Patent Publication Number: US-2022234710-A1

Title: Steering device and ship

Description:
CROSS-REFERENCE TO RELATED APPLICATION 
     This application is based upon and claims the benefit of priority to Japanese Patent Application No. 2021-009686, filed on Jan. 25, 2021, the entire contents of which are incorporated herein by reference. 
     FIELD OF THE INVENTION 
     The present invention relates to a steering device, and a ship. 
     BACKGROUND OF THE INVENTION 
     A ship includes a steering device configured to control a traveling direction of a ship body by swinging an outboard motor right and left. For example, JP-A-2020-185885 discloses technology about the steering device. The steering device disclosed in JP-A-2020-185885 includes a cylinder, a motor, a hydraulic source, a main valve, and an oil storage tank. The cylinder is demarcated into a first chamber and a second chamber by a piston. The steering device also includes a check valve that is opened when a hydraulic pressure to the cylinder rapidly increases when supplying an operating oil to a hydraulic circuit so that the piston slides from the first chamber-side toward the second chamber-side. The steering device also includes a check valve that is opened when the hydraulic pressure to the cylinder rapidly increases when supplying the operating oil to the hydraulic circuit so that the piston slides from the second chamber-side toward the first chamber-side. The steering device also includes a manual valve configured to enable manual steering of manually changing the traveling direction of the ship body by opening the valve. 
     An operation load when manually changing the traveling direction of the ship body is preferably small. 
     An object of the present invention is to provide a steering device and the like capable of reducing an operation load when manually changing a traveling direction of a ship body. 
     SUMMARY OF THE INVENTION 
     According to an aspect of the invention, there is provided a steering device including: a flow passage forming member including a first flow passage connecting to a first chamber in a cylinder and a second flow passage connecting to a second chamber in the cylinder; a movable member provided to be movable relative to the flow passage forming member and capable of being arranged between the first flow passage and the second flow passage; a seal member arranged between the movable member and the flow passage forming member and configured to seal a space between the movable member and the flow passage forming member when the seal member is in contact with the movable member and the flow passage forming member; an operation part capable of rotating an outboard motor when a pressure in the first chamber or the second chamber is increased and capable of applying a pressure to the first chamber or the second chamber to rotate the outboard motor when the operation part is manually operated; and a resistance reducing part configured to reduce a flow resistance so that a fluid flows between the first flow passage and the second flow passage even with a pressure generated in the first chamber or the second chamber due to an operation of the operation part by a load equal to or lower than a predetermined load, when sealing is not made by the seal member. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
         FIG. 1  depicts an example of a schematic configuration of a ship  100  in accordance with a first embodiment. 
         FIG. 2  depicts an example of a cylinder  4 , an arm  9 , a pump unit  3  and the like, as seen in a direction II of  FIG. 1 . 
         FIG. 3  depicts an example of a hydraulic circuit of a steering device  1 . 
         FIG. 4  depicts an example of a schematic configuration of a valve unit  50  in accordance with the first embodiment. 
         FIG. 5  depicts a state where the valve unit  50  is inserted up to a forefront side. 
         FIG. 6  depicts an example of a schematic configuration of a first valve  41 . 
         FIG. 7  depicts an example of a schematic configuration of a manual valve  243  in accordance with a second embodiment. 
         FIG. 8  depicts an example of a schematic configuration of a manual valve  343  in accordance with a third embodiment. 
         FIG. 9  depicts an example of a schematic configuration of a manual valve  443  in accordance with a fourth embodiment. 
         FIG. 10A  depicts an example of a schematic configuration of a second valve  542  in accordance with a fifth embodiment. 
         FIG. 10B  depicts an example of a schematic configuration of a manual valve  543  in accordance with the fourth embodiment. 
         FIG. 11  depicts an example of a schematic configuration of a valve unit  650  in accordance with a sixth embodiment. 
     
    
    
