Hydraulic system for work machine

A hydraulic system for a work machine includes a first control valve including a first direction switch to switch a direction in which the operation fluid is to flow through a first hydraulic actuator and a pressure compensator to maintain a differential pressure to a constant pressure, the differential pressure being a difference between a pressure of the operation fluid to be inputted to the pressure compensator and a pressure of the operation fluid to be outputted from the pressure compensator. And, the hydraulic system includes a second control valve including a second direction switch to switch a direction in which the operation fluid is to flow through a second hydraulic actuator and a flow rate prioritizer to prioritize a flow rate of the operation fluid to be outputted to the second hydraulic actuator.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2015-252270, filed Dec. 24, 2015. The contents of this application are incorporated herein by reference in their entirety.

BACKGROUND OF THE INVENTION

Field of the Invention

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

Discussion of the Background

A work machine described in Japanese Unexamined Patent Publication No. 2013-36276 is previously known. The work machine described in Japanese Unexamined Patent Publication No. 2013-36276 includes a variable displacement axial pump, a plurality of hydraulic actuators (a turn motor, a travel motor, an arm cylinder, a boom cylinder, and a bucket cylinder), and a plurality of control valves configured to control the plurality of hydraulic actuators. Each of the control valves is provided with a pressure compensation valve.

SUMMARY OF THE INVENTION

A hydraulic system for a work machine includes a first hydraulic actuator, a second hydraulic actuator, a hydraulic pump to supply an operation fluid, a first control valve to control the first hydraulic actuator, the first control valve including a first direction switch to switch a direction in which the operation fluid is to flow through the first hydraulic actuator and a pressure compensator to maintain a differential pressure to a constant pressure, the differential pressure being a difference between a pressure of the operation fluid to be inputted to the pressure compensator and a pressure of the operation fluid to be outputted from the pressure compensator. And, the hydraulic system includes a second control valve to control the second hydraulic actuator, the second control valve including a second direction switch to switch a direction in which the operation fluid is to flow through the second hydraulic actuator and a flow rate prioritizer to prioritize a flow rate of the operation fluid to be outputted to the second hydraulic actuator.

DESCRIPTION OF THE EMBODIMENTS

Referring to drawings, an embodiment of the present invention will be described below.

FIG. 3is a schematic view illustrating an overall configuration of a work machine according to an embodiment of the present invention. In the embodiment, the work machine will be explained on the basis of a backhoe that is a turning work machine. The work machine is not limited to the backhoe, and accordingly may be a Skid Steer Loader (SSL), a Compact Track Loader (CTL), and a Tractor, for example.

The work machine1includes a machine body2, a cabin3, a travel device4, and an operation device5.

Hereinafter, in explanations of the embodiment of the present invention and in explanations of the modified examples of the embodiment, a forward direction (a direction shown by an arrowed line F inFIG. 3) corresponds to a front side of an operator seating on an operator seat6of the cabin3, and a backward direction (a direction shown by an arrowed line B inFIG. 3) corresponds to a back side of the operator. In addition, a machine width direction corresponds to a horizontal direction that is a direction perpendicular to a front-back direction K1(refer toFIG. 3).

The machine body2includes a turn base7supported on the travel device4. The turn base7is supported on the travel device4by a turn bearing, and is capable of turning about a longitudinal axis X of the turn bearing, the longitudinal axis X extending vertically. The turn base7is turned by a motive power of a turn motor MT (refer toFIG. 1), the turn motor MT (referred to as a first hydraulic actuator or a second hydraulic actuator) being constituted of a hydraulic motor and the like. The turn base7includes a turn base plate8and a weight9, the turn base plate8being configured to turn about the longitudinal axis X. The turn base plate8is formed of a steel plate and the like, and is coupled to the turn bearing.

The cabin3is mounted on one side portion (on the left side portion) of the turn base plate8in the machine width direction, that is, on the turn base plate8. The operator seat6, an operation device (not shown in the drawings), and the like are disposed inside the cabin3. The travel device4includes a crawler device (a left crawler device)4L disposed on the left and a crawler device (a right crawler device)4R disposed on the right. As shown inFIG. 1, the left crawler device4L includes a left travel motor ML (referred to as a first hydraulic actuator or a second hydraulic actuator) configured to drive a crawler. The right crawler device4R includes a right travel motor MR (referred to as a first hydraulic actuator or a second hydraulic actuator) configured to drive another crawler. A dozer10is disposed on a front portion of the travel device4.

