Composite Worm Wheel Weight Reduction
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Solution Overview
Problem
The existing worm wheels for electric power steering devices are heavy due to their metal construction, which limits weight reduction opportunities.
Innovation Solution
A worm wheel design combining a metal core with a synthetic resin core, where the resin core surrounds the metal core and includes features like notches, concave-convex parts, and cylindrical surfaces to enhance holding power and reduce weight, while maintaining the metal core's structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the entire inner wheel element is made of metal, then the structural integrity and strength are improved, but the weight of the worm wheel increases
Solution Approach 1:
The inner wheel element is constructed as a composite structure with a metal core providing structural integrity and a synthetic resin outer layer reducing weight. This composite approach allows the worm wheel to maintain sufficient strength while significantly reducing overall weight compared to an all-metal construction.
Solution Approach 2:
The inner wheel element is divided into two distinct materials: a metal core and a synthetic resin outer layer. This segmentation allows each material to perform its optimal function - the metal core provides structural strength while the resin layer reduces weight, resolving the contradiction between strength and weight.
2Weight of moving object
If the inner wheel element is made entirely of synthetic resin, then the weight is reduced, but the holding power and structural integrity deteriorate
Solution Approach 1:
The composite structure combines metal and synthetic resin in the inner wheel element, where the metal core provides the necessary holding power and structural integrity that would be insufficient in an all-resin construction, while still achieving weight reduction compared to full metal.
Solution Approach 2:
Different regions of the inner wheel element have different material properties: the metal core provides localized strength and holding power where needed, while the synthetic resin outer layer provides weight reduction. This local differentiation of material quality resolves the contradiction between weight and holding power.
3Ease of manufacture
If the outer wheel element is made of synthetic resin, then the manufacturing cost and noise are reduced, but the weight reduction potential is limited by the metal inner wheel element
Solution Approach 1:
The outer wheel element is made of synthetic resin which is easier and cheaper to manufacture than metal, and the inner wheel element is now also composite (metal core + resin outer layer) rather than solid metal, further reducing weight while maintaining manufacturing efficiency and low noise characteristics.
Data Source
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AI summary
Provided is a worm wheel formed by combining a metal part and a synthetic resin part to realize a reduction in weight. The worm wheel (4a) is formed by combining an inner wheel element (15a) and an outer wheel element (16a). The inner wheel element (15a) includes a metal core (24) made of metal and formed in an annular shape, and a resin core (25) made of a synthetic resin and formed in an annular shape to surround an outer circumference of the metal core (24). The outer wheel element (16a) is made of a synthetic resin and formed in an annular shape, includes a worm wheel tooth part (19a) on an outer circumferential surface, and surrounds an outer circumference of the resin core (25).