Qualitative detection method for loosening fault of foundation bolt of reciprocating engine

Abstract

The invention discloses a qualitative detection method for a loosening fault of a foundation bolt of a reciprocating engine. The qualitative detection method comprises the following steps: step 1, respectively collecting vibration signals of the foundation bolt in a normal state and a fault state in an engine operation state; step 2, obtaining a corresponding speed signal; 3, calculating an average effective value, a difference value and a relative change rate of vibration acceleration signals of the body supporting seat and the foundation in normal and fault states; 4, the average effective value, the difference value and the relative change rate of the vibration speed signals of the body supporting seat and the foundation in the normal and fault states are calculated; 5, the relative change rate of the two feature values is calculated, and whether the engine breaks down or not is judged; 6, calculating an average amplitude spectrum and a difference spectrum of the normal and fault state speed signals; 7, extracting a frequency component, and calculating an energy ratio; and 8, comprehensively judging whether a foundation bolt loosening fault occurs or not. According to the invention, qualitative detection of the loosening fault of the engine foundation bolt can be accurately and efficiently realized.

Description

Technical Field

[0001] This invention belongs to the field of engine testing technology, specifically relating to a qualitative detection method for loose foundation bolts in reciprocating engines. Background Technology

[0002] Anchor bolts for reciprocating engines are critical fasteners connecting the engine support base to the foundation, and their most common failure mode is loosening. This failure is mainly caused by vibration and impact loads during engine operation. Anchor bolts are subjected to high-frequency, random, and complex dynamic loads over a long period, which can cause the preload to gradually decrease, leading to loosening. Loose bolts not only exacerbate engine vibration and induce local resonance, but may also further damage the connection structure and crack the base, or even cause engine displacement or overturning, seriously threatening equipment stability and personnel safety. Therefore, effectively detecting the loosening status of engine anchor bolts is of great significance for ensuring the long-term stable operation of the equipment.

[0003] Vibration signal-based bolt loosening detection technology has advantages such as convenient implementation, high sensitivity, and adaptability to various complex working conditions. However, there are currently no publicly reported vibration detection methods for loosening anchor bolts in reciprocating engines. Existing analysis techniques mostly focus on anchor bolts in rotating equipment, and the conventional approach is as follows (Huadian International Power Co., Ltd. Zouxian Power Plant, Huadian Zouxian Power Generation Co., Ltd. Diagnostic Method for Judging Loose Parts of Rotating Equipment: 202510785821.9 [P]. 2025-10-03.): First, vibration signals of key parts of the equipment are simultaneously collected in the horizontal, vertical, and axial directions to comprehensively obtain the vibration information of the equipment; then, the vibration signals are subjected to spectral analysis to extract the 1X component related to the rotational speed frequency; finally, by comparing the vibration differences of different structural levels in the same part, and combining auxiliary means such as listening and touching, it is determined whether the bolts have become loose. Obviously, reciprocating engines and rotating equipment have fundamental differences in vibration mechanism and spectral characteristics, and this method is clearly not applicable to the detection of loosening faults in reciprocating engine anchor bolts.

