Brushless Machine Rotor Yoke Segmentation for Demagnetization
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Solution Overview
Problem
Brushless electrical machines with permanent magnet excitation face reduced power output and increased mass due to reduced reluctance in the air gap, increased cross magnetic flux, and diversion of magnetic flux to the rotor yoke, leading to demagnetization and higher electrical losses.
Innovation Solution
The rotor yoke is divided into equal parts with non-magnetic discs and tapered edges forming void spaces with a large base-to-small base ratio greater than 10, allowing the magnetic flux to pass directly through the air gap, reducing cross magnetic fields and inductive reactance, and increasing resistance to demagnetization.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If permanent magnets are used in the rotor yoke, then the machine generates strong magnetic flux, but the cross magnetic flux increases and causes demagnetization
Solution Approach 1:
The rotor yoke is divided into multiple segments separated by non-magnetic strips, which segment the magnetic flux paths and reduce the cross magnetic flux that causes demagnetization of permanent magnets
Solution Approach 2:
Non-magnetic strips are introduced as intermediary elements between adjacent permanent magnets to block the cross magnetic flux paths, preventing demagnetization while allowing the magnets to generate strong magnetic flux
2Power
If the air gap between rotor and stator is reduced, then the magnetic flux density increases, but the inductive reactance of stator winding increases
Solution Approach 1:
The rotor yoke is segmented into multiple parts with non-magnetic strips between them, which reduces the inductive reactance of the stator winding by modifying the magnetic flux distribution, thereby reducing inductive voltage drop while maintaining high magnetic flux density
3Power
If more permanent magnets are added to increase power, then the mass of the machine increases
Solution Approach 1:
The invention changes the geometric parameters of the rotor yoke segments and the arrangement of permanent magnets to optimize the magnetic flux utilization, achieving higher power output with reduced mass of permanent magnets
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 power output by maximizing magnetic flux utilization, reducing electrical losses, and minimizing the mass of active components, while maintaining resistance to demagnetization even at higher pole counts.
Implementation Method 1
the increased reluctance in the path of this magnetic field through the created void non-magnetic spaces between adjacent parts of the rotor yoke
Implementation Method 2
the magnetic flux generated by the permanent magnets... even at an increased number of poles
Implementation Method 3
the magnetic flux generated by the stator winding
Data Source
Figure 1
Figure 2
AI summary
The machine is designed for traction motors in electrically driven vehicles, for regulable motors for drives in machine tools with CNC and for other servo-drives and generators running into overload duty. It provides reduced mass at increased resistance of the magnets against demagnetization at higher torque overloads. The rotor yoke / 2 / is divided into parts / 13 /, which are fixed on the non-magnetic disks / 14 /. On each two adjacent edges / 15 / of the parts / 13 / of the rotor yoke / 2 / is formed a common mounting pad /16 /, on which is located a permanent magnet / 3 /. The edges of the parts / 13 / are tapered and between them are formed void spaces / 17 / with a trapezoidal cross-section with small base A1 near the permanent magnet / 3 / and with a larger base A2, adjacent to non-magnetic disks / 14 /. The ratio of the larger base A2 towards the small base A1 is greater than 10.