Patent Publication Number: US-10787787-B2

Title: Hydraulic system for working machine

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     The present application claims priority under 35 U.S.C. § 119 to Japanese Patent Application No. 2018-150737, filed Aug. 9, 2018. The content of this application is incorporated herein by reference in their entirety. 
     BACKGROUND OF THE INVENTION 
     Field of the Invention 
     The present invention relates to a hydraulic system for a working machine such as a skid steer loader, a compact truck loader, and a backhoe, for example. 
     Description of Related Art 
     A hydraulic system for a working machine disclosed in Japanese Unexamined Patent Application Publication No. 2018-105081 is previously known as a technology for coupling a traveling pump to an operation valve. The hydraulic system for the working machine disclosed in Japanese Unexamined Patent Application Publication No. 2018-105081 includes a variable displacement pump, an operation configured to change a pressure of operation fluid in accordance with the operation of an operation member, and a traveling fluid tube coupling the operation valve to the variable displacement pump. 
     SUMMARY OF THE INVENTION 
     A hydraulic system for a working machine according to one aspect of the present invention, includes an operation member, an operation valve to change an output pressure of an operation fluid in accordance with operation of the operation member, a hydraulic device to be activated by the operation fluid outputted from the operation valve, a first fluid tube coupling the operation valve to the hydraulic device, and a bleed circuit connected to the first fluid tube and configured to output the operation fluid in the first fluid tube. The first fluid tube includes a first section fluid tube provided in a section between the operation valve and a coupling portion coupling the first fluid tube to the bleed circuit, and a second section fluid tube provided in a section between the coupling portion and the hydraulic device, the second section fluid tube having an inner diameter different from an inner diameter of the first section fluid tube. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       A more complete appreciation of the 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, wherein: 
         FIG. 1  is a view illustrating a hydraulic system (a hydraulic circuit) for a working machine according to an embodiment of the present invention; 
         FIG. 2  is an enlarged view of a first fluid tube and a second fluid tube according to the embodiment; 
         FIG. 3  is an enlarged view illustrating a configuration provided with a relay member according to the embodiment; and 
         FIG. 4  is a side view illustrating a skid steer loader that is one example of the working machine according to the embodiment. 
     
    
    
     DESCRIPTION OF THE EMBODIMENTS 
     The 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. 
     Hereinafter, an embodiment of the present invention will be described below with reference to the drawings as appropriate. 
     An embodiment of a hydraulic system for a working machine and the working machine having the hydraulic system according to the present invention will be described below with reference to the drawings. 
       FIG. 4  shows a side view of a working machine according to an embodiment of the present invention. In  FIG. 4 , a skid steer loader is shown as an example of the working machine. However, the working machine according to the present invention is not limited to the skid steer loader, and may be, for example, another type of loader working machine such as a compact track loader. In addition, a working machine other than the loader working machine may be employed. 
     As shown in  FIG. 4 , the working machine  1  includes a machine body  2 , a cabin  3 , a working device  4 , and a traveling device  5 . 
     In the embodiment of the present invention, the front side (the left side in  FIG. 4 ) of the operator seated on the operator seat  8  of the working machine  1  is referred to as the front, the rear side (the right side in  FIG. 4 ) of the operator is referred to as the rear, the left side of the operator is referred to as the left, and the right side of the operator is referred to as the right. 
     Moreover in the explanation of the embodiment, the horizontal direction which is a direction orthogonal to the front-rear direction is referred to as a machine width direction. The direction extending from the central portion of the machine body  2  to the right portion or the left portion will be described as a machine outward direction. In other words, the machine outward direction corresponds to the machine width direction and is the direction separating away from the machine body  2 . 
     A direction opposite to the machine outward direction will be described as a machine inward direction. In other words, the machine inward direction corresponds to the machine width direction and is the direction approaching the machine body  2 . 
     The cabin  3  is mounted on the machine body  2 . The cabin  3  is provided with an operator seat  8 . The working device  4  is attached to the machine body  2 . The traveling device  5  is provided on the outside of the machine body  2 . A prime mover is mounted at the rear portion of the machine body  2 . 
     The working device  4  includes a boom  10 , a working tool  11 , a lift link  12 , a control link  13 , a boom cylinder  14 , and a bucket cylinder  15 . 
     The boom  10  is provided on the right side of the cabin  3 , and another boom  10  is provided on the left side of the cabin  3 . The booms  10  is configured to be swung upward and downward. The working tool  11 , for example, is a bucket, and the bucket  11  is provided at the tip end portions (the front end portions) of the booms  10  so as to be swung upward and downward. 
     The lift link  12  and the control link  13  support the base portion (the rear portion) of each of the booms  10  so that the boom  10  can be swung upward and downward. The boom cylinder  14  is stretched and shortened to move the boom  10  upward and downward. The bucket cylinder  15  is stretched and shortened to swing the bucket  11 . 
