Patent Publication Number: US-2023160179-A1

Title: Hydraulic system for working machine

Description:
CROSS REFERENCE TO RELATED APPLICATIONS 
     This is a divisional of U.S. patent application Ser. No. 17/487,747, filed Sep. 28, 2021, which claims the benefit of priorities to Japanese Patent Application No. 2020-172797 filed on Oct. 13, 2020, and Japanese Patent Application No. 2020-165780 filed on Sep. 30, 2020. The disclosure of each of the above-mentioned documents, including the specification, drawings, and claims, is incorporated herein by reference in its entirety. 
    
    
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a hydraulic system for a working machine such as a skid steer loader or a compact track loader 
     Description of the Related Art 
     Japanese Unexamined Patent Publication No. 2016-125560 (Patent Document 1) discloses a working machine such as a skid steer loader or a compact track loader provided with a variable displacement pump and a plurality of control valves. 
     The working machine of Patent Document 1 includes a variable displacement hydraulic pump configured to change a flowrate of hydraulic fluid to be delivered, a plurality of hydraulic actuators to be operated with the hydraulic fluid, and a plurality of control valves each of which is configured to be shifted between a plurality of positions and control a flowrate of fluid to each of the hydraulic actuators according to its position-shift. 
     In addition, the working machine of Patent Document 1 includes a hydraulic fluid passage through which hydraulic fluid supplied from a main pump, an increasing fluid passage for increasing the hydraulic fluid in the hydraulic fluid passage by supplying hydraulic fluid supplied from a sub-pump different from the main pump, the increasing fluid passage being connected to the hydraulic fluid passage, a connecting device provided on an end portion of the hydraulic fluid passage connected to the increasing fluid passage, the connecting device being provided for connecting a hydraulic actuator, a high-flow valve provided in the increasing fluid passage and configured to control the increasing of hydraulic fluid in the increasing fluid passage, and a controller configured to control the increase of hydraulic fluid in the high-flow valve depending on types of operation means. 
     SUMMARY OF THE INVENTION 
     In the working machine of Patent Document 1, due to the variability in the flowrate of hydraulic fluid to be delivered by the variable displacement hydraulic pump, each of the hydraulic actuators can be supplied with hydraulic fluid whose flowrate corresponds to its required flowrate. Specifically, a small amount of hydraulic fluid can be supplied to a hydraulic actuator configured to be operated with a small amount of hydraulic fluid, and a large amount of hydraulic fluid can be supplied to a hydraulic actuator configured to be operated with a large amount of hydraulic fluid. In the working machine of Patent Document 1, the flowrate of hydraulic fluid is made variable by operating the variable displacement hydraulic pump so that an LS (Load Sensing) differential pressure is kept constant, but a horsepower loss may cause depending on a generated amount of the LS differential pressure. 
     To solve the above-mentioned problems of the conventional technique, a hydraulic system for a working machine capable of easily suppressing a horsepower loss is desired. 
     Technical solution means is characterized by the following points. 
     In an aspect, a hydraulic system for a working machine includes a variable displacement hydraulic pump to deliver hydraulic fluid having a variable flowrate, a plurality of hydraulic actuators actuated with hydraulic fluid, a plurality of control valves each of which is shiftable among a plurality of shift positions so that the control valve, when shifted to a shift position serving as one of the shift positions, controls a flowrate of hydraulic fluid flowing to the corresponding hydraulic actuator in correspondence to the shift position, a detection fluid passage, an interlocking control valve fluidly connected to the detection fluid passage, and a pressure detection unit for detecting a pilot pressure in the detection fluid passage. Each of the control valves includes an input port into which hydraulic fluid delivered from the variable displacement hydraulic pump is input, an output port from which the hydraulic fluid input into the input port is output, and a flowrate reduction section configured so that, when the control valve is shifted to a reduction position serving as a specific one of the shift positions, the flowrate reduction section reduces a flowrate of the hydraulic fluid entering the input port and outputs the flowrate-reduced hydraulic fluid to the output port. One of the control valves includes a flowrate increase section configured so that, when the control valve is shifted to an increase position serving as another of the shift positions different from the reduction position, the flowrate increase section outputs the hydraulic fluid having entered the input port to the output port at a flowrate larger than that of hydraulic fluid output by the flowrate reduction section. The interlocking control valve is configured to be shifted in accordance with a shift of the one of the control valves among the shift positions and to be shifted to a blocking position to block a pilot fluid introduced into the interlocking control valve from the detection fluid passage when the one of the control valves is shifted to the increase position. 
     The hydraulic system for the working machine further includes an operation member, a controller configured or programmed to output a control signal in accordance with an operation amount of the operation member, and an actuation valve configured to change a pilot pressure output therefrom in accordance with the control signal from the controller. The operation member is for operation of an auxiliary actuator included in the plurality of hydraulic actuators. The one of the control valves is an auxiliary control valve to control the auxiliary actuator. The actuation valve is fluidly connected to either a pressure-receiving portion of the auxiliary control valve for receiving a pilot pressure or a pressure-receiving portion of the interlocking control valve for receiving a pilot pressure. The controller is configured or programmed to, when the operation amount of the operation member is not less than a threshold, shift the auxiliary control valve to the increase position by increasing the pilot pressure output from the actuation valve so as to increase the pilot pressure detected by the pressure detection unit to a value not less than the threshold. 
     The plurality of hydraulic actuators further include a boom cylinder and a working tool cylinder. The plurality of control valves further include a boom control valve to control the boom cylinder and a working tool control valve to control the working tool cylinder. The controller is configured or programmed to, when the auxiliary control valve is shifted to the increase position and either the boom control valve or the working tool control valve is shifted to the reduction position, shift the auxiliary control valve to the reduction position by reducing the pilot pressure output from the actuation valve so as to reduce the pilot pressure in the detection fluid passage to a value less than the threshold. 
     The controller is configured or programmed to change the control signal output therefrom to the actuation valve to change the pilot pressure, and to store a value of the control signal when the pilot pressure detected by the pressure detection unit is a value not less than the threshold. 
     In another aspect, a hydraulic system for a working machine includes a variable displacement hydraulic pump to deliver hydraulic fluid having a variable flowrate, a plurality of hydraulic actuators actuated with hydraulic fluid, a plurality of control valves each of which is shiftable among a plurality of shift positions so that the control valve, when shifted to a shift position serving as one of the shift positions, controls a flowrate of hydraulic fluid flowing to the corresponding hydraulic actuator in correspondence to the shift position, a detection fluid passage, an interlocking control valve fluidly connected to the detection fluid passage, and a pressure detection unit for detecting a pilot pressure in the detection fluid passage. Each of the control valves includes an input port into which hydraulic fluid delivered from the variable displacement hydraulic pump is input, an output port from which the hydraulic fluid input into the input port is output, and a flowrate reduction section configured so that, when the control valve is shifted to a reduction position serving as a specific one of the shift positions, the flowrate reduction section reduces a flowrate of the hydraulic fluid entering the input port and outputs the flowrate-reduced hydraulic fluid to the output port. One of the control valves includes a flowrate increase section configured so that, when the control valve is shifted to an increase position serving as another of the shift positions different from the reduction position, the flowrate increase section outputs the hydraulic fluid having entered the input port to the output port at a flowrate larger than that of hydraulic fluid output by the flowrate reduction section. The interlocking control valve is configured to be shifted in accordance with a shift of the one of the control valves among the shift positions and to be shifted to an opening position to allow a pilot fluid introduced into the interlocking control valve from the detection fluid passage to pass through the interlocking control valve when the one of the control valves is shifted to the increase position. 
     The hydraulic system for the working machine further includes an operation member, a controller configured or programmed to output a control signal in accordance with an operation amount of the operation member, and an actuation valve configured to change a pilot pressure output therefrom in accordance with the control signal from the controller. The operation member is for operation of an auxiliary actuator included in the plurality of hydraulic actuators. The one of the control valves is an auxiliary control valve to control the auxiliary actuator. The actuation valve is fluidly connected to either a pressure-receiving portion of the auxiliary control valve for receiving a pilot pressure or a pressure-receiving portion of the interlocking control valve for receiving a pilot pressure. The controller is configured or programmed to, when the operation amount of the operation member is not less than a threshold, shift the auxiliary control valve to the increase position by reducing the pilot pressure output from the actuation valve so as to reduce the pilot pressure detected by the pressure detection unit to a value less than the threshold. 
     The plurality of hydraulic actuators further include a boom cylinder and a working tool cylinder. The plurality of control valves further include a boom control valve to control the boom cylinder and a working tool control valve to control the working tool cylinder. The controller is configured or programmed to, when the auxiliary control valve is shifted to the increase position and either the boom control valve or the working tool control valve is shifted to the reduction position, shift the auxiliary control valve to the reduction position by increasing the pilot pressure output from the actuation valve so as to increase the pilot pressure in the detection fluid passage to a value not less than the threshold. 
     The controller is configured or programmed to change the control signal output therefrom to the actuation valve to change the pilot pressure, and to store a value of the control signal when the pilot pressure detected by the pressure detection unit is a value less than the threshold. 
     According to the configuration, a horsepower loss can be minimized as much as possible. 
     The above and other elements, features, steps, characteristics and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiments with reference to the attached drawings. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of preferred embodiments of the present invention and many of the attendant advantages thereof will be readily obtained as the same becomes better understood by reference to the following detailed description when considered in connection with the accompanying drawings described below. 
         FIG.  1    is a schematic view of a hydraulic system for a working machine according to a first embodiment. 
         FIG.  2    is an enlarged view of a plurality of control valves. 
         FIG.  3    is a view showing a flowrate Q 1  of a first auxiliary control valve. 
         FIG.  4 A  is a schematic view of a hydraulic system for a working machine according to a second embodiment. 
         FIG.  4 B  is an enlarged view of a plurality of control valves. 
         FIG.  4 C  is a view showing a modified example of the second embodiment. 
         FIG.  4 D  is a view showing a modified example of a second auxiliary control valve. 
         FIG.  4 E  is a view showing a modified example of the auxiliary control valve and a proportional valve. 
         FIG.  4 F  is a view showing a modified example of the second auxiliary control valve. 
         FIG.  5    is a view showing a flowrate Q 3  that is a total of a flowrate Q 1  of the first auxiliary control valve and a second rate Q 2  of the second auxiliary control valve. 
         FIG.  6 A  is a schematic view of a hydraulic system for a working machine according to a third embodiment. 
         FIG.  6 B  is a view showing a modified example of the third embodiment. 
         FIG.  6 C  is a view showing a modified example different from  FIGS.  6 A and  6 B . 
         FIG.  7 A  is a view showing a change in a pilot pressure applied when a second auxiliary control valve  56 D of  FIG.  6 A . 
         FIG.  7 B  is a view showing a change in a pilot pressure applied when the second auxiliary control valve  56 D of  FIG.  6 B . 
         FIG.  7 C  is a view showing a change in a pilot pressure applied when the second auxiliary control valve  56 D of  FIG.  6 C . 
         FIG.  8    is a schematic view of a hydraulic system for a working machine according to a fourth embodiment. 
         FIG.  9    is a view showing a relationship between the pilot pressure and an operation amount. 
         FIG.  10 A  is a view showing a modified example of the hydraulic system for the working machine according to the fourth embodiment. 
         FIG.  10 B  is a view showing a modified example different from  FIG.  10 A . 
         FIG.  11 A  is a view showing a modified example of  FIG.  4 A . 
         FIG.  11 B  is a view showing a modified example of  FIG.  11 A . 
         FIG.  11 C  is a view showing a modified example of  FIG.  11 B . 
         FIG.  12 A  is a schematic view of a hydraulic system for a working machine according to a fifth embodiment. 
         FIG.  12 B  is a view showing a modified example of the hydraulic system for the working machine according to the fifth embodiment. 
         FIG.  12 C  is a view showing a modified example of the hydraulic system for the working machine according to the fifth embodiment. 
         FIG.  12 D  is a schematic view of a hydraulic system for a working machine according to a sixth embodiment. 
         FIG.  12 E  is a view showing a modified example of a throttle in the hydraulic system for the working machine. 
         FIG.  12 F  is a view showing a modified example of the throttle in the hydraulic system for the working machine. 
         FIG.  12 G  is a view showing a modified example of  FIG.  12 D . 
         FIG.  13    is a side view showing a track loader that is an example of the working machine. 
     
    
    
     DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS 
     The preferred embodiments will now be described with reference to the accompanying drawings, wherein like reference numerals designate corresponding or identical elements throughout the various drawings. The drawings are to be viewed in an orientation in which the reference numerals are viewed correctly. 
     Some preferred embodiments of a hydraulic system for a working machine and of a working machine having the hydraulic system will be described below with reference to drawings. 
     First Embodiment 
     First, an overall configuration of a working machine will be explained. As shown in  FIG.  13   , the working machine  1  includes a machine body  2 , a cabin  3 , a working device  4 , and traveling devices  5 . In  FIG.  13   , a compact track loader is shown as an example of the working machine; however, the working machine is not limited to the compact track loader, and may be, for example, a tractor, a skid steer loader, a backhoe, or the like. In the present invention, a direction corresponding to a forward direction (leftward in  FIG.  13   ) of a driver seated on a driver&#39;s seat  8  of the working machine is referred to as “front” or “forward”, a direction corresponding to a rearward direction (rightward in  FIG.  13   ) of the driver is referred to as “rear” or “rearward”, a direction corresponding to a leftward direction (toward a front surface side of  FIG.  13   ) of the driver is referred to as “left” or “leftward”, and a direction corresponding to a rightward direction (toward a back surface side of  FIG.  13   ) of the driver is referred to as “right” or “rightward”. 
