Earth Magnetic Field Sensor for TPMS Motion Detection
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Solution Overview
Problem
Current tire pressure monitoring systems (TPMS) face limitations in motion detection sensitivity, requiring calibration and being susceptible to electromagnetic interference, with acceleration sensors unable to detect vehicle motion below 20 km/h and shock sensors being costly and prone to breakage.
Innovation Solution
A magnetic sensor module that measures the Earth's magnetic field component, rotating about an axis to generate a sinusoidal signal, with a microcontroller calculating variance to determine motion, allowing for improved motion detection without the need for calibration or high-cost components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If acceleration sensors are used for motion detection, then motion detection capability is provided, but the minimum detectable speed is limited to 20 km/h due to offset error
Solution Approach 1:
The patent replaces the mechanical acceleration sensing system with a magnetic field sensing system. Instead of measuring mechanical acceleration and centrifugal force, the invention uses a magnetic sensor to detect changes in the Earth's magnetic field components as the vehicle moves, eliminating the offset error problem inherent in acceleration sensors.
Solution Approach 2:
The invention changes the measurement parameter from acceleration to magnetic field component magnitude. By measuring the magnitude of magnetic field components (Bx, By, Bz) projected on different axes and detecting their variations, the system achieves motion detection without the 20 km/h speed threshold limitation of acceleration-based systems.
2Measurement precision
If acceleration sensors require calibration to reduce offset error, then measurement accuracy improves, but manufacturing cost and time increase
Solution Approach 1:
The patent eliminates the need for calibration by replacing the acceleration sensor with a magnetic sensor. Magnetic field sensors do not suffer from offset drift and do not require the complex calibration processes (offset calibration, temperature calibration, sensitivity calibration) that acceleration sensors require during semiconductor production.
3Reliability
If shock sensors are used for motion detection, then motion detection is provided, but the device cost and PCB space increase
Solution Approach 1:
The patent merges the motion detection function with the existing magnetic sensor used for other purposes in the TPMS. The same magnetic sensor that measures magnetic field components for position identification is also used for motion detection by analyzing variations in magnetic field magnitude, eliminating the need for separate shock sensors and their associated signal conditioning circuitry.
Solution Approach 2:
The magnetic sensor serves multiple functions: it identifies wheel position through magnetic field direction detection and simultaneously detects vehicle motion through magnetic field magnitude variation detection. This multi-functionality eliminates the need for dedicated motion detection hardware, reducing PCB space and device complexity.
4Reliability
If shock sensors with signal conditioning circuitry are used, then motion detection capability is provided, but susceptibility to electromagnetic interference increases
Solution Approach 1:
The patent replaces the shock sensor system with high-impedance signal conditioning circuitry with a magnetic sensor system. Magnetic sensors inherently produce low-impedance signals that are much more resistant to electromagnetic interference, eliminating the EMI susceptibility problem of shock sensor systems.
5Reliability
If MEMS acceleration sensors are used, then motion detection is provided, but the risk of breakage due to mechanical resonance increases
Solution Approach 1:
The patent replaces the mechanical MEMS acceleration sensor with a magnetic field sensor. Magnetic sensors have no moving parts and are not susceptible to mechanical resonance or physical breakage, eliminating the durability issues inherent in MEMS acceleration sensors while maintaining motion detection functionality.
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
Enables robust motion detection at speeds below 20 km/h, reducing costs and energy consumption while avoiding calibration and breakage issues, with the magnetic sensor system effectively distinguishing between vehicle motion and stationary states.
Implementation Method 1
a magnetic sensor configured to measure a magnitude of a magnetic field component of an Earth magnetic field projected on a sensing axis of the magnetic sensor
Implementation Method 2
The magnetic sensor is further configured to rotate about an axis through the Earth magnetic field such that the measurement signal oscillates between a first extrema and a second extrema as the magnitude of the magnetic field component projected onto the sensing axis changes due to rotation
Data Source
AI summary
A sensor module is provided that includes a magnetic sensor and a microcontroller. The magnetic sensor is configured to measure a magnitude of a magnetic field component of an Earth magnetic field projected on a sensing axis of the magnetic sensor and is configured to generate a measurement signal. The magnetic sensor is configured to rotate about an axis through the Earth magnetic field such that the measurement signal oscillates between a first and second extremas as the magnitude of the magnetic field component projected onto the sensing axis changes due to rotation of the magnetic sensor about the axis. The microcontroller is configured to receive the measurement signal, acquire a predetermined number of measurement samples over a sampling period, calculate a variance value of the acquired measurement samples, and determine whether the magnetic sensor is rotating about the axis based on a threshold test of the variance value.