Phonic Wheel Axial Shift Detection for Gas Turbine Shafts
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Solution Overview
Problem
Existing shaft monitoring systems in gas turbine engines lack effective methods to accurately monitor axial position and other properties like shaft bow and torque, which are crucial for early detection of potential failures and preventing engine damage.
Innovation Solution
A monitoring system utilizing electronic circuitry already available in engine electronic controllers, featuring a phonic wheel with varying tooth thickness and a second sensor to generate alternating measurement signals, allowing for improved measurement accuracy and redundancy in detecting axial position shifts and other shaft properties.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If conventional phonic wheels with uniform teeth are used, then the system structure is simple, but the measurement precision of axial position is insufficient
Solution Approach 1:
The phonic wheel employs teeth with non-uniform thickness distribution, where specific teeth have different thicknesses than others. This local variation in tooth geometry creates distinct magnetic flux patterns that enable precise detection of axial position shifts, resolving the contradiction between measurement precision and structural simplicity.
Solution Approach 2:
The patent introduces asymmetric tooth thickness design in the phonic wheel, breaking the symmetry of conventional uniform teeth. This asymmetry creates unique magnetic reluctance patterns that provide directional sensitivity for axial position measurement, improving measurement precision without requiring complex additional components.
2Reliability
If a single sensor is used to detect phonic wheel teeth, then the device complexity is low, but the reliability of measurement is insufficient
Solution Approach 1:
The patent positions sensors at specific axial locations on the phonic wheel where teeth with particular thickness characteristics pass by. By strategically selecting sensor positions corresponding to specific tooth thickness zones, the system achieves reliable measurement without requiring multiple sensors, thus maintaining low device complexity while improving reliability.
Solution Approach 2:
The patent uses the phonic wheel itself as a reference structure with known tooth thickness patterns. The sensors detect these known patterns to establish baseline measurements, allowing for redundancy and verification without adding separate reference systems, thereby improving reliability without significantly increasing complexity.
3Measurement precision
If varying tooth thickness is implemented in the phonic wheel, then the measurement precision improves, but the manufacturing precision requirements increase
Solution Approach 1:
Instead of requiring high precision across all teeth, the patent applies varying thickness only to specific local regions of the phonic wheel teeth. The majority of teeth can maintain standard dimensions, while only particular teeth need the specialized thickness variation, thereby reducing overall manufacturing precision requirements while preserving measurement precision capability.
Solution Approach 2:
The phonic wheel teeth are segmented into different types based on their thickness characteristics. This segmentation allows for standardized manufacturing of most teeth while introducing controlled variations only in specific segments, making the manufacturing process more manageable and less demanding in terms of overall precision requirements.
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
Enables accurate monitoring of shaft axial position and properties, enhancing measurement precision and providing redundancy for early failure detection, thus preventing engine damage and improving operational reliability.
Implementation Method 1
there is a change in the magnetic flux experienced by a conductive wire wrapped around the pole piece, owing to the change in the reluctance of the magnetic circuit consisting of the pole piece, the phonic wheel and the air gap between the two
Implementation Method 2
a variable reluctance sensor which detects the passage of the row of teeth by generating an alternating measurement signal
Implementation Method 3
A hall sensor that produces a signal depending on presence or absence of magnetic markings in a detection range of the sensor
Data Source
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AI summary
A monitoring system for monitoring one or more properties associated with a rotating shaft is provided. In particular, the system is adapted to identify an axial shift of the rotating shaft, in addition to a rotational speed. The system includes a first phonic wheel which is mounted coaxially to the shaft for rotation therewith, the first phonic wheel comprising a circumferential row of teeth. The system further includes a first sensor configured to detect the passage of the row of teeth of the first phonic wheel by generating a first alternating measurement signal. The system further includes a processor unit configured to determine the durations of successive first speed samples. Each first speed sample is a block of n successive cycles of the first alternating measurement signal, where n is an integer (e.g. n=3), and in which the beginning of each cycle is a zero-crossing point from the previous cycle and the end of each cycle is the corresponding zero-crossing point to the next cycle. At at least one axial location of the first phonic wheel every mth tooth of the row of teeth of the first phonic wheel has a circumferential thickness or length which is different from that of the other teeth of the first phonic wheel, where m is an integer, m ≠ n, and m is neither a factor nor a multiple of n (e.g. m=4). When the first sensor is positioned at said axial location of the first phonic wheel and at any given rotational speed of the first phonic wheel, the durations of the successive first speed samples display a characteristic repeating pattern of longer and shorter sample durations relative to the average duration of the successive first speed samples. The amount by which the longer and shorter sample durations differ from the average duration is in proportion to the amount by which the circumferential thickness of the mth teeth differs from that of the other teeth at said axial location of the first phonic wheel. The processor unit monitors the properties associated with the rotating shaft from the characteristic repeating pattern.