Patent Publication Number: US-9902407-B2

Title: Parallel cardan driving system steering bogie

Description:
TECHNICAL FIELD 
     The present invention relates to a parallel cardan driving system steering bogie for a railcar. 
     BACKGROUND ART 
     Regarding a bogie of a railcar, conventionally proposed is a steering bogie configured such that an angle of an axle in a yawing direction is changed along a curved track (see PTLs 1 to 4, for example). According to this, lateral force (turning resistance force) acting on wheels when the bogie passes through a curved line is reduced. Therefore, running stability of the bogie when the bogie passes through a sharp curved line improves. In addition, fricative sounds generated between the wheel and a railway track are reduced, and wear of the wheels and the like can also be reduced. 
     However, if a parallel cardan driving system driving bogie is provided with a steering mechanism, the axle steered when the bogie turns is largely displaced in the yawing direction, and this exceeds an allowable deviation of a WN gear coupling connecting a reducer and an electric motor. The WN gear coupling allows the deviation by a backlash formed between an internal tooth of an outer tube and an external tooth of an inner tube. However, since proper meshing between the internal tooth and the external tooth needs to be maintained, increasing the backlash has a limit. Therefore, a parallel cardan driving system driving bogie having a steering function does not exist currently. 
     Here, PTL 5 proposes a steering bogie configured such that: one of axles is a driving shaft; the other axle is a driven shaft; and only the driven shaft has the steering function. According to this, only the driven shaft which does not require an electric motor, a joint, or a reducer is steered, it is unnecessary to consider the limit of the deviation of the joint by the steering. 
     CITATION LIST 
     Patent Literature 
     PTL 1: Japanese Laid-Open Patent Application Publication No. 6-135330 
     PTL 2: Japanese Laid-Open Patent Application Publication No. 10-203364 
     PTL 3: International Publication No. 2009/038068 
     PTL 4: Japanese Laid-Open Patent Application Publication No. 2010-167835 
     PTL 5: Japanese Laid-Open Patent Application Publication No. 2010-58650 
     SUMMARY OF INVENTION 
     Technical Problem 
     However, since only one of front and rear axles is steered, an effect of reducing the lateral force acting on the wheels changes by a running direction. Further, the driving bogie including a pair of axles is provided with only one driving shaft. Therefore, in a train in which a plurality of cars are coupled to one another, the number of cars (driving cars) each of which requires the driving bogie increases, and the number of cars (non-driving cars) each of which does not include devices (a voltage transformer, a converter, a power cable, and the like) for driving decreases. This causes an increase in cost and the like. 
     An object of the present invention is to realize a parallel cardan driving system driving bogie having a steering function while suppressing a change in the steering function by a running direction and an increase in cost of a railcar. 
     Solution to Problem 
