Camshaft Sensor Calibration Reducing Signal Jitter
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Solution Overview
Problem
Existing camshaft sensor calibration methods are prone to signal disturbances and non-repeatability due to recalculating the switching threshold for each tooth, leading to 'jitters' and impaired precision in determining engine cylinder positions, especially with imperfect target geometry and airgap defects.
Innovation Solution
A method that measures and stores magnetic field maximum and minimum values during the first revolution, then updates the switching threshold only if significant differences are detected in subsequent revolutions, using a single absolute minimum value for calibration to stabilize the output signal.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Adaptability or versatility
If the switching threshold is recalculated for each tooth passage, then the sensor adapts to target geometry imperfections and airgap variations, but signal disturbances and non-repeatability occur leading to jitters
Solution Approach 1:
The patent segments the calibration process into two distinct phases: an initial calibration phase where the switching threshold is determined based on the first revolution data, and a subsequent operation phase where the stored threshold is maintained constant. This segmentation prevents continuous recalculation that causes signal jitters while still allowing initial adaptation to target geometry imperfections.
Solution Approach 2:
The patent performs the threshold calculation and adaptation action in advance during the first revolution of the target, storing the results for subsequent use. This preliminary action ensures the sensor adapts to target imperfections before normal operation begins, eliminating the need for continuous recalculation during operation that would cause signal disturbances.
2Measurement precision
If the switching threshold is fixed at 75% of amplitude, then optimal precision is achieved for most existing targets, but performance degrades with out-of-roundness and airgap defects
Solution Approach 1:
The patent changes the switching threshold parameter from a fixed 75% of amplitude to a dynamically calculated value based on the actual magnetic field measurements during the first revolution. This parameter change allows the threshold to adapt to specific target geometry imperfections and airgap variations, improving measurement precision under non-ideal 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 significantly reduces signal variations and jitter, ensuring more stable and repeatable output signals, even with geometric imperfections and airgap variations, thereby improving the accuracy of engine timing detection.
Implementation Method 1
a magnetic field sensor placed near the target to detect the magnetic field variations induced by the passage of the teeth of the target near the sensor
Data Source
AI summary
A method for automatic calibration of a camshaft sensor for a motor vehicle, allowing reduction of the fluctuations on the output signal of the sensor. The method proposes comparing, on each target rotation, the new maximum values of the magnetic field of each tooth to the maximum values of the same teeth from the preceding target rotation. The switching thresholds are only calculated with the new maximum values if these differ from the maximum values of the preceding target rotation. Moreover, the invention proposes using a single minimum value of the magnetic field, i.e. the absolute minimum value on a target rotation in order to calculate the switching thresholds.