Abstract: A fuel tank includes metal-made upper and lower tank half bodies respectively having, on respective outer peripheries thereof, an upper joint flange and a lower joint flange joined thereto. The lower tank half body includes: a lower tank main body portion that is elongated in a direction parallel to a reference plane including joint surfaces of lower and upper planar flange portions as parts of the lower and upper joint flanges, respectively, includes, along a longitudinal direction thereof, a narrow portion narrower on one side than the other side, and bulges toward a lower side from the reference plane; and a pair of expansion tank portions that are disposed on opposite sides of the narrow portion as seen in a plan view from a direction orthogonal to the reference plane, formed to be shallower than the lower tank main body portion, and bulge downward from the reference plane.

Abstract: In a fuel tank in which an upper joint flange of an upper tank half body and a lower joint flange of a lower tank half body are sandwiched between and seam welded by a pair of roller electrodes, the lower tank half body includes a lower tank main body portion and expansion tank portions shallower than the lower tank main body portion and disposed on opposite sides of the lower tank main body portion. A side wall of at least one of the upper and lower tank half bodies is provided with roller escape recesses recessed inwardly, the roller escape recesses being formed at a position corresponding to a connection portion of a main body corresponding joint portion and expansion tank corresponding joint portions in a joint portion formed by seam welding, and avoiding a contact with at least one of the pair of roller electrodes.

Abstract: In a fuel tank in which an upper joint flange of an upper tank half body and a lower joint flange of a lower tank half body are sandwiched between and seam welded by a pair of roller electrodes, the lower tank half body includes a lower tank main body portion and expansion tank portions shallower than the lower tank main body portion and disposed on opposite sides of the lower tank main body portion. A side wall of at least one of the upper and lower tank half bodies is provided with roller escape recesses recessed inwardly, the roller escape recesses being formed at a position corresponding to a connection portion of a main body corresponding joint portion and expansion tank corresponding joint portions in a joint portion formed by seam welding, and avoiding a contact with at least one of the pair of roller electrodes.

Abstract: A fuel tank includes metal-made upper and lower tank half bodies respectively having, on respective outer peripheries thereof, an upper joint flange and a lower joint flange joined thereto. The lower tank half body includes: a lower tank main body portion that is elongated in a direction parallel to a reference plane including joint surfaces of lower and upper planar flange portions as parts of the lower and upper joint flanges, respectively, includes, along a longitudinal direction thereof, a narrow portion narrower on one side than the other side, and bulges toward a lower side from the reference plane; and a pair of expansion tank portions that are disposed on opposite sides of the narrow portion as seen in a plan view from a direction orthogonal to the reference plane, formed to be shallower than the lower tank main body portion, and bulge downward from the reference plane.