Gear Tooth Surface Fatigue Strength via Compressive Stress
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Solution Overview
Problem
Gears used in transmissions suffer from insufficient fatigue strength against pitting and chipping, despite being resistant to abrasion and scoring, due to lack of compressive residual stress on the tooth face or root, and introducing shot peening complicates the manufacturing process.
Innovation Solution
Forming a multitude of microscopic recesses on the tooth face with specific surface roughness parameters (Ryni: 2.0 to 5.5 μm, Rymax: 2.5 to 7.0 μm, Rqni: 0.3 to 1.1 μm) and smoothing the surface through polishing, then colliding microscopic hard particles to produce compressive residual stress, thereby enhancing resistance to abrasion, scoring, pitting, and chipping without increasing manufacturing steps.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If shot peening is applied to improve fatigue strength, then compressive residual stress is produced on the tooth face, but the manufacturing process becomes more complex
Solution Approach 1:
The patent combines the shot peening function (producing compressive residual stress) and the surface finishing function (polishing) into a single integrated process. The microscopic protrusions formed during polishing serve dual purposes: they create oil retention recesses for abrasion resistance and generate compressive residual stress for fatigue strength improvement, eliminating the need for a separate shot peening step.
Solution Approach 2:
The polishing process is given multiple functions: it smooths the tooth face for proper gear engagement, creates microscopic recesses for oil retention and abrasion resistance, and simultaneously generates compressive residual stress through the formation and subsequent removal of microscopic protrusions, thereby improving fatigue strength without requiring additional specialized equipment or processes.
2Reliability
If microscopic recesses are formed on the tooth face to improve abrasion resistance, then oil film formation is promoted, but fatigue strength against pitting and chipping is insufficient
Solution Approach 1:
The patent specifies precise parameter ranges for surface roughness (Ra: 0.3 to 1.1 μm, Ryni: 2.0 to 5.5 μm, Rqni: 2.5 to 7.0 μm) to optimize both abrasion resistance and fatigue strength. By controlling these surface parameters within specific ranges, the polishing process simultaneously achieves adequate oil retention for abrasion resistance while generating sufficient compressive residual stress for fatigue strength improvement.
3Manufacturing precision
If the tooth face is smoothed by polishing to reduce surface roughness, then gear engagement is improved, but compressive residual stress is not produced
Solution Approach 1:
The patent employs preliminary action by first forming microscopic protrusions on the tooth face during the polishing process, then removing these protrusions in a controlled manner. This sequence of actions - forming and then removing protrusions - generates compressive residual stress in the subsurface layer while maintaining an adequately smooth surface for proper gear engagement, achieving both surface smoothness and fatigue strength improvement.
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 method significantly improves fatigue strength against pitting and chipping, with the gears exhibiting higher resistance to pitting and chipping, and maintaining resistance to abrasion and scoring, as demonstrated by prolonged pitting resistance and increased fatigue limit point, without complicating the manufacturing process.
Implementation Method 1
by colliding the microscopic hard particles against the tooth face, a large compressive residual stress is produced on the tooth face
Implementation Method 2
The tooth face is smoothed by polishing
Implementation Method 3
improve the resistance to abrasion and scoring by randomly forming a multitude of microscopic recesses on the tooth face which serve to keep oil therein
Data Source
AI summary
The invention aims to improve not only the resistance to abrasion and scoring, but also the fatigue strength against pitting and chipping, without increasing the number of steps of the manufacturing process.The tooth face 2 of the gear is smoothed by gyro polishing. In the thus smoothed tooth face 2, a multitude of microscopic recesses 3 are randomly formed by liquid honing in which microscopic hard particles are collided with the tooth surface together with liquid. By the liquid honing, a large compressive residual stress is produced on the tooth face 2. This improves not only the resistance to abrasion and scoring, but also the fatigue strength against pitting and chipping, without increasing the number of steps of the manufacturing process.