CVT Metal Ring Nitride Layer Thickness Distribution

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Solution Overview

Problem

Conventional metal rings for power transmission belts in continuously variable transmissions experience a decrease in mechanical strength margin and tensile stress concentration due to the even nitride layer formation during the nitride treatment process, leading to reduced durability and increased production costs.

Innovation Solution

A metal ring design with a nitride layer configuration where the layer thickness at the widthwise end portions is smaller than at the central portions, and the use of nitride inhibition techniques to control the nitride layer thickness, reducing tensile residual stress and enhancing durability.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Strength

If the nitride layer thickness is increased to improve surface properties, then the mechanical strength margin decreases due to higher tensile residual stress, requiring more thin plate metal rings to be stacked, which increases production costs

Engineering Contradiction:

Improvesurface hardnessVSAvoidproduction cost

Core Design Contradiction:

StrengthVSEase of manufacture

Solution Approach 1:

The patent optimizes nitride layer thickness distribution to apply thicker layers (0.5-2.0 mm) only at the widthwise central portion where surface hardness is critical, and thinner layers (0.1-0.5 mm) at the end portions where stress concentration would otherwise require additional stacking. This localized approach achieves the required surface properties while minimizing the number of thin plate metal rings needed, thereby reducing production costs.

Inventive Principle:

Principle #3Local quality

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 the decrease in mechanical strength margin and tensile stress concentration at the widthwise end portions, enhancing the durability of the metal ring and reducing production costs by allowing for fewer thin plate metal rings to be stacked.

Implementation Method 1

performing an aging and nitride treatment to produce a plurality of thin plate metal rings

Methodology Applied

Scientific EffectNitride treatment: Nitriding

Implementation Method 2

executing a circumferential length correction treatment of plastically deforming the metal ring

Methodology Applied

Scientific EffectPlastic deformation: Plasticity

Implementation Method 3

performing a second solution treatment to the thin plate metal ring to restore its shape of metal structure deformed by the rolling process

Methodology Applied

Scientific EffectSolution treatment: Heat Treatment

Data Source

PatentUS8713786B2Metal ring and method of producing the same

Publication Date: 2014.05.06 TOYOTA JIDOSHA KK

AI summary

To provide a metal ring excellent in durability by reducing decrease in margin of strength and concentration of tensile stress at its both widthwise end portions and to efficiently realize a production method of the same, a metal ring is formed in an endless band-like body having a nitride layer on its surface portion and constituting part of a metal belt of a belt type continuously variable transmission, the nitride layer being constituted by a first nitride layer portion positioned on an outer circumferential side, a second nitride layer portion positioned on an inner circumferential side, and third nitride layer portions positioned on both widthwise end sides, and the layer thicknesses of the third nitride layer portions being smaller than either one of the layer thicknesses of the first nitride layer portion and the second nitride layer portion.