A method of obtaining a shaft speed of a driveline and a method of obtaining a driveline fault signature

Abstract

This invention discloses a method for obtaining the shaft speed of a transmission system and a method for obtaining fault characteristics of a transmission system. The shaft speed is obtained based on the relationship between instantaneous frequency and order. The instantaneous frequency is obtained from the vibration signal through an iterative method after satisfying the iteration conditions. The instantaneous frequency output in each iteration is the sum of the demodulated instantaneous frequency and the instantaneous frequency output in the previous iteration. The demodulated instantaneous frequency is obtained from the demodulated vibration signal through a spectrum-refined STFT and a time-frequency ridge tracking method. Except for the first iteration, in each iteration, the demodulated vibration signal is obtained from the vibration signal using the instantaneous frequency output in the previous iteration through a generalized demodulation transform. In the first iteration, the demodulated vibration signal is obtained from the vibration signal using the initial instantaneous frequency through a generalized demodulation transform. The initial instantaneous frequency is obtained from the vibration signal through an STFT and a time-frequency ridge tracking method. This method can obtain the shaft speed of the transmission system with high accuracy.

Description

Technical Field

[0001] This invention relates to the field of transmission systems, and more specifically to a method for obtaining the shaft speed of a transmission system and a method for obtaining fault characteristics of a transmission system. Background Technology

[0002] The helicopter transmission system is one of the most important components of a helicopter, with a complex mechanical structure containing numerous rotating parts. During field operations, it faces complex conditions such as drastic airflow changes and variable flight attitudes. Therefore, conducting condition monitoring and fault diagnosis of the helicopter's transmission system is of paramount importance for improving helicopter flight safety.

[0003] Vibration signal analysis has been widely applied in condition monitoring and fault diagnosis of helicopter transmission systems. However, due to the harsh working environment and the complex internal structure of the transmission system, vibration sensors cannot be directly mounted on the tested components; only a few sensors can be installed on the nearby casing. The complex transmission path causes vibration signals to attenuate during transmission, and the vibration signals from numerous rotating components couple with each other, increasing the difficulty of extracting fault features from the transmission system. Especially for weak signals indicating early component failures, accurate detection is difficult under the influence of complex background noise. Therefore, utilizing effective noise reduction techniques to improve the signal-to-noise ratio of vibration signals is crucial for vibration condition monitoring and fault diagnosis of transmission systems.

[0004] Time Synchronous Averaging (TSA) is an effective technique for reducing noise in vibration signals; however, the key to implementing TSA lies in obtaining accurate reference shaft speeds. Due to harsh operating conditions, the transmission speed measurement devices pre-installed on helicopters frequently malfunction, leading to distortion of the collected shaft speed information.

[0005] Extracting shaft velocity information from vibration signals is one feasible approach. This involves first obtaining the instantaneous frequency from the vibration signal, and then using that instantaneous frequency to determine the shaft velocity. Existing technologies have extensively researched shaft velocity extraction based on vibration signals. Boudraa et al. used Empirical Mode Decomposition (EMD) to separate single-component signals from a mixed signal, and then used the nonlinear Teager-Kaiser Energy (TKE) to demodulate and obtain the instantaneous frequency. Bonnardot et al. used a narrowband filter to separate the target single component from the mixed signal, then used Hilbert transform to demodulate and obtain the instantaneous phase, finally differentiating the instantaneous phase to obtain the instantaneous frequency. Urbanek et al. proposed a two-step method based on Short-Time Fourier Transform (STFT) time-frequency ridge tracking, mapping a one-dimensional time-domain signal to a two-dimensional time-frequency joint analysis domain, and tracking the distribution of the target component ridge in the time-frequency space to estimate its instantaneous frequency.

[0006] However, the accuracy of time-frequency ridge extraction is highly dependent on the computational accuracy of the time-frequency characterization algorithm. When processing non-stationary vibration signals, the accuracy of STFT is low, resulting in the low accuracy of existing STFT time-frequency ridge tracking methods. Summary of the Invention

