EPS Reducer Worm Wheel Structure for Higher Tooth Contact
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Solution Overview
Problem
Conventional electric power steering devices experience reduced power transmission rates and increased noise due to low teeth contact rates and large gaps between worm and worm wheel, leading to durability issues and vibration.
Innovation Solution
A reducer design with a gear portion having a tooth recess with a closed second end larger in radial length than the opened first end, and a connecting gear portion with constant thickness and increasing radial length, enhancing teeth contact and reducing manufacturing complexity and costs through injection-molding and cutting processes.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of manufacture
If the tooth recess has openings at two opposite side ends in the axial direction to provide easier processing, then the ease of manufacture is improved, but the teeth contact rate reduces, deteriorating the power transmission rate
Solution Approach 1:
The tooth recess is divided into two distinct portions: a first tooth recess portion with an opening at the first end for ease of manufacturing, and a second tooth recess portion that is closed at the second end to increase teeth contact rate. This segmentation allows each portion to serve its specific function while resolving the contradiction between manufacturability and power transmission efficiency
Solution Approach 2:
Different regions of the tooth recess are given different structural characteristics: the first end region has an opening for manufacturing access, while the second end region is closed to maximize contact. This local differentiation allows the structure to optimize for both manufacturing ease and operational performance in different locations
2Ease of operation
If a large gap between the teeth engagement portions of the worm and worm wheel is maintained, then the ease of operation is improved, but significant vibration and noise generated during rotation may be directly delivered to the driver, and the durability of internal components of the reducer may be deteriorated
Solution Approach 1:
The gap between teeth engagement portions is optimized to a specific range (0.02mm to 0.05mm) that balances operational ease with durability. This parameter optimization reduces vibration and noise while maintaining sufficient clearance for smooth operation, preventing excessive wear and component damage
3Power
If the closed second end of the tooth recess portion is larger in radial length than the opened first end, then the teeth contact rate increases, improving the power transmission rate, but the manufacturing complexity increases
Solution Approach 1:
The tooth recess is segmented into two portions with different structural characteristics. The first portion has uniform thickness and constant radial length for easy manufacturing, while the second portion has gradually reducing thickness and larger radial length for enhanced contact. This segmentation resolves the contradiction by distributing complexity only where necessary
Solution Approach 2:
The second tooth recess portion extends beyond the first portion in radial length to provide enhanced teeth contact rate and power transmission. This partial extension beyond the basic uniform structure provides the necessary performance improvement while limiting complexity to only the region where it is most beneficial
Data Source
AI summary
The present embodiments provide a reducer of an electric power steering device, comprising a boss having a coupling hole formed in a central portion to allow a steering shaft to be coupled thereto and a gear portion on an outer circumferential side of the boss and having a tooth recess portion engaged with a worm on an outer circumferential surface thereof, wherein the tooth recess portion has a first end and a second end in an axial direction of the gear portion, the first end being axially opened, and the second end being closed, and a method for manufacturing the same.