     The cabin  3  is mounted on the machine body  2 . The cabin  3  incorporates the driver seat  8 . The working device  4  is attached to the machine body  2 . The traveling devices  5  are arranged on the outside of the machine body  2 . A prime mover is mounted on a rear inside portion of the machine body  2 . The working device  4  includes booms  10 , a working tool  11 , lift links  12 , control links  13 , boom cylinders  14 , and working tool cylinders  15 . 
     The booms  10  are arranged on right and left sides of the cabin  3  swingably up and down. The working tool  11  is a bucket, for example. The bucket  11  is arranged at tip portions (that is, front end portions) of the booms  10  movably up and down. The lift links  12  and the control links  13  support base portions (that is, rear portions) of the booms  10  so that the booms  10  can be swung up and down. The boom cylinders  14  are extended and contracted to lift and lower the booms  10 . The working tool cylinders  15  are extended and contracted to swing the bucket  11 . 
     Front portions of the right and left booms  10  are connected to each other by a deformed connecting pipe. Base portions (that is, rear potions) of the booms  10  are connected to each other by a circular connecting pipe. 
     The lift links  12 , control links  13 , and boom cylinders  14  are arranged on right and left sides of the machine body  2  to correspond to the right and left booms  10 . The lift links  12  are extended vertically from rear portions of the base potions of the booms  10 . An upper portion (one end portion) of each of the lift links  12  is pivotally supported via each of pivot shafts  16  on a rear portion of a base portion of each of the booms  10  rotatably around a lateral axis defined by the pivot shaft  16 . In addition, a lower portion (the other end portion) of each of the lift links  12  is pivotally supported via each of pivot shafts  17  on a rear portion of the machine body  2  rotatably around a lateral axis defined by the pivot shaft  17 . The pivot shafts  17  are provided below the pivot shafts  16 . 
     An upper portion of each of the boom cylinders  14  is pivotally supported by each of pivot shafts  18  rotatably around a lateral axis defined by the pivot shaft  18 . Each of the pivot shafts  18  is provided on a front portion of a base portion of each of the booms  10 . A lower portion of the boom cylinder  14  is pivotally supported by each of pivot shafts  19  rotatably around a lateral axis defined by the pivot shaft  19 . The pivot shafts  19  are provided on a lower rear portion of the machine body  2  and below the pivot shafts  18 . 
     The control links  13  are provided in front of the lift links  12 . One end of each of the control links  13  is pivotally supported by each of the pivot shafts  20  rotatably around a lateral axis defined by the pivot shaft  20 . The pivot shafts  20  are provided on the machine body  2  forward of the lift links  12 . The other end of each of the control links  13  is pivotally supported by each of the pivot shafts  21  rotatably around a lateral axis defined by the pivot shaft  21 . The pivot shafts  21  are provided on the respective booms  10  in front of and above the pivot shafts  17 . 
     By extending and contracting the boom cylinders  14 , the booms  10  swing up and down around the pivot shafts  16  while the base portions of the booms  10  are supported by the lift links  12  and the control links  13 , and thus tip portions of the booms  10  are raised and lowered. The control links  13  are swung up and down around the pivot shafts  20  by the booms  10  swinging up and down. The lift links  12  are swung back and forth around the pivot shafts  17  by the control links  13  swinging up and down. 
     An alternative working tool instead of the bucket  11  can be attached to the front portions of the booms  10 . The alternative working tool is, for example, an attachment (that is, an auxiliary attachment) such as a hydraulic crusher, a hydraulic breaker, an angle broom, an earth auger, a pallet fork, a sweeper, a mower or a snow blower. A connecting member  50  is provided at the front portion of the left boom  10 . The connecting member  50  is a device configured to connect a hydraulic equipment attached to the auxiliary attachment to a first piping member such as a pipe provided on the left boom  10 . Specifically, the first piping member can be connected to one end of the connecting member  50 , and a second piping member connected to the hydraulic equipment of the auxiliary attachment can be connected to the other end. In this manner, a hydraulic fluid flowing in the first piping member passes through the second piping member and is supplied to the hydraulic equipment. 
     Each of the working tool cylinders  15  is located near the front portion of each of the booms  10 . By extending and contracting the working tool cylinders  15 , the bucket  11  is swung. In this embodiment, a crawler-type (including semi-crawler-type) traveling device is employed for each of the traveling devices  5  provided on the left and right. Alternatively, a wheel-type traveling device having front wheels and rear wheels may also be adopted. 
     The working machine  1  is provided with a hydraulic system (hydraulic circuit) for the working machine shown in  FIG.  1   . The hydraulic system for the working machine includes a first hydraulic pump P 1 , a second hydraulic pump P 2 , and a plurality of control valves  56 . 
     The first hydraulic pump P 1  is configured to deliver hydraulic fluid stored in the hydraulic fluid tank  22 . In particular, the first hydraulic pump P 1  delivers hydraulic fluid that is mainly used for control. The second hydraulic pump P 2  is a variable displacement pump disposed at a position different from the first hydraulic pump P 1 , and is configured to deliver the hydraulic fluid stored in the hydraulic fluid tank  22 , and change the flowrate of the hydraulic fluid. Of the hydraulic fluid delivered from the first hydraulic pump P 1 , the hydraulic fluid used for control is called pilot fluid, and a pressure of the pilot fluid is called a pilot pressure. 
     A delivery fluid passage  41  is extended from a delivery port of the second hydraulic pump P 2  so as to allow the hydraulic fluid delivered from the delivery port to flow therethrough. A plurality of control valves  56  are connected to the delivery fluid passage  41 . 
     Each of the plurality of control valves  56  is shiftable between a plurality of positions (shift positions) and is configured to control hydraulic actuators. The plurality of control valves  56  control the hydraulic actuators including, for example, the boom cylinder  14 , the working tool cylinder  15  and an auxiliary actuator (or a reserve actuator)  26  provided in the auxiliary attachment. The plurality of control valves  56  include a boom control valve  56 A, a working tool control valve  56 B, and a first auxiliary control valve  56 C. The boom control valve  56 A is a valve to control the boom cylinder  14 . The working tool control valve  56 B is a valve to control the working tool cylinder  15 . The boom control valve  56 A and the working tool control valve  56 B are three-position switching valves with pilot-operated direct-acting spools. The boom control valve  56 A can be shifted among a neutral position  80   c,  a first position  80   a,  and a second position  80   b.  The working tool control valve  56 B is shifted among a neutral position  82   c,  a first position  82   a,  and a second position  82   b  by a pilot pressure. 
     The boom control valve  56 A is connected to the boom cylinder  14  via a supply and discharge fluid passage  96 , and the working tool control valve  56 B is connected to the working tool cylinder  15  via a supply and discharge fluid passage  97 . 
     The boom  10  and bucket  11  can be operated through operation of an operation lever  58  provided around the driver&#39;s seat  8 . The operation lever  58  is supported to be tiltable back and forth, left and right, and diagonally from a neutral position. The operation lever  58  is provided at a lower portion thereof with pilot valves  59 A,  59 B,  59 C and  59 D, so that, through a tilting operation of the operation lever  58 , each of the pilot valves  59 A,  59 B,  59 C, and  59 D can be operated. 
     When the operation lever  58  is tilted forward, the pilot valve  59 A for lowering the booms  10  is operated, and a pilot pressure for lowering the booms  10  is output from the pilot valve  59 A. This pilot pressure acts on a pressure receiving portion of the boom control valve  56 A, thereby shifting the boom control valve  56 A to the first position  80   a,  and lowering the boom  10 . 
     When the control lever  58  is tilted backward, the pilot valve  59 B for raising the booms  10  is operated, and a pilot pressure for raising the booms  10  is output from the pilot valve  59 B. This pilot pressure acts on a pressure receiving portion of the boom control valve  56 A, thereby shifting the boom control valve  56 A to the second position  80   b,  and raising the boom  10 . 
     When the operation lever  58  is tilted rightward, the pilot valve  59 C for bucket dumping is operated, and a pilot pressure for dumping movement of the bucket is output from the pilot valve  59 C. This pilot pressure acts on a pressure receiving portion of the working tool control valve  56 B, thereby shifting the working tool control valve  56 B to the first position  82   a,  and moving the bucket  11  in a dumping operation direction. 
     When the operation lever  58  is tilted leftward, the pilot valve  59 D for bucket scooping is operated, and a pilot pressure for scooping movement of the bucket is output from the pilot valve  59 D. This pilot pressure acts on the pressure receiving portion of the working tool control valve  56 B, thereby shifting the working tool control valve  56 B to the second position  82   b,  and moving the bucket  11  in a scooping operation direction. 
     The first auxiliary control valve  56 C is a four-position switching valve with a pilot-operated direct-acting spool configured to control the auxiliary actuator  26 . The first auxiliary control valve  56 C is shifted among a neutral position  83   c,  a first position  83   a,  a second position  83   b,  and a third position  83   d  by a pilot pressure. That is, the first auxiliary control valve  56 C is selectively shifted from the neutral position  83   c  to one of the first, second and third positions  83   a,    83   b  and  83   d  so as to control a direction, a flowrate, and a pressure of hydraulic fluid supplied to the auxiliary hydraulic actuator  26 . 
     As shown in  FIGS.  1  and  2   , the first supply and discharge fluid passage  81   a  and the second supply and discharge fluid passage  81   b  are connected to the first auxiliary control valve  56 C. The first supply and discharge fluid passage  81   a  is connected at one end thereof to a first supply and discharge port  84  of the first auxiliary control valve  56 C, at an intermediate portion thereof to a connecting member  50 , and at the other end thereof to the auxiliary actuator  26 . The second supply and discharge fluid passage  81   b  is connected at one end thereof to the second supply and discharge port  85  of the first auxiliary control valve  56 C, at an intermediate portion thereof to the connecting member  50 , and at the other end thereof to the auxiliary actuator  26 . 
     As shown in  FIG.  1   , the first auxiliary control valve  56 C is operated by a plurality of proportional valves  60 . The proportional valves  60  are solenoid valves configured to be magnetized to change opening degrees thereof. The plurality of proportional valves  60  include a first proportional valve  60 A and a second proportional valve  60 B. The first proportional valve  60 A and the second proportional valve  60 B are connected to the first hydraulic pump P 1  via a fluid passage  100 . The proportional valves  60  (first proportional valve  60 A and second proportional valve  60 B) are fluidly connected to the first auxiliary control valve  56 C via respective pilot fluid passages  86 . Each of the pilot fluid passages  86  allows the pilot fluid to flow through each of the proportion valves  60 A (first and second proportional valves  60 A and  60 B) to the first auxiliary control valve  56 C. 
     Accordingly, when the first proportional valve  60 A is opened, the pilot fluid acts on a pressure receiving portion  87   a  ( FIG.  1   ) of the first auxiliary control valve  56 C through the pilot fluid passage  86 , and thus a pilot pressure applied to (acting on) the pressure receiving portion  87   a  is determined according to an opening degree of the first proportional valve  60 A. When the second proportional valve  60 B is opened, the pilot fluid acts on a pressure receiving portion  87   b  of the first auxiliary control valve  56 C through the pilot fluid passage  86 , and thus a pilot pressure applied to (acting on) the pressure receiving portion  87   b  is determined according to an opening degree of the second proportional valve  60 B. 
     The magnetization or the like of the proportional valves  60  (first proportional valve  60 A and second proportional valve  60 B) is performed by a controller (first controller)  88 . The controller  88  includes a CPU and other components. An operation member  89  such as a switch is operably connected to the controller  88 , and the opening degrees of the first proportional valve  60 A and the second proportional valve  60 B are set based on an operation amount of the operation member  89 , thereby causing either the first proportional valve  60 A or the second proportional valve  60 B to output a pilot pressure applied onto the corresponding pressure receiving portion  87   a  or  87   b  of the first auxiliary control valve  56 C. In this manner, the auxiliary actuator  26  can be operated. 
     The hydraulic system for the working machine is provided with a load sensing system. The load sensing system is configured to control the second hydraulic pump P 2  (controls a delivery flowrate of the second hydraulic pump P 2 ) so that a differential pressure between the maximum load pressure and a delivery pressure of the second hydraulic pump P 2  becomes constant when the hydraulic actuator is operated. The load sensing system includes pressure compensation valves  75  fluidly connected to the respective control valves  56 , a PLS fluid passage  70  connected to the pressure compensation valves  75 , a PPS fluid passage  71 , a regulator  72 , and a tilting piston  73 . 
     When one of the control valves  56  has the highest-loaded pressure, the highest-loaded pressure (PLS signal pressure) is transmitted to the regulator  72  by the PLS fluid passage  70 . A delivery pressure of hydraulic fluid of the second hydraulic pump P 2  (PPS signal pressure) is transmitted to the regulator  72  by the PPS fluid passage  71 . The regulator  72  actuates the tilting piston  73  so that a differential pressure between the PPS signal pressure and the PLS signal pressure (PPS signal pressure−PLS signal pressure) becomes constant. 
