Railcar primary suspension

A railcar primary suspension configured to couple an axle box, which accommodates a bearing for supporting an axle, to a truck frame by a coupling mechanism, the coupling mechanism comprising:

• a radius arm extending in a vehicle longitudinal direction from the axle box and including, at an end of the radius arm, a tubular part which has openings at both sides thereof in a vehicle width direction;
• a shaft inserted into an inner space of the tubular part and provided with projecting portions formed at both side surfaces of the shaft in the vehicle width direction;
• an elastic bushing interposed between the tubular part and the shaft;
• a pair of receiving seats provided at the truck frame and including fitting grooves in which the respective projecting portions are fitted;
• cover members configured to support the respective projecting portions which are fitted in the respective fitting grooves;
• and
• fastening members configured to fix the cover members to the respective receiving seats, wherein
• a portion of each fitting groove and a portion of the corresponding projecting portion, the portions contacting each other, respectively have arc surfaces, and a portion of each projecting portion and a portion of the corresponding cover member, the portions contacting each other, respectively have flat surfaces.