     A parallel cardan driving system steering bogie for a railcar according to the present invention includes: a bogie frame supporting a carbody of a railcar; first and second axles arranged at front and rear sides in a car longitudinal direction, respectively, and extending along a car width direction; a steering mechanism configured to rotate both the first and second axles relative to the bogie frame to perform steering; first and second electric motors supported by the bogie frame, arranged at the front and rear sides in the car longitudinal direction, respectively, and including first and second output shafts, respectively, the first and second output shafts being parallel to the first and second axles at the time of non-steering; first and second reducers connected to the first and second axles, respectively; and a first constant velocity ball joint by which the first output shaft is coupled to the first reducer and which follows rotations of the first axle at the time of steering to allow relative displacement between the first output shaft and the first reducer, and a second constant velocity ball joint by which the second output shaft is coupled to the second reducer and which follows rotations of the second axle at the time of the steering to allow relative displacement between the second output shaft and the second reducer. 
     According to the above configuration, the constant velocity ball joint is used as a joint between the output shaft and the reducer. Therefore, the backlash is unnecessary unlike the conventional WN gear coupling, and large deviation is allowable by spherical guide of the ball. On this account, even if the relative displacement of the axle in the yawing direction relative to the electric motor supported by the bogie frame occurs when the bogie passes through the curved line and the axle is steered, the constant velocity ball joint can follow the displacement. Since the constant velocity ball joint can follow the steering of the axle, both the first and second axles can be configured as the driving shafts which can be steered. As a result, it is possible to provide the parallel cardan driving system steering bogie capable of suppressing the change in the steering function by the running direction and the increase in the cost of the railcar. 
     Advantageous Effects of Invention 
     As is clear from the above explanation, the present invention can provide the parallel cardan driving system steering bogie capable of suppressing the change in the steering function by the running direction and the increase in the cost of the railcar. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view showing a parallel cardan driving system steering bogie according to an embodiment. 
         FIG. 2  is a plan view showing the parallel cardan driving system steering bogie of  FIG. 1 . 
         FIG. 3  is a cross-sectional view showing a constant velocity ball joint of the steering bogie of  FIG. 2 . 
         FIG. 4  is a major component plan view for explaining a groove portion of the constant velocity ball joint of  FIG. 3 . 
         FIG. 5  is a schematic plan view showing a state where a railcar including the parallel cardan driving system steering bogies of  FIG. 1  passes through a curved line. 
         FIG. 6  is an enlarged view showing major components of the parallel cardan driving system steering bogie of  FIG. 2 . 
         FIG. 7A  is a schematic diagram for explaining a car longitudinal direction displacement between an electric motor and a reducer by a suspension.  FIG. 7B  is a schematic diagram for explaining a car width direction displacement between the electric motor and the reducer by the suspension.  FIG. 7C  is a schematic diagram for explaining a vertical direction displacement between the electric motor and the reducer by the suspension. 
         FIG. 8A  is a schematic diagram showing a positional relation between the electric motor and the reducer in a non-steering state.  FIG. 8B  is a schematic diagram showing a state where an axle is steered in one direction by a steering mechanism.  FIG. 8C  is a schematic diagram showing a state where the axle is steered in the other direction by the steering mechanism. 
     
