Frustoconical Rotor Cup Geometry for Lightweight Low-Noise Fan Motors
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Solution Overview
Problem
Reducing the thickness of the rotor cup in fan motors for motor vehicle heating, ventilation, and air conditioning systems to minimize weight results in a lower frequency of the first natural mode, leading to unacceptable noise levels.
Innovation Solution
A rotor cup design with a frustoconical shape, featuring a specific angle and ratio of dimensions, along with additional structural elements such as annular portions and openings, to enhance stiffness while maintaining a reduced axial bulk and weight, is implemented. The cup exhibits symmetry about an axis, with a major portion having a frustoconical shape and specific geometric features like arms and recesses to improve structural integrity.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Weight of moving object
If the thickness of the rotor cup is reduced to minimize weight, then the weight of the fan motor is decreased, but the frequency of the first natural mode of the cup decreases, causing unacceptable noise levels
Solution Approach 1:
The rotor cup is designed with a frustoconical shape instead of a conventional cylindrical shape. This curvature change modifies the natural frequency characteristics of the cup, allowing it to maintain higher natural frequencies even with reduced thickness, thereby reducing noise while keeping weight low.
Solution Approach 2:
The cup thickness is optimized locally rather than uniformly. The frustoconical geometry creates varying thickness distribution that enhances stiffness in critical areas while maintaining overall weight reduction. This local optimization prevents noise issues without requiring uniform thickness increase throughout the entire cup.
2Weight of moving object
If the thickness of the rotor cup is reduced to minimize weight, then the weight of the rotor cup is decreased, but the stiffness of the rotor cup is reduced
Solution Approach 1:
The frustoconical shape provides inherent structural stiffness through its geometric form. The sloped sides create a more rigid structure compared to a thin-walled cylinder, maintaining sufficient stiffness even when the overall thickness is reduced for weight savings.
Solution Approach 2:
The design transitions from a two-dimensional thin wall approximation to a three-dimensional frustoconical geometry. This dimensional change adds structural rigidity through the conical form, compensating for reduced material thickness and maintaining necessary stiffness while achieving weight reduction.
Data Source
AI summary
A cup (28) of a external rotor with symmetry of revolution about the axis comprises: a first cylindrical portion (68) which is radially internal, a second cylindrical portion (32) which is radially external and a third portion (70) between the two cylindrical portions (32, 68). When viewed in cross-section, the third portion (70) extends between two points (P1, P2) which define a straight line which forms, with the axis of the rotor cup (28), an angle (a) of between 65° and 80°. The ratio between the distance (R-P1, R-p2) between the first point (P1, P2) which is radially internal or radially external, respectively, and the axis of symmetry of the rotor cup (28), on the one hand, and the radius (R32) of the second cylindrical portion (32), on the other hand, is between 0.04 and 0.32 or between 0.65 and 1.0, respectively.