Front-Bias Magnetic Speed Sensing With Stray-Field Shielding
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Solution Overview
Problem
Existing magnetic speed sensors, particularly Hall monocell sensors, are susceptible to stray-field disturbances and are expensive to manufacture due to the complexity of producing zero-gauss magnets, which are crucial for true-power-on functionality but require costly mold injection processes.
Innovation Solution
A magnetic sensor system utilizing a front-bias magnet with a radial magnetization direction and a magnetic sensor element aligned with this direction, encapsulated in a molded package, where the sensor is shielded by the toothed wheel, allowing for oscillating magnetic fields to be detected without external interference, and incorporating a differential sensing principle to cancel out stray fields.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a zero-gauss magnet is used for accurate position detection, then measurement precision is improved, but device complexity and manufacturing cost increase
Solution Approach 1:
The patent extracts the zero-gauss magnet from the system and replaces it with a conventional magnet combined with a ferromagnetic shield. The shield is positioned to block magnetic field lines, creating a zero-field region at the sensor location when no tooth is present, thereby achieving the same effect as a zero-gauss magnet without its manufacturing complexity
Solution Approach 2:
The ferromagnetic shield acts as an intermediary element between the conventional magnet and the sensor. It modifies the magnetic field distribution by concentrating flux lines within its structure, creating a controlled zero-field region that enables accurate position detection without requiring a specialized zero-gauss magnet
2Measurement precision
If a zero-gauss magnet is used for position detection, then measurement precision is improved, but manufacturing cost increases
Solution Approach 1:
The patent removes the expensive zero-gauss magnet from the system and substitutes it with a conventional magnet and ferromagnetic shield combination. This substitution dramatically reduces manufacturing cost while maintaining the ability to detect wheel position accurately through the creation of a zero-field region
Solution Approach 2:
The patent employs inexpensive conventional magnets and readily available ferromagnetic materials instead of costly specialized zero-gauss magnets. The simple shield structure can be easily manufactured using standard fabrication processes, making the overall system more cost-effective
3Ease of manufacture
If a conventional magnet is used, then manufacturing cost is reduced, but the sensor becomes sensitive to external stray fields
Solution Approach 1:
The patent converts the potential harmful effect of external stray fields into a beneficial configuration. The ferromagnetic shield is designed to preferentially attract and contain magnetic flux, including external stray fields, within its structure. This shielding effect protects the sensor from external magnetic interference while the conventional magnet provides the necessary bias field for operation
4Measurement precision
If a zero-gauss magnet is used, then position detection accuracy is improved, but reliability decreases due to temperature drift and mounting tolerance sensitivity
Solution Approach 1:
The patent extracts the temperature-sensitive zero-gauss magnet from the system and replaces it with a conventional magnet and ferromagnetic shield. The shield's geometry is designed to maintain a stable zero-field region that is less sensitive to temperature variations and mounting tolerances, thereby improving long-term reliability
Solution Approach 2:
The patent changes the approach from using a magnet with specialized magnetic properties (zero-gauss) to using a conventional magnet with a ferromagnetic shield. This parameter change in the magnetic circuit design creates a more stable system where the zero-field region is defined by the shield's physical geometry rather than by the magnet's magnetic properties, reducing sensitivity to temperature drift
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 system provides robust, twist-insensitive speed detection that is less affected by mounting tolerances and external magnetic interference, maintaining accuracy and reducing manufacturing costs by eliminating the need for complex zero-gauss magnets.
Implementation Method 1
a front-bias magnet arranged within the interior cavity of the toothed wheel, wherein the front-bias magnet is rotationally fixed and is magnetized with a magnetization direction that extends along a radial axis of the toothed wheel... a rotation of the toothed wheel causes the magnetic field to oscillate between a first extremum value and a second extremum value
Implementation Method 2
a magnetic sensor arranged exterior to the toothed wheel, wherein the magnetic sensor includes a first sensor element arranged on the radial axis that coincides with the magnetization direction of the front-bias magnet and the first sensor element is sensitive to a magnetic field of the front-bias magnet
Data Source
AI summary
A magnetic sensor system includes a toothed wheel configured to rotate about a rotation axis that extends in an axial direction, wherein the toothed wheel includes a plurality of teeth and a plurality of notches arranged that define a circumferential perimeter, wherein the toothed wheel further includes an interior cavity arranged within the circumferential perimeter; a front-bias magnet arranged within the interior cavity of the toothed wheel, wherein the front-bias magnet is rotationally fixed and is magnetized with a magnetization direction that extends along a radial axis of the toothed wheel; and a magnetic sensor arranged exterior to the toothed wheel, wherein the magnetic sensor includes a sensor element arranged on the radial axis that coincides with the magnetization direction of the front-bias magnet and the first sensor element is sensitive to a magnetic field of the front-bias magnet that is aligned with the radial axis.