Twist-Insensitive Magnetic Speed Sensor with Stray-Field Cancellation
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Solution Overview
Problem
Existing magnetic speed sensors, such as Hall monocell and differential Hall sensors, face challenges with stray-field robustness and twist-sensitivity, leading to performance issues in environments with external magnetic interference and during sensor mounting.
Innovation Solution
A magnetic sensor module with a differential pair of sensor elements and an axially polarized back bias magnet, generating a bias magnetic field that is redirected to create a loop, allowing for twist-insensitive and stray-field robust detection of rotational speed by canceling out homogeneous stray-fields and maintaining signal integrity across different mounting angles.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If Hall monocell sensor is used, then the sensor is twist-insensitive and assembly tolerances are relaxed, but the sensor has poor stray-field robustness
Solution Approach 1:
The sensor is divided into two separate Hall plates arranged in a differential configuration. Each Hall plate senses the magnetic field independently, and their outputs are subtracted to cancel homogeneous stray-fields while maintaining twist-insensitivity through geometric arrangement.
Solution Approach 2:
The two Hall plates are positioned at different locations with specific orientations relative to the back bias magnet. This local differentiation allows each plate to experience slightly different magnetic field conditions, enabling stray-field cancellation through differential measurement while maintaining insensitivity to rotational orientation.
2Object-affected harmful factors
If differential Hall sensor is used, then stray-field robustness is improved, but the sensor becomes twist-sensitive and signal decreases with twist angle
Solution Approach 1:
The two Hall plates are arranged asymmetrically with respect to the back bias magnet, with different orientations and positions. This asymmetric configuration creates a differential sensing pattern that cancels homogeneous stray-fields while maintaining insensitivity to rotational mounting angles through the specific geometric relationship between the plates.
Solution Approach 2:
The solution moves from a single-point sensing approach to a spatially distributed differential sensing approach. By arranging Hall plates in a specific geometric configuration in space, the system achieves both stray-field rejection and twist-insensitivity through the spatial relationship rather than relying on a single sensor orientation.
3Object-affected harmful factors
If differential Hall sensor is used, then stray-field robustness is improved, but the switching point changes requiring ECU reconfiguration
Solution Approach 1:
The back bias magnet and Hall plate geometry are designed in advance to generate a magnetic field pattern where the zero-crossing points occur at the same locations as traditional monocell sensors (at tooth edges). This preliminary design ensures compatibility with existing ECU switching logic without requiring reconfiguration, while still achieving stray-field robustness through the differential measurement.
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 provides a robust and twist-insensitive magnetic speed sensing system that maintains signal accuracy and reliability even in the presence of external magnetic fields and varying mounting orientations, without requiring reconfiguration of control units, thus enhancing the reliability and ease of installation.
Implementation Method 1
a back bias magnet including two opposing poles, where the back bias magnet is magnetized in a magnetized direction that is parallel to the in-plane axis and generates the bias magnetic field
Implementation Method 2
a first magnetic flux guide disposed at a first pole and configured to redirect a first portion of the bias magnetic field towards the magnetic sensor along the in-plane axis; and a second magnetic flux guide disposed at a second pole and configured to redirect a second portion of the bias magnetic field towards the back bias magnet along the magnetized direction
Implementation Method 3
a magnetic sensor having an in-plane axis and an out-of-plane axis, and includes a differential pair of sensor elements spaced apart from each other. The differential pair of sensor elements are configured to generate measurement values in response to sensing a bias magnetic field
Data Source
AI summary
A magnetic sensor module includes a magnetic sensor having an in-plane axis and an out-of-plane axis, and including a differential pair of sensor elements spaced apart from each other. The differential pair of sensor elements are configured to generate measurement values in response to sensing a bias magnetic field. The magnetic sensor module further includes a back bias magnet including two opposing poles, where the back bias magnet is magnetized in a magnetized direction that is parallel to the in-plane axis and generates the bias magnetic field; a first magnetic flux guide disposed at a first pole and configured to redirect a first portion of the bias magnetic field towards the magnetic sensor along the in-plane axis; and a second magnetic flux guide disposed at a second pole and configured to redirect a second portion of the bias magnetic field towards the back bias magnet along the magnetized direction.