     The front portions of the left boom  10  and the right boom  10  are coupled to each other by a deformed connecting pipe. The base portions (the rear portions) of the booms  10  are coupled to each other by a cylindrical connecting pipe. 
     A pair of the lift link  12 , the control link  13  and the boom cylinder  14  is provided on the left side of the machine body  2  corresponding to the boom  10  arranged on the left side, and another pair of the lift link  12 , the control link  13  and the boom cylinder  14  is provided on the right side of the machine body  2  corresponding to the boom  10  arranged on the right side. 
     The lift link  12  is provided vertically at the rear portion of the base portion of each of the booms  10 . The upper portion (one end side) of the lift link  12  is supported rotatably about a lateral axis by a pivot shaft  16  (a first pivot shaft) near the rear portion of the base portion of each of the booms  10 . 
     In addition, the lower portion (the other end side) of the lift link  12  is supported rotatably about the horizontal axis by a pivot shaft  17  (a second pivot shaft) near the rear portion of the machine body  2 . The second pivot shaft  17  is provided below the first pivot shaft  16 . 
     An upper portion of the boom cylinder  14  is supported rotatably about the lateral axis by a pivot shaft  18  (a third pivot shaft). The third pivot shaft  18  is provided at the base portion of each of the booms  10  and particularly at the front portion of the base portion. 
     The lower portion of the boom cylinder  14  is supported rotatably about the lateral axis by a pivot shaft  19  (a fourth pivot shaft). The fourth pivot shaft  19  is provided near the lower portion of the rear portion of the machine body  2  and below the third pivot shaft  18 . 
     The control link  13  is provided in front of the lift link  12 . One end of the control link  13  is supported rotatably about the lateral axis by a pivot shaft  20  (a fifth pivot shaft). The fifth pivot shaft  20  is provided at a position corresponding to the front of the lift link  12  in the machine body  2 . 
     The other end of the control link  13  is supported rotatably about the lateral axis by a pivot shaft  21  (a sixth pivot shaft). The sixth pivot shaft  21  is provided in front of the second pivot shaft  17  and above the second pivot shaft  17  in the boom  10 . 
     When the boom cylinder  14  is stretched and shortened, each of the booms  10  is swung upward and downward around the first pivot shaft  16  while the base portion of each of the booms  10  is supported by the lift link  12  and the control link  13 . In this manner, the tip end portion of each of the booms  10  moves upward and downward. 
     The control link  13  is swung upward and downward around the fifth pivot shaft  20  in accordance with the upward and downward swinging of each of the booms  10 . The lift link  12  is swung backward and forward around the second pivot shaft  17  in accordance with the upward and downward swinging of the control link  13 . 
     Instead of the bucket  11 , another working tool can be attached to the front portion of the boom  10 . Another working tool is, for example, an attachment (an auxiliary attachment) such as a hydraulic crusher, a hydraulic breaker, an angle broom, an earth auger, a pallet fork, a sweeper, a mower, a snow blower, or the like. 
     A connecting member  50  is provided at the front portion of the boom  10  arranged on the left side. The connecting member  50  is a device for coupling a hydraulic device provided in the auxiliary attachment to a tube member such as a pipe provided to the boom  10 . 
     In particular, the tube member can be connected to one end of the connecting member  50 , and the tube member coupled to the hydraulic device of the auxiliary attachment can be coupled to the other end of the connecting member  50 . In this manner, the operation fluid flowing in the tube material is supplied to the hydraulic device. 
     Each of the bucket cylinders  15  is respectively arranged near the front portion of each of the booms  10 . When the bucket cylinder  15  is stretched and shortened, the bucket  11  is swung. 
     In the present embodiment, a wheel-type traveling device having a front wheel and a rear wheel is adopted as each of the traveling device  5  arranged on the right and the traveling devices  5  arranged on the left. The traveling device may employ a crawler type traveling device (including a semi-crawler type traveling device). 
     Next, the hydraulic system for the working machine according to the embodiment of present invention will be described below. 
     As shown in  FIG. 1 , the hydraulic system of the traveling system is a system configured to drive the traveling device  5 . The traveling device  5  includes a left traveling motor device (a first traveling motor device)  31 L, a right traveling motor device (a second traveling motor device)  31 R, and a hydraulic device  34 . The hydraulic system of the traveling system includes a prime mover  32 , a direction switching valve  33 , and a first hydraulic pump P 1 . 
     The prime mover  32  is constituted of an electric motor, an engine, or the like. In the embodiment, the prime mover  32  is constituted of the engine. The first hydraulic pump P 1  is a pump configured to be driven by the power of the prime mover  32 , and is constituted of a constant displacement gear pump. The first hydraulic pump P 1  is configured to output the operation fluid stored in the tank  22 . 
     In particular, the first hydraulic pump P 1  outputs the operation fluid mainly used for control. For convenience of the explanation, the tank  22  for storing the operation fluid may be referred to as an operation fluid tank. 
