Non-contact sliding bearing oil film thickness measuring method

Abstract

The invention discloses a non-contact sliding bearing oil film thickness measurement method, and belongs to the technical field of lubricating oil film thickness measurement. Three monitoring nodes with ultrasonic probes and composite strain gauges are arranged on the back of a bearing bush, and ultrasonic echoes, original strain and in-situ temperature signals are synchronously collected; real mechanical strain of the bearing bush is obtained through thermal output correction, oil film pressure is inversed by combining the strain, and temperature and pressure correction is conducted on the sound velocity and density of an oil film; meanwhile, the propagation distance of ultrasonic waves in the bearing bush is corrected, and the single-point oil film thickness is inversed based on a spring stiffness model and a reflection coefficient measured through an experiment; and finally, reconstructing full-field mechanical deformation distribution of the bearing bush by utilizing an elastic mechanical modal theory, and calculating an axis position to realize accurate calculation of the full-field oil film thickness. The method is high in measurement precision, can present the full-field oil film distribution and axis track in real time, and provides reliable data support for large-scale rotating machinery bearing lubrication state evaluation and trend analysis.

Description

Technical Field

[0001] This invention relates to the field of lubricating oil film thickness measurement technology, and specifically to a non-contact method for measuring the oil film thickness of sliding bearings. Background Technology

[0002] Sliding bearings are core components of large rotating machinery (such as steam turbines, compressors, and generators), and the oil film thickness during operation is the most direct indicator of the bearing's lubrication condition. Traditional methods for measuring oil film thickness mainly include eddy current method, capacitance method, and ultrasonic method. Among them, the ultrasonic method has become a research hotspot in recent years due to its advantages such as non-contact (non-contact with the journal), strong penetration, and no need to damage the inner surface of the bearing bush. However, existing ultrasonic measurement technology faces the following problems in practical engineering applications:

[0003] First, the time-varying and nonlinear nature of the sound velocity parameter is not fully considered: the accuracy of ultrasonic thickness measurement is highly dependent on the sound velocity of the medium. The sound velocity of lubricating oil not only changes significantly with temperature, but also changes due to the acoustoelastic effect under high pressure in the load-bearing area. That is, the higher the pressure, the more likely the sound velocity will produce a nonlinear shift. However, existing technologies usually only perform temperature compensation for the time-varying line and ignore the influence of pressure. If this pressure-induced change in sound velocity is ignored, it will directly cause deviations in the measurement results.

[0004] Second, the geometric deformation of the bearing substrate is not fully considered: Under heavy load conditions, the bearing substrate undergoes micron-level elastic deformation, which alters the propagation path length of ultrasonic waves within the substrate. Existing technologies typically assume a constant wall thickness, introducing systematic errors.

[0005] Therefore, existing technologies need to be improved to enhance the accuracy of oil film measurement. Summary of the Invention

[0006] The purpose of this invention is to propose a non-contact method for measuring the oil film thickness of sliding bearings, so as to solve the problem of inaccurate oil film measurement in the prior art.

[0007] The technical solution adopted in this invention is: a non-contact method for measuring the oil film thickness of a sliding bearing, comprising the following steps:

[0008] Step S1: Three monitoring nodes A, B, and C are arranged on the back of the sliding bearing bush. Each measuring point is equipped with an ultrasonic probe and a composite strain gauge with a temperature sensor. The data generated by the three monitoring nodes are collected by the data acquisition unit and then sent to the data processing unit.

[0009] Step S2: Simultaneously acquire three signals from each monitoring node using the data acquisition unit: the reflected echo signal from the ultrasonic interface, the first grid signal and the second grid signal from the composite strain gauge, wherein the first grid signal is the original strain signal ɛ.raw The second grid signal is the in-situ temperature T;

[0010] Step S3: Eliminate the interference of thermal output on the original strain signal through temperature correction to obtain the true mechanical strain of the bearing;

[0011] Step S4: Based on the actual mechanical strain, the oil film pressure is inverted, and the oil film sound velocity and density are corrected by combining temperature and pressure.

[0012] Step S5: Combine mechanical deformation and thermal deformation to update the propagation path length of ultrasonic waves in the bearing bush in real time, eliminating the propagation distance error caused by bearing bush deformation;

[0013] Step S6: Construct a theoretical model for oil film thickness, measure the reflection coefficient experimentally, substitute the corrected acoustic parameters, and calculate the oil film thickness at a single measuring point.

[0014] Step S7: Based on the data from the three measuring points, reconstruct the mechanical deformation distribution of the bearing throughout the field, calculate the position of the shaft center, and finally obtain the oil film thickness of the entire field at any angle, realizing the measurement from a single point to the entire field.

