TECHNICAL FIELD 
       [0001]    The present invention relates to a bogie and a track-type vehicle. 
         [0002]    Priority is claimed on Japanese Patent Application No. 2013-246037, filed Nov. 28, 2013, the content of which is incorporated herein by reference. 
       BACKGROUND ART 
       [0003]    As new transportation means other than buses or railroads, track-based transportation systems that travel on a track by means of traveling wheels consisting of rubber tires are known. These types of track-based transportation systems are generally referred to as “new transportation systems”, “automated people movers (APMs)”, or the like. In the track-based transportation systems, guide wheels disposed at both side parts of a vehicle or the like are guided by guide rails provided along a track. 
         [0004]    In the vehicle of the above-described track-based transportation systems, the traveling wheels and the guide wheels are provided in a bogie disposed in a lower part of the vehicle. The bogie includes a mechanism that steers a traveling wheel (steered wheel), using a force (reaction force) with which a guide wheel is pressed against a guide rail when the vehicle passes through a curved portion (for example, refer to PTL 1). A bogie including a guide device that has a guide wheel and is turnably attached to the vehicle, and a steering mechanism (tie rod or tie-rod arm) that steers a steered wheel according to the turning of the guide device is disclosed in PTL 1. 
       CITATION LIST 
     Patent Literature 
       [0005]    [PTL 1] Japanese Unexamined Patent Application Publication No. 2010-195310 
       SUMMARY OF INVENTION 
     Technical Problem 
       [0006]    In recent years, an increase in the withstand load of a vehicle, an increase in the speed of a track-based transportation system, and the like are required, and it is considered that wide traveling wheels are used with this. 
         [0007]    However, if the width dimension of the steered wheels becomes large, the frictional force between a steered wheel and the track, the amount of kingpin offset, self aligning torque, and the like become large. Therefore, a force required for the steering of the steered wheel becomes large. That is, when the steered wheel is steered, a reaction force that the guide device receives from a guide rail becomes large. 
         [0008]    Meanwhile, since there are limitations on the strength and durability of the guide device or the guide rail, when the steered wheel is steered, there is also a limitation to the magnitude of the reaction force that the guide device receives from the guide rail. 
         [0009]    The invention provides a bogie and a track-type vehicle that can steer a wide steered wheel while suppressing a reaction force that a guide device receives to be small. 
       Solution to Problem 
       [0010]    According to a first aspect of the invention, a bogie is a bogie that travels while being guided by a guide rail provided along a track. The bogie includes a steered wheel; a main body that supports the steered wheel; a guide device that is supported so as to be turnable with respect to the main body and turns under a reaction force from the guide rail; a steering mechanism that applies a steering force to the steered wheel using the reaction force that the guide device has received; and an assist mechanism that applies an assist steering force, which assists the steering force applied by the steering mechanism, to the steered wheel. The assist mechanism includes a first operation arm that pivots in a steering direction of the steered wheel together with the steered wheel, a second operation arm that is attached so as to be rotatable around a rotation axis with respect to the main body, is coupled to the guide device, and rotates around the rotation axis according to the turning of the guide device, and an elastically deformable section that is coupled to the first operation arm and the second operation arm and is elastically deformable with a change in relative distance between the first operation arm and the second operation arm. A distance from the rotation axis to a coupling portion of the second operation arm with the guide device is longer than a distance from the rotation axis to a coupling portion of the second operation arm with the elastically deformable section. 
         [0011]    When the bogie having the above configuration travels along a curved portion of the track, the guide device is pressed against the guide rail, and thereby, the guide device turns under a reaction force from the guide rail. Additionally, as a steering force using the aforementioned reaction force is applied to the steered wheel by the steering mechanism, the steered wheel can be directed to a traveling direction of the bogie along the curved portion of the track. 
         [0012]    In the bogie having the above configuration, when the steered wheel is steered by the steering mechanism, the second operation arm rotates the rotation axis with the turning of the guide device. Accordingly, a force (rotative force) that rotates the second operation arm around the rotation axis is applied to the second operation arm. Here, the distance from the coupling portion of the second operation arm with the guide device to the rotation axis is longer than the distance from the coupling portion of the second operation arm with the elastically deformable section to the rotation axis. For this reason, when the second operation arm rotates and the relative distance between the second operation arm and the first operation arm varies, a greater force than the above rotative force acts on the elastically deformable section, and the elastically deformable section is elastically deformed. The elastic force of the elastically deformable section that is elastically deformed is transmitted to the first operation arm and is thereby applied to the steered wheel as the assist steering force. Additionally, since the reaction force of the assist steering force (elastic force) that the second operation arm receives from the elastically deformable section is received by the main body via the rotation axis of the second operation arm, the assist steering force can be efficiently applied to the steered wheel while reducing the reaction force that the guide device receives from the guide rail. 
         [0013]    As described above, as the assist steering force of the assist mechanism is applied to the steered wheel, it is possible to steer the steered wheel while suppressing the reaction force that the guide device receives from the guide rail to be small. 
