DC Motor Magnet Thickness Optimization for Length Reduction
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Solution Overview
Problem
DC motors used in electrical power tools face challenges in reducing total length while maintaining performance and extending life, as the use of low-cost magnets results in weaker magnetic fields and increased armature reaction, leading to shorter motor life.
Innovation Solution
A DC motor design with a magnet having a maximum energy product of 3 to 6 MGOe, where the ratio of magnet thickness to core outer diameter is 0.16 or more, and the ratio of core thickness to yoke outer diameter is less than 0.60, enhancing the magnetic field strength and alleviating armature reaction, thereby reducing total length and extending motor life.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of stationary object
If a low-cost magnet with reduced volume is adopted to reduce motor total length, then cost is reduced and total length is reduced, but magnetic field strength becomes weak and armature reaction increases leading to shorter motor life
Solution Approach 1:
The patent changes the geometric parameters of the magnet, specifically setting the ratio of magnet thickness to core outer diameter (T/d) to be 0.16 or more. This parameter optimization allows the magnet to generate sufficient magnetic field strength even with reduced volume, thereby maintaining motor life while achieving compact dimensions. The specific parameter range (T/d ≥ 0.16) was determined to balance magnetic field generation capability with spatial constraints.
2Length of stationary object
If a low-cost magnet with reduced volume is adopted to reduce motor total length, then cost is reduced and total length is reduced, but magnetic field strength becomes weak requiring enhanced armature magnetic field
Solution Approach 1:
The patent optimizes the magnet thickness parameter T to maintain adequate magnetic field strength. By setting T/d ≥ 0.16, the design ensures that the magnet retains sufficient volume to generate the required magnetic field, avoiding the need for excessive armature enhancement while achieving length reduction.
3Length of stationary object
If magnet volume is reduced to reduce total length, then total length is reduced, but the ratio of magnet magnetic field strength to armature magnetic field strength decreases
Solution Approach 1:
The patent maintains the magnetic field strength ratio by optimizing the magnet thickness parameter T. The condition T/d ≥ 0.16 ensures that even with reduced magnet volume, the magnetic field generated by the magnet remains sufficiently strong relative to the armature field, maintaining stable motor operation and preventing excessive armature reaction.
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 allows for a reduction in motor length while maintaining performance and extending motor life by increasing the magnet volume and reducing armature reaction, resulting in fewer sparks and longer brush and motor life.
Implementation Method 1
a magnet that is provided along the inner surface of the yoke and has four or more of magnet poles in the circumferential direction
Implementation Method 2
an armature that is arranged to face the magnet and composed of a core and a coil
Data Source
AI summary
A DC motor comprises: a tubular metal case; a magnet that is provided along the inner surface of the metal case and has four or more of magnet poles in the circumferential direction; an armature that is arranged to face the magnet and composed of a core and a coil; and a shaft. The magnet is formed of a material with a maximum energy product BHmax of 3 to 6 MGOe. When the thickness of the magnet in the radial direction of the armature is indicated by T [mm] and the outer diameter of the core is indicated by d [mm], the ratio T/d of the thickness T of the magnet to the outer diameter d of the core is 0.16 or more.