Midsole Cavity Structure for Delayed Energy Return and Shear Stability
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Solution Overview
Problem
Conventional solid foam midsoles face a trade-off between high compression travel and lateral shear stability, with increased travel compromising stability and early energy return reducing propulsion efficiency.
Innovation Solution
A midsole design featuring a resilient foam structure with a conical disk and lateral expansion limiter, allowing for high compression travel without sacrificing lateral shear stability, and delayed energy return through reduced spring rate during mid-range compression.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If solid foam midsole thickness is increased to provide greater compression travel, then impact reduction is improved, but lateral shear stability deteriorates
Solution Approach 1:
The midsole is segmented into multiple foam layers with different durometers - a lower durometer foam layer for impact absorption and an upper higher durometer foam layer for lateral shear stability. This segmentation allows each layer to perform its specialized function without compromising the other.
Solution Approach 2:
Different regions of the midsole have different foam durometers tailored to local requirements. The lower portion uses softer foam for impact reduction while the upper portion uses firmer foam for lateral stability, creating local quality variations that resolve the contradiction.
2Strength
If lower durometer foam is used to increase compression travel, then impact reduction is improved, but lateral shear stability deteriorates
Solution Approach 1:
The midsole employs local quality by using lower durometer foam specifically in the lower portion where impact absorption is needed, while using higher durometer foam in the upper portion where lateral shear stability is required. This spatial variation in material properties resolves the contradiction between impact reduction and lateral stability.
Solution Approach 2:
The foam midsole is segmented into distinct durometer zones - a softer lower layer and a firmer upper layer. This segmentation allows the lower layer to provide impact reduction through greater compression while the upper layer maintains lateral shear stability.
3Use of energy by moving object
If foam midsole is made thicker to delay energy return, then propulsion efficiency is improved, but lateral shear stability deteriorates
Solution Approach 1:
The midsole is segmented into foam layers with different durometers that work together to achieve both delayed energy return and lateral stability. The lower softer layer allows greater compression travel for energy storage while the upper firmer layer provides lateral shear stability.
Solution Approach 2:
Different foam durometers are applied to different vertical zones of the midsole - softer foam in the lower region for energy absorption and timing delay, and firmer foam in the upper region for lateral stability during the propulsion phase.
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 design achieves improved impact reduction and propulsion by maintaining midsole compression throughout the stride, enhancing lateral stability and energy return efficiency.
Implementation Method 1
A resilient structure, such as, but not limited to, foam, absorbs and returns energy
Implementation Method 2
highly resilient material may include resilient foam
Implementation Method 3
configured as a conical disk shape... provides increased lateral shear stability
Implementation Method 4
during a first part of the range of travel of the compression the structure deforms by bending of the resilient structure
Implementation Method 5
the resilient structure being arranged to collapse, under the compression by the downward force applied to the upper by the typical user, into the cavity
Data Source
AI summary
An energy return device for a midsole of a shoe comprises a resilient foam or matrix structure, such as a domed disk, around a cavity. The resilient structure is arranged to collapse into the cavity under foot strike pressure. The structure may initially resist the pressure primarily by compression forces directed around the cavity. As the cavity collapses these forces may provide decreasing vertical spring rate as the structure bends or as the forces become less vertical, causing the structure to stay more compressed through the midstride and energy return to be delayed until the user has moved further forward in their stance. At full collapse the material of the structure may resist further downward force of the user by direct compression. A lateral expansion limiter may resist lateral expansion to increase vertical force supplied by the compression forces around the cavity and reduce interference with other components. A support structure may help guide the collapse and increase spring force.