Ferrite Magnet Rotor With Cage Unit for EV High-Speed Torque
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Solution Overview
Problem
Permanent magnet motors used in electric vehicles face demagnetization issues due to high temperatures caused by eddy currents, leading to insufficient motor torque at high speeds, especially when using rare-earth magnets.
Innovation Solution
A motor design with a ferrite magnet permanent magnet unit, divided rotor parts, and a controller that switches between synchronous and asynchronous operation modes to manage temperature and torque requirements, using a cage unit to generate heat and reduce power consumption.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Force
If a permanent magnet motor is used to generate maximum motor torque in the slow rotation range, then the travel start capability is improved, but the motor torque becomes insufficient at high speed due to high counter electromotive force
Solution Approach 1:
The rotor is divided into two distinct parts: a permanent magnet unit for generating torque at low speeds and a cage unit for generating torque at high speeds. This segmentation allows each part to specialize in different speed ranges, resolving the contradiction between low-speed torque capability and high-speed performance.
Solution Approach 2:
The motor dynamically switches between synchronous operation mode (using permanent magnets) for low speeds and asynchronous operation mode (using cage unit) for high speeds. This dynamic operation strategy allows the motor to adapt to different speed requirements and maintain optimal torque output across the entire speed range.
2Volume of moving object
If the permanent magnet unit is disposed on the inner side of the cage unit in the rotor, then the motor structure is compact, but heat accumulates in the permanent magnet unit causing demagnetization
Solution Approach 1:
The invention converts the harmful eddy current effect into a beneficial heating source for the cage unit. By designing the cage unit to generate heat through eddy currents, the system creates a temperature differential that drives heat flow from the cage unit to the permanent magnet unit, preventing demagnetization while maintaining a compact structure.
Solution Approach 2:
The invention changes the material parameter of the permanent magnet unit from rare-earth magnets to ferrite magnets, which have higher temperature resistance. This parameter change allows the permanent magnet unit to withstand higher temperatures without demagnetization, resolving the contradiction between compact structure and temperature management.
3Force
If rare-earth magnets are used in the permanent magnet unit, then the motor torque is high, but the permanent magnet unit is susceptible to demagnetization at elevated temperatures
Solution Approach 1:
The invention uses ferrite magnets instead of expensive rare-earth magnets. While ferrite magnets have lower magnetic strength, the cage unit compensates for this by generating additional torque, especially at high speeds. This substitution reduces cost and improves temperature resistance without significantly compromising overall motor performance.
Solution Approach 2:
The motor uses a composite structure combining ferrite permanent magnets with a copper cage unit. The ferrite magnets provide stable low-speed torque with temperature resistance, while the copper cage unit provides high-speed torque through eddy current effects. This composite approach resolves the contradiction between torque requirements and temperature resistance.
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
Prevents demagnetization of the permanent magnet unit by using ferrite magnets, ensures sufficient motor torque across speed ranges, and reduces power consumption by switching operation modes based on torque demands.
Implementation Method 1
the permanent magnet unit is formed by a ferrite magnet
Implementation Method 2
when an eddy current is produced in the permanent magnet unit by the rotating magnetic field of the stator
Implementation Method 3
when an eddy current is produced in the permanent magnet unit by the rotating magnetic field of the stator
Implementation Method 4
the temperature of the permanent magnet unit is more likely to rise than the typical permanent magnet motor
Implementation Method 5
a stator having a cylindrical shape and a rotor having a cylindrical shape provided in the stator so as to be rotatable
Data Source
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AI summary
[Problem] To provide a motor and a vehicle driving system that can prevent demagnetization of a permanent magnet unit. [Means for Solution] A motor 2 includes a stator 17 having a cylindrical shape and a rotor 19 having a cylindrical shape provided in the stator 17 so as to be rotatable about an axis that is the same as a central axis of the stator 17 and is used to drive a front wheel FW of a vehicle 1 by rotation of the rotor 19. The motor 2 has a cage unit 31 provided for the rotor 19 and a permanent magnet unit 28 provided for the rotor 19 on an inner side of the cage unit 31. The permanent magnet unit 28 is formed by a ferrite magnet.