG. 1 is a circuit diagram of part of a hydraulic system; FIG. It is a circuit diagram of part of the control valve. FIG. 11 is a circuit diagram of another portion of the control valve; FIG. 4 is another partial circuit diagram of the control valve; 1 is a simplified diagram of a control system; FIG. 4 is a table showing setting of main relief pressure for each mode; 4 is a graph showing changes in main relief pressure; 9 is another graph showing changes in main relief pressure; FIG. 11 is another table showing setting of main relief pressure for each mode; FIG. FIG. 3 shows a detailed circuit diagram of a control valve with a pressure compensating valve; FIG. 4 is a detailed circuit diagram of a control valve with a flow rate priority valve;

An embodiment of the present invention will be described below with appropriate reference to the drawings.
FIG. 1 is a schematic side view showing the overall configuration of a working machine 1 according to this embodiment. FIG. 2 is a schematic side view of the working machine 1. FIG. In this embodiment, a backhoe, which is a turning work machine, is exemplified as the work machine 1 . The work machine is not limited to a backhoe, and may be a tractor, a wheel loader, a combine harvester, or the like.

As shown in FIGS. 1 and 2, the working machine 1 includes a traveling body 1A and a working device 4 mounted on the traveling body 1A. The traveling body 1</b>A has a traveling device 3 , a body (swivel base) 2 mounted on the traveling device 3 , and a cabin 5 mounted on the body 2 .
A driver's seat (seat) 6 on which an operator (driver) sits is provided in the interior of the cabin 5 . A driver's seat 6 is mounted on the fuselage 2 and a cabin 5 surrounds the driver's seat 6 . That is, the cabin 5 is a driver's seat protection device. The driver's seat protection device may be a canopy.

In the present embodiment, the front side of the operator seated in the driver's seat 6 of the working machine 1 (direction of arrow A1 in FIGS. 1 and 2) is forward, and the rear side of the operator (direction of arrow A2 in FIGS. 1 and 2) is backward. , the left side of the driver (in the direction of arrow A3 in FIG. 1) is defined as the left side, and the right side of the operator (in the direction of arrow A4 in FIG. 1) is defined as the right side.
Also, as shown in FIG. 1, the horizontal direction perpendicular to the longitudinal direction K1 will be described as the body width direction K2 (the width direction of the body 2). The direction from the central portion in the width direction of the body 2 to the right or left will be described as the outer side of the body (the outer side of the body width direction K2). That is, the outer side of the body means the direction away from the center of the body 2 in the width direction in the body width direction K2. The direction opposite to the outer side of the fuselage will be described as the inner side of the fuselage (the inner side of the fuselage width direction K2). In other words, the inward direction of the body is the width direction K2 of the body and the direction toward the center of the body 2 in the width direction.

As shown in FIGS. 1 and 2, the travel device 3 is a device that supports the body 2 so that it can travel. The traveling device 3 has a traveling frame 3A, a first traveling device 3L provided on the left side of the traveling frame 3A, and a second traveling device 3R provided on the right side of the traveling frame 3A. The first travel device 3L and the second travel device 3R are crawler travel devices. The first travel device 3L is driven by a first travel motor ML. The second travel device 3R is driven by a second travel motor MR. The first travel motor ML and the second travel motor MR are configured by hydraulic motors (hydraulic actuators).

A dozer device 7 is attached to the front portion of the traveling device 3 . The dozer device 7 is driven by a dozer cylinder C1. Specifically, the dozer cylinder C1 is configured by a hydraulic cylinder (hydraulic actuator), and the blade 7A of the dozer device 7 is raised and lowered by extending and retracting the dozer cylinder C1.
As shown in FIG. 1, the machine body 2 is supported on the travel frame 3A via a swivel bearing 8 so as to be swivelable about a swivel axis (vertical axis) X1. The turning axis X1 is an axis extending vertically through the center of the turning bearing 8 .

As shown in FIG. 2 , the cabin 5 is mounted on one side (left side) of the body 2 in the width direction K2. The cabin 5 is disposed closer to one side (left side) in the machine width direction K2 than a center line Y1 passing through the turning axis X1 and extending in the longitudinal direction K1. Also, the cabin 5 is provided near the front portion of the airframe 2 .
As shown in FIG. 2, a motor E1 is mounted on the other side (right side) of the body 2 in the width direction K2. The prime mover E1 is mounted vertically on the airframe 2 . “Longitudinal placement” means that the engine E1 is placed so that the axial center of the crankshaft of the engine E1 extends in the front-rear direction.

The prime mover E1 is arranged closer to the other side (right side) in the body width direction K2 than the center line Y1. Prime mover E1 is a diesel engine. The prime mover E1 may be a gasoline engine, an electric motor, or a hybrid type having an engine and an electric motor.
A pressure oil supply unit 18 is provided at the rear of the prime mover E1. The pressure oil supply unit 18 is driven by the power of the prime mover E1 and pressurizes and discharges the hydraulic oil used in the hydraulic drive section. The hydraulic drive unit is, for example, a hydraulic actuator or the like installed in the work machine 1 . A radiator R1, an oil cooler O1, and a condenser D1 are arranged and mounted on the airframe 2 in front of the prime mover E1. The radiator R1 is a cooling device (first cooling device) that cools the cooling water (fluid) of the prime mover E1, and the oil cooler O1 is a cooling device (second cooling device) that cools the hydraulic oil (fluid). Further, the condenser D1 is a cooling device (condenser) that cools the refrigerant (fluid) of the air conditioner (air conditioner) equipped in the working machine 1 .

A cooling fan F1 that generates cooling air for cooling the engine E1 is provided between the radiator R1 and the engine E1. The cooling fan F1 is driven by the power of the prime mover E1 to generate cooling air that flows from the front to the rear.
As shown in FIG. 2, the fuselage 2 has a board (hereinafter referred to as a turning board) 9 that turns around the turning axis X1. The swivel base plate 9 is made of a steel plate or the like, and constitutes the bottom of the fuselage 2 . The prime mover E1 is mounted on the turning base plate 9. As shown in FIG. Vertical ribs 9L and 9R, which are reinforcing members, are provided on the center side of the upper surface of the swivel base plate 9 from the front to the rear. The vertical rib 9L is arranged closer to one side from the center in the width direction K2 of the body 2, and the vertical rib 9R is arranged closer to the other side. In addition to the vertical ribs 9L and 9R, the swivel base plate 9 is provided with members for supporting mounted objects such as equipment to be mounted on the fuselage 2, thereby forming a swivel frame that serves as the skeleton of the fuselage 2. As shown in FIG. The horizontal periphery of the swivel frame is covered with a swivel cover.

A weight 10 is provided at the rear portion of the body 2 . The weight 10 is arranged at the rear part of the body 2 and attached to the turning base plate 9 at the lower part.
As shown in FIG. 2 , a fuel tank T1 and a hydraulic oil tank T2 arranged side by side along the width direction K2 of the aircraft body 2 are mounted on the rear portion of the aircraft body 2 . The fuel tank T1 is a tank that stores fuel for the prime mover E1. The hydraulic oil tank T2 is a tank that stores hydraulic oil.

As shown in FIG. 2, a turning motor MT is arranged at the front part of the turning board 9 (machine body 2) and at the center part in the machine body width direction K2. swivel driven. The turning motor MT is a hydraulic motor (hydraulic actuator). A swivel joint (hydraulic device) S1 is provided at the pivot axis X1 position. The swivel joint S1 is a hydraulic device that circulates hydraulic oil, and is a rotary joint that circulates hydraulic oil between the hydraulic device on the body 2 side and the hydraulic device on the travel device 3 side. A turning motor MT is arranged in front of the swivel joint S1. A control valve (hydraulic device) CV is arranged behind the swivel joint S1. The control valve CV is a sectional type composite control valve (hydraulic device) having a plurality of vertically stacked control valves (valves). Below the cabin 5, a control device U1 is provided.

Further, in the cabin 5, a control device 1B for controlling the working machine 1 is provided. The control device 1B is installed in front of the driver's seat 6. As shown in FIG. The driver's seat 6 and the operating device 1B constitute an operating section 1C.
As shown in FIG. 2, the fuselage 2 has a support bracket 13 at the front portion slightly rightward of the center in the fuselage width direction K2. The support bracket 13 is fixed to the front portions of the vertical ribs 9L and 9R and protrudes forward from the body 2 .

As shown in FIGS. 1 and 2, the front portion of the support bracket 13 (the portion protruding from the fuselage 2) has a swing bracket 14 around a vertical axis (an axis extending vertically) via a swing axis 14A. It is mounted swingably. Therefore, the swing bracket 14 is rotatable in the body width direction K2 (horizontally about the swing shaft 14A).
As shown in FIG. 1, at least a portion of the swing bracket 14 overlaps the center line Y1 in front of the pivot axis X1 and when the boom 15, which will be described later, faces the front of the aircraft (forward). placed in position. A center line Y1 is positioned between (substantially at the center) the right side surface of the cabin 5 and a longitudinal line Y2 passing through the axis (swing axis) X2 of the swing shaft 14A.

As shown in FIG. 1, the work device 4 is rotatably supported by the swing bracket 14 (body 2) about the swing axis X2. The working device 4 has a boom 15 , an arm 16 and a working tool (bucket) 17 . A base of the boom 15 is pivotally supported on an upper portion of the swing bracket 14 via a pivot. Specifically, the base of the boom 15 is pivotally attached to the upper part of the swing bracket 14 so as to be rotatable about the horizontal axis (the axis extending in the width direction K2 of the machine body) when the boom 15 faces the front of the machine body. there is This allows the boom 15 to swing vertically. In addition, the boom 15 is bent so that the central portion in the longitudinal direction is convex rearward at the highest position shown in FIG.

The arm 16 is pivotally supported on the tip side of the boom 15 via a pivot. Specifically, the arm 16 is pivotally attached to the boom 15 so as to be rotatable about the horizontal axis when the boom 15 faces the front of the machine body. This allows the arm 16 to swing in the front-rear direction K1 or in the vertical direction. In addition, the arm 16 can swing in a direction (cloud direction) and a direction away from the boom 15 (dump direction).

The work tool 17 is pivotally supported on the distal end side of the arm 16 via a pivot. Specifically, the work tool 17 is pivotally attached to the arm 16 so as to be rotatable about the horizontal axis when the boom 15 faces the front of the machine body. As a result, the work implement 17 can swing toward the arm 16 (crowding direction) and away from the arm 16 (dumping direction). A bucket as the work tool 17 is provided on the arm 16 so as to be able to perform scooping and dumping operations. The scooping operation is an operation for swinging the work implement 17 in a direction to approach the boom 15, and is an operation for scooping up earth and sand, for example. A dumping operation is an operation for swinging the work tool 17 in a direction away from the boom 15, and is an operation for dropping (discharging) scooped earth and sand, for example.

Instead of the bucket, the work tool 17 may be a work tool (attachment) such as a pallet fork or a mania fork, or a hydraulic actuator such as a grapple, a hydraulic crusher, an angle bloom, an earth auger, a snow blower, a sweeper, a mower, or a hydraulic breaker. It is possible to attach a work tool (hydraulic attachment) having
The swing bracket 14 is swingable by extension and contraction of a swing cylinder C2 provided inside the body 2 . The boom 15 is swingable by extension and contraction of the boom cylinder C3. The arm 16 can swing by extension and contraction of the arm cylinder C4. The work implement 17 is swingable by extension and contraction of a work implement cylinder (bucket cylinder) C5. The swing cylinder C2, the boom cylinder C3, the arm cylinder C4, and the work implement cylinder C5 are configured by hydraulic cylinders (hydraulic actuators).

Next, a hydraulic system for operating various hydraulic actuators ML, MR, MT, C1 to C6 provided in the work machine 1 will be described with reference to FIGS. 3 to 7. FIG.
The hydraulic system has a control valve CV, a pressure oil supply unit 18, and a flow controller 19, as shown in FIG.
The control valve CV includes control valves V1 to V10 for controlling various hydraulic actuators ML, MR, MT and C1 to C6, an inlet block B2 for taking in pressure oil, and a pair of outlet blocks B1 and B3 for discharging oil in one direction. It is arranged and aggregated.

