Magnet Shielding for Power Steering Sensor Accuracy
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Solution Overview
Problem
Conventional motor control apparatuses experience deterioration in magnetic sensor detection accuracy due to the influence of magnetic fields from bus bars, which is exacerbated by the magnetization of cover members made from magnetic materials during relative rotation.
Innovation Solution
A magnet-side shielding member made from magnetic material is provided on the outer periphery of the magnet, rotating integrally with it, to absorb and reduce the magnetic field interference from bus bars, thereby improving detection accuracy.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If a cover member made from magnetic material is used to shield the magnetic sensor from bus bar magnetic fields, then the magnetic field interference from bus bars is reduced, but the cover member becomes magnetized and generates its own magnetic field that interferes with the magnet's magnetic field during relative rotation
Solution Approach 1:
The patent extracts the shielding function from a separate cover member and integrates it into the magnet holder that rotates with the magnet. This eliminates the relative rotation between magnetic materials and the magnet, preventing the generation of interfering magnetic fields while maintaining shielding effectiveness.
Solution Approach 2:
The patent merges the magnet holder and magnet into a single integrated structure where the magnet holder rotates integrally with the magnet. This combination ensures that any magnetic material moves synchronously with the magnet, eliminating relative motion-induced magnetic interference.
2Object-affected harmful factors
If the magnet holder is made from magnetic material to provide shielding, then magnetic field absorption is improved, but the magnet may be damaged during press-fitting assembly
Solution Approach 1:
The patent segments the magnet holder into a magnetic material portion for shielding and a non-magnetic material portion for structural support and magnet protection. The non-magnetic portion acts as a protective sleeve during press-fitting, preventing direct impact on the magnet while the magnetic portion provides field shielding.
Solution Approach 2:
The patent uses composite construction for the magnet holder, combining magnetic material (for shielding) with non-magnetic material (for protection). This composite structure allows the holder to provide magnetic field absorption while the non-magnetic portion protects the magnet from mechanical damage during assembly.
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 solution effectively reduces magnetic field interference, enhancing the accuracy of the magnetic sensor and preventing deterioration, while also reducing the number of parts and potential damage to the magnet during assembly.
Implementation Method 1
a magnet-side shielding member configured to rotate integrally with a magnet and made from a magnetic material is provided on an outer peripheral side of the magnet
Implementation Method 2
detect a rotational angle of a motor rotor by detecting a change in a strength and a direction of a magnetic field of the magnet with use of a magnetic sensor
Data Source
AI summary
The prevent invention provides a motor control apparatus and a power steering apparatus capable of preventing or reducing deterioration of a detection accuracy of a magnetic sensor. A magnet holder configured to rotate integrally with a magnet and made from a magnetic material is provided on an outer peripheral side of the magnet provided so as to face a magnetic sensor.