Automobile Hood Decoupling Stiffness and Energy Absorption
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Solution Overview
Problem
Current automobile hood designs face a trade-off between energy absorption and stiffness, where improving one criterion compromises the other, necessitating complex balancing acts.
Innovation Solution
The hood assembly features an inner hood made of fiber-reinforced plastic for stiffness, an outer hood of thin metal for energy absorption, and a core with lower strength and stiffness than both, allowing these functions to be decoupled and designed independently.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the hood structure uses a traditional single-layer design with support ribs, then the stiffness is improved, but the energy absorption capability deteriorates
Solution Approach 1:
The hood is segmented into three distinct layers: an outer hood for energy absorption, an inner hood for stiffness, and a core sandwiched between them. This segmentation allows each layer to be optimized for its specific function, resolving the contradiction between stiffness and energy absorption.
Solution Approach 2:
The hood employs a composite structure combining three different materials: thin metal sheet for the outer hood, fiber reinforced plastic for the inner hood, and energy absorbing material for the core. This composite approach enables simultaneous achievement of stiffness and energy absorption capabilities.
2Strength
If the hood structure uses a thicker metal sheet for the outer hood, then the stiffness is improved, but the energy absorption capability deteriorates
Solution Approach 1:
The hood structure separates the stiffness function (inner hood) from the energy absorption function (outer hood and core), allowing the outer hood to be made of thin metal that safely deforms during pedestrian impact while the inner hood maintains structural stiffness.
Solution Approach 2:
Different parts of the hood have different material properties optimized for their specific functions: the outer hood uses thin metal for energy absorption and pedestrian safety, while the inner hood uses stiff fiber reinforced plastic for structural support.
3Ease of manufacture
If the space between outer hood and inner hood is left empty, then the manufacturing simplicity is maintained, but the energy absorption capability deteriorates
Solution Approach 1:
The core uses an energy absorbing material with a porous or cellular structure that efficiently absorbs impact energy through controlled collapse and deformation, providing superior energy absorption compared to empty space while maintaining manufacturing feasibility.
4Loss of energy
If an inflatable air bag is added to the hood assembly, then the energy absorption is improved, but the device complexity increases
Solution Approach 1:
The core energy absorbing material automatically activates upon impact through its inherent mechanical properties, absorbing energy through controlled deformation and collapse without requiring external power sources, sensors, or control systems.
Solution Approach 2:
The core uses a relatively simple, cost-effective energy absorbing material that deforms permanently during impact to absorb energy, replacing the need for complex inflatable air bag systems while maintaining effective pedestrian protection.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
This design enables independent optimization of stiffness and energy absorption, enhancing pedestrian safety without sacrificing structural integrity or increasing complexity.
Implementation Method 1
the core is made from an energy absorbing material... On impact, the foamed metal breaks down continuously to absorb the impact energy
Implementation Method 2
The inner hood is constructed of a fiber reinforced plastic (FRP) and configured to provide stiffness and stability to the hood assembly
Data Source
Figure 1~4
Figure 3
AI summary
The invention relates to an automobile hood assembly containing an inner hood, an outer hood, and a core sandwiched between the inner and outer hoods. The inner hood is constructed to provide strength and stiffness to the hood assembly; and the outer hood and core are constructed to provide energy absorption to provide pedestrian safety in case of pedestrian collision. The automobile hood assembly decouples the stiffness and energy absorption requirements of an automobile hood, so that those two design criteria may be accomplished independent of each other.