Bearing lubrication state monitoring method

Abstract

The invention relates to the technical field of bearing lubrication performance monitoring, and discloses a bearing lubrication state monitoring method, which comprises the following steps: establishing an oil film dragging force coefficient and thickness test experimental model, and obtaining a dragging force coefficient and a corresponding oil film thickness data set through the oil film dragging force coefficient and thickness test experimental model; establishing a calibration curve: according to the dragging force coefficient and the corresponding oil film thickness data set, calibrating an oil film dragging force coefficient and oil film thickness curve; the friction coefficient is equal to the oil film dragging power coefficient, the oil film dragging power coefficient of the to-be-measured bearing is substituted into the calibration curve to obtain the oil film thickness of the to-be-measured bearing, and a quantitative relation curve of the oil film dragging power coefficient and the oil film thickness is established through the oil film dragging power coefficient and the thickness test experiment model. Local measurement parameters are expanded to overall bearing lubrication state evaluation, and the defects that a traditional measurement technology cannot obtain overall bearing oil film thickness distribution and the lubrication state is difficult to comprehensively evaluate are overcome.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of bearing lubrication state monitoring, and particularly relates to a bearing lubrication state monitoring method. BACKGROUND

[0002] The lubrication state of a bearing is a core element determining its performance and service life, and directly affects the reliability and economy of equipment operation. Good lubrication can form a continuous oil film on the contact surface of the roller and the race, convert dry friction between metals into low-resistance fluid friction, effectively reduce the friction coefficient, and reduce wear and energy consumption. Therefore, real-time monitoring of the lubrication state is crucial to ensuring efficient and stable operation of the bearing.

[0003] The quality of the bearing lubrication state is mainly reflected by the oil film thickness, which is a core indicator for measuring the lubrication effect. Under ideal working conditions, a stable oil film thickness (usually above 2 pm) can form a continuous and complete fluid barrier on the contact surface of the roller and the race, achieve full film fluid lubrication, significantly reduce the friction coefficient to below 0.001, and effectively avoid direct contact and wear of the metal surface; on the contrary, if the oil film thickness is insufficient (such as below 0.1 pm), the bearing will enter a boundary lubrication or mixed lubrication state, the metal micro-convex bodies will be pressed and scraped against each other, leading to a sharp increase in the friction coefficient and accelerated wear, and even causing galling failure. Therefore, real-time and accurate monitoring of the oil film thickness is not only a key to evaluating the lubrication state of the bearing, but also a core technical means to ensure efficient and stable operation of the equipment.

[0004] Current methods for measuring the oil film thickness of a bearing (such as optical interference method, electrical contact method, ultrasonic method, etc.) can achieve local accurate measurement, but are difficult to apply to overall monitoring of the entire bearing. The core bottleneck lies in the limitations of the measurement technology and the complex three-dimensional dynamic working conditions of the bearing. For example, the optical interference method needs to be implemented on the transparent race surface, which can only cover the local contact area and cannot capture the dynamic changes of the oil film when the roller rolls in the circumferential direction; the electrical contact method relies on the resistance feedback of the probe and the metal surface, making it difficult to synchronously obtain full circumferential data in high-speed rotation; the ultrasonic method can penetrate the metal, but is disturbed by the reflection of the multiple interfaces of the bearing, making it difficult to distinguish the oil film distribution in the contact area between the roller and the inner and outer races. In addition, the uneven load distribution during the operation of the bearing and the combined motion of the roller's revolution and rotation result in a significant gradient of the oil film thickness in the axial and circumferential directions (such as the edge oil film thickness being only 1 / 3 of the central area), and the existing single-point or line measurement methods cannot restore the three-dimensional distribution of the oil film of the entire bearing, resulting in blind spots in the overall lubrication state evaluation. SUMMARY

[0005] To solve the above technical problems, the present application provides a bearing lubrication state monitoring method which can comprehensively evaluate the overall lubrication state.

[0006] The present application provides a bearing lubrication state monitoring method, comprising the following steps:

[0007] An oil film drag coefficient and thickness test experimental model is established, and a data set of the drag coefficient and corresponding oil film thickness is obtained through the oil film drag coefficient and thickness test experimental model;

[0008] A calibration curve is established: according to the data set of the drag coefficient and corresponding oil film thickness, the oil film drag coefficient and oil film thickness curve are calibrated;

[0009] The friction coefficient of the bearing to be measured is obtained, and the friction coefficient is equal to the oil film drag coefficient. The oil film drag coefficient of the bearing to be measured is substituted into the calibration curve to obtain the oil film thickness of the bearing to be measured.

