Side rail and manufacturing method for side rail

1. A side rail comprising:

a plurality of base members extending in a longitudinal direction of a vehicle body of a vehicle, the base members having a closed-section structure in a polygonal shape having a plurality of corner portions; and

reinforcement plate members having a greater plate thickness than a plate thickness of the base members,

wherein

a part of a region in the longitudinal direction of the vehicle body of the side rail includes a reinforcement region having the closed-section structure in the polygonal shape constituted by the base members and the reinforcement plate members,

and

the reinforcement region includes joined parts where in a state in which the reinforcement plate members are fitted in fitting portions provided at positions corresponding to at least the respective corner portions in the base members, the base members and the reinforcement plate members are joined to each other, a first vertical wall portion and a second vertical wall portion that face each other in a horizontal direction, first horizontal wall portions and second horizontal wall portions that face each other in a vertical direction, and a plurality of the corner portions configuring boundary portions between the first and second vertical wall portions and the first and second horizontal wall portions, and in the reinforcement region, the reinforcement plate members are applied throughout from the corner portions to the horizontal wall portions adjacent to the corner portions; and wherein

the base member and the reinforcement player members are joined to each other by laser welding.

2. The side rail according to claim 1 , wherein

the side rail includes:

a horizontal part extending in a horizontal direction along the longitudinal direction of the vehicle body within a predetermined range between an arrangement position of a front wheel of the vehicle and an arrangement position of a rear wheel of the vehicle;

a front curved part having a shape continued to a front end of the horizontal part and curved upward as the front curved part extends toward a frontward direction of the vehicle body; and

a rear curved part having a shape continued to a rear end of the horizontal part and curved upward as the rear curved part extends toward a rearward direction of the vehicle body,

and

the reinforcement region is provided in the horizontal part.

3. A side rail comprising:

a plurality of base members extending in a longitudinal direction of a vehicle body of a vehicle, the base members having a closed-section structure in a polygonal shape having a plurality of corner portions; and

reinforcement plate members having a greater plate thickness than a plate thickness of the base members,

wherein

a part of a region in the longitudinal direction of the vehicle body of the side rail includes a reinforcement region having the closed-section structure in the polygonal shape constituted by the base members and the reinforcement plate members,

and

the reinforcement region includes joined parts where in a state in which the reinforcement plate members are fitted in fitting portions provided at positions corresponding to at least the respective corner portions in the base members, the base members and the reinforcement plate members are joined to each other, wherein

the base members are joined to the reinforcement plate members in such a manner that surfaces located outward in the closed-section structure among surfaces perpendicular to a plate thickness direction of the base members are flush with surfaces located outward in the closed-section structure among surfaces perpendicular to a plate thickness direction of the reinforcement plate members.

4. A manufacturing method for a side rail, the manufacturing method comprising:

forming fitting portions in a plurality of base members in a flat-plate shape, the fitting portions being formed in regions to become at least corner portions in a reinforcement region that is previously defined;

fitting reinforcement plate members in a flat-plate shape having a greater plate thickness than a plate thickness of the base members into the fitting portions;

joining the reinforcement plate members fitted in the fitting portions to the base members;

bending, together with the reinforcement plate members, the base members to which the reinforcement plate members are joined so as to form a plurality of rail members having the corner portions; and

integrally joining the plurality of rail members to each other so as to form a closed-section structure in a polygonal shape by the plurality of rail members.

5. The manufacturing method for the side rail according to claim 4 , wherein

the reinforcement plate members are joined to the base members by laser welding.