JP2017180808A - Hydraulic system for work machine - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hydraulic system for a work machine which is the hydraulic system for controlling a hydraulic actuator of the same object by a plurality of pilot switching valves which is pilot-operated, and which has improved an operation of the pilot switching valves.SOLUTION: A hydraulic system for a work machine includes: a tank for storing a hydraulic fluid; a hydraulic actuator driven by the hydraulic fluid; a plurality of pilot switching valves for controlling the hydraulic actuator; an operation device capable of operating the plurality of pilot switching valves by the hydraulic fluid; and an air-bleeding circuit which is a circuit for returning one part of the hydraulic fluid for operating the plurality of pilot switching valves to the tank, and which is common with respect to the plurality of pilot switching valves.SELECTED DRAWING: Figure 3

Description

  The present invention relates to a hydraulic system for a work machine such as a backhoe.

Conventionally, a technique disclosed in Patent Document 1 is known as a hydraulic system for a working machine (backhoe).
The hydraulic system for a working machine disclosed in Patent Document 1 includes a dozer cylinder that drives a dozer device. In this hydraulic system, the dozer cylinder is controlled by two pilot switching valves that are operated simultaneously. The two pilot switching valves are simultaneously pilot operated by pilot oil output from one operating device.

JP2013-2241A

By the way, when a pilot hose for supplying pilot oil is assembled to the pilot switching valve, or for some other reason, air may be mixed or generated in the oil in the pilot hose. Further, if air exists in the oil in the pilot hose, the movement of the spool of the pilot switching valve becomes worse and the operation of the dozer cylinder becomes unstable.
For this reason, the pilot switching valve is provided with an air bleeding circuit. This air bleeding circuit is a circuit that discharges air present in the oil in the pilot hose by returning a part of the pilot oil supplied to the pilot switching valve to the tank. Conventionally, an air bleeding circuit is provided for each pilot switching valve.

However, in the structure in which one dozer cylinder is controlled by two pilot switching valves as in Patent Document 1, if an air bleeding circuit is provided for each of the two pilot switching valves, a pilot circuit for supplying pilot oil is provided. There are cases where the pressure does not increase sufficiently. In this case, the speed of the dozer device becomes slow without completely pushing the spool of the pilot switching valve.
Therefore, an object of the present invention is to stabilize the operation of a hydraulic actuator in a hydraulic system that controls the same hydraulic actuator by a plurality of pilot switching valves that are pilot operated.

  A hydraulic system for a working machine according to an aspect of the present invention includes a tank that stores oil, a hydraulic actuator that is driven by hydraulic oil, a plurality of pilot switching valves that control the hydraulic actuator, and the plurality of pilot switching valves. An operation device that simultaneously operates the pilot oil, and a circuit that returns part of the pilot oil that operates the plurality of pilot switching valves to the tank, and a common air vent circuit for the plurality of pilot switching valves; It is equipped with.

  According to the hydraulic system for the working machine, a common air vent circuit is provided for a plurality of pilot switching valves that control the hydraulic actuator. Thereby, the amount of pilot oil leakage from the air vent circuit can be made appropriate, and the stability of the operation of the hydraulic actuator can be improved.

It is a schematic diagram of an oil way system. It is an oil path circuit diagram of a control valve. It is an oil-path circuit diagram of a part of control valve. It is an oil-path circuit diagram of a part of control valve. It is an oil path circuit diagram which shows a merge position. It is an oil path circuit diagram which shows an independent position. It is an oil-path circuit diagram which shows a part of oil-path system. It is a side view which shows the whole structure of a working machine.

DESCRIPTION OF EXEMPLARY EMBODIMENTS Hereinafter, preferred embodiments of a working machine according to the invention will be described with reference to the drawings as appropriate.
FIG. 8 is a schematic side view showing the overall configuration of the work machine 1 according to the present embodiment. In the present embodiment, a backhoe that is a turning work machine is illustrated as the work machine 1.
<Overall configuration of work equipment>
First, the overall configuration of the work machine 1 will be described.

As shown in FIG. 8, the work machine 1 includes a machine body (swivel base) 2, a traveling device 3, and a work device 4. A cabin 5 is mounted on the body 2. A driver's seat 6 is provided in the cabin 5.
In the embodiment of the present invention, the front side (left side in FIG. 8) of the driver seated on the driver's seat 6 of the work machine 1 is front, the rear side (right side in FIG. 8) is rearward, and the left side of the driver (FIG. 8 on the left side and the right side of the driver (the back side in FIG. 8) as the right side. The horizontal direction, which is a direction orthogonal to the front-rear direction K1, will be described as the body width direction.

  As shown in FIG. 8, the traveling device 3 includes a first traveling device 3L provided on the left side of the frame of the traveling device 3 and a second traveling device 3R provided on the right side of the frame. In other words, the first traveling device 3 </ b> L is provided on the left side of the lower part of the body 2. The second traveling device 3 </ b> R is provided on the right side of the lower part of the body 2. In the present embodiment, the first traveling device 3L and the second traveling device 3R are configured by a crawler traveling device. The first travel device 3L is driven by the first travel motor M1. The second traveling device 3R is driven by a second traveling motor M2 that is different from the first traveling motor M1. The first travel motor M1 and the second travel motor M2 are constituted by hydraulic motors (hydraulic actuators).

A dozer device 7 is attached to the front portion of the traveling device 3. The dozer device 7 can be moved up and down (raising and lowering the blade) by expanding and contracting the dozer cylinder C1.
The machine body 2 is supported on the frame of the traveling device 3 so as to be rotatable about a vertical axis (an axis extending in the vertical direction) via a swing bearing 8. The machine body 2 is driven to turn by a turning motor M3 including a hydraulic motor (hydraulic actuator). The machine body 2 includes a substrate 9 (hereinafter referred to as a swivel substrate) that rotates around a vertical axis, and a weight 10. The swivel board 9 is made of a steel plate or the like and is connected to the swivel bearing 8. The weight 10 is provided at the rear part of the airframe 2. An engine E <b> 1 is mounted on the rear part of the body 2.

The airframe 2 has a support bracket 13 at a slightly right front part in the center of the airframe width direction. A swing bracket 14 is attached to the support bracket 13 so as to be swingable about the vertical axis. The working device 4 is attached to the swing bracket 14.
As shown in FIG. 8, the work device 4 includes a boom 15, an arm 16, and a bucket (work tool) 17. The base portion of the boom 15 is pivotally attached to the swing bracket 14 so as to be rotatable about a horizontal axis (axial center in the body width direction). As a result, the boom 15 can swing up and down. The arm 16 is pivotally attached to the distal end side of the boom 15 so as to be rotatable about a horizontal axis. As a result, the arm 16 can swing back and forth or up and down. The bucket 17 is provided on the distal end side of the arm 16 so that a squeeze operation and a dump operation can be performed. The work machine 1 can be mounted with another work tool (hydraulic attachment) that can be driven by a hydraulic actuator instead of or in addition to the bucket 17. Examples of other working tools include a hydraulic breaker, a hydraulic crusher, an angle bloom, an earth auger, a pallet fork, a sweeper, a mower, and a snow blower.

  The swing bracket 14 is swingable by expansion and contraction of a swing cylinder C2 provided in the body 2. The boom 15 is swingable by expansion and contraction of the boom cylinder C3. The arm 16 is swingable by the expansion and contraction of the arm cylinder C4. The bucket 17 is freely squeezed and dumped by expansion and contraction of a bucket cylinder (work implement cylinder) C5. The dozer cylinder C1, the swing cylinder C2, the boom cylinder C3, the arm cylinder C4, and the bucket cylinder C5 are configured by hydraulic cylinders (hydraulic actuators).

The boom 15 may be a two-piece specification. The two-piece specification is a specification in which the boom 15 is composed of two members, a front boom and a rear boom, and can be bent at a connecting portion between the front boom and the rear boom. In the case of the two-piece specification, in addition to the boom cylinder C3, a second boom cylinder for performing an operation of bending the boom 15 at the connecting portion is additionally mounted.
<Hydraulic system>
Next, referring to FIG. 1 to FIG. 7, various hydraulic actuators M <b> 1 to 3, C <b> 1 to 5 provided on the work machine 1 and a hydraulic system for operating the separately provided hydraulic actuator (hydraulic system of the work machine) Will be described.

As shown in FIG. 1, the hydraulic system includes a control valve CV1, a pressure oil supply unit SU1, and a tank T1 for storing hydraulic oil. The hydraulic fluid stored in the tank T1 is used for driving a hydraulic actuator, for control, or for signal. For convenience of explanation, the hydraulic oil used for control or signal is called “pilot oil”, and the pressure of the pilot oil is called “pilot pressure”. The hydraulic oil is sometimes referred to as “pressure oil”.
A load sensing system is adopted as the hydraulic system.

  The load sensing system functions as a load adjustment between the hydraulic actuators M1 to M3 and C1 to 5 when the plurality of hydraulic actuators M1 to M3 and C1 to 5 installed in the work machine 1 are simultaneously operated (load load). Pressure compensation valves E1 to 11, which will be described later, function as adjustments), causing the control valve V1 to 11 on the low load pressure side to generate a pressure loss corresponding to the differential pressure from the maximum load pressure, regardless of the magnitude of the load. In this system, a flow rate corresponding to an operation amount for operating V1 to V11 can be flowed (distributed) to the operated control valves V1 to V11.