[0010] Optionally, the oil film drag coefficient and thickness test experimental model comprises a base and an oil film drag coefficient test assembly and an oil film thickness test assembly connected to the base respectively, the oil film drag coefficient test assembly measures the oil film drag coefficient, and the oil film thickness test assembly measures the oil film thickness.

[0011] Optionally, the oil film drag coefficient test assembly comprises first and second driving motors connected to the base respectively, the output shaft of the first driving motor is vertically upward, the upper end of the output shaft is fixed with a transparent disc, the first driving motor is connected with a first load sensor at the bottom, the output shaft of the second driving motor is horizontally arranged, and a steel ball and a first torque sensor are connected to the output shaft, the steel ball is located above the transparent disc.

[0012] The oil film thickness test assembly comprises a spectrometer and a light source, the spectrometer is connected to the base, the spectrometer is located directly below the steel ball, and the light source is fixed to the upper end of the spectrometer.

[0013] Optionally, the second driving motor is connected with a second load sensor at the lower end, the first and second load sensors are connected with height adjustment assemblies between the base respectively, the height adjustment assembly comprises an adjusting shaft and a support, the bottom of the adjusting shaft is threadedly connected with the support, the support is fixed to the base, and a buffer spring is sleeved on the adjusting shaft.

[0014] Optionally, the oil film drag coefficient is calculated by the following formula:

[0015]

[0016] In the formula, μ is the oil film drag coefficient, T is the drag torque, the unit is N·m, which is measured by the first torque sensor, P is the radial load, the unit is N, which is measured by the first load sensor, and l is the radius of the steel ball, the unit is m.

[0017] Optionally, the oil obtains a data set of drag coefficient and corresponding oil film thickness when multiple working condition combinations are set, the working conditions including: rotating speed, load and lubricating oil viscosity, each working condition is continuously operated for 10 minutes, and the oil film drag coefficient and the oil film thickness are synchronously collected at a sampling frequency of 100 Hz.

[0018] Optionally, the calibration curve is established by:

[0019] The data set is nonlinearly fitted by using the least square method, and a quantitative relationship curve of the oil film drag coefficient mu and the oil film thickness d is established, and the expression is d=f(mu drag );

[0020] The quantitative relationship curve is cross-validated and error analyzed, so that the fitting error of the quantitative relationship curve under different working conditions is controlled within ±5%.

[0021] Optionally, the calibration curve is established for different types of bearings, and a series of calibration curve libraries are formed.

[0022] Optionally, the friction coefficient of the bearing to be measured is obtained through a test bench, the test bench comprising: a driving mechanism fixed on a base plate, a radial loading mechanism and an axial loading mechanism, a main shaft of the driving mechanism is connected with a second torque sensor, a first bearing, a second bearing and a test bearing, respectively, and the test bearing is connected with the radial loading mechanism and the axial loading mechanism, respectively.

[0023] Optionally, the friction coefficient of the bearing to be measured is calculated by the following formula:

[0024]

[0025] In the formula, mu actual is the friction coefficient of the bearing to be measured, M actual is the friction torque of the test bearing, in N·m, the total friction torque M total is calculated by the difference between the friction torque of the first bearing and the second bearing, d m-actual is the diameter of the rolling element of the rolling bearing, in m, F actual is the load under actual working conditions, in N, F actual =f p (XF r +YF a ), F r is the loading force applied by the radial loading mechanism, F a is the loading force applied by the axial loading mechanism, f p is the impact load coefficient, X is the radial dynamic load coefficient, and Y is the axial dynamic load coefficient.

[0026] The technical scheme provided by the embodiment of the application has the following advantages compared with the prior art:

[0027] The bearing lubrication state monitoring method provided by the embodiment of the application establishes a quantitative relationship curve of the oil film drag force coefficient and the oil film thickness through an oil film drag force coefficient and thickness test experiment model, expands the local measurement parameter to overall bearing lubrication state evaluation, overcomes the defects that the traditional measurement technology cannot obtain the oil film thickness distribution of the entire bearing and cannot comprehensively evaluate the lubrication state, and only needs to measure the overall friction coefficient of the bearing, so that the oil film thickness can be quickly calculated according to the calibration curve, the complex bearing structure is avoided to be measured one by one, the measurement cost and technical difficulty are significantly reduced, and the monitoring efficiency is improved. The method is suitable for bearings of different types and working conditions, has universality and high compatibility, can reflect the change of the bearing lubrication state in real time, provides accurate data support for equipment maintenance, prolongs the service life of the bearing, and reduces the risk of failure caused by lubrication failure. BRIEF DESCRIPTION OF DRAWINGS

[0028] Figure 1 A front view of a bearing lubrication state monitoring system based on reverse calibration of a friction coefficient is provided for the embodiment of the application.

