Brushless DC Motor Segmented Rotor Torque Density
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Solution Overview
Problem
Existing brushless DC machines for lightweight vehicles require improvements in efficiency and cost-effectiveness, particularly in minimizing weight while maintaining structural integrity for high starting torque and variable assistance.
Innovation Solution
A lightweight direct-drive brushless DC motor with a 42-pole outer rotor and stator core featuring a high number of slots and teeth, using permanent magnet segments and a three-phase winding configuration, which reduces iron volume and weight while maintaining power output.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the number of poles and slots is increased to improve torque density and efficiency, then the machine becomes more complex and heavier
Solution Approach 1:
The rotor is segmented into multiple magnetic poles (40 or 44 poles) with permanent magnet segments, and the stator is segmented into multiple slots (42 slots) with distributed windings. This segmentation allows for higher torque density through increased pole-slot interactions while maintaining manageable complexity through modular construction and standardized components.
2Weight of moving object
If the iron volume is reduced to decrease weight, then the structural integrity and magnetic path may be compromised
Solution Approach 1:
The patent optimizes the iron volume by changing geometric parameters such as the number of poles (40 or 44), number of slots (42), and the arrangement of windings. These parameter changes reduce the overall iron volume and weight while maintaining adequate structural integrity through careful design of the magnetic circuit path and support structures.
Solution Approach 2:
The machine uses composite construction with permanent magnet segments embedded in the rotor, combining magnetic materials with structural materials. This allows for reduced iron volume while maintaining both magnetic performance and structural integrity through the composite nature of the rotor assembly.
3Power
If permanent magnets are used to improve efficiency and torque output, then the cost and manufacturing complexity increase
Solution Approach 1:
The permanent magnets are divided into multiple segments distributed around the rotor periphery. This segmentation allows for simpler individual magnet components that are easier and less costly to manufacture, while the collective arrangement maintains high efficiency and torque output. The segmented approach also simplifies assembly and replacement.
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 solution results in a more efficient and cost-effective motor with reduced weight, suitable for lightweight vehicles, achieving high starting torque and variable assistance with improved structural integrity.
Implementation Method 1
Some brushless DC machines use a permanent magnet external rotor with three phases of driving coils on the stator core. The coils are activated by the drive electronics, based on the detection signals from either the sensors or from the back electromotive force (EMF).
Implementation Method 2
A brushless DC machine is particularly well adapted to these kinds of applications. The apparatus includes an outer rotor with poles constructed with segments of permanent magnet material alternatively magnetized north and south.
Implementation Method 3
The position of the rotor is sensed with sensors (e.g., Hall effect sensors) and the associated drive electronics.
Data Source
AI summary
A direct-drive brushless DC motorization apparatus is provided. The apparatus includes an outer rotor having poles constructed with segments of forty or forty-four permanent magnets alternatively magnetized north and south. The outer rotor is adapted to be part of a wheel and is rotatable with respect to an axis of the wheel. The outer rotor is mounted about a stator core of ferromagnetic material and is separated from the stator core by a clearance gap. The stator core has forty-two slots, and adjacent slots are separated by teeth. A three-phase winding with coils of insulated wire is wound around the teeth of the stator core. The three-phase winding is divided in two sets of consecutive teeth for each of the three phases, with each of the two sets of a same phase being diametrically opposed in the stator core.