Vehicle front section structure

1. A vehicle front section structure, comprising:

a front side member that is disposed at a vehicle width direction outer side of a vehicle body front section, and that extends with its length direction in a vehicle front-rear direction;

a gusset that juts out from a side face at a vehicle width direction outer side of a front end portion of the front side member toward the vehicle width direction outer side;

a bumper reinforcement that is disposed at a front end side of the vehicle body front section with its length direction in a vehicle width direction; and

a crash box that is disposed between front end portions of both the front side member and the gusset, and an outer side section in the vehicle width direction of the bumper reinforcement, that couples both of the front end portions and the outer side section together in the vehicle front-rear direction, and that has a tube shape which undergoes compressive plastic deformation in the vehicle front-rear direction due to collision load input toward a vehicle rear side,

wherein a flat portion is integrally formed at an end section of the bumper reinforcement at the vehicle width direction outer side, with a front face of the flat portion extending along the vehicle width direction and a vehicle up-down direction and, in vehicle front view, overlapping with a side wall portion at the vehicle width direction outer side of the crash box,

wherein a first curved portion is formed at the outer side section in the vehicle width direction of the bumper reinforcement, further to a vehicle width direction inner side than the flat portion in vehicle plan view, with a front face of the first curved portion curved in a shape bowing toward a vehicle front side on progression toward a central section of the bumper reinforcement,

wherein the crash box is disposed overlapping with both the flat portion and the first curved portion in vehicle front view, and

wherein a front end section of the crash box has a shape following the flat portion and the first curved portion.

2. The vehicle front section structure of claim 1 , wherein:

the first curved portion is disposed at the outer side section in the vehicle width direction of the bumper reinforcement, separated from the flat portion to the vehicle width direction inner side; and

a second curved portion is disposed at the outer side section in the vehicle width direction of the bumper reinforcement, between the flat portion and the first curved portion in vehicle plan view, and connecting the flat portion and the first curved portion together, with a front face of the second curved portion curved in a shape bowing substantially toward the vehicle rear side so as to lie on an extension line of the front face of the flat portion toward the vehicle width direction inner side or at a vehicle front side of the extension line.

3. The vehicle front section structure of claim 1 , wherein:

the bumper reinforcement is provided with a front end wall, an upper wall, and a lower wall, and is formed with an open cross-section profile open to the vehicle rear side; and

the front end section of the crash box is inserted into the interior of the cross-section of the bumper reinforcement, and the front end section of the crash box has a shape following a front end wall of the flat portion and the first curved portion.