Electric Power Steering Motor Rotor Cogging Torque Reduction
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Solution Overview
Problem
Electric power steering (EPS) systems experience noise and vibration due to cogging torque and torque ripple, particularly at high speeds, which affect the motor's quality and stability.
Innovation Solution
A rotor with a cylindrical core and strategically positioned magnets, where the ratio of specific angles and curvatures of the magnet's inner and outer surfaces is optimized to reduce cogging torque, and a stator with teeth is designed to align with the rotor's magnet configuration, increasing the number of cogging torque wave vibrations per unit rotation to minimize these issues.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the magnet width is increased to improve torque output, then the motor power is improved, but the cogging torque and torque ripple increase causing noise and vibration
Solution Approach 1:
The patent applies parameter changes by optimizing the magnet width to a specific range (0.05D to 0.08D where D is the rotor outer diameter) and setting the number of magnets to 6 or 8. These specific parameter values create a balance where sufficient torque is generated while the cogging torque and torque ripple are minimized, resolving the contradiction between power output and harmful vibrations.
2Power
If the number of magnets is increased to improve torque, then the motor power is improved, but the device complexity and manufacturing difficulty increase
Solution Approach 1:
The patent determines the optimal number of magnets (6 or 8) based on mathematical relationships with the number of stator teeth. This parameter optimization ensures that sufficient torque is generated while avoiding excessive complexity in the rotor structure and manufacturing processes, thus resolving the contradiction between power output and device complexity.
3Object-affected harmful factors
If the magnet width is decreased to reduce cogging torque, then the noise and vibration are reduced, but the motor power decreases
Solution Approach 1:
The patent establishes that the magnet width should be within the specific range of 0.05D to 0.08D (where D is the rotor outer diameter). This optimized parameter range ensures that the magnet is narrow enough to minimize cogging torque and resulting noise/vibration, while still being wide enough to generate sufficient magnetic flux and maintain adequate motor power output.
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 significantly reduces cogging torque and torque ripple, enhancing motor stability and performance, especially at high speeds, by adjusting the magnet width and angle ratios within specific ranges, thereby improving the overall quality of the EPS system.
Implementation Method 1
The motor includes a stator and a rotor. The stator may include teeth which form a plurality of slots, and the rotor may include a plurality of magnets facing the teeth.
Implementation Method 2
a cogging torque may be generated due to a difference in magnetic permeability between the stator formed of a metal, and the slot open, which is an empty space when the rotor rotates.
Data Source
AI summary
The present invention provides rotor including: a rotor core having a cylindrical shape; and a plurality of magnets disposed to surround an outer circumferential surface of the rotor core, wherein the magnet includes an inner circumferential surface in contact with the outer circumferential surface of the rotor core, when a first angle is defined by dividing an angle formed by the outer circumferential surface of the rotor core by the number of magnets, a second angle is formed by a first extension line and a second extension line which extend from both end points of the inner circumferential surface of the magnet to a center point of the rotor core on cross sections of the rotor core and the magnet, and a ratio of the second angle to the first angle is in a range of 0.87 to 0.93, thereby providing an advantageous effect of greatly reducing a cogging torque by decreasing a width of the magnet to double a cogging main degree.