         [0014]    According to a second aspect of the invention, in the bogie of the first aspect, a coupling portion of the second operation arm with the elastically deformable section may be located between a coupling portion of the second operation arm with the guide device, and the rotation axis. 
         [0015]    According to the above configuration, the length of the second operation arm can be set to be short, and miniaturization of the assist mechanism can be achieved. 
         [0016]    According to a third aspect, in the bogie of the first or second aspect, the guide device may further include a turning arm that is attached so as to be turnable around a turning axis with respect to the main body, and a distance from the turning axis to a coupling portion of the turning arm with the second operation arm may be longer than a distance from the turning axis to a coupling portion of the turning arm with the steering mechanism. 
         [0017]    According to the bogie having the above configuration, the movement (rotational angle) of the second operation arm with respect to the turning angle of the turning arm becomes greater than the movement of the steering mechanism. Therefore, it is possible to set the assist steering force applied by the assist mechanism to be larger. Therefore, the steered wheel can be steered, while suppressing the reaction force that the guide device receives from the guide rail to be smaller. 
         [0018]    Moreover, as the movement of the steering mechanism with respect to the turning angle of the turning arm becomes small, it is also possible to precisely adjust the steering angle of the steered wheel. 
         [0019]    According to a fourth aspect of the invention, in the bogie of any one aspect of the first to third aspects, the elastically deformable section may not be elastically deformed in a case where the steering angle of the steered wheel from a straight-running state is equal to or smaller than a predetermined angle. 
         [0020]    According to the bogie having the above configuration, if the guide device receives a minute reaction force from the guide rail and the steering angle of the steered wheel accompanying this is equal to or smaller than a predetermined angle when the bogie travels along a linear portion of the track, the elastically deformable section is not elastically deformed even if the second operation arm rotates around the rotation axis. Therefore, the assist steering force is not applied to the steered wheel. For this reason, even if the guide device receives the reaction force and the steered wheel is steered when the bogie travels along the linear portion of the track, it is possible to return the steered wheel to a straight-running state rapidly with self-aligning torque. Therefore, the bogie can travel in a stable state in the linear portion of the track. 
         [0021]    According to a fifth aspect of the invention, in the bogie of any one aspect of the first to fourth aspects, the steering mechanism may include an elastic member that couples the steered wheel and the guide device, and is elastically deformable. 
         [0022]    According to the bogie having the above configuration, the movement (rotation) of the second operation arm constituting the assist mechanism is kept from being constrained by the steering mechanism. Therefore, the assist steering force of the assist mechanism can be effectively applied to the steered wheel. 
         [0023]    Additionally, the bogie may include a rotation spring that is biased in a direction in which the guide device is returned to a straight-running state, and a turning damper that attenuates the rocking of the guide device in a rotational direction by the rotation spring. 
         [0024]    In this case, even if the guide device turns under the reaction force when the bogie travels along the linear portion of the track, the guide device can be more rapidly returned to the straight-running state by the rotation spring and the turning damper. Therefore, the bogie can travel in a more stable state in the linear portion of the track. 
         [0025]    According to a sixth aspect of the invention, a track-type vehicle includes the bogie of any one aspect of the first to fifth aspects; and a vehicle body that is supported by the bogie. 
       Advantageous Effects of Invention 
       [0026]    According to the above-described traveling bogie, the wide steered wheel can be steered while suppressing the reaction force that the guide device receives from the guide rail to be small. 
     
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         [0027]      FIG. 1  is a front view illustrating a track-type vehicle related to a first embodiment of the invention. 
           [0028]      FIG. 2  is a top view illustrating the track-type vehicle of  FIG. 1 . 
           [0029]      FIG. 3  is an enlarged sectional view illustrating an elastically deformable section of an assist mechanism that the track-type vehicle of  FIGS. 1 and 2  includes. 
           [0030]      FIG. 4  is a graph illustrating the elastic force characteristics of the elastically deformable section of  FIG. 3 . 
           [0031]      FIG. 5  is a front view illustrating a state where the track-type vehicle of  FIGS. 1 and 2  is traveling along a curved portion of a track. 
           [0032]      FIG. 6  is a top view illustrating a state where the track-type vehicle of  FIGS. 1 and 2  is traveling along the curved portion of the track. 
       
    
    
     DESCRIPTION OF EMBODIMENTS 
       [0033]    Hereinafter, a first embodiment of the invention will be described with reference to  FIGS. 1 to 6 . 
         [0034]    As illustrated in  FIGS. 1 and 2 , a track-type vehicle  1  (hereinafter simply referred to as a vehicle  1 ) in the present embodiment is guided by so-called side-guide type guide rails  3  that are provided at both side parts of a track  2  in a width direction and travels on traveling paths  4  of the track  2 . 
         [0035]    The vehicle  1  includes a vehicle body  5  and bogies  6 . The vehicle body  5  has a hollow, substantially rectangular parallelepiped shape that is long back and forth in a traveling direction. A space where passengers can be accommodated is formed inside the vehicle body  5 . 
