Patent Publication Number: US-2021163048-A1

Title: Railcar driving bogie

Description:
TECHNICAL FIELD 
     The present disclosure relates to a railcar bogie, i.e., a driving bogie on which a traction motor is mounted. 
     BACKGROUND 
     In a driving bogie of a railcar, a traction motor receiving seat including a keyway extending in a car width direction is provided at a cross beam of a bogie frame, and a traction motor is attached to the keyway. 
     SUMMARY 
     By, for example, vibrations generated while the railcar is traveling, the traction motor tends to swing about the keyway serving as a swing axis in an upper-lower direction. Since the traction motor is large in weight, the traction motor receiving seat itself and a joined portion between the traction motor receiving seat and the cross beam need to have adequate strength which can endure the swinging of the traction motor. Therefore, a weight increase is caused, and joining work requires skill. 
     A railcar bogie according to one aspect of the present disclosure includes: a cross beam extending in a car width direction; a first traction motor supported by a first car longitudinal direction portion of the cross beam; a second traction motor supported by a second car longitudinal direction portion of the cross beam; and a coupling member arranged under the cross beam and between the first traction motor and the second traction motor and coupling the first traction motor and the second traction motor to each other. 
    
    
     
       BRIEF DESCRIPTION OF DRAWINGS 
         FIG. 1  is a side view of a railcar bogie according to an embodiment. 
         FIG. 2  is a plan view of the bogie of  FIG. 1  when viewed from above. 
         FIG. 3  is a perspective view of a bogie frame of  FIG. 2  when viewed from above. 
         FIG. 4  is a perspective view of the bogie frame of  FIG. 2  when viewed from below. 
         FIG. 5  is a longitudinal sectional view of a pipe member of the bogie frame of  FIG. 3  when viewed from a car longitudinal direction. 
         FIG. 6  is a longitudinal sectional view of an intermediate member of the bogie frame of  FIG. 3  when viewed from the car longitudinal direction. 
         FIG. 7  is a longitudinal sectional view of an air spring seat and pressing member of the bogie of  FIG. 1  when viewed from a car width direction. 
         FIG. 8  is a perspective view for explaining brake receiving seats and a coupling member of  FIG. 4  when viewed from below. 
         FIG. 9  is a side view for explaining the brake receiving seats and coupling member of  FIG. 8 . 
         FIG. 10  is a bottom view for explaining traction motors and a coupling member in the bogie shown in  FIG. 2 . 
         FIG. 11  is a side view for explaining the traction motors and the coupling member shown in  FIG. 10 . 
     
    
    
     DETAILED DESCRIPTION 
     Hereinafter, an embodiment will be described with reference to the drawings. In the following description, a direction in which a railcar travels and a car body extends is defined as a car longitudinal direction, and a lateral direction perpendicular to the car longitudinal direction is defined as a car width direction. The car longitudinal direction is also called a front-rear direction, and the car width direction is also called a left-right direction. 
       FIG. 1  is a side view of a railcar bogie  1  according to the embodiment. As shown in  FIG. 1 , the bogie  1  supports a car body  2  from below through air springs  3  serving as secondary suspensions. The bogie  1  includes a bogie frame  4  on which the air springs  3  are mounted. The bogie frame  4  includes a cross beam  5  extending in the car width direction but does not include side sills extending in the car longitudinal direction from car width direction end portions  5   a  of the cross beam  5 . A pair of axles  6  each extending in the car width direction are arranged at both sides of the cross beam  5  in the car longitudinal direction. Wheels  7  are provided at both car width direction portions of each axle  6 . Bearings  8  rotatably supporting the axle  6  are provided at both car width direction end portions of the axle  6  so as to be located outside the corresponding wheels  7  in the car width direction. The bearings  8  are accommodated in axle boxes  9 . 
     Each car width direction end portion  5   a  of the cross beam  5  is coupled to the axle box  9  by an axle box suspension  10 . The axle box suspension  10  includes an axle beam  11  extending from the axle box  9  toward the cross beam  5  in the car longitudinal direction. A tubular portion  11   a  is provided at a tip end of the axle beam  11 . The tubular portion  11   a  is open toward both sides in the car width direction. A core rod  12  is inserted into an internal space of the tubular portion  11   a  so as to project from the tubular portion  11   a  toward both sides in the car width direction. An elastic bushing (not shown) is interposed between the core rod  12  and the tubular portion  11   a.    
     The bogie frame  4  includes receiving sills  14  each extending from the car width direction end portion  5   a  of the cross beam  5  toward both sides in the car longitudinal direction. A pair of receiving seats  15  are provided at each of tip ends of the receiving sills  14 . The pair of receiving seats  15  include fitting grooves  15   a  that are recessed downward. Both end portions of the core rod  12  are fitted into the fitting grooves  15   a  from above. Both end portions of the core rod  12  accommodated in the pair of fitting grooves  15   a  are pressed by lid members  16  from above, and the lid members  16  are fixed to the receiving seats  15  by fasteners  17  (for example, bolts). 
     A pair of axle boxes  9  arranged away from each other in the car longitudinal direction support both longitudinal direction end portions  13   b  of a plate spring  13  extending in the car longitudinal direction. A longitudinal direction middle portion  13   a  of the plate spring  13  supports the car width direction end portion  5   a  of the cross beam  5  from below. With this, the cross beam  5  is supported by the axle boxes  9  through the plate springs  13 . To be specific, the plate spring  13  has both the function of a primary suspension and the function of a conventional side sill. 