    
    
     DESCRIPTION OF EMBODIMENTS 
     Hereinafter, an embodiment will be explained in reference to the drawings. 
       FIG. 1  is a side view showing a parallel cardan driving system steering bogie  3  according to the embodiment.  FIG. 2  is a plan view showing the parallel cardan driving system steering bogie  3  of  FIG. 1 . In the following explanation, a direction in which a railcar  1  travels, that is, a length direction in which a carbody  2  extends is defined as a car longitudinal direction. A lateral direction perpendicular to the car longitudinal direction is defined as a car width direction (in the present embodiment, the car longitudinal direction is also called a “forward/rearward direction”, and the car width direction is also called a “leftward/rightward direction”). In the drawings, the same reference signs are used for the same components. 
     As shown in  FIGS. 1 and 2 , the bogie  3  of the present embodiment is a bogie which supports the carbody  2  of the railcar  1  from below. In a plan view, the bogie  3  is formed in a point symmetry when viewed from a center of the bogie. The bogie  3  includes a bolster  5  which supports the carbody  2  via air springs  4  and extends in the car width direction. The bolster  5  is connected to bolster anchors  16  by brackets  2   a  of the carbody  2 . The bolster  5  is connected to a bogie frame  7  through a turning guide mechanism  6  (for example, a center pin and a center plate) arranged at the center of the bogie in a plan view. To be specific, the bogie frame  7  slidably supports the bolster  5  from below so as to be able to horizontally turn relative to the bolster  5 . 
     The bogie frame  7  includes a cross beam  7   a  and a pair of side sills  7   b . The cross beam  7   a  is located under the bolster  5  and extends in the car width direction. The side sills  7   b  are connected to both respective car width direction end portions of the cross beam  7   a  and extend in the car longitudinal direction. The bogie frame  7  has an H shape in a plan view. First and second axles  9  extending in the car width direction are arranged in front of and behind the cross beam  7   a , respectively. Wheels  8  are provided at respective left and right sides of each axle  9 . Each of bearings  10  is provided at a car width direction end portion of the axle  9  so as to be located outside the wheel  8  in the car width direction. The bearings  10  rotatably support the axles  9 . The bearings  10  are accommodated in respective axle boxes  11 . Each of the axle boxes  11  is elastically coupled to and suspended from the side sill  7   b  by an axle box suspension  17  (suspension) including a coil spring (axle spring). Various types such as a publicly known axle beam type may be used as the axle box suspension  17 . 
     First and second electric motors  12  are arranged in front of and behind the cross beam  7   a , respectively. Each of the first and second electric motors  12  is not attached to the axle  9  but is fixed to the bogie frame  7  so as to be spaced apart from the axle  9 . First and second reducers  13  are connected to the first and second axles  9 , respectively. In a side view, the first and second reducers  13  are rotatable around the first and second axles  9 , respectively. An end portion of the reducer  13  is elastically coupled to the cross beam  7   a  by a support mechanism  14 , the end portion being located at the cross beam  7   a  side. To be specific, the first and second reducers  13  may be displaced relative to the bogie frame  7  in upward/downward, forward/rearward, and leftward/rightward directions. 
     An output shaft  28  of the first electric motor  12  is connected to an input shaft  29  of the first reducer  13  through a constant velocity ball joint  15 , and an output shaft  28  of the second electric motor  12  is connected to an input shaft  29  of the second reducer  13  via a constant velocity ball joint  15 . The output shaft  28  of the first electric motor  12  and the input shaft  29  of the first reducer  13  extend in parallel with the first axle  9  in the car width direction when a below-described steering mechanism  30  is in a non-steering state. The output shaft  28  of the second electric motor  12  and the input shaft  29  of the second reducer  13  extend in parallel with the second axle  9  in the car width direction when the steering mechanism  30  is in the non-steering state. The electric motor  12  and the reducer  13  are lined up in the car width direction so as to overlap each other in a side view. To be specific, the bogie  3  of the present embodiment is a so-called parallel cardan driving system driving bogie. 
     The bogie  3  is provided with the steering mechanism  30 . The steering mechanism  30  rotates both the first and second axles  9  relative to the bogie frame  7  in the yawing direction to perform the steering. The steering mechanism  30  includes swinging levers  18 . The swinging levers  18  are arranged at respective car width direction outer sides of the cross beam  7   a  so as to extend in a vertical direction. An upper portion of the swinging lever  18  is attached to the bolster  5  or the bolster anchor  16  through a link  19   a  so as to be rotatable around a fulcrum  19 . A portion of the swinging lever  18  is attached to a side surface of the bogie frame  7  so as to be rotatable around a fulcrum  20 , the portion being located under the fulcrum  19 . A portion of the swinging lever  18  is attached to one end portion of a coupling rod  24  so as to be rotatable around a fulcrum  21 , the portion being located between the fulcrums  19  and  20 . The other end portion of the coupling rod  24  is rotatably coupled to the axle box  11  located at one car longitudinal direction side. 
