Output Shaft Nitriding for Torque Detection Strength
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Solution Overview
Problem
Existing electric power steering devices face challenges in securing strength of the torque detection concavity and convexity when miniaturization and weight saving are intended, compromising durability and measurement sensitivity.
Innovation Solution
The electric power steering device incorporates a nitride layer formed on the outer peripheral surface of the output shaft, particularly at the torque detection encoder part, using a manufacturing method that includes cold forging followed by soft-nitriding treatment, enhancing the surface hardness and durability while maintaining measurement sensitivity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the output shaft diameter is reduced for miniaturization and weight saving, then the weight and size of the electric power steering device are reduced, but the strength of the torque detection encoder part deteriorates
Solution Approach 1:
The patent applies a nitride layer specifically to the torque detection encoder part of the output shaft, creating local quality enhancement. This surface treatment increases the surface hardness and strength of the critical torque detection area without requiring an increase in the overall shaft diameter, thus resolving the contradiction between miniaturization and strength maintenance.
Solution Approach 2:
The patent changes the physical-chemical parameters of the output shaft surface by forming a nitride layer through soft-nitriding treatment. This surface treatment modifies the surface hardness, wear resistance, and strength characteristics of the torque detection encoder part, allowing the shaft to maintain adequate strength with a reduced diameter.
2Volume of moving object
If the output shaft diameter is reduced for miniaturization, then the size of the electric power steering device is reduced, but the durability of the torque detection encoder part deteriorates
Solution Approach 1:
The nitride layer is applied locally to the torque detection encoder part, providing enhanced surface properties including improved durability and wear resistance. This localized treatment allows the shaft to be smaller overall while maintaining adequate durability at the critical measurement location.
Solution Approach 2:
The soft-nitriding treatment changes the surface parameters of the torque detection encoder part, creating a harder, more durable surface layer that compensates for the reduced shaft diameter and maintains reliability over time.
3Weight of moving object
If the output shaft diameter is reduced for weight saving, then the weight of the electric power steering device is reduced, but the antirust performance deteriorates
Solution Approach 1:
The nitride layer provides a protective surface coating on the torque detection encoder part, improving corrosion and rust resistance. This surface treatment creates a barrier that protects the underlying metal from environmental degradation, compensating for the reduced material volume in the smaller shaft.
Solution Approach 2:
The patent creates a composite structure with the nitride layer forming a surface coating on the steel substrate. This composite structure combines the benefits of the base metal with the protective properties of the nitride layer, providing improved rust resistance without increasing the overall shaft size or weight.
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 secures the strength and durability of the torque detection encoder part, even with a smaller diameter output shaft, improving antirust performance and robustness, and maintaining or enhancing torque measurement sensitivity.
Implementation Method 1
a nitride layer 57 having a predetermined depth dimension is formed on an outer peripheral surface of the output shaft 16a
Implementation Method 2
it is possible to detect the direction and magnitude of the torque on the basis of the impedance change
Data Source
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AI summary
An electric power steering device includes an input shaft, an output shaft, a torsion bar provided at an inner diameter side of the input shaft and the output shaft with coaxially coupling the input shaft and the output shaft each other; and, a torque detection sleeve which is arranged at an outer diameter side of the torque detection encoder part, and of which a rear end portion is externally fitted and fixed to the fitting part. A nitride layer is formed at least at a part, at which the torque detection encoder part is formed, of the outer peripheral surface of the output shaft.