Adaptive Time Watchdog for 0 Hz ABS Sensor Detection
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Solution Overview
Problem
Current rotation speed sensors based on Hall or xMR technology cannot simultaneously meet customer requirements for large magnetic air gap, specific duty ratio, low output jitter, and 0 Hz capability at reasonable costs for applications like indirect tire pressure monitoring and Hill-holder functionality.
Innovation Solution
A rotation speed sensor design incorporating a sensor element, time watchdog with programmable time constant, and output control circuit that adapts to changes in magnetic input signals, including an analog signal processing block and asynchronous logic to manage signal processing and output switching, ensuring compatibility with existing systems without additional circuit or algorithm costs.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Speed
If a rotation speed sensor uses conventional Hall or xMR technology with fixed time constants, then it can detect magnetic signals at normal speeds, but it cannot maintain reliable detection at very slow speeds or 0 Hz conditions
Solution Approach 1:
The patent implements a time watchdog mechanism with dynamically adjustable time constants that adapt to different operating conditions. The system switches between a first time constant for normal speeds and a second, longer time constant for slow speeds or 0 Hz conditions, enabling reliable detection across the entire speed range without losing synchronization at low speeds.
Solution Approach 2:
The patent changes the time constant parameter of the watchdog timer based on detected signal conditions. When slow speed or 0 Hz conditions are detected, the system transitions to a longer time constant to maintain proper signal sampling and detection, thereby expanding the operational speed range while maintaining reliability.
2Measurement precision
If the sensor operates with fixed time constants optimized for normal speeds, then it achieves good performance at typical operating speeds, but it fails to detect signals reliably at very slow speeds or when stationary
Solution Approach 1:
The system dynamically adjusts the watchdog time constant based on the operational mode detected by the control unit. When the sensor detects slow speed or 0 Hz conditions, it switches to a longer time constant optimized for those conditions, thereby maintaining measurement precision across diverse operating conditions including stationary states and very slow movement.
Solution Approach 2:
The dual time constant watchdog mechanism provides universal adaptability across multiple operating conditions. The same sensor hardware can accurately measure speeds from 0 Hz to high speeds by automatically selecting the appropriate time constant, eliminating the need for separate detection mechanisms for different speed ranges.
3Speed
If the time watchdog uses a long time constant to detect slow signals, then it can detect 0 Hz conditions, but it increases the time interval and may cause pulse loss at normal speeds
Solution Approach 1:
The system dynamically selects the appropriate time constant based on the current speed condition. At normal speeds, the shorter first time constant ensures rapid detection with minimal time intervals. When slow speed or 0 Hz conditions are detected, the system switches to the longer second time constant to maintain detection capability, thereby optimizing the time interval for each operational condition.
Solution Approach 2:
The watchdog time constant parameter is changed based on detected signal frequency. The control unit monitors signal characteristics and adjusts the time constant accordingly, ensuring that the detection time interval is appropriate for the current operating speed, thus preventing both pulse loss at normal speeds and enabling 0 Hz detection when stationary.
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 enables simultaneous fulfillment of customer and application requirements, including 0 Hz capability and Hill-Holder functionality, with no pulse loss and compatibility with ABS systems, at low additional costs, while maintaining standard behavior and avoiding software adaptations.
Implementation Method 1
rotation speed sensor based on the Hall technology or the xMR technology
Implementation Method 2
xMR sensor (e. g. Anisotropic Magneto Resistance sensor or a Giant Magneto Resistance sensor or a Tunnel Magneto Resistance sensor)
Data Source
AI summary
The present disclosure relates to a rotation speed sensor, including at least one sensor element to detect a magnetic input signal of the rotation speed sensor, a time watchdog with a programmable time constant and an output control circuit. The time watchdog generates a time-out event when no minimum or maximum or no output switching event of a magnetic input signal of the rotation speed sensor is detected within a time-interval equal to a programmed time constant of the time watchdog. Further, the output control circuit changes the output signal of the rotation speed sensor from a first value to a second value, when a minimum or a maximum or output switching event of the magnetic input signal is detected within the time interval and a change of the magnetic input signal is greater than a predetermined value.