Injection Molded Crank Arm With Metal Insert
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Solution Overview
Problem
The existing transmission shift mechanisms with crank arms are costly due to complex manufacturing and assembly processes, including staking of ball components which can result in inconsistent tolerances and durability issues, especially when using injection molded plastic components in non-rotational attachment.
Innovation Solution
A transmission shift mechanism featuring a torque-transfer member formed by injection molding with a metal insert, providing enhanced strength and efficiency in manufacturing, where a sheet metal insert is stamped and integrated into a polymeric body, allowing for a molded polymeric body with a spherical surface section to engage a non-linear camming slot, reducing material costs and assembly complexity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If a ball component is non-rotationally staked to an arm portion, then manufacturing cost is reduced, but manufacturing precision and reliability deteriorate due to inconsistent tolerances and ball separation failures
Solution Approach 1:
The invention uses a composite construction where a metal insert (providing strength and precision) is embedded within a polymeric body (providing cost-effectiveness and self-lubrication). This composite approach allows the crank arm to achieve both low manufacturing cost and high precision/reliability, as the metal insert provides consistent positioning tolerances while the polymeric material reduces manufacturing complexity compared to fully metal construction with staking operations.
Solution Approach 2:
The invention changes the material parameters by transitioning from solid metal or solid plastic to a composite of metal insert within polymeric body. This parameter change enables the crank arm to achieve both the cost benefits of plastic and the precision/strength benefits of metal, resolving the contradiction between manufacturing cost and precision.
2Ease of manufacture
If a ball component is non-rotationally staked to an arm portion, then manufacturing cost is reduced, but reliability deteriorates due to ball separation and durability issues
Solution Approach 1:
The metal insert provides structural strength and resistance to separation forces, while the polymeric body provides cost-effectiveness and self-lubricating properties. This composite structure eliminates the ball separation failures associated with staking while maintaining low manufacturing costs, as the metal insert is permanently embedded within the polymeric body during molding.
Solution Approach 2:
The invention replaces the mechanical staking process (which causes reliability issues) with an integrated molding process where the metal insert is embedded within the polymeric body during injection molding. This substitution eliminates the staking operation entirely, removing the source of ball separation failures while maintaining manufacturing cost efficiency.
3Ease of manufacture
If injection molded plastic components are used in crank arms, then manufacturing cost is reduced, but strength deteriorates compared to machined extruded plastic or metal components
Solution Approach 1:
The invention directly addresses the strength limitation of injection molded plastic by incorporating a metal insert within the polymeric body. The metal insert provides the necessary structural strength and load-bearing capacity, while the polymeric body maintains the cost and manufacturing efficiency benefits of injection molding. This composite structure allows the crank arm to achieve both low cost and high strength simultaneously.
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 enables a cost-effective and durable transmission shift mechanism with improved manufacturing efficiency, enhanced strength, and reduced material requirements, addressing the issues of inconsistent tolerances and durability in existing crank arm designs.
Implementation Method 1
The crank arm is formed by injection molding and includes a stamped sheet metal insert
Implementation Method 2
a molded polymeric body with a sheet metal insert disposed within the molded polymeric body
Data Source
AI summary
A transmission shift mechanism for use with a vehicle transmission. The transmission shift mechanism includes a user-operated selector and a sub-assembly operably disposed between said user-operated selector and the vehicle transmission. The sub-assembly includes a torque-transfer member having a first portion and a second portion wherein the first portion is pivotally secured to the transmission shift mechanism about a pivot axis and the second portion defines a section of a substantially spherical surface which is engageably disposed within a non-linear camming slot defined by the transmission shift section. The torque-transfer member takes the form of a molded polymeric body with a sheet metal insert disposed within the molded polymeric body. The second portion of the torque-transfer member may include flats to reduce the volume of polymeric material required in the manufacture of the member. A method of manufacturing such a torque-transfer member or crank arm is also disclosed.