Lubricating oil film thickness ultrasonic measurement method with temperature compensation function

Abstract

The invention belongs to the field of ultrasonic nondestructive testing and evaluation, and particularly relates to a lubricating oil film thickness ultrasonic measurement method with a temperature compensation function. According to the method, the same circuit and the electromagnetic ultrasonic sensor are adopted, two signals are obtained by sequentially adopting two frequencies meeting a certain relation, a reflection signal without a lubricating oil film is taken as a reference signal, a reflection signal with the lubricating oil film is taken as a detection signal, and the thickness of the lubricating oil film is calculated based on a spring model. The method can compensate the influence of the temperature change on the film thickness measurement precision, the system error is small, and the more accurate lubricating oil film thickness can be obtained.

Description

Technical Field

[0001] The invention belongs to the field of ultrasonic nondestructive testing and evaluation, and in particular relates to an ultrasonic measurement method for lubricating oil film thickness with a temperature compensation function. Background Art

[0002] Lubricating oil is widely used in many fields such as mechanical equipment, processing equipment, office equipment, and electronic appliances. Its main function is to reduce friction and wear and improve the operating efficiency and life of the equipment. In practical applications, it is necessary to select the appropriate lubricating oil film type and lubrication method according to the specific needs of the equipment and the working environment. In components such as pistons and cylinders, bearings, precision slides and guides, the lubrication state is an important factor affecting their performance and state. In many cases, the thickness of the lubricating oil film is in the micron level, which is difficult to measure under actual working conditions. Traditional methods for measuring the thickness of lubricating oil films include optical interference method, resistance method, capacitance method, etc., but due to the limitations of these methods themselves (transparent materials, shielding, and accuracy issues), they cannot be applied to the measurement of lubricating oil film thickness under real working conditions. Ultrasonic waves have the characteristics of high frequency, strong penetration ability, and good directivity. Ultrasonic non-destructive testing technology based on equivalent stiffness has become an important research method for domestic and foreign researchers to carry out film thickness measurement.

[0003] At present, the ultrasonic method for measuring oil film thickness uses piezoelectric ultrasonic technology and a longitudinal wave focusing probe. The reflection coefficient of oil films of different thicknesses is obtained (compared with the air interface reflection signal when there is no oil film), and the oil film thickness is calculated using a spring model. Due to the difficulty of temperature compensation, the calculation error of the oil film thickness is large. At present, there is no report on the method of measuring oil film thickness based on electromagnetic ultrasonic technology. Summary of the invention

[0004] In order to solve the deficiencies of the prior art, the present invention provides a lubricating oil film thickness ultrasonic measurement method with a temperature compensation function.

[0005] The present invention is achieved through the following technical solutions:

[0006] An ultrasonic measurement method for lubricating oil film thickness with temperature compensation function is completed based on an electromagnetic ultrasonic sensor, wherein the electromagnetic ultrasonic sensor comprises a permanent magnet A and a permanent magnet B adsorbed together with opposite magnetic poles, and a runway-shaped coil, wherein the bottom surfaces of the permanent magnet A and the permanent magnet B both cover the coil working area, and the coil working area is the coil straight area;

[0007] The lubricating oil film thickness ultrasonic measurement method with temperature compensation function comprises the following steps:

[0008] Step 1: The frequency relationship between the selected transverse wave and longitudinal wave satisfies the following formula:

[0009]

[0010] Here, σ is Poisson’s ratio.

[0011] Step 2: Based on the spring model, obtain the expression of lubricating oil film thickness.

[0012]

[0013] Where |R(f)| is the reflection coefficient of the longitudinal wave, ρ oil is the corrected density of the lubricating oil at the Hertzian contact mean pressure, c oil is the corrected sound velocity of the lubricating oil under the Hertzian contact mean pressure, f is the operating frequency of the electromagnetic ultrasonic sensor, ρ is the density of the object being measured, c L is the longitudinal wave velocity in the object being measured.