[0004] Therefore, how to extract characteristic indicators reflecting the loosening state of bolts from the vibration signals of reciprocating engines and achieve accurate identification of loose anchor bolt faults remains one of the urgent problems to be solved in the field of engine condition monitoring technology. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the present invention aims to provide a qualitative detection method for loose foundation bolts in reciprocating engines. By constructing characteristic indicators such as the relative change rate of the average effective value of vibration and its difference, and the energy proportion of the main fault components (consistent with the number of engine cylinders), the vibration information of dual vibration sensors and engine characteristic parameters can be fully utilized to achieve qualitative detection of loose foundation bolts in engines.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A qualitative detection method for loose foundation bolts in a reciprocating engine includes the following steps: Step 1: With the engine running, place one vibration acceleration sensor on each of the main support base and the foundation in the vertical direction to collect vibration signals of the anchor bolts under normal and fault conditions. Set the sampling frequency to fs and the number of sampling points to N. Select M sets of normal state signals under the same working conditions, where the vibration signals of the main support base measuring points are stored in a matrix. The vibration signals from the base measuring points are stored in a matrix. Correspondingly, vibration signals from the main body support and foundation under the same working conditions in M ​​groups of fault states are selected and stored in the matrix respectively. and ; Step 2, for the matrix , , , Each column of signal is integrated, detrended, and bandpass filtered to obtain the corresponding velocity signal. , , , The frequency range of the bandpass filter is Where: lower cutoff frequency Upper limit cutoff frequency , For engine speed; Step 3: Using the results obtained in Step 1, calculate the average effective value of the vibration acceleration signals of the main support and foundation under normal and fault conditions, the difference between the two, and their relative rate of change. ; Step 4: Using the results obtained in Step 2, calculate the average effective value of the vibration velocity signals of the main support and foundation under normal and fault conditions, the difference between the two, and their relative rate of change. ; Step 5: Using the results obtained in Step 3 and Step 4, extract the average effective values ​​of the vibration acceleration and velocity signals of the main support seat under normal and fault conditions, respectively, calculate the relative change rate of the two types of characteristic values, and preliminarily determine whether the engine has malfunctioned based on the relative change rate of the two types of characteristic values. Step 6: Measure the velocity signal at the support base. , Perform an FFT transformation on each column to obtain the corresponding velocity amplitude spectrum. , ; Calculate the average amplitude spectrum of the velocity signal under normal conditions : ,in, The first under normal conditions The velocity amplitude spectrum of the column is in the first The amplitude at each frequency point ; Calculate the average amplitude spectrum of the fault state velocity signal , ,in, For the fault state, the first The velocity amplitude spectrum of the column is in the first The amplitude at each frequency point; calculate the difference spectrum between the two. : ; Step 7, determine the number of cylinders L of the engine from the difference spectrum. Extract the L-order frequency component and calculate the energy proportion of the L-harmonic. ; Step 8, , , The results are compared with thresholds th3 to th5 to determine whether a loose anchor bolt fault has occurred. The process is as follows: If the conditions are met: , and If the anchor bolts at the support base are loose, it is determined that the bolts are loose; otherwise, it is determined that there is another fault.

[0008] Furthermore, in step 1, the value of M ranges from 10 to 30.

[0009] Furthermore, the specific process of step 3 is as follows: First, calculate the matrix under normal conditions. , The effective value of each column of signals is obtained, and its average value is calculated. , Then calculate the difference between the two. Then, for the matrix under fault conditions , Perform the same operation to obtain the corresponding average value. , Then calculate the difference between the two. Finally, the relative rate of change of the difference between the mean effective values ​​of vibration acceleration of the main support and the foundation under normal and fault conditions was calculated. : .

[0010] Furthermore, the specific process of step 4 is as follows: First, calculate the matrix under normal conditions. , The effective value of each column of signals is obtained, and its average value is calculated. , Then calculate the difference between the two. Then, for the matrix under fault conditions , Perform the same operation to obtain the corresponding average value. , Then calculate the difference between the two. Finally, the relative rate of change of the difference between the average effective values ​​of vibration velocities of the main support and the foundation under normal and fault conditions was calculated. : .

[0011] Furthermore, step 5 includes the following process: calculating the relative rate of change of the two types of eigenvalues: , , will R x R u Compare with thresholds th1 and th2 to preliminarily determine whether the engine has malfunctioned. The process is as follows: If the condition is met: R x >th1 or R u >th2 indicates a preliminary judgment that a fault has occurred, and the next step is continued; otherwise, it is judged that no fault has occurred.

[0012] Furthermore, in step 5, the thresholds th1 and th2 are determined through experiments or historical data analysis. The specific values ​​are adjusted accordingly based on the actual equipment model. Generally, the range of these thresholds is: th1 = 0.1~0.25, th2 = 0.1~0.25.

[0013] Furthermore, the specific process of step 7 is as follows: First, calculate the difference spectrum. Total energy Then, search for the position index of the Lth order frequency component, denoted as . l Finally, calculate the energy of the L-harmonic. Calculate the energy percentage of the L-harmonic. .

[0014] Furthermore, in step 8, the thresholds th3 to th5 are determined through experiments or historical data analysis. The specific values ​​are adjusted accordingly based on the actual equipment model. Generally, the range of these thresholds is: th3 = 0.25 to 0.35, th4 = 0.2 to 0.3, and th5 = 0.2 to 0.3.