     The plate spring  13  has a bow shape that is convex downward in a side view. Pressing members  18  are provided at lower portions of the car width direction end portions  5   a  of the cross beam  5 . Each of the pressing members  18  includes a circular-arc lower surface that is convex downward. The pressing members  18  are placed on and separably contact middle portions  13   a  of the plate springs  13  from above. To be specific, the plate springs  13  are not fixed to the pressing members  18  in the upper-lower direction, and the pressing members  18  contact upper surfaces of the plate springs  13  by a downward load from the cross beam  5 . To be specific, each pressing member  18  is not fixed to the corresponding plate spring  13  by fixtures, and a pressing state of the pressing member  18  against the plate spring  13  is maintained by pressure generated by a gravitational downward load from the cross beam  5  and reaction force of the plate spring  13  against the downward load. With this, the plate spring  13  can swing while changing a pressing region where the plate spring  13  is pressed against a lower surface of the pressing member  18 . 
     A supporting member  19  is attached to an upper end portion of the axle box  9 . The end portion  13   b  of the plate spring  13  is supported by the axle box  9  from below through the supporting member  19 . An upper surface of the supporting member  19  is inclined toward a bogie middle side in a side view. The end portion  13   b  of the plate spring  13  is placed on the supporting member  19  from above without being fixed to the supporting member  19  in the upper-lower direction. The supporting member  19  includes a vibration-proof member  20  (for example, rubber) and a receiving member  21 . The vibration-proof member  20  is provided on the axle box  9 , and the receiving member  21  is provided on and positioned at the vibration-proof member  20 . 
       FIG. 2  is a plan view of the bogie  1  of  FIG. 1  when viewed from above.  FIG. 3  is a perspective view of the bogie frame  4  of  FIG. 2  when viewed from above.  FIG. 4  is a perspective view of the bogie frame  4  of  FIG. 2  when viewed from below. As shown in  FIGS. 2 to 4 , the cross beam  5  extends in the car width direction, and a center pin arrangement space S is formed at a car width direction middle portion  5   b  (see  FIGS. 3 and 4 ) of the cross beam  5 . For example, the cross beam  5  is made of metal. Specifically, the cross beam  5  includes a pair of pipe members  22  and  23 , a pair of intermediate members  24  and  25 , a center pin accommodating member  26 , air spring seats  27 , and the pressing members  18 . 
     The pair of pipe members  22  and  23  extend in the car width direction and are lined up so as to be located away from each other in the car longitudinal direction. For example, the pipe members  22  and  23  are square pipes. Internal spaces of the pipe members  22  and  23  are sealed so as to be used as auxiliary air chambers for the air springs  3 . The pipe member  22  includes linear portions  22   a  and a curved portion  22   b , and the pipe member  23  includes linear portions  23   a  and a curved portion  23   b . The linear portions  22   a  and  23   a  are located at the car width direction end portions  5   a  of the cross beam  5  and extend linearly in the car width direction. The curved portions  22   b  and  23   b  are located at the car width direction middle portion  5   b  of the cross beam  5  and project outward in the car longitudinal direction such that a clearance between the pair of pipe members  22  and  23  increases. The center pin arrangement space S is provided at a space formed between the curved portions  22   b  and  23   b  of the pair of pipe members  22  and  23 . Therefore, the car width direction end portion  5   a  of the cross beam  5  is smaller in size in the car longitudinal direction than the car width direction middle portion  5   b  of the cross beam  5 . It should be noted that the internal spaces of the pipe members  22  and  23  do not have to be sealed when the internal spaces are not used as the auxiliary air chambers. 
     The pair of intermediate members  24  and  25  are arranged at both sides of the center pin arrangement space S in the car width direction and extend in the car width direction. Each of the intermediate members  24  and  25  is sandwiched between the linear portions  22   a  and  23   a  of the pair of pipe members  22  and  23 . The pair of intermediate members  24  and  25  are located away from each other in the car width direction to form a gap at a middle of the cross beam  5 . For example, the intermediate members  24  and  25  are square pipes. Internal spaces of the intermediate members  24  and  25  are sealed so as to be used as auxiliary air chambers for the air springs  3 . For example, vertical sizes of the intermediate members  24  and  25  are the same as vertical sizes of the pipe members  22  and  23 . For example, sizes of the intermediate members  24  and  25  in the car longitudinal direction are smaller than sizes of the pipe members  22  and  23  in the car longitudinal direction. 
     The center pin accommodating member  26  is arranged between the curved portions  22   b  and  23   b  of the pair of pipe members  22  and  23  and between the pair of intermediate members  24  and  25 . The center pin accommodating member  26  includes a tubular portion  26   a , a pair of longitudinal attaching portions  26   b , and a pair of lateral attaching portions  26   c . The tubular portion  26   a  forms the center pin arrangement space S. The pair of longitudinal attaching portions  26   b  project from the tubular portion  26   a  toward both sides in the car longitudinal direction. The pair of lateral attaching portions  26   c  project from the tubular portion  26   a  toward both sides in the car width direction. An internal space of the tubular portion  26   a  is open toward both sides in a vertical direction and serves as the center pin arrangement space S. A cylindrical elastic bushing  29  is fitted in the tubular portion  26   a . A center pin  30  projecting downward from the car body  2  is inserted into the elastic bushing  29 . 