     DETAILED DESCRIPTION OF THE INVENTION 
     Hereinbelow, embodiments of the present invention will be described in detail with reference to the accompanying drawings. Note that, the embodiments of the present invention to be described below are just exemplary, and the present invention is not limited to the embodiments. 
     First Embodiment 
       FIG. 1  depicts an example of a schematic configuration of a ship  100  in accordance with a first embodiment. 
       FIG. 2  depicts an example of a cylinder  4 , an arm  9 , a pump unit  3  and the like, as seen in a direction II of  FIG. 1 . 
       FIG. 3  depicts an example of a hydraulic circuit of a steering device  1 . 
     The ship  100  includes a ship body  101 , an outboard motor  102  mounted to the ship body  101  and configured to generate a propulsion force, and a steering device  1  configured to change a traveling direction of the ship  100  by using an oil that is an example of the fluid. In descriptions below, a traveling direction in a state where the ship  100  travels in a straight line may be referred to as the front, an opposite direction to the traveling direction may be referred to as the rear, the left side with respect to the traveling direction may be referred to as the left, and the right side with respect to the traveling direction may be referred to as the right. 
     The steering device  1  has a ring-shaped steering wheel  2  provided to a front part of the ship body  101 . The steering device  1  also includes a pump unit  3  configured to supply the oil according to rotation of the steering wheel  2 , and a cylindrical cylinder  4  into which the oil supplied by the pump unit  3  is caused to flow, which are provided to a rear part of the ship body  101 . The steering device  1  also includes a piston  5  by which a space in the cylinder  4  is demarcated into a first chamber Y 1  and a second chamber Y 2 , and a rod  6  axially penetrating the cylinder  4  and holding the piston  5 . The steering device  1  also includes a piping  7  connected to the pump unit  3  and the first chamber Y 1  of the cylinder  4 , and a piping  8  connected to the pump unit  3  and the second chamber Y 2  of the cylinder  4 . The oil is supplied to any one of the piping  7  and the piping  8 , according to a rotation direction of the steering wheel  2 . The steering device  1  also includes a flat plate-shaped arm  9  having one end attached to the outboard motor  102 , and a link  10  connected to the arm  9  and the cylinder  4 . 
     As shown in  FIG. 3 , the pump unit  3  has a motor  20 , a pump  21  having a pair of gears and configured to be driven to discharge the oil by the motor  20 , and a tank  22  in which the oil is stored. A flow passage  31  leading to the first chamber Y 1  and a flow passage  32  leading to the second chamber Y 2  are formed between the pump  21  and the cylinder  4 . 
     The pump unit  3  includes a main valve  23  arranged to straddle the flow passage  31  and the flow passage  32  and configured to switch a direction of the oil flowing toward the first chamber Y 1  or the second chamber Y 2 . 
     The pump unit  3  also includes a check valve  24  arranged on a supply path  33  through which the oil is supplied from the tank  22  to the pump  21 , and a check valve  25  arranged on a supply path  34  through which the oil is supplied from the tank  22  to the pump  21 . The supply path  33  is connected to a flow passage  31 A leading from the pump  21  to the main valve  23 . The supply path  34  is connected to a flow passage  32 A leading from the pump  21  to the main valve  23 . 
     The pump unit  3  also includes a first valve  41  that opens when a pressure in a flow passage  31 B leading from the main valve  23  to the first chamber Y 1  becomes equal to or higher than a preset pressure, thereby relieving the oil in the flow passage  31 B to a flow passage  32 B leading from the main valve  23  to the second chamber Y 2 . The pressure in the flow passage  31 B becomes equal to or higher than the preset pressure when an external force is applied to the outboard motor  102  and the piston  5  is thus rapidly moved toward the first chamber Y 1 , for example. 
     The pump unit  3  also includes a second valve  42  that opens when a pressure in the flow passage  32 B becomes equal to or higher than a preset pressure, thereby relieving the oil in the flow passage  32 B to the flow passage  31 B. The pressure in the flow passage  32 B becomes equal to or higher than the preset pressure when an external force is applied to the outboard motor  102  and the piston  5  is thus rapidly moved toward the second chamber Y 2 , for example. 
     The pump unit  3  also includes a manual valve  43  that is arranged on an flow passage between the flow passage  31 B and the flow passage  32 B and can be manually opened and closed by a user. 
     The pump unit  3  also includes a housing  30  (refer to  FIG. 2 ) in which the pump  21 , the main valve  23 , the check valve  24 , the check valve  25 , the first valve  41 , the second valve  42  and the manual valve  43  are accommodated. The housing  30  is formed with the flow passage  31 A and the flow passage  32 A. The housing  30  is connected to the piping  7  and the piping  8 . A part of the flow passage  31 B is constituted by the piping  7 , and the flow passage  31 B from the main valve  23  to the piping  7  is formed in the housing  30 . A part of the flow passage  32 B is constituted by the piping  8 , and the flow passage  32 B from the main valve  23  to the piping  8  is formed in the housing  30 . 
     In the steering device  1  configured as described above, when the steering wheel  2  is rotated in a clockwise direction, the oil is supplied to the second chamber Y 2  by the pump  21 , so that a pressure in the second chamber Y 2  is increased. Thereby, the cylinder  4  is moved leftward with respect to the piston  5  whose position is fixed via the rod  6 , so that the outboard motor  102  is rotated in an A direction (counterclockwise direction) shown in  FIG. 1 . As a result, the ship body  101  travels rightward. On the other hand, when the steering wheel  2  is rotated in a counterclockwise direction, the oil is supplied to the first chamber Y 1  by the pump  21 , so that a pressure in the first chamber Y 1  is increased. Thereby, the cylinder  4  is moved rightward with respect to the piston  5 , so that the outboard motor  102  is rotated in a B direction (clockwise direction) shown in  FIG. 1 . As a result, the ship body  101  travels leftward. 
     In the below, the first valve  41 , the second valve  42 , and the manual valve  43  are described. 
     (Valve Unit  50 ) 
       FIG. 4  depicts an example of a schematic configuration of a valve unit  50  in accordance with the first embodiment. 
     The pump unit  3  of the first embodiment includes a valve unit  50  where the second valve  42  and the manual valve  43  are integrally constituted. 
     The valve unit  50  includes a spherical valve body  51 , a movable member  52  on which the valve body  51  is seated, a holding member  53  configured to hold the valve body  51 , a coil-shaped spring  54 , and a cap  55  for plugging a through-hole  35  formed in the housing  30 . The valve unit  50  also includes a handle  57  that is gripped for operation with a hand by a user, and an annular seal member  58  configured to seal a gap between the movable member  52  and the housing  30 . 
