Variable Reluctance Sensor Arming Circuit with 1/t Threshold
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Solution Overview
Problem
Variable reluctance sensors face challenges in accurately measuring angular position and speed due to synchronous and asynchronous noise, dynamic signal range variations, and mechanical tolerances, which affect the detection of tooth transitions in crankshaft applications.
Innovation Solution
An arming threshold circuit that automatically adjusts its threshold signal (ATH) proportional to 1/t, dynamically maximizing the signal-to-noise ratio by matching hysteresis decay rate to the amplitude and frequency of the VR sensor signal, ensuring proper arming and detection of tooth transitions across varying crankshaft speeds.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a fixed threshold is used for detecting tooth transitions, then the detection is simple, but the detection accuracy deteriorates under varying speeds and dynamic conditions
Solution Approach 1:
The patent applies dynamics by making the threshold adaptive rather than fixed. The threshold automatically adjusts its magnitude based on the instantaneous frequency of the VR sensor signal, which varies with crankshaft speed. This dynamic threshold adaptation allows the detection circuit to maintain high accuracy across a wide speed range without requiring complex manual adjustment mechanisms.
Solution Approach 2:
The patent changes the threshold parameter dynamically according to operating conditions. Specifically, the threshold magnitude is modified based on the signal frequency, which correlates with crankshaft speed. This parameter change enables the system to optimize detection sensitivity for each operating condition, resolving the contradiction between simple fixed-threshold design and accurate variable-condition detection.
2Reliability
If the threshold is set high to avoid false detection, then false detection is reduced, but valid tooth transitions may be missed at lower speeds
Solution Approach 1:
The threshold dynamically adapts its magnitude based on the instantaneous frequency of the VR sensor signal. At higher speeds where false detection is more likely, the threshold increases to filter out noise. At lower speeds where valid transitions are more prominent, the threshold decreases to ensure detection. This dynamic behavior resolves the contradiction by allowing the threshold to be high when needed for reliability and low when needed for precision.
Solution Approach 2:
The system uses feedback from the VR sensor signal itself to adjust the threshold. The instantaneous frequency of the signal, which varies with crankshaft speed, is fed back to control the threshold magnitude. This feedback mechanism ensures that the threshold is always optimally set for current operating conditions, simultaneously reducing false detection and maintaining detection accuracy across the full speed range.
3Device complexity
If a fixed threshold is used, then the circuit is simple, but it cannot adapt to varying crankshaft speeds and mechanical tolerances
Solution Approach 1:
The threshold circuit is designed to be dynamic rather than static. It automatically adjusts its operating characteristics in response to changes in crankshaft speed and mechanical conditions. The instantaneous frequency detection enables the threshold to adapt to varying speeds, and the hysteresis mechanism provides adaptability to mechanical tolerances and noise conditions, all without requiring complex external adjustment mechanisms.
Solution Approach 2:
The threshold adjustment mechanism is self-service, meaning it automatically adapts to operating conditions without external intervention. The circuit uses its own output signal characteristics (instantaneous frequency) to control its threshold behavior, enabling it to self-optimize for different speeds and mechanical conditions. This self-service capability provides wide speed range coverage while keeping the overall circuit design relatively simple.
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 adaptive arming threshold effectively reduces the probability of false detection and ensures consistent capture of tooth transitions, maintaining high detection accuracy across a wide range of speeds and dynamic conditions.
Implementation Method 1
the VR sensor is used to sense each passing tooth during rotation of the crankshaft. Each tooth passing by the VR sensor changes the magnetic flux which is converted to an electrical voltage induced in the coil.
Implementation Method 2
dynamically maximizing the signal-to-noise ratio by matching hysteresis decay rate to the amplitude and frequency of the VR sensor signal
Data Source
AI summary
A variable reluctance sensor system for processing a variable reluctance sensor signal including an arming comparator and an arming circuit. The arming comparator compares the variable reluctance sensor signal with an arming threshold which decreases proportional to 1/t from a predetermined maximum level and asserts an armed signal when the variable reluctance sensor signal reaches the arming threshold. The arming threshold may be decreased based on a scaling factor multiplied by 1/t to ensure detection of each pulse of the variable reluctance sensor signal. The arming threshold may decrease to a predetermined minimum level sufficiently low to intersect the variable reluctance sensor signal and sufficiently high relative to an expected noise level. The arming threshold is reset in response to a timing event, such as zero crossing of the variable reluctance sensor signal.