Asymmetric Rotor Bell Rigidity for Quieter Outrunner Motors
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Solution Overview
Problem
Outrunner motors suffer from noise and vibration issues due to low natural frequencies and inadequate damping in their rotor bell structure, which is exacerbated by strong magnetic forces and imperfections in geometry and material, leading to resonance and increased vibration amplitudes.
Innovation Solution
The rotor bell is designed with asymmetrical tilting rigidity by varying its thickness or material distribution, with the center of gravity on the axis of rotation, and incorporating a ring-shaped damping element to separate tilting natural frequencies and enhance damping, reducing noise and vibrations.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the rotor bell is configured with thinnest possible walls to keep mass moment of inertia low, then the mass moment of inertia is reduced, but the rigidity decreases which favors vibrations
Solution Approach 1:
The rotor bell is designed with asymmetrical thickness distribution around its circumference. By making the wall thickness non-uniform, the structure achieves different local rigidities that help suppress vibrations while maintaining overall low mass. The asymmetrical design creates an uneven stiffness profile that disrupts resonant vibration modes.
Solution Approach 2:
Different regions of the rotor bell are given different wall thicknesses to optimize local properties. Areas subject to higher vibrational stresses are reinforced with greater thickness, while other areas maintain thinner walls to minimize mass. This local differentiation allows the structure to achieve adequate rigidity where needed while keeping overall mass low.
2Weight of moving object
If the rotor bell and bearing have very little damping, then the mass moment of inertia is kept low, but the vibration amplitude increases strongly near resonance
Solution Approach 1:
The asymmetrical thickness distribution creates an uneven damping profile around the rotor bell circumference. This asymmetry in damping characteristics helps to spread out and reduce the amplitude of resonant peaks by preventing uniform vibration modes, thereby reducing the maximum vibration amplitude experienced during operation.
3Object-generated harmful factors
If the rotor bell has asymmetrical tilting rigidity, then the tilting natural frequencies are strongly separated and damping is increased, but the manufacturing complexity increases
Solution Approach 1:
The rotor bell incorporates asymmetrical features in its thickness distribution and rib configurations to create different tilting rigidities in different directions. This asymmetry causes the natural frequencies corresponding to different tilting modes to be well-separated, preventing resonance between modes and reducing overall vibration and noise levels.
Solution Approach 2:
The rotor bell is divided into multiple segments or ribs with different thicknesses and orientations. This segmentation allows independent optimization of rigidity in different directions, creating the desired asymmetrical tilting rigidity. The rib structure acts as discrete elements that can be independently designed to achieve the target stiffness characteristics.
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 vibration amplitudes and noise by splitting resonance peaks and increasing damping, resulting in quieter and more balanced motor operation.
Implementation Method 1
incorporating a ring-shaped damping element to separate tilting natural frequencies and enhance damping, reducing noise and vibrations
Data Source
AI summary
The outrunner motor includes a rotor housing designed as a rotor bell with rotor poles situated in the rotor bell. The rotor bell is mountable in a stator of the outrunner motor so as to be rotatable about an axis of rotation and exhibits a rigidity that is asymmetrical in relation to the axis of rotation, in particular an asymmetrical tilting rigidity. The outrunner motor also has a motor shaft, a stator with a plurality of stator teeth, and a rotor surrounding the stator. The rotor allows the outrunner motor to be quieter and have lower levels of vibration. The center of gravity of the rotor bell is located on an axis of rotation.