String Trimmer Head Coupling for Low Vibration and Wear

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Solution Overview

Problem

Conventional string trimmers experience vibration and wear issues due to the lack of effective coupling between the housing and spool components, leading to damage and inefficient line dispensing.

Innovation Solution

A trimmer head design featuring a rotatable housing with a spool driven by a nut insert molded into the spool, a retainer with interlocking teeth, and wear rings to minimize vibration and protect against surface contact, allowing for smooth line dispensing and reduced wear.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Device complexity

If conventional string trimmers use simple coupling between housing and spool, then device complexity is reduced, but vibration and wear increase due to lack of effective coupling

Engineering Contradiction:

Improvecoupling structure complexityVSAvoidvibration and wear resistance

Core Design Contradiction:

Device complexityVSReliability

Solution Approach 1:

A coupling member with gear teeth is introduced as an intermediary component between the spool and housing. This coupling member engages with corresponding teeth on both the spool and housing, providing effective mechanical coupling that reduces vibration and wear while maintaining reasonable device complexity.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Productivity

If the spool is securely coupled to the drive shaft, then line dispensing efficiency improves, but manufacturing complexity increases due to insert molding process

Engineering Contradiction:

Improveline dispensing efficiencyVSAvoidmanufacturing process simplicity

Core Design Contradiction:

ProductivityVSEase of manufacture

Solution Approach 1:

The coupling member is insert molded directly into the spool, merging two components into a single integrated part. This secure coupling improves line dispensing efficiency while the insert molding process, though adding manufacturing complexity, creates a durable and reliable connection that simplifies assembly.

Inventive Principle:

Principle #5Merging (Combining)

3Duration of action of stationary object

If wear rings are added to protect housing from surface contact, then durability improves, but device complexity and manufacturing cost increase

Engineering Contradiction:

Improvehousing durabilityVSAvoidnumber of protective components

Core Design Contradiction:

Duration of action of stationary objectVSDevice complexity

Solution Approach 1:

Wear rings are installed on the housing as protective elements that contact the ground surface first, preventing direct contact between the housing and abrasive surfaces. This beforehand protection extends housing durability while the wear rings can be replaced independently when worn.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

4Strength

If the retainer with interlocking teeth is used to engage spool and housing, then mechanical coupling strength increases, but manufacturing precision requirements increase

Engineering Contradiction:

Improvemechanical coupling strengthVSAvoidteeth engagement precision

Core Design Contradiction:

StrengthVSManufacturing precision

Solution Approach 1:

The coupling member with gear teeth serves as an intermediary that distributes mechanical loads across multiple tooth engagements between the spool and housing. This increases mechanical coupling strength while the modular tooth design allows for tolerance compensation, reducing the impact of manufacturing precision variations.

Inventive Principle:

Principle #24Intermediary (Mediator)

Data Source

PatentUS12582029B2String trimmer head

Publication Date: 2026.03.24 MILWAUKEE ELECTRIC TOOL CORP

AI summary

A trimmer head for use with a string trimmer including a drive shaft includes a housing rotatable about a rotational axis. The housing includes a main body defining a cavity, and a cap removably coupled to the main body. The trimmer head further includes a spool supported in the cavity and operable to support line to be dispensed, a retainer positioned between the housing and the spool, and a nut positioned within the spool and configured to drivingly couple to the drive shaft.