     The longitudinal attaching portions  26   b  are joined to circular-arc inner side surfaces of the curved portions  22   b  and  23   b  of the pipe members  22  and  23 , the inner side surfaces being located close to a center of the cross beam  5 . Each of car longitudinal direction outer joining ends (tip ends) of the longitudinal attaching portions  26   b  has a circular-arc shape in a plan view. The car longitudinal direction outer joining ends (tip ends) of the longitudinal attaching portions  26   b  are joined to the inner side surfaces of the curved portions  22   b  and  23   b  by circumferential welding, the inner side surfaces being located close to the center of the cross beam  5 . Each of the longitudinal attaching portions  26   b  has such a shape as to gradually spread toward the joining end thereof. With this, tractive effort acting in the car longitudinal direction can be smoothly transmitted between the pipe member  22 ,  23  and the center pin  30  through the center pin accommodating member  26 . 
     Vertical sizes of the joining ends of the longitudinal attaching portions  26   b  are smaller than vertical sizes of the inner side surfaces of the curved portions  22   b  and  23   b , the inner side surfaces being located close to the center of the cross beam  5 . A welded portion W 1  by which the joining end of the longitudinal attaching portion  26   b  and the curved portion  22   b  are joined to each other is provided at and within the inner side surface of the curved portion  22   b , and another welded portion W 1  by which the joining end of the longitudinal attaching portion  26   b  and the curved portion  23   b  are joined to each other is provided at and within the inner side surface of the curved portion  23   b . Therefore, each welded portion W 1  can be completed on one side surface of the curved portion  22 ,  23   b , and stress generated at the welded portion W 1  can be suppressed. 
     Car width direction outer joining ends (tip ends) of the lateral attaching portions  26   c  are joined to end edges of the intermediate members  24  and  25  by welding, the end edges being located close to the center of the cross beam  5 . The joining ends of the lateral attaching portions  26   c  are the same in shape as the end edges of the intermediate members  24  and  25 , the end edges being opposed to the corresponding lateral attaching portions  26   c . The joining ends of the lateral attaching portions  26   c  are joined to the end edges of the intermediate members  24  and  25  by circumferential welding. With this, a load generated by the displacement of the center pin  30  in the left-right direction (car width direction) is transmitted through the center pin accommodating member  26  to the intermediate members  24  and  25 , and the intermediate members  24  and  25  suitably inhibit an excessive movement of the center pin  30  in the left-right direction. To be specific, the pair of intermediate members  24  and  25  serve as left-right movement stopper receivers configured to prevent the car body  2  from being excessively displaced relative to the bogie  1  in the left-right direction (car width direction). 
     In the present embodiment, the center pin accommodating member  26  includes the tubular portion  26   a , the longitudinal attaching portions  26   b , and the lateral attaching portions  26   c . However, the present embodiment is not limited to this. For example, the lateral attaching portions  26   c  may be omitted, and the intermediate members  24  and  25  may be directly joined to the tubular portion  26   a . Various modified examples are applicable. 
     Each of the air spring seats  27  is provided on upper surfaces of the pair of pipe members  22  and  23  and an upper surface of the intermediate member  24  or  25  so as to be located at the car width direction end portion  5   a  of the cross beam  5 . Each of the air spring seats  27  has a plate shape. Each of the pressing members  18  is provided on lower surfaces of the pair of pipe members  22  and  23  and a lower surface of the intermediate member  24  or  25  so as to be located at the car width direction end portion  5   a  of the cross beam  5 . The pair of pipe members  22  and  23  and the intermediate members  24  and  25  are fixed to each other through the air spring seats  27  and the pressing members  18 . Each of the pressing members  18  includes a pressing portion  18   a  and plate-shaped attaching portions  18   b . The pressing portion  18   a  includes a lower surface having a circular-arc shape when viewed from the car width direction. The attaching portions  18   b  are provided at both sides of the pressing portion  18   a  in the car width direction. In the present embodiment, the air spring seats  27  are provided at the car width direction end portions  5   a  of the cross beam  5 . However, the present embodiment is not limited to this, and the air spring seats  27  may be provided at desired positions in the car width direction depending on the type of a car. 
     Each of the pressing members  18  is fixed to the pipe members  22  and  23  and the intermediate member  24  or  25  by the attaching portions  18   b . With this, the pressing members  18  configured to transmit the downward load from the cross beam  5  to the plate springs  13  serve to connect the pipe members  22  and  23  and the intermediate members  24  and  25  with each other. Moreover, since the pressing members  18  are integrated with the cross beam  5 , the number of parts is made smaller than when, for example, the pressing members  18  configured as separate parts are engaged with the cross beam  5 . Therefore, the structure of the bogie and the assembly work are simplified. 
     At each of the car width direction end portions  5   a  of the cross beam  5 , a first brake receiving seat  31  is joined to the linear portion  22   a  of the pipe member  22 , and a second brake receiving seat  32  is joined to the linear portion  23   a  of the pipe member  23 . As shown in  FIG. 9 , a unit-type first wheel tread brake device B 1  configured to brake the wheel  7  located at one side in the car longitudinal direction is fixed to the first brake receiving seat  31 , and a unit-type second wheel tread brake device B 2  is fixed to the second brake receiving seat  32 . The first wheel tread brake device B 1  and the second wheel tread brake device B 2  are independent from each other and individually brake a pair of wheels  7  arranged away from each other in the car longitudinal direction. The wheel tread brake devices B 1  and B 2  are arranged so as to project downward beyond the cross beam  5 . 
     The car width direction end portion  5   a  of the cross beam  5  is smaller in size in the car longitudinal direction than the car width direction middle portion  5   b  of the cross beam  5 . Therefore, work spaces are secured such that the wheel tread brake devices B 1  and B 2  can be arranged easily. The curved portions  22   b  and  23   b  are formed at the pair of pipe members  22  and  23  so as to be located at the car width direction middle portion  5   b  of the cross beam  5 . Therefore, a clearance between the pair of pipe members at the car width direction middle portion  5   b  of the cross beam  5  is wide, but a clearance between the pair of pipe members at each of the car width direction end portions of the cross beam is narrow. On this account, by a simple step that is bending of the pipe members  22  and  23 , the arrangement spaces for the wheel tread brake devices B 1  and B 2  can be easily secured, and in addition, productivity improves. 