     In the valve unit  50 , the movable member  52  is press-fitted into the cap  55  and is thus integrated in a state where the spring  54 , the holding member  53  and the valve body  51  are accommodated in the cap  55 . The handle  57  is mounted to the cap  55 . The valve unit  50  is inserted in the through-hole  35  formed in the housing  30  from the movable member  52 -side. The valve unit  50  is arranged so that the movable member  52  is on the front side and the handle  57  is on the rear side with respect to the ship body  101 . 
     The movable member  52  has a cylindrical first part  521  provided on the forefront side, a cylindrical second part  522  provided behind the first part  521 , a cylindrical third part  523  provided behind the second part  522 , and a cylindrical fourth part  524  provided behind the third part  523 . 
     The first part  521  is formed with a through-hole  525  for communicating an inside and an outside. The through-hole  525  may be one or may be formed in plural with equal intervals in a circumferential direction. 
     An inner diameter of the second part  522  is the same as an inner diameter of the first part  521 , and an outer diameter of the second part  522  is larger than an outer diameter of the first part  521 . 
     An inner diameter of the third part  523  is larger than the inner diameter of the second part  522 , and an outer diameter of the third part  523  is the same as the outer diameter of the second part  522 . 
     An inner diameter of the fourth part  524  is the same as the inner diameter of the third part  523 , and an outer diameter of the fourth part  524  is smaller than the outer diameter of the third part  523 . 
     An end portion on a rear side of the fourth part  524  is formed with a concave portion  526  recessed from an inner peripheral surface. An end portion on a front side of the concave portion  526  is formed with a seating surface  527  on which the valve body  51  is seated and which is inclined relative to a center line C 1 . 
     The holding member  53  is a columnar member having an outer diameter smaller than an inner diameter of the spring  54 . The holding member  53  has a protrusion part  531  provided at an end portion on a front side and protruding outward from an outer peripheral surface. An outer diameter of the protrusion part  531  is larger than a center diameter of the spring  54 , and is equal to or smaller than the outer diameter of the fourth part  524  of the movable member  52 . The protrusion part  531  supports an end portion on a front side of the spring  54 . 
     The cap  55  has a cylindrical tubular part  551  provided on a front side, a columnar first pillar-shaped part  561  provided behind the tubular part  551 , and a columnar second pillar-shaped part  562  provided behind the first pillar-shaped part  561 . 
     An inner diameter of the tubular part  551  is larger than the outer diameter of the spring  54  and the outer diameter of the protrusion part  531  of the holding member  53 , so that the spring  54 , the holding member  53  and the valve body  51  are accommodated in the tubular part  551 . 
     The inner diameter of the tubular part  551  is smaller than the outer diameter of the fourth part  524  of the movable member  52 , and an outer diameter of the tubular part  551  is substantially the same as the outer diameter of the third part  523  of the movable member  52 . The tubular part  551  and the movable member  52  are fitted (press-fitted) by interference-fit. 
     In the tubular part  551 , a through-hole  553  for communicating an inside and an outside is formed behind a part in which the fourth part  524  of the movable member  52  is fitted. In the tubular part  551 , a male screw  554  that is fastened to a female screw  355  formed in the through-hole  35  is formed at a part behind the through-hole  553 . 
     The first pillar-shaped part  561  is formed with a groove  563  recessed from an outer peripheral surface over an entire circumference. In the groove  563 , an O-ring  564  for sealing a space between an outer peripheral surface of the cap  55  and an inner peripheral surface of the through-hole  35  is fitted. 
     An end portion on a rear side of the second pillar-shaped part  562  is formed with a female screw  565 . A bolt  59  is fastened to the female screw  565 , so that the handle  57  is attached to the second pillar-shaped part  562 . 
     The seal member  58  has an inner diameter that is larger than the outer diameter of the first part  521  of the movable member  52 , and an outer diameter that is substantially the same as the outer diameter of the second part  522 . 
     The through-hole  35  has a columnar first hole  351  formed on a front side and a columnar second hole  352  formed on a rear side and having a diameter larger than a diameter of the first hole  351 . The first hole  351  communicates with the flow passage  32 B. The second hole  352  communicates with the flow passage  31 B via a connection hole  353  formed in a direction of intersecting with the center line C 1  of the second hole  352 . Note that, an opening on a front side, which is opposite to a side in which the valve unit  50  is inserted, of the through-hole  35  is closed. 
     The valve unit  50  configured as described above is mounted to the housing  30  by operating the handle  57  to fasten the male screw  554  of the cap  55  to the female screw  355  formed in the through-hole  35 . The seal member  58  is attached to an outer side of the first part  521  of the movable member  52 , and the seal member  58  is arranged between the second part  522  of the movable member  52  and the housing  30 . 
       FIG. 5  depicts a state where the valve unit  50  is inserted up to the innermost side. 
     The user can change a screwing depth of the valve unit  50  to the housing  30  by operating the handle  57 . As shown in  FIG. 5 , the user can insert forward the valve unit  50  until the seal member  58  comes into contact with the second part  522  of the movable member  52  and the housing  30 . On the other hand, the user can move rearward the valve unit  50  until an end face on the rear side of the first pillar-shaped part  561  of the cap  55  is butted against a clip  354  attached to the housing  30 . 
     In a state (hereinbelow, also referred to as ‘first state’) where the seal member  58  is in contact with the second part  522  of the movable member  52  and the housing  30 , the seal member  58  seals the gap between the movable member  52  and the housing  30 . For this reason, in the first state, the oil is difficult to flow between the flow passage  31 B and the flow passage  32 B through a ring-shaped flow passage R 1  between an outer peripheral surface of the first part  521  of the movable member  52  and an inner peripheral surface of the first hole  351  of the through-hole  35  of the housing  30 . 
     In addition, in the first state, the valve body  51  is applied with a spring force of the spring  54  via the holding member  53  and is thus seated on the seating surface  527  of the movable member  52 , so that the valve body  51  is not opened unless the pressure in the flow passage  32 B becomes equal to or higher than a preset pressure. The preset pressure is set as a value that the pressure in the flow passage  32 B is difficult to reach simply by manually operating the arm  9 . 
     As a result, it is difficult to rotate the outboard motor  102  by manually operating the arm  9  in a direction in which the piston  5  moves toward the second chamber Y 2 -side. 
     Note that, in the first state, when the pressure in the flow passage  32 B becomes equal to or higher than the preset pressure, the valve body  51  moves rearward against the spring force of the spring  54 , so that a gap is formed between the valve body  51  and the seating surface  527  of the movable member  52 . For this reason, the oil flows from the flow passage  32 B to the flow passage  31 B through an inside of the movable member  52 , the gap between the valve body  51  and the seating surface  527  of the movable member  52 , and the through-hole  553  of the tubular part  551  of the cap  55 . 