The load sensing system controls the discharge amount of hydraulic oil discharged from a first pump 27 described later according to the load pressure of each of the hydraulic actuators M1 to C3 and C1 to 5 installed in the work machine 1 (load sensing). Control), and the hydraulic power required for the load is discharged from the first pump 27, whereby the power can be saved and the operability can be improved. <Outline of control valve>
The control valve CV1 is a valve unit in which a plurality of control valves V1 to V11, a plurality of end blocks B1 and B2, and a plurality of valve blocks B3 and B4 are arranged side by side in one direction. Further, the control valve CV1 has a valve block B5 provided in the valve block B4.

  The control valves V1 to V11, the end block B1, and the valve blocks B3 and B4 are shown in FIG. 1 from the right, from the right, the control valve V1, the control valve V2, the valve block B3, the valve block B4, the control valve V3, the control valve V4, and the control valve. V5, control valve V6, control valve V7, control valve V8, control valve V9, control valve V10, control valve V11, and end block B2 are arranged in this order and joined together.

The plurality of control valves V1 to V11 are valves for operating various hydraulic actuators M1 to M3 and C1 to C5 provided in the work machine 1 and separately provided hydraulic actuators.
The control valve V1 is a first dozer valve that controls the dozer cylinder C1. The control valve V2 is a first travel valve that controls the first travel motor M1. The control valve V3 is a second travel valve that controls the second travel motor M2. The control valve V4 is a valve that controls the dozer cylinder C1, and is a second dozer valve that is different from the control valve V1. The control valve V5 is a first spare valve that controls a separately attached hydraulic attachment. The control valve V6 is an arm valve that controls the arm cylinder C4. The control valve V7 is a bucket valve (work tool valve) that controls the bucket cylinder C5. The control valve V8 is a boom valve that controls the boom cylinder C3. The control valve V9 is a swing valve that controls the swing motor M3. The control valve V10 is a valve that controls a separately attached hydraulic attachment, and is a second preliminary valve that is different from the control valve V5. The control valve V11 is a swing valve that controls the swing cylinder C2.

The control valve V1 and the control valve V2 constitute a first control valve. That is, the first control valve is a valve that controls the hydraulic actuator (dozer cylinder C1, first travel motor M1). Further, the first control valve includes at least a first travel valve V2, and in the present embodiment also includes a first dozer valve V1.
The control valves V3 to V11 constitute a second control valve. That is, the second control valve is a valve that controls the hydraulic actuator (second traveling motor M2, dozer cylinder C1, hydraulic attachment, arm cylinder C4, bucket cylinder C5, boom cylinder C3, swing motor M3, swing cylinder C2). . Further, the second control valve includes at least a second traveling valve V3. In the present embodiment, the second dozer valve V4, the first preliminary valve V5, the arm valve V6, the bucket valve V7, the boom valve V8, the swing valve V9, A second preliminary valve V10 and a swing valve V11 are also included.

The first preliminary valve V5, the arm valve V6, the bucket valve V7, the boom valve V8, the swing valve V9, the second preliminary valve V10, and the swing valve V11 are provided in any one of the first control valve and the second control valve. It only has to be.
The control valve CV1 has input ports 18 to 22 and output ports 23 and 24. The input port 18 and the input port 19 are ports to which hydraulic oil discharged from a first pump 27 described later is input, and are provided in the valve block B5. The input port 20 is provided in the end block B1. The input port 21 is provided in the end block B2. The input port 22 is provided in the valve block B4. The output port 23 and the output port 24 are provided in the valve block B3. The output port 23 is a port for outputting a PLS signal pressure (PLS: Pressure of Load Sensing) which is the highest load pressure among the various hydraulic actuators M1 to M3 and C1 to C5. The output port 24 is a port that outputs a PPS signal pressure (PPS: Pressure of Pump Sensing) that is a discharge pressure of the first pump 27.
<Pressure oil supply unit>
The pressure oil supply unit SU <b> 1 includes a unit body 26, a first pump 27, a second pump 28, and a control unit 29. The first pump 27, the second pump 28, and the control unit 29 are incorporated in the unit body 26.

The first pump 27 is a hydraulic pump that sucks the oil in the tank T1 and discharges the hydraulic oil that operates the various hydraulic actuators M1 to M3 and C1 to C5 (supply the hydraulic oil). The second pump 28 is a hydraulic pump that discharges pilot oil. The first pump 27 and the second pump 28 are driven by the engine E1.
The first pump 27 is a hydraulic pump having a function of an equal flow double pump that discharges an equal amount of pressure oil (working oil) from two independent discharge ports, and is a swash plate type variable displacement axial capable of varying the discharge capacity. It consists of a pump. Specifically, the first pump 27 employs a split flow type hydraulic pump having a mechanism for alternately discharging pressure oil from one piston / cylinder barrel kit to discharge grooves formed inside and outside the valve plate.

  Of the two discharge ports from which the hydraulic oil is discharged from the first pump 27, one discharge port is referred to as a first pump port P1, and the other discharge port is referred to as a second pump port P2. Note that the first pump 27 may be constituted by two independent hydraulic pumps. In this case, the discharge port of one of the two hydraulic pumps is a first pump port, and the discharge port of the other hydraulic pump is a second pump port.

The second pump 28 is a constant capacity type gear pump. The second pump 28 is a hydraulic pump that sucks oil in the tank T1 and discharges pilot oil.
The unit body 26 is provided with output ports 30 to 32 and input ports 33 to 35. The output port 30 outputs hydraulic oil discharged from the first pump port P1. The output port 30 is connected to the input port 18 via a supply oil passage 36. The output port 31 outputs hydraulic oil discharged from the second pump port P2. The output port 31 is connected to the input port 19 via the supply oil passage 37. The output port 32 outputs hydraulic oil discharged from the second pump 28. The output port 32 is connected to the input port 20 via a supply oil passage 38 and a supply oil passage 39. The output port 32 is connected to the input port 21 via a supply oil passage 38, a supply oil passage 40, and a supply oil passage 41. The output port 32 is connected to the input port 22 via a supply oil passage 38, a supply oil passage 39, and a supply oil passage 58. The output port 32 is connected to the input port 35 via a supply oil passage 38, a supply oil passage 40, and a supply oil passage 42. The input port 33 is connected to the output port 24 via a signal oil path (PPS signal oil path) 47. That is, the PPS signal pressure is input to the input port 33. The input port 34 is connected to the output port 23 via a signal oil path (PLS signal oil path) 48. That is, the PLS signal pressure is input to the input port 34.

The controller 29 is a device that controls the flow rate of the hydraulic oil discharged from the first pump 27. In other words, the flow rate control unit 29 is a device that controls the swash plate of the first pump 27.
The control unit 29 includes a pressing device 43 that presses the swash plate of the first pump 27 and a flow rate compensation swash plate control device 44 that controls the swash plate of the first pump 27. The first pump 27 is configured such that the swash plate is pressed in the direction of increasing the pump flow rate via the pressing device 43 by the self-pressure of the first pump 27. In addition, a force that opposes the pressing force of the pressing device 43 is applied to the swash plate by the swash plate control device 44. By controlling the pressure acting on the swash plate control device 44, the discharge flow rate of the first pump 27 is controlled.

When the pressure acting on the control piston 44 is released, the first pump 27 discharges the maximum flow rate with the swash plate angle becoming MAX.
Further, the control unit 29 includes a control valve V12 for flow rate compensation. The swash plate control of the first pump 27 is performed by controlling the pressure acting on the swash plate control device 44 by the control valve V12.

  An input port 33 is connected to one side of the spool of the control valve V12 via an oil passage 49. That is, the discharge pressure (PPS signal pressure) of the first pump 27 acts on one end side of the spool of the control valve V12. An input port 34 is connected to the other side of the spool of the control valve V12 via an oil passage 50. That is, the maximum load pressure (PLS signal pressure) of the hydraulic actuator acts on the other end of the spool of the control valve V12. Further, a spring 51 and a differential pressure cylinder 52 for providing a control differential pressure to the control valve V12 are provided on the other end side of the spool of the control valve V12.

The control valve V12 controls the swash plate control device 43 based on the PLS signal pressure and the PPS signal pressure. The swash plate control device 43 controls the first pump 27 so that the pressure difference between the PPS signal pressure and the PLS signal pressure becomes the control differential pressure (so as to maintain the difference between the PPS signal pressure and the PLS signal pressure at a set value). The discharge flow rate (discharge pressure) is automatically controlled (load sensing control).
That is, the hydraulic system (load sensing system) includes the first pump port P1 and the second pump port based on the discharge pressure of the first pump 27 (first pump port P1 or second pump port P2) and the load pressure of the hydraulic actuator. It has the control part 29 which controls the flow volume of the hydraulic fluid discharged from P2.

The control unit 29 is provided with a spring 45 and a spool 46 for controlling the pump horsepower (torque) of the first pump 27. The spring 45 and the spool 46 are configured to limit the horsepower (torque) that the first pump 27 absorbs from the engine E1 when the discharge pressure of the first pump 27 reaches a preset pressure.
Next, details of the control valve CV1 will be described.

As shown in FIGS. 2-4, each control valve V1-V11 has incorporated the direction switching valves D1-D11 and the pressure compensation valves E1-E11 in the valve body.
The direction switching valves D1 to D11 are valves that switch the direction of pressure oil with respect to the hydraulic actuators M1 to M3 and C1 to C5 to be controlled. The direction switching valves D1 to D11 are direct-acting spool type three-position switching valves. The direction switching valves D1 to D11 are pilot (operation) switching valves that are switched by a pilot pressure (pilot oil). The spools of the direction switching valves D1 to D11 constitute the main spools of the control valves V1 to V11. Therefore, it can be said that the control valves V1 to V11 are pilot (operation) switching valves that are switched by the pilot pressure. Further, the spools of the direction switching valves D1 to D11 are moved in proportion to the operation amount of the operating device that operates the direction switching valves D1 to D11. Then, it is configured to supply an amount of pressure oil proportional to the amount of movement of the spool to the hydraulic actuators M1 to M3 and C1 to C5 to be controlled (the operation is performed in proportion to the operation amount of each operation device). The operating speeds of the target hydraulic actuators M1 to M3 and C1 to C5 can be changed).