As shown in FIG. 3, in this embodiment, the control valves CV include a first outlet block B1, a work implement control valve V1 that controls a work implement cylinder C5, a boom control valve V2 that controls a boom cylinder C3, a dozer cylinder C1, and a dozer cylinder C1. , a second travel control valve V4 that controls the travel motor MR of the second travel device 3R, an inlet block B2, and a first travel control that controls the travel motor ML of the first travel device 3L. A valve V5, a second dozer control valve V6 that controls the dozer cylinder C1, an arm control valve V7 that controls the arm cylinder C4, a swing control valve V8 that controls the swing motor MT, a swing control valve V9 that controls the swing cylinder C2, When a hydraulic attachment is attached as the work tool 17, the SP control valve V10 for controlling the hydraulic actuator C6 mounted on the hydraulic attachment and the second outlet block B3 are arranged in order (arranged from the right in FIG. 3). These are interconnected together with .

As shown in FIGS. 4 to 7, each of the control valves V1 to V10 includes direction switching valves DV1 to DV10 and a pressure compensation valve (compensator valve) V11 in a valve body. The direction switching valves DV1 to DV10 are valves for switching the direction of hydraulic fluid to the hydraulic actuators ML, MR, MT and C1 to C6 to be controlled. The pressure compensating valve V11 is provided on the downstream side of the pressure oil supply to the directional control valves DV1 to DV10 and on the upstream side of the pressure oil supply to the hydraulic actuators ML, MR, MT, C1 to C6 to be controlled. Pressure compensating valve V11 functions as a load regulator between hydraulic actuators ML, MR, MT and C1-C6 when using a plurality of control valves V1-V10.

A first relief valve V12 and a first unload valve V13 are incorporated in the first outlet block B1, and an independent travel valve V14 is incorporated in the inlet block B2. The first relief valve V12 is a main relief valve that regulates the pressure of hydraulic oil discharged from a first pressure oil discharge port P1, which will be described later.
The independent travel valve V14 is composed of a direct-acting spool type switching valve and a pilot-operated switching valve that is switched by pilot pressure.

A second relief valve V15 and a second unload valve V16 are incorporated in the second outlet block B3. The second relief valve V15 is a main relief valve that regulates the pressure of hydraulic oil discharged from a second pressure oil discharge port P2, which will be described later.
Each of the direction switching valves DV1 to DV10 is composed of a direct acting spool type switching valve. Each of the directional switching valves DV1 to DV10 is a control valve electrically controlled by the control device U1. Specifically, each of the directional switching valves DV1 to DV10 employs, for example, a pilot type solenoid valve. A pilot solenoid valve is a valve that controls the flow of hydraulic fluid by moving a spool with pilot pressure controlled by a solenoid.

As shown in FIG. 8, the solenoids of the direction switching valves DV1 to DV10 are connected to the control device U1, and the direction switching valves DV1 to DV10 are controlled by pilot pressure corresponding to command signals (current values) transmitted from the control device U1. The valves DV1 to DV10 are switched. Further, an operating member 41 (first operating tool 41A to seventh operating tool 41G) for operating the directional switching valves DV1 to DV10 is connected to the control device U1. The control device U1 transmits a current value corresponding to the amount of operation of the operation member 41 to the solenoids of the direction switching valves DV1 to DV10 to be operated. The first operating tool 41A, the second operating tool 41B, the third operating tool 41C, and the seventh operating tool 41G are provided, for example, in the operating device 1B, and are handles and levers that are gripped and operated by an operator seated in the driver's seat 6. Consists of The fourth operating tool 41D, the fifth operating tool 41E, and the sixth operating tool 41F are, for example, provided on the floor in front of the driver's seat 6 and configured by pedals operated by the operator's stepping operation.

The first operation tool 41A can operate two operation targets provided on the working machine 1. For example, the first operation tool 41A can operate the direction switching valve DV8 (capable of rotating the machine body 2) and operating the direction switching valve DV7. It is possible (the arm 16 can be swung). The first operation tool 41A also has a sensor 42 (first sensor 42A) that detects an operation direction and an operation amount. The first sensor 42A is connected to the control device U1. The controller U1 controls the swing control valve V8 and the arm control valve V7 based on the detection signal from the first sensor 42A.

The second operation tool 41B is also capable of operating two operation targets provided on the working machine 1, and is capable of operating, for example, the direction switching valve DV2 (capable of swinging the boom 15) and operating the direction switching valve DV1. It is operable (the work tool 17 can be operated to swing). The second operation tool 41B also has a sensor (operation detection unit) 42 (second sensor 42B) that detects the operation direction and the amount of operation. Although the configuration of the second sensor 42B is not particularly limited, for example, a potentiometer or the like can be used. The second sensor 42B is connected to the control device U1. The controller U1 controls the boom control valve V2 and the work implement control valve V1 based on the detection signal from the second sensor 42B.

The third operating tool 41C can operate the direction switching valve DV3 and the direction switching valve DV6 (can operate the dozer device 7). The third operation tool 41C also has a sensor 42 (third sensor 42C) that detects the operation direction and the amount of operation. The third sensor 42C is connected to the controller U1. The controller U1 controls the first dozer control valve V3 and the second dozer control valve V6 based on the detection signal from the third sensor 42C.

The fourth operation tool 41D can operate the direction switching valve DV9 (operate the swing bracket 14). Further, the fourth operation tool 41D has a sensor 42 (fourth sensor 42D) that detects the operation direction and the amount of operation. The fourth sensor 42D is connected to the controller U1. The controller U1 controls the swing control valve V9 based on the detection signal from the fourth sensor 42D.

The fifth operating tool 41E can operate the direction switching valve DV5 (can operate the first travel device 3L). In addition, the fifth operation tool 41E has a sensor 42 (fifth sensor 42E) that detects the operation direction and the amount of operation. The fifth sensor 42E is connected to the controller U1. The controller U1 controls the first travel control valve V5 based on the detection signal from the fifth sensor 42E.

The sixth operating tool 41F can operate the direction switching valve DV4 (can operate the second travel device 3R). Moreover, the sixth operation tool 41F has a sensor 42 (sixth sensor 42F) that detects the operation direction and the amount of operation. The sixth sensor 42F is connected to the control device U1. The controller U1 controls the second travel control valve V4 based on the detection signal from the sixth sensor 42F.

The seventh operation tool 41G can operate the direction switching valve DV10 (operate a hydraulic attachment as a working tool). The seventh operation tool 41G also has a sensor 42 (seventh sensor 42G) that detects the operation direction and the amount of operation. The seventh sensor 42G is connected to the controller U1. The controller U1 controls the SP control valve V4 based on the detection signal from the seventh sensor 42G.

The first sensor 42A to the seventh sensor 42G are composed of, for example, position sensors.
The spools of the directional switching valves DV1 to DV10 are moved in proportion to the amount of operation of the operating members 41 that operate the directional switching valves DV1 to DV10, and are proportional to the amounts by which the directional switching valves DV1 to DV10 are moved. is supplied to the hydraulic actuators ML, MR, MT, C1 to C6 to be controlled, and the operating speed of the operation target (control target) is proportional to the operation amount of each operation member 41 is considered to be variable.

Hydraulic pumps as pressure oil supply sources in this hydraulic system include a first pump 21 for supplying hydraulic oil for operating the hydraulic actuators ML, MR, MT, C1 to C6, and signal pressure oil such as pilot pressure and detection signals. is equipped with a second pump 22 for the supply of
The first pump 21 and the second pump 22 are provided in the pressure oil supply unit 18 and driven by the prime mover E1.

In this embodiment, the first pump 21 is composed of a swash plate type variable displacement axial pump having the function of an equal flow rate double pump that discharges an equal amount of hydraulic oil from two independent pressure oil discharge ports P1 and P2. ing. Specifically, the first pump 21 employs a split-flow hydraulic pump having a mechanism for alternately discharging working oil from one piston/cylinder barrel kit to discharge grooves formed inside and outside the valve plate.

One pressure oil discharge port discharged from the first pump 21 is called a first pressure oil discharge port P1, and the other pressure oil discharge port is called a second pressure oil discharge port P2.
In this embodiment, the pressure oil discharge ports discharged from the hydraulic pumps having two pump functions are the first and second pressure oil discharge ports P1 and P2. The pressure oil discharge port of one hydraulic pump may be the first pressure oil discharge port, and the pressure oil discharge port of the other hydraulic pump may be the second pressure oil discharge port.

The pressure oil supply unit 18 is also equipped with a pressing piston 23 that presses the swash plate of the first pump 21 and a flow rate compensating piston 24 that controls the swash plate of the first pump 21 .
The first pump 21 is constructed such that the self-pressure of the first pump 21 presses the swash plate in the direction of increasing the pump flow rate via the pressing piston 23, and the pressing force of the pressing piston 23 is counteracted. By controlling the pressure acting on the flow compensating piston 24, the discharge flow of the first pump 21 is controlled.

Therefore, when the pressure acting on the flow rate compensating piston 24 is released, the first pump 21 discharges the maximum flow rate with the swash plate angle at MAX.
The flow rate control unit 19 performs swash plate control of the first pump 21. The swash plate control of the first pump 21 is performed by controlling the pressure acting on the flow rate compensating piston 24. This is done by controlling the flow rate compensating valve V17.

In addition, the pressure oil supply unit 18 is provided with a spring 25 and a spool 26 for pump horsepower (torque) control of the first pump 21, and the discharge pressure of the first pump 21 is set in advance. Then, the first pump 21 is configured to limit the horsepower (torque) absorbed from the prime mover E1.
The second pump 22 is composed of a constant displacement gear pump, and the discharge oil of the second pump 22 is discharged from the third pressure oil discharge port P3.

The first pressure oil discharge port P1 is connected to the inlet block B2 via the first discharge passage a, and the second pressure oil discharge port P2 is connected to the inlet block B2 via the second discharge passage b.
The first discharge passage a is connected to a first pressure oil supply passage d. The first pressure oil supply passage d extends from the inlet block B2 to the valve body of the second travel control valve V4→the valve of the first dozer control valve V3. It is formed so as to reach the first outlet block B1 via the body→the valve body of the boom control valve V2→the valve body of the work tool control valve V1, and is branched at the first outlet block B1 (at the end of the flow path). are connected to the first relief valve V12 and the first unload valve V13.

From the first pressure oil supply path d, a pressure oil branch path to each direction switching valve DV4, DV3, DV2, DV1 of the second travel control valve V4, the first dozer control valve V3, the boom control valve V2, and the work tool control valve V1. Hydraulic oil can be supplied via f.
The first relief valve V12 and the first unload valve V13 are connected to the drain oil passage g. The drain oil passage g runs from the first outlet block B1 to the work implement control valve V1 valve body→boom control valve V2 valve body→dozer first control valve V3 valve body→second travel control valve V4 valve body→ Inlet block B2→valve body of first travel control valve V5→valve body of second dozer control valve V6→valve body of arm control valve V7→valve body of swing control valve V8→valve body of swing control valve V9→SP It is formed to reach the second outlet block B3 through the valve body of the control valve V10. Hydraulic oil flowing through the drain oil passage g is discharged from the second outlet block B3 to the hydraulic oil tank T2.

The second discharge passage b is connected to the second pressure oil supply passage e. The second pressure oil supply path e is from the inlet block B2 to the valve body of the first travel control valve V5→the valve body of the second dozer control valve V6→the valve body of the arm control valve V7→the valve body of the turning control valve V8→swing. It is formed so as to reach the second outlet block B3 via the valve body of the control valve V9→the valve body of the SP control valve V10, and is branched at the second outlet block B3 (at the end of the flow path) to form the second outlet block B3. It is connected to the relief valve V15 and the second unload valve V16.

Direction switching valves DV5 of a first travel control valve V5, a second dozer control valve V6, an arm control valve V7, a swing control valve V8, a swing control valve V9, and an SP control valve V10 are connected from the second pressure oil supply passage e. Hydraulic oil can be supplied to DV6, DV7, DV8, DV9, and DV10 via a pressure oil branch passage h.
The hydraulic fluid supplied to each control valve V1-V10 is supplied to and discharged from each hydraulic actuator ML, MR, MT, C1-C6. That is, the hydraulic system has a hydraulic circuit for supplying and discharging working oil to each of the hydraulic actuators ML, MR, MT, C1-C6.

The second relief valve V15 and the second unload valve V16 are connected to the drain oil passage g.
The first pressure oil supply path d and the second pressure oil supply path e are connected to each other via a communication path j that traverses the independent travel valve V14 in the inlet block B2.
The independent travel valve V14 is switchable between an independent position 27 that blocks the flow of pressure oil through the communication path j and a merge position 28 that permits the flow of pressure oil through the communication path j.