The operation device5is attached to a front portion of the turn base7. The operation device5includes a boom11, an arm12, and an operation tool13. The operation device5further includes a boom cylinder15, an arm cylinder16, and an operation tool cylinder17as hydraulic actuators (referred to as a first hydraulic actuator or a second hydraulic actuator) for the boom11, the arm12, and the operation tool13. Each of the boom cylinder15, the arm cylinder16, and the operation tool cylinder17is constituted of a hydraulic cylinder.

A base portion of the boom11is pivotally supported by a first bracket (a support bracket)20disposed on a right front portion of the turn base plate8, and is capable of turning about a lateral axis (an axis extending in the machine width direction) via a first axial shaft (a lateral shaft)21. A tip end portion of the boom11is pivotally supported to be capable of turning about the lateral axis via a second axial shaft22disposed on a base portion of the arm12. The operation tool13is pivotally supported by a tip end portion of the arm12, and is capable of turning about the lateral axis via a third axial shaft23.

In the embodiment, a bucket is attached as the operation tool13. Instead of and in addition to the bucket13, the operation tool13may be other operation tools (auxiliary attachments referred to as a first hydraulic actuator or a second hydraulic actuator) such as a breaker, an auger, a grapple, a mower.

The boom cylinder15is disposed between a second bracket25and an intermediate portion of the boom11, the intermediate portion being intermediate in a length of the boom11in a longitudinal direction. The second bracket25is disposed on a front portion of the turn base plate8. The second bracket25is provided with a fourth axial shaft (a lateral shaft)26. The fourth axial shaft (a lateral shaft)26is configured to pivotally support a base end portion of the boom cylinder15. When the boom cylinder15is stretched and shortened, the stretching and shortening swing the boom11about the first axial shaft21. The arm cylinder16is disposed between a base portion of the arm12and an intermediate portion of the boom11, the intermediate portion being intermediate in a length of the boom11in a longitudinal direction. When the arm cylinder16is stretched and shortened, the stretching and shortening swing the arm12about the second axial shaft22. The operation tool cylinder17is disposed between the base portion of the arm12and a linkage member. When the operation tool cylinder17is stretched and shortened, the stretching and shortening swing the operation tool13about the third axial shaft23.

Next, a hydraulic system for the work machine will be explained.

FIG. 1illustrates a schematic overall view of the hydraulic system of the work machine. As shown inFIG. 1, the hydraulic system (a hydraulic circuit) includes a hydraulic pump P1. The hydraulic pump P1is configured to discharge an operation fluid (an operation oil). The hydraulic pump P1is a variable displacement axial pump. The hydraulic pump P1is provided with a first hydraulic tube (first hydraulic path)31for feeding the hydraulic oil. A plurality of control valves40are connected to the first hydraulic tube31. The plurality of control valves40are configured to control hydraulic actuators. The hydraulic actuators are devices configured to be operated by the operation fluid, and are, for example, hydraulic cylinders, hydraulic motors, and the like.

The hydraulic system for the work machine includes a first detection fluid tube (first detection fluid path)32, a second detection fluid tube (second detection fluid path)33, a flow rate compensation valve80, and a swash plate control part (swash plate controller)81.

The first detection fluid tube32(also referred to as a PLS fluid tube (PLS fluid path)) is connected to the plurality of control valves40and is also connected to the flow rate compensation valve80. The first detection fluid tube32transmits a “PLS signal pressure” that is the highest load pressure of load pressures of the control valves40. The second detection fluid tube33(also referred to as a PPS fluid tube (PPS fluid path)) connects the flow rate compensation valve80to a discharge side of the hydraulic pump P1. The second detection fluid tube33transmits a “PPS signal pressure” that is a discharge pressure of the operation fluid from the hydraulic pump P1.

The swash plate control part81is a device including a piston, a housing portion, and a rod. The piston is moved by a pressure. The housing portion houses the piston. The rod is coupled to the piston. One end side of the housing portion is connected to the flow rate compensation valve80, and the other end side of the housing portion is connected to the discharge side of the hydraulic pump P1. The rod of the swash plate control part81(a moving portion) is connected to a swash plate of the hydraulic pump P1. Stretching and shortening of the rod change an angle of the swash plate.