     A first gear box G 1  and a first traction motor M 1  are arranged at one side of the cross beam  5  in the car longitudinal direction, and a second gear box G 2  and a second traction motor M 2  are arranged at the other side of the cross beam  5  in the car longitudinal direction. The traction motor M 1  is connected to the gear box G 1  through a universal joint  33 , and the traction motor M 2  is connected to the gear box G 2  through a universal joint  34 . The first and second gear boxes G 1  and G 2  are connected to the corresponding axles  6 . To be specific, in a plan view, the first gear box G 1  and the second gear box G 2  are arranged symmetrically about a point that is a center of the cross beam  5 , and the first traction motor M 1  and the second traction motor M 2  are arranged symmetrically about the point that is the center of the cross beam  5 . 
     A first gear box receiving seat  35  and a second gear box receiving seat  36  are joined to the cross beam  5  by circumferential welding. The first gear box G 1  is fixed to the first gear box receiving seat  35 , and the second gear box G 2  is fixed to the second gear box receiving seat  36 . The first gear box receiving seat  35  is arranged between a top of the curved portion  22   b  and the first brake receiving seat  31  in the car width direction, and the second gear box receiving seat  36  is arranged between a top of the curved portion  23   b  and the second brake receiving seat  32  in the car width direction. A vertical size of a joining end of the gear box receiving seat  35  which end is opposed to the curved portion  22   b  is smaller than a vertical size of an outer surface of the curved portion  22   b  which surface is located outside in the car longitudinal direction, and a vertical size of a joining end of the gear box receiving seat  36  which end is opposed to the curved portion  23   b  is smaller than a vertical size of an outer surface of the curved portion  23   b  which surface is located outside in the car longitudinal direction. A welded portion W 2  by which the joining end of the gear box receiving seat  35  and the curved portion  22   b  are joined to each other is provided at and accommodated in the outer surface of the curved portion  22   b . Another welded portion W 2  by which the joining end of the gear box receiving seat  36  and the curved portion  23   b  are joined to each other is provided at and accommodated in the outer surface of the curved portion  23   b.    
     The gear box receiving seat  35  is joined to the outer surface of the curved portion  22   b  which surface is inclined relative to the car width direction, and the gear box receiving seat  36  is joined to the outer surface of the curved portion  23   b  which surface is inclined relative to the car width direction. Therefore, the gear box receiving seat  35  projects diagonally from the curved portion  22   b  outward in the car longitudinal direction and outward in the car width direction, and the gear box receiving seat  36  projects diagonally from the curved portion  23   b  outward in the car longitudinal direction and outward in the car width direction. According to this configuration, even when the wheel tread brake device B 1  is arranged close to the gear box G 1  in the car width direction, and the wheel tread brake device B 2  is arranged close to the gear box G 2  in the car width direction, a portion of the pipe member  22  to which portion the gear box receiving seat  35  is joined is located away from the brake receiving seat  31  in the car width direction, and a portion of the pipe member  23  to which portion the gear box receiving seat  36  is joined is located away from the brake receiving seat  32  in the car width direction. Therefore, work of welding the gear box receiving seat  35  to the pipe member  22  and welding the gear box receiving seat  36  to the pipe member  23  is facilitated. 
     A first traction motor receiving seat  37  and a second traction motor receiving seat  38  are joined to the cross beam  5  by circumferential welding. The first traction motor M 1  is fixed to the first traction motor receiving seat  37 , and the second traction motor M 2  is fixed to the second traction motor receiving seat  38 . The first traction motor receiving seat  37  is arranged at an opposite side of the first gear box receiving seat  35  in the car width direction so as to be located between the top of the curved portion  22   b  and the first brake receiving seat  31 . The second traction motor receiving seat  38  is arranged at an opposite side of the second gear box receiving seat  36  in the car width direction so as to be located between the top of the curved portion  23   b  and the second brake receiving seat  32 . A vertical size of a joining end of the traction motor receiving seat  37  which end is opposed to the curved portion  22   b  is smaller than a vertical size of an outer surface of the curved portion  22   b  which surface is located outside in the car longitudinal direction, and a vertical size of a joining end of the traction motor receiving seat  38  which end is opposed to the curved portion  23   b  is smaller than a vertical size of an outer surface of the curved portion  23   b  which surface is located outside in the car longitudinal direction. A welded portion W 3  by which the joining end of the traction motor receiving seat  37  and the curved portion  22   b  are joined to each other is provided at and within the outer surface of the curved portion  22   b . Another welded portion W 3  by which the joining end of the traction motor receiving seat  38  and the curved portion  23   b  are joined to each other is provided at and within the outer surface of the curved portion  23   b.    
     The above-described receiving sills  14  are fixed to lower surfaces of the car width direction end portions  5   a  of the cross beam  5 . Each of the receiving sills  14  extends from the car width direction end portion  5   a  of the cross beam  5  toward both sides in the car longitudinal direction. The receiving sill  14  includes a pair of side wall portions  14   a  arranged away from each other in the car width direction, and the pressing member  18  is arranged in a space between the pair of side wall portions  14   a.    