     As shown in  FIG.  2   , each of the control valves  56  (boom control valve  56 A, working tool control valve  56 B, first auxiliary control valve  56 C) has an input port  90  and an output port  91 . The input port  90  is a port to which hydraulic fluid delivered from the second hydraulic pump P 2  (variable displacement hydraulic pump) is input. Specifically, the input port  90  of the boom control valve  56 A is connected to the delivery fluid passage  41  via a fluid passage  41   a.  The input port  90  of the working machine control valve  56 B is connected to the delivery fluid passage  41  via a fluid passage  41   b.  The input port  90  of the first auxiliary control valve  56 C is connected to the delivery fluid passage  41  via a fluid passage  41   c.  The output port  91  is a port from which hydraulic fluid input to the input port  90  is output. 
     In addition, each of the plurality of control valves  56  (boom control valve  56 A, working tool control valve  56 B, first auxiliary control valve  56 C) has a flowrate reduction section  92 . The flowrate reduction section  92  is configured to reduce hydraulic fluid input through the input port  90  and to output the hydraulic fluid to the output port  91 . In other words, the flowrate reduction section  92  is configured to generate a differential pressure between a pressure of the hydraulic fluid introduced into the input port  90  and a pressure of the hydraulic fluid output from the output port  91 . The flowrate reduction section  92  is provided at a reduction position (first positions  80   a,    82   a,  and  83   a,  second positions  80   b,    82   b  and  83 b) that is a specific shift position among a plurality of shift positions of the respective control valves  56  (first positions  80   a,    82   a,  and  83   a,  second positions  80   b,    82   b,  and  83   b , neutral positions  80   c,    81   c,  and  83   c,  third position  83   d ). 
     Specifically, the boom control valve  56 A includes the flowrate reduction section  92  which functions when the boom control valve  56 A is set at either one of the first position  80   a  and the second position  80   b  that serve as the reduction positions of the boom control valve  56 A. The working tool control valve  56 B includes the flowrate reduction section  92  which functions when the working tool control valve  56 B is set at either one of the first position  82   a  and the second position  82   b  that serve as the reduction positions of the working tool control valve  56 B. The first auxiliary control valve  56 C includes the flowrate reduction section  92  which functions when the first auxiliary control valve  56 C is set at either one of the first position  83   a  and the second position  83   b  that serve as the reduction positions of the first auxiliary control valve  56 C. 
     The flowrate reduction section  92  includes an internal fluid passage  92   a  and a throttle portion  92   b.  The internal fluid passage  92   a  fluidly connects the input port  90  to the output port  91  when the flowrate reduction section  92  functions in the corresponding control valve  56  set at the reduction position. The throttle portion  92   b  is provided in the internal fluid passage  92   a  and has a cross-sectional area (opening area) for allowing hydraulic fluid to pass therethrough, which is smaller than that of any other portion of the internal fluid passage  92   a  through which hydraulic fluid passes. The opening area of the throttle portion  92   b  is common to the boom control valve  56 A, the working tool control valve  56 B, and the first auxiliary control valve  56 C. 
     In each of the boom control valve  56 A, the working tool control valve  56 B, and the first auxiliary control valve  56 C, hydraulic fluid output from the output port  91  returns to the corresponding control valve  56  via a fluid passage  76 , passes through a fluid passage (internal fluid passage)  95  other than the flowrate reduction section  92  functionable at the reduction position, and then is output to each of the supply and discharge fluid passages  81   a,    81   b,    96 , and  97 . 
     In the embodiment as described above, while the plurality of control valves  56  (boom control valve  56 A, working tool control valve  56 B, first auxiliary control valve  56 C) have the respective flowrate reduction sections  92 , at least one of the control valves  56  has a flowrate increase section  93 . In this embodiment, the first auxiliary control valve  56 C has the flowrate increase section  93 . 
     The flowrate increase section  93  is configured to output larger amount of hydraulic fluid to the output port  91  than that output from the flowrate reduction section  92 . In other words, the flowrate increase section  93  is configured to generate a differential pressure, as little as possible, between the pressure of hydraulic fluid introduced into the input port  90  and the pressure of hydraulic fluid output from the output port  91 . The flowrate increase section  93  fluidly connects the input port  90  to the output port  91  and has an opening area (cross-sectional area) through which hydraulic fluid passes is larger than that of the flowrate reduction section  92 . More specifically, in the first auxiliary control valve  56 C, the flowrate increase section  93  functions when the auxiliary control valve  56 C is at the third position  83   d  that is the increase position of the first auxiliary control valve  56 C. The flowrate increase section  93  is configured to allow the substantially maximum amount of hydraulic fluid to pass therethrough when the delivery flowrate of the second hydraulic pump P 2  is maximized. The hydraulic fluid output from the first auxiliary control valve  56 C passes through a fluid passage (internal fluid passage)  99  other than the flowrate increase section  93  functionable at the increase position, and is output to the first supply and discharge fluid passage  81   a.    
       FIG.  3    shows an example of a flowrate Q 1  of hydraulic fluid that passes through the first auxiliary control valve  56 C when a spool of the first auxiliary control valve  56 C having the flowrate reduction section  92  and the flowrate increase section  93  is operated. In  FIG.  3   , a horizontal axis represents an amount of movement of the spool, and a vertical axis represents a flowrate of hydraulic fluid output from the output port  91 . In description of  FIG.  3   , it is assumed that the boom control valve  56 A and the working machine control valve  56 B are not operated. 
     The controller  88  increases an opening degree of the first proportional valve  60 A in accordance with an operation amount of the operation member  89 . A pilot pressure acting on the pressure receiving portion  87   a  of the first auxiliary control valve  56 C is increased in accordance with increase of the opening degree of the first proportional valve  60 A, and is shifted from the neutral position  82 C to the first position  83   a.  Here, in the first auxiliary control valve  56 C, when the spool is positioned at the reduction position (notch region), that is, the first position  83   a,  the flowrate Q 1  of hydraulic fluid gradually increases as rising along a line L 1 . On the other hand, when the spool passes the first position  83   a  serving as the reduction position (notch region) and reaches the third position  83   d  serving as the increase position (out-of-land region), the flowrate Q 1  of the hydraulic fluid increases rapidly as rising along a line L 2 . 
     When the first auxiliary control valve  56 C is shifted to the increase position and the boom control valve  56 A and the working machine control valve  56 B are operated, that is, when either the boom control valve  56 A or the working machine control valve  5 B is shifted to the reduction position (the first position  80   a  or  82   a,  or the second position  80   b  or  82   b ), the controller  88  reduces a value of a signal (control signal) that magnetizes the first proportional valve  60 A, i.e., reduces the current, to return the first auxiliary control valve  56 C from the increase position (third position  83   d ) to the reduction position (first position  83   a ), even when an operation amount of the operation member  89  is an operation amount corresponding to the increase position. That is, when the boom control valve  56 A and the working tool control valve  56 B are operated, the controller  88  switches the first auxiliary control valve  56 C from the increase position to the reduction position (first position  83   a ) by decreasing a stroke of the spool from the neutral position  83   c.    
     The hydraulic system for the working machine according to the first embodiment described above, includes the variable displacement hydraulic pump (second hydraulic pump) P 2  to deliver hydraulic fluid having a variable flowrate, the plurality of hydraulic actuators (boom cylinder  14 , working tool cylinder  15 , auxiliary actuator  26 ) actuated with hydraulic fluid, and the plurality of control valves  56  ( 56 A,  56 B,  56 C) each of which is shiftable among a plurality of positions so that the control valve  56 , when shifted to a shift position serving as one of the positions, controls a flowrate of hydraulic fluid flowing to the corresponding hydraulic actuator in correspondence to the shift position. Each of the control valves  56  ( 56 A,  56 B,  56 C) includes the input port  90  into which hydraulic fluid delivered from the variable displacement hydraulic pump P 2  is input, the output port  91  from which the hydraulic fluid input into the input port  90  is output, and the flowrate reduction section  92  configured so that, when the control valve  56  is shifted to the reduction position serving as a specific one of the shift positions, the flowrate reduction section  92  reduces a flowrate of the hydraulic fluid entering the input port  90  and outputs the flowrate-reduced hydraulic fluid to the output port  91 . At least one control valve  56 C among the plurality of control valves  56  ( 56 A,  56 B, and  56 C) includes the flowrate increase section  93  configured so that, when the control valve  56  is shifted to the increase position serving as another shift position different from the reduction position, the flowrate increase section  93  outputs the hydraulic fluid having entered the input port  90  to the output port  91  at the flowrate larger than that of hydraulic fluid output by the flowrate reduction section  92 . 
     According to this configuration, by switching each of the hydraulic actuators (boom cylinder  14 , working tool cylinder  15 , and auxiliary control actuator  26 ) to the reduction position corresponding to the flowrate reduction section  92  in the corresponding control valve  56 , hydraulic fluid having the amount required for the hydraulic actuators (boom cylinder  14 , working tool cylinder  15 , and auxiliary actuator  26 ) can be supplied by the variable displacement hydraulic pump (second hydraulic pump) P 2  as usual. On the other hand, by switching the corresponding control valve  56  to the increase position corresponding to the flowrate increase section  93 , hydraulic fluid having the larger amount can be supplied to the corresponding hydraulic actuator (boom cylinder  14 , working tool cylinder  15 , or auxiliary actuator  26 ) by the variable displacement hydraulic pump (second hydraulic pump) P 2 . That is, since at least one control valve  56  ( 56 C) among the plurality of control valves  56  ( 56 A,  56 B, and  56 C) includes the flowrate increase section  93 , the LS differential pressure generated by activating the variable displacement hydraulic pump (second hydraulic pump) P 2  can be made to be substantially zero, and accordingly the horsepower loss can be easily reduced as much as possible. 
     The plurality of hydraulic actuators include the boom cylinder  14 , the working tool cylinder  15 , and the auxiliary actuator  26 . The plurality of control valves  56  include the boom control valve  56 A for controlling the boom cylinder  14 , the working tool control valve  56 B for controlling the working tool cylinder  15 , and the first auxiliary control valve  56  for controlling the auxiliary actuator, each of the boom control valve  56 A and the working tool control valve  56 B includes the flowrate reduction section  92 , and the first auxiliary control valve  56 C includes the flowrate reduction section  92  and the flowrate increase section  93 . 
     According to this configuration, when the boom cylinder  14  (boom  10 ) and the working tool cylinder  15  (working tool such as the bucket  11 ) are operated, the boom control valve  56 A and the working tool control valve  56 B allow the boom  10  and the working tool such as the bucket  11  to be operated according to loads on the boom cylinder  14  and the working tool cylinder  15 . On the other hand, when a large-displacement auxiliary actuator that requires a large-amount of hydraulic fluid (auxiliary actuator with large-displacement) is attached to the working machine  1 , the first auxiliary control valve  56 C can operate the large-displacement auxiliary actuator  26 . In addition, when the auxiliary actuator  26  that operates with hydraulic fluid having a standard amount (standard auxiliary actuator) is attached to the working machine  1 , the auxiliary actuator  26  can be operated as usual. 
     The first auxiliary control valve  56 C having been shifted to the increase position returns from the increase position to the reduction position when either the boom control valve  56 A or the working tool control valve  56 B is shifted to the reduction position. According to this configuration, the working tools  11  such as the boom  10  and the bucket are allowed to be operated while operating the auxiliary actuator  26 . In other words, when the boom  10  and the working tool such as the bucket  11  are operated, hydraulic fluid can be prevented from being concentrated only to the auxiliary actuator  26 , and accordingly work can be performed in a well-balanced condition. 
     Second Embodiment 
     A hydraulic system for a working machine according to a second embodiment shown in  FIGS.  4 A and  4 B  is a modified example of the auxiliary control valve. As shown in  FIGS.  4 A and  4 B , the boom control valve  56 A and the working machine control valve  56 B are the same as the boom control valve  56 A and the working machine control valve  56 B according to the first embodiment described above. In addition, the hydraulic system for the working machine according to the second embodiment includes similar configurations to the hydraulic system for the working machine according to the first embodiment. Only the configurations according to the second embodiment different from those according to the first embodiment will be described below 
     As shown in  FIGS.  1 ,  4 A, and  4 B , the plurality of control valves  56  includes a second auxiliary control valve  56 D in addition to the boom control valve  56 A, the working tool control valve  56 B, and the first auxiliary control valve  56 C. The first auxiliary control valve  56 C is a pilot-operated three-position switching valve with a direct-acting spool that is shifted among the neutral position  83   c,  the first position  83   a,  and the second position  83   b,  and includes the flowrate reduction section  92  which functions when the first auxiliary control valve  56 C is set at either the first position  83   a  or the second position  83   b.  That is, in the second embodiment, the first auxiliary control valve  56 C is not provided with the flowrate increase section  93 . 
     The second auxiliary control valve  56 D is a pilot-operated three-position switching valve with a direct-acting spool and is configured to control the auxiliary actuator  26  in the same way as the first auxiliary control valve  56 C. The second auxiliary control valve  56 D is shifted among a first position  110   a,  a second position  110   b,  and a neutral position  110   c  by a pilot pressure. That is, the second auxiliary control valve  56 D is selectively shifted from the neutral position  110   c  to either the first or second position  110   a  or  110   b  so as to control a direction, flowrate, and pressure of the hydraulic fluid supplied to the auxiliary hydraulic actuator  26 . 