When the independent travel valve V14 is switched to the independent position 27, the hydraulic oil from the first pressure oil discharge port P1 is applied to the direction switching valves DV4 and DV3 of the second travel control valve V4 and the first dozer control valve V3. Hydraulic oil from the second pressure oil discharge port P2 can be supplied to the directional switching valves DV5 and DV6 of the first travel control valve V5 and the second dozer control valve V6. The hydraulic oil from the oil discharge port P1 is not supplied to the first travel control valve V5 and the second dozer control valve V6, and the hydraulic oil from the second pressure oil discharge port P2 is supplied to the second travel control valves V4 and V6. It is not supplied to the dozer first control valve V3.

Further, when the independent travel valve V14 is switched to the merging position 28, the hydraulic fluid from the first pressure oil discharge port P1 and the hydraulic fluid from the second pressure oil discharge port P2 are merged to operate the control valves V1 to V10. It can be supplied to the directional switching valves DV1 to DV10.
The third pressure oil discharge port P3 is connected to the inlet block B2 via a third discharge passage m, and the third discharge passage m is branched into a first branched oil passage m1 and a second branched oil passage m2. connected to the inlet block B2.

The first branch oil passage m1 is connected to the pressure receiving portion 14a on one side of the independent travel valve V14 via the first signal oil passage n1, and the second branch oil passage m2 is connected to the independent travel valve via the second signal oil passage n2. It is connected to the pressure receiving portion 14b on the other side of V14.
A first detection oil passage r1 is connected to the first signal oil passage n1, and a second detection oil passage r2 is connected to the second signal oil passage n2.

The first detection oil passage r1 is arranged from the first signal oil passage n1 to the direction switching valve DV6 of the second dozer control valve V6→the direction switching valve DV5 of the first travel control valve V5→the direction switching of the second travel control valve V4. The valve DV4 is connected to the drain oil passage g via the directional switching valve DV3 of the first dozer control valve V3.
The second detection oil passage r2 is arranged from the second signal oil passage n2 to the direction switching valve DV10 of the SP control valve V10→the direction switching valve DV9 of the swing control valve V9→the direction switching valve DV8 of the swing control valve V8→the arm control valve V7. directional switching valve DV7→direction switching valve DV6 of second dozer control valve V6→direction switching valve DV5 of first travel control valve V5→direction switching valve DV4 of second travel control valve V4→first dozer control valve V3 →the direction switching valve DV2 of the boom control valve V2→the direction switching valve DV1 of the work tool control valve V1 to the drain oil passage g.

The independent travel valve V14 is held at the merging position 28 by spring force when the directional switching valves DV1-DV10 of the respective control valves V1-V10 are neutral.
When any one of the direction switching valves DV of the second travel control valve V4, the first travel control valve V5, the first dozer control valve V3, and the second dozer control valve V6 is operated from the neutral position, The independent travel valve V14 is switched from the confluence position 28 to the independent position 27 when the pressure builds up in the first detection oil passage r1 and the first signal oil passage n1.

Therefore, when only traveling, when using the dozer device 7 while traveling, or when using only the dozer device 7, the hydraulic oil from the first pressure oil discharge port P1 is supplied to the second travel control valve V4 and the dozer device. Hydraulic oil supplied to the directional switching valves DV of the first control valve V3 for use and from the second pressure oil discharge port P2 is supplied to the directional switching valves DV of the first travel control valve V5 and the first control valve V3 for the dozer. supplied to

At this time, any of the SP control valve V10, the swing control valve V9, the swing control valve V8, the arm control valve V7, the boom control valve V2, and the directional switching valves DV10, DV9, DV8, DV7, DV2, and DV1 of the work implement control valve V1 When V is operated from the neutral position, pressure builds up in the second detection oil passage r2 and the second signal oil passage n2, and the travel independent valve V14 is switched from the independent position 27 to the merging position .

Further, when the directional switching valves DV1 to DV10 of the respective control valves V1 to V10 are neutral, the SP control valve V10, the swing control valve V9, the turning control valve V8, the arm control valve V7, the boom control valve V2, the work implement control valve The independent travel valve V14 is also at the merging position 28 when any one of the directional switching valves DV10, DV9, DV8, DV7, DV2 and DV1 of the valve V1 is operated from the neutral position.

Therefore, the boom 15, the arm 16, the work implement 17, the swing bracket 14, the machine body 2, and the dozer device 7 can be operated simultaneously during non-running or running.
This hydraulic system is also provided with an auto idling control system (AI system) that automatically operates the accelerator device of the prime mover E1.
This AI system includes an AI switch (pressure switch) 29 connected to the first branched oil passage m1 and the second branched oil passage m2 of the third discharge passage m via the sensing oil passage s and the shuttle valve V18, It has an electric actuator that controls the governor of E1 and a control device that controls this electric actuator, and the AI switch 29 is connected to the control device.

In this AI system, when the directional switching valves DV1 to DV10 of the control valves V1 to V10 are neutral, the first branch oil passage m1 and the second branch oil passage m2 are not pressurized. In this state, the governor is automatically controlled by an electric actuator or the like to decelerate to a preset idling position.

Further, when any one of the direction switching valves DV1 to DV10 of the control valves V1 to V10 is operated, the pressure rises in the first branch oil passage m1 or the second branch oil passage m2, and this pressure is applied to the AI switch. 29 to operate the AI switch 29 pressure-sensitively. Then, a command signal is sent from the control device to the electric actuator or the like, and the electric actuator or the like automatically controls the governor to accelerate up to the set accelerator position.

In addition, a load sensing system is employed in this hydraulic system.
The load sensing system of this embodiment includes a pressure compensating valve V11 provided in each of the control valves V1 to V10, a flow rate compensating piston 24 for controlling the swash plate of the first pump 21, and a flow rate It has a compensating valve V17, the first and second relief valves V12 and V15, and the first and second unload valves V13 and V16.

Further, the load sensing system of the present embodiment employs an after-orifice type load sensing system in which the pressure compensating valve V11 is arranged on the downstream side of the pressure oil supply to the direction switching valves DV1 to DV10.
In this load sensing system, when a plurality of the hydraulic actuators ML, MR, MT, C1-C6 provided in the working machine 1 are simultaneously operated, the load between the hydraulic actuators ML, MR, MT, C1-C6 The pressure compensating valve V11 functions as an adjustment for the direction switching valves DV1 to DV10. It is possible to flow (distribute) the flow rate according to the amount of operation of the spool.

In addition, the load sensing system controls the discharge amount of the first pump 21 according to the load pressure of each hydraulic actuator ML, MR, MT, C1 to C6 equipped in the work machine 1, and controls the discharge amount required for the load. By discharging hydraulic power from the first pump 21, it is possible to save power and improve operability.
The load sensing system of this embodiment will be described in more detail.

The load sensing system includes a PLS signal oil passage w that transmits the highest load pressure among the load pressures of the control valves V1 to V10 as a PLS signal pressure to the flow rate compensating valve V17, and a discharge pressure of the first pump 21 that is PPS. and a PPS signal oil passage x for transmitting the signal pressure to the flow rate compensating valve V17.
The PLS signal oil path w runs from the first outlet block B1 to the valve body of the work implement control valve V1→the valve body of the boom control valve V2→the valve body of the first dozer control valve V3→the valve body of the second travel control valve V4. The valve body of the first travel control valve V5→valve body of the second dozer control valve V6→valve body of the arm control valve V7→valve body of the swing control valve V8→swing across the independent travel valve V14. The PLS signal oil passage w extends from the valve body of the control valve V9 to the valve body of the SP control valve V10 to the second outlet block B3. It is connected.

The PLS signal oil passage w is connected from the second outlet block B3 to one side of the spool of the flow rate compensating valve V17, and the PPS signal pressure acts on one side of the spool of the flow rate compensating valve V17.
Further, the PLS signal oil passage w is connected to the first unload valve V13 and the drain oil passage g in the first outlet block B1, and is connected to the second unload valve V16 and the drain oil passage g in the second outlet block B3. ing.

When the independent travel valve V14 is at the merging position 28, a line w1 extending from the independent travel valve V14 to the first outlet block B1 and a line w2 extending from the independent travel valve V14 to the second outlet block B3 of the PLS signal oil passage w. , and when the independent travel valve V14 is switched from the merging position 28 to the independent position 27, the independent travel valve V14 shuts off the PLS signal oil passage w.

As a result, when the independent travel valve V14 is set to the independent position 27, the line w1 on the side to which hydraulic fluid is supplied from the first pressure oil discharge port P1 and the line w1 on the side to which the hydraulic oil is supplied from the second pressure oil discharge port P2 and a line w2 on the side to which pressure oil is supplied.
The PPS signal oil passage x extends from the independent travel valve V14 to the other side of the spool of the flow rate compensating valve V17. The PPS signal pressure (discharge pressure of the first pump 21) acts on the other side of the spool of the flow rate compensating valve V17, and the travel independent valve V14 is in the independent position. 27, the PPS signal oil passage x communicates with the drain oil passage g via the escape oil passage q, and the PPS signal pressure becomes zero.

A spring 30 and a differential pressure piston 31 for applying a control differential pressure to the flow compensation valve V17 are provided on one side of the spool of the flow compensation valve V17.
In the hydraulic system configured as described above, when the directional switching valves DV1 to DV10 of the respective control valves V1 to V10 are in the neutral position, the independent travel valve V14 is in the confluence position 28. At this time, the first pressure oil supply passage d is blocked by the first unload valve V13, and the flow path end side of the second pressure oil supply passage e is blocked by the second unload valve V16. Therefore, when the discharge pressure (PPS signal pressure) of the first pump 21 increases and the difference between the PPS signal pressure and the PLS signal pressure (which is zero at this time) becomes larger than the control differential pressure, the first pump 21 is controlled to decrease the discharge amount, and the first and second unload valves V16 are opened to drop the discharge oil from the first pump 21 into the hydraulic oil tank T2.

Therefore, in this state, the discharge pressure of the first pump 21 becomes the pressure set by the first and second unload valves V13 and V16, and the discharge flow rate of the first pump 21 becomes the minimum discharge amount.
Next, when any two or more of the boom cylinder C3, the arm cylinder C4, the work implement cylinder C5, the swing cylinder C2, the swing motor MT, and the hydraulic attachment are operated simultaneously, or when one or more of these and the left and right A case in which one or more of the travel motors ML, MR and the dozer cylinder C1 are simultaneously operated will be described.

In this case, the independent travel valve V14 is at the confluence position 28, and the maximum load pressure acting on the operated hydraulic actuators ML, MR, MT, C1-C6 becomes the PLS signal pressure, PPS signal pressure - PLS signal The discharge pressure (discharge flow rate) of the first pump 21 is automatically controlled so that the pressure becomes the control differential pressure (to maintain the difference between the PPS signal pressure and the PLS signal pressure at the set value).
That is, when the unload flow rate through the first and second unload valves V13 and V16 becomes zero, the discharge flow rate of the first pump 21 begins to increase, and the first The entire amount of the oil discharged from the pump 21 flows to the operated hydraulic actuators ML, MR, MT, C1-C6.

Further, the differential pressure across the spools of the directional switching valves DV1 to DV10 of the operated control valves V1 to V10 is made constant by the pressure compensating valve V11, and acts on the operated hydraulic actuators ML, MR, MT, C1 to C6. Regardless of the difference in the magnitude of the load, the discharge flow rate of the first pump 21 is diverted to each of the operated hydraulic actuators ML, MR, MT, C1-C6 by an amount corresponding to the operation amount.

When the required flow rate of the hydraulic actuators ML, MR, MT, C1 to C6 exceeds the maximum discharge flow rate of the first pump 21, the discharge oil of the first pump 21 is Proportional to C1-C6.
In the above case, simultaneous operations (compound operations) are possible in an efficient system.
Next, a case where earthwork is carried out by the dozer device 7 while traveling will be described.

In this case, the independent travel valve V14 is switched to the independent position 27, the independent travel valve V14 blocks the communication path j and the PLS signal oil path w, and the PPS signal oil path x is a relief oil path. It communicates with the drain oil passage g via q, and the PPS signal pressure becomes zero.
Therefore, hydraulic fluid from the first pressure oil discharge port P1 flows to the second travel control valve V4 and the first dozer control valve V3, but does not flow to the first travel control valve V5 and the second dozer control valve V6. The hydraulic oil from the second pressure oil discharge port P2 flows to the first travel control valve V5 and the second dozer control valve V6, but does not flow to the right travel control valve V4 and the first dozer control valve V3. Furthermore, since the PPS signal pressure is zero, the first pump 21 has a maximum swash plate angle and discharges the maximum flow rate.

