Camshaft Sensor Calibration for Reluctor Runout
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Solution Overview
Problem
Camshaft sensors in motor vehicles face precision issues due to varying raw signal amplitudes caused by temperature changes and geometric deficiencies in the target, leading to imprecise detection of tooth passages, which conventional methods fail to adequately address.
Innovation Solution
A method for automatic calibration using two distinct switching thresholds for each tooth, determined from local maxima and minima in the raw signal, generated from differential signals by secondary measurement cells, to improve precision in detecting tooth passage moments.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If a single switching threshold is used for all teeth, then the device complexity is reduced, but the measurement precision deteriorates due to varying raw signal amplitudes caused by temperature changes and geometric deficiencies
Solution Approach 1:
The patent divides the single switching threshold into multiple tooth-specific switching thresholds. Each tooth has its own threshold determined from its local maximum and minimum raw signal values, allowing precise detection of each tooth's passage despite variations in signal amplitude caused by geometric deficiencies and temperature changes.
Solution Approach 2:
The patent applies local quality by determining switching thresholds specific to each tooth based on local signal characteristics (local maxima and minima). This allows each tooth to have optimized detection parameters adapted to its specific geometric characteristics and operating conditions, rather than using a uniform threshold for all teeth.
2Measurement precision
If a switching threshold is updated for each new revolution based on observed minimum and maximum values, then the measurement precision improves, but the device complexity increases due to continuous calibration requirements
Solution Approach 1:
The patent performs preliminary determination of tooth-specific switching thresholds during a calibration phase before normal operation. The thresholds are stored and reused for multiple revolutions, eliminating the need for continuous recalibration while maintaining high precision in tooth passage detection.
Solution Approach 2:
The system performs self-calibration by automatically determining local maxima and minima from the raw signal and computing appropriate switching thresholds without external intervention. This self-service calibration reduces operational complexity while maintaining measurement precision.
3Measurement precision
If different switching thresholds are determined for each tooth, then the measurement precision improves by accounting for geometric deficiencies, but the device complexity increases due to multiple threshold management
Solution Approach 1:
The system automatically determines tooth-specific switching thresholds by analyzing local maxima and minima in the raw signal for each tooth. This self-service approach eliminates manual calibration complexity while maintaining high angular position determination precision, as the system autonomously adapts to each tooth's geometric characteristics.
Solution Approach 2:
The patent changes the switching threshold parameter dynamically based on the specific tooth being detected. Each tooth has its own threshold value derived from its local signal characteristics, allowing precise detection despite variations in tooth geometry and target runout conditions.
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
This approach enhances the precision of camshaft sensor output signals by adapting switching thresholds to specific tooth characteristics, effectively mitigating the effects of target runout and geometric deficiencies, resulting in more accurate angular position determination.
Implementation Method 1
a magnetic-field measurement cell (for example a Hall-effect cell or a magneto-resistive cell)... The teeth of the target are generally all of the same height, but may have spacings (gaps) and lengths that are not all identical so as to code the angular position of the target. Thus, the rotation of the target and the passing of the various teeth past the magnetic-field generator will generate variations in the magnetic field measured by the measurement cell
Implementation Method 2
a magnetic-field generator (for example a permanent magnet)... the passing of the various teeth past the magnetic-field generator will generate variations in the magnetic field measured by the measurement cell
Data Source
AI summary
A method for automatic calibration of a camshaft sensor for a motor vehicle engine. The sensor includes a processing module configured to generate, from a raw signal indicative of the variations in a magnetic field which are caused by a rotation of a target and measured by a primary cell, an output signal indicative of the moments at which teeth of the target pass past the primary cell. The sensor further includes two secondary measurement cells. The calibration method therefore makes it possible to determine two different switching thresholds for each tooth from a differential signal indicative of a difference in magnetic field measurement by the secondary cells. Also disclosed are a camshaft sensor implementing such a method, and a motor vehicle including such a sensor.