         [0036]    The bogies  6  support the vehicle body  5  from below, and travel on the track  2 . The bogies  6  are arranged below a front part and a rear part of the vehicle body  5 . The bogies  6  only have a difference in whether each traveling bogie is arranged at the front part of the vehicle body  5  or is arranged at the rear part. For this reason, in the following description, a bogie  6  arranged at the front part of the vehicle body  5  will be described. 
         [0037]    The bogie  6  includes a main body  11 , steered wheels  12 , a guide device  13 , and steering mechanisms  14 . The main body  11  supports the vehicle body  5  from below. The main body  11  includes a bogie frame  16 , a shock absorber  17 , and an axle  18 . 
         [0038]    The shock absorber  17  is provided between the vehicle body  5  and the bogie frame  16 . The shock absorber  17  prevents the vibration caused by the irregularities or the like on a road surface in the traveling paths  4  from being transmitted to the vehicle body  5 . The shock absorber  17  includes, for example, spring members  19 . Two spring members  19  are disposed, for example, at a distance from each other in the vehicle width direction of the vehicle body  5 . The spring members  19  may be, for example, air springs. 
         [0039]    The axle  18  is supported by the bogie frame  16 . The axle  18  extends to both sides in the vehicle width direction from a gear box  20  at a central part in a vehicle width direction. Mechanisms, such as a differential gear, which transmits the rotational power from a power source (not illustrated), such as a motor, to the axle  18 , are housed in the gear box  20 . In the illustrated example, the axle  18  is supported by the bogie frame  16  via the gear box  20  by the gear box  20  being fixed to the lower side of the bogie frame  16 . However, the invention is not limit to this. 
         [0040]    The steered wheels  12  are so-called wheels with a tire on which rubber tires are mounted. The steered wheels  12  are connected to both ends of each axle  18  extending to both sides in the vehicle width direction, and are configured so as to be rotatable around the axle  18  together with the axle  18 . Accordingly, the vehicle  1  can travel on the traveling paths  4  of the track  2 . Additionally, the steered wheels  12  are configured so as to be pivotable around steering shafts O 1  (for example, kingpins) disposed at ends of the axle  18  on both sides in the vehicle width direction with respect to the main body  11 . As the steered wheels  12  pivot around the steering shafts O 1 , the orientation of the vehicle  1  in the traveling direction can be changed. 
         [0041]    The guide device  13  is disposed below the main body  11 , and is supported so as to be turnable around the turning axis O 2  extending in an upward-downward direction with respect to the main body  11 . The guide device  13  turns under a reaction force from a guide rail  3 . The guide device  13  includes a guide frame  21  and guide wheels  22 . 
         [0042]    The guide frame  21  includes lateral beams  23 A and  23 B and a longitudinal beam (turning arm)  24 . The lateral beams  23 A and  23 B are formed to extend to both outer sides in the vehicle width direction more than the steered wheels  12 . Additionally, the lateral beams  23 A and  23 B are respectively arranged in front of and behind the steered wheels  12  in the traveling direction. The longitudinal beam  24  extends in the traveling direction of the steered wheels  12 , and connects the pair of front and rear lateral beams  23 A and  23 B at an intermediate portion thereof in the vehicle width direction. The longitudinal beam  24  is attached so as to be turnable around the turning axis O 2  with respect to the main body  11  at the intermediate portion thereof in an extending direction. 
         [0043]    The guide wheels  22  are guided by the guide rails  3  arranged on both sides of the track  2  in the vehicle width direction. The guide wheels  22  are attached to both ends of the respective lateral beams  23 A and  23 B, and are configured to be rotatable around axes O 3  extending in the upward-downward direction. When the vehicle  1  travels on the track  2 , the guide wheels  22  abut against the guide rails  3  and thereby roll along the guide rails  3 . 
         [0044]    In the guide device  13 , the width dimension of the guide device  13  in the extending direction of the lateral beams  23 A and  23 B is set to be smaller than the dimension between the guide rails  3 . Additionally, in the guide device  13 , a guide wheel  22  is pressed against a guide rail  3 , and thereby turning under a reaction force from the guide rail  3  (refer to  FIG. 6 ). 
         [0045]    The steering mechanisms  14  apply steering forces to the steered wheels  12  using the reaction force that the above-mentioned guide device  13  has received. The steering mechanisms  14  pivot the steered wheels  12  in the same direction as the turning direction of the guide device  13  around the steering shafts O 1  when the guide device  13  is turned by coupling the guide device  13  and the steering shafts O 1  of the steered wheels  12  to each other. A steering mechanism  14  is provided for each steered wheel  12 . Each steering mechanism  14  includes a first coupling arm  25  and a second coupling arm  26 . 
         [0046]    A first end of the first coupling arm  25  in its longitudinal direction is attached so as to be pivotable around (the steering direction of each steered wheel  12 ) of each steering shaft O 1  together with the steered wheel  12 . 