       FIG. 5  is a longitudinal sectional view of the pipe member  22  of the bogie frame  4  of  FIG. 3  when viewed from the car longitudinal direction. It should be noted that  FIG. 5  representatively shows the pipe member  22  that is one of the pair of pipe members  22  and  23 . The pipe member  23  is the same in structure as the pipe member  22 . As shown in  FIGS. 3 to 5 , first projecting members  41  and second projecting members  42  are provided at the pipe member  22 . The first projecting members  41  and the second projecting members  42  project upward and downward from the linear portions  22   a  located at the car width direction end portions of the pipe member  22 . Specifically, a fitting hole  22   e  and a fitting hole  22   f  are formed at an upper wall portion of each linear portion  22   a  of the pipe member  22  so as to be spaced apart from each other in the car width direction. The fitting holes  22   e  and  22   f  penetrate the upper wall portion of the linear portion  22   a  of the pipe member  22  in the vertical direction. An upper end portion of the first projecting member  41  is fitted in the fitting hole  22   e , and an upper end portion of the second projecting member  42  is fitted in the fitting hole  22   f  In the present embodiment, each of outer peripheral surfaces of the first projecting members  41  and the second projecting members  42  has a circular shape from the viewpoint of below-described weldability but may have a polygonal shape. The first projecting members  41  and the second projecting members  42  may be hollow or solid. The first projecting members  41  and the second projecting members  42  do not have to penetrate the pipe members  22  and  23  and may be fixed to the surfaces of the pipe members  22  and  23 . 
     An attaching hole  27   a  is formed at the air spring seat  27 . A diameter of the attaching hole  27   a  is larger than an outer diameter of a portion of the first projecting member  41  which portion projects from the pipe member  22 . When viewed from above, the attaching hole  27   a  includes the fitting hole  22   e . The upper end portion of the first projecting member  41  is inserted into the attaching hole  27   a  with some play. The upper end portion of the first projecting member  41  is joined to the pipe member  22  by circumferential welding through the attaching hole  27   a  of the air spring seat  27  and also joined to the air spring seat  27  by circumferential welding. The upper end portion of the second projecting member  42  is also joined to the pipe member  22  by circumferential welding. As above, the air spring seats  27  are fixed to the pipe members  22  and  23  through the first projecting members  41 , and therefore, the pair of pipe members  22  and  23  are connected to each other. A welded portion W 4  by which the first projecting member  41  and the air spring seat  27  are joined to each other is formed in a closed loop shape along the outer peripheral surface of the first projecting member  41 . A welded portion W 5  by which the second projecting member  42  and the pipe member  22  are joined to each other is also formed in a closed loop shape along the outer peripheral surface of the second projecting member  42 . Each welded portion is formed throughout the projecting member according to need, and with this, required strength as the bogie frame is secured. According to this, since each of the welded portions W 4  and W 5  is formed in a closed loop shape having no end edge, robot welding is easily performed, and therefore, productivity improves. 
     A fitting hole  22   g  and a fitting hole  22   h  are formed at a lower wall portion of each linear portion  22   a  of the pipe member  22  so as to be spaced apart from each other in the car width direction. The fitting holes  22   g  and  22   h  penetrate the lower wall portion of the linear portion  22   a  of the pipe member  22  in the vertical direction. A lower end portion of the first projecting member  41  is fitted in the fitting hole  22   g , and a lower end portion of the second projecting member  42  is fitted in the fitting hole  22   h . Attaching holes  18   c  are formed at the attaching portions  18   b  of the pressing member  18 . Diameters of the attaching holes  18   c  are larger than outer diameters of portions of the first and second projecting members  41  and  42  which portions project from the pipe member  22 . When viewed from below, the attaching holes  18   c  include the corresponding fitting holes  22   g  and  22   h . The lower end portions of the first and second projecting members  41  and  42  are inserted into the corresponding attaching holes  18   c  with some play. 
     The lower end portions of the first and second projecting members  41  and  42  are joined to the pipe member  22  by circumferential welding through the attaching holes  18   c  of the attaching portions  18   b  of the pressing member  18  and also joined to the attaching portions  18   b  of the pressing member  18  by circumferential welding. As above, the pressing members  18  are fixed to the pipe members  22  and  23  through the first projecting members  41  and the second projecting members  42 , and with this, the pair of pipe members  22  and  23  are connected to each other. A welded portion W 6  by which the pressing member  18  is joined to the first projecting member  41  is formed in a closed loop shape along the outer peripheral surface of the first projecting member  41 , and a welded portion W 7  by which the pressing member  18  is joined to the second projecting member  42  is formed in a closed loop shape along the outer peripheral surface of the second projecting member  42 . 
       FIG. 6  is a longitudinal sectional view of the intermediate member  24  of the bogie frame  4  of  FIG. 3  when viewed from the car longitudinal direction. It should be noted that  FIG. 6  representatively shows the intermediate member  24  that is one of the pair of intermediate members  24  and  25 . The intermediate member  25  is the same in structure as the intermediate member  24 . As shown in  FIGS. 3, 4, and 6 , a third projecting member  43  is provided at the intermediate member  24 . The third projecting member  43  projects upward and downward from the intermediate member  24  at a position which overlaps the pressing member  18  in a plan view. Moreover, a tubular body  44  is provided at the intermediate member  24  so as to be located at a position which overlaps the air spring seat  27 . The tubular body  44  makes the internal space of the intermediate member  24  communicate with the air spring  3 . 
