Resin-Metal Worm Wheel Structure for Stronger Tooth Molding
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Solution Overview
Problem
The existing worm wheel structures in electric power steering devices face challenges in securing adequate holding power between the synthetic resin outer wheel element and the metal inner wheel element, leading to manufacturing errors such as pitch errors due to uneven molding shrinkage and varying radial thicknesses of teeth.
Innovation Solution
The worm wheel design incorporates a metal inner wheel element with annular concave parts and a synthetic resin outer wheel element, where the resin is injection-molded to cover the entire circumference, including the radially outer end, to enhance holding power and uniformity, using a cylindrical surface part for consistent radial thickness and minimizing manufacturing errors.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If only the radially outer end part of the inner wheel element is embedded in the outer wheel element, then the structure is simple, but the holding power is insufficient
Solution Approach 1:
The patent transitions from radial embedding (single dimension) to axial embedding (another dimension). The inner wheel element is embedded in the outer wheel element in the axial direction, allowing the resin to penetrate and solidify within the axial space, thereby significantly improving holding power while maintaining manufacturing simplicity.
Solution Approach 2:
The patent implements a nested structure where the inner wheel element is positioned within the outer wheel element. The resin material fills the space between these nested components, creating a strong mechanical interlock that enhances the holding power between the two wheel elements.
2Ease of manufacture
If the radial thickness of the outer wheel element varies in different portions, then the molding process is easier, but manufacturing precision deteriorates due to uneven shrinkage
Solution Approach 1:
The patent applies local quality by making the radial thickness of the outer wheel element uniform specifically in the portions where teeth are formed, while other portions may have different thicknesses. This localized uniformity ensures consistent shrinkage and eliminates pitch errors in the critical tooth areas, while maintaining molding ease in non-critical areas.
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 significantly improves the holding power of the synthetic resin outer wheel element and reduces manufacturing errors like pitch errors by ensuring consistent radial thickness and uniform molding shrinkage across the worm wheel teeth, resulting in a more accurate and robust worm wheel assembly.
Implementation Method 1
The outer wheel element 16 is made of a synthetic resin, and a radially outer end part of the inner wheel element 15 is embedded therein over the entire circumference through an injection molding
Data Source
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AI summary
An inner wheel element (15a) is embedded in an outer wheel element (16a), such that a continuous range from an inner diameter side circumferential surface configuring an inner surface of a first annular concave part (22), through an outer circumferential surface of the inner wheel element (15a), to an inner diameter side circumferential surface configuring an inner surface of a second annular concave part (38) in a surface of the inner wheel element (15a) is covered over the entire circumference. Accordingly, a structure is achieved which easily secures a holding power of the synthetic resin outer wheel element with respect to the inner wheel element.