     The second auxiliary control valve  56 D includes the input port  90 , the output port  91 , a third supply and discharge port  104 , a fourth supply and discharge port  105 , the flowrate reduction section  92 , and a flowrate increase section  93 . 
     In the second auxiliary control valve  56 D, the input port  90  is connected to a fluid passage  41   d  that is branched from the delivery fluid passage  41 . The third supply and discharge port  104  is connected to a first supply and discharge fluid passage  81   a  via a fluid passage (third supply and discharge fluid passage)  107 , and the fourth supply and discharge port  105  is connected to a second supply and discharge fluid passage  81   b  via a fluid passage (fourth supply and discharge fluid passage)  108 . The input port  90  of the second auxiliary control valve  56 D is connected to the delivery fluid passage  41  via the fluid passage  41   d.    
     In addition, in the second auxiliary control valve  56 D, the flowrate reduction section  92  is configured to function when the second auxiliary control valve  56 D is set at the first position  110   a  serving as the reduction position of the second auxiliary control valve  56 D. The flowrate increase section  93  is configured to function when the second auxiliary control valve  56 D is set at the second position  110   b  serving as the increase position of the second auxiliary control valve  56 D. In the second auxiliary control valve  56 D, hydraulic fluid output from the output port  91  returns from the fluid passage  76  to the second auxiliary control valve  56 D, passes through a fluid passage (internal fluid passage)  99  other than the flowrate increase section  93  functionable at the increase position, and is output to the first supply and discharge fluid passage  81   a.    
     The second auxiliary control valve  56 D includes a first pressure receiving portion  121   a  and a second pressure receiving portion  121   b.  The first pressure receiving portion  121   a  is connected, via a fluid passage  125 , to a third proportional valve  60 C that is one of the plurality of proportional valves  60 . A fluid passage  100  is connected to the third proportional valve  60 C, and hydraulic fluid delivered from the first hydraulic pump P 1  is supplied to the third proportional valve  60 C through the fluid passage  100 . 
     The second pressure receiving portion  121   b  of the second auxiliary control valve  56 D is connected to the pilot fluid passage  86 . That is, the pressure receiving portion  87   b  of the first auxiliary control valve  56 C is connected to the second pressure receiving portion  121   b  of the second reserve control valve by the pilot fluid passage  86 . 
     As shown in  FIG.  4 A  and the like, the first auxiliary control valve  56 C is operated by the plurality of proportional valves  60 . The proportional valves  60  are solenoid valves configured to be magnetized to change opening degrees thereof. The plurality of proportional valves  60  include the first proportional valve  60 A, the second proportional valve  60 B, and the third proportional valve  60 C. The first proportional valve  60 A, the second proportional valve  60 B, and the third proportional valve  60 C are connected to the first hydraulic pump P 1  via the fluid passage  100 . 
     The first proportional valve  60 A and the second proportional valve  60 B are connected to the first auxiliary control valve  56 C by the respective pilot fluid passages  86 . Each of the pilot fluid passages  86  allows the pilot fluid to flow through each of the first proportional valve  60 A and the second proportional valve  60 B to the first auxiliary control valve  56 C. 
     Accordingly, when the first proportional valve  60 A is opened, the pilot fluid acts on the pressure-receiving portion  87   a  of the first auxiliary control valve  56 C through the pilot fluid passage  86 , and a pilot pressure to be applied to (acting on) the pressure-receiving portion  87   a  is determined according to an opening degree of the first proportional valve  60 A. In addition, when the second proportional valve  60 B is opened, a pilot fluid acts on the pressure-receiving portion  87   b  of the first auxiliary control valve  56 C through the pilot fluid passage  86 , and a pilot pressure to be applied to (acting on) the pressure-receiving portion  87   b  is determined according to an opening degree of the second proportional valve  60 B. In addition, when the third proportional valve  60 C is opened, a pilot fluid acts on the pressure-receiving portion  121   a  of the second auxiliary control valve  56 D through the pilot fluid passage  125 , and a pilot pressure to be applied to (acting on) the pressure-receiving portion  121   a  is determined according to an opening degree of the third proportional valve  60 C. 
     The magnetization and the like of the proportional valves  60  (first proportional valve  60 A, second proportional valve  60 B, third proportional valve  60 C) is performed by a controller (first controller)  88 . The controller  88  includes a CPU and the like. The operation member  89  such as a switch is operably connected to the controller  88 , and opening degrees of the first proportional valve  60 A, the second proportional valve  60 B, and the third proportional valve  60 C are set based on an operation amount of the operation member  89 . When a pilot pressure output from either the first proportional valve  60 A or the second proportional valve  60 B is applied onto the corresponding pressure-receiving portion  87   a  or  87   b  of the first auxiliary control valve  56 C, and when a pilot pressure output from the third proportional valve  60 C is applied onto the first pressure-receiving portion  121   a  of the third proportional valve  60 C, the auxiliary actuator  26  can be operated. 
       FIG.  5    shows a relationship among the flowrate Q 1  of hydraulic fluid flowing through the first auxiliary control valve  56 C when a spool of the first auxiliary control valve  56 C is operated, a flowrate Q 2  of hydraulic fluid flowing through the first auxiliary control valve  56 C when a spool of the second auxiliary control valve  56 D is operated, and a flowrate Q 3  of the hydraulic fluid flowing through the first supply and discharge fluid passage  81   a.  In  FIG.  5   , it is assumed that the boom control valve  56 A and the working tool control valve  56 B are not operated. 
     When an operation amount of the operation member  89  is in a first range (small to medium amount range) A 1  (less than a threshold), the controller  88  increases only an opening degree of the first proportional valve  60 A in accordance with increase of the operation amount. In this case, since the first auxiliary control valve  56 C is set at the first position  83   a  serving as the reduction position (notch region), the flowrate Q 1  of hydraulic fluid gradually increases as rising along a line L 10 . In addition, when an operation amount of the operation member  89  is in a second range (medium to slightly high amount range) A 2  (less than a threshold), the controller  88  increases an opening degree of the third proportional valve  60 C according to increase of the operation amount while gradually increasing the opening degree of the first proportional valve  60 A. In this case, since the second auxiliary control valve  56 D is set at the first position  110   a  serving as the reduction position (notch range), the flowrate Q 2  of hydraulic fluid gradually increases as rising along a line L 11 , and the total flowrate Q 3  also gradually increases as rising along a line L 12 . 
     In addition, when an operation amount of the operation member  89  is the threshold or more, that is, the operation amount is in a third range (slightly high to the maximum amount range) A 3 , the opening degree of the third proportional valve  60 C is maximized. Since the second auxiliary control valve  56 D is set at the second position  110   b  serving as the increase position (out-of-land range), the total flowrate Q 3  increases to the maximum as rising along the line L 12 . 
     When the second auxiliary control valve  56 D is shifted to the second position  110   b  serving as the increase position (out-of-land region) and the boom control valve  56 A and the working tool control valve  56 B are operated, the controller  88  lowers a value of a control signal (current) to be output to the third proportional valve  60 C to make the second auxiliary control valve  56 D back to the first position  110   a  serving as the reduction position (notch area) or to the neutral position  110   c.  Since the second pressure receiving portion  121   b  of the second auxiliary control valve  56 D is connected to the pilot fluid passage  86 , the second auxiliary control valve  56 D can be forced to return to the neutral position  110   c  when the first auxiliary control valve  56 C is shifted to the second position  83   b  with a pressure of pilot fluid (pilot pressure) output from the first proportional valve  60 A. 
     In the second embodiment described above, the plurality of control valves  56  include the boom control valve  56 A, the working tool control valve  56 B, the first auxiliary control valve  56 C, and the second auxiliary control valve  56 D. Each of the boom control valve  56 A, the working tool control valve  56 B, and the first auxiliary control valve  56 C includes the flowrate reduction section  92 . The second auxiliary control valve  56 D includes the flowrate increase section  93 . 
     According to this configuration, of the first and second auxiliary control valves  56 C and  56 D, the first auxiliary control valve  56 C is configured to actuate a standard auxiliary actuator while the second auxiliary control valve  56 D is configured to actuate a large-displacement auxiliary actuator. That is, the at least two auxiliary control valves, i.e., the first and second auxiliary control valves  56 C and  56 D, are configured to actuate the auxiliary actuator  26  whether it is the standard auxiliary actuator  26  or the large-displacement auxiliary actuator  26 . In particular, the at least two auxiliary control valves, the first auxiliary control valve  56 C and the second auxiliary control valve  56 D, can be used to change the flowrate of the hydraulic fluid supplied to the reserve actuator  26  between the reduced flowrate corresponding to the flowrate reduction section  92  and the increased flowrate corresponding to the flowrate increase section  93 . Thus, an apparent moving amount of the spool (the sum of a moving amount of the spool of the first auxiliary control valve  56 C and a moving amount of the spool of the second auxiliary control valve  56 D) becomes longer, and accordingly accuracy of the flow control of hydraulic fluid can be improved. 
     In addition, the hydraulic system for the working machine according to the second embodiment includes the operation member  89  for operating the auxiliary actuator  26 . The first auxiliary control valve  56 C is shifted to the reduction position when the operation amount of the operation member  89  is less than the threshold. The second auxiliary control valve  56 D is shifted to the increase position when the operation amount of the operation member  89  is not less than the threshold. 
     According to this configuration, for example, as shown in  FIG.  5   , when the operation amount of the operation member  89  is less than the threshold (first range A 1  (small to medium amount range) and second range A 2  (medium to slightly high amount range), the auxiliary actuator (whether it is the mainly-used auxiliary actuator or the large-displacement auxiliary actuator)  26  can be moved precisely and finely in correspondence to the operation amount. In addition, when the operation amount of the operation member  89  is the threshold or more (third range A 3  (slightly high to the maximum amount range)), the large-displacement auxiliary actuator  26  can be operated. 
     The second auxiliary control valve  56 D includes the flowrate reduction section  92 . The second auxiliary control valve  56 D having been shifted to the increase position is returned from the increase position to the reduction position when either the boom control valve  56 A or the working tool control valve  56 B is shifted to the reduction position. According to this configuration, the auxiliary actuator  26  can be operated while the boom  10  and the working tool  11  such as a bucket are operated. In other words, in a case where the boom  10  and the working tool  11  such as a bucket are operated, hydraulic fluid can be prevented from being concentrated only to the auxiliary actuator  26 , and the work can be performed in a well-balanced condition. 
     As shown in  FIG.  4 B , the hydraulic system for the working machine according to the second embodiment includes a first discharge fluid passage  161  and a second discharge fluid passage  162 . The first discharge fluid passage  161  is connected to the first auxiliary control valve  56 C so as to be configured to discharge hydraulic fluid flowing through either the first supply and discharge fluid passage  81   a  or the second supply and discharge fluid passage  81   b . For example, when the first auxiliary control valve  56 C is in the first position  83   a,  the first discharge fluid passage  161  is connected to the second supply and discharge port  85  so as to discharge hydraulic fluid flowing through the second supply and discharge fluid passage  81   b . In addition, when the first auxiliary control valve  56 C is in the second position  83   b,  the first discharge fluid passage  161  is connected to the first supply and discharge port  84  so as to discharge hydraulic fluid flowing through the first supply and discharge fluid passage  81   a.    
     The second discharge fluid passage  162  is connected to the second auxiliary control valve  56 D so as to be configured to discharge hydraulic fluid flowing through either the third supply and discharge fluid passage  107  or the fourth supply and discharge fluid passage  108 . For example, when the second auxiliary control valve  56 D is in the first position  110   a,  the second discharge fluid passage  162  is connected to the fourth supply and discharge port  105  so as to discharge hydraulic fluid flowing through the second supply and discharge fluid passage  81   b.  In addition, when the second auxiliary control valve  56 D is in the second position  83   b , the second discharge fluid passage  162  is connected to the third supply and discharge port  104  so as to discharge hydraulic fluid flowing through the first supply and discharge fluid passage  81   a.    
     An oil cooler  163  is connected to the second discharge fluid passage  162 . On the second discharge fluid passage  162 , a throttle portion  140  is provided upstream of the oil cooler  163 . The oil cooler  163  cools hydraulic fluid that has passed through the second auxiliary control valve  56 D. 
     The boom control valve  56 A, the working tool control valve  56 B, and the first auxiliary control valve  56 C described above are provided in a hydraulic control unit B 1 . A housing of the hydraulic control unit B 1  is formed of cast metal or the like, and the boom control valve  56 A, the working tool control valve  56 B, and the first auxiliary control valve  56 C are provided inside the housing. In addition, the hydraulic control unit B 1  is provided with all or some of the fluid passages (delivery fluid passage  41 , fluid passages  41   a,    41   b,  and  41   c,  supply and discharge fluid passages  96 ,  97 ,  81   a,    81   b,  and  161 , and pilot fluid passage  86 ) leading to the boom control valve  56 A, the working tool control valve  56 B, and the first auxiliary control valve  56 C. 
