Worm Wheel Tooth Flank Design for Smooth Rotation

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Solution Overview

Problem

Conventional worm wheels in electric power steering systems face issues with torque variations and uneven abrasion due to varying tooth strength and contact regions during forward and reverse rotation, leading to reduced service life and increased manufacturing complexity.

Innovation Solution

A worm wheel design where first and second tooth flanks have alternating helical and concavely curved surface portions, allowing for symmetrical tooth height and distance between flanks, ensuring constant strength and smooth rotation transmission, and a simplified molding die structure for efficient manufacturing.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Ease of manufacture

If the worm wheel is formed by molding with a conventional design where all tooth flanks have the same surface configuration, then the manufacturing process is simplified, but the tooth strength varies in the rotational axis direction and contact regions differ between forward and reverse rotation

Engineering Contradiction:

Improvemolding process simplicityVSAvoidtooth strength consistency

Core Design Contradiction:

Ease of manufactureVSStability of the object's composition

Solution Approach 1:

The tooth flank is divided into two distinct surface portions: a helical surface portion and a concavely curved surface portion. This segmentation allows each portion to serve a specific function - the helical portion provides consistent geometry for molding while the concave portion ensures uniform tooth strength and contact characteristics throughout the rotational axis direction

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Different surface configurations are applied to different portions of the tooth flank based on local requirements. The helical surface portion addresses manufacturing considerations, while the concavely curved surface portion addresses mechanical performance requirements, creating optimal local properties in each region

Inventive Principle:

Principle #3Local quality

2Reliability

If the tooth flanks are designed with varying tooth height and distance between flanks to follow convexly curved worm gear tooth flanks, then contact regions are increased, but the tooth strength varies within each tooth and manufacturing complexity increases

Engineering Contradiction:

Improvecontact region coverageVSAvoidtooth strength uniformity

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The tooth flank design employs asymmetric surface configurations - the concavely curved surface portion is specifically shaped to match the convex curvature of worm gear tooth flanks, creating optimal contact regions while the helical surface portion maintains geometric consistency. This controlled asymmetry ensures both increased contact area and uniform tooth strength

Inventive Principle:

Principle #4Asymmetry

3Reliability

If the worm wheel is designed with asymmetric tooth flank surfaces to match convexly curved worm gear tooth flanks, then contact regions are improved, but torque variations occur between forward and reverse rotation

Engineering Contradiction:

Improvecontact region qualityVSAvoidrotation smoothness

Core Design Contradiction:

ReliabilityVSStability of the object's composition

Solution Approach 1:

The tooth flank is segmented into helical and concavely curved surface portions, where the concave portion provides the asymmetric contact surface needed for matching worm gear curvature, while the helical portion maintains symmetric geometric properties that ensure consistent performance in both rotation directions

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Instead of making the entire tooth flank asymmetric to match the worm gear, the invention uses a hybrid approach where only the concavely curved surface portion is asymmetric, while the helical surface portion maintains symmetry. This inverted strategy achieves contact region improvement without sacrificing rotation smoothness

Inventive Principle:

Principle #13The other way round (Inversion)

Data Source

PatentUS8991277B2Worm wheel

Publication Date: 2015.03.31 JTEKT CORP

AI summary

Each tooth of a worm wheel has a first tooth flank in which a helical surface portion is arranged on one side in a rotational axis direction of the worm wheel and a concavely curved surface portion is arranged on the other side in the rotational axis direction, and a second tooth flank in which a concavely curved surface portion is arranged on the one side in the rotational axis direction and the helical surface portion is arranged on the other side in the rotational axis direction.