Plain Bearing Mixed Friction Detection via Envelope Analysis
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Solution Overview
Problem
Current methods for monitoring plain bearings in high-performance planetary gears, particularly in turbofan engines, fail to effectively detect mixed friction events which indicate lubrication issues, posing risks to engine components and overall aircraft safety.
Innovation Solution
A method and device utilizing a structure-borne noise sensor to record and process time-dependent signals, filtering out other mechanical vibrations, calculating an envelope curve, and combining it with rotation angle data to identify and localize mixed friction events, enabling early detection and condition-based maintenance.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If current monitoring methods are used for plain bearings in planetary gears, then general bearing defects can be detected, but mixed friction events indicating lubrication issues cannot be effectively detected
Solution Approach 1:
The patent utilizes structure-borne noise (vibrations) generated during mixed friction events as the primary detection mechanism. A sensor records vibrations in the frequency range of 50-300 kHz, which are characteristic of mixed friction between shaft and bearing surfaces. This allows direct detection of lubrication failures through mechanical vibration analysis.
Solution Approach 2:
The patent transforms the raw vibration signal into an envelope curve through signal processing, changing the parameter representation from time-domain vibrations to amplitude-envelope characteristics. This parameter transformation enables clear identification of mixed friction events by highlighting the characteristic amplitude modulations that occur during such events.
2Ease of manufacture
If a single structure-borne noise sensor is used for monitoring, then the sensor system becomes economical, but the system must effectively distinguish mixed friction events from other mechanical vibrations
Solution Approach 1:
The patent focuses on capturing mechanical vibrations in a specific frequency range (50-300 kHz) that is characteristic of mixed friction events. By filtering and analyzing vibrations within this specific frequency band, the single sensor can distinguish mixed friction signals from other mechanical vibrations occurring at different frequencies.
Solution Approach 2:
The patent applies signal processing transformations that convert the vibration signal into an envelope curve, changing the representation parameters to make mixed friction events distinguishable. The envelope curve extraction and subsequent smoothing transform the complex vibration data into a form where mixed friction events appear as distinct maxima, enabling easy identification despite using only one sensor.
3Measurement precision
If the envelope curve is calculated directly without smoothing, then the mixed friction events can be identified, but the sharp contours make it difficult to determine the maxima accurately
Solution Approach 1:
The patent applies smoothing to the envelope curve, transforming it from a sharp, difficult-to-analyze signal into a continuous function with clearly defined maxima. This parameter transformation maintains the location and significance of the maxima while removing the sharp contours that complicate determination, enabling accurate identification of mixed friction event positions.
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 allows for robust and economical monitoring of plain bearings, enhancing safety by predicting potential failures, extending machine lifespan, and optimizing maintenance schedules.
Implementation Method 1
At least one time-dependent structure-borne noise signal of the at least one structure-borne noise sensor is recorded
Implementation Method 2
First, the time-dependent structure-borne sound signal is filtered in order to suppress other mechanical vibrations in particular
Implementation Method 3
An envelope curve for the filtered structure-borne noise signal is then calculated, with the envelope curves enveloping the amplitude-modulated signal in the case of mixed friction events
Data Source
Figure 1~2
Figure 3A~5
Figure 6~7
AI summary
The invention relates to a method for monitoring a plain bearing (1) with a shaft (6) mounted therein, in particular rotating therein, for at least one mixed friction event (a, b, c, d), wherein at least one time-dependent structure-borne sound signal (S) is recorded by at least one structure-borne sound sensor (3), in particular exactly one structure-borne sound sensor (3) from the plain bearing (1), characterized by a) filtering (201) of the structure-borne sound signal (S), b) subsequent calculation (202) of an envelope for the filtered structure-borne sound signal (S), c) subsequent smoothing (203) of the envelope, and d) a combination (205) of the data for the smoothed envelope with a rotation angle signal (Z) that depends on the rotation of the shaft (6) in the plain bearing (1), e) a calculation of the maxima that correlate with the mixed friction events (a, b, c, d) from the combined data from step d) for determining a Angle specification for the at least one mixed lubrication event (a,b, c, d) on the circumference of the sliding bearing (1). The invention also relates to a device for monitoring a sliding bearing.