[0014] Step 3: The reflection coefficient of the longitudinal wave with temperature compensation function is calculated according to the following formula:

[0015]

[0016] Among them, A L-oil A is the frequency domain amplitude of the longitudinal wave reflection signal at the interface of the object under test / lubricating oil at the actual test temperature, S-oil A is the frequency domain amplitude of the shear wave reflection signal at the interface of the object under test / lubricating oil at the actual test temperature, L-air A is the frequency domain amplitude of the longitudinal wave reflection signal at the measured object / air interface at room temperature, S-air is the frequency domain amplitude of the shear wave reflection signal at the measured object / air interface at room temperature;

[0017] Step 4: Substitute the reflection coefficient |R(f)| of the longitudinal wave obtained by formula (25) into the lubricating oil film thickness expression (13) in step 2. At the same time, the transverse wave and the longitudinal wave satisfy the frequency relationship (12) calculated in step 1, and the lubricating oil film thickness is calculated.

[0018] As a preferred option:

[0019] The coil adopts a double-layer structure design, and the coil line width is 0.1mm.

[0020] The gap between the two sides of the coil working area is 0.4-0.5 mm.

[0021] The height of the permanent magnet A and the permanent magnet B is 20-40 mm.

[0022] The bottom surfaces of the permanent magnets A and B are covered with copper foil.

[0023] The specific process of step 1 includes:

[0024] Ignore the scattering attenuation of transverse waves and longitudinal waves, and define the attenuation coefficients of transverse waves and longitudinal waves as K′ respectively. S and K′ L , the absorption attenuation coefficients of transverse waves and longitudinal waves are a and aS and a aL ,but:

[0025]

[0026] From formulas (4)-(7), we can get:

[0027]

[0028] Where x is the propagation distance, f S is the frequency of the shear wave, f L is the frequency of the longitudinal wave, C S is the sound velocity of the transverse wave, C L is the sound velocity of the longitudinal wave, w is the ultrasonic angular frequency, ρ is the density of the object being measured, η′ is the shear viscosity coefficient of the material being measured, k c is the thermal conductivity of the material being tested, c V is the specific heat at constant volume, c P is the constant pressure specific heat, η″ is the low-frequency variable viscosity coefficient caused by the i-th relaxation process, τ i is the relaxation time of the i-th relaxation process.

[0029] When the ratio in the above formula (8) is constant, the temperature change has no effect on it, so the formula (8) needs to satisfy:

[0030]

[0031] The relationship between the sound speeds of transverse waves and longitudinal waves in a material is:

[0032]

[0033] From formulas (9) and (11), we can get:

[0034]

[0035] Here, σ is Poisson’s ratio.

[0036] The present invention is aimed at the ultrasonic oil film measurement method based on the spring model, and proposes an ultrasonic measurement method of lubricating oil film thickness with temperature compensation function, which is used to measure and calculate the micron-level lubricating oil film thickness, so as to diagnose the early failure of the equipment. The present invention adopts electromagnetic ultrasonic detection technology, which provides a new idea for ultrasonic oil film thickness measurement, and has certain theoretical and practical significance for reducing detection costs and improving detection accuracy. Compared with the existing piezoelectric ultrasonic method, the shortcomings overcome are:

[0037] (1) The high-frequency focusing sensor used in the traditional piezoelectric sensor requires water coupling and the probe installation is complicated. The electromagnetic ultrasonic sensor of the present invention has a simpler structure and is more convenient to install. The electromagnetic ultrasonic sensor consists of only a coil and a magnet. The coil only needs to be attached to the surface of the measured part and adsorbed by the magnet.

[0038] (2) The electromagnetic ultrasonic method proposed in the present invention has an electromagnetic ultrasonic sensor that can excite transverse waves and longitudinal waves at the same time. Since they are excited by the same set of magnets and coils, the ratio of transverse waves to longitudinal waves is stable. When reflected by the oil film interface, the transverse wave cannot propagate in the liquid and is therefore not affected by the oil film thickness. The longitudinal wave changes with the reflection signal of different oil film thicknesses. This method can compensate for the influence of temperature changes on the film thickness measurement accuracy, and the system error is small. BRIEF DESCRIPTION OF THE DRAWINGS

[0039] Figure 1 Schematic diagram of the coil structure of this embodiment;