[0015] As a further improvement of the present invention, in step S1, measuring point B is arranged in the negative direction of the Z-axis, measuring point A is located at an angle of 20° with the negative direction of the Z-axis, and measuring point C and measuring point A are symmetrically distributed about the negative direction of the Z-axis.

[0016] As a further improvement of the present invention, in step S3, the step of eliminating the interference of thermal output on the original strain signal through temperature correction to obtain the true mechanical strain of the bearing is specifically as follows:

[0017] Using the measured temperature T to measure the original strain signal ɛ of the first grid raw Thermal output correction is performed to eliminate the interference of temperature on the resistance strain effect, and the true mechanical strain α of the bearing substrate at the measuring point is obtained. real The corrected formula is:

[0018] ;

[0019] In the formula, ɛ raw α is the original strain signal output by the composite strain gauge. n γ n K is the thermal output correction factor for composite strain gauges on a specific substrate material. g T is the sensitivity coefficient of the composite strain gauge, T0 is the reference temperature, and T is the measured temperature.

[0020] As a further improvement of the present invention, in step S4, the correction of oil film sound velocity and density based on the oil film pressure inversion from real mechanical strain, combined with temperature and pressure, specifically involves:

[0021] Step S41, Contact Surface Stress Inversion: Based on the thick-walled cylinder theory in elasticity, the bearing bush is considered as a thick-walled circular tube under internal pressure. Within the elastic range, the true mechanical strain α on the outer surface of the bearing bush is... real There is a linear mapping relationship with the radial pressure P on the inner surface:

[0022] ;

[0023] In the formula, R in R out These are the inner and outer diameters of the bearing bush, E. shell The elastic modulus of the bearing bush;

[0024] Step S42, Temperature and Pressure Correction of Sound Velocity: Sound velocity is affected by the temperature and pressure of the medium. The temperature and pressure correction formula for sound velocity is:

[0025] ;

[0026] In the formula, c c Here, c0 is the corrected speed of sound, and a is the standard speed of sound. c β is the sound speed temperature drift coefficient. c The acoustic coefficient;

[0027] Step S43, Temperature and Pressure Correction for Density: The formula for calculating oil film thickness is affected by density, and the calculation formula is as follows:

[0028] ;

[0029] In the formula, ρ c The corrected density is ρ0, where ρ is the standard density and a is the density. v β is the coefficient of oil expansion, and βv is the coefficient of oil compressibility.

[0030] As a further improvement of the present invention, in step S5, the combined mechanical deformation and thermal deformation are used to update the propagation path length of the ultrasonic wave in the bearing bush in real time, eliminating the propagation distance error caused by bearing bush deformation, specifically as follows:

[0031] To eliminate the effect of temperature on the resistivity of the strain gauge, the actual mechanical strain α calculated in step S3 is used. real Calculate the mechanical deformation, calculate the thermal deformation based on the measured temperature T, and update the ultrasonic propagation distance Lc in the bearing bush in real time.

[0032] ;

[0033] in

[0034] ;

[0035] ;

[0036] In the formula, L0 is the initial thickness of the bearing bush, and ΔL me L represents the mechanical deformation. th α is the amount of thermal deformation. shell K is the coefficient of linear thermal expansion. cal The thickness-strain coefficient is given.

[0037] As a further improvement of the present invention, in step S6, the construction of the theoretical model for oil film thickness, by experimentally measuring the reflection coefficient and substituting the corrected acoustic parameters, calculates the oil film thickness at a single measuring point, specifically as follows:

[0038] Step S61, Theoretical Model Construction:

[0039] (1) The stiffness coefficient K of the oil film is defined using the spring stiffness model:

[0040] ;

[0041] In the formula, B is the bulk modulus, ρ c To correct for density, c c The corrected velocity of sound is h, and the thickness of the oil film to be measured is h.

[0042] (2) Establish the relationship between the oil film stiffness reflection coefficient |R| and the stiffness coefficient K, and form the theoretical formula for the reflection coefficient:

[0043] ;

[0044] In the formula, |R| is the magnitude of the reflection coefficient, and Z shell is the acoustic impedance of the bearing substrate, and f is the ultrasonic frequency;

[0045] (3) By combining the above two formulas and eliminating the stiffness coefficient K, the final formula for calculating the oil film thickness h is obtained:

[0046] ;

[0047] Step S62, Experimental measurement of the reflection coefficient |R|:

[0048] Because the theoretical formula for the reflection coefficient includes the unknown quantity h to be measured, |R| cannot be directly calculated. Therefore, it needs to be calculated inversely using experimental signals. The ultrasonic flight time is calculated using the propagation distance Lc corrected in step S5.