[0029] Figure 2 A side view of a bearing lubrication state monitoring system based on reverse calibration of a friction coefficient is provided for the embodiment of the application.

[0030] Figure 3 A structural schematic diagram of a test bed is provided for the embodiment of the application.

[0031] Figure 4 A calibration curve is provided for the embodiment of the application.

[0032] BRIEF DESCRIPTION OF DRAWINGS

[0033] 1, damping base; 2, nut; 3, first support; 4, first fixed shaft; 5, first spring; 6, first pressure head; 7, first load sensor; 8, first driving motor; 9, transparent disc; 10, lubricating oil injector; 11, steel ball; 12, first torque sensor; 13, second driving motor; 14, second support; 15, second fixed shaft; 16, second load sensor; 17, second pressure head; 18, third fixed shaft; 19, second spring; 20, third support; 21, light source; 22, spectrometer; 23, high-speed camera; 24, cage optical support; 25, second nut 25; 26, driving mechanism; 27, flange; 28, second torque sensor; 29, shaft coupling; 30, first bearing seat; 31, main shaft; 32, second bearing seat; 33, test bearing; 34, radial loading mechanism; 35, axial loading mechanism. DETAILED DESCRIPTION

[0034] One specific embodiment of the present application will be described in detail below with reference to the drawings, but it should be understood that the scope of protection of the present application is not limited by the specific embodiment.

[0035] In the description of the present application, it should be understood that the terms "center", "longitudinal", "transverse", "length", "width", "thickness", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", "axial", "radial", "circumferential" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the technical solutions of the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application.

[0036] The present application will be described below through several specific embodiments. In order to keep the following description of the embodiments of the present application clear and concise, detailed description of known functions and known components can be omitted. When any component of the embodiments of the present application appears in more than one figure, the component can be denoted by the same reference numeral in each figure.

[0037] The embodiments of the present application provide a bearing lubrication state monitoring method, comprising the following steps:

[0038] An oil film drag force coefficient and thickness test experimental model is established, and a data set of drag force coefficients and corresponding oil film thicknesses is obtained through the oil film drag force coefficient and thickness test experimental model;

[0039] A calibration curve is established: according to the data set of drag force coefficients and corresponding oil film thicknesses, the oil film drag force coefficient and oil film thickness curve are calibrated;

[0040] The friction coefficient of the bearing to be measured is obtained, which is equal to the oil film drag force coefficient, and the oil film drag force coefficient of the bearing to be measured is substituted into the calibration curve to obtain the oil film thickness of the bearing to be measured.

[0041] The bearing lubrication state monitoring method provided by the embodiment of the application establishes a quantitative relationship curve of the oil film drag coefficient and the oil film thickness through an oil film drag coefficient and thickness test experiment model, expands the local measurement parameters to the overall bearing lubrication state evaluation, overcomes the defects that the traditional measurement technology cannot obtain the oil film thickness distribution of the entire bearing and is difficult to comprehensively evaluate the lubrication state, and only needs to measure the overall friction coefficient of the bearing, so that the oil film thickness can be quickly calculated according to the calibration curve, the complex bearing structure is avoided to be measured one by one, the measurement cost and technical difficulty are significantly reduced, the monitoring efficiency is improved, the method is suitable for bearings of different types and working conditions, has universality and high compatibility, can reflect the bearing lubrication state change in real time, provides accurate data support for equipment maintenance, prolongs the service life of the bearing, and reduces the failure risk caused by lubrication failure.

[0042] Optionally, the oil film drag coefficient and thickness test experiment model comprises a base 1 and an oil film drag coefficient test assembly and an oil film thickness test assembly connected to the base 1 respectively, the oil film drag coefficient test assembly measures the oil film drag coefficient, and the oil film thickness test assembly measures the oil film thickness.