[0040] Figure 2 This is a schematic diagram of the working state structure of the electromagnetic ultrasonic sensor of this embodiment;

[0041] Figure 3 is the reflection signal of the bearing / air interface in this embodiment;

[0042] Figure 4 is the reflection signal of the bearing / lubricating oil interface in this embodiment;

[0043] Figure 5 is the longitudinal wave reference signal when there is air between the outer ring and the roller of the bearing in this embodiment;

[0044] Figure 6 is the shear wave reference signal when there is air between the outer ring and the roller of the bearing in this embodiment;

[0045] Figure 7 is the longitudinal wave detection signal when there is lubricating oil between the outer ring and the roller of the bearing of this embodiment;

[0046] Figure 8 This is the shear wave detection signal when there is lubricating oil between the outer ring and the roller of the bearing in this embodiment.

[0047] In the figure, 1 is permanent magnet A, 2 is permanent magnet B, 3 is copper foil, 4 is coil, 5 is outer ring, 6 is lubricating oil, 7 is roller, 8 is coil terminal, and 9 is coil working area. DETAILED DESCRIPTION

[0048] Specific embodiments of the present invention are given below. It should be noted that the present invention is not limited to the following specific embodiments, and all equivalent changes made on the basis of the technical solution of this application fall within the protection scope of the present invention.

[0049] The electromagnetic ultrasonic sensor for measuring oil film thickness of the present invention comprises two permanent magnets (permanent magnet A1 and permanent magnet B2) with opposite magnetic poles and a racetrack-shaped coil 4.

[0050] The above-mentioned runway-shaped coil 4 is pasted on the surface of the object to be measured when working. It is made of copper wire manually wound or PCB processed. The coil working area 9 (the straight area of ​​the coil 4) corresponds to the position of the measured area of ​​the object to be measured. The length and single-side width of the coil working area 9 along the wire direction are determined according to the measured area of ​​the object to be measured. The coil 4 can preferably adopt a double-layer structure design, with a line width of 0.1mm, a gap between the two sides of the coil working area 9 of 0.4-0.5mm, and the current directions on both sides of the coil working area 9 are opposite.

[0051] The two permanent magnets (permanent magnet A1 and permanent magnet B2) above the coil 4 are both NdFeB strong magnets, and the magnetic poles of permanent magnet A1 and permanent magnet B2 are oppositely adsorbed together. The bottom surfaces of both permanent magnet A1 and permanent magnet B2 can completely cover the coil working area 9. The height of the permanent magnet is preferably 20-40 mm according to the actual application. In order to prevent interference signals from being generated in the runway-shaped coil 4, it is preferred to stick copper foil 3 on the bottom surfaces of the two permanent magnets and adsorb them on the object to be measured for use.

[0052] When the electromagnetic ultrasonic sensor is working, a high-frequency alternating current is passed through the coil 4. The working frequency is selected according to the object to be measured. The permanent magnet combination is used to provide a vertical magnetic field and a horizontal magnetic field. The electromagnetic ultrasonic sensor can simultaneously excite transverse waves and longitudinal waves. The electromagnetic ultrasonic sensor adopts a self-generated and self-received working mode. The excited transverse waves and longitudinal waves propagate to the inner side in a direction perpendicular to the surface of the object to be measured. The reflected signal of the inner surface is received by the same electromagnetic ultrasonic sensor, wherein the inner surface is the surface in contact with the lubricating oil 6. The transverse wave is approximately fully reflected at the interface of the object to be measured / air and the interface of the object to be measured / lubricating oil. The reflection coefficient of the longitudinal wave at the interface is affected by the media on both sides. Therefore, the reflected signal when there is no lubricating oil film is taken as the reference signal, and the reflected signal when there is a lubricating oil film is taken as the detection signal. The thickness of the lubricating oil film is calculated based on the spring model.

[0053] Based on the above electromagnetic ultrasonic sensor, a lubricating oil film thickness ultrasonic measurement method with temperature compensation function of the present invention comprises the following steps:

[0054] Step 1: Calculate the frequency relationship between the shear wave and the longitudinal wave to compensate for the temperature change.

