Resin Worm Gear Retention via Axial Serration
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Solution Overview
Problem
Conventional methods for fixing a resin worm gear to a metal drive shaft in wiper motors lack sufficient retaining strength, leading to potential detachment and rotation issues, and increasing slit width or adding multiple slits complicates machining and reduces rotation prevention.
Innovation Solution
The use of serration grooves with concave and convex portions on the gear shaft, formed by rolling dies, provides stepped portions that prevent the worm gear from coming off and rotating, eliminating the need for a slit and enhancing machining efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Strength
If the worm gear is made thicker or the outer diameter of the serration is made larger than the shaft to increase retaining strength, then the size of the gear becomes very large, but machining the outer shaft becomes complicated
Solution Approach 1:
The invention segments the retention function into multiple concave and convex groups distributed along the axial direction, allowing the gear to maintain adequate thickness without increasing outer diameter. This segmentation enables effective retention strength while preserving simple gear geometry and reducing machining complexity.
Solution Approach 2:
Instead of increasing radial dimensions (thickness or outer diameter), the invention utilizes the axial dimension by arranging multiple concave and convex groups along the shaft axis. This dimensional shift achieves enhanced retaining strength without increasing gear size or complicating machining operations.
2Device complexity
If a conventional slit structure is used to prevent the worm gear from coming off, then the width of the slit must be narrow, but insufficient retaining strength results
Solution Approach 1:
The invention replaces the single slit structure with multiple segmented concave and convex groups arranged in the axial direction. This segmentation multiplies the retention interfaces, significantly increasing retaining strength while maintaining structural simplicity through a systematic repeating pattern.
Solution Approach 2:
The invention extends the retention structure from a single radial slit into the axial dimension by arranging multiple concave and convex groups along the shaft. This dimensional extension provides additional retention surfaces and phases, dramatically improving retaining strength without complicating the overall structure.
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
The solution effectively prevents the worm gear from coming off and rotating with increased strength, simplifies machining, and ensures reliable integration with the drive shaft without the need for a slit, improving the overall gear design.
Implementation Method 1
concave and convex portions that are formed by aligning in an axial direction the convex portions of a first rolling die with the concave portions of a second rolling die and rolling the first and second dies on an outer peripheral surface of the gear shaft
Data Source
AI summary
A gear including a gear shaft, and a gear wheel made of a resin material, the gear wheel being fixed to the gear shaft by molding. The gear having a plurality of concave portions and convex portions that repeat in a circumferential direction. The plurality of concave and convex portions are arranged such that they extend in the axial direction of the gear shaft, and arranged such that the convex portions of one concave and convex group are adjacent to the concave portions of the other concave and convex group. Due to the relative displacement of the concave portions and the convex portions, stepped portions are formed at a boundary between the concave and convex groups in the circumferential direction of the gear shaft.