In the hydraulic system of this embodiment, the first dozer control valve V3 and the second dozer control valve V6 evenly distribute the working oil from the first pressure oil supply path d and the second pressure oil supply path e. Since it is extracted and sent to the dozer cylinder C1, it is possible to ensure straight traveling of the work implement 1. - 特許庁
Further, when the work implement 1 is turned to one of the left and right sides, the pressure compensating valve V11 performs branch flow control. Since hydraulic oil exceeding the flow rate does not flow into the dozer cylinder C1, the hydraulic oil from the first pressure oil discharge port P1 is applied to the second travel control valve V4, and the hydraulic oil from the second pressure oil discharge port P2 is applied to the first travel control valve V4. Since the independent circuit configuration in which the control valve V5 is independently supplied to each of the control valves V5 can be maintained, and the hydraulic oil from the first and second pressure oil discharge ports P1 and P2 is evenly withdrawn, the left and right travel motors ML and MR can be supplied with the hydraulic oil. The pressure oil supply flow rate is ensured, and the turning performance can be ensured.

For example, when there is one dozer control valve for controlling the dozer cylinder, the dozer control valve is provided so that hydraulic oil is supplied from either the first pressure oil supply passage or the second pressure oil supply passage. However, in this case, if hydraulic oil is taken from the one pressure oil supply passage to the dozer cylinder, there arises a problem that the dozer cylinder travels obliquely when traveling straight ahead. Also, when turning, the pressure loss in the pressure oil supply system on the side where the dozer control valve is provided is large, and the movement becomes slow (specifically, the pressure oil supply system from the first pressure oil discharge port P1 When a dozer control valve is provided in the dozer, when the dozer device 7 is operated and the dozer device 7 is operated and the left turn is performed, the dozer device 7 is operated. Become).

Further, the dozer cylinder may be controlled by a single dozer control valve, and the working oil may be equally supplied to the dozer control valve from both the first pressure oil supply passage and the second pressure oil supply passage. Conceivably, in this case, although it is possible to ensure straightness, the turning performance is significantly degraded.
That is, at the time of turning, a large amount of hydraulic oil flows into the dozer cylinder from the pressure oil supply passage on the high pressure side, so that the turning performance is greatly deteriorated.

Further, in this case, it is not possible to determine whether the branch control is performed based on the signal of the hydraulic fluid from the first pressure oil discharge port P1 or the hydraulic fluid from the second pressure oil discharge port P2 due to the circuit configuration. , making it difficult to configure the load sensing system.
In the case of carrying out earthwork work with the dozer device 7 while traveling, when the independent travel valve V14 is in the independent position 27, the PLS signal oil passage w is also cut off, so that the oil from the first pressure oil discharge port P1 is blocked. Between the pressure oil supply system and the pressure oil supply system from the second pressure oil discharge port P2, there is no interference of the load signal, and the hydraulic oil is supplied to the travel control valves V4 and V5 and the dozer control valves V3 and V6. The control of diverting and discharging surplus hydraulic fluid from the unload valves V13 and V16 to the hydraulic fluid tank T2 is controlled by the pressure oil supply system from the first pressure oil discharge port P1 and the pressure from the second pressure oil discharge port P2. Each circuit of the oil supply system can be independently performed, and the function of the pressure compensating valve V11 can be ensured.

Also, when only the traveling body 1A or only the dozer device 7 is driven, the independent travel valve V14 is switched to the independent position 27, and the independent travel valve V14 is operated in the same manner as in the case where the dozer device 7 is used to perform earthwork while traveling. , the communication passage j and the PLS signal oil passage w are cut off, and the PPS signal oil passage x communicates with the drain oil passage g via the escape oil passage, and the PPS signal pressure becomes zero.

Further, since the travel control valves V4 and V5 are arranged on the most upstream side of the pressure oil supply system from the pressure oil discharge ports P1 and P2 of the first pump 21, the first pump 21 and the travel motors ML and MR are arranged. It is possible to reduce the pressure loss (pressure loss) in the hydraulic pipeline leading to.
In the hydraulic system having the above configuration, the first pump 21 is a split-flow type hydraulic pump, and the discharge flow rate from the first pressure oil discharge port P1 and the second pressure oil discharge port P2 Therefore, when the first pressure oil supply passage d and the second pressure oil supply passage e are made independent (when they are not merged), the discharge flow rate of the first pump 21 However, two hydraulic pumps are provided, and the discharge port of one of the two hydraulic pumps is the first pressure oil discharge port P1, and the discharge port of the other hydraulic pump is the first pressure oil discharge port P1. When the port is the second pressure oil discharge port P2, each hydraulic pump is configured to be independently controlled to discharge only the required flow rate even when the travel independent valve V14 is at the independent position 27 (in this case However, the two hydraulic pumps may be controlled to discharge the maximum flow rate at the same time when they merge).

It is also conceivable to configure the independent travel valve V14 to be in the confluence position 28 when only the dozer device 7 is operated. in the independent position 27, a third detection oil passage must be provided for detecting the operation of the direction switching valves DV3 and DV6 of the dozer control valves V3 and V6. Although the configuration is complicated, in this embodiment, it is configured to detect the operation of the travel control valves V4, V5 and/or the dozer control valves V3, V6 through the first detection oil passage r1. , the circuit configuration of the detection circuit can be simplified.

In the hydraulic system of this embodiment, the control valves V4 and V5 for travel and the control valves V3 and V6 for dozers are arranged side by side, and one travel control valve V4 and one dozer control valve Since V3, the other travel control valve V5 and the other dozer control valve V6 are arranged with the travel independent valve V14 interposed therebetween, the travel control valves V4, V5 and/or the dozer control valves V3, V6 It is possible to simplify the circuit configuration of the detection circuit that detects that the

The arrangement of the control valves V1 to V10 and the inlet block B2 is not limited to the arrangement shown in the drawing. , one traveling control valves V4, V5, one dozer control valves V3, V6, and one outlet block B1, B3 are provided. The arrangement of the other control valves V1, V2, V7-10 is not particularly limited as long as the other dozer control valves V3, V6 and the other outlet blocks B1, B3 are provided.

Also, the order in which the control valves V1 to V10 are arranged is not limited.
As shown in FIG. 4, the first relief valve V12 and the second relief valve V15 are composed of electromagnetic variable relief valves. The first relief valve V12 and the second relief valve V15 (variable relief valve) variably regulate the pressure of hydraulic fluid discharged from the first pump 21 (pump). Hereinafter, the relief set pressure, which is the set pressure defined (set) by the first relief valve V12 and the second relief valve V15, is referred to as main relief pressure.

As shown in FIG. 8, the solenoid V12a of the first relief valve V12 and the solenoid V15a of the second relief valve V15 are connected to the control device U1. That is, the first relief valve V12 and the second relief valve V15 are controlled by the control device U1.
As shown in FIG. 9, the work implement 1 has a plurality of modes for changing the main relief pressure. In this embodiment, the multiple modes are a first mode (hard mode), a second mode (normal mode), and a third mode (soft mode). For example, the hard mode is for standard work, the normal mode is for light work, and the soft mode is for leveling work.

As shown in FIG. 8, a mode changeover switch 43 is connected to the controller U1. The control device U1 also has a mode switching unit Ua for switching modes. The mode switching unit Ua switches the mode to hard mode, normal mode or soft mode by operating the mode switching switch 43 .
FIG. 9 is a table showing set values of the main relief pressure for each mode, and FIG. 10 is a graph showing changes in the main relief pressure with the main relief pressure on the vertical axis and the time on the horizontal axis. . The set value of the main relief pressure shown in FIG. 9 is an example, and can be changed in various ways without limitation.

In the following description, the current value corresponding to the amount of operation of the operating member 41, which is transmitted from the control device U1 to the solenoids of the direction switching valves DV1 to DV10, is referred to as the command current value. Further, when a plurality of hydraulic actuators ML, MR, MT, C1-C6 are operated, among the pilot pressures at the directional switching valves DV1-DV10 corresponding to the operated hydraulic actuators ML, MR, MT, C1-C6 The highest pilot pressure is called the maximum pilot pressure. When only one hydraulic actuator ML, MR, MT, C1-C6 is operated, the pilot pressure at the direction switching valves DV1-DV10 corresponding to the operated hydraulic actuator ML, MR, MT, C1-C6 is Maximum pilot pressure.

As shown in FIG. 8, the controller U1 has a relief controller Ub. The relief control unit Ub changes the main relief pressure (relief set pressure) to a plurality of set values according to the amount of operation of the operation member 41 . Specifically, the relief control unit Ub gradually increases the set value of the relief set pressure according to an increase in the amount of operation of the operation member 41 .
The control of the relief set pressure by the relief control unit Ub will be described in more detail below with reference to FIGS. 9 and 10. FIG.

As shown in FIG. 9, each mode has multiple set values. The multiple setting values include a first setting value P_A , a second setting value P_B and a third setting value P_C . The first set value P_A is the set value of the relief set pressure when the operation member 41 is not operated (when all the operation members 41 are not operated), and is 15.0 MPa. That is, the initial pressure of the main relief pressure is 15.0 MPa. Also, in the present embodiment, the first set value P_A is 15.0 MPa in all of the hard mode, normal mode, and soft mode.

The second set value P_B is a set value within a range in which the operation amount of the operation member 41 does not exceed a predetermined amount. More specifically, the second set value P_B is set so that the operating member 41 is within a range not exceeding a predetermined position (intermediate position) between the starting position (neutral position) and the terminal position (full operating position) of the operating range of the operating member 41. It is the set value when operated. The start position is the position where the operation member 41 is not operated (non-operated position), and the end position is the position where the operation member 41 is operated to the maximum. The second set value P_B is highest in the hard mode, lower in the normal mode than in the hard mode, and lower in the soft mode than in the normal mode. Specifically, the hard mode second set value P_B is 24.5 MPa, the normal mode second set value P_B is 20.6 MPa, and the soft mode second set value P_B is 15.0 MPa.

The third set value P_C is a set value when the operation amount of the operation member 41 exceeds a predetermined amount. Specifically, the third set value P_C is a set value when the operating member 41 is operated in a range exceeding a predetermined position between the starting end position and the terminal end position of the operating member 41 . The third set value P_C is highest in the hard mode, lower in the normal mode than in the hard mode, and lower in the soft mode than in the normal mode. Specifically, the hard mode third set value P_C is 27.4 MPa, the normal mode third set value P_C is 24.5 MPa, and the soft mode third set value P_C is 15.0 MPa. In this embodiment, in the soft mode, the first set value P_A , the second set value P_B , and the third set value P_C are all 15.0 MPa.

Next, referring to FIG. 10, changes in the main relief pressure according to the operation of the operating member 41 will be described. In this embodiment, there is a threshold value Ip that serves as a criterion for determining whether or not to change the main relief pressure to the third set value P_C . The threshold value Ip is a current value for operating each of the direction switching valves DV1 to DV10, and is a current value at a predetermined position (intermediate position) between the start position and the end position of the operating member 41. FIG. In the following description, the threshold value Ip is the pilot pressure for operating the directional control valves DV1 to DV10, and the threshold value Ip1, which is the pilot pressure corresponding to the threshold value Ip, will be described.

As shown in FIG. 10, when the mode is set to the hard mode or the normal mode, the maximum pilot pressure reaches the threshold Ip1 (the command current value is If the threshold value Ip) is not exceeded, the main relief pressure increases from the first set value P_A to the second set value P_B in proportion to the passage of time.
Further, when the maximum pilot pressure exceeds the threshold value Ip1 after the main relief pressure is changed from the first set value P_A to the second set value P_B , the main relief pressure is changed from the second set value P_B to the third set value P_B. Switch to value P_C . After that, when the maximum pilot pressure becomes less than the threshold value Ip1, the main relief pressure switches from the third set value P_C to the second set value P_B . After that, when all the operated operating members 41 are operated to the neutral position, the main relief pressure is switched from the second set value P_B to the first set value P_A .

Further, when the maximum pilot pressure exceeds the threshold value Ip1 (the command current value is the threshold value Ip) within the predetermined time t1 after operating any of the operation members 41, the main relief pressure is switched to the third set value P_C while increasing from the first set value P_A to the second set value P_B .
If the second set value P_B is set to the same value as the third set value P_C , and the threshold value Ip1 is set to be equal to or higher than the maximum pilot pressure at the directional switching valves DV1 to DV10, what kind of pilot pressure will be applied to the directional switching valves DV1 to DV10? Even if there is an input, setting of the maximum main relief pressure can be delayed for a certain period of time.

