Compact Axial Fan with Nested Inner-Rotor Motor
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Solution Overview
Problem
Existing axial fans with inner-rotor motors are not axially compact, and custom outer-rotor motor designs for compact applications are costly and time-consuming to develop, while prior art inner-rotor fans with reverse flow cooling can have adverse impacts on airflow.
Innovation Solution
An axial fan design featuring an inner-rotor motor with an overhung impeller having an axially deep cup surrounding the drive end, detachable support struts, and optional hub deflectors for airflow management, incorporating through-holes for reverse flow cooling to ventilate the motor cavity, resulting in a compact and thermally efficient design.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If an inner-rotor motor is used in an axial fan, then the motor can be mass-produced with better efficiency, but the axial length of the fan increases significantly
Solution Approach 1:
The impeller cup is nested over the drive end of the inner-rotor motor, with the cup extending axially beyond both ends of the motor. This nesting arrangement allows the motor and impeller to occupy overlapping axial spaces, reducing the total axial length of the fan while maintaining the benefits of the inner-rotor motor configuration.
Solution Approach 2:
The support struts extend radially outward from the drive end of the motor to connect to the shroud, utilizing the radial dimension for motor support rather than requiring additional axial length. This dimensional transition allows compact axial packaging while maintaining structural support.
2Length of moving object
If a custom outer-rotor motor design is developed for compact applications, then the axial length is reduced, but the development time and expense increase significantly
Solution Approach 1:
The inner-rotor motor configuration with the impeller cup nested over the drive end serves multiple functions: it provides compact axial packaging, enables mass production using standard motor components, and maintains efficient airflow. This universal design approach eliminates the need for custom outer-rotor motor development while achieving compact dimensions.
3Temperature
If the impeller cup is made axially deep to surround the motor, then thermal characteristics improve, but the device complexity increases
Solution Approach 1:
The impeller cup is merged with the impeller blades and hub to form an integrated impeller assembly. The cup itself serves as both a structural component and a thermal management feature, eliminating the need for separate cooling structures and reducing overall device complexity while improving thermal 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
The design achieves an axially compact fan with improved thermal characteristics and simplified motor replacement, suitable for applications with limited space, while maintaining efficient airflow and cooling capabilities.
Implementation Method 1
a pressure difference between the upstream and downstream ends of the impeller induces a portion of the airflow to flow through a number of openings in the downstream end of the impeller cup, through an annular space between the outer surface of the motor and the inner surface of the impeller cup, and back into the main flowpath
Implementation Method 2
a portion of the airflow (which is sometimes referred to as a bleed stream) to flow upstream through a number of inlet openings in the downstream end of the impeller cup, through the motor and back into the main flowpath
Data Source
AI summary
An axial fan has an inner-rotor motor which includes a drive end, a non-drive end and a shaft which extends axially from the drive end; and an impeller which includes a cylindrical impeller cup and a number of impeller blades that extend radially from the impeller cup. The impeller cup has an open upstream end and a closed downstream end which is connected to the shaft. In operation, the motor spins the impeller to generate an airflow in a direction from the non-drive end of the motor to the drive end of the motor. The impeller cup is configured to receive the motor therein and surround the drive end of the motor but not the non-drive end of the motor. As a result, the non-drive end of the motor is exposed to the airflow during operation of the fan.