Two-Shot Molded Vehicle Hitch Step Impact Absorption
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Solution Overview
Problem
Existing hitch steps are limited in width and unable to effectively absorb rear collision impacts due to their metal construction, which adds weight and restricts flexibility, leading to potential damage during vehicle collisions.
Innovation Solution
A two-shot molded hitch step assembly using a high flexural modulus polymer for the core and a thermoplastic elastomer for the shell, providing a wider platform with enhanced impact absorption and traction, while maintaining stability and resistance to torsional forces.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Area of stationary object
If a hitch step is made wider to provide a stable platform for users, then user accessibility and stability are improved, but the hitch step becomes more susceptible to torsional deformation and vertical deflection under load
Solution Approach 1:
The hitch step is divided into a two-shot molded structure with a rigid polymer core providing structural support and a softer TPE outer layer providing cushioning and grip. This segmentation allows each material to optimize for its specific function while working together to solve the width-stability contradiction.
Solution Approach 2:
The patent uses a composite structure combining a rigid polymer (polyester or polypropylene) with a thermoplastic elastomer (TPE). The rigid core maintains torsional stability while the TPE layer adds compliance and grip, enabling a wider platform without excessive deformation under load.
2Strength
If a hitch step is made from metal to withstand user weight and resist deformation, then structural strength is improved, but the vehicle's weight increases and impact absorption capability deteriorates
Solution Approach 1:
The patent replaces the traditional metal mechanical structure with a polymer-based structural system. The rigid polymer core provides the necessary structural strength to support user weight, while the elastomeric outer layer provides impact absorption through elastic deformation, eliminating the need for heavy metal construction.
Solution Approach 2:
The patent changes the material parameters from metal to polymer/TPE composite, fundamentally altering the weight-strength relationship. The polymer core maintains adequate structural strength while the elastomeric layer provides impact absorption, achieving both weight reduction and improved impact capability simultaneously.
3Stability of the object's composition
If a hitch step is made from metal to resist deformation, then structural rigidity is improved, but the ability to absorb rear collision impacts deteriorates
Solution Approach 1:
The TPE outer layer acts as a pre-positioned cushioning element that absorbs impact energy through elastic deformation before the force reaches the rigid polymer core. This beforehand cushioning protects the core structure from impact damage while maintaining overall structural rigidity.
Solution Approach 2:
The composite structure combines a rigid polymer core for structural integrity with a softer TPE layer for impact absorption. The rigid core maintains structural rigidity while the elastomeric layer dissipates impact energy through deformation, solving the rigidity-impact absorption contradiction.
4Area of stationary object
If the hitch step platform is extended farther from the hitch axis to accommodate wide vehicle bodies, then user accessibility is improved, but the lever arm increases causing greater cantilever deformation
Solution Approach 1:
The patent changes the material parameters by using a rigid polymer core with high flexural modulus to support the extended platform. This material parameter change allows the platform to extend farther from the hitch axis while maintaining sufficient cantilever deformation resistance that would be difficult to achieve with softer materials.
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 hitch step assembly offers increased protection for the vehicle's rear bumper and user accessibility with a wider platform, absorbing rear impacts without irreversible damage and providing a higher friction surface for safety.
Implementation Method 1
a thermoplastic elastomer for the shell, providing a wider platform with enhanced impact absorption
Implementation Method 2
a thermoplastic elastomer for the shell having a bonding affinity to the core
Data Source
AI summary
A hitch step assembly comprises a first shot component injection molded from a first polymer compound with a high flexural modulus and a second shot component injection molded from a second polymer compound having a lower flexural modulus relative to the first shot compound. A post and a step body core are molded from the first polymer compound. A shell of the step body is molded from the second polymer compound and is overmolded onto the step body core. The shell forms a compression zone that attenuates rear impact forces the hitch step encounters, thus offering some protection against rear impacts. The hitch step assembly exhibits satisfactory resistance to deflection and torsional bending about a hitch receiver axis when a force is applied on the top surface of the hitch step near its lateral ends.