Vehicle lower part structure

1. A vehicle lower part structure comprising:

a side frame extending in a vehicle front-rear direction on a side of a vehicle body lower part;

a floor crossmember disposed upward of the side frame in a vehicle up-down direction, the floor crossmember being formed of a first rectangular tubular member which is a single part, and the floor crossmember having an axis which extends along a vehicle-width direction;

a rectangular tubular rocker that is disposed laterally outward of the side frame in the vehicle-width direction and obliquely downward from an outer side of the floor crossmember in the vehicle-width direction, and the rectangular tubular rocker extending in the vehicle front-rear direction; and

a connection member that is provided downward of the floor crossmember in the vehicle up-down direction between the side frame and the rectangular tubular rocker, the connection member being in surface contact with and joined to each of a lower wall portion of the floor crossmember and a vertical wall portion on an inner side of the rectangular tubular rocker in the vehicle-width direction, the connection member being formed of a second rectangular tubular member which is a single part, and the connection member having a connection member axis which extends along the vehicle front-rear direction.

2. The vehicle lower part structure according to claim 1 , wherein the connection member has ribs that partition a hollow inside of the connection member.

3. The vehicle lower part structure according to claim 1 , wherein the connection member and the floor crossmember are joined to each other by a first screw member and a second screw member, the first screw member having a first head portion disposed on a lower surface side of an upper wall portion of the connection member and penetrating through the upper wall portion of the connection member and the lower wall portion of the floor crossmember, and the second screw member having a second head portion disposed on an upper surface side of an outer end portion of the lower wall portion of the floor crossmember in the vehicle-width direction and penetrating through the lower wall portion of the floor crossmember and the upper wall portion of the connection member.

4. The vehicle lower part structure according to claim 3 , wherein:

the floor crossmember has an open end at an outer end portion of the floor crossmember in the vehicle-width direction, the open end being inclined downward in the vehicle up-down direction and outward in the vehicle-width direction; and

the head portion of the second screw member is positioned outward in the vehicle-width direction from an outer edge of an upper wall portion of the floor crossmember, and the outer edge defines the open end.

5. The vehicle lower part structure according to claim 1 , wherein:

an upper wall portion of the floor crossmember is provided with a seat attachment portion to which a vehicle seat is attached; and

the connection member and the floor crossmember are jointed at a first portion positioned inward of the seat attachment portion in the vehicle-width direction and a second portion positioned outward of the seat attachment portion in the vehicle-width direction.

6. The vehicle lower part structure according to claim 5 , wherein the connection member has a connection wall portion that connects a third portion in the connection member adjacent to a lower end portion side of a rectangular tubular portion of the rocker to a fourth portion positioned between the first portion and the second portion in the connection member, and the connection wall portion is disposed along a straight line connecting the third portion to the fourth portion in a front view of a vehicle.

7. The vehicle lower part structure according to claim 1 , wherein an inner upper portion of the connection member in the vehicle-width direction protrudes upward in the vehicle up-down direction from an outer upper portion of the connection member in the vehicle-width direction, and the inner upper portion of the connection member is in contact with the lower wall portion of the floor crossmember.

8. The vehicle lower part structure according to claim 1 , wherein the connection member is a member extruded from an aluminum alloy.