     Further, of the operation fluid outputted from the first hydraulic pump P 1 , the operation fluid used for control may be referred to as a pilot fluid, and the pressure of the pilot fluid may be referred to as a pilot pressure. 
     An output fluid tube  40  for supplying the operation fluid (the pilot fluid) is provided on the output side of the first hydraulic pump P 1 . The output fluid tube (a second fluid tube)  40  is provided with a filter  35 , a direction switching valve  33 , a first travel motor device  31 L, and a second travel motor device  31 R. 
     Between the filter  35  and the direction switching valve  33 , a charging fluid tube  41  branched from the output fluid tube  40  is provided. The charging fluid tube  41  reaches the hydraulic device  34 . 
     The direction switching valve  33  is an electromagnetic valve configured to change the revolutions of the first travel motor device  31 L and the second travel motor device  31 R, and particularly is a two-position switching valve that can be magnetized to be switched between the first position  33   a  and the second position  33   b . The switching operation of the direction switching valve  33  is performed by an operation member or the like (not shown in the drawings). 
     The first travel motor device  31 L is a motor for transmitting power to the drive shaft of the traveling device  5  provided on the left side of the machine body  2 . The second travel motor device  31 R is a motor for transmitting power to the drive shaft of the traveling device provided on the right side of the machine body  2 . 
     The first traveling motor device  31 L includes an HST motor (a traveling motor)  36 , a swash plate switching cylinder  37 , and a traveling control valve (a hydraulic switching valve)  38 . 
     The HST motor  36  is constituted of a swash plate type variable displacement axial motor, that is, a motor configured to change the vehicle speed (the revolution) to the first speed or the second speed. In other words, the HST motor  36  is a motor configured to change the thrust power of the working machine  1 . 
     The swash plate switching cylinder  37  is a cylinder configured to be stretched and shortened to change the angle of the swash plate of the HST motor  36 . The travel control valve  38  is a valve configured to stretch and shortens the swash plate switching cylinder  37  to one side or the other side, that is, a two-position switching valve configured to be switched between the first position  38   a  and the second position  38   b.    
     The switching operation of the travel control valve  38  is performed by the direction switching valve  33  located on the upstream side connected to the travel control valve  38 . 
     As described above, according to the first travel motor device  31 L, when the direction switching valve  33  is set to the first position  33   a  through the operation of the operation member, the pilot fluid is released in the section between the direction switching valve  33  and the travel control valve  38 , and thereby the travel control valve  38  is switched to the first position  38   a . As the result, the swash plate switching cylinder  37  is shortened, and the HST motor  36  is set to be in the first speed. 
     In addition, when the direction switching valve  33  is set to the second position  33   b  through the operation of the operation member, the pilot fluid is supplied to the travel control valve  38  through the direction switching valve  33 , and the travel control valve  38  is switched to the second position  38   b . As the result, the swash plate switching cylinder  37  is stretched, and the HST motor  36  is set to be in the second speed. 
     The second travel motor device  31 R also operates in the same manner as the first travel motor device  31 L. The configuration and operation of the second travel motor device  31 R are the same as those of the first travel motor device  31 L, and thus the description thereof is omitted. 
     The hydraulic device  34  is a device configured to drive the first travel motor device  31 L and the second travel motor device  31 R, and includes a drive circuit (a drive circuit for the left)  34 L for driving the first travel motor device  31 L and a drive circuit (a drive circuit for the right)  34 R for driving the second travel motor device  31 R. 
     The drive circuits  34 L and  34 R respectively include the HST pumps (the traveling pumps)  53 L and  53 R, the speed-changing fluid tubes  57   h  and  57   i , and the second charging fluid tube  57   j . The speed-changing fluid tubes  57   h  and  57   i  are fluid tubes coupling the HST pumps  53 L and  53 R to the HST motor  36 . 
     The second charge fluid tube  57   j  is a fluid tube connected to the speed-changing fluid tubes  57   h  and  57   i , and configured to refill, to the speed-changing fluid tubes  57   h  and  57   i , the operation fluid outputted from the first hydraulic pump P 1 . 
     The HST pumps  53 L and  53 R are the swash plate type variable displacement axial pumps configured to be driven by the power of the prime mover  32 . The HST pumps  53 L and  53 R each have the forward-traveling pressure receiving portions  53   a  and the backward-traveling pressure receiving portions  53   b  on which the pilot pressures are applied. The angles of the swash plates of the HST pumps  53 L and  53 R are changed by the pilot pressure applied to the pressure receiving portions  53   a  and  53   b.    
     The HST pumps  53 L and  53 R are configured to change the angles of the swash plates to change the outputs (the output amounts of operation fluid) of the HST pumps  53 L and  53 R and the output directions of the operation fluids. 
     The outputs of the HST pumps  53 L and  53 R and the output direction of the operation fluid can be changed by the operation device  47  provided around the operator seat  8 . The operation device  47  has an operation member  54  supported swingably and a plurality of pilot valves (operation valves)  55 . 
