Rotor Bell Cover Plate for Fan Cooling Noise Reduction
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Solution Overview
Problem
Fans with external rotor motors experience increased noise levels when an additional cooling airflow is introduced through the rotor bell, which is not effectively mitigated by existing designs.
Innovation Solution
A fan design featuring a rotor bell with apertures for cooling airflow, combined with a cover plate that guides the airflow radially inward and outward, reducing noise by altering the flow direction and utilizing an overextension and overlap section to enhance airflow treatment, thereby minimizing acoustic deterioration.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If a cooling air flow is introduced through the rotor bell to cool motor components, then the cooling effect is improved, but the noise level of the fan increases
Solution Approach 1:
The cover plate acts as an intermediary element between the cooling air flow and the main volume flow. It guides the cooling air flow through a specific path (radially inward through the flow channel, then radially outward through the central opening) before mixing with the main flow, thereby mediating the interaction between cooling requirements and noise reduction
Solution Approach 2:
The cover plate features an inclined or curved outer surface that the cooling air flow contacts. This curved surface geometry redirects the cooling air flow in a controlled manner, changing its direction from purely axial to having both radial and axial components, which reduces turbulence and noise when the flow is released into the main volume flow
2Temperature
If cooling bores are provided in the rotor bell to enable cooling air flow, then the cooling capability is improved, but the device complexity increases
Solution Approach 1:
The cover plate serves multiple functions: it covers the apertures in the rotor bell base, guides the cooling air flow radially inward and outward, provides a curved surface for flow redirection, and facilitates the integration of cooling air flow into the main volume flow. This multi-functionality reduces the need for additional separate cooling components
Solution Approach 2:
The cooling air flow path is segmented into distinct zones: the axial flow through apertures, the radial inward flow through the flow channel between the rotor bell base and cover plate, and the radial outward flow through the central opening. This segmentation allows for controlled flow management at each stage
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 design effectively reduces noise levels by redirecting the cooling airflow, ensuring it is integrated into the main volume flow without increasing acoustic noise, while maintaining effective cooling of motor components.
Implementation Method 1
By the cover plate, the cooling air flow is here guided in a particular manner, namely from the axial outflow through the at least one aperture, first radially inward in the flow channel delimited by the cover plate, up to the central opening thereof, and subsequently in the opposite direction radially outward
Implementation Method 2
Due to the radially outward inclined or curved course of the outer surface of the cover plate in the direction of the rotor bell base, the direction of the cooling air flow, in addition to the radial component, also experiences an axial component along the outer surface of the cover plate. The flow direction of the cooling air flow here advantageously is in contact with the outer surface of the cover plate
Data Source
AI summary
A fan comprising a fan wheel with impeller hub and impeller blades, and electric motor with a stator and rotor that can rotate about rotation axis (RA) and has a rotor bell comprising an axially front-side rotor bell base. Impeller hub is fastened to the rotor bell wherein, in the rotor bell base, at least one aperture ensures a cooling air flow from the rotor bell. Fan comprises a cover plate arranged on the rotor bell base with a central opening, wherein cover plate covers at least one aperture of the rotor bell base axially spaced at least in sections, so that between the rotor bell base and an inner surface of the cover plate a radially inward extending flow channel toward the central opening of the cover plate is formed. The cover plate radially outward comprises an inclined or curved course in the direction of the rotor bell base.