Vehicle body rear structure

1. A vehicle body rear structure, comprising:

first and second rear frames disposed respectively on each side of a vehicle body; and

first and second tank lower frames disposed respectively beneath the rear frame on the each side of the vehicle body,

wherein the rear frames have a load-displacement characteristic having a ratio F/S of load F to displacement S larger than the ratio F/S of the tank lower frames, and a cross sectional deformation of the tank lower frames is suppressed so that the load F does not rapidly decrease after reaching a maximum of a bending strength,

the vehicle body rear structure, further comprising:

a rear floor end cross member ( 6 ) jointed to each rear end of the rear frames,

a rear floor cross member ( 10 ) located ahead of the rear floor end cross member ( 6 ) and extending in the vehicle width direction and jointed to each of the rear frames,

a middle floor cross member ( 3 ) extending in the vehicle width direction to be jointed to each of front floor frames ( 7 a ) and each of side sills ( 5 );

a rear floor panel extending toward a rear portion of the vehicle body (B) from the middle floor cross member ( 3 ),

a pair of spare pan frames ( 9 ) extending in the front-rear direction between the rear floor end cross member ( 6 ) and rear floor cross member ( 10 ) and jointed to the rear floor end cross member ( 6 ) and rear floor cross member ( 10 ), each of the spare pan frames ( 9 ) being arranged to be located on each side of a spare pan which is disposed in a rear portion of the rear floor panel and having a concave portion for storing a spare tire, and the spare pan frames ( 9 ) being disposed substantially horizontally from the rear floor end cross member ( 6 ) to rear floor cross member ( 10 ),

wherein each rear end of the tank lower frames is jointed to substantially a center of the rear floor cross member ( 10 ) in the vehicle width direction, each of the tank lower frames extends substantially in a V-shape toward each side of the vehicle body (B) from the rear floor cross member ( 10 ), and each front end of the tank lower frames is jointed to a portion close to a place, where the middle floor cross member ( 3 ) is jointed, of each of the side sills ( 5 ),

wherein the tank lower frames are disposed beneath the rear frames and a fuel tank (T), and extend substantially horizontally toward the middle floor cross member ( 3 ) from the rear floor cross member ( 10 ), and a horizontal height of the tank lower frames is set to be substantially identical to the height of the spare pan frames ( 9 ).

2. The vehicle body rear structure according to claim 1 ,

wherein each tank lower frame is made of a hollow member, and the cross sectional deformation is suppressed by making a side wall of the tank lower frame thicker than upper and bottom walls of the tank lower frame.

3. The vehicle body rear structure according to claim 1 ,

wherein each tank lower frame is made of a hollow member, and the cross sectional deformation is suppressed by disposing at least one of a rib, a plate, and a filler inside the tank lower frame.

4. The vehicle body rear structure according to claim 1 ,

wherein each tank lower frame is designed so that a bending deformation of the tank lower frame takes place in a direction getting away from the fuel tank.

5. The vehicle body rear structure according to claim 4 ,

wherein each tank lower frame is formed to protrude in a direction opposite to the fuel tank.

6. The vehicle body rear structure according to claim 4 ,

wherein each tank lower frame has a trigger for the bending deformation on a fuel tank side.

7. The vehicle body rear structure according to claim 1 ,

wherein an inflection point of each tank lower frame is set so that a neutral axis of the tank lower frame protrudes in a direction opposite to a fuel tank.

8. The vehicle body rear structure according to claim 7 ,

wherein a cross sectional shape of each tank lower frame and a thickness of a plate forming each tank lower frame are constant in a longitudinal direction of the tank lower frame, and the inflection point is set by forming an external shape of each tank lower frame so that an extending direction of the tank lower frame is displaced.

9. The vehicle body rear structure according to claim 7 , wherein the inflection point is set by varying a thickness distribution and material strength of a plate forming the tank lower frame in a longitudinal direction of the tank lower frame.

10. The vehicle body rear structure according to claim 7 , wherein each tank lower frame includes a rib extending along a longitudinal direction of the tank lower frame, and the inflection point is set by disposing the rib.

11. The vehicle body rear structure according to claim 1 , wherein:

the two spare pan frames are U-shaped members with an open upper face.

12. The vehicle body rear structure according to claim 1 , wherein each tank lower frame transmits a load upon a rear-end collision to a framework, which is located ahead of the tank lower frame, of the vehicle body.