     As shown in  FIG. 1 , the operation member  54  is an operation lever supported by the operation valve  55  and configured to be swung in the lateral direction (in the machine width direction) or in the front-rear direction. That is, with respect to the neutral position N, the operation member  54  can be operated rightward and leftward from the neutral position N and can be operated forward and backward from the neutral position N. 
     In other words, the operation member  54  can be swung in at least four directions with respect to the neutral position N. 
     For convenience of the explanation, the two directions, the forward direction and the backward direction, that is, the front-rear direction will be referred to as a first direction. In addition, the two directions, the right direction and the left direction, that is, the lateral direction (the machine width direction) may be referred to as a second direction. 
     Further, the plurality of operation valves  55  are operated by a common operation member, that is, a single of the operation member  54 . The plurality of operation valves  55  operate based on the swinging operation of the operation member  54 . An output fluid tube  40  is connected to the plurality of operation valves  55 , and the operation fluid (the pilot fluid) can be supplied from the first hydraulic pump P 1  through the output fluid tube  40 . 
     The plurality of control valves  55  include a operation valve  55 A, a operation valve  55 B, a operation valve  55 C, and a operation valve  55 D. 
     The operation valve  55 A changes the pressure of the outputted operation fluid in accordance with the operation extent of the forward operation (the movement) when the operation lever  54  is swung forward (to one side) in the front-rear direction (the first direction) (when the forward operation is performed). 
     The operation valve  55 B changes the pressure of the outputted operation fluid in accordance with the operation extent of the backward operation (the movement) when the operation lever  54  is swung backward (to the other side) in the front-rear direction (the first direction) (when the backward operation is performed). 
     The operation valve  55 C changes the pressure of the outputted operation fluid in accordance with the operation extent of the rightward operation (the movement) when the operation lever  54  is swung rightward (to one side) in the lateral direction (the second direction) (when the rightward operation is performed). 
     The operation valve  55 D changes the pressure of the outputted operation fluid in accordance with the operation extent of the leftward operation (the movement) when the operation lever  54  is swung leftward (to the other side) in the lateral direction (the second direction) (when the leftward operation is performed). 
     The plurality of operation valves  55  are coupled to the hydraulic devices  34  (the traveling pump  53 L and the traveling pump  53 R) of the traveling system by a plurality of traveling fluid tubes (the first fluid tubes)  45 . In other words, the traveling pump  53 L and the traveling pump  53 R are hydraulic devices each configured to be operated by the operation fluid outputted from the operation valves  55  (the operation valve  55 A, the operation valve  55 B, the operation valve  55 C, and the operation valve  55 D). 
     In addition, the plurality of operation valves  55  are coupled to the first hydraulic pump P 1  by an output fluid tube (a second fluid tube)  40 . 
     The plurality of traveling fluid tubes  45  include a first traveling fluid tube  45   a , a second traveling fluid tube  45   b , a third traveling fluid tube  45   c , a fourth traveling fluid tube  45   d , and a fifth traveling fluid tube  45   e.    
     The first traveling fluid tube  45   a  is a fluid tube connected to the forward-traveling pressure receiving portion  53   a  of the traveling pump  53 L. The second traveling fluid tube  45   b  is a fluid tube connected to the backward-traveling pressure receiving portion  53   b  of the traveling pump  53 L. 
     The third traveling fluid tube  45   c  is a fluid tube connected to the forward-traveling pressure receiving portion  53   a  of the traveling pump  53 R. The fourth traveling fluid tube  45   d  is a fluid tube connected to the backward-traveling pressure receiving portion  53   b  of the traveling pump  53 R. 
     The fifth traveling fluid tube  45   e  is a fluid tube coupling the operation valve  55 , the first traveling fluid tube  45   a , the second traveling fluid tube  45   b , the third traveling fluid tube  45   c , and the fourth traveling fluid tube  45   d.    
     The fifth traveling fluid tube  45   e  includes a bridge portion  45   e   1  having a plurality of shuttle valves  46 , and a coupling tube  45   e   2  coupling the operation valve  55  to the confluent portion of the bridge portion  45   e   1 . 
     When the operation lever  54  is swung forward (in the direction indicated by an arrowed line A 1  in  FIG. 1 ), the operation valve  55 A is operated to output a pilot pressure from the operation valve  55 A. 
     The pilot pressure is applied to the pressure receiving portion  53   a  of the traveling pump  53 L through the first traveling fluid tube  45   a , and is applied to the pressure receiving portion  53   a  of the traveling pump  53 R through the third traveling fluid tube  45   c . In this manner, the output shaft of the travel motor  36  revolves forward (the forward revolution) at a speed proportional to the swinging extent of the operation lever  54 , and thereby the working machine  1  travels straight forward. 
     In addition, when the operation lever  54  is swung backward (in the direction indicated by an arrowed line A 2  in  FIG. 1 ), the operation valve  55 B is operated to output a pilot pressure from the operation valve  55 B. 
