Brushless Motor Hall Sensor Positioning for Slim Fan Cooling
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Solution Overview
Problem
In slim cooling fans, the close proximity between the stator core and the Hall device or Hall IC hinders the sensing of the magnetic field generated by the rotor magnet due to strong magnetic flux attraction, leading to incorrect rotation control and potential impeller stoppage, especially at increased rotation speeds.
Innovation Solution
Optimizing the positional relationship between the Hall device or Hall IC, the stator core, and the rotor magnet by positioning the sensor element within a specific lead angle and radial distance range, ensuring accurate rotational position sensing and control, even in slim fan designs with limited axial dimensions.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Length of moving object
If the distance between the stator core and the Hall device or Hall IC is reduced to achieve a slim fan design, then the axial dimension is reduced, but the magnetic field sensing capability deteriorates due to strong magnetic flux attraction to the stator core
Solution Approach 1:
The patent applies local quality by creating a localized magnetic flux path through the protrusion structure on the stator core. The protrusion is positioned specifically between the rotor magnet and Hall device to guide magnetic flux away from the stator core surface, thereby locally modifying the magnetic field distribution only where needed while maintaining the overall slim design.
Solution Approach 2:
The protrusion structure acts as an intermediary element between the stator core and the Hall device. It mediates the magnetic flux by providing an alternative path that prevents direct attraction of magnetic flux to the stator core surface, thus protecting the Hall device's sensing capability while maintaining close proximity for slim design.
2Productivity
If the rotation speed of the impeller is increased to improve cooling performance, then the productivity is improved, but the magnetic field attraction to the stator core increases causing incorrect rotation control
Solution Approach 1:
The protrusion creates a localized modification in the magnetic flux path that specifically addresses the high-speed operation problem. By concentrating the flux guidance function in this localized structure, the patent ensures that even at high rotation speeds, the magnetic field remains stable and controllable near the Hall device.
Solution Approach 2:
The protrusion structure preemptively counteracts the harmful magnetic flux attraction that would otherwise occur at high speeds. By establishing this flux-guiding structure in advance, the patent prevents the deterioration of rotation control accuracy before it can occur during high-speed operation.
3Measurement precision
If the distance between the rotor magnet and the Hall device is reduced to improve sensing accuracy, then the measurement precision is improved, but the space between the stator core and Hall device becomes insufficient for slim design
Solution Approach 1:
The patent uses local quality by implementing the protrusion structure that creates a localized favorable magnetic environment. This allows the Hall device to be positioned close to the rotor magnet for accurate sensing, while the protrusion locally manages the magnetic flux to prevent stator core interference.
Solution Approach 2:
The protrusion structure introduces a dimensional solution by extending in the radial direction rather than requiring additional axial space. This allows the patent to maintain the slim axial dimension while creating the necessary magnetic flux management capability through radial protrusion.
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 allows for correct rotational control of the motor and impeller, maintaining performance even at increased rotation speeds, by ensuring the Hall device or Hall IC can effectively sense the magnetic field, thereby preventing impeller stoppage.
Implementation Method 1
the Hall device or the Hall IC senses a magnetic field (or a magnetic flux) generated by a rotor magnet
Data Source
AI summary
A rotor unit of a brushless motor includes a substantially cylindrical rotor magnet and a rotor holder arranged to retain an outer circumferential portion of the rotor magnet. A stator unit of the same includes a stator core around which coils are wound and a Hall IC for sensing magnetic flux generated from the rotor magnet. The stator core includes teeth disposed at positions separated in the circumferential direction, each of which has an arm portion extending outward in the radial direction around which the coil is wound, and a stretching portion extending from the arm portion outward in the radial direction and in the circumferential direction on both sides. A sensor element included in the Hall IC is positioned in the range within a lead angle of about four degrees or less as a mechanical angle in the circumferential direction from a line connecting radially the central axis and a point bisecting a line connecting neighboring stretching portions, and within a distance of about one millimeter or smaller outward in the radial direction from an arc connecting outer edges of the neighboring stretching portions.