[0049] ;

[0050] In the formula, t e For the ultrasonic flight time, c shell The speed of sound of the bearing;

[0051] Define a time window w with a width of Δt, the center position of which varies with t. e Real-time movement:

[0052] ;

[0053] FFT transformation is performed only on the ultrasonic radio frequency echo signal S(t) falling within the time window w to extract the center frequency amplitude A of the oil film interface echo. oil Calculate the measured reflection coefficient |R|:

[0054] ;

[0055] In the formula, A ref This is the static, oil-free reference echo amplitude.

[0056] Step S63, Oil film thickness calculation: Calculate the corrected density ρ c Correcting the speed of sound c c The reflection coefficient |R| and the acoustic impedance Z of the bearing substrate. shell Substitute the values ​​into the oil film thickness formula to calculate the oil film thickness h at the measuring point.

[0057] As a further improvement of the present invention, in step S7, the process of reconstructing the full-field mechanical deformation distribution of the bearing bush based on data from three measuring points, calculating the shaft center position, and finally obtaining the full-field oil film thickness at any angle, thereby realizing the oil film reconstruction from a single point to the entire field, specifically involves: using three monitoring nodes arranged in the bearing bush bearing area, and based on the modal theory of elasticity, reconstructing the full-field mechanical deformation distribution through analytical calculation, thereby obtaining a high-precision full-field oil film thickness; specifically including the following sub-steps:

[0058] Step S71: Construct modal functions: Define the mechanical radial deformation distribution ΔR on the inner surface of the bearing bush. me (θ):

[0059] ;

[0060] In the formula, θ is any angle in the circumferential direction; A0 is the undetermined average radial mechanical expansion coefficient, which characterizes the overall tensile amount of the bearing in the circumferential direction; A1 and B1 are the undetermined elliptical deformation characteristic coefficients, which characterize the magnitude and direction of the bearing cross-section changing from a circle to an ellipse.

[0061] Radial expansion y of the inner diameter of the bearing at the measuring point e The calculation formula is:

[0062] ;

[0063] In the formula, ν is the Poisson's ratio of the bearing material;

[0064] Radial expansion y measured at three points eConstruct a system of three linear equations HX=Y

[0065] ;

[0066] Since the three measuring points are arranged at different angles, matrix H is a non-singular matrix. Therefore, the matrix inverse operation X=H can be used to solve the problem. -1 Y uniquely calculates the three coefficients [A0, A1, B1] for the current bearing shape. T This allows us to construct the mechanical radial deformation distribution ΔR on the inner surface of the bearing bush. me The specific expression;

[0067] Step S72, Axis position calculation: After obtaining the radial expansion y at each measuring point... e Then, the oil film thickness h was measured at the measuring points. A h B h C Establish a system of linear equations with respect to the axis coordinates (x, z);

[0068] Step S73, Calculation of oil film thickness across the entire field: After obtaining the mechanical deformation distribution ΔR across the entire field... me (θ) and the thermal expansion distribution of the bearing ΔR th Given the journal center coordinates (x, z) determined above, the formula for calculating the oil film thickness at any angle h(θ) is as follows:

[0069] .

[0070] As a further improvement of the present invention, in step S72, the establishment of a system of linear equations about the axis coordinates (x, z) specifically includes:

[0071] First, determine the effective radius of the inner surface of the bearing bush at each measuring point after considering thermal-mechanical coupling deformation.

[0072] ;

[0073] In the formula, ΔR th This refers to the thermal expansion deformation of the bearing bush.

[0074] Based on the geometric relationship of the sliding bearing, the oil film thickness h at the measuring point t This can be expressed as the effective radius of the inner surface of the bearing bush. The projection of the difference between the journal radius and the journal radius onto the eccentric direction:

[0075] ;

[0076] In the formula, R j Let (x, z) be the journal radius, and (x, z) be the coordinates of the axis to be determined.

[0077] Let h be the theoretical thickness at each measuring point. t Equal to the measured thickness h i The following equation is obtained:

[0078] ;

[0079] In the formula, i represents the measurement point number (i=A, B, C), h i The actual measured oil film thickness at the measuring point corresponding to step S6;

[0080] Represented in matrix form:

[0081] ;

[0082] By combining the installation angles and data of the three measuring points, the equations are solved using the least squares method to obtain the axis coordinates (x, z).

[0083] As a further improvement of the present invention, the data processing unit displays the full-field oil film thickness distribution h(θ) and shaft center trajectory (x, z) obtained in step S7 in a graphical manner on the user interface in real time, and stores the calculation results together with the original monitoring data into the historical database for subsequent bearing condition trend analysis.

[0084] Compared with the prior art, the present invention has the following technical advantages:

[0085] (1) In view of the problem that the existing technology does not fully consider the time-varying and nonlinear nature of the sound velocity parameter, the present invention combines the real mechanical strain of the bearing to invert the oil film pressure, and introduces a dual correction mechanism of temperature and pressure to accurately calibrate the sound velocity and density of the oil film, effectively avoiding the measurement deviation caused by single temperature compensation, and making the acoustic parameters more in line with the actual working conditions.

