1. Field of the Invention
The present invention relates to a body frame structure for a vehicle which induces larger initial load in a collision and induces the bending deformation in the frame thereafter for effectively absorbing the collision energy with a simple structure and a method for manufacturing thereof.
2. Description of the Related Art
Body frames serving as automotive structural members are indispensably required to not only be excellent in stiffness, but also effective in absorption of energy during an automobile collision. To cope with a frontal collision as a typical example of an automotive collision, an approach to energy absorption has been often attempted which uses a pair of left and right front frames located in front of a passenger compartment and extending in the vehicular longitudinal direction, with axial (or lengthwise) stiffness gradually decreased from a rear section (or passenger-compartment side) towards a frontal section. Thus, in the vehicular frontal collision the front frames fold or are crushed progressively from the frontal section so as to absorb impact load caused by the collision. For different stiffness along the lengthwise of the frames as above, Japanese Patent Publication No. H 10-17933 (equivalent to EP 0 816 520 A2) discloses forming a quenched stratum with predetermined stiffness distribution on the body frames.
Another approach to energy absorption other than the one described above is to control the bending direction of the front frame. For example, Japanese Patent Publication No. 2000-53022 discloses that a beam diagonally extending from a front frame is provided for triggering the bending deformation of the frame in the predetermined direction so as to induce larger collision reaction (or load acting on the body frame in the collision) in an early-phase of the collision, and induce the bending deformation of the body frame after a middle-phase of the collision for absorbing the collision energy. This approach may limit the longitudinal deformation of the front frame to a relatively smaller amount.
In the frame structure disclosed in Japanese Patent Publication No. 2000-53022, however, the beams are required for triggering the bending deformation of the frame, which complicates the construction. In practice, it is therefore important to simplify the structure of the body frame which achieves the preferable impact absorption in such a way as to induce larger collision reaction (or to cause larger initial load) in the early-phase of the collision than in the late-phase of the collision, and to induce the bending deformation in the body frame thereafter within a predetermined limit of the longitudinal deformation of the body frame.
In view of the aspect above, the first object of the present invention is to provide a body frame structure which induces larger initial load in a collision and induces the bending deformation in the frame thereafter for effectively absorbing the collision energy with a simple structure. The second object of the present invention is to provide a manufacturing method of the body frame used for achieving the object above.
In accordance with a first aspect of the present invention, there is provided a body frame structure for a vehicle, the vehicle including at least one body frame having a brittle section which is formed at a predetermined section in a lengthwise direction relative to the body frame, and is more brittle than another section of the body frame. The brittle section is hardened by a hardening treatment so as to be approximately equal to the other section of the body frame in axial compressive strength.
Accordingly, because the brittle section is approximately equal to the other sections in axial compressive strength, the brittle section will not easily buckle, so as to induce larger collision reaction. Thereafter, the body frame will buckle at the brittle section and bend to effectively absorb the collision energy.
Preferably, the peripheral section and the peripheral section of the brittle section may be hardened by a hardening treatment. Accordingly, the boundaries between the brittle sections and the other sections are prevented from being unexpectedly and locally weakened, so as to reliably induce the buckling at the brittle section.
It is further preferred that the hardening be achieved by a heat treatment. Accordingly, the hardening treatment can be easily achieved by a conventional process.
Still further, it is preferred that the brittle section be achieved by a smaller cross-sectional area than the other sections of the body frame. Accordingly, the brittle section is ensured to be more brittle than other sections.
Moreover, the brittle section may be formed on a planar surface of the body frame. Accordingly, more freedom is available for the location of the brittle section, and the brittle section is easily formed on a planar surface of the body frame because the body frame generally includes a planar surface elongated in a lengthwise direction.
In accordance with a second aspect of the present invention, there is provided a method for manufacturing a body frame for a vehicle which includes the steps of forming a brittle section at a predetermined section in lengthwise direction relative to the body frame, the brittle portion being more brittle than other sections of the body frame, and hardening the brittle section by using a hardening treatment.
Accordingly, a method for manufacturing the body frame used for achieving the first object described above is provided. Preferably, the hardening may be achieved by a heat treatment.
It is further preferred that the peripheral section of the brittle section be hardened by the hardening treatment during the step of performing the hardening.
Still further, it is preferred that the body frame include a predetermined member with the predetermined cross-section formed from at least one sheet metal and the brittle section be simultaneously formed during forming the sheet metal into the predetermined member. Accordingly, the body frame with the brittle section is manufactured by effectively utilizing the existing manufacturing processes.
These and other objects, features, aspects, and advantages of the present invention will become more apparent from the following detailed description of the preferred embodiment relative to the accompanied drawings.