     On the other hand, as shown in  FIG. 4 , in a state (hereinbelow, also referred to as ‘second state’) where the seal member  58  is not in contact with the second part  522  of the movable member  52  and the housing  30 , the seal member  58  does not seal the gap between the movable member  52  and the housing  30 . Therefore, the oil can easily flow between the flow passage  31 B and the flow passage  32 B through the ring-shaped flow passage R 1 . As a result, when the user unfastens the male screw  554  and takes out the valve unit  50  rearward, it is possible to rotate the outboard motor  102  more easily by manually operating the arm  9 , as compared to the first state. 
     In addition, when the valve unit  50  is moved until the through-hole  525  formed in the first part  521  of the movable member  52  is located behind the first hole  351  of the housing  30 , the oil flows from the flow passage  32 B to the flow passage  31 B through the through-hole  525 . An area of the through-hole  525  is greater than a flow area of the ring-shaped flow passage R 1 . As a result, since a flow resistance of the oil flowing between the flow passage  31 B and the flow passage  32 B is reduced, an operation load is reduced when manually changing the traveling direction of the ship body  101  by operating the arm  9 . 
     From the above, the valve body  51 , the movable member  52 , the holding member  53 , the spring  54 , the cap  55 , the seal member  58  and the housing  30  constitute the second valve  42 . The movable member  52 , the cap  55 , the handle  57 , the seal member  58  and the housing  30  constitute the manual valve  43  that can open and close the flow passage between the flow passage  31 B and the flow passage  32 B by the user&#39;s operation. 
     Note that, the clip  354  is provided in a position where the end face on the rear side of the first pillar-shaped part  561  of the cap  55  is butted when the end portion on the front side of the first part  521  of the movable member  52  is located in the first hole  351  of the housing  30 . This is to locate the seal member  58  on the outer side of the first part  521  even when the male screw  554  is unfastened and the valve unit  50  is taken out rearward by the user. 
     (First Valve  41 ) 
       FIG. 6  depicts an example of a schematic configuration of the first valve  41 . 
     The first valve  41  includes a spherical valve body  61 , a movable member  62  on which the valve body  61  is seated, a holding member  63  configured to hold the valve body  61 , a coil-shaped spring  64 , and a cap  65  for plugging a through-hole  36  formed in the housing  30 . The first valve  41  also includes an annular seal member  68  for sealing a gap between the movable member  62  and the housing  30 . 
     Since the valve body  61 , the movable member  62 , the holding member  63  and the spring  64  are each similar to the valve body  51 , the movable member  52 , the holding member  53  and the spring  54  of the valve unit  50 , the detailed descriptions thereof are omitted. 
     The cap  65  is different from the cap  55 , in that it does not have the second pillar-shaped part  562  and the handle  57  is not attached thereto. 
     The first valve  41  is inserted in the through-hole  36 . The through-hole  36  has a columnar first hole  361  formed on a rear side and a columnar second hole  362  formed on a front side and having a diameter larger than a diameter of the first hole  361 . The first hole  361  is configured to communicate with the flow passage  31 B. The second hole  362  is configured to communicate with the flow passage  32 B via a connection hole (not shown) formed in a direction of intersecting with a center line of the second hole  362 . 
     The first valve  41  is inserted in the through-hole  36  until the seal member  68  comes contact with the movable member  62  and the housing  30 . The valve body  61  is applied with a spring force of the spring  64  via the holding member  63  and is thus in contact with a seating surface  627  of the movable member  62 . When the pressure in the flow passage  31 B becomes equal to or higher than the preset pressure, the valve body  61  separates from the seating surface  627 . When the pressure in the flow passage  31 B becomes equal to or higher than the preset pressure, the valve body  61  is moved forward against the spring force of the spring  64 , so that a gap is formed between the valve body  61  and the seating surface  627  of the movable member  62 . As a result, the oil flows from the flow passage  31 B to the flow passage  32 B through an inside of the movable member  62 , the gap between the valve body  61  and the seating surface  627  of the movable member  62 , and a through-hole  653  of a tubular part  651  of the cap  65 . 
     The preset pressure at which the valve body  61  starts to move is set as a value that the pressure in the flow passage  31 B is difficult to reach simply by manually operating the arm  9 . 
     As a result, it is difficult to rotate the outboard motor  102  by manually operating the arm  9  in a direction in which the piston  5  moves toward the first chamber Y 1 -side. 
     However, as shown in  FIG. 4 , the user unfastens the male screw  554  to take out the valve unit  50  rearward, and causes the seal member  58  not to seal the gap between the movable member  52  and the housing  30 , thereby enabling the oil to easily flow between the flow passage  31 B and the flow passage  32 B. Thereby, it is possible to easily rotate the outboard motor  102  by manually operating the arm  9 . 
     As described above, the steering device  1  includes the housing  30  as an example of the flow passage forming member where the flow passage  31 B as an example of the first flow passage connecting to the first chamber Y 1  in the cylinder  4  and the flow passage  32 B as an example of the second flow passage connecting to the second chamber Y 2  in the cylinder  4  are formed. The steering device  1  also includes the movable member  52  as an example of the movable member provided to be movable relative to the housing  30  and capable of being arranged between the flow passage  31 B and the flow passage  32 B. The steering device  1  also includes the seal member  58  arranged between the movable member  52  and the housing  30  and sealing a space between the movable member  52  and the housing  30  when the seal member  58  is in contact with the movable member  52  and the housing  30 . The steering device  1  also includes the arm  9  as an example of the operation part capable of rotating the outboard motor  102  when the pressure in the first chamber Y 1  or the second chamber Y 2  is increased and applying a pressure to the first chamber Y 1  or the second chamber Y 2  to rotate the outboard motor  102  when it is manually operated. The steering device  1  also includes the through-hole  525  as an example of the resistance reducing part that reduces a flow resistance so that the oil as an example of the fluid flows between the flow passage  31 B and the flow passage  32 B, when the sealing is not made by the seal member  58 . 
     Here, an area S (cm 2 ) of the through-hole  525  of the first part  521  of the movable member  52  is determined so that a manual steering load F of the arm  9  is equal to or lower than a preset upper limit load Fm. More specifically, the area S is calculated using following equations (1), (2) and (3). Note that, the upper limit load Fm may be 100(N), for example. 
     