     In detail, a discharge passage  165  is formed in the hydraulic control unit B 1 . The discharge passage  165  includes a first discharge fluid passage  161  connected to the first auxiliary control valve  56 C, a fourth discharge fluid passage  166  connected to the boom control valve  56 A, a fifth discharge fluid passage  167  connected to the working tool control valve  56 B, and a sixth discharge fluid passage  168  connecting the first discharge fluid passage  161 , the fourth discharge fluid passage  166 , and the fifth discharge fluid passage  167  to one another. The sixth discharge fluid passage  168  is connected to a discharge port  170  of the hydraulic control unit. That is, the first discharge fluid passage  161  is connected to the discharge port  170  via the sixth discharge fluid passage  168 . 
     The first discharge fluid passage  161  and the sixth discharge fluid passage  168  are connected by a connecting portion  171 . A check valve  173  is provided between the connecting portion  171  and the discharge port  170  to allow hydraulic fluid to flow from the connecting portion  171  to the discharge port  170  and to prevent the hydraulic fluid from flowing from the discharge port  170  to the connecting portion  171 . 
     The discharge port  170  of the hydraulic control unit B 1  is connected to the hydraulic fluid tank  22  by a third discharge fluid passage  175 . The second discharge fluid passage  162  is connected to the second auxiliary control valve  56 D and the third discharge fluid passage  175 . In the above-described embodiment, the third discharge fluid passage  175  is connected to the hydraulic fluid tank  22 , however, the third discharge fluid passage  175  may be connected to a suction portion  177  of the hydraulic pumps (first hydraulic pump P 1 , second hydraulic pump P 2 ). 
     The hydraulic fluid discharged from the boom control valve  56 A, the working tool control valve  56 B, and the first auxiliary control valve  56 C flows through the sixth discharge fluid passage  168  and the discharge port  170  to the hydraulic fluid tank  22 . On the other hand, the hydraulic fluid discharged from the second auxiliary control valve  56 D is cooled by the oil cooler  163 , and then flows to either the hydraulic fluid tank  22  or the suction section  177 . 
     In the second embodiment described above, the second auxiliary control valve  56 D is a control valve having the flowrate increase section  93 , however, as shown in  FIG.  4 C , the second auxiliary control valve  56 D may be a three-position switching valve having a flowrate reduction section  92  without the flowrate increase section  93 , similar to the first auxiliary control valve  56 C. In addition, the second auxiliary control valve  56 D is not limited to these configurations. 
     In the second embodiment, as shown in  FIG.  4 A , the second discharge fluid passage  162  includes the throttle portion  140 , however, not limited to this configuration. Alternatively, the fluid passage connected to the oil cooler  163  may include a throttle portion. For example, as shown in  FIG.  4 D , a fluid passage that functions in the second auxiliary control valve  56 D when disposed at the first position  110   a  may include a throttle portion  141 , or a fluid passage that functions in the second auxiliary control valve  56 D when disposed at the second position  110   b  may include a throttle portion  142 . These internal fluid passages of the second auxiliary control valve  56 D are configured to be connected to the oil cooler  163 . In addition, as shown in  FIG.  4 F , when the second auxiliary control valve  56 D is shifted to the first position  110   a , the second auxiliary control valve  56 D may be configured to block the flow of hydraulic fluid (i.e., to interrupt the fluidal connection between the input port and the output port). 
     The hydraulic system for the working machine according to the second embodiment includes the hydraulic pumps P 1  and P 2  to deliver hydraulic fluid, the boom control valve  56 A for controlling the boom cylinder  14 , the working tool control valve  56 B for controlling the working tool cylinder  15 , the first auxiliary control valve  56 C for controlling the auxiliary actuator  26 , the second auxiliary control valve  56 D for controlling the auxiliary actuator  26 , the first supply and discharge fluid passage  81   a  fluidly connecting the auxiliary actuator  26  to the first auxiliary control valve  56 C, the second supply and discharge fluid passage  81   b  fluidly connecting the auxiliary actuator  26  to the first auxiliary control valve  56 C, the third supply and discharge fluid passage  107  fluidly connecting the first supply and discharge fluid passage  81   a  to the second auxiliary control valve  56 D, the fourth supply and discharge fluid passage  108  fluidly connecting the second supply and discharge fluid passage  81   b  to the second auxiliary control valve  56 D, the first discharge fluid passage  161  fluidly connected to the first auxiliary control valve  56 C so as to discharge hydraulic fluid flowing in either the first supply and discharge fluid passage  81   a  or the second supply and discharge fluid passage  81   b,  the second discharge fluid passage  162  fluidly connected to the second auxiliary control valve  56 D so as to discharge hydraulic fluid flowing in either the third supply and discharge fluid passage  107  or the fourth supply and discharge fluid passage  108 , and the oil cooler  163  fluidly connected to the second discharge fluid passage  162 . 
     According to this configuration, by activating the second auxiliary control valve  56 D, the hydraulic fluid to be supplied to the auxiliary actuator  26  can be easily increased (increased in volume) by supplying the hydraulic fluid output from the second auxiliary control valve  56 D to the first or second supply and discharge fluid passage  81   a  or  81   b  connected to the first auxiliary control valve  56 C. Specifically, when hydraulic fluid supplied to the auxiliary actuator  26  is increased to operate the auxiliary actuator  26 , both the first and second auxiliary control valves  56 C and  56 D are actuated, thereby enabling fine operation of the auxiliary actuator  26 . In addition, hydraulic fluid that returning from the auxiliary actuator  26  to the second auxiliary control valve  56 D can be easily cooled by passing through the oil cooler  163 . In other words, an apparent moving amount of the spool (the sum of a moving amount of the spool of the first auxiliary control valve  56 C and a moving amount of the spool of the second auxiliary control valve  56 D) becomes longer, and accordingly accuracy of the flow control of hydraulic fluid can be improved. In addition, when the hydraulic fluid to be supplied to the auxiliary actuator  26  is increased in volume, the hydraulic fluid can be cooled by the oil cooler  163 . 
     In addition, the hydraulic system for the working machine according to the second embodiment includes the hydraulic fluid tank  22  storing hydraulic fluid, the suction portion  177  of the hydraulic pumps P 1  and P 2 , and the hydraulic pressure control unit B 1  incorporating the boom control valve  56 A, the working tool control valve  56 B, the first auxiliary control valve  56 C, and including the discharge port  170  for discharging hydraulic fluid therefrom. The first discharge fluid passage  161  is fluidly connected to the discharge port  170  of the hydraulic pressure control unit B 1 . The second discharge fluid passage  162  is fluidly connected to the discharge port  170  and to the third discharge fluid passage  175  fluidly connected to either the hydraulic fluid tank  22  or the suction portion  177 . 
     According to this configuration, in a case where the first auxiliary control valve  56 C is activated, hydraulic fluid can be discharged through the third discharge fluid passage  175  from the first discharge fluid passage  161  connected to the discharge port  170  of the hydraulic control unit B 1 . On the other hand, in a case where the second auxiliary control valve  56 D is activated, hydraulic fluid can be discharged through the second discharge fluid passage  162  including the oil cooler  163 . That is, in a case where the first auxiliary control valve  56 C alone operates the auxiliary actuator  26 , hydraulic fluid can be returned (drained) to the hydraulic pump P 1  and P 2  side without passing through the oil cooler  163 , when there is no need to cool the hydraulic fluid because an amount of hydraulic fluid to be supplied to the auxiliary actuator  26  is small and heat generation is also small. In addition, in a case where the auxiliary actuator  26  is operated by the second auxiliary control valve  56 D (or the first and second auxiliary control valves  56 C and  56 D), an amount of hydraulic fluid to be supplied to the auxiliary actuator  26  is increased and the heat generation becomes large, so that the hydraulic fluid can be returned to the hydraulic pumps P 1  and P 2  side through the oil cooler  163 . 
     Each of the first and second auxiliary control valves  56 C and  56 D is shiftable among the plurality of shift positions and includes a pressure-receiving portion to which a pilot pressure is applied. The pressure-receiving portion of the first auxiliary control valve  56 C and the pressure-receiving portion of the second auxiliary control valve  56 D are fluidly connected to each other via a pilot fluid passage, and the second auxiliary control valve  56 D is shiftable to the neutral position serving as one of the shift positions when a pressure is applied to the pressure-receiving portion thereof via the pilot fluid passage. 
     According to this configuration, the auxiliary actuator  26  is also operated while operating the boom  10  and the working tool  11  such as the bucket. In other words, when operating the boom  10  and the working tool  11  such as the bucket, hydraulic fluid can be prevented from being concentrated only to the auxiliary actuator  26 , and thus work can be performed in a well-balanced condition. 
     Each of the first and second auxiliary control valves  56 C and  56 D is shiftable among the plurality of shift positions, and includes the input port  90  into which hydraulic fluid delivered from the variable displacement hydraulic pump is input the output port  91  from which the hydraulic fluid input into the input port  90  is output, and the flowrate reduction section configured so that, when each of the first and second auxiliary control valves  56 C and  56 D is shifted to the reduction position serving as a specific one of the shift positions, the flowrate reduction section  92  reduces a flowrate of the hydraulic fluid entering the input port  90  and outputs the flowrate-reduced hydraulic fluid to the output port  91 , and the second auxiliary control valve  56 D includes the flowrate increase section  93  configured so that, when the second auxiliary control valve  56 D is shifted to the increase position serving as another specific shift position different from the reduction position, the flowrate increase section  93  outputs the hydraulic fluid having entered the input port  90  to the output port  91  at a flowrate larger than that of hydraulic fluid output by the flowrate reduction section  92 . 
     According to this configuration, when an auxiliary actuator that operates with standard amount of hydraulic fluid (standard auxiliary actuator) is attached to the control valves  56 C and  56 D, the auxiliary actuator can be normally operated by the first control valve  56 C. On the other hand, when a large-displacement auxiliary actuator that requires a large amount of hydraulic fluid is attached, the second auxiliary control valve  56 D can operate the large-displacement auxiliary actuator. 
     Third Embodiment 
     A hydraulic system for a working machine according to a third embodiment shown in  FIG.  6 A  additionally employs detection means that detects the increase positions of the control valves  56 C and  56 D. In  FIG.  6 A , the boom control valve  56 A and the working tool control valve  56 B are not shown, but they are the same as those in the embodiments described above and shown in  FIG.  1   . In addition, the hydraulic system for the working machine according to the third embodiment has the similar configuration to the hydraulic system for the working machine according to the first embodiment described above. Only the configurations according to the third embodiment different from those according to the first embodiment will be described below. 
     The hydraulic system for the working machine according to the third embodiment is provided with an interlocking control valve  130 . The interlocking control valve  130  is configured to be shifted in accordance with the shift of the second auxiliary control valve  56 D among the plurality of shift positions. That is, the interlocking control valve  130  is shifted in conjunction with movement of the spool of the second auxiliary control valve  56 D. The interlocking control valve  130  is a three-position switching valve shiftable among the blocking position  130   a  and a plurality of communicating positions  130   b  and  130   c.  When the second auxiliary control valve  56 D is shifted to the neutral position  110   c,  the interlocking control valve  130  is shifted to the communicating position  130   c.  When the second auxiliary control valve  56 D is shifted to the first position  110   a,  the interlocking control valve  130  is shifted to the communicating position  130   b.  When the second auxiliary control valve  56 D is shifted to the second position  110   b,  the interlocking control valve  130  is shifted to the blocking position  130   a.    
     That is, the interlocking control valve  130  can be shifted to the blocking position  130   a  by shifting the second auxiliary control valve  56 D to the second position  110   b  serving as the increase position (out-of-land region) among the plurality of shift positions ( 110   a,    110   b,    110   c ), and can be shifted to the communicating position  130   b  or  130   c  by shifting the second auxiliary control valve  56 D to a position other than the second position  110   b  serving as the increase position (out-of-land region). 
     The interlocking control valve  130  has a pressure receiving portion  139 . The pressure receiving portion  139  of the interlocking control valve  130  is connected to the third proportional valve  60 C, i.e., the actuation valve, via a fluid passage  134 . By changing a pressure of hydraulic fluid (pilot fluid) output from the third proportional valve  60 C (actuation valve), a position of the interlocking control valve  130  is shifted, and further a position of the second auxiliary control valve  56 D is shifted. 
     The interlocking control valve  130  is connected to the detection fluid passage  135 . Specifically, the interlocking control valve  130  has an input port  131  and an output port  132 , the detection fluid passage  135  is connected to the input port  131 , and the discharge fluid passage  136  is connected to the output port  132 . The detection fluid passage  135  is connected to a fluid passage  100 , and the throttle portion  137  is connected to the detection fluid passage  135 . A pressure detection unit  138  is connected to the detection fluid passage  135 . The pressure detection unit  138  includes a pressure sensor or a pressure switch such as to detect a pressure (pilot pressure) of hydraulic fluid (pilot fluid) flowing through the detection fluid passage  135 . 
