Spring Stop Post for Power Tool Brush Card

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Solution Overview

Problem

The existing brush assemblies in power tools are prone to spring disengagement during drops due to the heavy mass of the brushes overcoming the spring force, leading to incorrect or complete dislocation of the spring from its position, which compromises the electrical contact with the commutator.

Innovation Solution

Incorporating a spring stop post near each brush holder to limit the radial movement of the spring, ensuring it remains engaged with the brush groove both during assembly and under impact conditions, thereby maintaining effective electrical contact.

Engineering Contradictions & Design Principles

VSEngineering Contradiction Analysis

1Reliability

If the spring force is increased to prevent disengagement during drops, then the reliability of electrical contact is improved, but the brushes may be damaged and their lifespan reduced

Engineering Contradiction:

Improveelectrical contact reliabilityVSAvoidbrush durability

Core Design Contradiction:

ReliabilityVSStrength

Solution Approach 1:

The spring assembly is segmented into multiple components: the spring body, the leg portion, and the distinct stop post feature. This segmentation allows the stop post to independently limit spring expansion while the spring maintains its biasing force on the brush, resolving the contradiction between reliability and brush durability.

Inventive Principle:

Principle #1Segmentation

Solution Approach 2:

The stop post acts as an intermediary element between the spring and the brush card mount. It mediates the spring force by providing a mechanical stop that prevents excessive spring expansion, thereby protecting the brush from damage while maintaining sufficient contact force for reliable electrical contact.

Inventive Principle:

Principle #24Intermediary (Mediator)

2Ease of operation

If the spring is allowed to move freely to accommodate brush wear, then the ease of operation is improved, but the spring may disengage during impact events

Engineering Contradiction:

Improvebrush adjustment rangeVSAvoidspring engagement stability

Core Design Contradiction:

Ease of operationVSReliability

Solution Approach 1:

The spring assembly is designed to be dynamic, allowing free movement and expansion to accommodate brush wear during normal operation. The stop post provides a dynamic limit that only engages during extreme conditions such as drops, allowing the system to adapt to different operational states.

Inventive Principle:

Principle #15Dynamics

Solution Approach 2:

The stop post provides beforehand protection by limiting the maximum expansion of the spring before disengagement can occur. This preemptive mechanical stop cushions against the harmful effects of impact events, preventing the spring from disengaging during drops while allowing full range of motion during normal use.

Inventive Principle:

Principle #11Beforehand cushioning (Prior cushioning)

3Reliability

If a spring stop post is added to limit radial movement, then the spring engagement stability is improved, but the device complexity increases

Engineering Contradiction:

Improvespring position stabilityVSAvoidbrush assembly structure

Core Design Contradiction:

ReliabilityVSDevice complexity

Solution Approach 1:

The stop post is merged with the spring leg to form an integrated feature. Rather than being a separate component, the stop post is formed as part of the spring assembly itself, reducing the number of parts and simplifying the overall structure while maintaining the reliability benefit of limited radial movement.

Inventive Principle:

Principle #5Merging (Combining)

Solution Approach 2:

The spring assembly is designed with multi-functionality: the leg portion provides both the mounting function for attaching the spring to the brush card mount and the structural support for the stop post feature. This universal design consolidates multiple functions into a single integrated component, reducing device complexity.

Inventive Principle:

Principle #6Universality (Multi-functionality)

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 spring stop post effectively prevents the spring from backing out of its proper position, ensuring consistent electrical contact with the commutator even during drops, optimizing spring force for motor commutation without damaging the brushes or reducing their lifespan.

Implementation Method 1

Each spring includes an extended arm that engages a back surface of brush inside the brush holder to bias the brush towards the center of the brush card

Methodology Applied

Scientific EffectSpring force: Spring

Implementation Method 2

the distal end of the leg of the spring includes a hook engaging the groove of the brush

Methodology Applied

Scientific EffectMechanical engagement: Hook

Data Source

PatentEP3018799B1Spring post for brush card for a power tool

Publication Date: 2020.04.15 BLACK & DECKER CORP

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AI summary

An electric motor is provided including a stator and an armature rotatably received within the stator, the armature having an armature shaft on which a commutator is mounted. The motor also includes a brush assembly having a brush card mount disposed around the commutator, a brush holder mounted on a surface of the brush card mount, and a brush disposed within the brush holder in sliding contact with the commutator to supply electric current to the commutator. A torsion spring is secured to the brush card mount adjacent the brush holder, the spring having a leg arranged to engage the back surface of the brush. A spring stop post is disposed proximate an outer periphery of the brush card mount to limit an outward movement of the leg of the spring away from the back surface of the brush.