As shown in FIG. 9, the predetermined time t1 is 0.5 sec in the hard mode, and 1 sec in the normal mode.
When switching from the second setting value P_B to the third setting value P_C , when switching from the third setting value P_C to the second setting value P_B, when switching from the second setting value P_B to the first setting value P_A , is abruptly switched, but it may be changed with time. Also, the hard mode may be fixed at 27.4 MPa. That is, in the hard mode, the first set value P_A , the second set value P_B , and the third set value P_C may all be 27.4 MPa.

Also, when the soft mode is selected, the first set value P_A , the second set value P_B , and the third set value P_C are all 15.0 MPa.
When operating the operation member 41, by setting the main relief pressure to rise from a low level of 15.0 MPa, for example, when raising and lowering the boom 15, rotating the machine body 2, and driving the travel device 3. In such cases, when the operation member 41 is suddenly operated, the start of movement is mitigated (starting shock is moderated), and the shock upon starting can be suppressed.

Also, in hard mode, the third set value P_C of the main relief pressure is higher than in normal mode, so that high performance can be exhibited when an operation in which the main relief pressure becomes the maximum pressure is to be operated. can. Conversely, in the normal mode, the third set value P_C of the main relief pressure is lower than in the hard mode, so the load acting on the members constituting the operation target can be reduced, and the durability is improved. be able to.

In addition, in both the hard mode and normal mode, the second set value P_B of the main relief pressure is lower than the third set value P_C , so that in the intermediate operating range of the operating range of the operating member 41, the sensitivity peculiar to the load sensing system is reduced. Even if the operation member 41 is suddenly operated, the shock caused by the actuation motion of the operation target becomes mild.
In addition, there is a case where the working machine 1 is used for leveling work. For example, when leveling the ground with the work tool 17 while swinging the boom 15 or the arm 16, when leveling the ground with the work tool 17 while rotating the machine body 2, the work machine 1 is moved forward and backward and the traveling device 3 is used to level the ground. When leveling the ground, there is a case where the dozer device 7 is used to level the ground while moving the work machine 1 forward.

In the soft mode, the main relief pressure is lower than in the hard mode and the normal mode, so selecting the soft mode makes it easier to level the ground. In other words, since the load sensing system is for flow rate control, in the conventional case (when the main relief pressure is fixed and set to a high pressure), even if the operation member 41 is slightly operated, the operation target moves sensitively. In this embodiment, by selecting the soft mode, it is possible to reduce the sensitivity peculiar to the load sensing system, thereby making it easier to level the ground. In addition, since the power is not required more than necessary, it is easy to perform ground leveling work. Furthermore, it is possible to suppress the occurrence of problems in the movement of the operation target.

In the above embodiment, the operation of the operation member 41 is detected by the sensor 42, and the direction switching valves DV1 to DV10 are electrically controlled based on the detected information to operate the operation target. However, the operating member 41 may be configured by a pilot valve, and the directional switching valves DV1 to DV10 may be configured by pilot operated switching valves that are operated by the pilot pressure output from the operating member 41. FIG. A pilot valve is a control valve that outputs a pilot pressure corresponding to an operation amount and operates other valves with the output pilot pressure. A pilot-operated switching valve is a switching valve that is directly operated by a pilot pressure from a pilot valve.

The main relief pressure in the case where the operating member 41 is composed of a pilot valve and the directional switching valves DV1 to DV10 are composed of the operating member 41 pilot operated switching valve is as follows.
The AI switch 29 detects that the operating member 41 has been operated when the directional switching valves DV1 to DV10 are pilot-operated switching valves.

As shown in FIG. 12, the first set value P_A is 15.0 MPa. When the AI switch 29 detects that one or more of the operating members 41 are operated, the main relief pressure is changed from the first set value P_A to the second set value P_B after a predetermined time t1. Also in this case, as shown in FIG. 10, it increases from the first set value P_A to the second set value P_B in proportion to the passage of time. The predetermined time t1 is 0.5 sec in all of the hard mode, normal mode, and soft mode. In addition, in the hard mode, the second set value P_B = the third set value P_C = 27.4 MPa. In the normal mode, the second set value P_B =20.6 MPa and the third set value P_C =24.5 MPa. In the soft mode, the second set value P_B = the third set value P_C = 24.5 MPa.

In the normal mode, when changing from the second set value P_B to the third set value P_C , for example, by detecting the pressure output from the operating member (pilot valve) 41,
It is possible to cause the control device U1 to grasp the amount of operation of the operation member 41 . That is, when it is detected that the operation member 41 is being operated in the middle region of the operation range, the main relief pressure is maintained at the second set value P_B , and the operation member 41 is moved to the terminal position (full operation position) of the operation range. ), the main relief pressure is changed to the third set value P_C .

Note that the second set value P_B may be equal to the third set value P_C even in the normal mode. Further, when the directional switching valves DV1 to DV10 are pilot-operated switching valves, the pilot pressure output from the operating member 41 may be used to detect that the operating member (pilot valve) 41 has been operated.
Moreover, some of the directional switching valves DV1 to DV10 installed in the work machine 1 may be configured by pilot-type solenoid valves, and other portions may be configured by pilot-operated switching valves. For example, the directional switching valves DV1, DV2, DV7, and DV8 for operating the machine body 2 and the work device 4 are configured by pilot-type solenoid valves, and the directional switching valves DV3 to DV6, DV9, and DV10 for operating other operation targets are provided. , a pilot-operated switching valve. When a part of the directional switching valves DV1 to DV10 is composed of a pilot-type solenoid valve and the other part is composed of a pilot-operated switching valve, both the pilot-type solenoid valve and the pilot-operated switching valve are operated. In this case, priority is given to the set values shown in FIG. 12 for the main relief pressure.

Further, when a part of the directional switching valves DV1 to DV10 is composed of a pilot type solenoid valve and the other part is composed of a pilot operated switching valve, for example, the directional switching valve DV1 for operating the machine body 2 and the working device 4 , DV2, DV7, and DV8 are composed of pilot-type solenoid valves, direction switching valves DV4 and DV5 for operating the traveling device 3 are composed of pilot-operated switching valves, and when the soft mode is selected, the machine body 2 and the work When the device 4 is operated to level the ground, excessive force can be prevented, and when traveling, the necessary force can be applied.

As shown in FIG. 8, the working machine 1 has an oil temperature sensor 44 that detects the oil temperature of the working oil. The oil temperature sensor 44 is, for example, a sensor that detects the oil temperature of the hydraulic oil on the suction side of the first pump 21 (for example, the hydraulic oil in the hydraulic oil tank T2). Oil temperature sensor 44 is connected to control device U1. Control device U1 can acquire detection information of oil temperature sensor 44 . The control device U1 has an automatic switching unit Uc that automatically switches the mode according to the oil temperature of the hydraulic oil. The automatic switching unit Uc selects the normal mode or the soft mode regardless of the mode selection when the oil temperature is determined to be a low temperature lower than the first predetermined temperature (for example, -10°C or lower). automatically switch to hard mode. After that, when the oil temperature is determined to be normal temperature equal to or higher than the second predetermined temperature (for example, 0° C. or higher), the automatic switching unit Uc automatically returns to the original selected mode.

When the temperature is low, the operating pressure of the hydraulic fluid that actuates the hydraulic actuators ML, MR, MT, C1-C6 increases due to pressure loss in the hydraulic fluid flowing through the hydraulic hoses, and if the main relief pressure is low, the speed decreases. Therefore, if the normal mode or soft mode is selected, the speed of the operation target will decrease. In such a case, by automatically switching to the hard mode, even if the operator does not manually switch the mode to the hard mode, it is possible to automatically avoid the speed drop after startup at low temperature.

The work machine 1 includes an operation member 41, hydraulic actuators ML, MR, MT, and C1 to C6 that operate according to the amount of operation of the operation member 41, and an operation that operates the hydraulic actuators ML, MR, MT, and C1 to C6. A pump (first pump 21) that discharges oil, variable relief valves V12 and V15 that variably regulate the pressure of hydraulic oil discharged from the pump 21, and the pressure defined by the variable relief valves V12 and V15. and a relief control unit Ub that controls the relief set pressure, and the relief control unit Ub changes the relief set pressure according to the amount of operation of the operation member 41 .

With this configuration, it is possible to keep the relief set pressure low when the operation member 41 is not operated. As a result, when the operating member 41 is suddenly operated, the relief set pressure is raised from a low position, so that starting shocks of the hydraulic actuators ML, MR, MT, C1 to C6 can be suppressed.
Further, the relief control unit Ub sets the relief set pressure to one of a plurality of set values, and gradually increases the set value of the relief set pressure according to an increase in the amount of operation of the operating member 41 .

With this configuration as well, the relief set pressure when the operation member 41 is not operated can be kept low, and the activation shock of the hydraulic actuators ML, MR, MT, C1 to C6 can be suppressed.
Further, the relief control unit Ub sets the relief set pressure to the first set value P_A when the operation member 41 is not operated, and sets the relief set pressure to the first set value P_A at a predetermined time t1 after the operation member 41 is operated . is changed to a second set value P_B higher than the second set value P_B, and changed to a third set value P_C higher than the second set value P_B when the operation amount of the operation member 41 exceeds a predetermined amount.

According to this configuration, it is possible to set the force required for various operations according to the amount of operation of the operation member 41 .
Further, if the amount of operation of the operation member 41 exceeds a predetermined amount within a predetermined time t1 after the operation of the operation member 41, the relief control unit Ub changes the relief set pressure to the third set value P_C .

According to this configuration, responsiveness can be improved.
In addition, a plurality of modes having different set values of the relief set pressure are provided, and the plurality of modes have different set values of the maximum pressure of the relief set pressure.
According to this configuration, by switching the mode according to the type of work, it is possible to perform the work with a force corresponding to the type of work.

The plurality of modes are a first mode having the highest set value of the maximum relief set pressure, a second mode having a lower set value of the maximum relief set pressure than the first mode, and a mode having the highest set value of the relief set pressure. Including a third mode in which the set value of the high pressure is lower than that in the second mode, the relief set pressure when the operation member 41 is not operated in the first mode, the second mode, and the third mode is the same set value.
Also with this configuration, it is possible to work with a force corresponding to the type of work.

Also, an oil temperature sensor 44 for detecting the oil temperature of the hydraulic oil, and when the oil temperature is lower than the first predetermined temperature, switching to the mode with the highest set value of the relief set pressure among the plurality of modes. and an automatic switching unit Uc that returns to the original mode when the oil temperature becomes higher than a second predetermined temperature higher than the first predetermined temperature.
According to this configuration, even if the operator does not manually switch the mode, it is possible to automatically avoid a decrease in speed after startup at low temperatures.

The work machine 1 includes a plurality of hydraulic actuators ML, MR, MT, C1 to C6, and the pump 21 is configured as a variable displacement type. A load sensing system is provided to control the pump 21 so that the differential pressure obtained by subtracting the highest load pressure among C6 is constant.
As shown in FIGS. 5, 6 and 7, the control valves V1, V2, V6, V7 and V10 are provided with hydraulic actuators C1, C3-C6 to prevent overloads acting on the corresponding hydraulic actuators C1, C3-C6. An overload relief valve (port relief valve) V19 is incorporated that defines the maximum pressure (relief set pressure) acting on C1, C3-C6.

As shown in FIG. 6, an overload relief valve V19 communicating with a port C5a on the bottom side (cloud side) of the work implement cylinder C5 (work implement drive actuator) is an electromagnetic variable overload relief valve V19 capable of changing the relief set pressure. It is composed of a relief valve V19A.
The variable overload relief valve V19A is connected via a first connection oil passage 52 to a supply/discharge oil passage 51 connecting the work implement control valve V1 (actuator control valve) and the cloud-side port C5a of the work implement cylinder C5. ing. Also, the variable overload relief valve V19A is connected to the drain oil passage g via the second connection oil passage 53 .