[0007] The purpose of this invention is to overcome the above-mentioned defects or problems in the prior art and to provide a method for obtaining the shaft speed of a transmission system and a method for obtaining fault characteristics of a transmission system, which can obtain the shaft speed of the transmission system with high accuracy.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] The first technical solution relates to a method for obtaining the shaft speed of a transmission system, wherein the shaft speed is obtained based on the relationship between instantaneous frequency and order. The instantaneous frequency is obtained from the vibration signal through an iterative method after satisfying the iteration conditions. The instantaneous frequency output in each iteration is the sum of the demodulated instantaneous frequency and the instantaneous frequency output in the previous iteration. The demodulated instantaneous frequency is obtained from the demodulated vibration signal through a spectrum-refined STFT and a time-frequency ridge tracking method. Except for the first iteration, in each iteration, the demodulated vibration signal is obtained from the vibration signal through a generalized demodulation transform using the instantaneous frequency output in the previous iteration. In the first iteration, the demodulated vibration signal is obtained from the vibration signal through a generalized demodulation transform using the initial instantaneous frequency, which is obtained from the vibration signal through an STFT and a time-frequency ridge tracking method.

[0010] The second technical solution is based on the first technical solution, wherein the iteration condition is that the standard deviation of the demodulation instantaneous frequency is less than the iteration stopping error.

[0011] The third technical solution is based on the first technical solution, wherein the STFT based on spectrum refinement is represented as follows:

[0012]

[0013] in,

[0014] n represents the number of discrete points in the time-domain signal.

[0015] f nin Represents the left boundary of the frequency in time-frequency transformation

[0016] m represents the number of discrete points.

[0017] Δf represents the spectral resolution.

[0018] L w Indicates window length

[0019] h[k] represents the window function at point k.

[0020] x represents the time-domain signal.

[0021] k represents the time scale of the discrete points of the signal captured by a single-step time window.

[0022] The fourth technical solution relates to a method for obtaining fault characteristics of a transmission system. The method for obtaining the shaft speed of the transmission system is described in any one of technical solutions 1-3. After obtaining the shaft speed, a virtual key phase signal is generated based on the shaft speed. The original time-domain sampled non-stationary signal is digitally resampled based on the virtual key phase signal to obtain an angular-domain cyclic stationary signal synchronized with the shaft speed. An integer-cycle angular-domain cyclic stationary signal is selected and subjected to order analysis or TSA to extract fault characteristics.

[0023] As can be seen from the above description of the present invention, compared with the prior art, the present invention has the following beneficial effects:

[0024] This invention utilizes a generalized demodulation transform (STFT) to demodulate non-stationary vibration signals, transforming them into approximately stationary demodulated vibration signals to improve the accuracy of the STFT. Furthermore, a spectral refinement-based STFT is employed to enhance the accuracy of the time-frequency ridge tracking method, thereby improving the accuracy of the extracted demodulated instantaneous frequency. Through continuous experimentation, it has been found that the demodulated instantaneous frequency obtained by demodulating the vibration signal should theoretically be a constant. Therefore, it can be used as a criterion for judging the accuracy of the obtained transmission system shaft speed; for example, it can be used to determine whether the standard deviation of the demodulated instantaneous frequency approaches zero. Based on this discovery, this invention employs an iterative calculation method to obtain the transmission system shaft speed. Experimental results show that the iterative calculation converges. Therefore, compared to existing technologies, the method provided by this invention can obtain the transmission system shaft speed with higher accuracy at a lower iterative calculation cost. Attached Figure Description

[0025] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments are briefly introduced. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0026] Figure 1 This is a flowchart illustrating the method for obtaining the shaft speed of the transmission system in this embodiment. Detailed Implementation

[0027] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are preferred embodiments of the present invention and should not be considered as excluding other embodiments. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0028] Unless otherwise expressly defined, the use of terms such as "first," "second," or "third" in the claims, description, and accompanying drawings of this invention is for distinguishing different objects and not for describing a specific order.

[0029] Unless otherwise expressly defined, in the claims, description, and accompanying drawings of this invention, the use of directional terms such as "center," "lateral," "longitudinal," "horizontal," "vertical," "top," "bottom," "inner," "outer," "upper," "lower," "front," "rear," "left," "right," "clockwise," and "counterclockwise" to indicate orientation or positional relationships is based on the orientation and positional relationships shown in the accompanying drawings and is only for the convenience of describing the invention and simplifying the description, and is not intended to indicate or imply that the device or element referred to must have a specific orientation or be constructed and operated in a specific orientation, and therefore should not be construed as limiting the specific scope of protection of this invention.

