Rotary Electric Machine Case Design for Magnetic Flux Leakage Control
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Solution Overview
Problem
The existing rotary electric machines suffer from reduced detection accuracy due to magnetic flux leakage, which affects the semiconductor magnetic sensor's performance, and the use of stamping to prevent magnetic saturation is costly and difficult to implement.
Innovation Solution
A rotary electric machine design with a specific case configuration, including a tubular portion, a ring-shaped plate portion, and a protrusion portion, which separates the bearing and bearing-supporting portion from the rotor core and detecting magnet, ensuring proper separation and reducing magnetic flux leakage, thereby maintaining detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If the gap between the bottom portion of the bottomed cylindrical case and the rotor core is excessively small, then the magnetic resistance of the gap decreases so that the magnetic flux passing through the bottomed cylindrical case increases, but the center portion becomes magnetically saturated and the magnetic flux leaked from the bottomed cylindrical case toward the semiconductor magnetic sensor increases
Solution Approach 1:
The invention transitions from controlling only the radial gap distance to a three-dimensional structural solution by adding axial dimension elements (protrusion portion and recessed portion) to the case design, thereby managing magnetic flux distribution in multiple spatial dimensions simultaneously
Solution Approach 2:
The protrusion portion and recessed portion act as intermediary magnetic flux management structures between the rotor core and the bottom portion, creating controlled magnetic flux paths that prevent direct leakage toward the sensor while maintaining necessary mechanical clearances
2Object-generated harmful factors
If the bottom portion is formed by stamping to have a thickness increasing in accordance with a decrease in distance to the center portion, then the center portion can be prevented from becoming magnetically saturated, but it is difficult to use stamping to form the bottom portion and a cost may increase
Solution Approach 1:
The bottom portion is segmented into functional zones: a protrusion portion extending toward the rotor core for magnetic flux management, a recessed portion for structural support, and a bearing-supporting portion for mechanical function. This segmentation allows each zone to be optimized for its specific purpose using standard manufacturing processes
Solution Approach 2:
Instead of continuously varying thickness (which is difficult to manufacture), the invention uses discrete structural parameters (protrusion height, recessed portion depth, bearing-supporting portion dimensions) to achieve magnetic flux control while maintaining manufacturability through standard deep drawing processes
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 restricts the reduction in detection accuracy by minimizing magnetic flux leakage and preventing magnetic saturation, while also reducing costs by using a deep drawing process for the magnetic shield.
Implementation Method 1
The detecting magnet is disposed at an end portion of the rotary shaft opposite to the rotor core with respect to the bearing, and generates a magnetism field for detecting a rotary position of the soft magnetic pole and the magnetic pole
Implementation Method 2
the semiconductor magnetic sensor may be a MR sensor including a magnetoresistive element
Data Source
AI summary
A motor includes a stator core fitted to a cylindrical portion of a case, a rotor core being rotatable in the stator core, soft magnetic poles radially extending from the rotor core, and magnet poles disposed between the soft magnetic poles. The case includes a bottom portion having a ring-shaped plate portion, a protrusion portion, and a bearing-supporting portion extending from the protrusion portion. A condition that L2≧t and a condition that L1≧L2 are met, wherein t represents a thickness of the bottom portion, L1 represents a distance in an axial direction between a side surface of the ring-shaped plate portion close to the stator core and a protrusion end of the protrusion portion close to the rotor core, and L2 represents a distance in the axial direction between the side surface and an end surface of a bearing opposite to the rotor core.