External Rotor Motor Cooling With Axial Airflow Openings
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Solution Overview
Problem
High-speed external rotor motors with high torques face inefficiencies in cooling, which cannot be effectively addressed by standard cooling concepts, leading to suboptimal motor efficiency and economic viability.
Innovation Solution
An external rotor motor design featuring a stator with a non-rotatably mounted shaft, a rotatably mounted rotor bell with open spoke-like cooling blades, and a cooling device with axial flow openings between the shaft and stator core, utilizing a stator-side bearing shield with radially extending cooling vanes and a labyrinth seal for enhanced cooling and protection.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a closed or encapsulated motor housing with high IP degree of protection is used, then protection against environmental factors is improved, but cooling effectiveness deteriorates due to limited annular gap and sealed labyrinth seal
Solution Approach 1:
The bearing shield is segmented into a first shield portion and a second shield portion with a gap between them, creating multiple flow paths for cooling air. This segmentation allows cooling air to pass through the bearing shield structure while maintaining the sealed housing protection, resolving the contradiction between environmental protection and cooling effectiveness.
Solution Approach 2:
The bearing shield acts as an intermediary element between the sealed housing and the cooling air flow. It provides a controlled pathway for cooling air to reach the rotor and stator components while maintaining the overall sealed structure for environmental protection.
2Device complexity
If standard cooling concepts are used in external rotor motors with high torques and high speeds, then structural simplicity is maintained, but cooling effectiveness deteriorates leading to suboptimal motor efficiency
Solution Approach 1:
The bearing shield serves multiple functions: it provides mechanical support for rotation, enables cooling air flow through its segmented structure with gaps, and maintains structural simplicity. This multi-functionality improves motor efficiency without adding complex separate cooling mechanisms.
Solution Approach 2:
The bearing shield structure is designed to work dynamically with the rotating rotor, creating effective cooling air flow paths that adapt to the rotation. The gaps between shield portions allow cooling air to follow the rotational motion, enhancing cooling effectiveness for high-speed operation.
3Volume of moving object
If the annular gap between stator housing and external rotor is reduced for compact design, then motor compactness is improved, but cooling flow capability deteriorates
Solution Approach 1:
The cooling air flow is directed through the axial dimension via the bearing shield gaps rather than relying solely on the radial annular gap. This dimensional shift allows effective cooling flow through the compact radial space by utilizing the axial flow paths created by the segmented bearing shield structure.
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 design significantly enhances motor efficiency and cooling effectiveness, allowing for improved thermal management and increased motor utilization, particularly in high-torque applications, while maintaining structural stability and protection.
Implementation Method 1
A cooling device, which connects the shaft and the stator core, is arranged therebetween. It causes cooling when the motor rotates during operation. The cooling device has a plurality of axial flow openings arranged in the circumferential direction for this purpose.
Implementation Method 2
only a small annular gap remains, usually sealed via a labyrinth seal, where a cooling flow can be generated between the stator housing and the external rotor
Data Source
AI summary
An electric motor (1), in particular, an external rotor motor, has a stator (10) with a stator core (11), a non-rotatably attached shaft (20), that extends in the axial direction (A) of the motor, and a rotor bell (30), rotatably arranged relative to the non-rotatable shaft (20). The rotor bell (30) has cooling ribs in an open, spoke-like design rotatably mounted on the shaft (20) by at least one first stator-side bearing shield (31). A cooling device (40) is arranged between and connects the shaft (20) and the stator core (11). The cooling device (40) has a plurality of axial flow openings (41) arranged in the circumferential direction that causes cooling when the motor rotates during operation.