Worm Reducer Labyrinth Structure for Grease Retention

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Solution Overview

Problem

Conventional worm reducers in electric power steering devices face issues with maintaining lubricity at the meshing portion between wheel teeth and worm teeth over a long period, as grease used for lubrication can be pushed out and escape into rolling bearings, reducing the effectiveness of lubrication.

Innovation Solution

The design incorporates a housing side step surface on the inner circumferential surface of the worm accommodating portion and a worm side step surface on the outer circumferential surface of the worm, creating a labyrinth effect that prevents grease from escaping, thus maintaining lubricity by ensuring it remains within the meshing portion.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If grease is used for lubrication at the meshing portion, then lubrication effectiveness is improved, but grease escapes into rolling bearings over time reducing lubrication effectiveness

Engineering Contradiction:

Improvelubrication effectivenessVSAvoidgrease retention

Core Design Contradiction:

ReliabilityVSLoss of substance

Solution Approach 1:

The worm accommodating portion is segmented into multiple chambers by partition walls, creating separate grease retention spaces. The first grease retention space is positioned between the worm teeth meshing portion and the rolling bearings, preventing grease from escaping into the bearings while maintaining lubrication at the meshing portion.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

Partition walls act as intermediary structures that selectively block grease flow paths. The partition walls are positioned to prevent grease from moving from the meshing portion into the rolling bearings, while still allowing the meshing portion to maintain adequate lubrication.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Device complexity

If a simple worm reducer structure is used, then device complexity is reduced, but grease escape into rolling bearings occurs

Engineering Contradiction:

Improvestructural simplicityVSAvoidgrease retention

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

The housing is divided into multiple chambers using partition walls that create distinct grease retention spaces. This segmentation approach adds minimal structural complexity while effectively preventing grease escape into the rolling bearings, maintaining reliability without significantly increasing device complexity.

Inventive Principle:

Principle #1Segmentation

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

This configuration effectively prevents grease from moving axially and escaping, maintaining lubricity for a longer duration and preventing interference between tooth surfaces, thereby reducing wear and ensuring reliable operation.

Implementation Method 1

creating a labyrinth effect that prevents grease from escaping

Methodology Applied

Scientific EffectLabyrinth effect:

Implementation Method 2

a coil spring 21 is provided between the pressing piece 20 and the worm accommodating portion 16. The distal end portion of the worm 14 is elastically pressed toward the worm wheel 13

Methodology Applied

Scientific EffectElasticity: Elasticity

Implementation Method 3

The proximal end portion of the worm 14 is supported to allow slight swing with respect to the worm accommodating portion 16 via the rolling bearing 19a on the proximal end side among the pair of rolling bearings 19a, 19b

Methodology Applied

Scientific EffectFriction: Friction

Data Source

PatentUS11466767B2Worm reducer

Publication Date: 2022.10.11 NSK LTD

AI summary

A worm reducer includes: a housing including a wheel accommodating portion, and a worm accommodating portion; a worm wheel including wheel teeth disposed on an outer circumferential surface and rotatably supported inside the wheel accommodating portion; and a worm including worm teeth disposed on an outer circumferential surface to mesh with the wheel teeth and rotatably supported inside the worm accommodating portion, wherein a proximal end portion of the worm is connected to a drive shaft such that torque can be transmitted. An inner circumferential surface of the worm accommodating portion includes a housing side step surface which faces a proximal end side in an axial direction of the worm. An outer circumferential surface of the worm includes a worm side step surface which closely faces the housing side step surface in the axial direction at a portion axially deviated from a portion where the worm teeth are disposed.