Pedestrian Protection Hood Actuator Interference Fit
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Solution Overview
Problem
Existing hood lifting mechanisms in vehicles, which use linear actuators to absorb pedestrian impact, rely on expensive and cumbersome double-backed adhesive tape to secure the piston, leading to gaps exposed to environmental elements and inefficiencies due to temperature expansion.
Innovation Solution
A hood lifting mechanism featuring a housing and piston with an interference fit that prevents lateral, rotational, and axial movement in the stored position, utilizing a gas generator to overcome this fit and extend the piston, thereby eliminating the need for adhesive tape and enhancing reliability across temperature ranges.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If double backed adhesive tape is used to secure the piston, then the piston is held in place to prevent rattling and maintain position during temperature changes, but the solution becomes expensive and cumbersome for manufacturing
Solution Approach 1:
The patent removes the adhesive tape component entirely from the system. Instead of using tape to secure the piston, the design extracts this function and replaces it with a mechanical interference fit between the piston and housing, eliminating the need for adhesive materials and their associated manufacturing steps.
Solution Approach 2:
The patent replaces the chemical/adhesive bonding system (adhesive tape) with a mechanical system (interference fit). The piston features an engagement area that forms an interference fit with the housing opening, providing mechanical retention through friction and geometric constraint rather than adhesive bonding.
2Reliability
If adhesive tape is used to hold the piston during thermal expansion, then the piston remains positioned, but gaps form that expose the actuator to environmental elements
Solution Approach 1:
The patent removes the adhesive tape that was creating gaps during thermal expansion. By extracting this component and replacing it with an interference fit design, the system maintains continuous contact between the piston and housing throughout the full range of thermal expansion, preventing gap formation and environmental exposure.
Solution Approach 2:
The patent designs the interference fit with specific dimensional parameters that accommodate thermal expansion. The engagement area and mating surface are dimensioned to maintain interference contact throughout the expected temperature range, ensuring the piston remains retained while preventing gaps that would expose internal components to the environment.
3Ease of manufacture
If an interference fit is used to secure the piston, then adhesive tape is eliminated and manufacturing is simplified, but the piston must overcome the interference fit force to extend
Solution Approach 1:
The patent applies local quality by creating the interference fit only in specific regions where needed for retention, while leaving other regions free for actuation. The engagement area is localized to provide mechanical retention during storage and thermal expansion, while the actuation mechanism applies force at a different location to overcome this localized interference and enable piston extension.
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
The solution provides a cost-effective and reliable mechanism for lifting the hood, ensuring consistent performance across varying temperatures and reducing manufacturing complexity, while maintaining the necessary force to absorb pedestrian impact effectively.
Implementation Method 1
A gas generator provides a threshold actuating force to overcome the interference fit and extend the piston from the stored position to an extended position.
Implementation Method 2
the mating surface and the engagement area form an interference fit that prevents lateral, rotation, and axial movement of the piston in the stored position
Implementation Method 3
The adhesive tape also holds the piston in place during expansion due to temperature changes in the combustion chamber.
Data Source
AI summary
A hood lifting mechanism according to various implementations includes a housing and a piston. A distal end of the piston is urged away from a distal end of the housing to lift a hood upwardly away from a vehicle body in response to the vehicle hitting a pedestrian. To prevent the piston from rattling or moving within the housing while in a stored position, a portion of the piston and a portion of the housing form an interference fit in the stored position. A gas generator in fluid communication with a proximal end of the housing provides sufficient force to overcome the interference fit and urge the distal end of the piston out of the housing.