[0015] Compared with the prior art, the present invention has the following beneficial effects: This invention proposes a qualitative detection method for loose foundation bolts in reciprocating engines. This method utilizes vibration signals from two measuring points—the engine body support and the foundation—to construct characteristic indicators such as the average effective value of vibration and the relative rate of change of their difference, as well as the energy proportion of the main fault components (consistent with the number of engine cylinders). This enables the qualitative detection of loose foundation bolts. This method fully integrates vibration information from dual vibration sensors with engine characteristic parameters, overcoming the limitations of traditional single-sensor analysis. It can efficiently identify loose foundation bolt faults, significantly improve diagnostic accuracy, and provide reliable technical support for efficient on-site engine maintenance. Attached Figure Description

[0016] Figure 1 This is a flowchart of an embodiment of the present invention.

[0017] Figure 2 This is a diagram showing the reciprocating engine support structure and sensor measurement point arrangement according to an embodiment of the present invention.

[0018] Figure 3 This is the vibration acceleration waveform of the measuring point of the main support base in the embodiment of the present invention at a certain moment under normal and fault conditions.

[0019] Figure 4 It is the vibration acceleration waveform of the basic measuring point in the embodiment of the present invention at a certain moment under normal and fault conditions.

[0020] Figure 5 This is the vibration velocity waveform of the measuring point of the main support base in the embodiment of the present invention at a certain moment under normal and fault conditions.

[0021] Figure 6 These are the vibration velocity waveforms of the basic measuring points in the embodiments of the present invention at a certain moment under normal and fault conditions.

[0022] Figure 7 It is the average amplitude spectrum of the velocity signal at the measuring point of the main support seat in the embodiment of the present invention under normal and fault states.

[0023] Figure 8 This is a velocity difference spectrum of the measuring points on the main support base in an embodiment of the present invention. Detailed Implementation

[0024] The present invention will be further described in detail below with reference to embodiments and accompanying drawings: The judgment logic and steps in the implementation process of this method are as follows: Figure 1 As shown, the vibration signal acquisition in this embodiment relies on an R6105AZLD diesel engine. This diesel engine is a six-cylinder inline engine with a maximum power of 132kW and a design speed of 1500rpm. It has four mounting feet, and each mounting foot is connected to the engine body support base and the foundation by two anchor bolts. Its structure and the arrangement of measuring points are as follows. Figure 2 As shown. During the experimental simulation, the nut of one of the anchor bolts was loosened to simulate an anchor bolt failure. Two vibration acceleration sensors, model AC192-1D, were used for data acquisition. During the data acquisition process, the diesel engine speed remained stable at 1500 rpm, and the engine frequency... .

[0025] Reference Figure 1 A qualitative detection method for loose foundation bolts in reciprocating engines includes the following steps: 1) With the engine running, install one vibration acceleration sensor on both the main support base and the foundation to collect vibration signals from the anchor bolts under normal and fault conditions, respectively. Set the sampling frequency to [frequency value missing]. f s =2048Hz, sampling points N=4096; select M groups (M=10) of normal state signals under the same working conditions, among which the signals of the body support base measuring points are stored in a matrix. The signals from the basic measuring points are stored in a matrix. Accordingly, M sets of fault state signals are selected and stored in a matrix. and ; Figure 3 The vibration acceleration waveform of the main support base at a certain moment under normal and fault conditions is shown. Figure 4 The vibration acceleration waveforms of the base measuring points at a certain moment under normal and fault conditions are displayed. 2) For the matrix , , , Each column of signal is integrated, detrended, and bandpass filtered to obtain the corresponding velocity signal. , , , The frequency range of the bandpass filter is Where: lower cutoff frequency Upper limit cutoff frequency ; Figure 5 The vibration velocity waveforms at the measuring points of the main support base at a certain moment under normal and fault conditions are displayed. Figure 6The vibration velocity waveforms of the base measuring points at a certain moment under normal and fault conditions are displayed. 3) Calculate the average effective value of the vibration acceleration signals of the main support and foundation under normal and fault conditions, the difference between the two, and their relative rate of change. The process is as follows: First, calculate the matrix under normal conditions. , The effective values ​​of each column of signals are shown in Table 1, and their average values ​​are calculated. , Then calculate the difference between the two. Then, for the matrix under fault conditions , Performing the same operation yielded the results shown in Table 2, with the corresponding average values ​​obtained. , Then calculate the difference between the two. Finally, the relative rate of change of the difference between the mean effective values ​​of vibration acceleration of the main support and the foundation under normal and fault conditions was calculated. : ; Table 1. Effective values ​​of vibration acceleration signals for each group under normal conditions.