     A portion of the swinging lever  18  is attached to one end portion of a coupling rod  25  so as to be rotatable around a fulcrum  22 , the portion being located under the fulcrum  20 . The other end portion of the coupling rod  25  is rotatably coupled to the axle box  11  located at the other car longitudinal direction side. Each of the fulcrums  19  to  22  is constituted by a connector (such as a pin) by which two members are rotatably connected to each other. With this, when the bogie  3  passes through the curved line, the swinging lever  18  swings around the fulcrum  19  in a vertical plane, and therefore, both the front and rear axles  9  can be steered. At the time of the steering, the constant velocity ball joint  15  deviates and flexibly follows the rotation of the axle  9 . With this, the relative displacement between the output shaft  28  of the electric motor  12  and the input shaft  29  of the reducer  13  is allowed. 
       FIG. 3  is a cross-sectional view showing the constant velocity ball joint  15  of the steering bogie  3  of  FIG. 2 .  FIG. 4  is a major component plan view for explaining groove portions  31   b  and  36   a  ( 32   b  and  37   a ) of the constant velocity ball joint  15  of  FIG. 3 . As shown in  FIGS. 3 and 4 , the constant velocity ball joint  15  includes a first inner tube  31  and a second inner tube  32 . The first inner tube  31  includes an insertion hole  31   a  to which the output shaft  28  of the electric motor  12  is splined. The second inner tube  32  includes an insertion hole  32   a  to which the input shaft  29  of the reducer  13  is splined. The first inner tube  31  and the second inner tube  32  are spaced apart from each other. A plurality of groove portions  31   b  extending in an axial direction of the output shaft  28  are formed on an outer peripheral surface of the inner tube  31  at equal intervals in the circumferential direction. A plurality of groove portions  32   b  extending in an axial direction of the input shaft  29  are formed on an outer peripheral surface of the inner tube  32  at equal intervals in the circumferential direction. 
     A first outer tube  36  is provided at a radially outer side of the first inner tube  31 , and a second outer tube  37  is provided at a radially outer side of the second inner tube  32 . The first outer tube  36  and the second outer tube  37  are coupled to each other via a partition plate  33 . A plurality of groove portions  36   a  extending in the axial direction of the output shaft  28  are formed on an inner peripheral surface of the outer tube  36  at equal intervals in the circumferential direction. A plurality of groove portions  37   a  extending in the axial direction of the input shaft  29  are formed on an inner peripheral surface of the outer tube  37  at equal intervals in the circumferential direction. Each of balls  34  is slidably sandwiched between the groove portion  31   b  of the inner tube  31  and the groove portion  36   a  of the outer tube  36 . Each of balls  35  is slidably sandwiched between the groove portion  32   b  of the inner tube  32  and the groove portion  37   a  of the outer tube  37 . An annular ball retainer  38  locked with the inner tube  31  is arranged between the inner tube  31  and the outer tube  36 , and an annular ball retainer  39  locked with the inner tube  32  is arranged between the inner tube  32  and the outer tube  37 . A plurality of ball holes each of which slidably holds the ball  34  are formed on the ball retainer  38  at equal intervals in the circumferential direction. A plurality of ball holes each of which slidably holds the ball  35  are formed on the ball retainer  39  at equal intervals in the circumferential direction. The groove portions  31   b  of the inner tube  31  and the groove portions  36   a  of the outer tube  36  extend in a direction along the axial direction of the output shaft  28 , and the groove portions  32   b  of the inner tube  32  and the groove portions  37   a  of the outer tube  37  extend in a direction along the axial direction of the input shaft  29 . 
       FIG. 5  is a schematic plan view showing a state where the railcar  1  including the parallel cardan driving system steering bogie  3  of  FIG. 1  passes through the curved line. In  FIG. 5 , a track line  100  is a curved line that indicates a center line extending between a pair of rails (not shown). When the railcar  1  passes through the curved line, the steering mechanism  30  (see  FIGS. 1 and 2 ) operates by lateral force applied from the rails to the wheels  8  of the bogie  3 . Thus, self-steering is performed such that each of the axles  9  faces in a direction substantially perpendicular to the track line  100 . A steering angle θ s  is represented by Formula 1 below where a half of a distance between the axles of the bogie  3  is denoted by L, a curvature radius of the track line  100  is denoted by R, and a steering additional coefficient is denoted by λ. 
     