[0086] (2) In response to the systematic error caused by the geometric deformation of the bearing substrate, this invention obtains the real mechanical strain through strain decoupling and synchronously corrects the ultrasonic propagation distance by combining temperature data, which fully compensates for the influence of mechanical deformation and thermal expansion on the propagation path, breaks the assumption of constant bearing wall thickness in traditional methods, and further consolidates the foundation of measurement accuracy.

[0087] (3) This invention innovatively adopts a three-point monitoring layout and elastic mechanical modal theory. By reconstructing the mechanical deformation distribution of the bearing bush in the whole field and accurately calculating the shaft center position, it realizes the leap from single-point measurement to full-field oil film thickness reconstruction. It can not only obtain local oil film data, but also present the full circumferential oil film distribution characteristics, providing a more comprehensive basis for judging the lubrication status of the bearing.

[0088] (4) Through the collaborative design of multi-parameter correction, deformation compensation and full-field reconstruction, this invention comprehensively solves the core problems faced by existing ultrasonic measurement technology in practical engineering applications, greatly improves the accuracy, comprehensiveness and reliability of oil film thickness measurement, and provides a stronger technical guarantee for the safe and stable operation of large rotating machinery. Attached Figure Description

[0089] The present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0090] Figure 1 This is a structural diagram of the measurement system used in the non-contact sliding bearing oil film thickness measurement method of the present invention.

[0091] Figure 2 This is a flowchart of the non-contact sliding bearing oil film thickness measurement method of the present invention.

[0092] Figure 3 This is a schematic diagram illustrating the calculation of oil film thickness in the non-contact sliding bearing oil film thickness measurement method of the present invention.

[0093] In the diagram: 1-shaft; 2-bearing bush; 3-ultrasonic sensor; 4-composite strain gauge; 5-data acquisition card; 6-industrial control computer. Detailed Implementation

[0094] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention are within the scope of protection of the present invention.

[0095] Please see Figure 2 The present invention provides a method for monitoring the oil film of a sliding bearing based on ultrasonic waves and a composite strain sensor, comprising the following steps:

[0096] Step S1, Hardware system configuration, such as Figure 1As shown. The ultrasonic sensor 3 is a piezoelectric ultrasonic straight probe with a center frequency of 10MHz, bonded to the outer surface of the bearing bush using a high-temperature coupling agent. A foil-type composite strain gauge with a temperature sensor is attached adjacent to the probe. The data acquisition unit 5 is a high-speed multi-channel data acquisition card. The ultrasonic acquisition channel has a sampling rate >100MS / s and a resolution >12bit. The analog acquisition channel (strain / temperature) has a sampling rate >10KS / s and a resolution >16bit. The data processing unit is an industrial computer 6, which performs preprocessing of the acquired signals and real-time calculation of the oil film thickness algorithm. In the sliding bearing, shaft 1 and bearing bush 2 have a clearance fit. Three monitoring nodes, defined as measuring points A, B, and C, are arranged on the back of bearing bush 2. Each measuring point consists of an ultrasonic probe and a composite strain gauge 4 with a temperature sensor attached adjacent to it. The composite strain gauge 4 is located less than 5mm from the edge of the ultrasonic probe to ensure the in-situ accuracy of the measurement. Measuring point B is located in the negative Z-axis direction, measuring point A is located at an angle of 20° to the negative Z-axis direction, and measuring point C is symmetrically distributed with measuring point A about the negative Z-axis direction.

[0097] Step S2, Multi-physics signal synchronous acquisition: Simultaneously acquire three signals using a data acquisition system: the reflected echo signal from the ultrasonic interface, the first grid signal of the composite strain gauge (original strain α). raw ) and the second grid signal (measured temperature T).

[0098] Step S3, Strain Decoupling of Bearing Matrix: Resistance strain gauges detect strain by measuring the minute changes in the resistance of the material under stress. When the temperature rises, the bearing metal expands, causing strain in the strain gauge. Simultaneously, the resistivity of the strain gauge itself changes with temperature. To obtain the true mechanical strain α of the bearing matrix... real This eliminates the two interfering factors: deformation caused by thermal expansion and changes in resistivity. The corrected formula is:

[0099] ;

[0100] In the formula, ɛ raw α is the original strain signal output by the composite strain gauge. n γ n K is the thermal output correction factor for a thick-walled cylindrical theoretical strain gauge on a specific substrate material. g T is the sensitivity coefficient of the composite strain gauge, T0 is the reference temperature, and T is the measured temperature.