         [0047]    The second coupling arm  26  couples the first coupling arm  25 , and the longitudinal beam  24  of the guide frame  21 . 
         [0048]    A first end of the second coupling arm  26  in its longitudinal direction is rotatably coupled to a second end of the first coupling arm  25 . A second end of the second coupling arm  26  is rotatably coupled to the longitudinal beam  24  of the guide frame  21 . A coupling portion of the longitudinal beam  24  with the second coupling arm  26  is located between the turning axis O 2  and an end (a connection portion with the lateral beam  23 A or  23 B) of the longitudinal beam  24 . In the illustrated example, a coupling portion between the first and second coupling arms  25  and  26  is located further to the front side in the traveling direction of the vehicle  1  (traveling bogie  6 ) than the steering shaft O 1 , and the coupling portion of the longitudinal beam  24  with the second coupling arm  26  is located further to the front side in the traveling direction of the vehicle  1  (traveling bogie  6 ) than the turning axis O 2 . However, the invention is not limited to this. For example, the coupling portion between the first and second coupling arms  25  and  26  may be located further to the rear side in the traveling direction of the vehicle  1  (traveling bogie  6 ) than the steering shaft O 1 , and the coupling portion of the longitudinal beam  24  with the second coupling arm  26  may be located further to the rear side in the traveling direction of the vehicle  1  (traveling bogie  6 ) than the turning axis O 2 . 
         [0049]    Additionally, in one steering mechanism (the left in  FIG. 2 )  14 A, a second coupling arm  26 A is an elastic member that is elastically deformable. It is preferable that the elastic modulus of the second coupling arm  26 A is set to be large so that the steering angle of the steered wheel  12  with respect to the turning angle of the guide device  13  is uniquely determined. Additionally, it is preferable that the elastic modulus of the second coupling arm  26 A is set to be larger than the elastic modulus of an elastically deformable section of an assist mechanism to be described below. 
         [0050]    In the steering mechanism  14  having the above configuration, the second coupling arm  26  is displaced when the guide device  13  turns around the turning axis O 2  under a reaction force from a guide rail  3 . Moreover, as the first coupling arm  25  pivots around the steering shaft O 1 , the steered wheel  12  is steered in a direction in the same direction as the turning direction of the guide device  13  (refer to  FIG. 6 ). That is, the steering mechanism  14  applies a steering force to the steered wheel  12  using the reaction force that the guide device  13  receives, thereby steering the steered wheel  12  in the same direction as the turning direction of the guide device  13 . 
         [0051]    In a configuration in which the steering mechanism  14  is provided between the steered wheel  12  and the guide device  13  as described above, a first distance L 1 , a second distance L 2 , and a third distance L 3  satisfy the following relationship. The first distance L 1  is a distance from the turning axis O 2  to the connection portion of the longitudinal beam  24  with the lateral beam  23 A or  23 B. The second distance L 2  is a distance from the turning axis O 2  to the coupling portion of the longitudinal beam  24  with the second coupling arm  26  (steering mechanism  14 ). The third distance L 3  is a distance from the steering shaft O 1  to the coupling portion of the first coupling arm  25  with the second coupling arm  26 . 
         [0000]      L1&gt;L2 
         [0000]      L2&gt;L3 
         [0052]    Moreover, the bogie  6  includes an assist mechanism  15  that applies an assist steering force, which assists the steering force applied by the above-mentioned steering mechanism  14 , to the steered wheel  12 . The assist mechanism  15  includes a first operation arm  31 , a second operation arm  32 , and an elastically deformable section  33 . 
         [0053]    A first end of the first operation arm  31  in its longitudinal direction is attached so as to be pivotable around the steering shaft O 1  together with the steered wheel  12 . The first operation arm  31  is provided so as to extend in a direction opposite to the first coupling arm  25  of the steering mechanism  14  from the steering shaft O 1  regarding the traveling direction of the vehicle  1 . 
         [0054]    The second operation arm  32  is attached so as to be rotatable around a rotation axis O 4  extending in the upward-downward direction with respect to the main body  11 . 
         [0055]    In the present embodiment, a first end of the second operation arm  32  in the longitudinal direction is attached so as to be rotatable around the rotation axis O 4 . 
         [0056]    The second operation arm  32  is coupled to the guide device  13  so as to rotate around the rotation axis O 4  according to the turning of the guide device  13 . In the present embodiment, a second end of the second operation arm  32  is coupled to the longitudinal beam  24  of the guide frame  21 . Moreover, in the present embodiment, the second end of the second operation arm  32  is coupled to the longitudinal beam  24  via a third operation arm  34 . A first end of the third operation arm  34  is rotatably coupled to the second end of the second operation arm  32 . A second end of the third operation arm  34  is rotatably coupled to the longitudinal beam  24 . 
