Worm Wheel Hub Structure for High-Torque Steering Durability
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Solution Overview
Problem
The existing worm wheel constructions combining a metal hub and synthetic resin gear portion in electric power steering apparatuses lack sufficient strength and durability when subjected to large auxiliary torques, leading to potential loosening and reduced durability.
Innovation Solution
The worm wheel design incorporates two annular concave portions on the hub, with the gear portion engaging at these locations to increase the strength and rigidity of the connecting portion, preventing damage from large moments and ensuring durability even under high torque applications.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If a single annular concave portion is used for connecting the gear portion to the hub, then the manufacturing process is simple, but the connecting strength is insufficient under large auxiliary torques
Solution Approach 1:
The single annular concave portion is divided into multiple (first and second) annular concave portions at different radial positions. This segmentation allows the gear portion to engage the hub at multiple locations, distributing the torque load and significantly increasing the connecting strength without requiring a completely different hub structure.
Solution Approach 2:
The solution transitions from a single-plane engagement (one annular concave portion) to a multi-radial-position engagement (multiple annular concave portions at different radial distances from the hub center). This dimensional change in the radial direction creates multiple engagement points that collectively resist the large auxiliary torques.
2Ease of manufacture
If the gear portion is made from synthetic resin to reduce manufacturing cost, then the manufacturing cost decreases and gear rattle noise is reduced, but the durability under large auxiliary torques is compromised
Solution Approach 1:
The worm wheel combines a metal hub (ferrous or non-ferrous alloy) with a synthetic resin gear portion. This composite construction leverages the high strength and rigidity of metal for the hub while utilizing the cost-effectiveness, noise reduction, and ease of molding of synthetic resin for the gear teeth, achieving both economic and performance benefits.
3Stability of the object's composition
If the gear portion engages the hub at a single location, then the structure is simple, but the rigidity of the connecting portion is insufficient preventing loosening under large moments
Solution Approach 1:
The single engagement location is segmented into multiple engagement locations (first and second annular concave portions) positioned at different radial distances from the hub center. This creates a distributed engagement system that significantly enhances the rigidity of the connecting portion, preventing loosening and damage under large auxiliary torques.
Data Source
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AI summary
Worm wheel construction that is able to sufficiently increase the strength of the connecting portion between a hub 11a and a gear portion 12a, and to maintain sufficient durability even when applied to an electric power steering apparatus that applies a large auxiliary torque, is achieved. A synthetic resin gear portion 12a is molded and formed in the end portion on the outer-diameter side of a metal hub 11a. A first annular concave portion 15 is provided on one surface side in the axial direction of the hub 11a, and a second annular concave portion 22 is provided on the other surface side in the axial direction thereof. Part of the synthetic resin of the gear portion 12a is fed into the portions near the outer diameter of the first annular concave portion 15 and the second annular concave portion 22 to form a first restraining portion 18 and a second restraining portion 23. These restraining portions 18, 23 tightly hold the end portion on the outer-diameter side of the hub 11a, and improve the strength and rigidity of the connecting portion between the hub 11a and the gear portion 12a.