[0101] Step S4, Multi-parameter correction of acoustic parameters: The physical properties of the oil film (sound velocity, density) are affected by both temperature and pressure, and the following corrections are made:

[0102] (1) Stress inversion at the contact surface: Since it is impossible to directly install a pressure sensor in the oil film gap, the pressure of the fluid is inverted by the deformation of the bearing solid. Based on the thick-walled cylinder theory in elasticity, the bearing is regarded as a thick-walled circular tube under internal pressure. Within the elastic range, the actual mechanical strain α on the outer surface of the bearing is... real There is a linear mapping relationship with the radial pressure P on the inner surface.

[0103] ;

[0104] In the formula, R in R out These are the inner and outer diameters of the bearing bush, E. shell This is the elastic modulus of the bearing bush.

[0105] (2) Temperature and pressure correction for sound velocity: Sound velocity is affected by the temperature and pressure of the medium. The temperature and pressure correction formula for sound velocity is as follows:

[0106] ;

[0107] In the formula, c c Here, c0 is the corrected speed of sound, and a is the standard speed of sound. c β is the sound speed temperature drift coefficient. c is the acoustic coefficient.

[0108] (3) Temperature and pressure correction for density: The formula for calculating oil film thickness is affected by density, and the formula is as follows:

[0109] ;

[0110] In the formula, ρ c The corrected density is ρ0, where ρ is the standard density and a is the density. v Oil expansion coefficient, β v Oil compressibility coefficient.

[0111] Step S5, Ultrasonic Propagation Distance Correction: The thickness of the oil film measured by ultrasound depends on its flight time within the bearing bush. Under load, the bearing bush undergoes elastic deformation and thermal expansion due to temperature, causing a change in the ultrasonic propagation path (i.e., bearing bush thickness). To eliminate the effect of temperature on the resistivity of the strain gauge (temperature drift), the actual mechanical strain α calculated in step S3 is corrected. real Calculate the mechanical deformation, and calculate the thermal deformation based on the measured temperature T, taking into account the ultrasonic wave propagation distance L in the bearing bush. c Real-time updates:

[0112] ;

[0113] in,

[0114] ;

[0115] ;

[0116] In the formula, L0 is the initial thickness of the bearing bush, and ΔL me L represents the mechanical deformation. th α is the amount of thermal deformation. shell K is the coefficient of linear thermal expansion. cal The thickness-strain coefficient is given.

[0117] Step S6: Inversion of single-point oil film thickness based on the spring model:

[0118] (1) Theoretical model construction: First, the spring stiffness model is adopted, and the stiffness coefficient K of the oil film is defined as follows:

[0119] ;

[0120] In the formula, B is the bulk modulus, ρ c To correct for density, c c The corrected velocity of sound is h, and the thickness of the oil film to be measured is h.

[0121] Secondly, establish the relationship between the oil film stiffness reflection coefficient |R| and the stiffness coefficient K:

[0122] ;

[0123] In the formula, |R| is the magnitude of the reflection coefficient, and Z shell f is the acoustic impedance of the bearing substrate, and f is the ultrasonic frequency.

[0124] Finally, by combining the two formulas above and eliminating the stiffness coefficient K, the final formula for calculating the oil film thickness h can be obtained.

[0125] ;

[0126] (2) Experimental measurement of reflection coefficient |R|: Since the theoretical formula for reflection coefficient above includes the unknown quantity h, the reflection coefficient |R| cannot be directly calculated. Therefore, it is necessary to inversely calculate the reflection coefficient |R| through experimental signals. The propagation distance L corrected in step S5 is used... c Calculate the time of flight of ultrasound:

[0127] ;

[0128] In the formula, t e For the ultrasonic flight time, c shell The speed of sound in the bearing.

[0129] Define a time window w with a width of Δt, the center position of which varies with t. e Real-time movement:

[0130] ;

[0131] FFT transformation is performed only on the ultrasonic radio frequency echo signal S(t) falling within the time window w to extract the center frequency amplitude A of the oil film interface echo. oil Calculate the measured reflection coefficient |R|

[0132] ;

[0133] In the formula, A ref This is the static, oil-free reference echo amplitude.

[0134] (3) Oil film thickness calculation: The corrected density ρ c Correcting the speed of sound c c Reflection coefficient |R|, Acoustic impedance of bearing substrate Z shell Substitute the values ​​into the oil film thickness formula to calculate the oil film thickness h at the measuring point.

[0135] Step S7: Full-field oil film reconstruction, as follows Figure 3 As shown. Under heavy load conditions, significant radial expansion deformation (including thermal expansion and mechanical elastic deformation) exists at the bearing bush measuring points. Traditional rigid circular geometric calculation models can lead to shaft center positioning errors. Using three monitoring nodes (measuring point A, measuring point B, and measuring point C) arranged in the bearing bush bearing load area, based on the modal theory of elasticity, the full-field mechanical deformation distribution is reconstructed through analytical calculation, thereby obtaining a high-precision full-field oil film thickness. Specifically, the following steps are included:

[0136] (1) Constructing the modal function: Define the mechanical radial deformation distribution ΔR on the inner surface of the bearing bush. me (θ):

[0137] ;

[0138] In the formula, θ is any angle in the circumferential direction, A0 is the undetermined average radial mechanical expansion coefficient, characterizing the overall tensile amount of the bearing in the circumferential direction, and A1 and B1 are undetermined elliptical deformation characteristic coefficients, characterizing the magnitude and direction of the bearing cross-section changing from a circle to an ellipse.