As shown in FIG. 8, the solenoid V19a of the variable overload relief valve V19A is connected to the controller U1. That is, the controller U1 can control the variable overload relief valve V19A.
As shown in FIG. 8, the control device U1 has a turning detector Ud. The turning detection unit Ud detects that the turning control valve V8 (direction switching valve DV8) is being operated, that is, the machine body 2 is being turned. Specifically, when the first manipulating tool 41A is operated in the direction of operating the turning motor MT, the control device U1 detects an operation signal transmitted from the first manipulating tool 41A. It should be noted that the turning operation of the machine body 2 may be detected by a rotation sensor that detects the rotation of the machine body 2 or the rotation of the turning motor MT. In this case, by connecting the rotation sensor to the control device U1, it is possible to cause the control device U1 (turn detection unit Ud) to recognize that the body 2 has made a turning motion. Further, when the directional switching valve DV8 of the swing control valve V8 is composed of a pilot-operated switching valve, the pilot pressure applied to the pilot-operated switching valve is detected to detect that the machine body 2 is rotating. may

As shown in FIG. 8, a motion sensor (work implement motion detector) 54 is connected to the control device U1. The motion sensor 54 detects whether the work implement 17 is in motion. The motion sensor 54 is composed of a potentiometer that directly detects swinging of the work implement 17, a stroke sensor that detects the expansion and contraction state of the work implement cylinder C5, and the like.
Further, the control device U1 has a work motion detector Ue. The work motion detection unit Ue operates the work tool 17 with the second manipulating tool 41B (the operation member 41) and the motion sensor 54 detects that the work tool 17 is not moving. It is detected that the main relief valve V12 (V15) is in a relief state (high load working state). An example of a high-load work state is a state in which, when the work tool 17 is a bucket, the work tool 17 is operated in the crowd direction, and the work tool 17 grips a work (rock or the like) and remains stationary. At this time, the main relief pressure is controlled at, for example, 24.5 MPa.

As shown in FIG. 8, the controller U1 has an overload controller Ug. The overload control unit Ug reduces the relief set pressure of the variable overload relief valve V19A when the body 2 turns with the main relief valve V12 (V15) in the relief state. For example, if the maximum pressure at the cloud-side port C5a of the work implement cylinder C5 defined by the variable overload relief valve V19A is 29.4 MPa, it is reduced to 20.6 MPa, which is lower than the main relief pressure. This numerical value is an example and is not limited.

Conventionally, when the machine body 2 is rotated while the work implement cylinder C5 remains in relief, the work implement cylinder C5 is operated at the relief pressure and the turning motor MT is operated at the low pressure. Then, in the load sensing system, the pressure compensating valve V11 of the swing control valve V8 on the low pressure side creates a pseudo load to even out the load between the hydraulic actuators in order to properly divide the hydraulic fluid. That is, the load is made uniform by creating a pseudo load in accordance with the lightly loaded section and the heavily loaded section. In this case, pressure loss occurs at the place where the pseudo load is created, and the temperature of the hydraulic oil rises. As a result, the components (seal members) of the turning motor MT may deteriorate.

In such a case, that is, when the fuselage 2 swings with the variable overload relief valve V19A in the relieved state, the relief set pressure of the variable overload relief valve V19A is reduced to reduce the pressure compensation valve V11 of the swing control valve V8. Pseudo load (pseudo pressure loss) generated by is reduced. As a result, it is possible to suppress an increase in the oil temperature of the hydraulic oil due to the pseudo load. That is, it is possible to suppress an increase in the oil temperature of the hydraulic oil flowing to the turning motor MT. Also, energy saving can be achieved.

In the present embodiment, the case where the work tool 17 is a bucket has been described as an example, but the work tool 17 may be a work tool other than a bucket. For example, work implement 17 may be a grapple. When the work implement 17 is a grapple, the variable overload relief valve V19A is employed as the overload relief valve V19 of the SP control valve V10. That is, a hydraulic actuator (work tool drive actuator) C6 for opening and closing the gripper mounted on the grapple to grip or release the gripper is operated by the SP control valve V10. Therefore, of the two overload relief valves V19 of the SP control valve V10, the variable overload relief valve V19A is adopted as the overload relief valve V19 connected to the grip side port of the hydraulic actuator C6. That is, when the work implement 17 is a grapple, when the machine body 2 swings while gripping a work such as wood with the grapple, the relief set of the variable overload relief valve V19A connected to the grip side port of the hydraulic actuator C6 is Reduce pressure.

Further, in this embodiment, when the work tool 17 is operated by the second operation tool 41B and the operation sensor 54 detects that the work tool 17 is not operating, the relief set pressure of the variable overload relief valve V19A is set to is lowering. Therefore, even when the main relief valve V12 (V15) is in the relief state, the relief set pressure of the variable overload relief valve V19A is not lowered when the work implement 17 is operating. For example, as an excavation work, there is a revolving horizontal contact excavation work in which the machine body 2 is turned to press the work tool 17 against a wall or the like and the work tool 17 is rocked to excavate. If the relief set pressure of the variable overload relief valve V19A is lowered when performing this work, the force of the work tool 17 is reduced and the excavation force is reduced. Therefore, when performing such a swinging horizontal impact excavation work, the relief set pressure of the variable overload relief valve V19A is not lowered, so that the force of the work implement 17 is not lowered.

As shown in FIG. 8, the control device U1 has a stroke limiter Uh.
The stroke limiter Uh limits the stroke of the spool V1a of the work implement control valve V1 to a predetermined amount when the overload controller Ug reduces the relief set pressure of the variable overload relief valve V19A. In the case of the SP control valve V10, the spool V10a is limited to a predetermined amount. As a result, it is possible to reduce the flow rate of hydraulic oil that is wastefully drained, so that energy saving can be achieved.

That is, when a workpiece is gripped by the work implement 17 or the like, the operating member 41 is fully operated, and the entire amount of hydraulic oil flowing from the work implement control valve V1 toward the port C5a is applied to the variable overload relief valve V19A. drained to no avail. That is, when the workpiece is gripped by the work tool 17 or the like (the variable overload relief valve V19A is in the relief state), the relief set pressure of the variable overload relief valve V19A is lowered to reduce the force of the work tool 17. Since the flow rate of the hydraulic oil remains large even though the valve is on, the spool V10a is returned by a predetermined amount to reduce the excess flow rate of the hydraulic oil and save energy.

In the present embodiment, the work implement control valve V1 (direction switching valve DV1) controls the stroke of the spool V10a by pilot pressure. can be done That is, the stroke limiting unit Uh has a threshold value, and when the pilot pressure acting on the work implement control valve V1 (the solenoid of the direction switching valve DV1) is higher than the threshold value, the stroke of the spool V10a is reduced by reducing it to the threshold value. Restrict. The same applies to the SP control valve V10.

The work machine 1 includes a machine body 2, a turning motor MT for turning the machine body 2, a work tool 17 mounted on the machine body 2, and a work tool drive actuator (work tool cylinder C5) for driving the work tool 17. , a hydraulic actuator C6), a hydraulic circuit for supplying and discharging hydraulic oil to the turning motor MT and the work implement actuators C5 and C6, and relieving the hydraulic oil when the pressure of the hydraulic oil in the hydraulic circuit exceeds a set pressure. a main relief valve V12 (V15), a variable overload relief valve V19A that relieves the working oil when the pressure of the working oil in the work implement drive actuators C5 and C6 exceeds a predetermined level, and a variable overload relief valve V19A. and an overload control unit Ug that controls the variable overload relief valve V19A when the body 2 turns in a relief state in which the main relief valve V12 (V15) is relieved. Decrease the relief set pressure.

According to this configuration, when the machine body 2 turns while the main relief valve V12 (V15) is in relief, the relief set pressure of the variable overload relief valve V19A is reduced, so that the hydraulic oil flowing to the turning side is reduced. temperature rise can be suppressed.
Further, an operation detection unit (second sensor 42B) that detects the operation of an operation member (second operation tool 41B) that operates the work tool 17, and a work tool operation detection unit (operation sensor 54) that detects the operation of the work tool 17. ), and the overload control unit Ug sets the relief set of the variable overload relief valve V19A when the machine body 2 swings while the work implement 17 is operated by the operation member and the work implement 17 is not operating. Even if the pressure is reduced and the machine body turns, the relief set of the variable overload relief valve V19A is set when the operating member is not operating the work implement 17 and when the work implement 17 is in motion. Do not let the pressure drop.

According to this configuration, the relief set pressure of the variable overload relief valve V19A is not lowered when the work implement 17 is in operation, so that workability using the work implement 17 can be prevented from deteriorating.
Further, actuator control valves (work implement control valve V1 and SP control valve V10) that control the work implement drive actuators C5 and C6 are provided, and when the overload control unit Ug reduces the relief set pressure of the variable overload relief valve V19A, is provided with a stroke limiter Uh that limits the strokes of the spools V1a and V10a of the actuator control valves V1 and V10 to a predetermined amount. According to this configuration, the amount of hydraulic oil drained unnecessarily is reduced to save energy. can be achieved.

Further, the actuator control valves V1 and V10 are operated by the pilot pressure, and the stroke limiter Uh limits the stroke by reducing the pilot pressure acting on the actuator control valves V1 and V10 to the threshold when the pilot pressure is higher than the threshold. do.
According to this configuration, the stroke limiting portion Uh can be easily configured.
The work machine 1 also includes a turning motor MT for turning the machine body 2 and a plurality of hydraulic actuators ML, MR, MT, C1 to C6 including work implement drive actuators C5, C6, and a plurality of hydraulic actuators ML, MR, MT, A pump 21 for discharging hydraulic oil to be supplied to C1 to C6 and a differential pressure obtained by subtracting the highest load pressure among the plurality of hydraulic actuators ML, MR, MT, C1 to C6 from the discharge pressure of the pump 21 is made constant. and a load sensing system that controls the pump 21 as follows.

13 and 14 show another embodiment. FIG. 13 shows the boom control valve (first control valve) V2. FIG. 14 shows the swing control valve (second control valve) V8. Another embodiment will be described below with reference to FIGS. 13 and 14. FIG.
As described above, the load sensing system adjusts the pressure difference between the PPS signal pressure and the PLS signal pressure (PPS signal pressure - PLS signal pressure: first differential pressure) to a predetermined pressure (first differential pressure is constant), the angle of the swash plate of the first pump 21 is changed, and the discharge amount of the first pump 21 is adjusted.

As shown in FIG. 13, the boom control valve V2 has a directional switching valve DV2 and a pressure compensating valve V11 (V11A). The directional switching valve DV2 is capable of switching the direction of hydraulic fluid toward the boom cylinder (high-load hydraulic actuator) C3, for example, switching between a first position 61, a second position 62, and a third position (neutral position) 63. It is a three-position switching valve to replace.
When the directional switching valve DV2 is in the first position 61, the directional switching valve DV2 switches to the direction in which hydraulic fluid flows to the bottom side of the boom cylinder C3, and the hydraulic fluid returning from the rod side of the boom cylinder C3 (return oil) to the drain oil passage g (operating oil tank T2). Further, when the directional switching valve DV2 is in the second position 62, the directional switching valve DV2 directs hydraulic oil (return oil) returning from the bottom side of the boom cylinder C3 to the drain oil passage g (hydraulic oil tank T2). , and switches to the direction of flowing hydraulic oil to the rod side of the boom cylinder C3. When the directional switching valve DV2 is in the third position 63, the directional switching valve DV2 does not supply hydraulic fluid to the boom cylinder C3.

A pump port 64 of the direction switching valve DV2 is connected to a pressure oil branch passage f branched from the first pressure oil supply passage d. Hydraulic oil discharged from the first pump 21 is supplied to the direction switching valve DV2 through the pressure oil branch passage f. A connection oil passage 65 connects the direction switching valve DV2 and the pressure compensating valve V11A. The connection oil passage 65 includes a first connection oil passage 65a and a second connection oil passage 65b. The first connection oil passage 65a is an oil passage that connects the first output port 66 of the directional control valve DV2 and the introduction port 67 of the pressure compensating valve V11A. The second connection oil passage 65b is an oil passage that connects the pump port 64 of the direction switching valve DV2 and the first output port 66 of the direction switching valve DV2. The second connection oil passage 65b is formed in the direction switching valve DV2. A throttle (flow path throttle) 68 is provided in the second connection oil passage 65b.

A connection oil passage 69 connects the pressure compensating valve V11A and the boom cylinder C3. The connecting oil passages 69 include a first connecting oil passage 69a, a second connecting oil passage 69b, a third connecting oil passage 69c, and a fourth connecting oil passage 69d. The first connection oil passage 69a is an oil passage that connects the output port 70 of the pressure compensating valve V11A and the first input port 71 of the directional control valve DV2. The second connecting oil passage 69b is an oil passage that connects the output port 70 of the pressure compensating valve V11A and the second input port 72 of the direction switching valve DV2. The third connection oil passage 69c is an oil passage that connects the second output port 73 of the direction switching valve DV2 and the bottom side port of the boom cylinder C3. The fourth connection oil passage 69d is an oil passage that connects the third output port 74 of the directional control valve DV2 and the rod-side port of the boom cylinder C3. The output port 70 of the pressure compensating valve V11A and the load transmission line y are connected via a check valve 75. As shown in FIG.

