Vehicle Lower Structure Torsional Rigidity via Battery Pack Cross Coupling
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Solution Overview
Problem
The existing vehicle lower structure with a battery mounted under the floor lacks sufficient torsional rigidity, leading to deformation under torsional loads as the floor and battery cross members oscillate asynchronously.
Innovation Solution
The vehicle lower structure incorporates an external pack cross and internal pack cross system, where the external pack crosses are alternately coupled with internal pack crosses along the vehicle longitudinal direction using bolts and nuts or spot welding, enhancing torsional rigidity by interposing the bottom plate of the case tray between flanges and securing the battery stacks to paired internal pack crosses.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If floor crosses and battery crosses are connected using thin plate members (floor panel and battery pack case), then the structure is simple and easy to manufacture, but the torsional rigidity is insufficient and deformation occurs under torsional loads
Solution Approach 1:
The battery pack structure is divided into internal pack crosses (inside the battery pack) and external pack crosses (outside the battery pack), which are alternately arranged along the vehicle longitudinal direction. This segmentation creates multiple connection points that work together to resist torsional loads, preventing the asynchronous oscillation that occurs with single-cross configurations.
Solution Approach 2:
The invention combines the internal pack crosses and external pack crosses into a unified fastening system. The internal and external crosses are fastened to each other through the bottom plate of the case tray, creating an integrated structure that leverages both the internal battery pack framework and the external vehicle floor structure to achieve high torsional rigidity.
2Strength
If multiple floor crosses and battery crosses are provided along the vehicle longitudinal direction to improve torsional rigidity, then the structural strength increases, but the number of parts and assembly complexity increases
Solution Approach 1:
The pack crosses are designed to serve multiple functions: they provide structural support for the battery pack, act as fastening points to the vehicle floor, and form a torsion-resistant framework when alternately connected. The internal and external crosses share a common design language and connection method, allowing standardized manufacturing and assembly procedures to be used throughout the vehicle.
3Weight of moving object
If the battery pack case is made as a thin plate member to reduce weight, then the battery pack is lighter and easier to install, but the case deforms when torsional loads are applied
Solution Approach 1:
The case tray bottom plate is designed with localized reinforcement at the fastening positions where it connects the internal and external pack crosses. This allows the majority of the case to remain as a lightweight thin plate member, while the critical connection zones have enhanced stiffness to prevent deformation under torsional loads.
Data Source
AI summary
A battery pack is mounted under a floor panel. A case of the battery pack includes a case tray. On an inner surface of a bottom plate of the case tray, plural internal pack crosses are provided. On an outer surface of the bottom plate of the case tray, plural external pack crosses are provided. An internal pack cross front flange is fastened to an external pack cross rear flange that is arranged in front of the internal pack cross in the vehicle longitudinal direction in a state of matching the external pack cross rear flange in the vehicle longitudinal direction. An external pack cross front flange is fastened to an internal pack cross rear flange that is arranged in front of the external pack cross in the vehicle longitudinal direction in a state of matching the internal pack cross rear flange in the vehicle longitudinal direction.