Cage Brush Assembly Spring Retention for Electric Motors
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Solution Overview
Problem
Constant force spring brush systems in electric motors can disconnect from the cage at the end of brush life, posing safety risks, especially in high voltage motors, due to the lack of a mechanism to prevent disconnection and potential electrical shocks and fires.
Innovation Solution
The cage is designed with fingers to capture the constant force spring, preventing disconnection and including a stopper to avoid coil entanglement or contact with electrical components, ensuring the spring remains securely attached throughout the brush's life cycle.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Duration of action of moving object
If a constant force spring is used to maintain brush pressure throughout brush life, then brush life is extended and brush pressure is maintained, but the spring may disconnect from the cage at end of brush life creating safety hazards
Solution Approach 1:
The cage is divided into functional sections including fingers that segment the spring retention mechanism. The spring itself is segmented into coiled end portions and a middle portion, with each segment serving a specific function in the retention and force application system.
Solution Approach 2:
The fingers act as an intermediary component between the spring and the cage body, providing a secure retention mechanism. The fingers capture the coiled end portions of the spring, preventing disconnection while allowing the spring to maintain constant force on the brush.
2Force
If the spring is allowed to extend freely to maintain constant force, then brush pressure is maintained, but the coil portions may become entangled or contact electrical components
Solution Approach 1:
Different portions of the spring have different structural qualities - the end portions are coiled for flexibility and force application, while the middle portion is substantially flat for stable engagement with the brush. The fingers provide localized constraint at specific points along the spring's path.
Solution Approach 2:
The fingers are positioned to preemptively capture the coiled end portions of the spring before they can become entangled or contact electrical components. This preliminary constraint prevents potential harmful actions while allowing the spring to extend and maintain force.
3Ease of manufacture
If the cage structure is simplified, then manufacturing is easier, but the spring retention and guidance functionality is compromised
Solution Approach 1:
The fingers serve multiple functions simultaneously - they retain the spring, guide its movement, prevent entanglement, and provide structural support. This multi-functionality is achieved through a simple geometric form that can be integrated into the cage manufacturing process.
Solution Approach 2:
The spring is constructed as a flexible ribbon of spring material that can be wound into coils at the ends while maintaining a flat middle portion. This flexible structure allows the spring to conform to the cage geometry and be retained by simple finger structures without requiring complex retention mechanisms.
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 design enhances safety and extends brush life by maintaining constant force application from new to worn-out states, preventing short circuits and ensuring reliable operation in high voltage motors.
Implementation Method 1
a spring for resiliently urging the brush along the path through the cage, wherein the spring is a constant force spring formed from a ribbon of resiliently deformable material
Data Source
AI summary
An electric motor 10 has a stator 14; a wound rotor 20, including a commutator 28; and brush gear for connecting the commutator to a source of electrical power. The brush gear has at least two cage brush assemblies 34. Each cage brush assembly 34 having a brush 40 for making sliding electrical contact with the commutator of the motor; a cage 50 for guiding the brush 40 along a path towards the commutator; and a spring 70 for resiliently urging the brush 40 along the path through the cage 50. The spring 70 is a constant force spring having two coiled end portions which engage the cage 50 at a commutator end portion. The cage 50 has two fingers about which the coiled end portions of the spring 70 locate.