[0139] Radial expansion y of the inner diameter of the bearing at the measuring point e Calculation formula:

[0140] ;

[0141] In the formula, ν is the Poisson's ratio of the bearing material;

[0142] Radial expansion y measured at three points e Construct a system of three linear equations HX=Y

[0143] ;

[0144] Since the three measuring points are arranged at different angles, matrix H is a non-singular matrix. Therefore, the matrix inverse operation X=H can be used to solve the problem. -1 Y uniquely calculates the three coefficients [A0, A1, B1] for the current bearing shape. T This allows us to construct the mechanical radial deformation distribution ΔR on the inner surface of the bearing bush. me Specific expression.

[0145] (2) Calculation of axis position: After obtaining the radial expansion y at each measuring point e Then, the oil film thickness h was measured at the measuring points. A h B h C Establish a system of linear equations about the axis coordinates (x, z). First, determine the effective radius of the inner surface of the bearing bush after considering thermo-mechanical coupling deformation at each measuring point.

[0146] ;

[0147] In the formula, ΔR th This represents the amount of thermal expansion deformation of the bearing bush.

[0148] Based on the geometric relationship of the sliding bearing, the oil film thickness h at the measuring point t This can be expressed as the effective radius of the inner surface of the bearing bush. The projection of the difference between the journal radius and the journal radius onto the eccentric direction:

[0149] ;

[0150] In the formula, R j Let (x, z) be the journal radius, and (x, z) be the coordinates of the axis to be determined.

[0151] Let h be the theoretical thickness at each measuring point. t Equal to the measured thickness h i The following equation is obtained:

[0152] ;

[0153] In the formula, i represents the measurement point number (i=A, B, C), h i The measured oil film thickness is the actual thickness at the measuring point corresponding to step S6.

[0154] Represented in matrix form:

[0155] ;

[0156] By combining the installation angles and data of the three measuring points, the equations are solved using the least squares method to obtain the axis coordinates (x, z).

[0157] (3) Calculation of oil film thickness across the entire field: After obtaining the mechanical deformation distribution ΔR across the entire field... me (θ) and the thermal expansion distribution of the bearing ΔR th Given the journal center coordinates (x, z) determined above, the formula for calculating the oil film thickness at any angle h(θ) is as follows:

[0158] .

[0159] The data processing unit (industrial control computer) displays the full-field oil film thickness distribution h(θ) and shaft center trajectory (x, z) obtained from step S7 in a graphical manner on the user interface in real time, and stores the calculation results along with the original monitoring data (temperature, strain, ultrasonic waveform) into the historical database for subsequent bearing condition trend analysis.

[0160] Measurement termination: When a measurement termination command is received, the system automatically saves all data files for the current measurement cycle, then disconnects the power supply to the high-speed data acquisition card and the ultrasonic generator, completing the measurement process.

[0161] In summary, this invention effectively solves the core problems of sound velocity nonlinearity offset and bearing deformation interference in existing measurement methods through multi-parameter collaborative correction and full-field reconstruction technology, and significantly improves the accuracy and comprehensiveness of oil film thickness measurement.

[0162] The embodiments of the present invention have been described in detail above with reference to the accompanying drawings. However, the present invention is not limited thereto. Various changes that can be made within the scope of knowledge possessed by those skilled in the art without departing from the spirit of the present invention are all within the protection scope of the claims of the present invention.

Claims

1. A non-contact method for measuring the oil film thickness of a sliding bearing, characterized in that, Includes the following steps: Step S1: Arrange three monitoring nodes A, B, and C on the back of the sliding bearing bush. Each measuring point is equipped with an ultrasonic probe and a composite strain gauge with a temperature sensor. The data generated by the three monitoring nodes are collected by the data acquisition unit and then sent to the data processing unit. Step S2: Simultaneously acquire three signals from each monitoring node using the data acquisition unit: the reflected echo signal from the ultrasonic interface, the first grid signal and the second grid signal from the composite strain gauge, wherein the first grid signal is the original strain signal ɛ. raw The second grid signal is the in-situ temperature T; Step S3: Eliminate the interference of thermal output on the original strain signal through temperature correction to obtain the true mechanical strain of the bearing; Step S4: Based on the actual mechanical strain, the oil film pressure is inverted, and the oil film sound velocity and density are corrected by combining temperature and pressure. Step S5: Combine mechanical deformation and thermal deformation to update the propagation path length of ultrasonic waves in the bearing bush in real time, eliminating the propagation distance error caused by bearing bush deformation; Step S6: Construct a theoretical model for oil film thickness, measure the reflection coefficient experimentally, substitute the corrected acoustic parameters, and calculate the oil film thickness at a single measuring point. Step S7: Based on the data from the three measuring points, reconstruct the mechanical deformation distribution of the bearing throughout the field, calculate the position of the shaft center, and finally obtain the oil film thickness of the entire field at any angle, realizing the measurement from a single point to the entire field.

