Vehicle Rear Cross Member Segmentation for Rigidity and Space
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Solution Overview
Problem
Existing vehicle body rear structures face challenges in supporting the sub-frame while maintaining vehicle height and reducing fuel tank sloshing noise, often requiring increased vehicle weight or height to accommodate the sub-frame and fuel tank.
Innovation Solution
A vehicle body rear structure design where a lower cross member is connected to the mounting portions on both sides and forms a closed section with the rear floor panel, and an upper cross member is joined to the upper surface of the rear floor panel, with overlaid flange portions to support loads and maintain rigidity, allowing for a smaller sectional area and increased space for accessories without height increase.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the cross member is made larger to increase support rigidity of the rear suspension, then the support rigidity is improved, but the space for vehicle accessories such as fuel tank is reduced
Solution Approach 1:
The cross member structure is divided into an upper cross member and a lower cross member that are joined together. The lower cross member has a smaller sectional area that provides space for accessories, while the upper cross member provides the necessary support rigidity. This segmentation allows each part to fulfill different functions simultaneously.
Solution Approach 2:
The solution transitions from a single-plane cross member to a multi-level structure with upper and lower cross members positioned at different heights. This dimensional change allows the lower cross member to provide accessory space while the upper cross member provides structural support, resolving the space-strength contradiction.
2Area of stationary object
If the vehicle height is increased to ensure space for accessories, then the space for vehicle accessory is improved, but the maneuverability of the vehicle is reduced
Solution Approach 1:
Instead of increasing vehicle height vertically, the invention utilizes the vertical space between the upper and lower cross members to accommodate accessories. This approach creates accessory space without increasing the overall vehicle height, thereby maintaining maneuverability while providing sufficient space for fuel tanks and other accessories.
3Area of stationary object
If the lower cross member does not support the sub-frame, then the sectional area of the lower cross member can be reduced, but the support rigidity of the fuel tank is low and fuel flow noise is generated
Solution Approach 1:
The support function is segmented between the upper and lower cross members. The lower cross member provides support for the fuel tank and accessory space, while the upper cross member supports the sub-frame. This segmentation allows the lower cross member to have a smaller sectional area while still providing sufficient support to prevent fuel sloshing noise.
Data Source
AI summary
A vehicle body rear structure includes a lower cross member joined to the lower surface of a rear floor panel, and an upper cross member joined to the upper surface of the rear floor panel along the lower cross member. The lower cross member forms a closed section together with the rear floor panel, and is connected to front mounting portions on both sides. The upper cross member forms a closed section together with the rear floor panel. A rear flange of the lower cross member and a front flange of the upper cross member are joined to be overlaid via the rear floor panel.