         [0057]    A coupling portion of the longitudinal beam  24  with the second operation arm  32  is located between the turning axis O 2  and the end (the connection portion with the lateral beam  23 A or  23 B) of the longitudinal beam  24 . Additionally, the coupling portion of the longitudinal beam  24  with the second operation arm  32  is located so that the turning axis O 2  is disposed between the coupling portion of the longitudinal beam  24  with the second coupling arm  26 . 
         [0058]    The elastically deformable section  33  is coupled to the first operation arm  31  and the second operation arm  32 . The elastically deformable section  33  is elastically deformed with a change in relative distance between the first operation arm  31  and the second operation arm  32 . 
         [0059]    A first end  33   a  of the elastically deformable section  33  in its longitudinal direction is rotatably coupled to a second end of the first operation arm  31 . A second end  33   b  of the elastically deformable section  33  is rotatably coupled to a portion of the second operation arm  32  apart from the rotation axis O 4 . In the present embodiment, a coupling portion of the second operation arm  32  with the elastically deformable section  33  is located between a coupling portion of the second operation arm  32  with the longitudinal beam  24 , and the rotation axis O 4 . 
         [0060]    Additionally, the elastically deformable section  33  of the present embodiment is configured so as not to be elastically deformed irrespective of a change in relative distance between the first operation arm  31  and the second operation arm  32 , in a case where the steering angle of the steered wheel from a straight-running state is equal to or smaller than a predetermined angle. 
         [0061]    Hereinafter, the specific configuration of the elastically deformable section  33  of the present embodiment will be described. 
         [0062]    The elastically deformable section  33 , as illustrated in  FIG. 3 , includes a case  35 , a piston rod  36 , spring members  37 A and  37 B, and cushions  38 . The case  35  is formed in a tubular shape. 
         [0063]    A first end of the case  35  in its axial direction forms, for example, a first end  33   a  of the elastically deformable section  33 . 
         [0064]    The piston rod  36  protrudes from a second end of the case  35 . The piston rod  36  is provided so as to be extendable and retractable with respect to the case  35 . A tip of the piston rod  36  its protruding direction forms, for example, a second end  33   b  of the elastically deformable section  33 . A base end of the piston rod  36  located inside the case  35  is provided with a partition plate  39  that splits the internal space of the case  35  in the axial direction of the case  35 . 
         [0065]    The spring members  37 A and  37 B are linear springs of which the elastic modulus is constant, for example like coil springs. The spring members  37 A and  37 B are disposed one by one in respective space portions  35 A and  35 B of the case  35  split by the partition plate  39 . However, both ends of each of the spring members  37 A and  37 B are not fixed to an inner surface of the case  35 , or the partition plate  39 . 
         [0066]    The cushions  38  have characteristics that the elastic modulus there is very small as compared to the spring members  37 A and  37 B, and elastic forces are hardly generated even if external forces are applied to the cushions. The cushions  38  are made of, for example, low-resilient urethane materials or the like. The cushions  38  are disposed one by one between the inner surface of the case  35  that faces the partition plate  39  and the respective spring members  37 A and  37 B. 
         [0067]    The elastically deformable section  33  of the present embodiment configured as described above has elastic force characteristics illustrated in  FIG. 4 . Hereinafter, the elastic force characteristics will be specifically described with reference to  FIGS. 3 and 4 . 
         [0068]    For example, when the piston rod  36  is displaced up to a predetermined displacement x1 in a direction in which the piston rod is extended with respect to the case  35 , only a cushion  38  between the first spring member  37 A and the inner surface of the case  35  is compressively deformed, and the first spring member  37 A is not elastically deformed. Then, if the piston rod  36  is displaced to be larger than the predetermined displacement x1, the cushion  38  is completely crushed and is not compressively deformed. Therefore, the first spring member  37 A is compressed and is elastically deformed. In this case, the second spring member  37 B is not elastically deformed. Accordingly, in the elastically deformable section  33 , an elastic force in a direction in which the piston rod  36  is retracted is generated with the elastic deformation of the first spring member  37 A. 
         [0069]    On the other hand, when the piston rod  36  is displaced up to a predetermined displacement −x1 in a direction in which the piston rod is retracted with respect to the case  35 , only a cushion  38  between the second spring member  37 B and the inner surface of the case  35  is deformed, and the second spring member  37 B is not elastically deformed. Then, if the piston rod  36  is displaced to be larger than the predetermined displacement −x1, the cushion  38  is completely crushed and is not compressively deformed. Therefore, the second spring member  37 B is compressed and is elastically deformed. In this case, the first spring member  37 A is not elastically deformed. Accordingly, in the elastically deformable section  33 , an elastic force in a direction in which the piston rod  36  is extended is generated with the elastic deformation of the second spring member  37 B. 
         [0070]    The above-described elastic forces of the elastically deformable section  33  are transmitted to the steered wheel  12  via the first operation arm  31 , and are applied to the steered wheel  12  as an assist steering force. 