       
         
           
             
               
                 
                   Q 
                   = 
                   
                     C 
                     * 
                     S 
                     ⁢ 
                     
                       
                         
                           2 
                           * 
                           G 
                           * 
                           
                             ( 
                             
                               
                                 P 
                                 1 
                               
                               - 
                               
                                 P 
                                 2 
                               
                             
                             ) 
                           
                         
                         r 
                       
                     
                   
                 
               
               
                 
                   ( 
                   1 
                   ) 
                 
               
             
           
         
       
     
     Q is a flow rate (cm 3 /sec) of the oil to flow per a unit time and is determined by the equation (2). P 1  is a pressure (MPa) on a high pressure-side (for example, the pressure in the flow passage  32 B when the arm  9  is steered so that the piston  5  moves toward the second chamber Y 2 ) and is a value determined by the equation (3). C is a resistance coefficient of a flow passage, G is the acceleration of gravity (=980 cm/sec), P 2  is a pressure (MPa) on a lower pressure-side, and r is a specific gravity (Kgf/cm 3 ). 
         Q=Sp×Lp/t   (2)
 
     Lp is a stroke (cm) of the piston  5 , and t is an operating time (sec) of the arm  9  (piston  5 ). 
         P   1   =k×Fm/Sp   (3)
 
     k is a coefficient corresponding to a length of the arm  9  and Sp is a sectional area (cm 2 ) of the piston  5 . 
     Note that, in a case of Fm=100 (N), C=0.7, P 2 =0 (MPa), r=0.000851 (Kgf/cm 3 ), Sp=36.32 (cm 2 ), Lp=3.79 (cm), t=3 (sec) and k=6.9, the area S is 0.0322 (cm 2 ). 
     In the case of the area S=0.0322 (cm 2 ), when the through-hole  525  is one, the hole diameter is 0.202 (cm), and when the through-hole  525  is two, the hole diameter is 0.143 (cm). When the two through-holes  525  are provided and the hole diameter is set to 0.15 (cm), the manual steering load F can be made equal to or lower than the upper limit load Fm. 
     As described above, when the sealing is not made by the seal member  58 , the through-hole  525  of the first part  521  of the movable member  52  reduces the flow resistance so that the oil flows between the flow passage  31 B and the flow passage  32 B even with the pressure generated in the first chamber Y 1  or the second chamber Y 2  due to the operation of the arm  9  with the load equal to or lower than the upper limit load Fm. 
     The flow resistance reducing function of the through-hole  525  is exhibited as the through-hole  525  is provided as described above. That is, in the steering device  1 , the movable member  52  has the first part  521  as an example of the cylindrical part that is fitted in the first hole  351  as an example of the hole formed in the housing  30  and communicating with the flow passage  32 B. When the sealing is made by the seal member  58 , the through-hole  525  is located inside the first hole  351 , and when the sealing is not made by the seal member  58 , the through-hole  525  is located outside the first hole  351  so that the fluid flows between the flow passage  31 B and the flow passage  32 B via the through-hole  525 . 
     In the steering device  1 , the movable member  52  is cylindrical, and has the seating surface  527  provided at the end portion on the opposite side to the flow passage  32 B in the direction of the center line C 1  and being in contact with the spherical valve body  51 . The steering device  1  has the cap  55  configured to accommodate therein the valve body  51 , the holding member  53  as an example of the pressing part for pressing the valve body  51  to the seating surface  527  and the spring  54  together with the movable member  52 , and having the through-hole  553  formed on a further opposite side to the flow passage  32 B than the valve body  51  and provided as an example of the communication hole for communicating an inside and an outside. In other words, the steering device  1  includes the valve unit  50  where the second valve  42  and the manual valve  43  are integrally provided. For this reason, as compared to a configuration where the second valve  42  and the manual valve  43  are provided as separate bodies, the steering device  1  has a simpler configuration and is more lightweight. 
     Second Embodiment 
       FIG. 7  depicts an example of a schematic configuration of a manual valve  243  in accordance with a second embodiment. 
     A steering device  200  of the second embodiment is different from the steering device  1  of the first embodiment, in a manual valve  243  corresponding to the manual valve  43 . The manual valve  243  is different from the manual valve  43 , in a movable member  252  corresponding to the movable member  52 . Hereinbelow, differences from the steering device  1  are described. The parts having the same functions between the steering device  1  and the steering device  200  are denoted with the same reference signs, and the detailed descriptions thereof are omitted. 
     The movable member  252  is different from the movable member  52  of the first embodiment, in a first part  2521  corresponding to the first part  521 . The first part  2521  is not formed with the through-hole  525  that is formed in the first part  521 . An outer diameter of the first part  2521  is smaller than the outer diameter of the first part  521 . For this reason, in the manual valve  243 , a flow area of a ring-shaped flow passage R 2  between an outer peripheral surface of the first part  2521  and the inner peripheral surface of the first hole  351  of the through-hole  35  of the housing  30  is greater than the flow area of the ring-shaped flow passage R 1  of the first embodiment. 
     For this reason, when the male screw  554  (refer to  FIG. 4 ) is unfastened by the user and the seal member  58  does not seal the gap between the movable member  252  and the housing  30 , the resistance when the oil flows between the flow passage  31 B and the flow passage  32 B through the ring-shaped flow passage R 2  is reduced, as compared to the resistance when the oil flows through the ring-shaped flow passage R 1 . As a result, even when the first part  2521  is not formed with a through-hole corresponding to the through-hole  525 , the operation load when manually operating the arm  9  is reduced. 
     Here, a gap h 2  (cm) (=(the outer diameter d (cm) of the first part  2521 −the diameter (D) (cm) of the first hole  351 )/2) between the outer peripheral surface of the first part  2521  and the inner peripheral surface of the first hole  351  of the through-hole  35  of the housing  30  is determined so that the manual steering load F of the arm  9  is equal to or lower than the upper limit load Fm. More specifically, the gap h 2  is calculated using a following equation (4). 
     
       
         
           
             
               
                 
                   Q 
                   = 
                   
                     
                       
                         
                           π 
                           ⁡ 
                           
                             ( 
                             
                               D 
                               - 
                               
                                 2 
                                 ⁢ 
                                 h2 
                               
                             
                             ) 
                           
                         
                         ⁢ 
                         
                           h2 
                           3 
                         
                       
                       
                         12 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         μ 
                       
                     
                     × 
                     
                       
                         ( 
                         
                           
                             P 
                             1 
                           
                           - 
                           
                             P 
                             2 
                           
                         
                         ) 
                       
                       L 
                     
                   
                 
               
               
                 
                   ( 
                   4 
                   ) 
                 
               
             
           
         
       
     