     The pilot pressure is applied to the pressure receiving portion  53   b  of the traveling pump  53 L through the second traveling fluid tube  45   b , and is applied to the pressure receiving portion  53   b  of the traveling pump  53 R through the fourth traveling fluid tube  45   d . In this manner, the output shaft of the traveling motor  36  revolves backward (the backward revolution) at a speed proportional to the swinging extent of the operation lever  54 , and thereby the working machine  1  travels straight forward. 
     In addition, when the operation lever  54  is swung rightward (in the direction indicated by an arrowed line A 3  in  FIG. 1 ), the operation valve  55 C is operated to output a pilot pressure from the operation valve  55 C. 
     The pilot pressure is applied to the pressure receiving portion  53   a  of the traveling pump  53 L through the first traveling fluid tube  45   a , and is applied to the pressure receiving portion  53   b  of the traveling pump  53 R through the fourth traveling fluid tube  45   d . In this manner, the output shaft of the traveling motor  36  arranged on the left revolves forward and the output shaft of the traveling motor  36  arranged on the right revolves backward, and thereby the working machine  1  turns rightward. 
     In addition, when the operation lever  54  is swung leftward (in the direction indicated by an arrowed line A 4  in  FIG. 1 ), the operation valve  55 D is operated to output a pilot pressure from the operation valve  55 D. 
     The pilot pressure is applied to the pressure receiving portion  53   a  of the traveling pump  53 R through the third traveling fluid tube  45   c , and is applied to the pressure receiving portion  53   b  of the traveling pump  53 L through the second traveling fluid tube  45   b . In this manner, the output shaft of the traveling motor  36  arranged on the left revolves backward and the output shaft of the traveling motor  36  arranged on the right revolves forward, and thereby the working machine  1  turns leftward. 
     In addition, when the operation lever  54  is swung in an oblique direction, the pressure difference between the pilot pressures applied to the pressure receiving portion  53   a  and the pressure receiving portion  53   b  determines the revolution direction and the revolution speed of the output shafts of the traveling motor  36  arranged on the left and the traveling motor  36  arranged on the right. The working machine  1  turns right or left while traveling forward or backward. 
     That is, when the operation lever  54  is operated to be swung obliquely forward to the left, the working machine  1  turns left while traveling forward at a speed corresponding to the swing angle of the operation lever  54 . When the operation lever  54  is operated to be swung obliquely forward to the right, the working machine  1  turns right while traveling forward at a speed corresponding to the swing angle of the operation lever  54 . 
     When the operation lever  54  is operated to be swung obliquely backward to the left, the working machine  1  turns left while traveling backward at a speed corresponding to the swing angle of the operation lever  54 . When the operation lever  54  is operated to be swung obliquely backward to the right, the working machine  1  turns right while traveling backward at a speed corresponding to the swing angle of the operation lever  54 . 
     As shown in  FIG. 1  and  FIG. 2 , a plurality of bleed circuits (fluid tubes)  60  are connected to the plurality of traveling fluid tubes  45 . The bleed circuit  60  includes a first bleed circuit  60   a , a second bleed circuit  60   b , a third bleed circuit  60   c , and a fourth bleed circuit  60   d.    
     The first bleed circuit  60   a  is a fluid tube connected to the first traveling fluid tube  45   a . The second bleed circuit  60   b  is a fluid tube connected to the second traveling fluid tube  45   b.    
     The third bleed circuit  60   c  is a fluid tube connected to the third traveling fluid tube  45   c . The fourth bleed circuit  60   d  is a fluid tube connected to the fourth traveling fluid tube  45   d.    
     Each of the first bleed circuit  60   a , the second bleed circuit  60   b , the third bleed circuit  60   c , and the fourth bleed circuit  60   d  is provided with a throttle portion  61  for reducing the flow rate of the hydraulic fluid. 
     The first bleed circuit  60   a , the second bleed circuit  60   b , the third bleed circuit  60   c , and the fourth bleed circuit  60   d  are joined in one, and the joined bleed circuit  60   e  after the joining reaches a discharge portion for discharging the operation fluid stored in the tank  22  or the like. Thus, it is possible to release the air from the traveling fluid tube  45 , for example. 
     Here, focusing on the coupling portion  62   a  between the first traveling fluid tube  45   a  and the first bleed circuit  60   a , on the coupling portion  62   b  between the second traveling fluid tube  45   b  and the second bleed circuit  60   b , on the coupling portion  62   c  between the third traveling fluid tube  45   c  and the third bleed circuit  60   c , and on the coupling portion  62   d  between the fourth traveling fluid tube  45   d  and the third bleed circuit  60   d , the inner diameters of the upstream sides of the plurality of traveling fluid tubes  45  ( 45   a ,  45   b ,  45   c ,  45   d ) are different from the inner diameters of the downstream sides of the plurality of traveling fluid tubes  45  ( 45   a ,  45   b ,  45   c ,  45   d ) in comparison with the coupling portion  62   a , the coupling portion  62   b , the coupling portion  62   c , and the coupling portion  62   d.    