         [0071]    The displacement of the elastically deformable section  33  having the above characteristics is set so as to correspond to the steering angle of the steered wheel  12 , on the basis of the orientation of the steered wheel  12  that is brought into the straight-running state. That is, in a case where the steered wheel  12  is in the straight-running state, the displacement of the elastically deformable section  33  is set to reach 0. Additionally, in a case where the steering angle of the steered wheel  12  has a predetermined angle, the displacement of the elastically deformable section  33  is set to reach the predetermined displacement x1 or −x1. 
         [0072]    In the present embodiment, the assist mechanism  15  having the above configuration is provided only between one steered wheel  12  and the guide device  13  (on the left in  FIG. 2 ). However, the assist steering force of the elastically deformable section  33  is also applied to the other steered wheel  12  via the steering mechanism  14 A coupled to the one steered wheel  12 , the longitudinal beam  24 , and the steering mechanism  14  coupled to the other steered wheel  12 . 
         [0073]    As illustrated in  FIG. 2 , in the bogie  6  provided with the assist mechanism  15  as described above, the first distance L 1  and the second distance L 2  in the longitudinal beam  24 , and the third distance L 3 , a fourth distance L 4 , a fifth distance L 5 , a sixth distance L 6 , and a seventh distance L 7  in the first coupling arm  25 , satisfy the following relationship. The fourth distance L 4  is a distance from the steering shaft O 1  to a coupling portion of the first operation arm  31  with the elastically deformable section  33 . The fifth distance L 5  is a distance from the turning axis O 2  to the coupling portion of the longitudinal beam  24  with the second operation arm  32 . The sixth distance L 6  is a distance from the rotation axis O 4  to the coupling portion of the second operation arm  32  with the longitudinal beam  24 . The seventh distance L 7  is a distance from the rotation axis O 4  to the coupling portion of the second operation arm  32  with the elastically deformable section  33 . 
         [0000]      L3&gt;L4 
         [0000]      L1&gt;L5 
         [0000]      L6&gt;L7 
         [0000]      L7&gt;L4 
         [0000]      L2&lt;L5 
         [0074]    Moreover, the bogie  6  of the present embodiment includes a rotation spring  41  and a turning damper  42 . The rotation spring  41  is provided between the main body  11  and the guide device  13  (guide frame  21 ), and is biased in a direction in which the guide device  13  is returned to the straight-running state. The rotation spring  41  is elastically deformed when the guide device  13  turns with respect to the main body  11 , and is biased in the direction in which the guide device  13  is returned to the straight-running state. The turning damper  42  is provided between the main body  11  and the guide device  13  (guide frame  21 ), and attenuates the rocking of the guide device  13  in the turning direction by the rotation spring  41 . 
         [0075]    In the bogie  6  of the present embodiment, respective first ends of the rotation spring  41  and the turning damper  42  in the longitudinal direction are rotatably coupled to the main body  11 . Respective second end of the rotation spring  41  and the turning damper  42  are rotatably coupled to the portion of the guide devices  13  away from the turning axis O 2 . 
         [0076]    In the illustrated example, the respective second ends of the rotation spring  41  and the turning damper  42  are coupled to the longitudinal beam  24 , but may be coupled to, for example, the lateral beams  23 A and  23 B. Additionally, in the illustrated example, the coupling portions between the guide device  13  and the respective second ends of the rotation spring  41  and the turning damper  42  are located further to the front side in the traveling direction of the vehicle  1  (traveling bogie  6 ) than the turning axis O 2 . However, for example, the coupling portions may be located further to the rear side in the traveling direction of the vehicle  1  (traveling bogie  6 ) than the turning axis O 2 . Moreover, in the illustrated example, the rotation spring  41  is disposed on one side in the vehicle width direction with respect to the longitudinal beam  24 , and the turning damper  42  is disposed on the other side in the vehicle width direction with respect to the longitudinal beam  24 . However, for example, both the rotation spring  41  and the turning damper  42  may be collectively disposed on one side or the other side in the vehicle width direction with respect to the longitudinal beam  24 . 
         [0077]    Next, the operation of the vehicle  1  of the present embodiment configured as described above will be described. 
         [0078]    As illustrated in  FIGS. 5 and 6 , when the vehicle  1  is traveling along a curved portion of the track  2 , mainly a guide wheel  22  on a front outer rail side in the guide wheels  22  of the guide device  13  receive a reaction force F from an outer side in the vehicle width direction, from a guide rail  3  disposed on an outer rail side of the curved portion. The guide device  13  turns around the turning axis O 2  so that the front side (lateral beam  23 A side) of the guide device  13  approaches a guide rail  3  on an inner rail side, on the basis of this reaction force F. Additionally, a steering force using the aforementioned reaction force F is applied to the steered wheel  12  by the steering mechanism  14  with the turning of the guide device  13 , and the steered wheel  12  is steered in the same direction as the turning direction of the guide device  13  around the steering shaft O 1 . That is, the steered wheel  12  can be directed to the traveling direction of the vehicle  1  along the curved portion of the track  2 . Accordingly, the vehicle  1  travels along the curved portion of the track  2 . 