The flow rate compensation valve80is a valve capable of controlling the swash plate control part81on the basis of the PLS signal pressure and the PPS signal pressure. The flow rate compensation valve80applies a pressure to one end side of the swash plate control part81, and thereby maintains a pressure difference (a first differential pressure) between the PPS signal pressure and the PLS signal pressure so as to be a pressure preliminarily determined. That is, the flow rate compensation valve80stretches and shortens the rod disposed on the other end side of the swash plate control part81, and thereby maintains the pressure difference (the first differential pressure) between the PPS signal pressure and the PLS signal pressure so as to be constant.

As described above, the angle of the swash plate is changed to maintain the first differential pressure to be constant, and thus a discharge amount of the hydraulic pump P1can be adjusted on the basis of the load pressure. The hydraulic system includes an unload valve83. The unload valve83is connected to a branched fluid tube (branched fluid path)31bbranched from the first fluid tube31. The unload valve83is capable of being switched to a first position83aand a second position83b. The first position83aallows the operation fluid of the first fluid tube31(the branched fluid tube31b) to be discharged to an operation fluid tank14. The second position83ballows the branched fluid tube31bto be closed. The unload valve83is switched depending on the highest load pressure of and the discharge pressure of the hydraulic pump P1, the highest load pressure and the discharge pressure each being inputted to the unload valve83.

The plurality of control valves40will be explained below.

The plurality of control valves40include a boom control valve40A, an arm control valve40B, an operation control valve40C, a first travel control valve40D, a second travel control valve40E, and a turn control valve40F. The boom control valve40A is configured to control the boom cylinder15. The arm control valve40B is configured to control the arm cylinder16. The operation control valve40C is configured to control the operation tool cylinder17. The first travel control valve40D is configured to control the left travel motor ML. The second travel control valve40E is configured to control the right travel motor MR. The turn control valve40F is configured to control the turn motor MT. The plurality of control valves40are not limited to the control valves mentioned in the embodiment.

As described inFIG. 1andFIG. 2, the boom control valve40A includes a first direction switch part (first direction switch)41A and a pressure compensation part (a pressure compensator)42A. The first direction switch part41A is configured to switch a direction of the operation fluid supplied to the boom cylinder15, and is, for example, a three-position switch valve configured to be switched to a first position43, a second position44, and a third position (neutral position)45. In a case where the first direction switch part41A is in the first position43, the first direction switch part41A is switched to a direction allowing the operation fluid to be fed to a bottom side of the boom cylinder15and a direction allowing the operation fluid (return fluid) to be discharged to an operation fluid tank, the operation fluid (return fluid) returning from a rod side of the boom cylinder15. In a case where the first direction switch part41A is in the second position44, the first direction switch part41A is switched to a direction allowing the operation fluid (return fluid) to be discharged to the operation fluid tank, the operation fluid (return fluid) returning from the bottom side of the boom cylinder15and a direction allowing the operation fluid to be fed to the rod side of the boom cylinder15. In a case where the first direction switch part41A is in the third position45, the first direction switch part41A does not feed the operation fluid to the boom cylinder15.

The first direction switch part41A is switched by an operation of a operation member disposed around the operator seat6and the like. For example, the hydraulic system includes another hydraulic pump (referred to as a pilot pump) in addition to the hydraulic pump P1, the hydraulic pump (the pilot pump) being configured to discharge an operation fluid (a pilot fluid) used for control and signal. The pilot pump is connected to a remote control valve through a fluid tube (fluid path), the remote control valve being configured to vary a pressure on the basis of the operation of the operation member; thus the pilot pressure based on the operation is outputted from the remote control valve and is applied to a pressure reception part of the first direction switch part41. The pilot pressure applied to the pressure reception part of the first direction switch part41switches the position of the first direction switch part41. In the example described above, the pilot pressure switches the position of the first direction switch part41A; however, the position of the first direction switch part41A may be switched by an electric power (for example, an electric current) applied to the first direction switch part41A.

