Bearing Surface Microstructure for Longer Rolling Fatigue Life
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Solution Overview
Problem
Conventional rocker arm and planetary gear mechanism bearings suffer from reduced rolling fatigue life due to local high surface pressures, attachment errors, load imbalances, foreign matter introduction, lubricant deterioration, and interference between rolling elements, leading to issues like skew and insufficient lubrication.
Innovation Solution
The bearing parts, including rolling elements and shafts, feature a quench-hardened layer with a specific distribution of martensite crystal grains, classified into groups with varying sizes and aspect ratios, and a high nitrogen content, optimized to enhance rolling fatigue life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If conventional quenching is applied to bearing parts, then a martensite phase layer is formed in the surface, but the rolling fatigue life is reduced due to local high surface pressures and other operational factors
Solution Approach 1:
The patent applies local quality by creating a non-uniform martensite crystal grain size distribution within the quench-hardened layer. Specifically, it establishes a first region near the surface with finer martensite grains (average size 0.5-2.0 μm) and a second region deeper in the material with coarser martensite grains (average size 2.0-5.0 μm). This gradient structure optimizes surface hardness and fatigue resistance while maintaining overall structural integrity, directly addressing the contradiction between surface strength and rolling fatigue life.
2Strength
If the martensite crystal grain size is reduced to improve surface hardness, then the surface becomes more susceptible to fatigue failure under local high pressures
Solution Approach 1:
The patent resolves this contradiction by transitioning from a uniform to a dimensional gradient structure. Instead of using a single martensite grain size throughout, it creates a depth-dependent gradient where grain size varies from the surface inward. The finer grains (0.5-2.0 μm) at the surface provide high hardness, while the progressively coarser grains (2.0-5.0 μm) at depth provide fatigue resistance, effectively solving the problem in the dimensional domain of depth distribution.
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 optimized martensite crystal grain distribution and nitrogen content improve the rolling fatigue life and static load capacity of rocker arm and planetary gear mechanism bearings.
Implementation Method 1
a quench-hardened layer having a structure mainly composed of a martensite phase is formed in the surface of the bearing part
Implementation Method 2
A rolling fatigue life of a bearing part is improved by carbonitriding a surface of the bearing part
Data Source
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AI summary
A bearing part is a rolling element (13) used for a rocker arm bearing, a shaft (11) used for the rocker arm bearing, or a shaft (21) used for a planetary gear mechanism bearing. The bearing part includes a quench-hardened layer in a surface of the bearing part. The quench-hardened layer (15, 16, 24) includes a plurality of martensite crystal grains. A ratio of a total area of the plurality of martensite crystal grains in the quench-hardened layer is more than or equal to 70%. The plurality of martensite crystal grains are classified into a first group and a second group. A minimum value of crystal grain sizes of the martensite crystal grains belonging to the first group is larger than a maximum value of crystal grain sizes of the martensite crystal grains belonging to the second group. A value obtained by dividing a total area of the martensite crystal grains belonging to the first group by the total area of the plurality of martensite crystal grains is more than or equal to 0.5. A value obtained by dividing, by the total area of the plurality of martensite crystal grains, a total area of the martensite crystal grains belonging to the first group except for a martensite crystal grain that has a minimum crystal grain size and that belongs to the first group is less than 0.5.