The pressure compensating valve V11A is a valve that sets the differential pressure between the pressure of hydraulic fluid introduced into the pressure compensating valve V11A and the pressure of hydraulic fluid output from the pressure compensating valve V11A within a predetermined range (predetermined value). In other words, the pressure compensating valve V11A keeps the differential pressure across the spool of the directional control valve DV2 constant (the differential pressure between the pressure of the hydraulic fluid on the upstream side and the pressure of the hydraulic fluid on the downstream side), so that To divert hydraulic oil in an amount corresponding to an operation amount regardless of the magnitude of the load acting on the hydraulic actuator. Specifically, the pressure compensating valve V11A has a pressure receiving portion 76a that receives the pressure of the hydraulic fluid introduced into the introduction port 67 and a pressure receiving portion 76b that receives the pressure of the hydraulic fluid output from the output port 70. A connection oil passage 77 connects the introduction port 67 and the pressure receiving portion 76a. A connection oil passage 78 connects the output port 70 and the pressure receiving portion 76b.

Therefore, the pressure of the hydraulic fluid output from the direction switching valve DV2 toward the pressure compensating valve V11A acts on the pressure receiving portion 76a, and the pressure of the hydraulic fluid output from the output port 70 of the pressure compensating valve V11A acts on the pressure receiving portion 76b. do. The spool 98 of the pressure compensating valve V11A moves according to the pressure difference between the two hydraulic fluids, and the opening area of the pressure compensating valve V11A changes.
The configuration of the pressure compensating valve V11A of the boom control valve V2 and the connection structure between the pressure compensating valve V11A and the directional switching valve DV2 consist of the work implement control valve V1, the dozer first control valve V3, the second travel control valve V4, the 1 travel control valve V5, second dozer control valve V6, arm control valve V7, swing control valve V9, and SP control valve V10.

Now, in the hydraulic system, as described above, the discharge amount of the first pump 21 is controlled according to the maximum load pressure when the hydraulic actuators ML, MR, MT, and C1 to C6 are operated. It compensates for the pressure of hydraulic fluid supplied to the hydraulic actuators ML, MR, MT, C1-C6.
However, depending on the control valve, it is also necessary to give priority to the flow rate of hydraulic fluid supplied to the hydraulic actuators ML, MR, MT, C1-C6.

In this other embodiment, a work implement control valve V1, a boom control valve V2, a first dozer control valve V3, a second travel control valve V4, a first travel control valve V5, a second dozer control valve V6, and an arm control. The valve V7, the swing control valve V9, and the SP control valve V10 are control valves that compensate for the pressure of hydraulic fluid, and the swing control valve V8 is a control valve that can prioritize the flow rate of hydraulic fluid.

As shown in FIG. 14, the swing control valve V8 has a directional switching valve (low load side directional switching valve) DV8 and a flow rate priority valve V11B. The directional switching valve DV8 is capable of switching the direction of hydraulic fluid toward the turning motor (low-load hydraulic actuator) MT, and switches to, for example, a first position 81, a second position 82, and a third position (neutral position) 83. It is a three-position switching valve to replace. When the directional switching valve DV8 is in the first position 81, the directional switching valve DV8 switches to the direction in which the hydraulic oil flows to one side of the swing motor MT, and the hydraulic oil returned from the other side of the swing motor MT. (return oil) to the drain oil passage g (operating oil tank T2). When the directional switching valve DV8 is in the second position 82, the directional switching valve DV8 switches to the direction in which the hydraulic oil flows to the other side of the swing motor MT and returns from the one side of the swing motor MT. The direction is switched to discharge the hydraulic oil (return oil) to the drain oil passage g (the hydraulic oil tank T2). When the directional switching valve DV8 is in the third position 83, the directional switching valve DV8 does not supply hydraulic fluid to the swing motor MT.

The flow rate priority valve V11B is a valve that, by moving the spool 98, gives priority to the flow rate of hydraulic fluid that is output to the hydraulic actuator. The spool 98 of the flow priority valve V11B is movable between a first position 84a and a second position 84b. The first position 84a is a position for increasing the flow rate of the hydraulic oil output from the directional control valve DV8. The second position 84b is a position that reduces (reduces) the flow rate of the hydraulic oil that is output from the directional control valve DV8. That is, compared to the flow rate of hydraulic fluid at an intermediate position between the first position 84a and the second position 84b, the flow rate of the hydraulic fluid when the flow rate priority valve V11B is at the first position 84a is large, and the flow rate of the hydraulic fluid is high at the second position 84b. The flow rate of hydraulic oil in the case of is small.

The flow rate priority valve V11B has a pressing member 85, a first pressure receiving portion 86, and a second pressure receiving portion 87. The pressing member 85 is a member provided on the first position 84a side. The pressing member 85 presses the spool 98 of the flow rate priority valve V11B to the first position 84a, that is, to the open side. The pressing member 85 is composed of, for example, a spring. The force of the pressing member 85 that presses the spool 98 to the first position 84a, that is, the set pressure (second differential pressure) of the flow rate priority valve V11B when the spool 98 is in a full stroke (maximum area) is PPS signal pressure - PLS It is set to be equal to or less than the first differential pressure, which is the differential pressure with respect to the signal pressure. If the set pressure (set pressure by the pressing member 85) in the flow rate priority valve V11B exceeds the first differential pressure, the flow rate output from the flow rate priority valve V11B may become larger than in the single operation.

Although the pressing member 85 that presses the spool 98 toward the first position 84a is composed of a spring, the spool 98 may be pressed by the pressure of hydraulic oil (pressure of pilot oil). For example, the flow priority valve V11B is provided with a pressure receiving portion such as a control pin for pressing the spool 98, and the pilot pressure is applied to the pressure receiving portion. The pilot pressure applied to the pressure receiving portion may be the pressure of a remote control valve whose pilot pressure changes according to the operation member, or may be the pressure obtained by reducing the pressure of the remote control valve with a pressure reducing valve.

The first pressure receiving portion 86 is a portion that receives the pressure of hydraulic fluid output from the direction switching valve DV8. The second pressure receiving portion 87 is a portion that receives pressure of hydraulic oil discharged from the first pump 21 to the swing control valve V8. In other words, the second pressure-receiving portion 87 is a portion that receives hydraulic fluid on the upstream side of the spool 98 of the direction switching valve DV8.
A connection oil passage (second oil passage) 88 connects the flow rate priority valve V11B and the direction switching valve DV8. The connection oil passage (second oil passage) 88 includes a first connection oil passage (connection oil passage) 88a, a second connection oil passage (connection oil passage) 88b, and a third connection oil passage (connection oil passage) 88c. including. The first connection oil passage 88a is an oil passage that connects the first output port (output port) 66 of the direction switching valve DV8 and the introduction port 89 of the flow priority valve V11B. The second connection oil passage 88b is an oil passage that connects the pump port 64 of the direction switching valve DV8 and the first output port 66 of the direction switching valve DV8. The second connection oil passage 88b is formed in the directional switching valve DV8. A throttle (flow path throttle) 90 is provided in the second connection oil passage 88b. The third connecting oil passage 88 c is an oil passage that connects the introduction port 89 of the flow rate priority valve V<b>11</b>B and the first pressure receiving portion 86 .

It should be noted that the pressure loss due to the flow path restriction 90 on the first position 81 side and the pressure loss due to the flow path restriction 90 on the second position 82 side are set to the same numerical value.
A connecting oil passage (third oil passage) 92 connects the first pressure oil supply passage d and the second pressure receiving portion 87 of the flow rate priority valve V11B. Specifically, the connection oil passage (third oil passage) 92 is an oil passage that connects the pressure oil branch passage f of the first pressure oil supply passage d and the second pressure receiving portion 87 .

A connection oil passage 93 connects the flow rate priority valve V11B and the turning motor MT. The connection oil passages 93 include a first connection oil passage 93a, a second connection oil passage 93b, a third connection oil passage 93c, and a fourth connection oil passage 93d. The first connection oil passage 93a is an oil passage that connects the output port 91 of the flow rate priority valve V11B and the first input port 71 of the direction switching valve DV8. The second connection oil passage 93b is an oil passage that connects the output port 91 of the flow rate priority valve V11B and the second input port 72 of the direction switching valve DV8. The third connection oil passage 93c is an oil passage that connects the second output port 73 of the directional control valve DV8 and one side port of the turning motor MT. The fourth connection oil passage 93d is an oil passage that connects the third output port 74 of the directional control valve DV8 and the other side port of the turning motor MT. The output port 91 of the flow priority valve V11B and the load transmission line y are connected via a check valve 94. As shown in FIG.

Therefore, the spool 98 of the flow rate priority valve V11B receives the pressure of the hydraulic fluid received by the first pressure receiving portion 86 (the pressure of the hydraulic fluid output from the first output port 66 of the direction switching valve DV8) and the pressing member 85 to the first position. 84a is pressed. Further, the pressure of the hydraulic fluid received by the second pressure receiving portion 87 (the pressure of the hydraulic fluid on the upstream side of the spool of the directional control valve DV8) presses to the second position 84b.

According to the hydraulic system described above, during a combined operation in which the boom cylinder C3 and the swing motor MT are operated, for example, the load pressure when the boom cylinder C3 is actuated is 10 MPa, the load pressure when the swing motor MT is actuated is 3 MPa, and the flow rate is controlled. Assume that the set pressure of the portion 19 is 1.4 MPa. In this case, the maximum load pressure of hydraulic fluid is 10 MPa, and the pressure of hydraulic fluid discharged from the first pump 21 is 11.4 MPa. Here, assuming that the set pressure of the flow rate priority valve V11B is 1.0 MPa, the spool 98 of the flow rate priority valve V11B moves so that the set pressure is maintained at 1.0 MPa, and the opening area of the flow rate priority valve V11B changes. do. The flow rate output from the flow rate priority valve V11B is set constant. In other words, the flow rate priority valve V11B sets the differential pressure across the direction switching valve DV8 to 1.0 MPa (operates to generate a pressure loss of 1.0 MPa), and regardless of the load on the boom cylinder C3, the swing motor MT Hydraulic oil can be preferentially flowed.

Therefore, even with the work machine 1 having the pressure compensating valve V11, it is possible to secure the flow rate of the hydraulic oil output from the predetermined control valve, thereby reducing the change in the swing speed between the single operation and the combined operation. can do.
Even when the turning motor MT is operated alone (when other control valves are not operated), the flow rate output from the flow rate priority valve V11B can be set constant. That is, it is possible to preferentially flow hydraulic oil from the direction switching valve DV8 toward the turning motor MT.

However, since the flow rate priority valve V11B controls the spool 98 by the pressing member 85, for example, when the boom control valve V1 and swing control valve V8 are operated in combination, the flow rate priority is given by the operating pressure on the boom 15 side. It is conceivable that the spool 98 of the valve V11B may move slightly and the turning speed of the airframe 2 may change slightly. That is, since the operating pressure of the boom cylinder C3 is high and the operating pressure of the swing motor MT is low, the pressure difference between the single swing operation and the combined operation of the swing (body 2) and the boom 15 is determined by the pressure difference. The control position of the flow rate priority valve V11B changes slightly from time to time, and the turning speed changes.

In order to suppress this, a dummy load is formed on the directional switching valve DV8 that switches the direction of the hydraulic fluid to the turning motor MT. Specifically, as shown in FIG. 14, a pseudo load forming section 97 for forming a pseudo load on the directional switching valve DV8 (swing control valve V8) of the other embodiment is directed to the swing motor MT. It is provided in the channel 96 for flowing. The flow path 96 includes a first flow path 96a, which is a flow path through which hydraulic oil flows to one side of the turning motor MT when the direction switching valve DV8 is in the first position 81, and a flow path 82 in which the direction switching valve DV8 is in the second position. , it includes a second flow passage 96b, which is a flow passage through which hydraulic oil flows to the other side of the turning motor MT. The pseudo load forming portion 97 is configured by throttles 97a and 97b provided in the first flow path 96a and the second flow path 96b, respectively. That is, the pseudo load forming portion 97 includes a first throttle 97a provided in the first flow path 96a and a second throttle 97b provided in the second flow path 96b. The pressure loss due to the first throttle 97a and the pressure loss due to the second throttle 97b are the same. Also, the pressure loss caused by the first throttle 97 a and the pressure loss caused by the second throttle 97 b are greater than the pressure loss caused by the throttle 90 .