         [0079]    When the vehicle  1  travels along the curved portion of the track  2  as described above, the steering angle of the steered wheel  12  steered becomes equal to more than a predetermined angle. When the steered wheel  12  is steered in the curved portion of the track  2 , the assist steering force applied by the assist mechanism  15  is also applied to the steered wheel  12 . This will be specifically described below. 
         [0080]    When the guide device  13  turns under the reaction force F from the guide rail  3 , a force (rotative force) that rotates the second operation arm  32  around the rotation axis O 4  is applied to the second operation arm  32 . Here, the sixth distance L 6  in the second operation arm  32  is longer than the seventh distance L 7  in the second operation arm  32 . For this reason, when the second operation arm  32  rotates and the relative distance between the second operation arm  32  and the first operation arm  31  varies, a greater force than the above rotative force acts on the elastically deformable section  33 , and the elastically deformable section  33  is elastically deformed. Accordingly, an elastic force F 1  of the elastically deformable section  33  that has been elastically deformed becomes greater than the rotative force that acts on the second operation arm  32 . That is, the second operation arm  32  constitutes a so-called “lever”. In the second operation arm  32 , the rotation axis O 4  becomes a fulcrum of the “lever”, the coupling portion with the guide device  13  becomes a point of effort of the “lever”, and the coupling portion with the elastically deformable section  33  becomes a working point of the “lever”. 
         [0081]    The elastic force F 1  of the elastically deformable section  33  is transmitted to the first operation arm  31 . Here, since the steered wheel  12  is steered by the steering mechanism  14  as described above, the first operation arm  31  is also pivoted around a steering shaft O 1  with this steering. Additionally, as the first to seventh distances L 1  to L 7  are appropriately set, the elastic force F 1  of the elastically deformable section  33  acts in the steering direction of the steered wheel  12 . That is, the elastic force F 1  of the elastically deformable section  33  is applied to the steered wheel  12  as the assist steering force. 
         [0082]    As described above, according to the vehicle  1  including the bogie  6  of the present embodiment, when the steered wheel  12  is steered by the steering mechanism  14 , the assist steering force applied by the assist mechanism  15  is also applied to the steered wheel  12 . For this reason, it is possible to steer the steered wheel  12  while suppressing the reaction force that the guide device  13  receives from the guide rail  3  to be small, even if the steered wheel  12  is wide. Therefore, the vehicle  1  that can cope with an increase in withstand load and an increase in the speed of the track-based transportation system can be provided. 
         [0083]    Additionally, the reaction force of the assist steering force (elastic force F 1 ) that the second operation arm  32  receives from the elastically deformable section  33  is received by the main body  11  via the rotation axis O 4  of the second operation arm  32 . For this reason, the assist steering force can be efficiently applied to the steered wheel  12  while reducing the reaction force that the guide device  13  receives from the guide rail  3 . 
         [0084]    Moreover, according to the bogie  6  and the vehicle  1  of the present embodiment, the coupling portion (working point of a “lever”) of the second operation arm  32  with the elastically deformable section  33  is located between the coupling portion (the point of effort of the “lever”) of the second operation arm  32  with the guide device  13  and the rotation axis O 4  (the fulcrum of the “lever”). For this reason, as compared to a configuration in which the second operation arm  32 , and the elastically deformable section  33  and the guide device  13  are coupled, respectively, so that the fulcrum of the “lever” may be located between the working point and point of effort, the length of the second operation arm  32  can be short set, and miniaturization of the assist mechanism  15  can be achieved. 
         [0085]    Additionally, according to the bogie  6  and the vehicle  1  of the present embodiment, the fifth distance L 5  in the longitudinal beam  24  is longer than the second distance L 2 . Therefore, the movement of the second operation arm  32  with respect to the turning angle of the longitudinal beam  24  becomes greater than the movement of the steering mechanism  14 . For this reason, it is possible to set the assist steering force applied by the assist mechanism  15  to be larger. Therefore, the steered wheel  12  can be steered, while suppressing the reaction force that the guide device  13  receives from the guide rail  3  to be smaller. 
         [0086]    Moreover, as the movement of the steering mechanism  14  with respect to the turning angle of the longitudinal beam  24  becomes small, it is also possible to precisely adjust the steering angle of the steered wheel  12 . 
         [0087]    Additionally, in the bogie  6  and the vehicle  1  of the present embodiment, if the guide device  13  receives a minute reaction force from the guide rail  3  and the steering angle of the steered wheel  12  accompanying this is equal to or smaller than a predetermined angle when the bogie  6  travels along the linear portion of a track  2 , the elastically deformable section  33  is not elastically deformed even if the second operation arm  32  rotates around the rotation axis O 4 . For this reason, the assist steering force is not applied to the steered wheel  12 . For this reason, even if the guide device  13  receives the minute reaction force and the steered wheel  12  is steered when the vehicle  1  travels along the linear portion of the track  2 , it is possible to return the steered wheel  12  to the straight-running state rapidly with self-aligning torque. Therefore, the vehicle  1  can travel along the linear portion of the track  2  in a stable state. 