A pump port60included in the first direction switch part41A is connected to the branched fluid tube31abranched from the first fluid tube31. The branched fluid tube31asupplies the operation fluid to the first direction switch part41A, the operation fluid being discharged from the hydraulic pump P1. The first direction switch part41A and the second direction switch part42A are connected to each other by a connecting fluid tube (connecting fluid path)34. The connecting fluid tube34includes a first connecting fluid tube34aand a second connecting fluid tube34b. The first connecting fluid tube34ais a fluid tube (fluid path) connecting a first output port61of the first direction switch part41A to an input port62of the pressure compensation part42A. The second connecting fluid tube34bis a fluid tube (fluid path) connecting the pump port60of the first direction switch part41A to the first output port61of the first direction switch part41A. The second connecting fluid tube34bis formed in the first direction switch part41A.

The pressure compensation part42A and the boom cylinder15are connected to each other by a connecting fluid tube (connecting fluid path)35. The connecting fluid tube35includes a first connecting fluid tube35a, a second connecting fluid tube35b, a third connecting fluid tube35c, and a fourth connecting fluid tube35d. The first connecting fluid tube35ais a fluid tube (fluid path) connecting an output port67of the pressure compensation part42A to a first input port63of the first direction switch part41A. The second connecting fluid tube35bis a fluid tube (fluid path) connecting the output port67of the pressure compensation part42A to a second input port64of the first direction switch part41A. The third connecting fluid tube35cis a fluid tube (fluid path) connecting a second output port65of the first direction switch part41A to a port of the bottom side of the boom cylinder15. The fourth connecting fluid tube35dis a fluid tube (fluid path) connecting a third output port66of the first direction switch part41A to a port of the rod side of the boom cylinder15. The output port67of the pressure compensation part42A is connected to the first detection fluid tube32via a check valve68.

The pressure compensation part42A is a pressure compensation valve. The pressure compensation part42A sets a differential pressure to be in a preliminarily determined range (to be a preliminarily determined value), the differential pressure being generated between a pressure of the operation fluid inputted to the pressure compensation part42A and a pressure of the operation fluid to be outputted from the pressure compensation part42A. In other words, the pressure compensation part42A maintains a differential pressure to be constant, the differential pressure being generated between in front of and behind a spool of the first direction switch part41A (a differential pressure between a pressure of the operation fluid on an upper stream side and a pressure of the operation fluid on a downstream side), and thereby the pressure compensation part42A branches the operation fluid so that the operation fluid has an amount based on an operation amount of the operation member. For details, the pressure compensation part42A includes a pressure reception part (pressure receptor)42A1and a pressure reception part (pressure receptor)42A2. The pressure reception part42A1is configured to receive a pressure of the operation fluid inputted to the input port62. The pressure reception part42A2is configured to receive a pressure of the operation fluid to be outputted from the output port67. The input port62and the pressure reception part42A1are connected to each other by a connecting fluid tube36. The output port67and the pressure reception part42A2are connected to each other by a connecting fluid tube37.

In this manner, the pressure of the operation fluid outputted from the first direction switch part41A to the pressure compensation part42A is applied to the pressure reception part42A1, and the pressure of the operation fluid to be outputted from the output port67of the pressure compensation part42A is applied to the pressure reception part42A2. Then, the spool of the pressure compensation part42A moves depending on the pressure difference between both of the operation fluids, and thus the pressure compensation part42A varies an opening area.

As shown inFIG. 1, the arm control valve40B includes a first direction switch part (first direction switch)41B and a pressure compensation part (pressure compensator)42B. The operation control valve40C includes a first direction switch part (first direction switch)41C and a pressure compensation part (pressure compensator)42C. The first travel control valve40D includes a first direction switch part (first direction switch)41D and a pressure compensation part (pressure compensator)42D. The second travel control valve40E includes a first direction switch part (first direction switch)41E and a pressure compensation part (pressure compensator)42E. The first direction switch part41B, the first direction switch part41C, the first direction switch part41D, and the first direction switch part41E are three-position switch valves. And thus, the hydraulic actuators are controlled in a method same as the method of the first direction switch part41A described above. The explanation of the controls is omitted.