     In particular, the first traveling fluid tube  45   a  has a first section fluid tube  45   al  arranged on the upstream side of the coupling portion  62   a  and a second section fluid tube  45   a   2  arranged on the downstream side of the coupling portion  62   a . The inner diameter UR 1  of the first section fluid tube  45   a   1  is different from the inner diameter DR 1  of the second section fluid tube  45   a   2 . The inner diameter UR 1  is larger than the inner diameter DR 1 . 
     Similarly, the second traveling fluid tube  45   b  has a first section fluid tube  45   b   1  arranged on the upstream side of the coupling portion  62   b  and a second section fluid tube  45   b   2  arranged on the downstream side of the coupling portion  62   b . The inner diameter UR 2  of the first section fluid tube  45   b   1  is different from the inner diameter DR 2  of the second section fluid tube  45   b   2 . The inner diameter UR 2  is larger than the inner diameter DR 2 . 
     The third traveling fluid tube  45   c  has a first section fluid tube  45   c   1  arranged on the upstream side of the coupling portion  62   c  and a second section fluid tube  45   c   2  arranged on the downstream side of the coupling portion  62   c . The inner diameter UR 3  of the first section fluid tube  45   c   1  is different from the inner diameter DR 3  of the second section fluid tube  45   c   2 . The inner diameter UR 3  is larger than the inner diameter DR 3 . 
     The fourth traveling fluid tube  45   d  has a first section fluid tube  45   d   1  arranged on the upstream side of the coupling portion  62   d  and a second section fluid tube  45   d   2  arranged on the downstream side of the coupling portion  62   d . The inner diameter UR 4  of the first section fluid tube  45   d   1  is different from the inner diameter DR 4  of the second section fluid tube  45   d   2 . The inner diameter UR 4  is larger than the inner diameter DR 4 . 
     As described above, in the case where the connection portions (the coupling portion  62   a , the coupling portion  62   b , the coupling portion  62   c , and the coupling portion  62   d ) to which the plurality of bleed circuits  60  are considered as starting points in the plurality of traveling fluid tubes  45 , the inner diameters UR (UR 1  to UR 4 ) of the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1  and  45   d   1  which are fluid tubes arranged on the upstream side are larger than the inner diameters DR (DR 1  to DR 4 ) of the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2  which are fluid tubes arranged on the downstream side. 
     Here, as for the inner diameters UR (UR 1  to UR 4 ) of the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1  and  45   d   1 , the inner diameters DR (DR 1  to DR 4 ) of the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2  and  45   d   2 , and the inner diameter PR of the output fluid tube  40 , the inner diameter PR is equal to or larger than the inner diameters UR, and the inner diameters UR are larger than the inner diameters DR. 
     In addition, the inside diameters (the cross-sectional area through which the operation fluid flows) of the throttle portions  61  provided in the first bleed circuit  60   a , the second bleed circuit  60   b , the third bleed circuit  60   c , and the fourth bleed circuit  60   d  are indicated as inner diameters OR. In that case, as for a relation between the inner diameter OR of the throttle portion  61 , the inner diameters UR (UR 1  to UR 4 ) of the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1  and  45   d   1 , and the inner diameters DR (DR 1  to DR 4 ) of the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2  and  45   d   2 , the inner diameter PR is equal to or more than the inner diameters UR, the inner diameters UR are larger than the inner diameters DR, and the inner diameters DR are larger than the inner diameters OR. 
     The hydraulic system for the working machine includes the operation member  54 , the operation valve  55  to change an output pressure of the operation fluid in accordance with the operation of the operation member  54 , the hydraulic device  34  (the traveling pump  53 L and the traveling pump  53 R) to be activated by the operation fluid outputted from the operation valve  55 , the travel fluid tube (the first fluid tube)  45  coupling the operation valve  55  to the hydraulic device  34  (the traveling pump  53 L and the traveling pump  53 R), and the bleed circuit  60  connected to the travel fluid tube (the first fluid tube)  45  and configured to output the operation fluid in the travel fluid tube (the first fluid tube)  45 . The travel fluid tube (the first fluid tube)  45  includes the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1 , and  45   d   1  provided in a section between the operation valve  55  and the coupling portions  62   a ,  62   b ,  62   c , and  62   d  coupling the travel fluid tube (the first fluid tube)  45  to the bleed circuit  60 , and the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2  provided in a section between the coupling portions  62   a ,  62   b ,  62   c , and  62   d  and the hydraulic device  34  (the traveling pump  53 L and the traveling pump  53 R), the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2  each having the inner diameters different from the inner diameters of the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1 , and  45   d   1 . 