[0030] Unless otherwise expressly defined, the terms "fixed connection" or "fixed connection" used in the claims, description and drawings of this invention should be interpreted broadly to refer to any connection in which there is no displacement or relative rotation relationship between the two parties, including non-removable fixed connection, detachable fixed connection, integral connection and fixed connection by other means or components.

[0031] In the claims, description and accompanying drawings of this invention, the terms "comprising," "having," and variations thereof are used to mean "including but not limited to."

[0032] In the claims, description and accompanying drawings of this invention, the term "IGD" as used refers to the method for obtaining the shaft speed of a transmission system provided by this invention.

[0033] See Figure 1 This embodiment provides a method for obtaining the shaft speed of a transmission system. The shaft speed is obtained based on the relationship between instantaneous frequency and order. The instantaneous frequency is obtained from the vibration signal through an iterative method after satisfying the iteration conditions. The instantaneous frequency output in each iteration is the sum of the demodulated instantaneous frequency and the instantaneous frequency output in the previous iteration. The demodulated instantaneous frequency is obtained from the demodulated vibration signal through a spectrum-refined STFT and a time-frequency ridge tracking method. Except for the first iteration, in each iteration, the demodulated vibration signal is obtained from the vibration signal using the instantaneous frequency output in the previous iteration through a generalized demodulation transform. In the first iteration, the demodulated vibration signal is obtained from the vibration signal using the initial instantaneous frequency through a generalized demodulation transform. The initial instantaneous frequency is obtained from the vibration signal through an STFT and a time-frequency ridge tracking method. In this embodiment, the iteration condition is that the standard deviation of the demodulated instantaneous frequency is less than the iteration stopping error.

[0034] In this embodiment, the STFT based on spectrum refinement is represented as follows:

[0035]

[0036] in,

[0037] n represents the number of discrete points in the time-domain signal.

[0038] f min Represents the left boundary of the frequency in time-frequency transformation

[0039] m represents the number of discrete points.

[0040] Δf represents the spectral resolution.

[0041] L w Indicates window length

[0042] h[k] represents the window function at point k.

[0043] x represents the time-domain signal.

[0044] k represents the time scale of the discrete points of the signal captured by a single-step time window.

[0045] Taking the acquisition of the shaft speed of a helicopter transmission system as an example, the specific application of this embodiment for acquiring the shaft speed of the transmission system is as follows.

[0046] This embodiment designs a simulation signal based on the gearbox meshing signal model to verify the method described in this embodiment. The parallel gearbox meshing signal can be expressed by the following formula:

[0047]

[0048] Where f(t) is the axis velocity, A0, The amplitude and phase of the speed synchronization fundamental frequency are given by T, where T is the number of teeth, m is the order of the meshing frequency, and A is the amplitude and phase of the fundamental frequency. m , They are respectively the mth th The amplitude and initial phase of the meshing harmonics are given by M, where M is the total order of the synchronization components in the signal.

[0049] The simulated relationship between the axis velocity and time is as follows:

[0050] f(t)=5+0.5cos(0.4πt)+0.25t+0.02t 2

[0051] The simulated signal contains a velocity fundamental frequency harmonic and a third-order meshing harmonic component. The values ​​of each parameter in this embodiment are shown in the table below. In this embodiment, the sampling frequency is 1024Hz and the signal length is 10s.

[0052]

[0053] Calculations show that the bandwidth of the fundamental frequency is BP. f =|f max -f min |=1.27Hz, according to the order relationship, the frequency bandwidths of the third-order meshing frequencies are respectively

[0054] The method for obtaining the shaft speed of the transmission system provided in this embodiment is used to calculate the shaft speed of the transmission system. Specifically, frequency resolutions Δf = 0.05Hz and Δf = 0.01Hz are set respectively, and the estimated spectral range of the first-order meshing component after generalized demodulation is approximately [f min ,f max = [-3Hz, 3Hz], the iteration stopping error is 0.001.

[0055] The calculation results indicate that the iterations gradually converged. After the fifth iteration, the standard deviation of the demodulated instantaneous frequency decreased to below 0.005 for both frequency resolutions. Furthermore, the smaller the frequency resolution Δf, the smaller the standard deviation of the demodulated instantaneous frequency. Without considering endpoint errors, the maximum estimation error between the estimated instantaneous frequency and the true frequency after five iterations was less than 0.001 Hz. The computation time for five iterations at the two frequency resolutions was 0.87 s and 1.41 s, respectively. In summary, a smaller frequency resolution Δf for refining the spectrum results in a smaller standard deviation of the demodulated instantaneous frequency for the same number of iterations, leading to higher instantaneous frequency tracking accuracy, but also a longer computation time.