       
         
           
             
               
                 
                   
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                   Formula 
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       FIG. 6  is an enlarged view showing major components of the parallel cardan driving system steering bogie  3  of  FIG. 2 . As shown in  FIG. 6 , the electric motor  12  is arranged on a virtual line SL extending in the car longitudinal direction through a steering center O of the axle  9 . The electric motor  12  includes a casing  27  which accommodates a rotor and a stator. The casing  27  includes an intermediate portion  27   a  and an outside portion  27   b . The intermediate portion  27   a  is located at a car width direction intermediate region. The outside portion  27   b  is located at a car width direction outside region relative to the intermediate portion  27   a . To be specific, the outside portion  27   b  is provided further away from the virtual line SL than the intermediate portion  27   a  in the car width direction. 
     A surface  27   ba  of the outside portion  27   b  is provided further away from the axle  9  than a surface  27   aa  of the intermediate portion  27   a , the surfaces  27   ba  and  27   aa  being close to the axle  9 . Specifically, the surface  27   ba  of the outside portion  27   b  is inclined such that a distance from the surface  27   ba  to the axle  9  in the car longitudinal direction increases toward an outer side in the car width direction. In the present embodiment, the surface  27   ba  of the outside portion  27   b  has a tapered shape but may have a circular-arc shape. The casing  27  shown in  FIG. 6  has a substantially symmetrical shape in the car width direction but does not have to be symmetrical. 
     As shown by broken lines in  FIG. 6 , when the axle  9  is steered by the steering mechanism  30  (see  FIGS. 1 and 2 ), a car width direction outside portion of the axle  9  may move close to the electric motor  12 . As described above, the casing  27  of the electric motor  12  has the above shape. Therefore, in a state where a gap is secured between the surface  27   ba  of the outside portion  27   b  of the casing  27  and the axle  9 , the axle  9  can intersect with a virtual extended line VL in a plan view, the virtual extended line VL extending in the car width direction from the surface  27   aa  of the intermediate portion  27   a.    
       FIG. 7A  is a schematic diagram for explaining a car longitudinal direction displacement between the electric motor  12  and the reducer  13  by the axle box suspension  17 .  FIG. 7B  is a schematic diagram for explaining a car width direction displacement between the electric motor  12  and the reducer  13  by the axle box suspension  17 .  FIG. 7C  is a schematic diagram for explaining a vertical direction displacement between the electric motor  12  and the reducer  13  by the axle box suspension  17 . The axle box suspension  17  (see  FIG. 1 ) of the bogie  3  has flexibility in the upward/downward, forward/rearward, and leftward/rightward directions. Therefore, each of the relative displacement generated by the axle box suspension  17  in the forward/rearward direction ( FIG. 7A ), the relative displacement generated by the axle box suspension  17  in the leftward/rightward direction ( FIG. 7B ), and the relative displacement generated by the axle box suspension  17  in the upward/downward direction ( FIG. 7C ) may occur between the electric motor  12  attached to the bogie frame  7  and the reducer  13  attached to the axle  9 . 