     Specifically, fitting holes  24   b  and  24   c  are formed at an upper wall portion of the intermediate member  24  so as to be spaced apart from each other in the car width direction. The fitting holes  24   b  and  24   c  penetrate the upper wall portion of the intermediate member  24  in the vertical direction. An upper end portion of the third projecting member  43  is fitted in the fitting hole  24   c , and an upper end portion of the tubular body  44  is fitted in the fitting hole  24   b . A fitting hole  24   d  in which the third projecting member  43  is fitted is formed at a lower wall portion of the intermediate member  24 . In the present embodiment, each of an outer peripheral surface of the third projecting member  43  and an outer peripheral surface of the tubular body  44  has a circular shape but may have a polygonal shape. The tubular body  44  is required to be hollow and be configured such that an internal space thereof is open upward and downward. However, the third projecting member  43  may be hollow or solid. The third projecting member  43  does not have to penetrate the intermediate member  24  ( 25 ) and may be fixed to a surface of the intermediate member  24  ( 25 ). In the present embodiment, the number of projecting members  41  to  44  is one example and may be suitably increased or decreased according to need. 
     An insertion hole  27   b  is formed at the air spring seat  27 . A diameter of the insertion hole  27   b  is larger than an outer diameter of a portion of the tubular body  44  which portion projects upward from the intermediate member  24 . When viewed from above, the insertion hole  27   b  includes the fitting hole  24   b . The upper end portion of the tubular body  44  is inserted into the insertion hole  27   b  with some play. The upper end portion of the tubular body  44  is joined to the intermediate member  24  by circumferential welding through the insertion hole  27   b  of the air spring seat  27 . A welded portion W 8  by which the tubular body  44  and the intermediate member  24  are joined to each other does not have to be joined to the air spring seat  27 . Welded portions W 9  and W 10  by which the third projecting member  43  and the intermediate member  24  are joined to each other are the same as the welded portions W 5  and W 7  by which the second projecting member  42  and the pipe member  22  are joined to each other. 
       FIG. 7  is a longitudinal sectional view of the air spring seat  27  and pressing member  18  of the bogie  1  of  FIG. 1  when viewed from the car width direction. As shown in  FIG. 7 , the clearance between the pipe members  22  and  23  is adequately shorter than a size of a lower end surface  3   a  of the air spring  3  in the car longitudinal direction. To be specific, at a position that is the same in the car width direction as the position of the air spring  3 , a distance L 1  between a center P 1  of the linear portion  22   a  of the pipe member  22  and a center P 2  of the linear portion  23   a  of the pipe member  23  in the car longitudinal direction is shorter than the car longitudinal direction size of the lower end surface  3   a  of the air spring  3  mounted on the air spring seat  27 . The lower end surface  3   a  of the air spring  3  overlaps the pipe members  22  and  23  so as to include the car longitudinal direction centers P 1  and P 2  of the car width direction end portions of the pipe members  22  and  23  when viewed from above. Similarly, the air spring seat  27  overlaps the pipe members  22  and  23  so as to include the centers P 1  and P 2  of the car width direction end portions of the pipe members  22  and  23  when viewed from above. A load transmitted from the air spring  3  through the air spring seat  27  to the cross beam  5  is transmitted to the middle portion  13   a  of the plate spring  13  by the pressing member  18 . 
     The curved portions  22   b  and  23   b  are formed at the pair of pipe members  22  and  23  so as to be located at the car width direction middle portion  5   b  of the cross beam  5 . Therefore, the clearance between the pair of pipe members  22  and  23  at the car width direction middle portion  5   b  of the cross beam  5  is wide, but the clearance between the pair of pipe members  22  and  23  at each of the car width direction end portions  5   a  of the cross beam  5  is narrow. On this account, even when the center pin arrangement space S is formed between the pair of pipe members  22  and  23  at the car width direction middle portion  5   b  of the cross beam  5 , the pipe members  22  and  23  are prevented from largely protruding from the lower end surface  3   a  of the air spring  3  outward in the car longitudinal direction. Thus, smooth load transmission from the air springs  3  to the pipe members  22  and  23  is realized while adequately securing the center pin arrangement space S. As above, the downward loads from the air springs  3  are smoothly transmitted to the centers P 1  and P 2  of the car width direction end portions of the pipe members  22  and  23 . Therefore, stress generated at the air spring seats  27  themselves and stress generated at joined portions between the air spring seat  27  and the pipe members  22  and  23  are effectively reduced. 
       FIG. 8  is a perspective view for explaining the brake receiving seats  31  and  32  and a coupling member  49  of  FIG. 4  when viewed from below.  FIG. 9  is a side view for explaining the brake receiving seats  31  and  32  and coupling member  49  of  FIG. 8 . As shown in  FIGS. 8 and 9 , the first brake receiving seat  31  includes an attaching portion  45  and a receiving seat portion  47 . The attaching portion  45  projects from the cross beam  5  outward in the car longitudinal direction, and the receiving seat portion  47  extends from the attaching portion  45  in the vertical direction. Moreover, the second brake receiving seat  32  includes an attaching portion  46  and a receiving seat portion  48 . The attaching portion  46  projects from the cross beam  5  outward in the car longitudinal direction, and the receiving seat portion  48  extends from the attaching portion  46  in the vertical direction. The attaching portion  45  of the first brake receiving seat  31  is joined to an outer surface of the pipe member  22  which surface is located outside in the car longitudinal direction. The first wheel tread brake device B 1  is fixed to the receiving seat portion  47  of the first brake receiving seat  31 . The attaching portion  46  of the second brake receiving seat  32  is joined to an outer surface of the pipe member  23  which surface is located outside in the car longitudinal direction. The second wheel tread brake device B 2  is fixed to the receiving seat portion  48  of the second brake receiving seat  32 . 