     Q and P 1  are values determined by the above equations (2) and (3). μ is a viscosity (Pa·sec) of the oil, and L is a wrap length (cm) of the first part  2521  and the first hole  351 . 
     In a case of Fm=100 (N), D=0.325 (cm), P 2 =0 (MPa) and L=0.1 (cm), the gap h 2 =0.062 (cm) is calculated, and d 0 =0.201 (cm) is calculated using an equation of d 0  (cm)=D−2×h 2 . The outer diameter d of the first part  2521  is set smaller than d 0 , so that the manual steering load F can be made equal to or lower than the upper limit load Fm. 
     As described above, in the steering device  200 , the movable member  252  has the first part  2521  as an example of the cylindrical part that is fitted in the first hole  351  formed in the housing  30  and communicating with the flow passage  32 B. The ring-shaped flow passage R 2  between the outer peripheral surface of the first part  2521  and the inner peripheral surface of the first hole  351  functions as the resistance reducing part that reduces the flow resistance so that the oil flows between the flow passage  31 B and the flow passage  32 B even with the pressure generated in the first chamber Y 1  or the second chamber Y 2  due to the operation of the arm  9  with the load equal to or lower than the upper limit load, when the sealing is not made by the seal member  58 . 
     Since the inner diameter of the first part  2521  is the same as the inner diameter of the first part  521 , the resistance when the oil passes through the inside of the first part  2521  can be made to be the same as the resistance when the oil passes through the inside of the first part  521 . For this reason, also in the second embodiment, the second valve  42  is opened when the pressure in the flow passage  32 B becomes equal to or higher than the preset pressure, so that the oil in the flow passage  32 B can be relived to the flow passage  31 B. In the meantime, the inner diameter of the first part  2521  may be set small within a range in which the second valve  42  can be opened when the pressure in the flow passage  32 B becomes equal to or higher than the preset pressure. 
     Note that, the first part  2521  may also be formed with a through-hole corresponding to the through-hole  525 . Thereby, as compared to the configuration where the movable member  252  is used, the resistance when the oil flows between the flow passage  31 B and the flow passage  32 B is reduced. As a result, the operation load when manually operating the arm  9  is reduced. 
     Third Embodiment 
       FIG. 8  depicts an example of a schematic configuration of a manual valve  343  in accordance with a third embodiment. 
     A steering device  300  of the third embodiment is different from the steering device  1  of the first embodiment, in a manual valve  343  corresponding to the manual valve  43 . The manual valve  343  is different from the manual valve  43 , in a movable member  350  corresponding to the movable member  52  and a housing  330  corresponding to the housing  30 . Hereinbelow, differences from the steering device  1  are described. The parts having the same functions between the steering device  1  and the steering device  300  are denoted with the same reference signs, and the detailed descriptions thereof are omitted. 
     The movable member  350  is different from the movable member  52 , in a first part  3521  corresponding to the first part  521 . The first part  3521  is not formed with the through-hole  525  that is formed in the first part  521 . 
     The housing  330  is different from the housing  30 , in a through-hole  335  corresponding to the through-hole  35 . The through-hole  335  has a columnar first hole  3351  corresponding to the first hole  351 , and the second hole  352 . A diameter of the first hole  3351  is larger than the diameter of the first hole  351 . 
     For this reason, in the manual valve  343 , a flow area of a ring-shaped flow passage R 3  between an outer peripheral surface of the first part  3521  and an inner peripheral surface of the first hole  3351  of the through-hole  335  of the housing  330  is greater than the flow area of the ring-shaped flow passage R 1  of the first embodiment. 
     For this reason, when the male screw  554  (refer to  FIG. 4 ) is unfastened by the user and the seal member  58  does not seal the gap between the movable member  350  and the housing  330 , the resistance when the oil flows between the flow passage  31 B and the flow passage  32 B through the ring-shaped flow passage R 3  is reduced, as compared to the resistance when the oil flows through the ring-shaped flow passage R 1 . As a result, even when the first part  3521  is not formed with a through-hole corresponding to the through-hole  525 , the operation load when manually operating the arm  9  is reduced. 
     Here, a gap h 3  (cm) (=(the outer diameter d (cm) of the first part  3521 −the diameter (D) (cm) of the first hole  3351 )/2) between the outer peripheral surface of the first part  3521  and the inner peripheral surface of the first hole  3351  of the through-hole  335  of the housing  330  is determined so that the manual steering load F of the arm  9  is equal to or lower than the upper limit load Fm. More specifically, the gap h 3  is calculated using a following equation (5). 
     
       
         
           
             
               
                 
                   Q 
                   = 
                   
                     
                       
                         π 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         dh 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         
                           3 
                           3 
                         
                       
                       
                         12 
                         ⁢ 
                         
                             
                         
                         ⁢ 
                         μ 
                       
                     
                     × 
                     
                       
                         ( 
                         
                           
                             P 
                             1 
                           
                           - 
                           
                             P 
                             2 
                           
                         
                         ) 
                       
                       L 
                     
                   
                 
               
               
                 
                   ( 
                   5 
                   ) 
                 
               
             
           
         
       
     
