1. Field of the Invention
The present invention relates to a vehicle body rear structure.
2. Description of Related Art
Conventionally, a vehicle body rear structure provided with approximately a Y-shaped stiffening structure in plane view has been known. This is disclosed in, for example, U.S. Pat. No. 6,834,910. FIG. 11A is a bottom plane view schematically showing a conventional vehicle body rear structure as seen from a bottom side of a vehicle body. FIG. 11B is a side view schematically showing a conventional vehicle body rear structure as seen from a side of the vehicle body.
As shown in FIG. 11A, the stiffening structure is formed in approximately the Y-shape by a support member 109 and a pair of tension-compression bars 101 (tank lower frames). The support member 109 is disposed at approximately a center of a vehicle body B in a vehicle width direction, and extends in a front-rear direction of the vehicle body B. A rear end of the support member 109 is jointed to a cross support member 106 (rear floor end cross member), and a front end of the support member 109 is jointed to a receiving bracket 110. It is noted that the cross support member 106 is jointed to each rear end portion of the rear frames 102.
Each rear end of the tension-compression bars 101 is jointed to the receiving bracket 110 at a position close to a center of the vehicle body B in the vehicle width direction, and each front end of the tension-compression bars 101 extending to each of side sills 105 in approximately a V-shape is jointed to the each of the side sills 105.
The vehicle body rear structure described above has a reinforced structure from the cross support member 106 disposed on a rear side of the vehicle body B to the side sills 105 disposed on right and left sides of the vehicle body B via the support member 109, receiving bracket 110, and tension-compression bars 101.
However, in the vehicle body rear structure, as shown in FIG. 11B, the support member 109 has been disposed to be inclined downward from the cross support member 106 to the receiving bracket 110. Therefore, when a load upon a rear-end collision is input to the cross support member 106, there has been a possibility that the load may not be sufficiently transmitted to the receiving bracket 110 from the cross support member 106 via the support member 109. As a result, in the conventional vehicle body rear structure described above, it has been difficult to effectively disperse the input load from the receiving bracket 110 to the tension-compression bars 101 and side sills 105 via the tension-compression bars 101.
Therefore, for solving the above issue, a vehicle body rear structure may be conceivable, in which the support member 109 is horizontally disposed and jointed between the cross support member 106 and receiving bracket 110. Therefore, in the vehicle body rear structure described above, a load input from the cross support member 106 upon a rear-end collision is transmitted to the tension-compression bars 101 via the support member 109, which is disposed horizontally.
However, in the vehicle body rear structure, when the tension-compression bars 101 are deformed by a large load upon a rear-end collision, a load-displacement characteristic of an ordinary tension-compression bars 101, which are formed by a hollow member (tubular member), shows a rapid decrease of the load after reaching a maximum of the load, which increases in response to the displacement. Therefore, the vehicle body rear structure described above can not sufficiently bear the large load input upon the rear-end collision.
In addition, in the conventional vehicle body rear structure, if front and rear portion structures of the stiffening members such as the support member 109, receiving bracket 110, and tension-compression bars 101, and strengths of the stiffening members are not balanced, it is difficult to deform the vehicle body rear structure by turns upon a rear-end collision from a rear portion of the structure. As a result, in the vehicle body rear structure, uncrushed portions are left in these stiffening members, thereby resulting in insufficient collision energy absorption upon the rear-end collision.
In addition, in the vehicle body rear structure, if the structures and strengths are not balanced as described above, an increase of a strength of each of the stiffening members is required for improving the strength of the vehicle body rear structure and collision energy absorption performance. Specifically, it is required to, for example, increase thicknesses of materials forming the stiffening members and cross sections of the stiffening members, or to apply a material having a higher strength to the stiffening members. As a result, in the vehicle body rear structure, a weight and manufacturing cost of the vehicle body rear structure are increased.
It is, therefore, an object of the present invention to provide a vehicle body rear structure which can bear a large load upon a rear-end collision and has an excellent collision energy absorption performance, in addition to enabling reductions in weight and manufacturing cost of the vehicle body rear structure.