The pressure compensation part42B, the pressure compensation part42C, the pressure compensation part42D, and the pressure compensation part42E are pressure compensation valves. And thus, the differential pressure generated between a pressure of the operation fluid inputted to the pressure compensation valve and a pressure of the operation fluid to be outputted from the pressure compensation valve is set to be in a preliminarily determined range in a method same as the method of the pressure compensation part42A described above. The explanation of the setting is omitted. In addition, the first fluid tube31, the first direction switch parts41B,41C,41D, and41E, the pressure compensation parts42B,42C,42D, and42E, and the hydraulic actuators (the arm cylinder16, the operation tool cylinder17, the left travel motor ML, and the right travel motor MR) are connected in a method same as the methods of the first direction switch part41A and the pressure compensation part42A. The explanation of the connections is omitted. That is, configurations of the connecting fluid tubes34(the first connecting fluid tube34aand the second connecting fluid tube34b), the connecting fluid tubes35(the first connecting fluid tube35a, the second connecting fluid tube35b, the third connecting fluid tube35c, and the fourth connecting fluid tube35d), the connecting fluid tube36, and the connecting fluid tube37are capable of being applied to the control valves (the arm control valve40B, the operation control valve40C, the first travel control valve40D, and the second travel control valve40E) other than the boom control valve40A. The explanation of the configurations is omitted.

As described above, the hydraulic system controls a discharge rate of the hydraulic pump P1on the basis of the highest load pressure in the operation of the hydraulic actuators. On the other hand, the pressure compensation parts described above compensate the pressures of the operation fluids to be supplied to the hydraulic actuators. The hydraulic system according to the embodiment is capable of prioritizing a flow rate of the operation fluid to be supplied to the hydraulic actuator. For convenience of explanation, a control valve having a pressure compensation part configured to compensate a pressure of the operation fluid may be referred to as a “first control valve”, and a control valve capable of prioritizing the flow rate of the operation fluid may be referred to as a “second control valve”. In the embodiment, the boom control valve40A, the arm control valve40B, the operation control valve40C, the first travel control valve40D, and the second travel control valve40E serve as the first control valve. The turn control valve40F serves as the second control valve.

As shown inFIG. 1andFIG. 2, the turn control valve40F includes a second direction switch part (second direction switch)41F and a flow rate prioritizing part (flow rate prioritizer)42F. The second direction switch part41F is configured to switch a direction of the operation fluid flowing to the turn motor MT, and is, for example, a three-position switch valve configured to be switched to a first position46, a second position47, and a third position (neutral position)48.

In a case where the second direction switch part41F is in the first position46, the second direction switch part41F is switched to a direction allowing the operation fluid to be fed to one side of the turn motor MT and a direction allowing the operation fluid (return fluid) to be discharged to the operation fluid tank, the operation fluid (return fluid) returning from the other side of the turn motor MT.

In a case where the second direction switch part41F is in the second position47, the second direction switch part41F is switched to a direction allowing the operation fluid to be fed to the other side of the turn motor MT and a direction allowing the operation fluid (return fluid) to be discharged to the operation fluid tank, the operation fluid (return fluid) returning from the one side of the turn motor MT.

In a case where the second direction switch part41F is in the third position48, the second direction switch part41F does not feed the operation fluid to the turn motor MT. The second direction switch part41F is switched by an operation of an operation member disposed around the operator seat6and the like.

The flow rate prioritizing part42F is a valve configured to move a spool to prioritize a flow rate of the operation fluid to be outputted to the hydraulic actuator. The spool of the flow rate prioritizing part42F is capable of moving between a first position50aand a second position50b. The first position50ais a position allowing a flow rate of the operation fluid to be increased, the operation fluid being to be outputted from the second direction switch part41F. The second position50bis a position allowing the flow rate of the operation fluid to be reduced, the operation fluid being to be outputted from the second direction switch part41F.

That is, the flow rate of the operation fluid of the case where the flow rate prioritizing part42F is in the first position50ais larger than a flow rate of the operation fluid at an intermediate position between the first position50aand the second position50b, and the flow rate of the operation fluid of the case where the flow rate prioritizing part42F is in the second position50bis smaller than the flow rate of the operation fluid at the intermediate position.

