Vehicle Rolling Bearing Hardness Control for Crack Resistance
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Solution Overview
Problem
Vehicle drive units in electric and hybrid electric vehicles face challenges with increased efficiency demands, leading to poor lubrication and potential crack formation in rolling bearings due to high loads and reduced lubrication, especially with downsizing and higher motor output.
Innovation Solution
A rolling bearing with inner and outer rings, and rolling elements made of high carbon chromium steel, subjected to quenching and tempering, with a hardness of 865 Hv to 1245 Hv, and controlled austenite retention and dislocation density to prevent crack formation and improve lubrication resistance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If tempering at high temperature is performed to improve toughness, then toughness is improved, but hardness at the rolling surface decreases making crack formation more likely
Solution Approach 1:
The patent applies different heat treatment conditions to different regions of the bearing components. The rolling surface region receives controlled tempering at 150-250°C to maintain high hardness (865-1245 Hv), while the internal structure undergoes tempering that ensures toughness. This local differentiation of heat treatment parameters resolves the contradiction between surface hardness and internal toughness.
Solution Approach 2:
The patent precisely controls the tempering temperature parameter within a specific range (150-250°C) and maintains hardness within a specific range (865-1245 Hv). By optimizing these parameters, the patent achieves both sufficient toughness and high surface hardness, preventing crack formation while maintaining component stability.
2Loss of energy
If lubrication is reduced to improve efficiency, then energy efficiency is improved, but crack formation in rolling surface increases
Solution Approach 1:
The patent performs preliminary hardening treatment on the rolling surface before the bearing enters service, achieving hardness of 865-1245 Hv through controlled tempering. This preliminary strengthening of the rolling surface provides inherent resistance to crack formation that persists even under poor lubrication conditions, allowing the bearing to operate efficiently with reduced lubrication.
3Volume of moving object
If bearing size is reduced to downsize drive unit, then drive unit size is reduced, but load density and crack risk increase
Solution Approach 1:
The patent concentrates the highest hardness (865-1245 Hv) specifically at the rolling surface region where contact stress occurs, while the core material maintains appropriate toughness. This local quality differentiation allows small bearings to withstand high load densities without cracking, as the critical surface region is optimally strengthened.
Solution Approach 2:
The patent creates a composite microstructure with a hardened rolling surface layer (martensite with retained austenite) over a tougher core structure. This composite arrangement enables the bearing to achieve high strength-to-weight ratio, maintaining load bearing capacity even as overall bearing size is reduced for drive unit downsizing.
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 effectively suppresses crack formation and improves rolling fatigue life, resistance to stress concentration, and maintains dimensional stability under poor lubrication conditions, enhancing the performance and reliability of vehicle drive units.
Implementation Method 1
made of steel subjected to quenching and tempering
Implementation Method 2
made of steel subjected to quenching and tempering
Data Source
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AI summary
A rolling bearing (100) supports a rotation shaft of a vehicle drive unit. The rolling bearing includes an inner ring (10), an outer ring (20), and a rolling element (30) which are made of steel subjected to quenching and tempering. Each of the inner ring, the outer ring, and the rolling element has a rolling surface (10da, 20ca, 30a). A hardness at the rolling surface of at least one of the inner ring, the outer ring, and the rolling element is 865 Hv or more and 1245 Hv or less.