     According to that configuration, the flow rates of the operation fluids flowing in the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1 , and  45   d   1  which are arranged on the upstream sides of the coupling portions  62   a ,  62   b ,  62   c , and  62   d  for connecting the bleed circuit  60  can be different from the flow rates of the operation fluids flowing in the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2  which are arranged on the downstream sides of the coupling portions  62   a ,  62   b ,  62   c , and  62   d.    
     In this manner, the first section fluid tubes  45   a ,  45   b   1 ,  45   c   1 , and  45   d   1  and the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2  form a fluid passage suitable for the balance of the operation fluids flowing toward the hydraulic device. Thus, the operation fluid can be adequately supplied to the hydraulic device. 
     The inner diameters UR of the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1 , and  45   d   1  are larger than the inner diameters DR of the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2 . In this manner, in the travel fluid tube  45 , the inner diameters DR of the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2  arranged on the downstream side can have a size corresponding to the bleed circuit  60 . 
     That is, the tube members such as the hoses constituting the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2  and  45   d   2  can be made smaller than the tube members constituting the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1  and  45   d   1 . Thus, it is possible to reduce the arrangement space for placement of the tube members, and to improve the freedom of the piping arrangement. 
     The hydraulic system for the working machine includes the hydraulic pump P 1  configured to output the operation fluid, and the output fluid tube (the second fluid tube)  40  coupling the hydraulic pump P 1  to the operation valve  55  and having an inner diameter larger than inner diameters of the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2 . 
     According to that configuration, the inner diameter of the output fluid tube  40  arranged on the side to supply the operation fluid to the operation valve  55 , and additionally the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2  can be made smaller, the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2  requiring to have a relatively small flow rate of the operation fluid. 
     Thus, the flow rate of the hydraulic fluid entering the operation valve  55  is ensured, and additionally the flow rate of the operation fluid from the operation valve  55  on the downstream side can be made the flow rate necessary for the hydraulic devices  34  (the traveling pumps  53 L and  53 R). In this manner, the hydraulic device  34  can be operated efficiently. 
     As for the inner diameters UR of the first section fluid tubes, the inner diameters DR of the second section fluid tubes, and the inner diameter PR of the output fluid tube (the second fluid tube)  40 , the inner diameter PR is equal to or larger than the inner diameters UR, and the inner diameters UR are larger than the inner diameters DR. According to that configuration, a balance between the flow rate of the operation fluid to be supplied to the operation valve  55 , the flow rate of the operation fluid outputted from the operation valve  55 , and the flow rate of a part of the operation fluid discharged from the bleed circuit  60  toward the hydraulic devices  34  (the traveling pump  53 L and the traveling pump  53 R) can be optimized. Thus, the hydraulic device  34  can be operated efficiently. 
     Then,  FIG. 3  shows a hydraulic system provided with a relay member. Hereinafter, the relationship between the fluid tubes of the case where of constituting the hydraulic system including the relay member will be described. 
     The relay member  100  is configured by forming the fluid passages (an internal flow passage  93 , and a discharge flow passage  94 ) inside a metal block or the like. The relay member  100  includes a plurality of input ports  90   a ,  90   b ,  90   c , and  90   d , a plurality of output ports  91   a ,  91   b ,  91   c , and  91   d , and a discharge port  92 . 
     The internal flow passage  93  is communicated with the plurality of input ports  90   a ,  90   b ,  90   c , and  90   d . And, the discharge flow passage  94  is communicated with the discharge port  92 . 
     More specifically, the plurality of internal flow passage  93  includes an internal flow tube  93   a  to communicate the input port  90   a  with the output port  91   a , an internal flow tube  93   b  to communicate the input port  90   b  with the output port  91   b , and an internal flow tube  93   c  to communicate the input port  90   c  with the output port  91   c , and an internal flow tube  93   d  to communicate the input port  90   d  with the output port  91   d.    
     The discharge flow passages  94  are branched from the plurality of internal flow passages  93  ( 93   a ,  93   b ,  93   c , and  93   d ), and are communicated with the discharge port  92 . 
     The plurality of input ports  90   a ,  90   b ,  90   c , and  90   d  are coupled to the operation device  47  (the operation valve  55 ) by a plurality of first tube members  96 . The plurality of first tube members  96  are pipes (hoses) or the like, and couple the output ports  95   a ,  95   b ,  95   c , and  95   d  of the operation device  47  to the input ports  90   a ,  90   b ,  90   c , and  90   d  of the relay member  100 . 
     In particular, the plurality of first tube members  96  include a first tube member  96   a  coupling the input port  90   a  to the output port  95   a , a first tube member  96   b  coupling the input port  90   b  to the output port  95   b , a first tube member  96   c  coupling the input port  90   c  to the output port  95   c , and a first tube member  96   d  coupling the input port  90   d  to the output port  95   d.    
     The plurality of output ports  91   a ,  91   b ,  91   c , and  91   d  are coupled to the hydraulic devices  34  (the traveling pumps  53 L and  53 R) by a plurality of second tube members  97 . The plurality of second tube members  97  are pipes (hoses) or the like, and couple the pressure receiving portions  53   a  and  53   b  of the traveling pumps  53 L and  53 R to the output ports  91   a ,  91   b ,  91   c , and  91   d  of the relay member  100 . 