  The pressure compensation valves E1 to E11 are arranged on the downstream side of the pressure oil supply to the direction switching valves D1 to D11 and on the upstream side of the pressure oil supply to the hydraulic actuators M1 to M3 and C1 to C5 to be controlled. That is, the load sensing system of the present embodiment employs an after orifice type load sensing system in which the pressure compensation valves E1 to E11 are arranged on the downstream side of the pressure oil supply to the direction switching valves D1 to D11.

The pressure compensation valves E1 to E11 function as a load adjustment between the hydraulic actuators M1 to M3 and C1 to C5 when a plurality of the hydraulic actuators M1 to M3 and C1 to C5 are simultaneously operated, and a control valve on the low load pressure side A pressure loss corresponding to the differential pressure from the maximum load pressure is generated in V1 to V11, and a flow rate corresponding to the operation amount of the spool of the direction switching valves D1 to D11 is allowed to flow (distribute) regardless of the magnitude of the load. it can.
<Air release circuit for pilot oil passage of dozer valve>
As shown in FIG. 3, the hydraulic system includes a remote control valve (operation device) 56 that operates the dozer device 7. The remote control valve 56 has a dozer lever (operation member) 56A. The remote control valve 56 is provided in the vicinity of the driver's seat 6. The remote control valve 56 is a pilot valve that pilot-operates the control valve V1 (first dozer valve) and the control valve V4 (second dozer valve) by operating the dozer lever 56A. The remote control valve 56 simultaneously outputs pilot oil to the direction switching valve D1 and the direction switching valve D4 by operating the dozer lever 56A. Thereby, the direction switching valve D1 and the direction switching valve D4 are simultaneously operated (operated simultaneously). Hereinafter, for convenience of explanation, the direction switching valve D1 may be referred to as a “first pilot switching valve”, and the direction switching valve D4 may be referred to as a “second pilot switching valve”.

  The hydraulic system includes a pilot circuit 53 that supplies pilot oil from the remote control valve 56 to the control valve V1 (first pilot switching valve D1) and the control valve V4 (second pilot switching valve D4). The pilot circuit 53 is a circuit for supplying pilot oil for switching command for switching the direction switching valve D1 and the direction switching valve D4 from the remote control valve 56 to the control valve V1 and the control valve V4. That is, the pilot circuit 53 constitutes a hydraulic oil flow path through which pilot oil supplied from the remote control valve 56 (operation device) to the first pilot switching valve D1 and the second pilot switching valve D4 flows.

The pilot circuit 53 includes a first supply circuit 54 that supplies pilot oil to the control valve V1, and a second supply circuit 55 that supplies pilot oil to the control valve V4. The first supply circuit 54 includes a first pilot oil passage 54A and a second pilot oil passage 54B. The second supply circuit 55 includes a third pilot oil passage 55A and a fourth pilot oil passage 55B.
The first pilot oil passage 54A has one end connected to the remote control valve 56 and the other end connected to a pressure receiving portion (first pressure receiving portion) 57A of the direction switching valve D1. The second pilot oil passage 54B has one end connected to the remote control valve 56 and the other end connected to a pressure receiving part (second pressure receiving part) 57B of the direction switching valve D1. The third pilot oil passage 55A has one end connected to the first pilot oil passage 54A and the other end connected to a pressure receiving portion (third pressure receiving portion) 57C of the direction switching valve D4. The fourth pilot oil passage 55B has one end connected to the second pilot oil passage 54B and the other end connected to a pressure receiving portion (fourth pressure receiving portion) 57D of the direction switching valve D4. In the present embodiment, the first supply circuit 54 is a circuit that supplies pilot oil from the remote control valve 56 (operation device) to the first pilot switching valve D1. The second supply circuit 55 is a circuit that supplies pilot oil from the first supply circuit 54 to the second pilot switching valve D4. The first supply circuit 54 is a circuit that supplies pilot oil from the remote control valve 56 to the second pilot switching valve D4, and the second supply circuit 55 supplies pilot oil from the first supply circuit 55 to the first pilot switching valve D1. It may be a circuit. That is, the pilot circuit 53 includes a first supply circuit 54 that supplies pilot oil from the operating device 56 to one of the first pilot switching valve D1 or the second pilot switching valve D4, and the first pilot switching valve from the first supply circuit 54. And a second supply circuit 55 for supplying pilot oil to the other of D1 or the second pilot switching valve D4.

  In this embodiment, when the dozer lever 56A is swung forward, the pilot pressure acts on the first pressure receiving portion 57A via the first pilot oil passage 54A and the third pressure receiving portion 57C via the third pilot oil passage 55A. Pilot pressure acts. Thus, the direction switching valve D1 and the direction switching valve D4 are switched in the direction in which the dozer device 7 is raised. When the dozer lever 56A is swung rearward, the pilot pressure acts on the second pressure receiving portion 57B via the second pilot oil passage 54B and the pilot pressure is applied to the fourth pressure receiving portion 57D via the fourth pilot oil passage 55B. Works. Thereby, the direction switching valve D1 and the direction switching valve D4 are switched in the direction in which the dozer device 7 is lowered.

  Of the control valve V1 (first pilot switching valve D1) and the control valve V4 (second pilot switching valve D4), the control valve V4 is provided with an air bleeding circuit 59, and the control valve V1 has an air bleeding circuit. No circuit is provided. That is, the air bleeding circuit 59 is a common air bleeding circuit 59 for the first pilot switching valve D1 and the second pilot switching valve D4 (for a plurality of pilot switching valves). Further, the control valve 4 (pilot switching valve D4) on the downstream side of the oil flow path through which the pilot oil for switching command for switching the direction switching valve (first pilot switching valve) D1 and the direction switching valve (second pilot switching valve) D4 flows. ) Is provided with an air vent circuit 59. In other words, the air bleeding circuit 59 is downstream of the oil flow path through which the pilot oil supplied from the operating device 56 is flowed out of the first pilot switching valve D1 or the second pilot switching valve D2 (among the plurality of pilot switching valves). On the pilot switching valve side.

The air vent circuit 59 is not limited to the downstream side of the pilot oil flow passage, and may be provided upstream of the pilot oil passage. That is, it is only necessary to be provided on one of the control valve V1 (first pilot switching valve D1) and the control valve V4 (second pilot switching valve D2).
In some cases, air is mixed into the pilot oil passages 54A, 54B, 55A, and 55B when assembling a hydraulic routing member such as a hydraulic hose constituting the pilot oil passages 54A, 54B, 55A, and 55B. Further, when the oil (hydraulic oil) stagnates in the pilot oil passages 54A, 54B, 55A, 55B when the control valves V1, V2 are not used, the gas contained in the oil may precipitate as fine bubbles. is there. If there is air in the pilot oil passages 54A, 54B, 55A, 55B, the movement of the dozer cylinder C1 (hydraulic actuator) becomes worse. The air vent circuit 59 is a circuit that vents air (bubbles) in the pilot oil passages 54A, 54B, 55A, and 55B by returning the pilot oil in the pilot oil passages 54A, 54B, 55A, and 55B to the tank T1.

  The air vent circuit 59 has a first escape path 59A, a second escape path 59B, a first aperture 59C, and a second aperture 59D. The first escape passage 59A has one end connected to the third pilot oil passage 55A and the other end connected to the drain oil passage 60. One end of the first escape passage 59A is connected to the vicinity of the pressure receiving portion 57C. The second escape path 59B has one end connected to the fourth pilot oil path 55B and the other end connected to the first escape path 59A. One end of the second escape passage 59B is connected to the vicinity of the pressure receiving portion 57D.

The first diaphragm 59C is provided in the first escape path 59A. The first throttle 59C is preferably provided in the vicinity of the connection portion between the third pilot oil passage 55A and the first escape passage 59A. The second diaphragm 59D is provided in the second escape path 59B. The second throttle 59D is preferably provided in the vicinity of the connection portion between the fourth pilot oil passage 55B and the second escape passage 59B.
The drain oil passage 60 is provided in the control valve CV1, and extends from the end block B3 to the end block B1 through the control valves V11 to V1 and the valve blocks B4 and B3. The drain oil passage 60 communicates with the tank T1 through the relief valve V22 at the end block B1. Further, the drain oil passage 60 communicates with the tank T1 through the oil passage 61 by the control valve V8.

When the pilot oil flows through the pilot oil passages 54A, 54B, 55A, 55B, a part of the pilot oil flows through the first throttle 59C or the second throttle 59B to the drain oil passage 60 and is returned to the tank T1. Accordingly, when air is present in the pilot oil passages 54A, 54B, 55A, 55B, the air is discharged.
If an air vent circuit is provided in both the control valve V1 (first pilot switching valve D1) and the control valve V4 (second pilot switching valve D2), the amount of pilot oil leakage increases. 54B, 55A, and 55B may be difficult to boost. If the pilot oil passages 54A, 54B, 55A, and 55B are not sufficiently boosted, the operating speed of the dozer device 7 is slowed down without pushing down the spools of the direction switching valves D1 and D4. By providing an air vent circuit 59 in one of the control valve V1 (first dozer valve) and the control valve V4 (second dozer valve), the air in the pilot oil passages 54A, 54B, 55A, 55B is appropriately At the same time, the pilot oil passages 54, 54B, 55A, 55B can be sufficiently boosted to make the operating speed of the dozer device 7 appropriate.