     The pressure detection unit  138  is operably connected to the controller  88 . The controller  88  is configured to output a control signal to the third proportional valve (actuation valve)  60 C and to change the control signal. For example, the controller  88  can change a value of the control signal, i.e., a current value, in a range from the minimum value of the control signal (corresponding to the neutral position) corresponding to the minimum of the operation amount of the operation member  89  (at its neutral position) to the maximum value of the control signal (corresponding to the maximum operation position) corresponding to the maximum of the operation amount (at the maximum operation position). That is, the controller  88  controls the third proportional valve (actuation valve)  60 C to shift the spool of the second auxiliary control valve  56 D from the neutral position  110   c  to the second position  110   b  serving as the increase position (out-of-land region) through the first position  110   a  serving as the decreased position (out-of-land region). 
     Here, when the second auxiliary control valve  56 D is shifted to the neutral position  110   c  or the first position  110   a  serving as the reduction position (notch region), the interlocking valve  130  is shifted to the communicating position  130   b  or  130   c,  so that a pilot pressure V 10  detected by the pressure detection unit  138  is substantially zero, as shown in  FIG.  7 A . When the second auxiliary control valve  56 D is shifted from the first position  110   a  serving as the reduction position (notch region) to the second position  110   b  serving as the increase position (out-of-land region), the interlocking control valve  130  is shifted to the blocking position  130   a , so that the pilot pressure V 10  detected by the pressure detection unit  138  rises rapidly. That is, a point P 10  at which the pilot pressure V 10  (pilot pressure generated when the third proportional valve  60 C (actuation valve) is actuated) detected by the pressure sensing unit  138  rapidly rises and reaches the maximum coincides to a point at which the second auxiliary control valve  56 D shifted from the first position  110   a  serving as the reduction position (notch region) reaches the second position  110   b  serving as the increase position (out-of-land region). That is, in  FIG.  7 A , a pilot pressure at the point P 10  is a threshold V 11  such as to shift the second auxiliary control valve  56 D to the second position  110   b  serving as the increase position (out-of-land region). 
     The controller  88  stores a value (current value) of the control signal such as to rapidly increase the pilot pressure V 10  detected by the pressure detection unit  138  to the pressure at the point P 10  and a current value of the third proportional valve (actuation valve)  60 C corresponding to a value (current value) of the control signal to set the pilot pressure at the point P 10 . The controller  88  stores a relationship between a value (referred to as a valve-shifting current value) of the control signal and the shifting operation amount of the operation member  89  under a condition where the second auxiliary control valve  56 D is shifted to the second position  110   b  serving as the increase position (out-of-land region). In summary, the controller  88  controls the third proportional valve (actuation valve)  60 C after storing the current value (valve-shifting current value) of the third proportional valve (actuation valve)  60 C, that is, the pilot pressure output by the third proportional valve (actuation valve)  60 C, obtained when the pilot pressure V 10  detected by the pressure detection unit  138  exceeds the threshold V 11 . In this manner, the second auxiliary control valve  56 D is shifted to the increase position (out-of-land region). 
     In addition, when an operation amount of the operation member  89  is equal to or greater than a threshold (shifting operation amount), the controller  88  increases a pilot pressure to be output from the third proportional valve  60 C (actuation valve) so that the pilot pressure V 10  detected by the pressure detection unit  138  becomes equal to or greater than the threshold V 11 , thereby shifting the second auxiliary control valve  56 D to the second position  110   b  serving as the increase position (out-of-land region). The controller  88  makes the value of the control signal, i.e., a current value, to be output to the third proportional valve  60 C (actuation valve) equal to or higher than the valve-shifting current value. 
     In addition, when the second auxiliary control valve  56 D is shifted to the second position  110   b  serving as the increase position (out-of-land area), and either the boom control valve  56 A or the working tool control valve  56 B is shifted to the reduction position (i.e., the first position  80   a  or  82   a  or the second position  80   b  or  82   b ), the controller  88  lowers the pilot pressure to be output from the third proportional valve  60 C (actuation valve) so that the pilot pressure in the detection fluid passage  135  becomes less than the threshold V 11 . In this manner, the second auxiliary control valve  56 D is shifted to the first position  110   a  serving as the reduction position (notch region). The controller  88  reduces a value of the control signal, i.e., a current value, output therefrom to the third proportional valve  60 C (actuation valve) to be less than the valve-shifting current value. 
     As a modified example, the interlocking control valve  130  may be modified as shown in  FIG.  6 B . Specifically, the interlocking control valve  130  is configured to be shifted to the blocking position  130   a  by shifting the second auxiliary control valve  56 D to the neutral position  110   c.  The interlocking valve  130  is configured to be shifted to the communicating position  130   b  by shifting the second auxiliary control valve  56 D to the first position  110   a,  and the interlocking control valve  130  is shifted to the blocking position  130   c  by shifting the second auxiliary control valve  56 D to the second position  110   b.    
     When the interlocking control valve  130  shown in  FIG.  6 B  is employed, the pilot pressure V 10  detected by the pressure detection unit  138  varies as shown in  FIG.  7 B , for example. In an example shown in  FIG.  7 B , as in the example shown in  FIG.  7 A , the point P 10  at which the pilot pressure V 10  (pilot pressure generated when the third proportional valve  60 C (actuation valve) is actuated) rapidly increases and reaches the maximum coincides to a point at which the second auxiliary control valve  56 D shifted from the first position  110   a  serving as the reduction position (notch region) reaches the second position  110   b  serving as the increase position (out-of-land region). When an operation amount of the operation member  89  is equal to or greater than a threshold (referred to as a valve-shifting operation amount), the controller  88  increases a pilot pressure output from the third proportional valve  60 C (actuation valve) so that the pilot pressure V 10  detected by the pressure detection unit  138  becomes equal to or greater than the threshold V 11 , thereby shifting the second auxiliary control valve  56 D to the second position  110   b  serving as the increase position (out-of-land region). 
     Alternatively, the interlocking control valve  130  may be modified as shown in  FIG.  6 C . Specifically, when the second auxiliary control valve  56 D is shifted to the neutral position  110   c,  the interlocking control valve  130  is shifted to the blocking position  130   a . When the second auxiliary control valve  56 D is shifted to the second position  110   b,  the interlocking control valve  130  is shifted to the communicating position  130   c.  When the second auxiliary control valve  56 D is shifted to the first position  110   a,  the interlocking control valve  130  is shifted to the blocking position  130   b.  That is, when the second auxiliary control valve  56 D is shifted to the second position  110   b,  the pilot pressure detected by the pressure detection unit  138  is lowered, thereby informing that the second auxiliary control valve  56 D has been shifted to the second position  110   b.    
     When the interlocking control valve  130  shown in  FIG.  6 C  is employed, the pilot pressure V 10  detected by the pressure detection unit  138  varies as shown in  FIG.  7 C . In the example shown in  FIG.  7 C , unlike the examples shown in  FIGS.  7 A and  7 B , the point P 11  at which the pilot pressure V 10  (pilot pressure when the third proportional valve  60 C (actuation valve) is actuated) drops rapidly and reaches the minimum coincides to a point at which the second auxiliary control valve  56 D is shifted from the first position  110   a  serving as the reduction position (notch region) to the second position  110   b  serving as the increase position (out-of-land area). When an operation amount of the operation member  89  is equal to or greater than a threshold (referred to as a valve-shifting operation amount), the controller  88  lowers a pilot pressure output from the third proportional valve  60 C (actuation valve) so that the pilot pressure V 10  detected by the pressure detection unit  138  becomes less than the threshold V 12  (e.g., the pilot pressure V 10  becomes substantially zero), thereby causing the second reserve the control valve  56 D to be shifted to the second position  110   b  serving as the increase position (out-of-land region). 
     In the example shown in  FIG.  6 C , the controller  88  stores a value (current value) of the control signal such as to rapidly decreasing the pilot pressure V 10  detected by the pressure detection unit  138  to the pressure at the point P 11  and a current value of the third proportional valve (actuation valve)  60 C corresponding to a value (current value) of the control signal to set the pilot pressure at the point P 11 . The controller  88  stores a relationship between the shifting operation amount of the operation member  89  and a value (referred to as a valve-shifting current value) of the control signal to be output to the third proportional valve (actuation valve)  60 C when the second auxiliary control valve  56 D is shifted from the first position  110   a  serving as the reduction position (notch region) to the second position  110   b  serving as the increase position (out-of-land region). In summary, the controller  88  stores the current value (referred to as a valve-shifting current value) of the third proportional valve (actuation valve)  60 C obtained when the pilot pressure V 10  detected by the pressure detection unit  138  becomes less than the threshold V 12 , that is, the pilot pressure output by the third proportional valve (actuation valve)  60 C, and then, the controller  88  controls the third proportional valve (actuation valve)  60 C to shift the second auxiliary control valve  56 D to the increase position (out-of-land area). 
     In addition, when the second auxiliary control valve  56 D is shifted to the second position  110   b  serving as the increase position (out-of-land area) and either the boom control valve  56 A or the working tool control valve  56 B is shifted to the reduction position (i.e., the first position  80   a  or  82   a  or the second position  80   b  or  82   b ), the controller  88  increases a pilot pressure outputted from the third proportional valve  60 C (actuation valve) so as to increase a pilot pressure of the detection fluid passage  135  to a value higher than the threshold V 11 , thereby shifting the second auxiliary control valve  56 D to the first position  110   a  serving as the reduction position (notch area). The controller  88  increases a value of the control signal, i.e., a current value, output to the third proportional valve  60 C (actuation valve) to a value higher than the valve-shifting current value. 
     The hydraulic system for the working machine according to the third embodiment described above, includes the detection fluid passage  135 , the interlocking control valve  130  fluidly connected to the detection fluid passage  135  and configured to be shifted in correspondence to which of the shift positions the second auxiliary control valve  56 D is shifted to, and the pressure detection unit  138  for detecting a pilot pressure in the detection fluid passage  135 . The interlocking control valve  130  is shiftable to the blocking position  130   a  to block the pilot fluid introduced into the interlocking control valve  130  from the detection fluid passage  135  when the second auxiliary control valve  56 D is shifted to the increase position of the shift positions. 
     According to this configuration, by shifting the interlocking control valve  130  to the blocking position  130   a  in accordance with the shift position (the reduction position or the increase position) of the second auxiliary control valve  56 D. In this manner, it is possible to judge more accurately whether the second control valve  56 D reaches the second position  110   b  serving as the increase position (out-of-land area) or not based on a pressure (pilot pressure) detected by the pressure detection unit  138 . 
     In addition, the hydraulic system for the working machine, includes the operation member  89  for operating the auxiliary actuator, the controller  88  configured or programmed to output the control signal in correspondence to an operation amount of the operation member  89 , and the actuation valve (proportional valve  60 C) configured to change a pilot pressure output therefrom in correspondence to the control signal from the controller  88 . The actuation valve (proportional valve  60 C) is fluidly connected to either the pressure-receiving portion of the second auxiliary control valve  56 D for receiving a pilot pressure or the pressure-receiving portion of the interlocking control valve  130  for receiving a pilot pressure. When the operation amount of the operation member  89  is not less than a threshold, the controller  88  is configured or programmed to shift the second auxiliary control valve  56 D to the increase position by increasing the pilot pressure output from the actuation valve (proportional valve  60 C) so as to increase the pilot pressure detected by the pressure detection unit  138  to a value not less than a threshold. According to this configuration, it possible to accurately shift the second auxiliary control valve  56 D to the second position  110   b  serving as the increase position (out-of-land region) when an operation amount of the operation member  89  is equal to or greater than the threshold. 
     When the second auxiliary control valve  56 D is shifted to the increase position and either the boom control valve  56 A or the working tool control valve  56 B is shifted to the reduction position, the controller  88  is configured or programmed to shift the second auxiliary control valve  56 D to the reduction position by reducing the pilot pressure output from the actuation valve (proportional valve  60 C) so as to reduce the pilot pressure in the detection fluid passage  135  to a value less than the threshold. According to this configuration, it possible to accurately shift the second auxiliary control valve  56 D to the first position  110   a  serving as the reduction position (notch area) when an operation amount of the operation member  89  is less than a threshold. 
     The controller  88  is configured or programmed to change the control signal output therefrom to the actuation valve (proportional valve  60 C), and to store, when the control signal is changed, a value of the changed control signal such as to change the pilot pressure detected by the pressure detection unit  138  to a value not less than the threshold. According to this configuration, a value of a control signal to be output by the controller  88  to set the second auxiliary control valve  56 D to the first position  110   a  serving as the reduction position (notch region) can be accurately associated with a value of the control signal to be output by the controller  88  to set the second auxiliary control valve  56 D to the second position  110   b  serving as the increase position (out-of-land area), and accordingly accuracy of a flowrate control of hydraulic fluid can be improved. 
     The interlocking control valve  130  is shiftable to an opening position to allow the pilot fluid introduced into the interlocking control valve  130  from the detection fluid passage  135  to pass through the interlocking control valve  130  when the second auxiliary control valve  56 D is shifted to the increase position of the shift positions. According to this configuration, by shifting the interlocking control valve  130  to the communicating position  130   c,  it is possible to more accurately judge whether the interlocking control valve  130  reaches the second position  110   b  serving as the increase position (out-of-land area) based on a pressure (pilot pressure) detected by the pressure detection unit  138 . 
     The controller  88  is configured or programmed to shift the second auxiliary control valve  56 D to the increase position by reducing the pilot pressure output from the actuation valve (proportional valve  60 C) so as to reduce the pilot pressure detected by the pressure detection unit  138  to a value less than a threshold V 12 . According to this configuration, the second auxiliary control valve  56 D can be accurately shifted to the second position  110   b  serving as the increase position (out-of-land region) when an operation amount of the operation member  89  is greater than a threshold. 