2. The non-contact sliding bearing oil film thickness measurement method according to claim 1, characterized in that, In step S1, measuring point B is arranged in the negative direction of the Z-axis, measuring point A is located at an angle of 20° to the negative direction of the Z-axis, and measuring point C is symmetrically distributed with measuring point A about the negative direction of the Z-axis.

3. The non-contact sliding bearing oil film thickness measurement method according to claim 1, characterized in that, In step S3, the process of eliminating the interference of thermal output on the original strain signal through temperature correction to obtain the true mechanical strain of the bearing is specifically as follows: Using the measured temperature T to measure the original strain signal ɛ of the first grid raw Thermal output correction is performed to eliminate the interference of temperature on the resistance strain effect, and the true mechanical strain α of the bearing substrate at the measuring point is obtained. real The corrected formula is: ； In the formula, ɛ raw α is the original strain signal output by the composite strain gauge. n γ n K is the thermal output correction factor for composite strain gauges on a specific substrate material. g T is the sensitivity coefficient of the composite strain gauge, T0 is the reference temperature, and T is the measured temperature.

4. The non-contact sliding bearing oil film thickness measurement method according to claim 1, characterized in that, In step S4, the oil film pressure is inverted based on the actual mechanical strain, and the oil film sound velocity and density are corrected by combining temperature and pressure, specifically as follows: Step S41, Contact Surface Stress Inversion: Based on the thick-walled cylinder theory in elasticity, the bearing bush is considered as a thick-walled circular tube under internal pressure. Within the elastic range, the true mechanical strain α on the outer surface of the bearing bush is... real There is a linear mapping relationship with the radial pressure P on the inner surface: ； In the formula, R in R out These are the inner and outer diameters of the bearing bush, E. shell The elastic modulus of the bearing bush; Step S42, Temperature and Pressure Correction of Sound Velocity: Sound velocity is affected by the temperature and pressure of the medium. The temperature and pressure correction formula for sound velocity is: ； In the formula, c c Here, c0 is the corrected speed of sound, and a is the standard speed of sound. c β is the sound speed temperature drift coefficient. c The acoustic coefficient; Step S43, Temperature and Pressure Correction for Density: The formula for calculating oil film thickness is affected by density. The calculation formula is as follows: ； In the formula, ρ c The corrected density is ρ0, where ρ is the standard density and a is the density. v β is the coefficient of oil expansion, and βv is the coefficient of oil compressibility.

5. The non-contact sliding bearing oil film thickness measurement method according to claim 1, characterized in that, In step S5, the combined mechanical deformation and thermal deformation are used to update the propagation path length of the ultrasonic wave in the bearing bush in real time, eliminating the propagation distance error caused by bearing bush deformation. Specifically: To eliminate the effect of temperature on the resistivity of the strain gauge, the actual mechanical strain α calculated in step S3 is used. real Calculate the mechanical deformation, and calculate the thermal deformation based on the measured temperature T, taking into account the ultrasonic wave propagation distance L in the bearing bush. c Real-time updates: ； in ； ； In the formula, L0 is the initial thickness of the bearing bush, and ΔL me L represents the mechanical deformation. th α is the amount of thermal deformation. shell K is the coefficient of linear thermal expansion. cal The thickness-strain coefficient is given.