     Through holes  47   a  are formed at the receiving seat portions  47  and  48 . The attaching portion  45  is inserted into the through hole  47   a  of the receiving seat portion  47  and joined to the receiving seat portion  47  by circumferential welding, and the attaching portion  46  is inserted into the through hole  47   a  of the receiving seat portion  48  and joined to the receiving seat portion  48  by circumferential welding. To be specific, a welded portion W 11  by which the receiving seat portion  47  and the attaching portion  45  inserted into the through hole  47   a  of the receiving seat portion  47  are joined to each other is formed in a closed loop shape along a peripheral edge of the through hole  47   a , and another welded portion W 11  by which the receiving seat portion  48  and the attaching portion  46  inserted into the through hole  47   a  of the receiving seat portion  48  are joined to each other is formed in a closed loop shape along a peripheral edge of the through hole  47   a . As above, since each of the welded portions W 11  is formed in a closed loop shape having no end edge, the robot welding is easily performed, and therefore, the productivity improves. 
     A vertical size of a joining end of the attaching portion  45  which end is located close to the pipe member  22  is smaller than a vertical size of the outer surface of the pipe member  22  which surface is located outside in the car longitudinal direction. A vertical size of a joining end of the attaching portion  46  which end is located close to the pipe member  23  is smaller than a vertical size of the outer surface of the pipe member  23  which surface is located outside in the car longitudinal direction. A welded portion W 12  by which the joining end of the attaching portion  45  and the pipe member  22  are joined to each other is provided at and within the outer surface of the pipe member  22 . Another welded portion W 12  by which the joining end of the attaching portion  46  and the pipe member  23  are joined to each other is provided at and within the outer surface of the pipe member  23 . With this, since stress generated when a car body load is applied to the air spring seats  27  mainly concentrates on the upper surface and lower surface of the cross beam  5 , stress generated at the welded portions W 12  provided at not the upper and lower surfaces of the cross beam  5  but the side surfaces of the cross beam  5  is small. Fastening holes  47   b  and  47   c  to which the wheel tread brake device B 1  is fastened are formed at upper and lower portions of the receiving seat portion  47 , and fastening holes  47   b  and  47   c  to which the wheel tread brake device B 2  is fastened are formed at upper and lower portions of the receiving seat portion  48 . 
     The coupling member  49  is arranged under the cross beam  5 . The coupling member  49  is sandwiched between the receiving seat portion  47  of the first brake receiving seat  31  and the receiving seat portion  48  of the second brake receiving seat  32 . The coupling member  49  couples the lower portion of the receiving seat portion  47  of the first brake receiving seat  31  and the lower portion of the receiving seat portion  48  of the second brake receiving seat  32 . The coupling member  49  is located at substantially a height of the center of the axle and extends in a direction perpendicular to brake supporting surfaces  47   d  and  48   d  of the receiving seat portions  47  and  48 . For example, the coupling member  49  has a rod shape. The number of coupling members  49  is one in the present embodiment but may be plural. 
     An insertion hole  47   e  is formed at the lower portion of the receiving seat portion  47  of the brake receiving seat  31 , and an insertion hole  48   e  is formed at the lower portion of the receiving seat portion  48  of the brake receiving seat  32 . Car longitudinal direction end portions of the coupling member  49  are inserted into the insertion holes  47   e  and  48   e  and joined to the receiving seat portions  47  and  48  by circumferential welding. To be specific, a welded portion W 13  by which the end portion of the coupling member  49  inserted into the insertion hole  47   e  and the receiving seat portion  47  are joined to each other is formed in a closed loop shape along a peripheral edge of the insertion hole  47   e . Another welded portion W 13  by which the end portion of the coupling member  49  inserted into the insertion hole  48   e  and the receiving seat portion  48  are joined to each other is formed in a closed loop shape along a peripheral edge of the insertion hole  48   e . According to this, since the coupling member  49  is positioned with respect to the receiving seat portions  47  and  48  by being inserted into the insertion holes  47   e  and  48   e , work of welding the coupling member  49  to the receiving seat portions  47  and  48  can be easily performed. 
     As shown in  FIG. 9 , brake reaction force applied from the wheel  7  to the wheel tread brake device B 1  during braking is transmitted to the receiving seat portion  47  of the brake receiving seat  31 , and brake reaction force applied from the wheel  7  to the wheel tread brake device B 2  during braking is transmitted to the receiving seat portion  48  of the brake receiving seat  32 . The coupling member  49  serves as a tension rod that acts against the brake reaction force. Therefore, the brake reaction force applied to the first brake receiving seat  31  and the brake reaction force applied to the second brake receiving seat  32  are canceled out through the coupling member  49 , and therefore, the necessity of providing strong reinforcing members at the brake receiving seats  31  and  32  can be eliminated. 
       FIG. 10  is a bottom view for explaining the traction motors M 1  and M 2  and a coupling member  50  in the bogie shown in  FIG. 2 .  FIG. 11  is a side view for explaining the traction motors M 1  and M 2  and the coupling member  50  shown in  FIG. 10 . As shown in  FIGS. 10 and 11 , the coupling member  50  is arranged under the cross beam  5 . The coupling member  50  is sandwiched between the first traction motor M 1  and the second traction motor M 2 . The coupling member  50  couples the first traction motor M 1  and the second traction motor M 2  to each other. The coupling member  50  has, for example, a substantially I shape, and both end portions of the coupling member  50  are fixed to the traction motors M 1  and M 2 . The number of coupling members  50  is one but may be plural. 