     Q and P 1  are values determined by the above equations (2) and (3). μ is a viscosity (Pa·sec) of the oil, and L is a wrap length (cm) of the first part  3521  and the first hole  3351 . 
     In a case of Fm=100 (N), D=0.325 (cm), P 2 =0 (MPa) and L=0.1 (cm), the gap h 3 =0.053 (cm) is calculated, and D 0 =0.431 (cm) is calculated using an equation of D 0  (cm)=d+2×h 2 . The outer diameter D of the first hole  3351  is set larger than D 0 , so that the manual steering load F can be made equal to or lower than the upper limit load Fm. 
     As described above, in the steering device  300 , the movable member  350  has the first part  3521  as an example of the cylindrical part that is fitted in the first hole  3351  formed in the housing  330  and communicating with the flow passage  32 B. The ring-shaped flow passage R 3  between the outer peripheral surface of the first part  3521  and the inner peripheral surface of the first hole  3351  functions as the resistance reducing part that reduces the flow resistance so that the oil flows between the flow passage  31 B and the flow passage  32 B even with the pressure generated in the first chamber Y 1  or the second chamber Y 2  due to the operation of the arm  9  with the load equal to or lower than the upper limit load, when the sealing is not made by the seal member  58 . 
     In addition, since the movable member  62  and the movable member  350  of the first valve  41  can be made to be the same, it is possible to reduce the number of components of the steering device  300 . 
     Note that, the first part  3521  may also be formed with a through-hole corresponding to the through-hole  525 . Thereby, as compared to the configuration where the movable member  350  is used, the resistance when the oil flows between the flow passage  31 B and the flow passage  32 B is reduced. 
     In addition, the movable member  252  of the second embodiment may also be used instead of the movable member  350 . Thereby, as compared to the configuration where the movable member  350  is used, the resistance when the oil flows between the flow passage  31 B and the flow passage  32 B is reduced. As a result, the operation load when manually operating the arm  9  is reduced. 
     Fourth Embodiment 
       FIG. 9  depicts an example of a schematic configuration of a manual valve  443  in accordance with a fourth embodiment. 
     A steering device  400  of the fourth embodiment is different from the steering device  1  of the first embodiment, in a manual valve  443  corresponding to the manual valve  43 . The manual valve  443  is different from the manual valve  43  of the first embodiment, in a movable member  452  corresponding to the movable member  52 , a seal member  458  corresponding to seal member  58  and a housing  430  corresponding to the housing  30 . Hereinbelow, differences from the steering device  1  are described. The parts having the same functions between the steering device  1  and the steering device  400  are denoted with the same reference signs, and the detailed descriptions thereof are omitted. 
     The movable member  452  is different from the movable member  52 , in a second part  4522  corresponding to the second part  522 . An outer diameter of the second part  4522  is smaller than the outer diameter of the second part  522 . That is, the outer diameter of the second part  4522  is smaller than the outer diameter of the third part  523 , and the outer diameters are larger in order of the first part  521 , the second part  4522  and the third part  523  in the flow direction of the oil from the flow passage  32 B toward the flow passage  31 B. 
     An outer diameter of the seal member  458  is smaller than the outer diameter of the seal member  58  and is substantially the same as the outer diameter of the second part  4522 . 
     The housing  430  is different from the housing  30 , in a through-hole  435  corresponding to the through-hole  35 . The through-hole  435  has the first hole  351 , and a second hole  4352  corresponding to the second hole  352 . The through-hole  435  is also formed with a columnar first intermediate hole  4353  having a diameter larger than the diameter of the first hole  351  and a truncated conical second intermediate hole  4354  formed behind the first intermediate hole  4353  and having an outer diameter that becomes larger in the flow direction of the oil from the flow passage  32 B toward the flow passage  31 B, between the first hole  351  and the second hole  4352 . That is, the diameter of the through-hole  435  becomes larger in order of the first hole  351 , the first intermediate hole  4353 , the second intermediate hole  4354  and the second hole  4352  in the flow direction of the oil from the flow passage  32 B toward the flow passage  31 B. 
     For this reason, when the male screw  554  (refer to  FIG. 4 ) is unfastened by the user and the seal member  458  does not seal a gap between the movable member  452  and the housing  430 , the oil flows in a direction inclined relative to the center line C 1  while the oil flows between the flow passage  31 B and the flow passage  32 B, particularly, while the oil flows through the second intermediate hole  4354 . In addition, a gap between an outer peripheral surface of the second part  4522  of the movable member  452  and an inner peripheral surface of the second hole  4352  is greater than the gap between the outer peripheral surface of the second part  522  of the movable member  52  of the first embodiment and the inner peripheral surface of the second hole  352 . For this reason, the resistance when the oil flows between the flow passage  31 B and the flow passage  32 B is reduced, as compared to the resistance in the first embodiment. As a result, the operation load when manually operating the arm  9  is reduced. 
     As described above, in the steering device  400 , the movable member  452  has the second part  4522  as an example of the first protrusion, which protrudes to have an outer diameter larger than the outer diameter of the first part  521  and is in contact with the seal member  458 , on a further downstream side than the first part  521  in the flow direction of the oil from the flow passage  32 B toward the flow passage  31 B. The movable member  452  also has the third part  523  as an example of the second protrusion, which protrudes to have an outer diameter larger than the outer diameter of the second part  4522 , on a further downstream side than the second part  4522  in the flow direction of the oil from the flow passage  32 B toward the flow passage  31 B. For this reason, according to the steering device  400 , since the oil is likely to flow in the direction inclined relative to the center line C 1 , the flow resistance is reduced, as compared to a configuration where the oil flows in a direction orthogonal to the center line C 1  and then flows in a direction parallel to the center line C 1 , so that the operation load when manually operating the arm  9  is reduced. 
     Further, the steering device  400  is provided with the second intermediate hole  4354  as an example of the truncated conical connection path formed concentrically with the flow passage  32 B on a further downstream side than the flow passage  32 B in the flow direction of the oil from the flow passage  32 B toward the flow passage  31 B and having an outer diameter that becomes larger in the flow direction. For this reason, according to the steering device  400 , since the oil is likely to flow in the direction inclined relative to the center line C 1 , the flow resistance is reduced, as compared to a configuration where the oil flows in a direction orthogonal to the center line C 1  and then flows in a direction parallel to the center line C 1 , so that the operation load when manually operating the arm  9  is reduced. 
     Fifth Embodiment 
       FIG. 10A  depicts an example of a schematic configuration of a second valve  542  in accordance with a fifth embodiment.  FIG. 10B  depicts an example of a schematic configuration of a manual valve  543  in accordance with the fourth embodiment. 
     A steering device  500  of the fifth embodiment is different from the steering device  1  of the first embodiment, in a second valve  542  and a manual valve  543  corresponding to the second valve  42  and the manual valve  43 . The second valve  542  and the manual valve  543  are different from the second valve  42  and the manual valve  43  of the first embodiment, in that the second valve  542  and the manual valve  543  are separate bodies. Hereinbelow, differences from the steering device  1  are described. The parts having the same functions between the steering device  1  and the steering device  500  are denoted with the same reference signs, and the detailed descriptions thereof are omitted. 
     Similarly to the first valve  41  described with reference to  FIG. 6 , the second valve  542  has the valve body  61 , the movable member  62 , the holding member  63 , the spring  64 , the cap  65 , and the seal member  68 . The second valve  542  is inserted in a through-hole  37  formed in the housing  30 . The through-hole  37  is formed in parallel to the through-hole  35 , and has a columnar first hole  371  formed on a front side and a columnar second hole  372  formed on a rear side and having a diameter larger than a diameter of the first hole  371 . The first hole  371  communicates with the flow passage  32 B, and the second hole  372  communicates with the flow passage  31 B. 