     When the second auxiliary control valve  56 D is shifted to the increase position and either the boom control valve  56 A or the working tool control valve  56 B is shifted to the reduction position, the controller  88  is configured or programmed to shift the second auxiliary control valve  56 D to the reduction position by increase the pilot pressure output from the actuation valve (proportional valve  60 C) so as to increase the pilot pressure in the detection fluid passage  135  to a value not less than the threshold V 12 . According to this configuration, the second auxiliary control valve  56 D can be accurately shifted to the first position  110   a  serving as the reduction position (notch region) when the operation amount of the operation member  89  is less than a threshold. 
     The controller  88  is configured or programmed to change the control signal output therefrom to the actuation valve (proportional valve  60 C), and to store, when the control signal is changed, a value of the changed control signal such as to change the pilot pressure detected by the pressure detection unit  138  to a value less than the threshold V 12 . According to this configuration, a value of a control signal to be output by the controller  88  to set the second auxiliary control valve  56 D to the first position  110   a  serving as the reduction position (notch area) can be accurately associated with a value of the control signal to be output by the controller  88  to set the second auxiliary control valve  56 D to the second position  110   b  serving as the increase position (out-of-land area), and accordingly accuracy of a flowrate control of hydraulic fluid can be improved. 
     Fourth Embodiment 
       FIG.  8    shows a hydraulic system for a working machine according to a fourth embodiment. The hydraulic system for the working machine according to the fourth embodiment is a modification of the hydraulic system for the working machine according to the first embodiment. As shown in  FIG.  8   , the first auxiliary control valve  56 C is not provided with the third position  83   d.  That is, the first auxiliary control valve  56 C is not provided with the flowrate increase section  93 . The other configurations of the control valves  56 , including the boom control valve  56 A and the working tool control valve  56 B, are the same as those of the respective control valves  56  according to the first embodiment. 
       FIG.  9    shows an operation amount of the operation member  89  and a moving amount of the spool of the first auxiliary control valve  56 C, that is, a pilot pressure acting on the pressure receiving portion  87   a  from the first proportional valve  60 A. As shown in  FIG.  9   , in a state where only the operation member  89  (only the first auxiliary control valve  56 C) is operated (single operation), the controller  88  raises a value of a control signal (current) or the like to be output to the first proportional valve  60 A in accordance with increase of an operation amount of the operation member  89  as rising along a line L 51 , and gradually increases a pressure acting on the pressure receiving portion  87   a  of the first auxiliary control valve  56 C. 
     On the other hand, in a state (combined operation) in which the operation member  89  (first auxiliary control valve  56 C) and the operation lever  58  (either or both the boom control valve  56 A or/and the working tool control valve  56 B) are operated, the controller  88  increases the value of the control signal (current) or the like to be output to the first proportional valve  60 A to an intermediate level according to increase of the operation amount of the operation member  89  as rising along a line L 52  in  FIG.  9   . And, when an operation amount of the operation member  89  exceeds a predetermined level, the controller  88  lowers the value of the control signal (current) to be output to the first proportional valve  60 A so that the current becomes lower than a value on the line L 51 . 
     That is, the controller  88  moves the spool of the first auxiliary control valve  56 C from the minimum position to the maximum position gradually according to an operation of the operation member  89  when the first auxiliary control valve  56 C is operated alone. On the other hand, when the first auxiliary control valve  56 C is in the combined operation, the controller  88  gradually moves the spool of the first auxiliary control valve  56 C from the minimum position to an intermediate position according to an operation of the operation member  89 , and stops the second auxiliary control valve  56 D in the intermediate position (closer to the neutral position than the maximum position) so that the operation lever  89  does not reach the maximum position. 
     Specifically, in a case where the boom control valve  56 A and the first auxiliary control valve  56 C are combinedly operated, the controller  88  can make a pilot pressure to be output from the first proportional valve  60 A smaller than the maximum value, even when an operation amount of the operation member  89  is the maximum. 
     In the above description, the pilot pressure to be output from the first proportional valve  60 A is made smaller. Alternatively, a pilot pressure output from the second proportional valve  60 B may be made smaller than the maximum value based on a position of the second auxiliary control valve  56 D. That is, in the description of the fourth embodiment described above, the first proportional valve  60 A may be replaced by the second proportional valve  60 B. 
     As another modification, the interlocking valve  230  may be applied to the first auxiliary control valve  56 C as shown in  FIG.  10 A . As shown in  FIG.  10 A , an interlocking valve  230  is connected to the detection fluid passage  135 . A pressure detection unit  138  that detects a pressure (pilot pressure) of the hydraulic fluid (pilot fluid) flowing in the detection fluid passage  135  is connected to the detection fluid passage  135 . The pressure detection unit  138  is a pressure sensor or a pressure switch. The fluid passage leading to the detection fluid passage  135  and the second hydraulic pump P 2  is provided with a throttle portion  240 . 
     When the first auxiliary control valve  56 C is shifted to the neutral position  81   c,  the interlocking valve  230  is shifted to the communicating position  230   c.  When the first auxiliary control valve  56 C is shifted to the first position  83   a,  the interlocking valve  230  is shifted to the communicating position  230   a.  When the first auxiliary control valve  56 C is shifted to the second position  83   b,  the interlocking valve  230  is shifted to the communicating position  230   b.  When the first auxiliary control valve  56 C is shifted to the third position  83   d , the interlocking valve  230  is shifted to the blocking position  230   d.  That is, when the first auxiliary control valve  56 C is shifted to the third position  83   d,  a pilot pressure of the pressure detection unit  138  is increased, thereby informing that the first auxiliary control valve  56 C has been shifted to the third position  83   d.    
     In addition, the interlocking valve  230  may be modified as shown in  FIG.  10 B . When the first auxiliary control valve  56 C is shifted to the neutral position  81   c,  the interlocking valve  230  is shifted to the blocking position  230   c.  When the first auxiliary control valve  56 C is shifted to the first position  83   a,  the interlocking valve  230  is shifted to the blocking position  230   a.  When the first auxiliary control valve  56 C is shifted the second position  83   b,  the interlocking valve  230  is shifted to the blocking position  230   b.  When the first auxiliary control valve  56 C is shifted to the third position  83   d,  the interlocking valve  230  is shifted to the communicating position  230   d.  That is, when the first auxiliary control valve  56 C is shifted to the third position  83   d,  a pilot pressure of the pressure detection unit  138  is decreased, thereby informing that the first auxiliary control valve  56 C has been shifted to the third position  83   d.    
     In addition, the second auxiliary control valve  56 D may be modified as shown in  FIG.  11 A . The second auxiliary control valve  56 D shown in  FIG.  11 A  includes a main control valve  190  and a switching valve  191 . The main control valve  190  is a two-position switching valve shiftable between a first position  190   a  and a second position  190   b.  The main control valve  190  is provided with the flowrate increase section  94  that functions when the main control valve  190  is at a position corresponding to the first position  190   b.  The input port  90  of the main control valve  190  is connected to the fluid passage  41   d,  and the third supply and discharge port  104  is connected to the fluid passage  107 . The fluid passage  107  includes a check valve  195  to allow hydraulic fluid to flow from the main control valve  190  toward the first supply and discharge fluid passage  81   a  and to prevent the hydraulic fluid from flowing from the first supply and discharge fluid passage  81   a  to the main control valve  190 . The switching valve  191  is configured to shift the main control valve  190 . The input port side of the switching valve  191  is connected to the pilot fluid passage  86  via the fluid passage  196 , and the output port side of the switching valve  191  is connected to the pressure receiving portion of the main control valve  190 . The fluid passage  196  includes a throttle portion  197 . 
     The switching valve  191  is shiftable between the first position  191   a  and the second position  191   b  according to a control signal from the controller  88 . When the switching valve  191  is shifted to the second position  191   b,  a pilot pressure of the hydraulic fluid (pilot fluid) in the pilot fluid passage  86  is applied to the main control valve  190 , and the main control valve  190  is shifted to the second position  190   b.  In this manner, the hydraulic fluid in the fluid passage  41   d  can be supplied to the fluid passage  107  through the main control valve  190  (flowrate increase section  94 ). 
     As shown in  FIG.  11 B , when the flowrate reduction section  92  and the internal fluid passage  99  are provided to the first auxiliary control valve  56 C, an output port  144  side of the main control valve  190  may be connected to the fluid passage  76 . In addition, in  FIG.  11 A , the second auxiliary control valve  56 D is constituted of a main control valve  190  and a switching valve  191 , and the main control valve  190  is shifted by pilot fluid. Alternatively, as shown in  FIG.  11 C , the main control valve  190  may be replaced by a direct-acting switching valve that is shifted directly by an operation member such as a lever. 
     In addition, in  FIGS.  11 A to  11 C , when the boom control valve  56 A (boom  10 ) and the working tool control valve  56 B (a working tool) are activated, the flowrate increase section  94  of the main control valve  190  is closed. That is, even when an operation member such as a switch is operated to give an instruction to increase hydraulic fluid, the controller  88  shifts the switching valve  191  to the first position  191   a  when at least one of the boom control valve  56 A and the working tool control valve  56 B (the working tool) is to be activated, thereby shifting the main control valve  190  from the second position  190   b  to the first position  190   a . Additionally, when at least either the boom control valve  56 A or the working tool control valve  56 B (the working tool) is activated, the first auxiliary control valve  56 C is held at the first position  83   a  so as to supply hydraulic fluid to the auxiliary attachment  26  via the flow reduction section  92 . 
     In addition, in  FIGS.  11 A to  11 C , the fluid passage  196  is connected to the pilot fluid passage  86 . However, the fluid passage  196  may be connected to the fluid passage  100 . 
     In the embodiments described above, any method may be adopted to detect the operations of the boom control valve  56 A (the boom  10 ) and the working tool control valve  56 B (the working tool). For example, the controller  88  may include a state detector  103 . The state detector  103  is configured to detect the operation and movement of at least either one of the boom  10  and the working tool such as the bucket  11 . For example, the state detector  103  may include an angle sensor for detecting angles of the boom  10  and bucket  11 , a pressure sensor for detecting pressures of the pilot valves  59 A to  59 D, a telescopic detection sensor for detecting the extension and contraction of the boom cylinder  14  or working tool cylinder  15 , or a sensor for detecting an operational direction of the operation lever  58 . The state detector  103  is capable of detecting that the boom control valve  56 A (boom  10 ) and the working tool control valve  56 B (operation tool) have been operated. 
     Fifth Embodiment 
       FIG.  12 A  shows a hydraulic system for a working machine according to a fifth embodiment. Referring to  FIG.  12 A , the hydraulic system for the working machine is provided with a drain fluid passage  284  and a switching valve  285 . The drain fluid passage  284  includes a first drain fluid passage  284   a  connecting the first supply and discharge fluid passage  81   a  to the switching valve  285 , a second drain fluid passage  284   b  connecting the switching valve  285  to the oil cooler  263 , and a third drain fluid passage  284   c  connecting the oil cooler  263  to the hydraulic fluid tank  22 . 
     The switching valve  285  is a valve configured to change an opening degree thereof, and is a two-position switching valve shiftable between a first position  285   a  and a second position  285   b.  When the switching valve  285  is in the first position  285   a,  the opening degree is substantially zero, and the fluidal connection between the first drain fluid passage  284   a  and the second drain fluid passage  284   b  is interrupted. When the switching valve  285  is in the second position  285   b,  the opening degree is full, and the first drain fluid passage  284   a  is connected to the second drain fluid passage  284   b.    
     The operation of the switching valve  285  between the first position  285   a  and the second position  285   b  is performed by a pilot pressure. The switching valve  285  includes a pressure receiving portion  291  and a pressure receiving portion  292  each of which receives the pilot pressure. The pressure receiving portion  291  of the switching valve  285  is connected to a pilot fluid passage  286   a  that is connected to the first proportional valve  60 A and a pressure receiving portion  87   a  of the first auxiliary control valve  56 C. The pressure receiving portion  292  of the switching valve  285  is connected to a pilot fluid passage  286   b  that is connected to the second proportional valve  60 B and a pressure receiving portion  87   b  of the first auxiliary control valve  56 C. 
     In the drain fluid passage  284 , a check valve  278  is interposed between the switching valve  285  and the hydraulic fluid tank  22 . The check valve  278  is configured to block hydraulic fluid flowing from the oil cooler  263  toward the switching valve  285 . 
     In addition, the drain fluid passage  284  includes a throttle portion  279 . Specifically, the throttle portion  279  is provided at a portion of the second drain fluid passage  284   b  of the drain fluid passage  284  closer to the oil cooler  263  than the check valve  278 . Due to the throttle portion  279 , a pressure of the hydraulic fluid (drained fluid) flowing to the oil cooler  263  can be restricted. 