The flow rate prioritizing part42F includes a pressing member51, a first pressure reception part52, and a second pressure reception part53. The pressing member51is disposed on a side close to the first position50a. The pressing member51presses the spool of the flow rate prioritizing part42F toward the first position50a, that is, an opening side. The pressing member51is, for example, constituted of a spring.

Regarding the pressing member51(the spring52), a force pressing the spool toward the first position50a, that is, a set pressure (a second differential pressure) of the flow rate prioritizing part42F in fully stroking the spool (at the maximum area) is set to be equal to or less than a first differential pressure that is a differential pressure between the PPS signal pressure and the PLS signal pressure.

The flow rate outputted from the flow rate prioritizing part42F may be larger than the flow rate at a solo operation of the hydraulic actuator when the set pressure in the flow rate prioritizing part42F (the set pressure by the spring51) exceeds the first differential pressure.

In this embodiment, the pressing member51is constituted of a spring to press the spool toward the first position50a. However, the spool may be pressed by a pressure of the operation fluid (a pressure of the pilot fluid). For example, the flow rate prioritizing part42F can be provided with a pressure reception part such as a control pin used for pressing the spool, and in this manner, the pilot pressure can be applied to the pressure reception part.

The pilot pressure to be applied to the pressure reception part may be a pressure of the remote control valve that varies the pilot pressure in accordance with an operation of the operation member, and may be a pressure obtained by depressurizing the pressure of the remote control valve with a depressurizing valve.

The first pressure reception part52is configured to receive a pressure of the operation fluid outputted from the second direction switch part41F. The second pressure reception part53is configured to receive a pressure of the operation fluid discharged from the hydraulic pump P1to the turn control valve40F. In other words, the second pressure reception part53is configured to receive a pressure of the operation fluid on an upper steam side of the spool of the second direction switch part41F.

The flow rate prioritizing part42F and the second direction switch part41F are connected to each other by a connecting fluid tube (second fluid tube)70. The connecting fluid tube (second fluid tube)70includes a first connecting fluid tube (first connecting fluid path)70aand a second connecting fluid tube (second connecting fluid path)70b, and a third connecting fluid tube (third connecting fluid path)70c.

The first connecting fluid tube70ais a fluid tube (fluid path) connecting a first output port61of the second direction switch part41F to an input port55of the flow rate prioritizing part42F.

The second connecting fluid tube70bis a fluid tube (fluid path) connecting a pump port60of the second direction switch part41F to the first output port61of the second direction switch part41F. The second connecting fluid tube70bis formed in the second direction switch part41F. The third connecting fluid tube70cis a fluid tube (fluid path) connecting the input port55of the flow rate prioritizing part42F to the first pressure reception part52.

The first hydraulic tube31and the second pressure reception part53of the flow rate prioritizing part42F are connected to each other by a connecting hydraulic tube (third hydraulic tube)71. In particular, the connecting hydraulic tube (third hydraulic tube)71is a hydraulic tube connecting the branched hydraulic tube31aof the first hydraulic tube31to the second pressure reception part53.

The flow rate prioritizing part42F and the turn motor MT are connected to each other by a connecting hydraulic tube72. The connecting hydraulic tube72includes a first connecting hydraulic tube72a, a second connecting hydraulic tube72b, a third connecting hydraulic tube72c, and a fourth connecting hydraulic tube72d.

The first connecting hydraulic tube72ais a hydraulic tube connecting the output port56of the flow rate prioritizing part42F to the first input port63of the second direction switch part41F.

The second connecting hydraulic tube72bis a hydraulic tube connecting the output port56of the flow rate prioritizing part42F to the second input port64of the second direction switch part41F.

The third connecting hydraulic tube72cis a hydraulic tube connecting the second output port65of the second direction switch part41F to a port of one side of the turn motor MT.

The fourth connecting hydraulic tube72dis a hydraulic tube connecting the third output port66of the second direction switch part41F to a port of the other side of the turn motor MT.

The output port56of the flow rate prioritizing part42F is connected to the first detection fluid tube32via a check valve69.

The spool of the flow rate prioritizing part42F accordingly is pressed to the first position50aby a pressure of the operation fluid, the pressure being received by the first pressure reception part52, (a pressure of the operation fluid outputted from the first output port61of the second direction switch part41F) and by the pressing member51. In addition, the spool is pressed to the second position50bby a pressure of the operation fluid, the pressure being received by the second pressure reception part53, (a pressure of the operation fluid on an upper stream side of the spool of the second direction switch part41F).