  Further, when the air vent circuit 59 is provided on one of the control valve V1 (first pilot switching valve D1) and the control valve V4 (second pilot switching valve D2), the air vent circuit 59 is provided on the control valve V4. Yes. That is, the air vent circuit 59 is provided in the control valve 4 on the downstream side of the oil flow path through which the pilot oil for switching command for switching the direction switching valve D1 and the direction switching valve D4 flows. As a result, the air existing upstream of the pilot oil passages 54A, 54B, 55A, 55B can be extracted well. In other words, air can be vented satisfactorily (air venting can be ensured).

  In this embodiment, an air bleeding circuit is provided in one of the two control valves for the dozer device, but the present invention is not limited to the dozer device. In short, in a hydraulic system in which the same target (one) hydraulic actuator is controlled by a plurality of pilot switching valves that are pilot operated simultaneously, a common air vent circuit may be provided for the plurality of pilot switching valves. .

In the present embodiment, the first pilot switching valve is provided in the valve body of the first control valve and the second pilot switching valve is provided in the valve body of the second control valve. However, the present invention is not limited to this. A plurality of pilot switching valves may be assembled in one valve body, and a common air vent circuit may be provided for the plurality of pilot switching valves.
<Load pressure return circuit of load sensing system>
As shown in FIGS. 2, 3, and 4, a first relief valve V <b> 21 is incorporated in the end block B <b> 1. A first shuttle valve V14, a second shuttle valve V15, a first unload valve V18, and a second unload valve V19 are incorporated in the valve block B3. The valve block B4 incorporates a first switching valve V13, a second switching valve V20, a second relief valve V17, and a first return circuit 66. A bypass valve V16 is incorporated in the valve block B5. A second return circuit 67 is incorporated in the end block B2.

  The control valve CV1 has a first hydraulic fluid passage 68 for flowing hydraulic fluid from the first pump port P1, and a second hydraulic fluid passage 69 for flowing hydraulic fluid from the second pump port P2. One end of the first hydraulic oil passage 69 is connected to the input port 18. The first hydraulic oil passage 68 passes through the valve block B5 and enters the valve block B4, and passes from B4 to the end block B1 via the control valve V2 and the control valve V1. In the end block B1, the other end of the first hydraulic oil passage 68 is connected to the drain oil passage 60. In the end block B1, the first relief valve V21 is provided in the first hydraulic oil passage 68. The first relief valve V21 is a variable relief valve that can change the set pressure to a first set pressure and a second set pressure that is a set pressure higher than the first set pressure. In the present embodiment, the first relief valve V21 is a pilot operated variable relief valve whose set pressure is changed by the pilot pressure.

As shown in FIGS. 5 and 6, the first relief valve V <b> 21 includes a pressure receiving portion 64 and a setting spring 65. The first relief valve V21 becomes the first set pressure set by the setting spring 65 when the pilot pressure does not act on the pressure receiving portion 64. Further, when the pilot pressure acts on the pressure receiving portion 64, the pressure is changed to the second set pressure.
As shown in FIGS. 2, 3, and 4, the first hydraulic oil passage 68 is connected to the direction switching valves D <b> 1 and D <b> 2 by oil passages, and the direction switching valves D <b> 1 and D <b> 2 are connected to the first hydraulic oil passage 68. It is possible to supply hydraulic oil.

  One end of the second hydraulic oil passage 69 is connected to the input port 19. The second hydraulic oil passage 69 passes through the valve block B5 and enters the valve block B4, and reaches from the B4 through the control valves V3 to V10 to the control valve V11. The other end of the second hydraulic oil passage 69 is closed. The second hydraulic oil passage 69 is connected to the direction switching valves D3 to D11 by oil passages, respectively, and hydraulic oil can be supplied from the second hydraulic oil passage 69 to the direction switching valves D3 to D11.

  The bypass valve V16 is a direct acting spool type three-position switching valve operated by a pilot pressure. The bypass valve V16 is provided in the oil passage 104 and the oil passage 105 that connect the first hydraulic oil passage 68 and the second hydraulic oil passage 69 in parallel. The bypass valve V16 has a blocking position (neutral position) 106 that blocks the pressure oil circulation of the oil path 104 and the oil path 105, and a first position 107 that allows the pressure oil circulation of the oil path 104 and blocks the oil path 105. And a second position 104 that shuts off the oil passage 104 and allows the pressure oil to flow through the oil passage 105.

  The pilot pressure output from the operation valve (operation device) V26 that operates the control valve V3 acts in a direction to switch the bypass valve V16 from the cutoff position 106 to the first position 107. Further, the pilot pressure output from the operation valve (operation device) V27 that operates the control valve V2 acts in a direction to switch the bypass valve V16 from the shut-off position 106 to the second position 108. Further, the bypass valve V16 has a first pressure 107 or a second position 108 that is changed from the shut-off position 106 to the first position 107 or the second position 108 by a high-pressure side pilot pressure when a differential pressure greater than a predetermined pressure is generated in the pilot pressure between the operation valve V26 and the operation valve V27. Can be switched to.

The first hydraulic oil passage 68 is connected to the first switching valve V13 by the first connecting oil passage 71. The second hydraulic oil passage 69 is connected to the first switching valve V <b> 13 by the second connecting oil passage 72.
The first hydraulic oil path 68 is connected to one input port of the first shuttle valve V14 by a signal oil path 79, and the hydraulic oil in the first hydraulic oil path 68 is input to the first shuttle valve V14. The second hydraulic oil passage 69 is connected to the other input port of the first shuttle valve V14 via the second connecting oil passage 72 and the signal oil passage 80, and the hydraulic oil in the second hydraulic oil passage 69 is connected to the first shuttle valve. V14 is input. The first shuttle valve V14 outputs from the output port the hydraulic oil having the higher pressure among the hydraulic oil input from the input port (in the case of the same pressure, the hydraulic fluid from the open input port is output). ) The output port of the first shuttle valve V14 is connected to the output port 24. As a result, the PPS signal pressure (the discharge pressures of the first pump port P1 and the second pump port P2) is output from the output port 24.

  The signal oil passage 79 is connected to the first unload valve V18 via the oil passage 86. The signal oil passage 80 is connected to the second unload valve V19 via the oil passage 87. The first unload valve V18 is biased in the closing direction by the biasing force of the spring and acts in the direction in which the oil passage 86 is closed. The second unload valve V19 is urged in the closing direction by the urging force of the spring and acts in the direction in which the oil passage 87 is closed.

The first switching valve V13 is a direct acting spool type two-position switching valve. The first switching valve V13 is a pilot operation switching valve that is switched by a pilot pressure.
As shown in FIGS. 5 and 6, the first switching valve V <b> 13 has six ports 73 a to 73 f. A first connecting oil passage 71 is connected to the port 73a. A second connection oil passage 72 is connected to the port 73b. One end of the first transmission oil passage 74 is connected to the port 73c. One end of the second transmission oil passage 75 is connected to the port 73d. One end of a relief oil passage 76 is connected to the port 73e. One end of an oil drainage passage 77 is connected to the port 73f.

  As shown in FIGS. 2 and 3, the first transmission oil passage 74 is provided from the valve block B4 to the control valve V1 via the control valve V2. The other end of the first transmission oil passage 74 is closed. In the first transmission oil passage 74, pressure compensation valves E1, E2 are connected via load transmission oil passages Y1, Y2. The load pressures of the hydraulic actuators (dozer cylinder C1, first travel motor M1) to be controlled by the control valves V1, V2 are transmitted to the first transmission oil path 74 by the load transmission oil paths Y1, Y2.

  As shown in FIGS. 2 and 4, the second transmission oil passage 75 reaches from the valve block B4 to the end block B2 via the control valves V3 to V11. A second return circuit 67 is connected to the other end of the second transmission oil passage 75. The second return circuit 67 is connected to the drain oil passage 60 at the end block B2. Pressure compensation valves E3 to E11 are connected to the second transmission oil passage 75 via load transmission oil passages Y3 to Y11. By these load transmission oil paths Y3 to Y11, hydraulic actuators to be controlled by the control valves V3 to V11 (second travel motor M2, dozer cylinder C1, hydraulic attachment, arm cylinder C4, bucket cylinder C5, boom cylinder C3, swing motor M3) The load pressure of the swing cylinder C2) is transmitted to the first transmission oil passage 74.

  The second return circuit 67 includes a connection oil passage (second connection oil passage) 67A, a throttle 67B, and an oil filter 67C. The second connection oil passage 67 </ b> A has one end connected to the other end of the second transmission oil passage 75 and the other end connected to the drain oil passage 60. The restrictor 67B and the oil filter 67C are provided in the second connection oil passage 67A. The restrictor 67B is provided on the downstream side of the oil filter 67C. The second return circuit 67 is a circuit that returns the pressure oil in the second transmission oil passage 75 to the tank T1.

  The relief oil passage 76 is provided with a second relief valve V17. The second relief valve V17 is a relief valve whose set pressure is determined by the setting spring 91. The set pressure of the second relief valve V17 is the same set pressure as the second set pressure of the first relief valve V21. The other end of the relief oil passage 76 is connected to the drain oil passage 60 and communicates with the tank T1.