[0043] As Figure 2 and Figure 3As shown, the oil film drag coefficient test assembly comprises: a first drive motor 8 and a second drive motor 13 connected to the base 1 respectively, the base 1 adopts a thick metal flat plate structure, and a damping rubber pad can be arranged at the bottom. A stable support foundation is provided for the whole device, external vibration interference is weakened through damping design, the relative position of each component is stable during the measurement process, the measurement accuracy is improved, the output shaft of the first drive motor 8 is vertically upward, the upper end of the output shaft is fixed with a transparent disc 9, the first drive motor 8 drives the transparent disc 9 to rotate around its own axis, and one moving end of the oil film contact pair is constructed, the first drive motor 8 is connected with the first load sensor 7 at the bottom, the output shaft of the second drive motor 13 is arranged horizontally, and a steel ball 11 and a first torque sensor 12 are connected to the output shaft, the steel ball 11 is located above the transparent disc 9, the second drive motor 13 drives the steel ball 11 to rotate, and another direction movement is provided for the contact pair to simulate the relative movement state of the oil film under the actual working condition. The lubricating oil injector 10 is equipped with a needle, which can accurately control the drop amount of lubricating oil, and drops lubricating oil to the contact pair area of the transparent disc 9 and the steel ball 11 to construct the basic condition of the oil film formation. By controlling the oil injection amount and frequency, different lubrication conditions (such as boundary lubrication, mixed lubrication and fluid lubrication) are simulated to meet the diversified oil film measurement requirements. The oil film thickness test assembly comprises a spectrometer 22 and a light source 21, the spectrometer 22 is connected to the base 1, the spectrometer 22 is located directly below the steel ball 11, and the light source 21 is fixed to the upper end of the spectrometer 22. The oil film thickness test assembly (light source 21, spectrometer 22 and high-speed camera 23) is arranged below the transparent disc 9 through a cage type optical support 24, the optical axis is vertically upward and aligned with the oil film contact pair area to ensure the effective transmission of incident light and reflected / interfered light. The lubricating oil injector 10 is arranged on one side above the transparent disc 9, the needle is aligned with the contact pair area, and the lubricating oil can be accurately dropped. The steel ball 11 is made of high-strength and high-hardness metal material (such as bearing steel), the surface is smooth, and it is in contact with the transparent disc 9 to form an oil film bearing area therebetween. Its movement state (driven by the second drive motor 13) is matched with the movement of the transparent disc 9 to construct the oil film shear and bearing condition, and it also serves as a reflection / scattering interface for optical detection and participates in the optical measurement of oil film thickness. The transparent disc 9 is a circular flat plate structure, the material is selected from high-transmittance optical glass (such as quartz glass), the surface is polished to ensure the optical detection effect, and it serves as a "moving matrix" for oil film bearing and forms an oil film contact pair with the steel ball 11. Its transparent property provides a measurement path for the oil film thickness test assembly, so that the light source 21 can penetrate the transparent disc 9 to form an interference or reflected light signal in the oil film area for oil film thickness measurement. The first torque sensor 12 is adapted to the output shaft of the second drive motor 13, and a torque sensing element (such as a strain gauge or a magneto-inductive structure) is built-in and installed in the transmission path between the second drive motor 13 and the steel ball 11 (between the output shaft and the connecting shaft of the steel ball 11) to detect the torque signal received by the steel ball 11 during rotation in real time.Since the torque is directly related to the oil film drag coefficient (through the mechanical conversion relationship), the first torque sensor 12 provides the core mechanical parameter for drag coefficient measurement; the first load sensor 7 detects the vertical load force received by the transparent disc 9. The light source 21 adopts a narrow-band light source (such as a monochromatic LED, a laser light source), which has a columnar or block shape and is equipped with an optical collimation output end, providing stable, monochromatic incident light for oil film thickness optical measurement. The light emitted by the light source 21 is incident to the oil film region through the transparent disc 9, and reflection / interference occurs on the upper and lower surfaces of the oil film (the interfaces of the transparent disc 9, the oil film, the oil film, and the steel ball 11), forming an optical signal carrying oil film thickness information. The spectrometer 22 is built-in with a light splitting element (such as a grating, a prism) and a photodetector, which receives the light signal reflected / interfered by the oil film, and converts the light signal into spectral data through light splitting and photoelectric conversion. The spectral analysis algorithm (such as optical interference spectrum analysis) is used to extract the oil film thickness information from the spectral data, realizing high-precision measurement of the oil film thickness. The high-speed camera 23 has high-speed image acquisition capability (such as kilo frames per second), and the lens is adapted to the optical detection requirements. The high-speed camera 23 assists optical measurement and collects dynamic images of the oil film region. On the one hand, it can be used to verify the accuracy of the measurement results of the spectrometer 22 (by analyzing the oil film interference fringes through images); on the other hand, it can capture the dynamic change process of the oil film (such as oil film rupture, reconstruction, etc.), providing intuitive image data for oil film characteristic research. The cage optical support 24 is a frame structure composed of metal rods and connecting pieces, which can flexibly adjust the spatial position and angle of the light source 21, the spectrometer 22 and the high-speed camera 23, and provide stable and adjustable installation support for the oil film thickness test assembly. By adjusting the cage optical support 24, the optical axes of the light source 21, the spectrometer 22 and the high-speed camera 23 are accurately aligned with the oil film measurement area, ensuring the accuracy and stability of optical signal acquisition.

[0044] The present application mainly synchronously measures the oil film drag coefficient and the oil film thickness through experiments, and calibrates the oil film drag coefficient and the oil film thickness curve. The calibrated curve is applied to the monitoring of the entire bearing lubrication state. By measuring the oil film drag coefficient of the bearing, the oil film thickness of the bearing can be obtained through the curve, and then the lubrication state of the bearing can be obtained.

