Rack Bar Hardening Profile for Steering Strength Without Embrittlement
Find Innovative SolutionsGenerate Solutions
Solution Overview
Problem
The formation of a deep hardened layer on rack bars for steering apparatuses, primarily composed of a martensite structure, can embrittle the material, reducing the toughness and hardness of the center portion and compromising the axial and bending strength, especially when the rack diameter is reduced for weight optimization.
Innovation Solution
A rack bar design with a hardened layer continuously formed over the entire circumference, where the depth of the hardened layer increases from the bottom land, side, and back of the rack bar, reducing the embrittlement and maintaining sufficient axial and bending strength, achieved through quenching and tempering by induction heating.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a deep hardened layer is formed on the rack bar to increase axial and bending strength, then the strength is improved, but the center portion becomes embrittled due to decreased toughness and hardness
Solution Approach 1:
The patent applies different hardened layer depths at different locations on the rack bar. The hardened layer depth is greatest at the tooth tip (first position), intermediate at the tooth side (second position), and smallest at the tooth root (third position). This localized variation in hardness distribution optimizes strength where needed while preserving toughness in the center portion, resolving the contradiction between overall strength and center portion reliability.
2Weight of moving object
If the rack diameter is reduced for weight optimization, then the weight is decreased, but the axial and bending strength are compromised
Solution Approach 1:
The patent changes the physical parameters of the rack bar by forming a hardened layer with specific depth variations at different locations. This heat treatment process modifies the material properties (hardness and strength) without changing the overall rack dimensions, allowing weight reduction while maintaining required strength through optimized material properties rather than increased size.
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 design enhances the axial and bending strength of the rack bar while minimizing embrittlement, ensuring the rack bar can withstand impact loads and maintain required strength without excessive weight, thus optimizing both performance and weight reduction.
Implementation Method 1
achieved through quenching and tempering by induction heating
Data Source
AI summary
A rack bar includes: a rack tooth row including a plurality of rack teeth meshing with pinion teeth; a hardened layer provided continuously over an entire circumference of the rack tooth row; and a center portion provided inside the hardened layer and having lower hardness than the hardened layer. When the rack bar is viewed in an axial direction of the rack bar, a depth of the hardened layer from the following positions i), ii), and iii) increases in this order: i) a bottom land of the rack teeth; ii) a side of the rack bar relative to the bottom land; and iii) a back of the rack bar relative to the bottom land.