[0056] This embodiment also provides the error of the transmission system shaft speed obtained by the method in the prior art under the same conditions, and compares it with the result error of the method in this embodiment. The specific results are shown in the table below.

[0057]

[0058] It is evident that the method provided by this invention has a relatively smaller error compared to the prior art, and can obtain the shaft speed of the transmission system with high accuracy.

[0059] This embodiment also provides a method for obtaining fault characteristics of a transmission system. After obtaining the shaft speed of the transmission system using the method for obtaining the shaft speed of the transmission system in this embodiment, a virtual key phase signal is generated based on the shaft speed of the transmission system. The original time-domain sampled non-stationary signal is digitally resampled based on the virtual key phase signal to obtain an angular domain cyclic stationary signal synchronized with the shaft speed of the transmission system. After selecting the angular domain cyclic stationary signal with an integer cycle, order analysis or TSA is performed to extract fault characteristics.

[0060] In this embodiment, a generalized demodulation transform is used to demodulate the non-stationary vibration signal, transforming it into an approximately stationary demodulated vibration signal to improve the accuracy of the STFT. Furthermore, a spectrum-refined STFT is employed to enhance the accuracy of the time-frequency ridge tracking method, thereby improving the accuracy of the extracted demodulated instantaneous frequency. Iterative calculations are introduced to obtain the shaft speed of the transmission system with high accuracy while incurring relatively low computational costs.

[0061] The foregoing description of the specifications and embodiments is intended to explain the scope of protection of this invention, but does not constitute a limitation on the scope of protection of this invention. Modifications, equivalent substitutions, or other improvements to the embodiments of this invention or a portion thereof that can be obtained by those skilled in the art through logical analysis, reasoning, or limited experimentation, based on the teachings of this invention or the foregoing embodiments, in conjunction with common knowledge, general technical knowledge, and / or existing technology, should all be included within the scope of protection of this invention.

Claims

1. A method of acquiring shaft speed of a driveline system, characterized by, The shaft velocity is obtained based on the relationship between instantaneous frequency and order. The instantaneous frequency is obtained from the vibration signal through an iterative method after satisfying the iteration conditions. The instantaneous frequency output in each iteration is the sum of the demodulated instantaneous frequency and the instantaneous frequency output in the previous iteration. The demodulated instantaneous frequency is obtained from the demodulated vibration signal through a short-time Fourier transform based on spectral refinement and a time-frequency ridge tracking method. Except for the first iteration, in each iteration, the demodulated vibration signal is obtained from the vibration signal using the instantaneous frequency output in the previous iteration through a generalized demodulation transform. In the first iteration, the demodulated vibration signal is obtained from the vibration signal using the initial instantaneous frequency through a generalized demodulation transform. The initial instantaneous frequency is obtained from the vibration signal through a short-time Fourier transform and a time-frequency ridge tracking method. The short-time Fourier transform based on spectrum refinement is expressed as follows: in, STFT represents Short-Time Fourier Transform. number of points representing the time-domain signal The left boundary of the frequency representing the time-frequency transformation number of points representing spectral dispersion indicates the spectral resolution Indicates window length representing the k point window function representing a time domain signal representing the time scale of the discrete points of the signal taken in the single step time window; The vibration signal is represented as, in For shaft velocity, The amplitude and phase of the speed synchronization fundamental frequency, Number of teeth The order of meshing frequency. The first The amplitude and initial phase of the first meshing harmonic. This represents the total order of the synchronization components in the signal; Shaft speed The relationship over time is 。 2. A method of acquiring shaft speed of a driveline system as claimed in claim 1, characterised in that, The iteration condition is that the standard deviation of the demodulated instantaneous frequency is less than the iteration stopping error.

3. A method of acquiring a drive train fault signature, characterized by, After obtaining the shaft speed of the transmission system using the method described in any one of claims 1-2, a virtual key phase signal is generated based on the shaft speed. The original time-domain sampled non-stationary signal is digitally resampled based on the virtual key phase signal to obtain an angular domain cyclic stationary signal synchronized with the shaft speed of the transmission system. After selecting the angular domain cyclic stationary signal with an integer cycle, order analysis or time-synchronous averaging techniques are performed to extract fault features.

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