[0026] Table 2. Effective values ​​of vibration acceleration signals for each group under fault conditions.

[0027] 4) Calculate the average effective value of the vibration velocity signals of the main support and foundation under normal and fault conditions, the difference between the two, and their relative rate of change. The process is as follows: First, calculate the matrix under normal conditions. , The effective values ​​of each column of signals are shown in Table 3, and their average values ​​are calculated. , Then calculate the difference between the two. Then, for the matrix under fault conditions , Performing the same operation yielded the results shown in Table 4, with the corresponding average values ​​obtained. , Then calculate the difference between the two. Finally, the relative rate of change of the difference between the average effective values ​​of vibration velocities of the main support and the foundation under normal and fault conditions was calculated. : ; Table 3. Effective values ​​of each group of velocity signals under normal conditions

[0028] Table 4. Effective values ​​of each group of speed signals under fault conditions.

[0029] 5) Extract the average effective values ​​of the vibration acceleration and velocity signals of the main support under normal and fault conditions, and calculate their relative rate of change: , , will R x R u Compare with thresholds th1 and th2 to initially determine whether a fault has occurred; determine the thresholds through experiments or historical data analysis: th1=0.1, th2=0.1, satisfying the condition: R x =0.12>th1, continue to the next step; 6) Velocity signal measured at the support base of the main body , Perform an FFT transformation on each column to obtain the corresponding velocity amplitude spectrum. , ; Calculate the average amplitude spectrum of the velocity signal under normal conditions : , ; Calculate the average amplitude spectrum of the fault state velocity signal , Calculate the difference spectrum between the two. : ; Figure 7 The average amplitude spectrum waveforms of the velocity signals at the measuring points of the main support base under normal and fault conditions are shown. It can be seen that the vibration velocity spectrum under both conditions is dominated by the first harmonic component, followed by the sixth harmonic component. Figure 8 The velocity difference spectrum was displayed. The spectral structure shows that the change in the 6th harmonic component is most significant after the fault occurs. 7) Determine the number of cylinders in the engine to be L=6, from the difference spectrum. Extract the 6th-order frequency component and calculate the energy percentage of the 6th harmonic. The process is as follows: Calculate the total energy of C ; Search for the location index of the 6th-order frequency component. l =151; Calculate the energy of the 6th harmonic. ; Calculate the energy percentage of the 6th harmonic. ; 8) , , Comparing with thresholds th3 to th5, the thresholds were determined through experiments or historical data analysis: th3 = 0.3, th4 = 0.3, th5 = 0.2, satisfying the following conditions: , and The anchor bolts at the support were found to be loose, a conclusion consistent with the experimental setup, thus verifying the effectiveness of the method.