The other end of the oil discharge passage 77 is connected to a relief oil passage 76 via an oil passage 78. Further, the other end of the oil discharge passage 77 is connected to the downstream side of the second relief valve V <b> 17 in the relief oil passage 76. As a result, the oil drain passage 77 communicates with the tank T1.
The first transmission oil passage 74 is connected to one input port of the second shuttle valve V15 via the signal oil passage 81, and the pressure oil in the first transmission oil passage 74 is input to the second shuttle valve V15. . The second transmission oil path 75 is connected to the other input port of the second shuttle valve V15 via the signal oil path 82, and the pressure oil in the second transmission oil path 75 is input to the second shuttle valve V15. The second shuttle valve V15 outputs the hydraulic oil having the higher pressure among the hydraulic oil input from the input port from the output port (in the case of the same pressure, the hydraulic oil is output from the open input port). ) The output port of the second shuttle valve V15 is connected to the output port 23. As a result, the PLS signal pressure (the maximum load pressure of the hydraulic actuator) is output from the output port 23.

As shown in FIGS. 3, 5, and 6, the first switching valve V <b> 13 can be switched between a merging position 83 and an independent position 84. The first switching valve V13 is biased in a direction to be switched to the joining position 83 by the spring 85.
When the 1st switching valve V13 is the merge position 83 (refer FIG. 5), the 1st connection oil path 71 and the 2nd connection oil path 72 are connected. That is, the first hydraulic oil passage 68 and the second hydraulic oil passage 69 are communicated (connected) via the first connection oil passage 71 and the second connection oil passage 72. Thereby, the discharge oil of the first pump port P1 and the discharge oil of the second pump port P2 are merged and can be supplied to the direction switching valves D1 to D11 of the control valves V1 to V11. Further, at the merge position 83, the first transmission oil passage 74 and the second transmission oil passage 75 are connected. That is, at the merging position 83, the first switching valve V13 allows the hydraulic oil from the first pump port P1 and the second pump port P2 to merge and supply them to the first control valve and the second control valve, and the first transmission. The oil passage 74 and the second transmission oil passage 75 are connected.

  When the first switching valve V13 is at the independent position 84 (see FIG. 6), the connection between the first connection oil passage 71 and the second connection oil passage 72 is released (cut off). That is, the communication between the first hydraulic oil passage 68 and the second hydraulic oil passage 69 is released. As a result, the oil discharged from the first pump port P1 can be supplied to the directional control valves D2 and D1 of the control valve (first travel valve valve) V2 and the control valve (first dozer valve) V1, and the second pump port. Pressure oil from P2 can be supplied to the directional control valves D3 and D4 of the control valve (second travel valve) V3 and the control valve (second dozer valve) V4. Further, at the independent position 84, the pressure oil from the second pump port P2 can be supplied to the direction switching valves D5 to D11 of the control valves V5 to V11.

In addition, at the independent position 84, the connection between the first transmission oil passage 74 and the second transmission oil passage 75 is released. That is, at the independent position 84, the hydraulic oil from the first pump port P1 can be supplied to the first control valve, the hydraulic oil from the second pump port P2 can be supplied to the second control valve independently, and the first transmission oil can be supplied. The communication between the path 74 and the second transmission oil path 75 is released.
As shown in FIGS. 5 and 6, the first switching valve V <b> 13 includes a communication oil path 88 and a first return circuit 66. The communication oil path 88 connects the port 73 b and the port 73 e at the independent position 84. As a result, the second connecting oil passage 72 (second hydraulic oil passage 69) and the relief oil passage 76 are connected at the independent position 84. Further, at the joining position 83, the communication oil passage 88 is detached from the port 73b and the port 73e (disengaged from the second connection oil passage 72 and the relief oil passage 76). As a result, the connection between the port 73b and the port 73e by the communication oil passage 88 is released, and the connection between the second connection oil passage 72 (second hydraulic oil passage 69) and the relief oil passage 76 is released.

The first return circuit 66 includes a connection oil path (first connection oil path) 66A, a throttle 66B, and an oil filter 66C. The restrictor 66B and the oil filter 66C are provided in the first connection oil passage 66A. The restrictor 66B is provided on the downstream side of the oil filter 66C.
66 A of 1st connection oil paths are provided in the spool of the 1st switching valve V13, and are comprised by the groove | channel, hole, etc. which were formed in the 1st spool, for example.

  In the independent position 84, one end of the first connection oil passage 66A is connected to the first transmission oil passage 74 (port 73c), and the other end of the first connection oil passage 66A is connected to the oil discharge passage 77 (port 73f). . That is, the first connection oil passage 66 </ b> A connects the first transmission oil passage 74 and the oil discharge passage 77 at the independent position 84. Thereby, at the independent position 84, the first transmission oil passage 74 communicates with the tank T1 via the first connection oil passage 66A, the drain oil passage 77, the oil passage 78, the relief oil passage 76, the drain oil passage 60, and the like. .

  Further, at the joining position 83, the first connection oil passage 66A is disengaged from the first transmission oil passage 74 (port 73c) and the drain oil passage 77 (port 73f). That is, the first connection oil passage 66 </ b> A releases the connection between the first transmission oil passage 74 and the oil discharge passage 77 at the joining position 83. In other words, at the merging position 83, the connection between the first transmission oil passage 74 and the drainage passage 77 by the first connection oil passage 66A (first return circuit 66) is released.

The first return circuit 66 is a circuit that is connected to the first transmission oil path 74 at the independent position 83 and returns the pressure oil in the first transmission oil path 74 to the tank T <b> 1. Is a circuit that is disconnected.
The second return circuit 67 is a circuit that returns the pressure oil in the second transmission oil passage 75 to the tank T1 at the merge position 83 and the independent position 84.

  Since the first return circuit 66 is disconnected from the first transmission oil path 74 at the merge position 83, the second return circuit 66 is connected when the first transmission oil path 74 and the second transmission oil path 75 are connected. Only the circuit 67 functions as a return circuit for returning the pressure oil in the first transmission oil passage 74 and the second transmission oil passage 75 to the tank T1. Therefore, the pressure oil in the first transmission oil passage 74 and the second transmission oil passage 75 is not excessively returned to the tank T1, and the load pressure in the first transmission oil passage 74 and the second transmission oil passage 75 is favorably increased. To do. As a result, the flow rate control (load sensing control) of the discharge oil of the first pump 27 when the first transmission oil path 74 and the second transmission oil path 75 are connected can be performed satisfactorily.

  Further, since the first return circuit 66 is connected to the first transmission oil passage 74 at the independent position 84, the first return circuit 66 is connected to the first transmission oil passage 74 when the communication between the first transmission oil passage 74 and the second transmission oil passage 75 is released. The pressure oil in the transmission oil passage 74 is returned to the tank T1 by the first return circuit 66, and the pressure oil in the second transmission oil passage 75 is returned to the tank T1 by the second return circuit 67. Accordingly, the flow rate control (load sensing control) of the discharge oil of the first pump 27 when the first transmission oil passage 74 and the second transmission oil passage 75 are shut off can be performed satisfactorily.

Further, by providing the first return circuit 66 in the first switching valve V13, the first return circuit 66 can be easily configured, and the hydraulic circuit can be simplified.
As shown in FIGS. 3, 5, and 6, the first switching valve V13 is switched by the second switching valve V20. The second switching valve V20 is constituted by a direct acting spool type two-position switching valve. The second switching valve V20 is a pilot operation switching valve that is switched by a pilot pressure.

  The second switching valve V20 has a release position 89 and a switching position 90. The second switching valve V <b> 20 is urged in a direction to be switched to the release position 89 by the spring 92. The second switching valve V20 is connected to the input port 22 via the supply oil passage 93, and can supply the discharge oil (pilot oil) discharged from the second pump 28 to the second switching valve V20. The second switching valve V20 is connected to the pressure receiving portion 95 of the first switching valve V13 via a pilot oil passage 94. The pressure receiving unit 95 is a pressure receiving unit that applies switching pressure (pilot pressure) for switching the first switching valve V13 to the independent position 84. At the release position 89, the communication between the supply oil passage 93 and the pilot oil passage 94 is released (communication is cut off), and the pilot oil passage 94 communicates with the tank T1. Accordingly, since the switching pressure (pilot oil) from the supply oil passage 93 is not output at the release position 89 (because pilot pressure does not act on the pressure receiving portion 95), the first switching valve V13 is at the merging position 83. . Further, at the switching position 90, the supply oil passage 93 is connected to the pilot oil passage 94. Therefore, the switching pressure from the supply oil passage 93 is output to the pilot oil passage 94 at the release position 89. As a result, a switching pressure acts on the pressure receiving portion 95, and the first switching valve V13 is switched to the independent position 84.

That is, the second switching valve V20 has a switching position 90 that outputs a switching pressure for switching the first switching valve V13 from the merge position to the independent position 84, and a release position 89 that does not output the switching pressure.
The second switching valve V <b> 20 includes a pressure receiving part 96 and a pressure receiving part 97. One end of a pilot oil passage 98 is connected to the pressure receiving portion 96, and one end of a pilot oil passage 99 is connected to the pressure receiving portion 97. As shown in FIG. 3, the other end of the pilot oil passage 98 is connected to the first detection oil passage 100 at an end block B1. One end of the first detection oil passage 100 is connected to the input port 20. The first detection oil passage 100 is provided from the end block B1 to the control valve V4. The first detection oil passage 100 is provided through the direction switching valve D1, the direction switching valve D2, the direction switching valve D3, and the direction switching valve D4. The other end of the first detection oil passage 100 is connected to the drain oil passage 60 via the oil passage 102 by the control valve V4.

