Cellulose Nanofiber Resin Gear for Low-Roughness High-Torque Meshing
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Solution Overview
Problem
Existing gear systems, particularly those used in electric power steering (EPS), face challenges in achieving high slidability, durability, and continuous moldability under high-torque conditions, with previous solutions failing to adequately address issues of surface roughness, void formation, and dimensional stability.
Innovation Solution
A gear system comprising a resin composition with a thermoplastic resin and cellulose nanofibers, where the thermoplastic resin has a specific molecular weight and the cellulose nanofibers have an average diameter of 1000 nm or smaller, with a surface roughness of 3.0 μm or lower, and a thixotropic index of 1 to 10, enhancing the gear's mechanical properties and moldability.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If glass fibers are used as reinforcing material in thermoplastic resin, 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, which has fundamentally different density characteristics. Cellulose fibers have a specific gravity of approximately 1.5, compared to glass fibers at 2.5-2.6, allowing the same mechanical strengthening function to be achieved with significantly reduced weight.
Solution Approach 2:
The patent creates a composite material system using cellulose fibers combined with thermoplastic resins, replacing the conventional glass fiber-reinforced plastic. This composite approach maintains the reinforcing function while utilizing the lighter density of cellulose to reduce overall component weight.
2Strength
If glass fibers are used in resin composition for injection molding, then mechanical properties are improved, but orientation of glass fibers produces stress concentration and inferior durability
Solution Approach 1:
The patent changes the fiber morphology parameter from macroscopic glass fibers to nanoscale cellulose fibers with average diameter of 100 nm or less. This dimensional change eliminates orientation-induced stress concentration because the nanoscale fibers can be distributed uniformly in three dimensions without significant alignment, thereby improving durability while maintaining mechanical properties.
Solution Approach 2:
The patent transitions from one-dimensional fiber reinforcement to nanoscale multi-dimensional distribution. The ultrafine cellulose fibers distribute uniformly throughout the resin matrix in all directions, eliminating the directional stress concentration problems associated with conventional fiber orientation during injection molding.
3Strength
If glass fibers are used in resin composition for thick parts injection molding, then structural strength is improved, but interior voids form due to cooling rate difference, leading to stress concentration and inferior durability
Solution Approach 1:
The patent changes the fiber size parameter to nanoscale dimensions (average diameter 100 nm or less), which fundamentally alters the cooling and solidification behavior during injection molding. The nanoscale cellulose fibers can follow the resin flow and distribute uniformly even in thick sections, preventing void formation that occurs with larger glass fibers due to thermal gradient differences between surface and interior.
Solution Approach 2:
The patent applies uniform nanoscale reinforcement throughout the entire molded part, including thick interior sections. The ultrafine cellulose fibers provide localized strengthening at the micro level throughout the bulk material, preventing the formation of voids and stress concentration points that occur with conventional glass fiber reinforcement in thick-walled parts.
4Ease of manufacture
If cellulose nanofibers are dried into powder form for resin distribution, then processing is enabled, 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 that coats the cellulose nanofibers. This surface treatment modifies the fiber surface properties, reducing hydrogen bonding between fibers and preventing aggregation during drying and storage. The treatment agent acts as a mediator that maintains dispersion stability while enabling processing.
Solution Approach 2:
The patent changes the surface chemical parameters of the cellulose nanofibers through surface treatment. This chemical modification alters the surface energy and hydrogen bonding characteristics, transforming the fibers from a state prone to strong aggregation into a state that maintains stable dispersion even after drying into powder form.
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 slidability, durability, and reduced voids, ensuring high torque performance and silent operation, while maintaining dimensional stability and low surface roughness.
Implementation Method 1
hydrolyzing the hemicellulose portion to weaken the pulp, and then defibrating it using a pulverizing method with a high-pressure homogenizer
Implementation Method 2
defibrating it using a pulverizing method with a high-pressure homogenizer, microfluidizer, ball mill or disk mill
Implementation Method 3
The aggregating force is exhibited due to hydrogen bonding by the hydroxyl groups of the cellulose, and is considered to be extremely strong.
Implementation Method 4
a thixotropic index of 1 to 10
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.