In the swing control valve V8 configured as described above, the first throttle 97a and the second throttle 97b create a pseudo load on the directional switching valve DV8 of the swing control valve V8 to increase the operating pressure of the swing motor MT from the beginning. By doing so, it is possible to balance the working pressure when the boom cylinder C3 with a high working pressure and the swing motor MT with a low load are operated in combination. Specifically, if the load pressure during operation of the turning motor MT is 3 MPa, and the pressure loss caused by the first throttle 97a and the pressure loss caused by the second throttle 97b are each 3 MPa, then the load pressure (operating pressure of the turning motor MT) becomes 6 MPa. If the turning speed is adjusted in accordance with the load pressure, the pressure difference in the combined operation can be reduced. As a result, the control area change amount of the flow rate priority valve V11B is reduced (the pseudo load generated by the flow rate priority valve V11B is decreased), and the combined operation of the machine body 2 (swing) and the boom 15 is performed during the single swing operation. It is possible to suppress the speed change of the turning speed of the airframe 2 over time. Also, the control position of the flow rate priority valve V11B can be stabilized when combined operation is performed.

In the other embodiments described above, the boom cylinder C3 is exemplified as the high-load hydraulic actuator and the swing motor MT is exemplified as the low-load hydraulic actuator, but the present invention is not limited to this.
The work machine 1 also includes a plurality of hydraulic actuators C3 and MT, and a plurality of directional switching valves DV2 and DV8 provided corresponding to the plurality of hydraulic actuators C3 and MT for switching the direction of hydraulic fluid to the hydraulic actuators C3 and MT. and a combined operation of the high-load hydraulic actuator C3 having a high operating pressure among the plurality of hydraulic actuators C3 and MT and the low-load hydraulic actuator MT having a lower operating pressure than the high-load hydraulic actuator C3; In order to suppress the change in the operating speed of the low-load hydraulic actuator MT from when the actuator MT is operated alone, a dummy load is applied to the low-load side directional switching valve DV8 that switches the direction of the hydraulic oil to the low-load hydraulic actuator MT. and a pseudo load forming portion 97 that forms a .

According to this configuration, the dummy load generator 97 generates a dummy load in advance on the direction switching valve DV8 on the low load side to increase the operating pressure of the low load hydraulic actuator MT, thereby increasing the operating pressure of the high load hydraulic actuator C3. It is possible to reduce the pressure difference when performing combined operation with the low-load hydraulic actuator MT. As a result, it is possible to suppress the change in the operating speed of the low-load hydraulic actuator MT between when the high-load hydraulic actuator C3 and the low-load hydraulic actuator MT are operated in combination and when the low-load hydraulic actuator MT is operated singly. can.

Further, the low-load-side directional switching valve DV8 has a flow path 96 through which hydraulic oil flows toward the low-load hydraulic actuator MT. It is configured.
According to this configuration, the pseudo load forming portion 97 can be provided in the direction switching valve DV8 on the low load side.

Also, the first control valve V2, which is a control valve for controlling the high-load hydraulic actuator C3, has a pressure compensating valve V11A for setting a constant differential pressure between the pressure of the introduced hydraulic fluid and the pressure of the hydraulic fluid to be output. and a control valve for controlling the low-load hydraulic actuator MT, which is a direction-switching valve DV8 on the low-load side and the flow rate of hydraulic oil output to the low-load hydraulic actuator MT via the direction-switching valve DV8 on the low-load side. and a second control valve V8 having a preferential flow rate priority valve V11B.

According to this configuration, even if the high-load hydraulic actuator C3 is provided with the pressure compensating valve V11A, hydraulic fluid can be preferentially supplied to the low-load hydraulic actuator MT.
In addition, the flow rate priority valve V11B has a first position 84a that increases the flow rate of hydraulic oil output from the low load side directional switching valve DV8, and a first position 84a that decreases the flow rate of hydraulic oil output from the low load side directional switching valve DV8. The low load side direction switching valve DV8 includes a spool 98 movable between the second position 84b and a pressing member 85 that presses the spool 98 toward the first position 84a. A pseudo load forming section including a first flow passage 96a, which is a flow passage 96 for flowing hydraulic oil on one side, and a second flow passage 96b, which is a flow passage 96 for flowing hydraulic oil on the other side of the low load hydraulic actuator MT. 97 includes a first throttle 97a, which is a throttle provided in the first flow path 96a, and a second throttle 97b, which is a throttle provided in the second flow path 96b.

According to this configuration, when the high-load hydraulic actuator C3 and the low-load hydraulic actuator MT are operated in combination, the flow rate of hydraulic oil output from the flow rate priority valve V11B does not fluctuate depending on the setting of the pressing member 85. can be suppressed, the control position of the flow rate priority valve V11B can be stabilized, and the speed change of the low-load hydraulic actuator MT can be suppressed.

The direction switching valve DV8 on the low load side connects the pump port 64 to which hydraulic fluid is supplied, the output port 66 that outputs hydraulic fluid to the flow rate priority valve V11B, and the pump port 64 and the output port 66. It has an oil passage 88b and a flow path restrictor 90 provided in the connecting oil path 88b, and the pressure loss due to the first restrictor 97a and the pressure loss due to the second restrictor 97a are larger than the pressure loss due to the flow path restrictor 90. is.

According to this configuration, a dummy load can be formed in the direction switching valve DV8 on the low load side.
In addition, the machine body 2 that can turn around the vertical axis, the turning motor MT that turns the machine body 2, the boom 15 that is provided on the front part of the machine body 2 so that it can swing up and down, and the boom cylinder that swings the boom 15 up and down. C3, the high-load hydraulic actuator is composed of the boom cylinder C3, and the low-load hydraulic actuator is composed of the swing motor MT.

According to this configuration, it is possible to suppress the change in the operating speed of the swing motor MT between when the boom cylinder C3 and the swing motor MT are operated in combination and when the swing motor MT is operated singly.
In addition, a variable displacement pump 21 for discharging hydraulic fluid for operating the plurality of hydraulic actuators ML, MR, MT, C1 to C6, and a plurality of hydraulic actuators ML, MR, MT, C1 to C6 from the discharge pressure of the pump 21 A load sensing system may be provided to control the pump 21 so that the differential pressure obtained by subtracting the highest load pressure among them is kept constant.

Although one embodiment of the present invention has been described above, it should be considered that the embodiment disclosed this time is illustrative in all respects and is not restrictive. The scope of the present invention is indicated by the scope of the claims rather than the above description, and is intended to include all modifications within the scope and meaning equivalent to the scope of the claims.

2 fuselage 15 boom 21 pump (first pump)
64 pump port 66 output port 84a first position 84b second position 85 pressing member (spring)
88b Connection oil passage 90 Flow passage throttle 96 Flow passage 96a First flow passage 96b Second flow passage 97 Dummy load forming portion 97a Throttle (first throttle)
97b aperture (second aperture)
98 Spool C1 Hydraulic actuator (dozer cylinder)
C2 Hydraulic actuator (swing cylinder)
C3 High-load hydraulic actuator (boom cylinder)
C4 hydraulic actuator (arm cylinder)
C5 Hydraulic actuator (work tool cylinder)
ML Hydraulic actuator (first traveling motor)
MR hydraulic actuator (second traveling motor)
MT low-load hydraulic actuator (turning motor)
DV2 Directional switching valve on the low load side DV8 Directional switching valve V2 First control valve V8 Second control valve V11A Pressure compensating valve V11B Flow priority valve

Claims (7)

a plurality of hydraulic actuators;
a plurality of directional switching valves provided corresponding to the plurality of hydraulic actuators for switching the direction of hydraulic fluid to the hydraulic actuators;
When a high-load hydraulic actuator having a high operating pressure and a low-load hydraulic actuator having a lower operating pressure than the high-load hydraulic actuator among the plurality of hydraulic actuators are operated in combination, and when the low-load hydraulic actuator is operated singly. and a dummy load forming unit that forms a dummy load on a directional switching valve on the low load side that switches the direction of hydraulic oil to the low load hydraulic actuator in order to suppress a change in the operating speed of the low load hydraulic actuator. ,
with
The directional switching valve on the low load side includes an input port to which hydraulic fluid is input, an output port that communicates with the low load hydraulic actuator, and a low load hydraulic actuator that communicates with the input port and the output port. and a flow path for flowing hydraulic oil toward
The pseudo load forming unit is configured by a throttle provided in the flow path,
A high-load side directional switching valve for switching the direction of hydraulic fluid to the high-load hydraulic actuator includes an input port to which hydraulic fluid is input, an output port communicating with the high-load hydraulic actuator, and a high-load side directional control valve. A non-throttled flow passage that communicates the input port of the directional switching valve with the output port of the directional switching valve on the high load side to flow hydraulic oil toward the high load hydraulic actuator. and a working machine. a plurality of hydraulic actuators;
a plurality of directional switching valves provided corresponding to the plurality of hydraulic actuators for switching the direction of hydraulic fluid to the hydraulic actuators;
When a high-load hydraulic actuator having a high operating pressure and a low-load hydraulic actuator having a lower operating pressure than the high-load hydraulic actuator among the plurality of hydraulic actuators are operated in combination, and when the low-load hydraulic actuator is operated singly. and a dummy load forming unit that forms a dummy load on a directional switching valve on the low load side that switches the direction of hydraulic oil to the low load hydraulic actuator in order to suppress a change in the operating speed of the low load hydraulic actuator. ,
A control valve for controlling the high-load hydraulic actuator, comprising: a high-load side directional switching valve for switching the direction of hydraulic fluid to the high-load hydraulic actuator;
a first control valve having a pressure compensating valve that sets a constant differential pressure between the force and the output hydraulic fluid pressure;
A control valve for controlling the low-load hydraulic actuator, wherein priority is given to the flow rate of hydraulic oil output to the low-load hydraulic actuator via the low-load side directional switching valve and the low-load side directional switching valve. a second control valve having a flow priority valve;
A work machine equipped with a plurality of hydraulic actuators;
a plurality of directional switching valves provided corresponding to the plurality of hydraulic actuators for switching the direction of hydraulic fluid to the hydraulic actuators;
When a high-load hydraulic actuator having a high operating pressure and a low-load hydraulic actuator having a lower operating pressure than the high-load hydraulic actuator among the plurality of hydraulic actuators are operated in combination, and when the low-load hydraulic actuator is operated singly. and a dummy load forming unit that forms a dummy load on a directional switching valve on the low load side that switches the direction of hydraulic oil to the low load hydraulic actuator in order to suppress a change in the operating speed of the low load hydraulic actuator. ,
A control valve for controlling the high-load hydraulic actuator, comprising : a direction-switching valve on the high-load side for switching the direction of hydraulic fluid to the high-load hydraulic actuator; a first control valve having a pressure compensating valve that sets a constant differential pressure with respect to the pressure;
A control valve for controlling the low-load hydraulic actuator, wherein priority is given to the flow rate of hydraulic oil output to the low-load hydraulic actuator via the low-load side directional switching valve and the low-load side directional switching valve. a second control valve having a flow priority valve;
with
the low-load side directional switching valve has a flow path through which hydraulic oil flows toward the low-load hydraulic actuator;
The working machine, wherein the dummy load forming section is configured by a throttle provided in the flow path . The flow rate priority valve is
It is movable between a first position for increasing the flow rate of hydraulic fluid output from the low load side directional switching valve and a second position for decreasing the flow rate of hydraulic fluid output from the low load side directional switching valve. spool and
a pressing member that presses the spool toward the first position;
The direction switching valve on the low load side includes a first flow passage, which is the flow passage for flowing hydraulic oil to one side of the low load hydraulic actuator, and the flow passage, which is the flow passage for flowing hydraulic oil to the other side of the low load hydraulic actuator. and a second flow path that is
4. The dummy load forming part according to claim 3, wherein the dummy load forming part includes a first throttle, which is the throttle provided in the first flow passage, and a second throttle, which is the throttle provided in the second flow passage. working machine. The direction switching valve on the low load side includes a pump port to which hydraulic fluid is supplied, an output port that outputs hydraulic fluid to the flow rate priority valve, a connection oil passage that connects the pump port and the output port, a flow path restriction provided in the connection oil path,
5. The working machine according to claim 4, wherein the pressure loss caused by the first throttle and the pressure loss caused by the second throttle are greater than the pressure loss caused by the passage throttle. A fuselage that can turn around its vertical axis;
a turning motor for turning the airframe;
a boom provided on the front part of the airframe so as to be able to swing up and down;
a boom cylinder for vertically swinging the boom;
with
The high-load hydraulic actuator is composed of the boom cylinder,
The work machine according to any one of claims 1 to 5, wherein the low-load hydraulic actuator is composed of the swing motor. a variable displacement pump that discharges hydraulic fluid for operating the plurality of hydraulic actuators;
a load sensing system that controls the pump so that a differential pressure obtained by subtracting the highest load pressure among the plurality of hydraulic actuators from the discharge pressure of the pump is constant;
The work machine according to any one of claims 1 to 6, comprising:

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