6. The non-contact sliding bearing oil film thickness measurement method according to claim 1, characterized in that, In step S6, the construction of the theoretical model for oil film thickness involves experimentally measuring the reflection coefficient, substituting the corrected acoustic parameters, and calculating the oil film thickness at a single measuring point. Specifically: Step S61, Theoretical Model Construction: (1) The stiffness coefficient K of the oil film is defined using the spring stiffness model: ； In the formula, B is the bulk modulus, ρ c To correct for density, c c The corrected velocity of sound is h, and the thickness of the oil film to be measured is h. (2) Establish the relationship between the oil film stiffness reflection coefficient |R| and the stiffness coefficient K, and form the theoretical formula for the reflection coefficient: ； In the formula, |R| is the magnitude of the reflection coefficient, and Z shell is the acoustic impedance of the bearing substrate, and f is the ultrasonic frequency; (3) By combining the above two formulas and eliminating the stiffness coefficient K, the final formula for calculating the oil film thickness h is obtained: ； Step S62, Experimental measurement of the reflection coefficient |R|: Because the theoretical formula for the reflection coefficient includes the unknown quantity h to be measured, |R| cannot be directly calculated. Therefore, it needs to be calculated inversely using experimental signals. The ultrasonic flight time is calculated using the propagation distance Lc corrected in step S5. ； In the formula, t e For the ultrasonic flight time, c shell The speed of sound of the bearing; Define a time window w with a width of Δt, the center position of which varies with t. e Real-time movement: ； FFT transformation is performed only on the ultrasonic radio frequency echo signal S(t) falling within the time window w to extract the center frequency amplitude A of the oil film interface echo. oil Calculate the measured reflection coefficient |R|: ； In the formula, A ref This is the static, oil-free reference echo amplitude. Step S63, Oil film thickness calculation: Calculate the corrected density ρ c Correcting the speed of sound c c The reflection coefficient |R| and the acoustic impedance Z of the bearing substrate. shell Substitute the values ​​into the oil film thickness formula to calculate the oil film thickness h at the measuring point.

7. The non-contact sliding bearing oil film thickness measurement method according to claim 1, characterized in that, In step S7, based on data from three measuring points, the full-field mechanical deformation distribution of the bearing bush is reconstructed, the shaft center position is calculated, and the full-field oil film thickness at any angle is finally obtained, realizing the oil film reconstruction from a single point to the entire field. Specifically, using three monitoring nodes arranged in the bearing bush bearing area, based on the modal theory of elasticity, the full-field mechanical deformation distribution is reconstructed through analytical calculation, thereby obtaining a high-precision full-field oil film thickness; specifically including the following sub-steps: Step S71: Construct modal functions: Define the mechanical radial deformation distribution ΔR on the inner surface of the bearing bush. me (θ): ； In the formula, θ is any angle in the circumferential direction; A0 is the undetermined average radial mechanical expansion coefficient, which characterizes the overall tensile amount of the bearing in the circumferential direction; A1 and B1 are the undetermined elliptical deformation characteristic coefficients, which characterize the magnitude and direction of the bearing cross-section changing from a circle to an ellipse. Radial expansion y of the inner diameter of the bearing at the measuring point e The calculation formula is: ； In the formula, ν is the Poisson's ratio of the bearing material; Radial expansion y measured at three points e Construct a system of three linear equations HX=Y ； Since the three measuring points are arranged at different angles, matrix H is a non-singular matrix. Therefore, the matrix inverse operation X=H can be used to solve the problem. -1 Y uniquely calculates the three coefficients [A0, A1, B1] for the current bearing shape. T This allows us to construct the mechanical radial deformation distribution ΔR on the inner surface of the bearing bush. me The specific expression; Step S72, Axis position calculation: After obtaining the radial expansion y at each measuring point... e Then, the oil film thickness h was measured at the measuring points. A h B h C Establish a system of linear equations with respect to the axis coordinates (x, z); Step S73, Calculation of oil film thickness across the entire field: After obtaining the mechanical deformation distribution ΔR across the entire field... me (θ) and the thermal expansion distribution of the bearing ΔR th Given the journal center coordinates (x, z) determined above, the formula for calculating the oil film thickness at any angle h(θ) is as follows: 。 8. The non-contact sliding bearing oil film thickness measurement method according to claim 7, characterized in that, In step S72, establishing a system of linear equations about the axis coordinates (x, z) specifically involves: First, determine the effective radius of the inner surface of the bearing bush at each measuring point after considering thermal-mechanical coupling deformation. : ； In the formula, ΔR th This refers to the thermal expansion deformation of the bearing bush. Based on the geometric relationship of the sliding bearing, the oil film thickness h at the measuring point t This can be expressed as the effective radius of the inner surface of the bearing bush. The projection of the difference between the journal radius and the journal radius onto the eccentric direction: ； In the formula, R j Let (x, z) be the journal radius, and (x, z) be the coordinates of the axis to be determined. Let h be the theoretical thickness at each measuring point. t Equal to the measured thickness h i The following equation is obtained: ； In the formula, i represents the measurement point number (i=A, B, C), h i The actual measured oil film thickness at the measuring point corresponding to step S6; Represented in matrix form: ； By combining the installation angles and data of the three measuring points, the equations are solved using the least squares method to obtain the axis coordinates (x, z).

9. The non-contact sliding bearing oil film thickness measurement method according to claim 8, characterized in that, The data processing unit displays the full-field oil film thickness distribution h(θ) and shaft center trajectory (x, z) obtained from step S7 in a graphical manner on the user interface in real time, and stores the calculation results along with the original monitoring data into the historical database for subsequent bearing condition trend analysis.

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