Rack Shaft Hardness Control via Pre-Cutting Tempering
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Solution Overview
Problem
The manufacturing of rack shafts for rack and pinion steering apparatuses is hindered by the need for quenching, which can cause distortion and defects like quench cracks, and requires costly processes such as heat treatment and straightening.
Innovation Solution
A method involving refining CrMo steel to achieve a uniform hardness, tempering to create a fine mixed structure, and then gear-cutting without subsequent quenching, ensuring the rack shaft has a uniform hardness and reduced wear, eliminating the need for heat treatment processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If quenching is performed after gear cutting to increase surface hardness, then durability is improved, but distortion and quench cracks occur
Solution Approach 1:
The patent applies preliminary heat treatment (quenching and tempering) to the rod-shaped material before gear cutting to achieve the desired hardness. By performing the heat treatment in advance rather than after gear cutting, the material is pre-hardened, eliminating the need for post-cutting quenching that would cause distortion and cracks. The rod-shaped material is quenched and tempered to obtain a fine mixed structure of cementite and ferrite with Brinell hardness of 300-360 before the gear cutting process.
2Manufacturing precision
If heat treatment and straightening processes are applied after gear cutting, then mesh accuracy is maintained, but manufacturing cost and complexity increase
Solution Approach 1:
The patent performs heat treatment before gear cutting rather than after, eliminating the need for post-cutting straightening processes. By pre-hardening the material and completing the gear cutting on the hardened material, the process avoids subsequent heat treatment and straightening steps, simplifying the manufacturing process while maintaining mesh accuracy.
Solution Approach 2:
The patent changes the hardness parameter of the material through preliminary heat treatment to a range of Brinell hardness 300-360, which provides sufficient hardness for the rack shaft without requiring additional post-processing heat treatment. This parameter change enables the elimination of complex post-cutting processes.
3Ease of manufacture
If conventional gear cutting is performed on soft material, then manufacturing is easier, but wear resistance of the rack teeth is insufficient
Solution Approach 1:
The patent performs preliminary heat treatment to harden the rod-shaped material before gear cutting. The material is quenched and tempered to achieve Brinell hardness of 300-360, then gear cutting is performed on this pre-hardened material. This approach ensures adequate wear resistance while the gear cutting process can still be completed successfully.
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 enhances the strength and durability of the rack and pinion steering apparatus by reducing wear and the incidence of cracks, while lowering costs by eliminating quenching and tempering processes, and preventing distortion.
Implementation Method 1
quenching a rod-shaped material formed of CrMo steel to generate a martensitic structure
Implementation Method 2
tempering the rod-shaped material at a temperature of 400 to 650° C. to generate a fine mixed structure of cementite and ferrite
Data Source
AI summary
A rack and pinion steering apparatus which does not need quenching of the rack shaft after gear cutting of the rack shaft in manufacturing processes is provided. The rack and pinion steering apparatus comprises a pinion shaft and a rack shaft meshing with the pinion shaft. The rack shaft is formed to have a substantially uniform hardness.