[0045] Optionally, the second driving motor 13 is connected with the second load sensor 16 at the lower end, and the first load sensor 7 and the second load sensor 16 are respectively connected with the base 1 through a height adjustment assembly, which comprises an adjusting shaft and a support, the bottom of the adjusting shaft is threadedly connected with the support, the support is fixed with the base 1, a buffer spring is sleeved on the adjusting shaft, specifically, the first driving motor 8 is sequentially connected with the first load sensor 7, the first pressure head 6, the first fixed shaft 4, the first support 3 is fixed with the base 1, the first fixed shaft 4 is threadedly connected with the first support 3 and is fixed through the nut 2, the first spring 5 (such as a disc spring principle) is sleeved on the first fixed shaft 4 to play a buffering role, so as to adjust the height of the transparent disc 9. The second driving motor 13 is sequentially connected with the second support 14, the second fixed shaft 15, the second load sensor 16, the second pressure head 17 and the third fixed shaft 18, the lower end of the third fixed shaft 18 is fastened with the third support 20 through a nut, the second spring 19 is arranged between the second pressure head 17 and the third fixed shaft 18 and the third support 20 to realize elastic loading, the steel ball 11 is installed at the front end of the output shaft of the second driving motor 13 and is in contact with the upper surface of the transparent disc 9, all the pressure heads are columnar structures, one end of which is adapted to the motor shaft / axle system connection, and the other end is matched with the first fixed shaft 4 and the third fixed shaft 18. As a load transmission component, the force signal detected by the load sensor is transmitted to the axle system to realize stable loading of the transparent disc 9 and the steel ball 11 contact pair, and to ensure the stability of the oil film contact pressure. All the fixed shafts are motion and force transmission components, which transmit the motor driving force and the loading force to ensure the motion synchronization and force transmission stability of each motion component. The first support 3 is a vertical support structure, which is adapted to the installation of the first fixed shaft 4 and the first pressure head 6; the second support 14 and the third support 20 are horizontal / vertical combined support structures (combined Figure 2 ), which are respectively used for positioning and supporting the second fixed shaft 15 and the third fixed shaft 18. The axle system, the pressure head and other components are provided with installation reference and support to ensure the coaxiality and position accuracy of each transmission component, ensure the stable motion of the contact pair, and the spring has elastic deformation ability. Installed between the pressure head and the support (such as between the second pressure head 17 and the third support 20), the spring absorbs the impact and vibration in the loading process through elastic deformation to ensure the stability of the loading force, and at the same time provides a certain force buffering and adjusting ability for the loading system. The nut 5 is adapted to the threaded structure of the first fixed shaft 4 and the first support 3, and is used for fastening connection of the first fixed shaft 4 and the first support 3, and the threaded pre-tightening force is used to ensure the stability of the axle system installation and prevent the axle system from loosening during transmission. At the same time, the adjusting screw can realize the loading of the radial load in cooperation with the disc spring.

[0046] Two load sensors incorporate strain-sensing or piezoelectric sensing elements. The first load sensor 7 is installed between the first drive motor 8 and the first pressure head 6 to detect the vertical loading force on the transparent disk 9. The second load sensor 16 is installed between the second pressure head 17 on the side of the second drive motor 13 and the shaft system to detect the loading force on the contact pair of the steel ball 11. Together, they provide loading force monitoring for oil film bearing conditions, ensuring stable test forces. Before the experiment, the transparent disk 9 can be leveled using the first load sensor 7 and the second load sensor 16, while also providing a load basis for calculating oil film parameters.

[0047] Optionally, the oil film drag coefficient is calculated using the following formula:

[0048]

[0049] In the formula, μ is the oil film drag force coefficient, T is the drag torque in N·m, measured by the first torque sensor 12, P is the radial load in N, measured by the first load sensor 7, and l is the radius of the steel ball 11 in m.

[0050] Optionally, when obtaining the data set of oil drag force coefficient and corresponding oil film thickness, multiple working condition combinations are set, including: speed, load and lubricating oil viscosity. Each working condition is run continuously for 10 minutes, and the oil film drag force coefficient and oil film thickness are collected synchronously at a sampling frequency of 100Hz.

[0051] Optionally, establishing calibration curves includes:

[0052] The least squares method was used to perform nonlinear fitting on the dataset to establish a quantitative relationship curve between the oil film traction coefficient μ and the oil film thickness d, expressed as d = f(μ). drag );

[0053] Cross-validation and error analysis were performed on the quantitative relationship curves to ensure that the fitting error of the quantitative relationship curves under different working conditions was controlled within ±5%.