[0055] The attenuation of ultrasonic waves during propagation mainly includes scattering attenuation and absorption attenuation. The attenuation coefficient is defined as K and the absorption attenuation coefficient is defined as a. a , the scattering attenuation coefficient is a s , the propagation distance is x, then the expression of the attenuation coefficient K is:

[0056]

[0057] Among them, the scattering attenuation coefficient a s The expression is:

[0058]

[0059] Among them, C1 is a constant, f is the ultrasonic frequency, c is the ultrasonic speed, d is the grain diameter of the material being tested, and n0 is the number of grains per unit volume.

[0060] Absorption attenuation coefficient a a The expression is:

[0061]

[0062] Where w is the ultrasonic angular frequency, ρ is the density of the object being measured, η′ is the shear viscosity coefficient of the material being measured, and k c is the thermal conductivity of the material being tested, c V is the specific heat at constant volume, c P is the constant pressure specific heat, η″ is the low-frequency variable viscosity coefficient caused by the i-th relaxation process, τ i is the relaxation time of the i-th relaxation process.

[0063] Parts that use thin oil film lubrication are mostly precision components. The grain size of their materials is mostly a few microns to tens of microns, which is much smaller than the wavelength of ultrasound. Therefore, scattering attenuation can be ignored and only absorption attenuation is considered.

[0064] Then for transverse waves and longitudinal waves, the attenuation coefficients are defined as K′ S and K′ L , the absorption attenuation coefficients are a aS and a aL , from formula (1) we can get:

[0065]

[0066] Because the propagation medium and path of the transverse wave and the longitudinal wave in the present invention are exactly the same, the material parameters are exactly the same, and the parameter symbols defined in formula (3) are used. From formula (3), it can be obtained that:

[0067]

[0068] From formulas (4)-(7), we can get:

[0069]

[0070] Among them, f S is the frequency of the shear wave, f L is the frequency of the longitudinal wave, CS is the sound velocity of the transverse wave, C L is the speed of sound of longitudinal waves.

[0071] It can be seen that when the ratio in the above formula (8) is constant, the temperature change has no effect on it, so the formula (8) needs to satisfy:

[0072]

[0073] Therefore, at different temperatures, the following conditions are met:

[0074] So it can be used to compensate for the effects of temperature changes.

[0075] It is also known that the relationship between the sound speeds of transverse waves and longitudinal waves in a material is:

[0076]

[0077] From formulas (9) and (11), we can get:

[0078]

[0079] Where σ is Poisson's ratio. It can be seen that when the frequencies of the transverse wave and the longitudinal wave satisfy the relationship of formula (12), the influence of temperature change can be compensated.

[0080] Step 2: Based on the spring model, obtain the expression for lubricating oil film thickness.

[0081] Based on the spring model, the expression of lubricating oil film thickness is:

[0082]

[0083] Where |R(f)| is the reflection coefficient of the longitudinal wave, ρ oil is the corrected density of lubricating oil 6 at the Hertzian contact mean pressure, c oil is the corrected sound velocity of the lubricating oil 6 under the Hertz contact mean pressure, f is the working frequency of the electromagnetic ultrasonic sensor, ρ is the density of the object being measured, c L is the longitudinal wave velocity in the object being measured.

[0084] In the above formula, |R(f)| is the main factor affecting the calculation accuracy of the lubricating oil film thickness when the temperature changes. Therefore, it is necessary to further calculate the longitudinal wave reflection coefficient |R(f)| with temperature compensation function based on the frequency relationship between the transverse wave and the longitudinal wave obtained in step 1.

[0085] Step 3: Calculate the longitudinal wave reflection coefficient |R(f)| with temperature compensation function.

[0086] The parameters of the measured object / air interface at room temperature are defined as follows: The frequency domain amplitude of the longitudinal wave incident signal is I L, the attenuation coefficient of the longitudinal wave propagation process is K L , the frequency domain amplitude of the incident shear wave signal is I S , the attenuation coefficient of the shear wave propagation process is K S , A L-air is the frequency domain amplitude of the longitudinal wave reflection signal, A S-air is the frequency domain amplitude of the shear wave reflection signal.