     According to the above configuration, when the opening degree of the second proportional valve  60 B is increased to a predetermined opening degree (threshold) or more, a pilot pressure applied to the pressure receiving portion  292  of the switching valve  285  can be increased. The switching valve  285  includes a spool that is biased toward the first position  285   a  by a biasing member  293  such as a spring. When a pilot pressure applied to the pressure receiving portion  292  of the switching valve  285  is made equal to or higher than a predetermined value for moving the spool, the spool moves against the biasing member  293  to shift the switching valve  285  to the second position  285   b,  thereby discharging hydraulic fluid from the first supply and discharge fluid passage  81   a  to the drain fluid passages  284  (first drain fluid passage  284   a,  second drain fluid passage  284   b,  and third drain fluid passage  284   c ) through the switching valve  285 . 
     On the other hand, when an opening degree of the first proportional valve  60 A is increased to a predetermined opening degree (threshold) or greater, a pilot pressure can be applied to the pressure receiving portion  291  of the switching valve  285 , and the switching valve  285  can be shifted to the first position (initial position)  285   a.  That is, by opening the first proportional valve  60 A, the switching valve  285  can be forced back to the initial position. 
       FIG.  12 B  shows a modification of the hydraulic system for the working machine according to the second embodiment. The hydraulic system for the working machine shown in  FIG.  12 B  includes a switching valve (first switching valve)  285 A and a switching valve (second switching valve)  285 B. 
     The first switching valve  285 A has the same configuration as the switching valve  285  shown in  FIG.  12 A . The second switching valve  285 B, like the first switching valve  285 A, is a two-position switching valve configured to be shifted between the first position  285   a  and the second position  285   b.  The second switching valve  285 B includes a pressure receiving portion  294  and a pressure receiving portion  295  each of which receives the pilot pressure. The pressure receiving portion  294  of the switching valve  285 B is connected to a pilot fluid passage  286   b  that is connected to the second proportional valve  60 B and the pressure receiving portion  87   b  of the first auxiliary control valve  56 C. The pilot fluid passage  286   b  is also connected to the pressure receiving portion  292  of the first switching valve  285 A. 
     The pressure receiving portion  295  of the second switching valve  285 B is connected to the pilot fluid passage  286   a  that is connected to the first proportional valve  60 A and the pressure receiving portion  87   a  of the first auxiliary control valve  56 C. The pilot fluid passage  286   a  is also connected to the pressure receiving portion  291  of the first switching valve  285 A. 
     The drain fluid passage  284  shown in  FIG.  12 B  includes a fourth drain fluid passage  284   d  and a fifth drain fluid passage  284   e  in addition to the first drain fluid passage  284   a,  the second drain fluid passage  284   b,  and the third drain fluid passage  284   c.  The fourth drain fluid passage  284   d  connects the second supply and discharge fluid passage  81   b  to the second switching valve  285 B. The fifth drain fluid passage  284   e  connects the second switching valve  285 B to the second drain fluid passage  284   b,  and is merged with the second drain fluid passage  284   b.    
     According to the fifth embodiment mentioned above, when an opening degree of the second proportional valve  60 B is increased to a predetermined opening degree (threshold) or more, a pilot pressure applied on the pressure receiving portion  292  of the first switching valve  285 A and the pressure receiving portion  294  of the second switching valve  285 B can be increased. 
     The switching valve  285 A includes a spool that is biased toward the first position  285   a  by a biasing member  293 . When a pilot pressure applied to the pressure receiving portion  292  of the first switching valve  285 A is increased to be equal to or higher than a predetermined value for moving the spool, the spool is moved against the biasing member  293  to shift the switching valve  285 A to the second position  285   b  thereby discharge the hydraulic fluid from the first supply and discharge fluid passage  81   a  to the drain fluid passage  284 . In addition, when an opening degree of the second proportional valve  60 B is made equal to or greater than a predetermined opening degree (threshold), a pilot pressure acts on the pressure receiving portion  294  of the second switching valve  285 B, thereby forcing the second switching valve  285 B back to the first position  285   a  (initial position). 
     On the other hand, when an opening degree of the first proportional valve  60 A is made equal to or greater than a predetermined opening degree (threshold), a pilot pressure applied to the pressure receiving portion  291  of the first switching valve  285 A and the pressure receiving portion  295  of the second switching valve  285 B can be increased. 
     The switching valve  285 B includes a spool that is biased toward the first position  285   a  by a biasing member  296 . When a pilot pressure applied to the pressure receiving portion  295  of the second switching valve  285 B is made equal to or higher than a predetermined value for moving the spool, the spool of the second switching valve  285 B is moved against the biasing member  293  to shift the switching valve  285 B, thereby discharging hydraulic fluid from the second supply and discharge fluid passage  81   b  to the drain fluid passage  284 . In addition, when an opening degree of the first proportional valve  60 A is made equal to or greater than a predetermined opening degree (threshold), a pilot pressure acts on the pressure receiving portion  291  of the first switching valve  285 A, thereby forcing the first switching valve  285 A back to the first position  285   a  (initial position). 
     As another modification, an actuation valve  289  may be provided on the pilot fluid passage  286   b  as shown in  FIG.  12 C . The actuation valve  289  is configured to shift the switching valve  285  and has a variable opening degree. The actuation valve  289  is a solenoid valve or a manual valve whose opening degree can be changed manually. When the actuation valve  289  is a manual valve, a pilot pressure acting on the pressure receiving portion  292  of the switching valve  285  can be set by manually opening or closing the actuation valve  289  fully. 
     In the examples shown in  FIGS.  12 A to  12 C , the throttle portion  279  is provided on the second drain fluid passage  284   b.  Alternatively, as shown in  FIG.  12 E , a throttle portion  279  may be provided on the fluid passage in the switching valve  285  functionable when the switching valve  285  is shifted to the second position  285   b.    
     Sixth Embodiment 
       FIG.  12 D  shows a hydraulic system for a working machine according to a sixth embodiment. Explanations for configurations common to the above-mentioned embodiments will be omitted. The hydraulic system according to the fifth embodiment is not provided with the load sensing system. 
     The hydraulic system for the working machine shown in  FIG.  12 D  includes a third hydraulic pump P 3 , an actuation valve  320 , an actuation valve  321 , a fluid passage  323 , the second switching valve  285 B, and the oil cooler  263 . 
     The third hydraulic pump P 3  is configured to be driven by a power of the prime mover  32  and is installed at a different location from the first hydraulic pump P 1  and the second hydraulic pump (working hydraulic pump). The second hydraulic pump P 2  and the third hydraulic pump P 3  are configured to be driven by a power of the prime mover  32 , and they are constant displacement gear pumps. That is, the first hydraulic pump P 1 , the second hydraulic pump P 2 , and the third hydraulic pump P 3  are constant displacement gear pumps. In particular, the third hydraulic pump P 3  serves as a flowrate-increasing hydraulic pump for increasing a flowrate of hydraulic fluid. 
     The fluid passage  323  branches from the first fluid passage  83  and is connected to the third hydraulic pump P 3 . In detail, the fluid passage  323  is connected at one end thereof to the first supply and discharge fluid passage  81   a,  and at the other end thereof to a delivery port of the third hydraulic pump P 3 . 
     The actuation valve (high-flow valve)  320  is provided on an intermediate portion of the fluid passage  323  and has a variable opening degree. The actuation valve  320  is a two-position switching valve to be operated by a pilot pressure, so that the actuation valve  320  can be shifted between two shift positions (first position  320   a  and second position  320   b ) by a pilot pressure. When the actuation valve  320  is in the first position  320   a,  an opening degree of the actuation valve  320  is substantially zero (i.e., fully closed), and a flowrate of hydraulic fluid flowing into the fluid passage  323  becomes zero (=0). In addition, when the actuation valve  320  is in the second position  320   b,  the actuation valve  320  is fully opened, and a flowrate of hydraulic fluid flowing into the fluid passage  323  becomes a predetermined amount greater than zero. In other words, the actuation valve  320  blocks the fluid passage  323  when the actuation valve  320  is in the first position  320   a,  and opens the fluid passage  323  when the actuation valve  320  is in the second position  320   b.    
     Accordingly, by shifting the actuation valve  320  to the second position  320   b , hydraulic fluid delivered from the third hydraulic pump P 3  can be supplied to the fluid passage  323 . The hydraulic fluid flowing into the fluid passage  323  is merged with the hydraulic fluid flowing in the first fluid passage  83 . As a result, a flowrate of hydraulic fluid to be supplied to the auxiliary actuator  26  can be increased. 
     The actuation valve  320  is shifted by the actuation valve  321 . The actuation valve  321  is a two-position switching solenoid valve. The actuation valve  321  can be shifted between a first position  321   a  and a second position  321   b.  The actuation valve  321  is connected to the actuation valve  320  by a fluid passage  325 . In detail, the actuation valve  320  has a pressure receiving portion  320   c.  The pressure receiving portion  320   c  is capable of receiving pilot fluid. The pressure receiving portion  320   c  of the actuation valve  320  is connected to the actuation valve  321  by the fluid passage  325 . 
     When the actuation valve  321  is in the first position  321   a,  a pilot pressure is not applied to the pressure-receiving portion  320   c  of the actuation valve  320 , thereby shifting the actuation valve  320  to the first position  320   a.  When the actuation valve  321  is in the second position  321   b,  a pilot pressure is applied to the pressure receiving portion  320   c  of the actuation valve  320 , thereby shifting the actuation valve  320  to the second position  320   b.    
     The shifting between the first position  321   a  and the second position  321   b  in the actuation valve  321  is performed by the controller  88 . A fluid passage  305  is connected to the fluid passage  325 . An actuation valve  389  is connected to the fluid passage  305 . The actuation valve  389  is a valve to shift the second switching valve  285 B and configured to change an opening degree thereof. The actuation valve  389  is a solenoid valve or a manual valve whose opening degree can be changed manually. When the actuation valve  389  is a manual valve, the pilot pressure acting on the pressure receiving portion  295  of the second switching valve  285 B can be set by manually opening or closing the actuation valve  389  fully. 
     The drain fluid passage  284  includes a sixth drain fluid passage  284   f  connecting the second switching valve  285 B to the oil cooler  263 . In the drain fluid passage  284 , a throttle portion  299  is provided upstream of the oil cooler  263 . 
     As described above, in the sixth embodiment, under a state where a flowrate of hydraulic fluid is increased, a pilot pressure acting on the pressure receiving portion  295  of the second switching valve  285 B can be increased by increasing an opening degree of the actuation valve  389  to a threshold or more, thereby shifting the second switching valve  285 B to the second position  285   b.  In this manner, hydraulic fluid of the second supply and discharge fluid passage  81   b  can be supplied to the oil cooler  263  via the sixth drain fluid passage  284   f.  On the other hand, when an opening degree of the second proportional valve  60 B is increased to a predetermined opening degree (threshold) or more, a pilot pressure to be applied to the pressure receiving portion  294  of the second switching valve  285 B can be supplied, and the second switching valve  285 B can be forced to return to the first position  285   a  (initial position). 
     In the example shown in  FIG.  12 D , the throttle portion  299  is provided in the drain fluid passage  284 . However, a throttle portion may be provided in a fluid passage communicating to the oil cooler  263  in the same manner as the aforementioned modifications of the embodiments. For example, as shown in  FIG.  12 F , the throttle portion  299  may be provided in the internal fluid passage of the second switching valve  285 B that functions when the second switching valve  285 B is set at the second position  285   b.    
     In addition, as shown in  FIG.  12 G , a fluid passage  350  may be provided to connect the input port of the actuation valve  321  to the pressure receiving portion  87   a  of the first auxiliary control valve  56 C, so that the actuation valve  321  can be supplied with hydraulic fluid when hydraulic fluid acts on the pressure receiving portion  87   a.  In addition, the fluid passage  305  may be connected to the pressure receiving portion  295  of the second switching valve  285 B as shown in  FIG.  12 G  without the actuation valve  389  shown in  FIG.  12 D . 
     In the above embodiments, the first auxiliary control valve  56 C and the second auxiliary control valve  56 D are separately configured. Alternatively, the first auxiliary control valve  56 C and the second auxiliary control valve  56 D may be integrated as shown in  FIG.  4 E , for example. In the example shown in  FIG.  4 E , the first auxiliary control valve  56 C is a four-position switching valve and can be shifted to the third position  83   d  in addition to the first position  83   a,  the second position  83   b,  and the neutral position  83   c.  In addition, the first auxiliary control valve  56 C includes the output port  144 , and the second discharge fluid passage  162  is connected to the output port  144 . 
     When the first auxiliary control valve  56 C is in the third position  83   d,  a fluid passage  181  connected to the second supply and discharge port  85  and a fluid passage  182  branched from the fluid passage  181  are provided inside the first auxiliary control valve  56 C. The fluid passage  182  is a fluid passage that communicates to the output port  144  (the second discharge fluid passage  162 ) when the first auxiliary control valve  56 C is in the third position  83   d.  The fluid passage  182  includes a throttle portion  279 . 
     In the above description, the embodiment of the present invention has been explained. However, all the features of the embodiment disclosed in this application should be considered just as examples, and the embodiment does not restrict the present invention accordingly. A scope of the present invention is shown not in the above-described embodiment but in claims, and is intended to include all modifications within and equivalent to a scope of the claims. 
     While preferred embodiments of the present invention have been described above, it is to be understood that variations and modifications will be apparent to those skilled in the art without departing from the scope and spirit of the present invention. The scope of the present invention, therefore, is to be determined solely by the following claims.