[0054] Optionally, calibration curves can be established for different types of bearings to form a series of calibration curve libraries.

[0055] like Figure 3 As shown, the friction coefficient of the bearing to be tested is obtained through a test bench. The test bench includes a drive mechanism 26, a radial loading mechanism 34, and an axial loading mechanism 35 fixed on a base plate. A second torque sensor 28, a first bearing, a second bearing, and a test bearing 33 are respectively connected to the main shaft 31 of the drive mechanism 26. The test bearing 33 is connected to the radial loading mechanism 34 and the axial loading mechanism 35 respectively. The output shaft of the drive mechanism 26 is connected to the second torque sensor 28 through a flange 27. The main shaft 31 is connected to the second torque sensor 28 through a coupling 29.

[0056] Optionally, the friction coefficient of the bearing to be determined is calculated by the following formula:

[0057]

[0058] In the formula, μ actual is the friction coefficient of the bearing to be determined, M actual is the friction torque of the test bearing 33, in units of N·m, the total friction torque M total is calculated by the difference between the friction torques of the first bearing and the second bearing, d m-actual is the diameter of the rolling element of the rolling bearing, in units of m, F actual is the load under actual working conditions, in units of N, F actual = f p (XF r + YF a ), F r is the loading force applied by the radial loading mechanism 34, F a is the loading force applied by the axial loading mechanism 35, f p is the impact load coefficient, X is the radial dynamic load coefficient, and Y is the axial dynamic load coefficient.

[0059] The first bearing and the second bearing are respectively supported on the bottom plate by the first bearing seat 30 and the second bearing seat 32, and are selected as bearings with known friction coefficients. The total friction torque M total of the bearing system is measured and calculated in real time by the second torque sensor 28. The friction torques of the first bearing and the second bearing can be calculated according to the friction coefficients and empirical formulas, M1 and M2. Then, the friction torque of the test bearing 33 is M actual = M total -M1-M2. Combined with the load F actual under actual working conditions and the diameter d m-actual of the rolling element (such as the rolling ball of a ball bearing) of the rolling bearing, the actual friction coefficient, i.e., the oil film drag coefficient μ actual , is calculated according to the formula . The load F actual under actual working conditions is F p = f r (XF a + YF r ), F a is respectively read by the radial loading mechanism 34 and the axial loading mechanism 35 containing load sensors, f p is the impact load coefficient, which can be referred to the mechanical design manual, and X and Y are respectively the radial dynamic load coefficient and the axial dynamic load coefficient, which can be obtained from the bearing manual according to the working conditions.

[0060] The embodiment of the present application provides a bearing lubrication state monitoring method, a first driving motor 8 drives a transparent disc 9 to rotate, a second driving motor 13 drives a steel ball 11 to rotate, relative movement of the two makes lubricating oil between the contact pair form an oil film, a load sensor cooperates with a pressure head and a disc spring to provide a stable loading force for the contact pair, and the actual oil film bearing and shearing working conditions are simulated. Lubricating oil is injected to the contact pair of the transparent disc 9 and the steel ball 11 through a lubricating oil injector 10, and an initial oil film is formed. The first driving motor 8 and the second driving motor 13 are controlled to stably operate, the loading force of the pressure head is adjusted through load sensor feedback, and the contact pair is in a target bearing working condition.

[0061] Drag coefficient measurement:

[0062] When the steel ball 11 rotates, the oil film drag force acts on the steel ball 11, so that the output shaft of the second driving motor 13 bears a torque, and the first torque sensor 12 detects the torque in real time; in combination with the first load sensor 7 and the second load sensor 16, the radial load borne by the steel ball 11 is measured (when the steel ball 11 is not in contact with the transparent disc 9, the initial readings (i.e. the self-weight) of the first load sensor 7 and the second load sensor 16 are read, and after the steel ball 11 is in contact with the transparent disc 9, the reading of the first load sensor 7 is read minus the self-weight, which is the radial load, and the reading of the second load sensor 16 is also read minus the self-weight, and the two values are used to calibrate the test bench at the beginning of the experiment, and if the values are inconsistent, it indicates that the verticality of the test bench is not enough, and the test bench is adjusted as a whole, that is, the base 1 is adjusted, and the formula T = μPl (T is the drag torque, measured by the first torque sensor 12, P is the radial load, measured by the first load sensor 7, and l is the equivalent radius of the steel ball 11) is used to calculate the drag coefficient μ of the oil film. That is, the drag coefficient μ of the oil film can be calculated.