         [0088]    Moreover, in the present embodiment, the second coupling arm  26 A of one steering mechanism  14 A is made of an elastic member. Therefore, the movement (rotation) of the second operation arm  32  constituting the assist mechanism  15  is kept from is constrained by the steering mechanism  14 . For this reason, the assist steering force of the assist mechanism  15  can be effectively applied to the steered wheel  12 . 
         [0089]    Additionally, the bogie  6  and the vehicle  1  of the present embodiment include the rotation spring  41  and the turning damper  42 . For this reason, even if the guide device  13  turns under the reaction force when the bogie  6  travels along the linear portion of the track  2 , the guide device  13  can be more rapidly returned to the straight-running state by the rotation spring  41  and the turning damper  42 . Therefore, the bogie  6  is enabled to travel in a more stable state in the linear portion of the track  2 . 
         [0090]    Although the invention has been described above in detail, the invention is not limited to the above-described embodiment, and various changes can be made without departing from the scope of the invention. 
         [0091]    For example, the assist mechanism  15  is not limited to being provided only between one steered wheel  12  and the guide device  13 , and assist mechanisms are respectively provided between both the steered wheels  12  and the guide device  13 . 
         [0092]    Additionally, in the assist mechanism  15 , the position of the coupling portion of the second operation arm  32  with the elastically deformable section  33  is not limited to being set like the above embodiment. The above position of the coupling portion may be set to, for example, a position where the rotation axis O 4  is disposed between the coupling portion of the second operation arm  32  with the longitudinal beam  24  so that at least the seventh distance L 7  in the second operation arm  32  becomes shorter than the sixth distance L 6 . 
         [0093]    Moreover, the elastically deformable section  33  having characteristics of being not elastically deformed in a case where the steering angle of the steered wheel  12  from the straight-running state is equal to or smaller than a predetermined angle may be arbitrarily configured without being limited to being configured like the above embodiment. 
         [0094]    Additionally, the elastically deformable section  33  is not limited to being configured so as not to be elastically deformed in a case where the steering angle of the steered wheel  12  from a straight-running state is equal to or smaller than a predetermined angle. For example, the elastically deformable section may be configured so as to be elastically deformed when the steered wheel  12  is steered from the straight-running state. In this case, the elastically deformable section  33  may have, for example, a configuration in which the cushions  38  are eliminated. Additionally, the elastically deformable section  33  may be constituted of, for example, only spring member, such as one coil spring. 
         [0095]    Additionally, the invention is not limited to the bogie  6  that travels while being guided by the side guide type guide rails  3  provided at both ends of the track  2  in the width direction like the above embodiment. For example, the invention is also applicable to a bogie that travels while being guided by a center guide type guide rail provided at a central part in the track width direction. 
       INDUSTRIAL APPLICABILITY 
       [0096]    According to this traveling bogie, the wide steered wheel can be steered while suppressing the reaction force that the guide device receives from the guide rail to be small. 
       REFERENCE SIGNS LIST 
       [0000]    
       
         
           
               1 : TRACK-TYPE VEHICLE 
               2 : TRACK 
               3 : GUIDE RAIL 
               5 : VEHICLE BODY 
               6 : TRAVELING BOGIE 
               11 : MAIN BODY 
               12 : STEERED WHEEL 
               13 : GUIDE DEVICE 
               14 ,  14 A: STEERING MECHANISM 
               15 : ASSIST MECHANISM, 
               24 : LONGITUDINAL BEAM (TURNING ARM) 
               26 A: SECOND COUPLING ARM (ELASTIC MEMBER) 
               31 : FIRST OPERATION ARM 
               32 : SECOND OPERATION ARM 
               33 : ELASTICALLY DEFORMABLE SECTION 
               35 : CASE 
               36 : PISTON ROD 
               37 A,  37 B: SPRING MEMBER 
               38 : CUSHION 
             L 2 : SECOND DISTANCE 
             L 5 : FIFTH DISTANCE 
             L 6 : SIXTH DISTANCE 
             L 7 : SEVENTH DISTANCE 
             O 2 : TURNING AXIS 
             O 4 : ROTATION AXIS
This traveling bogie is provided with: steered wheels; a main body for supporting the steered wheels; a guide device turning when subjected to a reaction force from a guide rail; a steering mechanism for applying a steering force to the steered wheels utilizing the reaction force applied to the guide device; and an assist mechanism for applying an assist steering force to the steered wheels, the assist steering force assisting the steering force applied by the steering mechanism. The assist mechanism is provided with: a first operation arm pivoting together with the steered wheels in the direction in which the steered wheels are steered; a second operation arm rotating about a rotation axis relative to the main body in response to the turning of the guide device; and an elastically deformable section connected to the first operation arm and the second operation arm and elastically deformable.