     As shown in  FIG. 7A , a forward/rearward direction allowable displacement amount between the electric motor  12  and the reducer  13  in the bogie  3  by the axle box suspension  17  is denoted by δ x . As shown in  FIG. 7B , a car width direction allowable displacement amount between the electric motor  12  and the reducer  13  in the bogie  3  by the axle box suspension  17  is denoted by δ y . As shown in  FIG. 7C , an upward/downward direction allowable displacement amount between the electric motor  12  and the reducer  13  in the bogie  3  by the axle box suspension  17  is denoted by δ z . Each of the allowable displacement amounts δ x , δ y , and δ z  denotes an upper limit of a relative displacement amount between the electric motor  12  and the reducer  13  based on a neutral state where: an axis of the output shaft  28  (see  FIG. 2 ) of the electric motor  12  and an axis of the input shaft  29  (see  FIG. 2 ) of the reducer  13  coincide with each other; and a center of each axle  9  coincides with a center of the bogie frame  7  (see  FIG. 2 ) in the leftward/rightward direction. The values of the allowable displacement amounts δ x , δ y , and δ z  depend on structures of the bogie  3  including the axle box suspension  17 , and the like. 
       FIG. 8A  is a schematic diagram showing a positional relation between the electric motor  12  and the reducer  13  in the non-steering state.  FIG. 8B  is a schematic diagram showing a state where the axle  9  is steered in one direction by the steering mechanism  30 .  FIG. 8C  is a schematic diagram showing a state where the axle  9  is steered in the other direction by the steering mechanism  30 . The steering bogie  3  is provided with the steering mechanism  30  which can rotate the axle  9  in the yawing direction. Therefore, the forward/rearward direction relative displacement and the leftward/rightward direction relative displacement ( FIGS. 8B and 8C ) by the steering mechanism  30  may be generated between the electric motor  12  attached to the bogie frame  7  and the reducer  13  attached to the axle  9 . 
       FIG. 8A  shows the positional relation between the electric motor  12  and the reducer  13  in the non-steering state. In a planar coordinate system in which a steering center point O (0, 0) is a base point in a plan view, a center of the constant velocity ball joint  15  in the non-steering state is denoted by B (x, y). It should be noted that the non-steering state is a state where: the axles  9  are parallel to the cross beam  7   a ; and the front axle  9  and the rear axle  9  are parallel to each other. The center of the constant velocity ball joint  15  when the axle  9  is steered in one direction by the steering mechanism  30  (see  FIG. 1 ) as shown in  FIG. 8B  is denoted by B 1  (x 1 , y 1 ), and the center of the constant velocity ball joint  15  when the axle  9  is steered in the other direction by the steering mechanism  30  (see  FIG. 1 ) as shown in  FIG. 8C  is denoted by B 2  (x 2 , y 2 ). Those values x 1 , y 1 , x 2 , and y 2  are represented by Formulas 2 and 3 below. The steering angle θ s  in Formula 2 denotes an allowable steering angle that is an upper limit of the steering angle. The value of the steering angle θ s  depends on the structures of the bogie  3  including the steering mechanism  30 , a maximum curvature of the track, and the like. 
     