[0063] Oil film thickness measurement:

[0064] Monochromatic light emitted by the light source 21 is incident on the oil film area, and reflection occurs on the upper and lower surfaces of the oil film (the interfaces of the transparent disc 9, the oil film, the oil film and the steel ball 11), forming double-beam interference, and the interference light carries the oil film thickness information (the optical path difference is related to the oil film thickness, Δ = 2nd cosθ (n is the refractive index of the oil film, and θ is the refraction angle of light in the oil film), and the formula That is, the oil film thickness d can be calculated. The spectrometer 22 receives the interference light and analyzes the spectral data, calculates the oil film thickness through spectral fitting, phase analysis and other algorithms (such as Fourier transform spectroscopy). The high-speed camera 23 assists in collecting interference images, verifies the spectral measurement results, and records the dynamic changes of the oil film at the same time.

[0065] Working condition parameter setting:

[0066] The system sets multiple working condition combinations, including different rotating speeds (500 rpm, 1500 rpm, 3000 rpm, etc.), loads (5 kN, 15 kN, 30 kN, etc.), and lubricating oil viscosities (10 cSt, 32 cSt, 68 cSt, etc.), each of which is continuously operated for 10 minutes, and after the system is stabilized, the oil film drag coefficient, the oil film thickness, and other auxiliary data are synchronously collected at a sampling frequency of 100 Hz.

[0067] Curve calibration

[0068] As shown in Figure 4 , the experimental data are nonlinearly fitted by using the least square method to establish the quantitative relationship curve of the oil film drag coefficient μ and the oil film thickness d, and the expression is d = f(μ drag ). Through cross-validation and error analysis, it is ensured that the fitting error of the curve under different working conditions is controlled within ±5%. In order to improve the universality of the curve, different types of bearings (deep groove ball bearings, cylindrical bearings, etc.) are calibrated respectively to form a series of calibration curve library.

[0069] Friction coefficient measurement

[0070] The total friction torque M total of the bearing system is measured in real time by the second torque sensor 28, and the friction torques of the first bearing and the second bearing can be calculated according to the friction coefficient and the empirical formula, that is, M1 and M2. Then the friction torque of the test bearing 33 is M actual = M total -M1-M2, combined with the load F actual under the actual working condition and the diameter d m-actual of the rolling elements (such as the rolling balls of the ball bearing) of the rolling bearing, the actual friction coefficient, that is, the oil film drag coefficient μ actual , is calculated according to the formula . The load F actual under the actual working condition is F p = f r (XF r +YF a ), F r and F a are read by the radial loading mechanism 34 and the axial loading mechanism 35 containing load sensors, respectively, and f p is the impact load coefficient, which can be referred to the mechanical design manual, and X and Y are the radial dynamic load coefficient and the axial dynamic load coefficient, respectively, which can be obtained from the bearing manual according to the working condition.

[0071] Oil film thickness calculation

[0072] The actually measured friction coefficient μ actual is substituted into the calibrated oil film drag coefficient and oil film thickness curve d = f(μ drag), the thickness d of the whole bearing under the corresponding working condition is obtained by interpolation or numerical calculation method. Further evaluation of the uniformity of the oil film thickness distribution can be combined with the data of the pressure sensor array to correct the oil film thickness of different contact areas. (The refractive index of the material is affected by the load, so the oil film thickness is corrected by correcting the refractive index. The correction of the refractive index: Oil film thickness: Corrected oil film thickness: )

[0073] Lubrication state evaluation

[0074] According to the calculated oil film thickness d, the film thickness ratio is calculated according to the formula When the film thickness ratio λ≤0.001, the contact interface is in dry friction state; when 0.001≤λ≤0.06, the contact interface is in boundary lubrication state; when 0.06≤λ≤3, the contact interface is in mixed lubrication state; when λ≥3, the contact interface is in full film lubrication state.

[0075] The above invention is only a few specific embodiments of the present invention, but the embodiments of the present invention are not limited thereto, and any changes that can be thought of by those skilled in the art shall fall within the scope of the present invention.

Claims

1. A method of monitoring the lubrication state of a bearing, characterized in that, Includes the following steps: An experimental model for testing the drag force coefficient and thickness of an oil film was established, and a dataset of the drag force coefficient and the corresponding oil film thickness was obtained through the experimental model. Establish calibration curves: Based on the dataset of drag force coefficient and corresponding oil film thickness, calibrate the oil film drag force coefficient and oil film thickness curves; Obtain the friction coefficient of the bearing to be tested, which is equal to the oil film drag force coefficient. Substitute the oil film drag force coefficient of the bearing to be tested into the calibration curve to obtain the oil film thickness of the bearing to be tested.

