Torsion Bar Spring Shaft Buckling Prevention
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Solution Overview
Problem
The existing electric power steering devices require dedicated jigs and equipment to assemble the torsion bar components, leading to increased costs and potential buckling of the spring shaft portion due to high axial compressive forces, which affects vibration transmission and torque detection sensitivity.
Innovation Solution
The electric power steering device incorporates a torsion bar with coupling shaft portions and a spring shaft portion, featuring a diametrical extension portion that contacts the opposing surface to prevent buckling, allowing for reduced stiffness and improved torque detection sensitivity without the need for dedicated assembly equipment.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the torsion bar is assembled with both end portions press-fitted into coupling holes of input shaft and output shaft, then torque transmission is achieved, but high axial compressive force causes buckling of the spring shaft portion
Solution Approach 1:
The torsion bar is divided into three functional segments: a first coupling shaft portion for press-fitting into the input shaft, a spring shaft portion for elastic deformation and torque detection, and a second coupling shaft portion for press-fitting into the output shaft. This segmentation allows each portion to be optimized independently - the coupling shaft portions are designed for strong mechanical connection while the spring shaft portion is designed for controlled elasticity, resolving the contradiction between torque transmission and buckling resistance.
Solution Approach 2:
Different portions of the torsion bar are given different mechanical properties and dimensions. The coupling shaft portions have larger diameters and higher stiffness for strong mechanical connection, while the spring shaft portion has smaller diameter and controlled elasticity for torque detection. This local differentiation allows the spring shaft to flexibly detect torque without buckling under assembly compressive forces.
2Stability of the object's composition
If the stiffness of the spring shaft portion is increased to prevent buckling, then buckling resistance is improved, but vibration transmission from steered wheels to steering wheel increases and torque detection sensitivity is lowered
Solution Approach 1:
The torsion bar employs local quality differentiation where the spring shaft portion has optimized dimensions (smaller diameter, controlled length) to achieve the right balance between buckling resistance and torque detection sensitivity. The coupling shaft portions have larger dimensions for structural stability, while the spring shaft portion is specifically designed with lower stiffness to detect torque through elastic deformation without transmitting excessive vibration.
Solution Approach 2:
The patent optimizes the physical parameters of the spring shaft portion including its diameter, length, and material properties to achieve the desired stiffness. By carefully controlling these parameters, the spring shaft portion can resist buckling under assembly forces while maintaining sufficient flexibility for accurate torque detection through elastic torsional deformation.
3Manufacturing precision
If dedicated jig and equipment are used to form through hole at matching positions, then manufacturing precision is improved, but device complexity and cost increase
Solution Approach 1:
The coupling shaft portions are designed with features that enable preliminary positioning and alignment before final assembly. The press-fitting process itself serves as a positioning mechanism, allowing the through hole to be formed at the correct position through the natural alignment of the press-fitted components, eliminating the need for complex dedicated jigs and equipment.
Solution Approach 2:
The assembly structure is designed to be self-aligning during the press-fitting process. The coupling shaft portions naturally position themselves relative to the input shaft and output shaft during assembly, allowing the through hole to be formed at the correct matching position without requiring external positioning devices or complex assembly equipment.
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 configuration prevents buckling of the spring shaft portion during assembly, reduces vibration transmission, and enhances the detection sensitivity of steering torque, while eliminating the need for costly assembly jigs and equipment.
Implementation Method 1
a torque detector configured to detect the steering force based on elastic torsional deformation of the torsion bar 14
Implementation Method 2
when press-fitting the rear end portion of the torsion bar 14 into the coupling hole 17 of the input shaft 12, a high axial compressive force is applied to a spring shaft portion, which is an axially intermediate portion of the torsion bar 14
Data Source
AI summary
An axially intermediate portion of a spring shaft portion 36 of a torsion bar 14a is provided with a large diameter portion 37, and an outer peripheral surface of the large diameter portion 37 is in contact with or is positioned close to an inner peripheral surface of a hollow output shaft 13a. Accordingly, in an electric power steering device, when one of a pair of coupling shaft portions, which are axially end portions of the torsion bar, to be coupled to a coupling hole of a counter-shaft later is press-fitted into the coupling hole of the counter-shaft, the spring shaft portion of the torsion bar can be prevented from buckling.