  As shown in FIG. 4, the other end of the pilot oil passage 99 is connected to the second detection oil passage 101 at the end block B2. The second detection oil passage 101 is provided from the end block B2 to the control valve V4. The second detection oil passage 101 is provided through the direction switching valve D11, the direction switching valve D10, the direction switching valve D9, the direction switching valve D8, the direction switching valve D7, the direction switching valve D6, and the direction switching valve D5. ing. The other end of the second detection oil passage 101 is connected to the other end of the first detection oil passage 100 by the control valve V4 and is connected to the drain oil passage 60 through the oil passage 102.

When all the direction switching valves D1 to D11 are in the neutral position (when all the direction switching valves D1 to D11 are not operated), the first detection oil passage 100, the second detection oil passage 101, and the pilot oil passage No pilot pressure is generated in 98 and pilot oil passage 99. In this case, the 2nd switching valve V20 is the cancellation | release position 89, and the 1st switching valve V13 is the merge position 83 (refer FIG. 5).
When any one or more of the direction switching valves D1 to D4 (the dozer device 7, the first traveling device 3L, and the second traveling device 3R) are operated from this state, the middle part of the first detection oil passage 100 is blocked. The As a result, a pilot pressure is generated in the pilot oil passage 98, and the second switching valve V20 is switched to the switching position 90. Then, the pilot pressure acts on the pressure receiving portion 95, and the first switching valve V13 is switched to the independent position 84 (see FIG. 6).

  One or more of the direction switching valves D5 to 11 (hydraulic attachment, arm 16, bucket 17, boom 15, swivel base 2, swing bracket 14) in a state where the first switching valve V13 is switched to the independent position 84. Is operated, the middle part of the second detection oil passage 101 is blocked. As a result, a pilot pressure is generated in the pilot oil passage 99, and a pilot pressure corresponding to the pilot pressure in the pilot oil passage 98 acts on the pressure receiving portion 97. Then, the second switching valve V20 is switched to the release position 89, and the first switching valve V13 is switched to the merge position 83.

The first switching valve V13 is also at the merging position 83 when any one or more of the direction switching valves D5 to D11 are operated without operating the direction switching valves D1 to D4.
As described above, when the hydraulic system drives the working device 4, the first switching valve V13 is in the joining position. Further, when driving the traveling device 3 without driving the work device 4 and when operating at least one of the first traveling device 3L or the second traveling device 3R, the position is switched to the independent position 84.

In addition, when driving the working device 4, the independent position 84 may be set, and when the traveling device 3 is driven, the joining position 83 may be set.
<Switching of relief valve set pressure>
As shown in FIGS. 3, 5, and 6, one end of the switching oil passage 103 is connected to the pilot oil passage 94. The other end of the switching oil passage 103 is connected to the pressure receiving portion 64 of the first relief valve V21. When the pilot pressure does not act on the pilot oil passage 94, the pilot pressure does not act on the switching oil passage 103 and the pressure receiving portion 64, so the set pressure of the first relief valve V21 is the first set pressure. When the pilot pressure acts on the pilot oil passage 94, the pilot pressure acts on the switching oil passage 103 and the pressure receiving portion 64, and is changed to the second set pressure. That is, the first relief valve V21 is a variable relief valve that is switched to the second set pressure by the switching pressure output from the second switching valve V20.

  As shown in FIG. 5, at the merge position 83, the connection between the second connecting oil passage 72 (second hydraulic oil passage 69) and the relief oil passage 76 is released (one end of the relief oil passage 76 is closed). Therefore, the second relief valve V17 does not set the circuit pressure of the second hydraulic oil passage 69. (The second relief valve V17 does not function as a relief valve for setting the circuit pressure of the second hydraulic oil passage 69). The first hydraulic oil passage 68 and the second hydraulic oil passage 69 communicate with each other, and the first relief valve V21 is provided in the first hydraulic oil passage 68. Therefore, in this case, the relief valve that sets the circuit pressure of the first hydraulic oil passage 68 and the second hydraulic oil passage 69 (the circuit pressure of the discharge circuit of the first pump 27) is the first relief valve V21. Further, the set pressure of the first relief valve V21 at this time is the first set pressure. That is, when the working device 4 is driven, the circuit pressures of the first hydraulic oil passage 68 and the second hydraulic oil passage 69 are the first set pressure of the first relief valve V21. The same applies when driving the swivel base 2, the swing bracket 14, and the hydraulic attachment.

  As shown in FIG. 6, at the independent position 84, the second hydraulic oil passage 69 is connected to the relief oil passage 76 via the second connection oil passage 72 and the communication oil passage 88. In this case, the second relief valve V17 functions as a relief valve that sets the circuit pressure of the second hydraulic oil passage 69 (circuit pressure of the discharge circuit of the second pump port P2). Further, at the independent position 84, the first relief valve V21 functions as a relief valve that sets the circuit pressure of the first hydraulic fluid path 68. The set pressure of the first relief valve V21 at this time is a second set pressure that is higher than the first set pressure. The set pressure of the second relief valve V17 is the same set pressure as the second set pressure. That is, when only the traveling device 3 is driven, the circuit pressure is set with a higher set pressure than when the working device 4 is driven. The same applies when only the dozer device 7 and only the traveling device 3 and the dozer device 7 are driven.

As described above, the first relief valve V21 is a relief valve that can set the circuit pressures of the first hydraulic oil passage 68 and the second hydraulic oil passage 69 to the first set pressure at the merge position 83, and is an independent position 84. Thus, the variable relief valve can change the circuit pressure of the first hydraulic oil passage 68 to a second set pressure higher than the first set pressure.
The second relief valve V <b> 17 is a relief valve that sets the circuit pressure of the second hydraulic oil passage 69 at the independent position 84 to the same set pressure as the second set pressure, and at the merging position 83, the second hydraulic oil passage 69. This is a relief valve for releasing the setting of the circuit pressure.

  In the conventional working machine, in addition to the relief valve for driving the working device, in order to maintain the traction force of the traveling device, a relief valve for the first traveling device, a relief valve for the second traveling device, Is provided. That is, three relief valves are provided. However, since hydraulic hoses are concentrated around the control valve, there is a demand for making the hose arrangement space as wide as possible. There is also a desire to reduce the number of components and make them inexpensive.

  In this embodiment, when driving the working device 4, the first relief valve V21 functions, while the second relief valve V17 does not function. When driving the travel devices 3L and 3R without driving the working device 4, the first relief valve V21 functions. Both the first relief valve V21 and the second relief valve V17 function. The first relief valve V21 is used both when driving the working device 4 and when driving the traveling device 3 without driving the working device 4. Note that the set pressure of the first relief valve V21 is changed between when the working device 4 is driven and when the traveling device 3 is driven without driving the working device 4. Thereby, the number of relief valves can be reduced, and the control valve CV1 can be formed compactly. By forming the control valve CV1 in a compact manner, a large space for hose arrangement can be taken. Further, the control valve CV1 can be manufactured at a low cost by reducing the number of parts. In addition, even when the hydraulic system is also used for work machines having different weights, it is possible to secure the traveling traction force of the heavy work machine.

  In the illustrated hydraulic circuit, the pilot pressure for switching the first relief valve V21 is taken from the pilot oil passage 94, but is not limited to this. It is only necessary that the first relief valve V21 be changed to the second set pressure when the first switching valve V13 reaches the independent position 84. For example, the pilot pressure output from the operation valve V27 that operates the control valve V2 and the operation valve V26 that operates the control valve V3 is applied to the first relief valve V21 to change the set pressure of the first relief valve V21. It may be.

In addition, the first relief valve V21 may be electrically switched by a solenoid valve, or the set pressure of the first relief valve V21 may be switched by a pilot pressure from the solenoid valve.
<Return path of hydraulic oil return oil>
As shown in FIG. 7, the hydraulic system has a line switching valve V23. The line switching valve V23 is a two-position switching valve that can be switched between a first switching position 109 and a second switching position 110. The first switching position 109 is a position for returning the return oil returned from the hydraulic actuator connected to the control valve V5 to the control valve V5. The first switching position 109 is a position that allows the return oil that returns from the hydraulic actuator connected to the control valve V5 to be returned to the tank T1 without passing through the control valve V5.

  A return oil path (first return oil path) 111 and a return oil path (second return oil path) 112 are connected to the line switching valve V23. The first return oil path 111 is an oil path that returns the return oil from the hydraulic actuator to the control valve V5. The second return oil passage 112 is an oil passage that returns the return oil from the hydraulic actuator to the tank T1 without passing through the control valve V5. The second return oil passage 112 is connected to an oil passage 114 connected to an oil discharge port (makeup port) 113 of the turning motor M3. A return oil path (third return oil path) 115 and a return oil path (fourth return oil path) 116 are connected to the oil path 114.

The third return oil passage 115 communicates with the tank T1 via the oil cooler 117. The third return oil passage 115 is provided with a check valve V24. As shown in FIG. 4, the fourth return oil passage 116 is connected to a tank port 118 provided in the control valve V8. The tank port 118 communicates with the drain oil passage 60.
Conventionally, when the return oil from the hydraulic actuator is returned to the tank T1 without passing through the control valve V5, it is directly returned to the tank T1. If it does so, heat balance may worsen. Accordingly, when returning the return oil from the hydraulic actuator to the tank T1 without passing through the control valve V5, the deterioration of the heat balance can be prevented by returning it to the tank T1 through the oil cooler 117.

  Further, by connecting the second return oil passage 112 to the turning motor M3, the hydraulic hose constituting the second return oil passage 112 can be passed through a wide space between the turning motor M3 and the control valve CV1. Thereby, when a breaker or the like is used, it is possible to prevent the hydraulic hose from coming into contact with the surrounding portion and being damaged by the pulsation and vibration of the hydraulic hose.