[0087] The parameters of the measured object / lubricant interface at the actual test temperature are defined as follows: A L-oil is the frequency domain amplitude of the longitudinal wave reflection signal, A S-oil is the frequency domain amplitude of the shear wave reflection signal.

[0088] The reflection coefficient should be the ratio of the incident signal to the reflected signal. However, since the incident signal is difficult to obtain and the object / air interface is approximately a total reflection, the reflected signal of the object / air interface is usually used instead of the incident signal.

[0089] Since the temperature during actual detection is unknown and cannot be measured, but the temperature change will affect the reference signal, it is difficult to compensate for the influence of the actual detection temperature in the traditional method, resulting in a large error. Therefore, the present invention defines the following parameters, the purpose of which is to calculate the frequency domain amplitude A of the longitudinal wave reflection signal at the interface of the object under test / air at the actual detection temperature L-air1 .

[0090] The parameters of the measured object / air interface at the actual test temperature are defined as follows: A L-air1 is the frequency domain amplitude of the longitudinal wave reflection signal, A S-air1 is the frequency domain amplitude of the shear wave reflection signal, and the frequency domain amplitude of the longitudinal wave incident signal is I L1 , the attenuation coefficient of the longitudinal wave propagation process is K L1 , the frequency domain amplitude of the incident shear wave signal is I S1 , the attenuation coefficient of the shear wave propagation process is K S1 .

[0091] Because shear waves can only propagate in solids, at the same temperature, shear waves are totally reflected at both the measured object / lubricant interface and the measured object / air interface, so we can get:

[0092] A S-oil =A S-air1 (14)

[0093] Then, the reflection coefficient expression of the longitudinal wave considering temperature compensation is:

[0094]

[0095] However, in the above formula (15), AL-air1 It is difficult to measure directly. In the present invention, A is given by shear wave L-air1 The calculation method is as follows:

[0096] According to public knowledge:

[0097] A L-air =I L ·K L (16)

[0098] A S-air =I S ·K S (17)

[0099] A L-air1 =I L1 ·K L1 (18)

[0100] A S-air1 =I S1 ·K S1 (19)

[0101] From formula (14) and formula (16)-(19), we can get:

[0102]

[0103] Because the transverse wave and the longitudinal wave in the present invention use the same coil 4 and the same power supply circuit, when the temperature change affects the excitation signal, the transverse wave and the longitudinal wave are affected in equal proportion, that is:

[0104]

[0105] Using the same circuit and the same coil 4, only changing the excitation frequency, when taking two consecutive signals, the condition of formula (22) is still satisfied. At this time, from formulas (20)-(22), and considering temperature compensation, that is, the transverse wave and longitudinal wave frequencies satisfy the relationship of formula (12) in step 1, it can be obtained:

[0106]

[0107] From formula (23), we can get:

[0108]

[0109] Substituting formula (24) into formula (15), we can obtain:

[0110]

[0111] The reflection coefficient of the longitudinal wave |R(f)| can be calculated by formula (25), A L-oil , As-air , A s-oil , A L-air Can be measured.

[0112] Step 4: Substitute the reflection coefficient |R(f)| of the longitudinal wave obtained by formula (25) into the lubricating oil film thickness expression formula (13) obtained in step 2. At the same time, the shear wave and the longitudinal wave satisfy the frequency relationship calculated in step 1, that is, the frequency relationship between the shear wave and the longitudinal wave satisfies formula (12), and the lubricating oil film thickness is calculated.

[0113] In summary, based on the ultrasonic measurement method for lubricating oil film thickness with temperature compensation function proposed in the present invention, the same circuit and electromagnetic ultrasonic sensor are used, and two signals are obtained by using two frequencies in turn as reference signals, wherein the relationship between the two frequencies satisfies formula (12). The frequency domain amplitudes of the two signals satisfying the relationship of formula (12) are taken, A L-air and A S-air is the frequency domain amplitude of the reference signal. When measuring the lubricating oil film thickness under actual working conditions, the same method is used to obtain two sets of signals, and A S-air A corresponding to the frequency S-oil , and obtain the reference signal A L-air1 After that, combined with the detection signal A of the corresponding frequency L-oil , the reflection coefficient of the longitudinal wave is calculated by formula (25), and it is substituted into formula (13) to calculate the lubricating oil film thickness. This method fully considers the influence of temperature on material parameters and can obtain a more accurate lubricating oil film thickness.

