Vehicle Wheel Bearing Inner Ring Hoop Stress Control
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Solution Overview
Problem
Existing vehicle wheel bearing apparatuses face challenges in preventing hoop stress in the outer diameter portion of the inner ring, which can lead to rust and delayed fracture, and current methods for measuring hoop stress are not efficient for mass production.
Innovation Solution
The solution involves measuring and controlling the radial expansion of the inner ring's outer circumferential surface before and after caulking, establishing a predetermined relationship to limit hoop stress below a specific level, using a linear proportional relationship, and incorporating a hardened layer on the wheel hub and inner ring, along with a stepped portion and annular recess to manage stress and deformation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the end portion of the axially extending portion is radially outwardly plastically deformed to form a caulked portion for securing the inner ring, then the inner ring is strongly secured to the wheel hub, but hoop stress is generated in the outer diameter portion of the inner ring which can lead to rust and delayed fracture
Solution Approach 1:
The patent applies different surface hardness characteristics to different regions: the caulked portion maintains original surface hardness (softer) while the outer diameter portion of the inner ring has increased surface hardness (harder) due to induction hardening. This local differentiation allows the caulked portion to provide strong securing force while the hardened outer diameter portion resists hoop stress and prevents delayed fracture.
Solution Approach 2:
The induction hardening treatment is performed in advance on the outer diameter portion of the inner ring before the caulking process. This preliminary hardening creates a hardened layer that will later resist the hoop stress generated during and after the caulking operation, preventing rust and delayed fracture while maintaining the required securing strength.
2Reliability
If high frequency induction hardening is applied to form a hardened layer on the wheel hub, then durability is improved, but the caulked portion remains as original surface hardness which may be insufficient
Solution Approach 1:
The induction hardening is selectively applied only to specific regions (the hardened layer formation region) while deliberately excluding the caulked portion. This creates a local quality difference where the wheel hub has high durability in the hardened region while the caulked portion maintains its original surface hardness to provide adequate securing strength.
3Reliability
If the amount of plastic deformation during caulking is reduced to suppress hoop stress, then delayed fracture is prevented, but the strength of the caulked portion may be insufficient to secure the inner ring
Solution Approach 1:
The patent creates a local quality difference in surface hardness between the caulked portion (original hardness) and the outer diameter portion (hardened). This allows the caulked portion to maintain sufficient securing strength while the hardened outer diameter portion resists hoop stress, eliminating the need to reduce plastic deformation amount.
Solution Approach 2:
Instead of trying to prevent the generation of hoop stress during caulking, the patent converts the potentially harmful hoop stress into a beneficial situation by hardening the outer diameter portion in advance. The hardened layer transforms the stress that would cause delayed fracture into a controlled condition that actually strengthens the overall assembly.
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
This approach effectively limits hoop stress in the inner ring, preventing cracking and delayed fracture, thereby enhancing the durability and reliability of the bearing apparatus while maintaining cost-effectiveness.
Implementation Method 1
The inner ring 52 is axially immovably secured to the wheel hub 51, by a caulked portion 51c, to prevent it from falling off of the axially extending portion 51b. The caulked portion 51c is formed by radially outwardly plastically deforming the end portion of the axially extending portion 51b.
Implementation Method 2
The wheel hub 51 is formed with a hardened layer (shown by cross-hatching) in a region from the base of the wheel mounting flange 55 to the axially extending portion 51b through the inner raceway surface 51a. The hardened layer is formed by high frequency induction hardening.
Implementation Method 3
The inner ring 52 is made of high carbon chrome bearing steel such as SUJ2 and is hardened to its core by quenching.
Data Source
AI summary
A vehicle wheel bearing apparatus which limits hoop stress generated in the inner ring during caulking, to below a predetermined level, can improve durability and reliability of the inner ring. Radial expansion of the outer circumferential surface of the inner ring, before and after said plastic deformation, is measured so that the amount of radial expansion of the inner ring is controlled based on a predetermined relationship between the hoop stress and the amount of radial expansion of the inner ring. The hoop stress in the inner member is limited below a predetermined level. Thus, it is possible to easily and exactly control the hoop stress in the inner ring caulked onto the hub. This prevents the generation of cracking or delayed fracture of the inner ring, to provide a bearing apparatus with an inner ring with superior durability and reliability.