Claims

1. A qualitative detection method for loose foundation bolts in a reciprocating engine, characterized in that, Includes the following steps: Step 1: With the engine running, place one vibration acceleration sensor on each of the main support base and the foundation in the vertical direction to collect vibration signals of the anchor bolts under normal and fault conditions. Set the sampling frequency to fs and the number of sampling points to N. Select M sets of normal state signals under the same working conditions, where the vibration signals of the main support base measuring points are stored in a matrix. The vibration signals from the base measuring points are stored in a matrix. Correspondingly, vibration signals from the main body support and foundation under the same working conditions in M ​​groups of fault states are selected and stored in the matrix respectively. and ; Step 2, for the matrix , , , Each column of signal is integrated, detrended, and bandpass filtered to obtain the corresponding velocity signal. , , , The frequency range of the bandpass filter is Where: lower cutoff frequency Upper limit cutoff frequency , For engine speed; Step 3: Using the results obtained in Step 1, calculate the average effective value of the vibration acceleration signals of the main support and foundation under normal and fault conditions, the difference between the two, and their relative rate of change. ; Step 4: Using the results obtained in Step 2, calculate the average effective value of the vibration velocity signals of the main support and foundation under normal and fault conditions, the difference between the two, and their relative rate of change. ; Step 5: Using the results obtained in Step 3 and Step 4, extract the average effective values ​​of the vibration acceleration and velocity signals of the main support seat under normal and fault conditions, respectively, calculate the relative change rate of the two types of characteristic values, and preliminarily determine whether the engine has malfunctioned based on the relative change rate of the two types of characteristic values. Step 6: Measure the velocity signal at the support base. , Perform an FFT transformation on each column to obtain the corresponding velocity amplitude spectrum. , ; Calculate the average amplitude spectrum of the velocity signal under normal conditions : ,in, The first under normal conditions The velocity amplitude spectrum of the column is in the first The amplitude at each frequency point ; Calculate the average amplitude spectrum of the fault state velocity signal , ,in, For the fault state, the first The velocity amplitude spectrum of the column is in the first The amplitude at each frequency point; calculate the difference spectrum between the two. : ; Step 7, determine the number of cylinders L of the engine from the difference spectrum. Extract the L-order frequency component and calculate the energy proportion of the L-harmonic. ; Step 8, , , The results are compared with thresholds th3 to th5 to determine whether a loose anchor bolt fault has occurred. The process is as follows: If the conditions are met: , and If the anchor bolts at the support base are loose, it is determined that the bolts are loose; otherwise, it is determined that there is another fault.

2. The qualitative detection method for loose foundation bolts in a reciprocating engine as described in claim 1, characterized in that, In step 1, the value of M ranges from 10 to 30.

3. The qualitative detection method for loose foundation bolts in a reciprocating engine as described in claim 1, characterized in that, The specific process of step 3 is as follows: First, calculate the matrix under normal conditions. , The effective value of each column of signals is obtained, and its average value is calculated. , Then calculate the difference between the two. Then, for the matrix under fault conditions , Perform the same operation to obtain the corresponding average value. , Then calculate the difference between the two. ; Finally, the relative rate of change of the difference between the mean effective values ​​of vibration acceleration of the main support and the foundation under normal and fault conditions was calculated. : .

4. The qualitative detection method for loose foundation bolts in a reciprocating engine as described in claim 1, characterized in that, The specific process of step 4 is as follows: First, calculate the matrix under normal conditions. , The effective value of each column of signals is obtained, and its average value is calculated. , Then calculate the difference between the two. Then, for the matrix under fault conditions , Perform the same operation to obtain the corresponding average value. , Then calculate the difference between the two. ; Finally, the relative rate of change of the difference between the mean effective values ​​of vibration velocities of the main support and the foundation under normal and fault conditions was calculated. : .

5. The qualitative detection method for loose foundation bolts in a reciprocating engine as described in claim 1, characterized in that, Step 5 includes the following process: Calculate the relative rate of change of the two types of eigenvalues: , , will R x R u Compare with thresholds th1 and th2 to preliminarily determine whether the engine has malfunctioned. The process is as follows: If the condition is met: R x >th1 or R u >th2 indicates a preliminary judgment that a fault has occurred, and the next step is continued; otherwise, it is judged that no fault has occurred.

6. The qualitative detection method for loose foundation bolts in a reciprocating engine as described in claim 5, characterized in that, In step 5, the thresholds th1 and th2 are determined through experiments or historical data analysis. The specific values ​​are adjusted according to the actual equipment model. Generally, the range of these thresholds is: th1 = 0.1~0.25, th2 = 0.1~0.

25.

7. The qualitative detection method for loose foundation bolts in a reciprocating engine as described in claim 1, characterized in that, The specific process of step 7 is as follows: First, calculate the difference spectrum. Total energy ; Then, search for the position index of the Lth order frequency component, denoted as . l Finally, calculate the energy of the L-harmonic. Calculate the energy percentage of the L-harmonic. .

8. The qualitative detection method for loose foundation bolts in a reciprocating engine as described in claim 1, characterized in that, In step 8, the thresholds th3 to th5 are determined through experiments or historical data analysis. The specific values ​​are adjusted according to the actual equipment model. Generally, the range of these thresholds is: th3 = 0.25 to 0.35, th4 = 0.2 to 0.3, and th5 = 0.2 to 0.3.

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