As described above, according to the hydraulic system, in a multi operation where the boom cylinder15, the arm cylinder16, and the turn motor MT are operated at the same time, a flow rate outputted from the flow rate prioritizing part42F is set to be constant. For example, it is supposed that a load pressure of the boom cylinder15in operation is 10 MPa, a load pressure of the arm cylinder16in operation is 5 MPa, a load pressure of the turn motor MT in operation is 3 MPa, and the set pressure of the flow rate compensation valve80is 1.4 MPa. In that case, the highest load pressure of the operation fluid is 10 MPa, and a pressure of the operation fluid discharged from the hydraulic pump P1is 11.4 MPa. Here, supposing that the set pressure in the flow rate prioritizing part42F is 1.0 MPa, the spool of the flow rate prioritizing part42F moves to vary the opening area of the flow rate prioritizing part42F, and thereby the set pressure is maintained to 1.0 MPa. Thus, a flow rate outputted from the flow rate prioritizing part42F is set to be constant.

In other words, a differential pressure between in front of and behind the second direction switch part41F is set to 1.0 MPa by the flow rate prioritizing part42F (the flow rate prioritizing part42F generates a pressure loss of 1.0 MPa), the operation fluid can be supplied preferentially to the turn motor MT regardless of the loads of the boom cylinder15and the arm cylinder16.

Accordingly, a flow rate of the operation fluid to be outputted from a preliminarily determined control valve can be sufficiently obtained even in the work machine having a pressure compensation part. In particular, the operation fluid can be supplied to the hydraulic actuator without a conventional priority valve.

In addition, in a configuration of a single pump LS (load sensing system) where a single hydraulic pump P1operates the plurality of hydraulic actuators, differentiation of a turn speed between the solo operation and the multi operation can be reduced.

Also in a configuration of two pump LSs where two hydraulic pumps P1operate the plurality of hydraulic actuators, differentiation of a turn speed between the solo operation and the multi operation can be reduced in the same manner.

In a conventional technique, a work machine having an unload valve controls the flow rate with the differential pressure for the unloading fluctuated with respect to movement of the spool (an opening area of the spool) of the control valve in a case of a slightly-moving operation (an unload area).

That is, in the conventional technique, the operation cannot be controlled in proportion to the opening area of the spool of the control valve in the slightly-moving operation (the unload area); however, in the hydraulic system according to the embodiment of the present invention, the control valve40controls the differential pressure between in front of and behind a main spool to be constant by using the spring51, and in this manner, the hydraulic system is capable of supplying a flow rate to the hydraulic actuator in proportion to the opening area of the spool even in the unload area.

Even in the solo operation where the turn motor MT is solely operated (without operating other control valve), the flow rate outputted from the flow rate prioritizing part42F can be set to be constant. That is, even in the solo operation, the operation fluid can be supplied preferentially from the second direction switch part41F toward the turn motor MT.

In the embodiment, the turn control valve40F is exemplified as a second control valve having the second direction switch part and the flow rate prioritizing part. The second control valve however may be other control valves. For example, the hydraulic system may include a control valve (auxiliary control valve) configured to control a hydraulic actuator of an auxiliary attachment (an operation tool referred to as a first hydraulic actuator or a second hydraulic actuator), and the auxiliary control valve may be employed as the second control valve. In this manner, in a case where the auxiliary attachment is disposed on a tip end of the arm12for example, the operation fluid can be supplied preferentially to the auxiliary attachment, and thus the auxiliary attachment can be operated stably.

In addition, the travel control valve configured to control the travel device may be employed as the second control valve. In this manner, the operation fluid can be supplied preferentially to the travel device, and thus the travel device can be operated stably.

According to the embodiment described above, even in the configuration having the pressure compensation part, the operation fluid can be supplied preferentially to a preliminarily determined hydraulic actuator.

In the above description, the embodiment of the present invention has been explained. However, all the features of the embodiments disclosed in this application should be considered just as examples, and the embodiments do not restrict the present invention accordingly. A scope of the present invention is shown not in the above-described embodiments but in claims, and is intended to include all modifications within and equivalent to a scope of the claims.