     The manual valve  543  has a cap  570  for plugging the through-hole  35  formed in the housing  30 , the handle  57 , and the annular seal member  58  for sealing a gap between the cap  570  and the housing  30 . 
     The cap  570  has a first part  571  corresponding to the first part  521  of the movable member  52 , and a second part  572  corresponding to the second part  522  of the movable member  52 . The cap  570  also has a first pillar-shaped part  573  corresponding to the first pillar-shaped part  561  of the cap  55 , and a second pillar-shaped part  574  corresponding to the second pillar-shaped part  562  of the cap  55 . The cap  570  also has a columnar third pillar-shaped part  575  having substantially the same diameter as an outer diameter of the second part  572  and a columnar fourth pillar-shaped part  576  having a diameter larger than the diameter of the third pillar-shaped part  575  between the second part  572  and the first pillar-shaped part  573 . 
     The first part  571  is formed with a through-hole  577  corresponding to the through-hole  525  of the movable member  52 . The fourth pillar-shaped part  576  is formed with a male screw  578  that is fastened to the female screw  355  formed in the through-hole  35 . An end portion on a rear side of the second pillar-shaped part  574  is formed with a female screw  579 , and the bolt  59  is fastened to the female screw  579 , so that the handle  57  is attached. 
     Also in the manual valve  543  configured as described above, when the male screw  578  is unfastened by the user and thus the seal member  58  does not seal the gap between the cap  570  and the housing  30 , the oil flows between the flow passage  31 B and the flow passage  32 B through the through-hole  577  formed in the first part  571  of the cap  570 . As a result, similarly to the manual valve  43  of the first embodiment, the operation load when manually operating the arm  9  is reduced. 
     Note that, the outer diameter of the first part  571  may be set small, like the outer diameter of the first part  2521  of the second embodiment. In this case, the through-hole  577  may not be provided. 
     Alternatively, the diameter of the first hole  351  of the through-hole  35  may be set large, like the diameter of the first hole  3351  of the third embodiment. In this case, the through-hole  577  may not be provided. 
     Alternatively, like the second part  4522  of the fourth embodiment, a cylindrical part having an outer diameter larger than the outer diameter of the first part  571  and smaller than the outer diameter of the second part  572  may be provided between the first part  571  and the second part  572  of the cap  570 . In addition, the through-hole  35  of the housing  30  may be formed to have a similar shape to the through-hole  435  of the housing  430  of the fourth embodiment. 
     Sixth Embodiment 
       FIG. 11  depicts an example of a schematic configuration of a valve unit  650  in accordance with a sixth embodiment. 
     A steering device  600  of the sixth embodiment is different from the steering device  1  of the first embodiment, in a valve unit  650  corresponding to the valve unit  50 . The valve unit  650  is different from the valve unit  50 , in that a first valve  641 , a second valve  642 , and a manual valve  643  of the sixth embodiment are integrally provided. The parts having the same functions between the steering device  1  and the steering device  600  are denoted with the same reference signs, and the detailed descriptions thereof are omitted. 
     The valve unit  650  has the valve body  51 , the movable member  52 , the holding member  53 , the handle  57 , the seal member  58 , the valve body  61 , and the holding member  63 . The valve unit  650  also has a coil-shaped spring  654  for applying a spring force to the valve body  51  via the holding member  53  and applying the spring force to the valve body  61  via the holding member  63 , and a cap  655  for plugging a through-hole  38  formed in the housing  30 . 
     The through-hole  38  has a columnar first hole  381  formed on a front side, and a columnar second hole  382  formed behind the first hole  381  and having a diameter larger than a diameter of the first hole  381 . The through-hole  38  also has a columnar third hole  383  formed behind the second hole  382  and having a diameter larger than the diameter of the second hole  382 , and a columnar fourth hole  384  formed behind the third hole  383  and having a diameter larger than the diameter of the third hole  383 . The first hole  381  communicates with the flow passage  32 B. The second hole  382  communicates with the flow passage  31 B. The third hole  383  communicates with the flow passage  32 B. The fourth hole  384  communicates with the flow passage  31 B. 
     The cap  655  has a cylindrical first tubular part  661  provided on a front side, a cylindrical second tubular part  662  provided behind the first tubular part  661 , and a cylindrical third tubular part  663  provided behind the second tubular part  662 . The cap  655  also has a columnar first pillar-shaped part  664  provided behind the third tubular part  663  and a second pillar-shaped part  665  provided behind the first pillar-shaped part  664 . 
     The first tubular part  661  is similar to the tubular part  551  of the cap  55  and is formed with the through-hole  553 , and the movable member  52  is press-fitted therein. 
     An outer diameter of the second tubular part  662  is larger than an outer diameter of the first tubular part  661 . The second tubular part  662  is formed with a groove  666  recessed from an outer peripheral surface over an entire circumference. In the groove  666 , an O-ring  667  for sealing a space between an outer peripheral surface of the second tubular part  662  and an inner peripheral surface of the second hole  382  of the through-hole  38  is fitted. 
     An outer diameter of the third tubular part  663  is larger than the outer diameter of the second tubular part  662 . An outer peripheral surface of the third tubular part  663  is formed with a male screw  668  that is fastened to a female screw  385  formed in the through-hole  38 . In the third tubular part  663 , a seating surface  669  on which the valve body  61  is seated is formed. In the third tubular part  663 , a through-hole  670  that communicates an inside and the fourth hole  384  of the through-hole  38  located at an outside is formed in a direction of intersecting with the center line C 1 . 
     The first pillar-shaped part  664  is formed with a groove  671  recessed from an outer peripheral surface over an entire circumference. In the groove  671 , an O-ring  672  for sealing a space between an outer peripheral surface of the first pillar-shaped part  664  and an inner peripheral surface of the fourth hole  384  of the through-hole  38  is fitted. 
     The second pillar-shaped part  665  is similar to the second pillar-shaped part  562  of the cap  55 , and is formed with a female screw  565  to which the bolt  59  for attaching the handle  57  is fastened. 
     In the valve unit  650  configured as described above, the valve body  61 , the holding member  63 , the spring  654 , the cap  655  and the housing  30  constitute the first valve  641 . The valve body  51 , the movable member  52 , the holding member  53 , the spring  654 , the cap  655 , the seal member  58  and the housing  30  constitute the second valve  642 . The movable member  52 , the cap  655 , the handle  57 , the seal member  58  and the housing  30  constitute the manual valve  643 . 
     Also in the manual valve  643  configured as described above, when the male screw  668  is unfastened by the user and thus the seal member  58  does not seal the gap between the cap  655  and the housing  30 , the oil flows between the flow passage  31 B and the flow passage  32 B through the through-hole  525  formed in the first part  521  of the movable member  52 . As a result, similarly to the manual valve  43  of the first embodiment, the operation load when manually operating the arm  9  is reduced. 
     Note that, the outer diameter of the first part  521  of the movable member  52  may be set small, like the outer diameter of the first part  2521  of the second embodiment. In this case, the through-hole  525  may not be provided. 
     Alternatively, the diameter of the first hole  381  of the through-hole  38  may be set large, like the diameter of the first hole  3351  of the third embodiment. In this case, the through-hole  525  may not be provided. 
     Alternatively, like the second part  4522  of the fourth embodiment, a cylindrical part having an outer diameter larger than the outer diameter of the first part  571  and smaller than the outer diameter of the second part  572  may be provided between the first part  521  and the second part  522  of the movable member  52 . In addition, the through-hole  38  of the housing  30  may be formed to have a similar shape to the through-hole  435  of the housing  430  of the fourth embodiment. 
     According to the present invention, it is possible to reduce an operation load when manually changing the traveling direction of the ship body.