[0114] According to the method of the present invention, taking a roller bearing made of steel material as an example, the calculation of the lubricating oil film thickness on the bearing is specifically described.

[0115] As attached Figure 1 As shown, the coil 4 adopts a double-layer structure design with a line width of 0.1mm, wherein the coil terminal 8 is connected to the circuit, and the coil working area 9 is divided into two sides, the current directions of the two sides are opposite, the length of the coil working area 9 along the wire direction is consistent with the length of the roller 7 of the measured bearing, the width of the coil working area 9 on one side is 2.5mm, and the gap between the two sides is 0.4mm. During operation, eddy currents are induced on the surface of the outer ring 5 of the bearing. Based on the working principle of electromagnetic ultrasound, when this coil 4 is in a vertical magnetic field, a transverse wave is excited in the measured object, and when this coil 4 is in a horizontal magnetic field, a longitudinal wave is excited in the measured object.

[0116] As attached Figure 2As shown, the structure of the electromagnetic ultrasonic sensor includes a permanent magnet A1, a permanent magnet B2, a copper foil 3 and a coil 4. The bearing is the object to be measured. The lubricating oil 6 is located between the outer ring 5 and the roller 7 of the bearing. The thickness of the lubricating oil 6 between the outer ring 5 and the roller 7 of the bearing is the thickness of the lubricating oil film to be detected. The electromagnetic ultrasonic sensor is adsorbed on the surface of the bearing and excites transverse waves and longitudinal waves in the bearing at the same time. Among them, the magnetic poles of the permanent magnet A1 and the permanent magnet B2 are adsorbed together with opposite poles. In order to prevent the generation of interference signals in the coil 4, a layer of copper foil 3 with a thickness of 0.2 mm is attached to the bottom surface of the magnet. This combination of magnets enables the coil 4 to have both a vertical magnetic field and a horizontal magnetic field, so that transverse waves and longitudinal waves can be excited at the same time. The transverse waves and longitudinal waves excited by the electromagnetic ultrasonic sensor propagate in a direction perpendicular to the bearing surface. After reaching the inner surface of the bearing, the generated reflected echo is received by the same coil 4. Through the method described in the present invention, signal analysis and processing are performed to calculate the thickness of the lubricating oil film.

[0117] As attached Figure 3 As shown in the figure, they are the reflected signals of the bearing / air interface and the bearing / lubricating oil interface, respectively. The part enclosed by the elliptical dotted circle in the figure is the effective signal, among which the larger amplitude is the shear wave, and the smaller amplitude is the longitudinal wave. Because the longitudinal wave has a fast wave speed, the first reflected echo of the longitudinal wave here is submerged in the starting signal, and the second reflected echo can be seen, while the reflected echo of the shear wave can be seen twice. Comparing the two signals, it can be seen that the shear wave amplitude of the two signals does not change much, and when the interface is the bearing / lubricating oil interface, the longitudinal wave signal is significantly reduced.

[0118] According to the method of the present invention, the calculation steps of the bearing lubricating oil film are:

[0119] 1) Assume that the actual working temperature range of the tested bearing is 20-100℃. For bearing steel materials, the Poisson's ratio σ is relatively stable within this temperature range. Here, σ is taken as 0.3. According to formula (12), we can calculate In this embodiment, the excitation frequency of the longitudinal wave is 5 MHz, and the excitation frequency of the shear wave is 1.95 MHz.

[0120] 2) Two pulse signals with frequencies of 5 MHz and 1.95 MHz are applied sequentially to the same coil 4. When there is air between the outer ring 5 and the roller 7 of the bearing, two echo signals are obtained, which are called reference signals. Figure 5 and 6 As shown, the longitudinal wave signal with a frequency of 5 MHz is selected for Fourier transform to obtain the frequency domain amplitude A L-air , select the shear wave signal at a frequency of 1.95MHz and perform Fourier transform to obtain the frequency domain amplitude A S-air , select the reference signal to obtain A L-air and A S-air Used to calculate accurate reflection coefficients.

