Worm Wheel Core Recess Structure for Higher Steering Torque
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Solution Overview
Problem
Conventional worm wheels in electric power steering systems face challenges in increasing the coupling strength between the metal core and synthetic resin rim portion, especially under higher assistant torque conditions, leading to potential mechanical weaknesses.
Innovation Solution
The introduction of a second annular recess on the core, in addition to the first, enhances the fixation of the rim portion, with the outer circumferential wall surface of the second recess being perpendicular to the bottom surface, and the use of injection molding techniques that minimize resin flow disturbances to prevent weld lines, thereby increasing coupling strength.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single annular recess is formed on the core for fixing the rim portion, then the structure is simple, but the coupling strength between the core and rim portion is insufficient under high torque conditions
Solution Approach 1:
The single annular recess is divided into two separate annular recesses (first and second annular recesses) positioned at different axial locations on the core. This segmentation allows the rim portion to be fixed at multiple points, significantly increasing the coupling strength and resistance to torque-induced moments while maintaining a relatively simple overall structure.
2Strength
If the outer circumferential wall surface of the second annular recess is not perpendicular to the bottom surface, then the manufacturing is easier, but the coupling strength is reduced
Solution Approach 1:
The orientation parameter of the outer circumferential wall surface of the second annular recess is changed to be perpendicular (at 90 degrees) to the bottom surface. This parameter change maximizes the fixation area and mechanical interlocking between the rim portion and core, thereby enhancing coupling strength. The perpendicular configuration provides better resistance to the tilting moment caused by assistant torque.
3Strength
If injection molding is performed with disturbed resin flow, then the manufacturing process is simpler, but weld lines occur which decrease the strength of the rim portion
Solution Approach 1:
The gate position and injection molding parameters are preliminarily optimized to ensure smooth resin flow into the annular recesses. By planning the injection path and gate location in advance, the resin flow is directed to avoid disturbances and weld line formation. This preliminary action prevents strength reduction in the rim portion while maintaining manufacturing efficiency.
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 significantly enhances the coupling strength between the core and rim portion, improving the mechanical integrity and reducing the likelihood of mechanical failures under increased torque conditions.
Implementation Method 1
The rim portion 2 is integrally formed with the core 1 by injection molding of synthetic resin
Data Source
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AI summary
A core of a worm wheel has an axial end surface formed with a first annular recess nad and another axial end surface formed with a second annular recess. A rim portion has a first inner circumferential portion fixed to the first annular recess and a second inner circumferential portion fixed to the second annular recess. An outer circumferential wall surface of the second annular recess extends from a bottom surface of the second annular recess so as to be perpendicular to the bottom surface. A depth of the second annular recess is at least 0.1 mm but not deeper than half of a gate thickness.