Vehicle Floor Cross Member Flange Width Optimization
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Solution Overview
Problem
Conventional vehicle body structures face challenges in suppressing deformation and enhancing torsional rigidity, particularly when using high tensile strength steel, which often results in flange rupture during press forming and compromises load transmission and collision safety.
Innovation Solution
A vehicle body design featuring a widthwise member with a flange formed continuously around the web and vertical surfaces, having a specific radius of curvature and flange width ratio, and spot-welded joints to improve rigidity and load transmission without notches, allowing for the use of high tensile strength steel.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a flange is formed along the ridge part of the widthwise member to ensure large cross-sectional area and improve joining, then deformation suppression and torsional rigidity are improved, but the flange may rupture at the edge during press forming due to concentration of extensional deformation
Solution Approach 1:
The flange width is made non-uniform along the ridge part, with the width at the center of the curved part being larger than at both ends. This local variation in geometry redistributes the extensional deformation during press forming, preventing concentration at the edges while maintaining adequate cross-sectional area for strength and joining purposes.
Solution Approach 2:
The ridge part is designed with a curved cross-section having a specific radius of curvature (5mm to 20mm). This curvature, combined with the non-uniform flange width, allows the flange to be formed by press molding without edge rupture by distributing the deformation more evenly throughout the flange structure.
2Reliability
If the flange width at the center of the curved part is made larger than at the ends, then extensional deformation is distributed more evenly and rupture is prevented, but the flange geometry becomes more complex
Solution Approach 1:
The flange width parameter is varied continuously along the ridge part according to a specific pattern (larger at center, smaller at ends), with the radius of curvature controlled within 5mm to 20mm. This parameter optimization achieves reliable flange formation without requiring complex additional structures or manufacturing processes.
3Weight of moving object
If high tensile strength steel is used to reduce weight while maintaining strength, then weight is reduced and strength is maintained, but flange formation becomes difficult and rupture occurs more easily
Solution Approach 1:
The non-uniform flange width design specifically addresses the formability issue of high tensile strength steel by distributing extensional deformation away from the edges during press forming. This allows high strength steel to be used successfully, achieving weight reduction while maintaining both manufacturability and structural performance.
4Reliability
If the flange width is minimized at the ridge part center to prevent rupture, then edge rupture is avoided, but the cross-sectional area is reduced and torsional rigidity deteriorates
Solution Approach 1:
Instead of minimizing the flange width at the center as conventionally done, the invention inverts this approach by making the flange width at the center larger than at the ends. This counterintuitive design simultaneously prevents edge rupture through proper deformation distribution and maintains large cross-sectional area for high torsional rigidity.
Data Source
Figure 1A~1C
Figure 2A~2B
Figure 3A~3D
AI summary
In a floor cross member configured by a web surface (4a) as the top surface, a ridge part (4b) contiguous to the web surface (4a), and a vertical wall surface (4c) contiguous to the ridge part (4b), having a tensile strength of 440 MPa or larger, flanges (4e) are formed at both longitudinal ends continuously around at least the web surface (4a), the ridge part (4b) and the vertical wall surface (4c), and the floor cross member (4) is connected through the flanges (4e) to a tunnel part (2a) and to a side sill (3). The flange (4e) has a flange width lfc, at the center in the perimeter direction of the curved part (4e-2), not smaller than the minimum flange width lfs of the curved part (4e-2). Accordingly, a vehicle body, which is suppressed in deformation of the floor cross member (4) and improved in the torsional rigidity, is successfully provided.