Aircraft Engine Shaft Speed Measurement Noise Filtering
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Solution Overview
Problem
Existing methods for measuring the rotation speed of an aircraft engine shaft using phonic wheel sensors are disrupted by spurious noise, leading to inaccurate measurements due to electromagnetic disturbances and mechanical vibrations, and existing filtering solutions either phase-shift the signal or reduce its amplitude, making it difficult to achieve precise frequency measurements, especially at low engine ratings.
Innovation Solution
A post-processing method is implemented at the digital interface of the engine control system to reconstitute the desired period of the signal by summing and averaging consecutive period samples, comparing these sums to likelihood thresholds, and using a theoretical numerical model during initialization to estimate the period, thereby reducing the impact of spurious noise without requiring full periods.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Object-affected harmful factors
If low-pass filtering is applied to reduce spurious noise, then noise reduction is improved, but phase shift and amplitude reduction occur
Solution Approach 1:
The patent segments the noisy period measurements into individual period samples and processes them separately through summation and averaging operations. Instead of filtering the continuous signal, it divides the measurement into discrete period intervals that can be individually validated and combined, thereby reducing noise without introducing phase shift or amplitude reduction.
Solution Approach 2:
The patent applies partial action by using only the valid portion of period measurements. It validates each period sample against expected ranges and uses only those that meet criteria, rather than processing all measurements equally. This selective approach reduces the impact of noisy measurements without requiring aggressive filtering.
2Object-affected harmful factors
If simple averaging of period measurements is used, then noise reduction is improved, but accuracy at low engine ratings deteriorates
Solution Approach 1:
The patent implements feedback by continuously validating period measurements against expected ranges derived from engine operating conditions. Each period sample is checked against minimum and maximum expected values, and only valid samples are used in the averaging process. This feedback mechanism ensures that measurements remain accurate across different engine ratings, particularly at low ratings where noise has greater impact.
Solution Approach 2:
The patent changes the parameter validation approach by establishing dynamic minimum and maximum expected period values based on engine operating conditions. Rather than using fixed thresholds, the validation criteria adapt to different engine ratings and operating states, maintaining measurement accuracy across the full operating range while effectively filtering out spurious measurements.
3Reliability
If period validation with minimum and maximum thresholds is applied, then measurement reliability is improved, but device complexity increases
Solution Approach 1:
The patent applies self-service by having the measurement system validate its own measurements using internally derived expected ranges. The system uses the engine's operating parameters and the known characteristics of the phonic wheel to establish validation criteria, eliminating the need for external calibration or complex reference systems. This self-validating approach improves reliability without proportionally increasing complexity.
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 method effectively reduces the effect of spurious noise on rotation speed measurements, providing accurate and reliable engine speed data without phase-shifting or amplitude reduction, even in noisy conditions, and is more effective than simple averaging or low-pass filtering.
Implementation Method 1
Using a winding, the sensor creates a magnetic field which closes either on an air gap between two teeth of the phonic wheel, or on one tooth of the phonic wheel. Thus, the magnetic flux measured varies as a function of the passing of the teeth of the phonic wheel
Implementation Method 2
the magnetic flux measured varies as a function of the passing of the teeth of the phonic wheel, in a manner proportional to the phonic wheel rotation speed
Implementation Method 3
The frequency of the alternating voltage thus generated is equal to the frequency of the passing of the teeth of the phonic wheel, itself illustrative of the rotation speed of the shaft
Data Source
AI summary
A method for measuring rotation speed of an aircraft engine shaft includes: acquisition of an alternating rotation speed detection signal across terminals of a phonic wheel sensor, conversion of the alternating signal into a square signal; comparison of a plurality of previously-stored square signal period samples to lower and upper period limits, to determine valid samples of a value included between the terminals; if the number of valid samples is greater than a first threshold, determination on the basis of the valid samples of a desired period of the square signal; and at least on the condition that the number of valid samples is less than the first threshold, computation of a plurality of sums of samples, and computation of the average of a set comprising a number of valid period samples and a number of sums from among the plurality of sums of at least two samples.