A selection valve V25 may be provided in the second return oil passage 112. The selection valve V25 has a first position 119 for flowing the return oil of the hydraulic actuator to the third return oil passage 115 and a second position 120 for returning the return oil of the hydraulic actuator directly to the tank T1 (without passing through the oil cooler 117). It is a two-position switching valve that can be switched between.
《Brake release circuit of turning brake》
As shown in FIG. 7, the hydraulic system has a brake release circuit 121. The brake release circuit 121 is a circuit that outputs a pilot pressure for releasing the turning brake 122 provided in the turning motor M3 to the brake switching valve V28.

  The turning brake 122 is a negative brake, and includes a brake disk 123, a brake cylinder (hydraulic cylinder) 124, and a brake spring 125. The brake disc 123 is provided so as to be rotatable integrally with the output shaft 126 of the turning motor M3. The brake cylinder 124 extends to press the brake disc 123 to brake the turning motor M3. Further, the brake cylinder 124 contracts to release the pressure on the brake disc 123 and release the braking of the turning motor M3. The brake spring 125 is incorporated in the brake cylinder 124 and biases the brake cylinder 124 in the extending direction. The brake cylinder 124 is contracted by hydraulic pressure.

  The brake switching valve V28 has a port 127, a port 128, and a port 129. As shown in FIG. 1, the port 127 is connected to the output port 32 via the supply oil passage 130, the supply oil passage 40, and the supply oil passage 38. Accordingly, the pilot pressure (pilot oil) discharged from the second pump 28 is supplied to the port 127. The port 128 communicates with the rod side of the brake cylinder 124 (the side opposite to the side where the spring 125 is provided). The port 129 communicates with the tank T1.

  The brake switching valve V28 has a braking position 131 and a release position 132. The braking position 131 is a position where the hydraulic pressure is released from the brake cylinder 124 by connecting the port 128 and the port 129. That is, it is a position where the turning brake 122 is operated. The release position 132 is a position where the hydraulic pressure is supplied to the brake cylinder 124 by connecting the port 127 and the port 128. That is, it is a position where the turning brake 122 is released.

  The turning brake 122 has a delay function for maintaining the brake released state for several seconds when the brake is released from the brake released state. This delay function is constituted by, for example, a throttle 162 provided in a flow path for releasing hydraulic pressure from the brake cylinder 124 at the braking position 131. According to this, when the brake switching valve V28 is switched from the release position 132 to the brake position 131 (when the turning brake 122 is changed from the released state to the activated state), the pressure release from the brake cylinder 124 is delayed by the throttle 162. As a result, the brake release state is maintained for several seconds.

The brake switching valve V28 is biased in a direction to be switched to the braking position 131 by the spring 133, and is switched to the release position 132 by the pilot pressure acting on the pressure receiving port 134.
The brake release circuit 121 has one output port 135, five input ports 136 to 140, and four shuttle valves V30 to 33. The output port 135 is connected to the pressure receiving port 134 via the pilot oil passage 140. Pilot pressure from a remote control valve (operation device) 141 is input to the input ports 136 to 139. Pilot pressure from a remote control valve (operation device) 152 is input to the input port 140.

  The remote control valve 141 is a device that operates the control valve V9 (the swivel base 2) and the control valve V6 (arm 16). The remote control valve 141 has an operation lever 141A. When the operating lever 141A is swung forward, the pilot pressure is output to the control valve V6 so that the arm 16 swings (moves away from the turntable 2 or upwards). When the operating lever 141A is swung later, the pilot pressure is output to the control valve V6 via the pilot oil passage 142 so that the arm 16 is cloud-operated (swung toward or below the swivel 2). Pilot pressure is output to the control valve V9 via the pilot oil passage 144 so that the swivel base 2 turns right when the operation lever 141A is swung to the right. When the operation lever 141A is swung to the left, the pilot pressure is output to the control valve V6 via the pilot oil passage 146 so that the swivel base 2 turns to the left.

The input port 136 is connected to the pilot oil passage 142 via the pilot oil passage 143. The input port 137 is connected to the pilot oil passage 144 via the pilot oil passage 145. The input port 138 is connected to the pilot oil passage 146 via the pilot oil passage 147.
The remote control valve 152 is a device that operates the control valve V11 (swing bracket 14). The remote control valve 152 has an operation lever 152A. Pilot pressure is output to the control valve V11 via the pilot oil passage 148 so that the swing bracket 14 swings to the right when the operation lever 152A swings to the right. Pilot pressure is output to the control valve V11 via the pilot oil passage 150 so that the swing bracket 142 swings to the left when the operation lever 152A swings to the left.

The input port 139 is connected to the pilot oil passage 148 via the pilot oil passage 149. The input port 140 is connected to the pilot oil passage 150 via the pilot oil passage 151.
The shuttle valves V30 to V33 have two input ports and one output port, and output the higher pilot pressure from the output port among the pilot pressures input from the input port (in the case of the same pressure, Hydraulic fluid is output from the open input port).

  One input port of the shuttle valve V30 is connected to the input port 136 via a pilot oil passage 153. The other input port of the shuttle valve V30 is connected to the output port of the shuttle valve V31 via a pilot oil passage 156. The output port of the shuttle valve V30 is connected to one input port of the shuttle valve V33 via a pilot oil passage 157. One input port of the shuttle valve V31 is connected to the input port 137 via a pilot oil passage 154. The other input port of the shuttle valve 31 is connected to the input port 138 via a pilot oil passage 155. One input port of the shuttle valve 32 is connected to the input port 139 via a pilot oil passage 158. The other input port of the shuttle valve 32 is connected to the input port 140 via a pilot oil passage 159. The output port of the shuttle valve 32 is connected to the other input port of the shuttle valve V33 via the pilot oil passage 160.

From the above, when the turning operation of the turntable 2, the cloud operation of the arm 16, and the swinging operation of the swing bracket 14 are not performed, the turning brake 122 is activated. Further, when any one or more of the turning operation of the turntable 2, the swinging operation of the swing bracket 14, and the cloud operation of the arm 16 are performed, the turning brake 122 is released.
The slewing bearing 8 includes an outer race fixed to the frame of the traveling device 3 and an inner race fixed to the swivel base 2, and an internal gear is formed on the inner peripheral surface of the inner race. The turning motor M3 has a pinion that meshes with the internal gear of the turning bearing 8, and turns the turntable 2 by driving the pinion.

  When swinging the swing bracket 14, if the turning brake 122 is in an operating state, a force is applied to the meshing portion between the internal gear and the pinion. In this embodiment, when the swing bracket 14 is operated, the force applied to the meshing portion between the internal gear and the pinion can be released by releasing the turning brake 122. Further, the work device 4 is provided offset from the center of the swivel base 2 to one side (right side). As a result, even when the arm 16 is cloud-operated (pick-up operation), if the turning brake 122 is in an activated state, force is applied to the meshing portion between the internal gear and the pinion, so the turning brake 122 is also released in this case. Like to do.

In addition, a large inertia force is generated when the swing bracket 14 is operated (for example, when soil is piled on the bucket 17 or when the boom 15 and the arm 16 are extended forward). Thus, when the swing of the swing bracket 14 is suddenly stopped, a large force is applied to the meshing portion between the internal gear and the pinion if the turning brake 122 is in an operating state. Also in this case, the force applied to the meshing portion between the internal gear and the pinion can be released. That is, when the operation of the swing bracket 14 is stopped, the swing brake 122 tries to switch from the released state to the activated state, but when the swing brake 122 switches from the released state to the activated state, the swing brake 122 is released for several seconds. Therefore, the force applied to the meshing portion between the internal gear and the pinion can be released.
<Effect>
The hydraulic system for a working machine according to this embodiment includes first control valves V1 and V2 that control a hydraulic actuator, second control valves V3 to V11 that control the hydraulic actuator, a tank T1 that stores hydraulic oil, and hydraulic oil. Is supplied to the first control valves V1 and V2, a first hydraulic oil path 68 that is capable of supplying hydraulic oil to the second control valves V3 to V11, and a first control valve V1. A first transmission oil passage 74 through which the load pressure of the hydraulic actuator controlled by V2 is transmitted, a second transmission oil passage 75 through which the load pressure of the hydraulic actuator controlled by the second control valves V3 to V11 is transmitted, A merging position 83 that communicates the first hydraulic fluid path 68 and the second hydraulic fluid path 69 and communicates the first transmission fluid path 74 and the second transmission fluid path 75, and the first hydraulic fluid path 68 and the second actuation. The communication with the oil passage 69 is released, and the first transmission oil passage 74 2 The first switching valve V13 that can be switched to the independent position 84 for releasing the communication with the transmission oil path 75, and the hydraulic oil in the first transmission oil path 74 connected to the first transmission oil path 74 at the independent position 84. A circuit for returning to the tank T 1, a first return circuit 66 that is disconnected from the first transmission oil path 74 at the merge position 83, and a hydraulic oil for the second transmission oil path 75 at the merge position 83 and the independent position 84. And a second return circuit 67 for returning to the tank T1.

  As a result, the first return circuit 66 is disconnected from the first transmission oil passage 74 at the merge position 83, so when the first transmission oil passage 74 and the second transmission oil passage 75 are connected, Only the second return circuit 67 functions as a return circuit for returning the hydraulic oil in the first transmission oil passage 74 and the second transmission oil passage 75 to the tank T1. Therefore, the load pressure in the first transmission oil passage 74 and the second transmission oil passage 75 is increased well without excessively returning the hydraulic oil in the first transmission oil passage 74 and the second transmission oil passage 75 to the tank T1.