     In particular, the plurality of second tube members  97  include a second tube member  97   a  coupling the output port  91   a  to the pressure receiving portion  53   a  of the traveling pump  53 L, a second tube member  97   b  coupling the output port  91   b  to the pressure receiving portion  53   b  of the traveling pump  53 L, a second tube member  97   c  coupling the output port  91   c  to the pressure receiving portion  53   a  of the traveling pump  53 R, and a second tube member  97   d  coupling the output port  91   d  to the pressure receiving portion  53   b  of the traveling pump  53 R. 
     As described above, when the operation valve  55  is coupled to the traveling pumps  53 L and  53 R by the relay member  100 , the plurality of first tube members  96 , and the plurality of second tube members  97 , the first section fluid tube  45   a   1  includes the first tube member  96   a  and the inner flow passage (inner flow tube)  93   a , the first section fluid tube  45   b   1  includes the first tube member  96   b  and the inner flow passage (inner flow tube)  93   b , the first section fluid tube  45   c   1  includes the first tube member  96   c  and the inner flow passage (inner flow tube)  93   c , and the first section fluid tube  45   d   1  includes the first tube member  96   d  and the inner flow passage (inner flow tube)  93   d.    
     The second section fluid tube  45   a   2  includes the second tube member  97   a  and the inner flow passage  93   a , the second section fluid tube  45   a   2  includes the second tube member  97   b  and the inner flow passage  93   b , the second section fluid tube  45   c   2  includes the second tube member  97   c  and the inner flow passage  93   c , and the second section fluid tube  45   d   2  includes the second tube member  97   d  and the inner flow passage  93   d.    
     The inner diameters of the first tube members  96   a ,  96   b ,  96   c , and  96   d  are the inner diameters UR of the first section fluid tube described above, the inner diameters of the second tube members  97   a ,  97   b ,  97   c , and  97   d  are the inner diameters DR of the second section fluid tube described above, and the inner diameters UR of the first tube members  96   a ,  96   b ,  96   c , and  96   d  are larger than the inner diameters DR of the second tube members  97   a ,  97   b ,  97   c , and  97   d.    
     In the case where the first tube members  96   a ,  96   b ,  96   c , and  96   d  are connected to the relay member  100 , it is preferred that the inner diameters of the first tube members  96   a ,  96   b ,  96   c , and  96   d  are the same as the inner diameters of the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1 , and  45   d   1 . 
     In the case where the second tube members  97   a ,  97   b ,  97   c , and  97   d  are connected to the relay member  100 , it is preferred that the inner diameters of the second tube members  96   a ,  96   b ,  96   c , and  96   d  are the same as the inner diameters of the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2 . 
     Meanwhile, the relay member  100  may include a plurality of pump ports  98  and a pump flow tube  99  to communicate the plurality of pump ports  98  with each other. In that case, the output fluid tube (the second fluid tube) includes the pump flow tube  99 , and the inner diameter of the pump flow tube  99  is formed to have the inner diameter PR mentioned above. 
     In addition, the inner diameter of the third tube member  110  coupling the pump port  98  to the operation device  47  may be determined to be the inner diameter PR mentioned above. And, the inner diameter of the fourth tube member  111  coupling the pump port  98  to the first hydraulic pump P 1  may be determined to be the inner diameter PR mentioned above. 
     The hydraulic system for the working machine includes a relay member  100  having the input ports  90   a ,  90   b ,  90   c ,  90   d , the output ports  91   a ,  91   b ,  91   c ,  91   d , the discharge port  92 , the internal flow tube  93 , and the discharge flow tube  94 . The hydraulic system includes the first tube member  96  and the second tube member  97 . The bleed circuit  60  includes the discharge flow passage (discharge flow tube)  94 . Each of the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1 , and  45   d   1  includes the first tube member  96  and the internal flow passage  93 . And, the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2 , and  45   d   2  include the second tube member  97  and the internal flow passage  93 . 
     According to that configuration, simply by changing the inner diameters of the first tube member  96  and the second tube member  97 , the inner diameters of the first section fluid tubes  45   a   1 ,  45   b   1 ,  45   c   1 , and  45   d   1  and the second section fluid tubes  45   a   2 ,  45   b   2 ,  45   c   2  and  45   d   2  can be easily changed. 
     The inner diameter of the first tube member  96  is larger than the inner diameter of the second tube member  97 . According to that configuration, only by increasing the inner diameter of the first tube member  96 , a balance between the flow rate of the operation fluid outputted from the operation valve  55  and the flow rate of a part of the operation fluid discharged from the bleed circuit  60  toward the hydraulic devices  34  (the traveling pump  53 L and the traveling pump  53 R) can be optimized. Thus, the hydraulic device  34  can be operated efficiently. 
     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.