2. A method of monitoring the lubrication condition of a bearing as claimed in claim 1, wherein, The experimental model for testing the oil film drag force coefficient and thickness includes: a base (1) and an oil film drag force coefficient testing component and an oil film thickness testing component respectively connected to the base (1). The oil film drag force coefficient testing component measures the oil film drag force coefficient, and the oil film thickness testing component measures the oil film thickness.

3. The bearing lubrication condition monitoring method as described in claim 2, characterized in that, The oil film drag force coefficient test assembly includes: a first drive motor (8) and a second drive motor (13) respectively connected to the base (1). The output shaft of the first drive motor (8) is vertically upward, and a transparent disk (9) is fixed at the upper end of the output shaft. A first load sensor (7) is connected to the bottom of the first drive motor (8). The output shaft of the second drive motor (13) is horizontally set, and a steel ball (11) and a first torque sensor (12) are connected on the output shaft. The steel ball (11) is located above the transparent disk (9). The oil film thickness testing assembly includes a spectrometer (22) and a light source (21). The spectrometer (22) is connected to the base (1) and is located directly below the steel ball (11). The light source (21) is fixed to the upper end of the spectrometer (22).

4. A method of monitoring the lubrication condition of a bearing as claimed in claim 3, wherein, The second drive motor (13) is connected to a second load sensor (16) at its lower end. The first load sensor (7), the second load sensor (16) and the base (1) are respectively connected to a height adjustment assembly. The height adjustment assembly includes an adjustment shaft and a support. The bottom of the adjustment shaft is threaded with the support. The support is fixed to the base (1). A buffer spring is sleeved on the adjustment shaft.

5. A method of monitoring the lubrication condition of a bearing as claimed in claim 3, wherein, The oil film drag force coefficient is calculated using the following formula: ， wherein is the oil film drag force coefficient, is the drag torque, in N·m, measured by the first torque sensor (12), is the radial load, in N, measured by the first load sensor (7), is the radius of the steel ball (11), in m.

6. A method of monitoring the lubrication condition of a bearing as claimed in claim 3, wherein, When the oil obtains the data set of traction force coefficient and corresponding oil film thickness, multiple working condition combinations are set. The working conditions include: speed, load and lubricating oil viscosity. Each working condition is run continuously for 10 minutes, and the oil film traction force coefficient and oil film thickness are collected synchronously at a sampling frequency of 100Hz.

7. A method of monitoring the lubrication condition of a bearing as claimed in claim 1, wherein, The establishment of the calibration curve includes: The data set is non-linearly fitted by least square method to establish the oil film drag force coefficient The quantitative relationship curve between the oil film thickness and the oil film drag force coefficient is established, and the expression is ; Cross-validation and error analysis were performed on the quantitative relationship curves to ensure that the fitting error of the quantitative relationship curves under different working conditions was controlled within ±5%.

8. A method of monitoring the lubrication condition of a bearing as claimed in claim 1, wherein, The calibration curves are established for different types of bearings to form a series of calibration curve libraries.

9. A method of monitoring the lubrication condition of a bearing as claimed in claim 1, wherein, The friction coefficient of the bearing to be measured is obtained through a test bed, the test bed comprising a driving mechanism (26) fixed on a base plate, a radial loading mechanism (34) and an axial loading mechanism (35), a main shaft (31) of the driving mechanism (26) being connected with a second torque sensor (28), a first bearing, a second bearing and a test bearing (33) respectively, the test bearing (33) being connected with the radial loading mechanism (34) and the axial loading mechanism (35) respectively.

10. A method of monitoring the lubrication condition of a bearing as claimed in claim 9, wherein, The friction coefficient of the bearing to be measured is obtained through a test bed, the test bed comprising a driving mechanism (26) fixed on a base plate, a radial loading mechanism (34) and an axial loading mechanism (35), a main shaft (31) of the driving mechanism (26) being connected with a second torque sensor (28), a first bearing, a second bearing and a test bearing (33) respectively, the test bearing (33) being connected with the radial loading mechanism (34) and the axial loading mechanism (35) respectively. The friction coefficient of the bearing to be measured is obtained through a test bed, the test bed comprising a driving mechanism (26) fixed on a base plate, a radial loading mechanism (34) and an axial loading mechanism (35), a main shaft (31) of the driving mechanism (26) being connected with a second torque sensor (28), a first ， In the formula, is the friction coefficient of the bearing to be measured, is the friction torque of the test bearing (33) in N·m, the total friction torque measured by the second torque sensor (28) is calculated by the difference between the friction torques of the first bearing and the second bearing, is the diameter of the rolling element of the rolling bearing in m, is the load under actual working conditions in N, , is the loading force applied by the radial loading mechanism (34), is the loading force applied by the axial loading mechanism (35), is the impact load coefficient, is the radial dynamic load coefficient, is the axial dynamic load coefficient.

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