Rotor Core Magnetic Pole Design for Torque Ripple Reduction
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Solution Overview
Problem
Existing brushless motors, particularly those of the interior permanent magnet type, face challenges in reducing torque ripple and cogging torque, which contribute to vibration and noise in electric power steering systems, due to non-sinusoidal magnetic flux distribution and high magnet costs.
Innovation Solution
A rotor core configuration using laminated plates with magnetic poles having bases and bridges, where the bridges are connected to the magnetic poles and protrude outward, forming a storage space for magnets, helps to reduce torque ripple by controlling the magnetic field distribution and minimizing magnet usage.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Quantity of substance
If rectangular magnets with uniform magnetization are arranged in the circumferential direction in an annular integral rotor core, then magnet cost is reduced, but the magnetic flux distribution becomes non-sinusoidal, causing increased torque ripple and cogging torque
Solution Approach 1:
The magnetic pole is divided into multiple regions with different properties: the tip portion has different magnetic permeability than the base portion, creating local quality variations that shape the magnetic flux distribution to be more sinusoidal while maintaining rectangular magnets throughout
Solution Approach 2:
The invention changes the magnetic permeability parameter of the magnetic pole tip portion relative to the base portion, creating a gradient or step change in magnetic properties that controls flux distribution without changing the magnet geometry or arrangement
2Force
If the air gap length is shortened to increase torque, then torque increases, but magnetic flux leakage from the magnet storage space bridge increases, reducing efficiency
Solution Approach 1:
The magnetic pole tip portion is given different magnetic permeability properties than the base portion, creating a local quality enhancement that guides and concentrates magnetic flux through the air gap while reducing leakage through the bridge structure
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 effectively reduces torque ripple and cogging torque, enhancing the performance of electric motors by improving magnetic field sinusoidality and reducing magnet costs, thus minimizing vibration and noise in electric power steering systems.
Implementation Method 1
the magnetic pole has a tip portion and a base portion, and a magnetic permeability of the magnetic pole tip portion is different from a magnetic permeability of the magnetic pole base portion
Implementation Method 2
an electromagnetic excitation force generated between the stator and the rotor of the electric motor
Implementation Method 3
the vibration energy due to the electromagnetic excitation force propagates into the vehicle interior via the mechanical parts of the EPS device
Data Source
AI summary
A torque ripple in a rotary electric machine is sufficiently reduced. At least two of the plurality of laminated plates in the rotor core include a magnetic pole having the base formed on the outer peripheral side of the storage space, and a bridge part connected to the magnetic pole. A plurality of magnetic poles are provided in the circumferential direction, and the first space is formed between the bases of a pair of magnetic poles adjacent in the circumferential direction. The q-axis outer peripheral portion, which is located between the pair of circumferentially adjacent magnetic poles and is in contact with the first space, is provided on the inner peripheral side of the base. The base includes the side surface portion which is in contact with the first space, and the protrusion which is provided on the outer peripheral side of the side surface portion and protrudes in the circumferential direction with respect to the side surface portion. The bridge are arranged on the inner peripheral side of the side surface portion.