Cellulose Nanofiber Resin Gear for Void-Free High-Torque Meshing
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Solution Overview
Problem
Existing gear systems, particularly those used in electric power steering (EPS), face challenges with high-torque durability, slidability, and continuous moldability, as well as issues with voids and surface roughness leading to inferior mechanical properties.
Innovation Solution
A gear system comprising a resin composition with a thermoplastic resin and cellulose nanofibers, where the resin composition has a specific molecular weight range and surface roughness, along with a thixotropic index, and includes a surface treatment agent and metal ion component to enhance durability and slidability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If glass fibers are used as reinforcing material in resin compositions, then mechanical strength is improved, but specific gravity increases and weight increases
Solution Approach 1:
The patent changes the key parameter from traditional glass fiber reinforcement to cellulose fiber reinforcement. Cellulose fibers have a specific gravity of approximately 1.5, significantly lighter than glass fibers (specific gravity 2.5-2.6), while maintaining comparable or superior mechanical strength properties. This parameter substitution directly resolves the contradiction between strength and weight.
Solution Approach 2:
The patent creates a composite material system using cellulose fibers combined with thermoplastic resins (polyamide, polyester, polyacetal, or polyolefin). This composite approach allows achieving high mechanical strength through optimized fiber-resin interaction while maintaining low weight, as the cellulose fibers provide reinforcement without the weight penalty of glass fibers.
2Strength
If glass fibers are used in resin compositions for gear manufacturing, then mechanical strength is improved, but surface roughness increases and roundness is lowered at sliding portions
Solution Approach 1:
The patent changes the fiber material parameter from glass to cellulose, which has different surface characteristics and interaction properties with thermoplastic resins. Cellulose fibers produce smoother surfaces and better roundness at sliding portions while maintaining mechanical strength, directly addressing the manufacturing precision issue.
Solution Approach 2:
The patent optimizes the local quality of the gear material by selecting cellulose fibers that provide appropriate surface characteristics for sliding portions. The fiber material is specifically chosen to ensure smooth sliding surfaces and accurate gear tooth geometry, differentiating the surface properties from the bulk strength requirements.
3Productivity
If glass fibers are continuously used in injection molding under the same conditions, then production efficiency is maintained, but significant deviation of molded article dimensions occurs between articles
Solution Approach 1:
The patent changes the fiber reinforcement parameter from glass to cellulose, which exhibits different flow and packing characteristics during injection molding. Cellulose fibers provide better dimensional consistency and reduced variation between molded articles while maintaining production efficiency, likely due to their different aspect ratio, surface properties, and interaction with the molten resin.
4Strength
If resin compositions containing glass fibers are used for round bar extrusion or injection molding, then structural strength is improved, but interior voids form leading to stress concentration and inferior durability
Solution Approach 1:
The patent changes the fiber material parameter from glass to cellulose, which has different viscosity characteristics and flow behavior during molding. Cellulose fibers reduce the formation of interior voids (vacuum cavities) during round bar extrusion or injection molding, eliminating stress concentration points and improving durability while maintaining structural strength.
Solution Approach 2:
The patent converts the potential harm of fiber reinforcement (which can cause void formation and stress concentration) into a benefit by selecting cellulose fibers that naturally reduce void formation during molding. The fiber characteristics are chosen to eliminate the harmful void formation effect while preserving the strength-enhancing benefit.
5Ease of manufacture
If cellulose nanofibers are separated from water to form powder, then they can be distributed in resin, but they change from microdispersed state to strong aggregates making redispersion difficult
Solution Approach 1:
The patent introduces a surface treatment agent as an intermediary substance between cellulose nanofibers and thermoplastic resin. This surface treatment prevents strong aggregation of cellulose nanofibers during separation from water and maintains their microdispersed state, enabling easy redispersion and uniform distribution in the resin matrix.
Solution Approach 2:
The patent applies surface treatment to change the surface properties of cellulose nanofibers, reducing their tendency to aggregate through hydrogen bonding. This parameter modification maintains the nanofibers in a microdispersed state during processing and ensures stable dispersion in the final resin composite.
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 gear system with improved high-torque durability, reduced voids, and enhanced slidability, ensuring both mechanical strength and silent operation.
Implementation Method 1
hydrolyzing the hemicellulose portion to weaken the pulp, and then defibrating it using a pulverizing method with a high-pressure homogenizer, microfluidizer, ball mill or disk mill, and in water they form a very finely dispersed state known as a 'nanodispersion'
Implementation Method 2
in water they form a very finely dispersed state known as a 'nanodispersion'
Implementation Method 3
The aggregating force is exhibited due to hydrogen bonding by the hydroxyl groups of the cellulose
Implementation Method 4
the resin composition has a thixotropic index of 1 to 10 at a temperature of 25° C. higher than the melting point of the thermoplastic resin (A)
Data Source
AI summary
A gear is provided that has excellent continuous moldability for practical use, and both high slidability and high durability. The provided gear is a molded resin constructed of a resin composition comprising a thermoplastic resin (A) and cellulose nanofibers (B) with an average fiber diameter of 1000 nm or smaller, and having a number average molecular weight of the thermoplastic resin (A) in the range of 10,000 to 150,000, wherein a sliding surface of the gear with another gear teeth has an arithmetic mean surface roughness Sa of 3.0 μm or lower.