     The traction motor receiving seat  37  includes a keyway  37   a  to which the traction motor M 1  is locked and which extends along the cross beam  5 . The traction motor receiving seat  38  includes a keyway  38   a  to which the traction motor M 2  is locked and which extends along the cross beam  5 . The traction motor M 1  is fastened to the traction motor receiving seat  37  while being locked to the keyway  37   a , and the traction motor M 2  is fastened to the traction motor receiving seat  38  while being locked to the keyway  38   a . The traction motor receiving seat  37  is joined to an outer surface of the curved portion  22   b  which surface is inclined relative to the car width direction, and the traction motor receiving seat  38  is joined to an outer surface of the curved portion  23   b  which surface is inclined relative to the car width direction. Therefore, the keyways  37   a  and  38   a  are inclined relative to the car width direction. The first traction motor M 1  is attached to the first traction motor receiving seat  37  so as to swing about the keyway  37   a  serving as a first swing axis X 1 , and the second traction motor M 2  is attached to the second traction motor receiving seat  38  so as to swing about the keyway  38   a  serving as a second swing axis X 2 . The traction motor receiving seats  37  and  38  are only required to be arranged such that the swing axes X 1  and X 2  are perpendicular to a virtual line V. The keyways  37   a  and  38   a  do not necessarily have to be inclined relative to the car width direction. 
     In a plan view, each of the swing axis X 1  of the first traction motor M 1  and the swing axis X 2  of the second traction motor M 2  is inclined relative to the car width direction in such a direction that a bogie middle side of the swing axis X 1 , X 2  extends away from the center of the cross beam  5 . In a plan view, the swing axis X 1  of the first traction motor M 1  and the swing axis X 2  of the second traction motor M 2  are substantially perpendicular to a virtual line V connecting a gravity center C 1  of the first traction motor M 1  and a gravity center C 2  of the second traction motor M 2 . The coupling member  50  extends along the virtual line V. When the number of coupling members  50  is one, the coupling member  50  is only required to overlap the virtual line V in a plan view. 
     With this, when the traction motors M 1  and M 2  are about to swing in the upper-lower direction, the coupling member  50  serves as a tension rod that acts against the swinging, and therefore, the swinging of the first traction motor M 1  and the swinging of the second traction motor M 2  are canceled out through the coupling member  50 . On this account, the requirement of the strength of a support structure for the traction motors M 1  and M 2  can be lowered by a simple configuration. Since the swing axes X 1  and X 2  of the traction motors M 1  and M 2  are substantially perpendicular to the virtual line V in a plan view, a load generated by the swinging of the traction motor M 1  and a load generated by the swinging of the traction motor M 2  are opposed to each other, and therefore, the generation of torsional force at the coupling member  50  is suppressed. Then, since the coupling member  50  extends along the virtual line V, the strength of the coupling member  50  in a pulling direction and a compressing direction is only required to be secured. Therefore, the swinging of the traction motor M 1  and the swinging of the traction motor M 2  can be effectively canceled out while reducing the weight of the coupling member  50 . 
     The present disclosure is not limited to the above embodiment, and modifications, additions, and eliminations may be made with respect to the configuration of the embodiment. For example, the above embodiment has described the bogie which omits the side sills of the bogie frame and includes the plate springs. However, the above embodiment may adopt a general bogie including side sills extending from both car width direction end portions of a cross beam in a car longitudinal direction. The general bogie is only required to be configured such that the car width direction end portions  5   a  of the cross beam  5  are fixed to the side sills by welding or the like. Moreover, the general bogie does not require the pressing members  18  that press the plate springs  13 . Therefore, instead of the pressing members  18 , plate-shaped members are simply used for mutual connections among the lower surfaces of the pipe members  22  and  23  and the lower surfaces of the intermediate members  24  and  25 , and as with the air spring seat  27 , the pipe members  22  and  23  and the intermediate members  24  and  25  are only required to be fixed to each other through the projecting members. The curved portion ( 22   b ) may be formed at only one of the pair of pipe members  22  and  23 . The center pin may be connected to a single link type traction device through the center pin arrangement space S without providing the center pin accommodating member  26 . The above embodiment has described a driving bogie but may adopt a non-driving bogie. The non-driving bogie does not require structures related to the traction motor and the gear box, but the structures of the cross beam  5  and the brake receiving seat may be suitably adopted in the non-driving bogie. 
     REFERENCE SIGNS LIST 
     
         
         
           
               1  bogie 
               3  air spring 
               3   a  lower end surface 
               4  bogie frame 
               5  cross beam 
               5   a  car width direction end portion 
               5   b  car width direction middle portion 
               13  plate spring 
               13   a  car width direction middle portion 
               13   b  car width direction end portion 
               18  pressing member 
               22  pipe member 
               22   a  linear portion 
               22   b  curved portion 
               24 ,  25  intermediate member 
               26  center pin accommodating member 
               26   a  tubular portion 
               26   b  longitudinal attaching portion 
               26   c  lateral attaching portion 
               27  air spring seat 
               30  center pin 
               31  first brake receiving seat 
               32  second brake receiving seat 
               35  first gear box receiving seat 
               36  second gear box receiving seat 
               37  first traction motor receiving seat 
               37   a  keyway 
               38  second traction motor receiving seat 
               38   a  keyway 
               41  first projecting member 
               42  second projecting member 
               43  third projecting member 
               45 ,  46  attaching portion 
               47 ,  48  receiving seat portion 
               49  coupling member 
               50  coupling member 
             B 1  first wheel tread brake device 
             B 2  second wheel tread brake device 
             C 1 , C 2  gravity center 
             G 1  first gear box 
             G 2  second gear box 
             M 1  first traction motor 
             M 2  second traction motor 
             P 1 , P 2  center 
             S center pin arrangement space 
             V virtual line 
             W 1  to W 13  welded portion 
             X 1  first swing axis 
             X 2  second swing axis