       
         
           
             
               
                 
                   
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     The forward/rearward direction allowable displacement amount between the electric motor  12  and the reducer  13  by the steering mechanism  30  is denoted by δ sx , and the leftward/rightward direction allowable displacement amount between the electric motor  12  and the reducer  13  by the steering mechanism  30  is denoted by δ sy . The allowable displacement amounts δ sx  and δ sy  are represented by Formulas 4 and 5 below.
 
δ sx =Max{| x   1   −x|,|x   2   −x|}   Formula 4
 
δ sy =Max{| y   1   −y|,|y   2   −y|}   Formula 5
 
     According to the above configuration, in the steering bogie  3  of the present embodiment, an allowable deviation amount δ r  of the constant velocity ball joint  15  in a direction perpendicular to the axial direction of the output shaft  28  (see  FIG. 2 ) of the electric motor  12  is set so as to satisfy Formula 6 below.
 
δ r =√{square root over (δ z   2 +(δ x+δsx ) 2 )}  Formula 6
 
     In the steering bogie  3  of the present embodiment, an allowable deviation amount δ a  of the constant velocity ball joint  15  in the axial direction of the output shaft  28  of the electric motor  12  is set so as to satisfy Formula 7.
 
δ a=δy+δsy   Formula 7
 
     Specifically, the allowable deviation amount δ r  of the constant velocity ball joint  15  in the direction perpendicular to the axial direction of the output shaft  28  of the electric motor  12  is set to a value which is not less than 17 mm and not more than 20 mm, and the allowable deviation amount δ a  of the constant velocity ball joint  15  in the axial direction of the output shaft  28  of the electric motor  12  is set to a value which is not less than 15 mm and not more than 17 mm. 
     According to the configuration explained above, the constant velocity ball joint  15  is used as a joint between the output shaft  28  of the electric motor  12  and the input shaft  29  of the reducer  13 . Therefore, the backlash is unnecessary unlike the conventional WN gear coupling, and large deviation is allowable by spherical guide of the balls  34 . On this account, even if the relative displacement of the axle  9  in the yawing direction relative to the electric motor  12  supported by the bogie frame  7  occurs when the bogie  3  passes through the curved line and the axle  9  is steered, the constant velocity ball joint  15  can follow the displacement. Since the constant velocity ball joint  15  can follow the steering of the axle  9 , both the front axle  9  and the rear axle  9  can be configured as the driving shafts which can be steered. As a result, it is possible to provide the parallel cardan driving system steering bogie  3  capable of suppressing the change in the steering function by the running direction and the increase in the cost of the railcar  1 . 
     Extending directions of the groove portions  36   a  and  37   a  of the outer tubes  36  and  37  of the constant velocity ball joint  15  and extending directions of the groove portions  31   b  and  32   b  of the inner tubes  31  and  32  of the constant velocity ball joint  15  do not intersect with each other but are the same as each other. Therefore, when the balls  34  and  35  guide the groove portion  31   b ,  32   b ,  36   a , and  37   a  to deviate the joint  15 , structural resistance between the ball ( 34  or  35 ) and the groove portion ( 31   b ,  32   b ,  36   a , or  37   a ) is reduced. Even when the bogie  3  passes through the sharp curved line, the constant velocity ball joint  15  largely deviates, and therefore, the steering is smoothly performed. 
     The allowable deviation amounts δ r  and δ a  of the constant velocity ball joint  15  are set so as to satisfy Formulas 6 and 7, respectively, and each of the allowable deviation amounts δ r  and δ a  is larger than the allowable displacement amount between the electric motor  12  and the reducer  13  by the axle box suspension  17  and the steering mechanism  30 . Therefore, the parallel cardan driving system driving bogie which can perform stable steering running can be realized. More specifically, the allowable deviation amount δ r  of the constant velocity ball joint  15  in the direction perpendicular to the axial direction of the output shaft  28  is set to a value which is not less than 17 mm and not more than 20 mm, and the allowable deviation amount δ a  of the constant velocity ball joint  15  in the axial direction of the output shaft  28  is set to be a value which is not less than 15 mm and not more than 17 mm. Therefore, the constant velocity ball joint  15  allows the deviation which is about 1.5 times the deviation allowed by the conventional WN gear coupling. Thus, the parallel cardan driving system driving bogie which can perform stable steering running can be realized. 
     Further, the steering mechanism  30  is configured to steer the axle  9  such that in a plan view, the axle  9  can intersect with the virtual extended line VL extending in the car width direction from the surface  27   aa  of the intermediate portion  27   a  of the casing  27  of the electric motor  12 , the surface  27   aa  being close to the axle  9 . Therefore, while preventing the interference between the axle  9  and the electric motor  12  by the steering, devices mounted on the bogie  3  can be efficiently arranged. 
     The present invention is not limited to the above-described embodiment, and modifications, additions, and eliminations may be made within the scope of the present invention. 
     INDUSTRIAL APPLICABILITY 
     As above, the parallel cardan driving system steering bogie according to the present invention has the above-described excellent effects. It is useful to widely apply the present invention to railcar bogies which can achieve the significance of these effects. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  railcar 
               2  carbody 
               3  steering bogie 
               7  bogie frame 
               9  axle 
               12  electric motor 
               13  reducer 
               15  constant velocity ball joint 
               17  axle box suspension (suspension) 
               27  casing 
               27   a  intermediate portion 
               27   b  outside portion 
               28  output shaft 
               30  steering mechanism 
               31 ,  32  inner tube 
               34 ,  35  ball 
               36 ,  37  outer tube 
               38 ,  39  retainer 
               31   b ,  32   b ,  36   a ,  37   a  groove portion 
             VL virtual extended line