  The first pump port P1 that discharges hydraulic fluid to the first hydraulic fluid passage, the second pump port P2 that discharges hydraulic fluid to the second hydraulic fluid passage, the first pump port or the second pump A controller for controlling the flow rate of hydraulic oil discharged from the first pump port and the second pump port based on a discharge pressure of the port and a load pressure of the first transmission oil passage or the second transmission oil passage; You may have. As a result, the first return circuit 66 is disconnected from the first transmission oil passage 74 at the merge position 83, so when the first transmission oil passage 74 and the second transmission oil passage 75 are connected, Only the second return circuit 67 functions as a return circuit for returning the hydraulic oil in the first transmission oil passage 74 and the second transmission oil passage 75 to the tank T1. Therefore, the load pressure in the first transmission oil passage 74 and the second transmission oil passage 75 is increased well without excessively returning the hydraulic oil in the first transmission oil passage 74 and the second transmission oil passage 75 to the tank T1. When the first transmission oil passage 74 and the second transmission oil passage 75 are connected by increasing the load pressure in the first transmission oil passage 74 and the second transmission oil passage 75 satisfactorily, the first pump It is possible to satisfactorily control the flow rate of the hydraulic oil discharged from the port P1 and the second pump port P2.

Further, by providing the first return circuit 66 in the first switching valve V13, the hydraulic system (hydraulic circuit) can be simplified.
Further, a drain oil passage 77 communicating with the tank T1 is provided, and the first return circuit 66 connects the first transmission oil passage 74 and the drain oil passage 77 at the independent position 84, and the first transmission oil at the junction position 83. A connection oil passage 66A for releasing the connection between the passage 74 and the oil discharge passage 77 and a throttle 66B interposed in the connection oil passage 66A are provided. Thereby, the 1st return circuit 66 can be comprised easily and a hydraulic system (hydraulic circuit) can be simplified.

  Further, the working device 4 having a boom cylinder C3 that drives the boom 15, an arm cylinder C4 that drives the arm 16, and a work tool cylinder C5 that drives the work tool 17, and a first traveling motor M1 is used. 1 traveling device 3L, traveling device 3 having second traveling device 3R driven by second traveling motor M2, boom valve V8 controlling boom cylinder C3, arm valve V6 controlling arm cylinder C4, A work tool valve V7 for controlling the work tool, a first travel valve V2 for controlling the first travel motor M1, and a second travel valve V3 for controlling the second travel motor M2, and a first control valve V1, V2 includes the first travel valve V2, the second control valves V3 to V11 include the second travel valve V3, the boom valve V8, the arm valve V6, and the work tool valve V7 include the first control valves V1, V2, and 2 is included in any one of the control valves V3 to V11 and is switched to the merging position 83 when operating at least one of the boom valve V8, the arm valve V6, and the work tool valve V7, and the travel device 4 is not driven. 3 is switched to the independent position 84 when at least one of the first travel valve V2 or the second travel valve V3 is operated. Thereby, the load pressure in the 1st transmission oil path 74 and the 2nd transmission oil path 75 raises well at the time of work. Therefore, during the operation, the flow rate of the hydraulic oil discharged from the first pump port P1 and the second pump port P2 can be controlled satisfactorily, and workability can be ensured.

  The relief valve sets the circuit pressure of the first hydraulic oil passage 68 and the second hydraulic oil passage 69 to the first set pressure at the merge position 83, and the circuit pressure of the first hydraulic oil passage 68 is set to the independent position 84. A first relief valve V21 that can be set and changed to a second set pressure that is higher than the first set pressure, and a relief valve that sets the circuit pressure of the second hydraulic oil passage 69 at the independent position 84 to the same set pressure as the second set pressure. In addition, the merging position 83 includes a second relief valve V17 that cancels the setting of the circuit pressure of the second hydraulic oil passage 69. As a result, the first relief valve V21 has a relief valve that sets the circuit pressure of the first hydraulic oil passage 68 and the second hydraulic oil passage 69 at the merging position 83, and the circuit pressure of the first hydraulic oil passage 68 at the independent position 84. This can also be used as a relief valve for setting the number of relief valves, and the number of relief valves can be reduced.

  The first switching valve V13 includes a second switching valve having a switching position 90 for outputting a switching pressure for switching the merging position 83 to the independent position 84 and a release position 89 for not outputting the switching pressure, and the first relief valve V21. Is a variable relief valve that is switched to the second set pressure by the switching pressure output from the second switching valve. By using the switching pressure output from the second switching valve as the pressure for switching the first relief valve V21 to the second set pressure, the hydraulic system (hydraulic circuit) can be simplified.

  In addition, a relief oil passage 76 in which a second relief valve V17 is interposed is provided, and the first switching valve V13 communicates the second hydraulic oil passage 69 and the relief oil passage 76 at the independent position 84, and at the joining position 83. The communication oil passage 88 for releasing the communication between the second hydraulic oil passage 69 and the relief oil passage 76 is provided. In other words, the communication oil path 88 is provided in the first switching valve V13, and the second relief valve V17 is switched between the use state and the non-use state by the communication oil path 88. Thereby, a hydraulic system (hydraulic circuit) can be simplified.

  Further, the hydraulic system of the working machine according to the present embodiment includes a tank T1 that stores hydraulic oil, a hydraulic actuator C1, and a plurality of pilot pressure switching valves D1 and D4 that control the hydraulic actuator C1 driven by the hydraulic oil. An operation device 56 capable of operating a plurality of pilot pressure switching valves D1, D4 with hydraulic oil, and a circuit for returning a part of the hydraulic oil for operating the pilot pressure switching valves D1, D4 to the tank T1, And a common air vent circuit 59 for the pilot pressure switching valves D1 and D4. As a result, the amount of leakage of pilot oil from the air vent circuit 59 can be made appropriate, and the pilot circuit 53 that supplies hydraulic oil to the plurality of pilot pressure switching valves D1 and D4 can be sufficiently boosted. . As a result, the stability of the operation of the hydraulic actuator C1 can be improved.

In addition, the air vent circuit 59 is provided for the pilot pressure switching valve D4 on the downstream side of the hydraulic oil passage for flowing the hydraulic oil supplied from the operating device 56 among the plurality of pilot pressure switching valves D1, D4. Yes. As a result, the air present on the upstream side in the hydraulic oil flow channel through which the hydraulic oil supplied from the operating device 56 flows can be extracted well. In other words, the air can be vented well (air venting can be ensured).
The plurality of pilot pressure switching valves D1 and D4 include a first pilot pressure switching valve D1 and a second pilot pressure switching valve D4, and the air vent circuit 59 includes the first pilot pressure switching valve D1 or the second pilot pressure switching valve D1. It is provided on one side of the pressure switching valve D4. As a result, the amount of leakage of pilot oil from the air vent circuit 59 can be made appropriate, and the pilot circuit 53 that supplies hydraulic oil to the first pilot pressure switching valve D1 and the second pilot switching valve D4 can be sufficiently provided. The voltage can be boosted. As a result, the stability of the operation of the hydraulic actuator C1 can be improved.

  In addition, a first supply circuit 54 that supplies hydraulic fluid from the operating device 56 to one of the first pilot pressure switching valve D1 or the second pilot pressure switching valve D4, and the first pilot pressure switching valve D1 or A pilot circuit 53 having a second supply circuit 55 for supplying hydraulic fluid to the other of the second pilot pressure switching valve D4 is provided, and the air vent circuit 59 is connected to the second supply circuit 55. As a result, air existing in the first supply circuit 54 on the upstream side in the pilot circuit 53 can also be extracted well.

The dozer device 7 is provided, and the hydraulic actuator C1 is a dozer cylinder that drives the dozer device 7. Thereby, the stability of the operation of the dozer device 7 can be improved.
As mentioned above, although this invention was demonstrated, it should be thought that embodiment disclosed this time is an illustration and restrictive at no points. The scope of the present invention is defined by the terms of the claims, rather than the description above, and is intended to include any modifications within the scope and meaning equivalent to the terms of the claims.

7 Dozer Device 53 Pilot Circuit 54 First Supply Circuit 55 Second Supply Circuit 56 Operating Device 59 Air Bleed Circuit C1 Hydraulic Actuator (Dozer Cylinder)
D1 1st pilot selector valve D4 2nd pilot selector valve T1 tank

Claims (5)

A tank for storing hydraulic oil;
A hydraulic actuator driven by hydraulic fluid;
A plurality of pilot switching valves for controlling the hydraulic actuator;
An operating device capable of operating the pilot switching valves with hydraulic oil;
A circuit for returning a part of the hydraulic oil for operating the plurality of pilot switching valves to the tank, and a common air vent circuit for the plurality of pilot switching valves;
The working machine's hydraulic system.   The said air vent circuit is provided with respect to the pilot switching valve of the downstream of the hydraulic-fluid channel which flows the hydraulic fluid supplied from the said operating device among these pilot switching valves. Hydraulic system for work equipment. The plurality of pilot switching valves include a first pilot switching valve and a second pilot switching valve;
3. The hydraulic system for a working machine according to claim 1, wherein the air vent circuit is provided on one side of the first pilot switching valve or the second pilot switching valve. A first supply circuit for supplying hydraulic fluid from the operating device to one of the first pilot switching valve or the second pilot switching valve; and the first pilot switching valve or the second pilot switching valve from the first supply circuit. A pilot circuit having a second supply circuit for supplying hydraulic oil to the other of
The working machine hydraulic system according to claim 3, wherein the air vent circuit is connected to the second supply circuit. Equipped with a dozer device,
The hydraulic system for a working machine according to any one of claims 1 to 4, wherein the hydraulic actuator is a dozer cylinder that drives the dozer device.