[0121] 3) Under the actual detection condition when there is lubricating oil 6, the same electromagnetic ultrasonic detection system as in the above steps is used to sequentially apply two pulse signals with frequencies of 5 MHz and 1.95 MHz to the same coil 4 to obtain two echo signals, which are called detection signals. Figure 7 and 8 As shown in the figure, the longitudinal wave signal with a frequency of 5 MHz is selected for Fourier transformation to obtain the frequency domain amplitude A L-oil , select the shear wave signal at a frequency of 1.95MHz and perform Fourier transform to obtain the frequency domain amplitude A S-oil , combined with the reference signal to obtain A L-air and A S-air Used to calculate accurate reflection coefficient. The ultrasonic reflection coefficient with temperature compensation function is calculated according to formula (25), and then substituted into formula (13) to calculate the lubricating oil film thickness between the outer ring 5 and the roller 7 of the bearing. With the method of the present invention, the temperature change of the outer ring 5, lubricating oil 6 and roller 7 of the bearing during operation will not have a significant impact on the calculation accuracy.

[0122] The processing method of the present invention has certain theoretical and practical significance for reducing the detection cost of lubricating oil film thickness and improving the detection accuracy, and can also provide a reference for the application of electromagnetic ultrasonic technology in the detection of metal-based components.

[0123] The present invention may also have many other embodiments. Without departing from the spirit and essence of the present invention, those skilled in the art may make various corresponding changes and modifications based on the present invention, but these corresponding changes and modifications should all fall within the scope of protection of the claims attached to the present invention.

Claims

1. A method for ultrasonic measurement of lubricating oil film thickness with temperature compensation function, based on an electromagnetic ultrasonic sensor, characterized in that: The electromagnetic ultrasonic sensor comprises a permanent magnet A and a permanent magnet B adsorbed together with opposite magnetic poles, and a runway-shaped coil, wherein the bottom surfaces of the permanent magnet A and the permanent magnet B cover the coil working area, and the coil working area is a coil straight area; The lubricating oil film thickness ultrasonic measurement method with temperature compensation function comprises the following steps: Step 1: The frequency relationship between the selected transverse wave and longitudinal wave satisfies the following formula: Where, σ is Poisson’s ratio; Step 2: Based on the spring model, obtain the expression of lubricating oil film thickness. Where |R(f)| is the reflection coefficient of the longitudinal wave, ρ oil is the corrected density of the lubricating oil at the Hertzian contact mean pressure, c oil is the corrected sound velocity of the lubricating oil under the Hertzian contact mean pressure, f is the operating frequency of the electromagnetic ultrasonic sensor, ρ is the density of the object being measured, c L is the longitudinal wave velocity in the object being measured; Step 3: The reflection coefficient of the longitudinal wave with temperature compensation function is calculated according to the following formula: Among them, A L-oil A is the frequency domain amplitude of the longitudinal wave reflection signal at the interface of the measured object / lubricating oil at the actual test temperature, S-oil A is the frequency domain amplitude of the shear wave reflection signal at the interface of the measured object / lubricating oil at the actual test temperature, L-air A is the frequency domain amplitude of the longitudinal wave reflection signal at the measured object / air interface at room temperature, S-air is the frequency domain amplitude of the shear wave reflection signal at the measured object / air interface at room temperature; Step 4: Substitute the reflection coefficient |R(f)| of the longitudinal wave obtained by formula (25) into the lubricating oil film thickness expression (13) in step 2. At the same time, the transverse wave and the longitudinal wave satisfy the frequency relationship (12) calculated in step 1, and the lubricating oil film thickness is calculated.

2. The method for ultrasonically measuring lubricating oil film thickness with temperature compensation function according to claim 1, characterized in that: The coil adopts a double-layer structure design, and the coil line width is 0.1mm.

3. The method for ultrasonically measuring lubricating oil film thickness with temperature compensation function according to claim 1, characterized in that: The gap between the two sides of the coil working area is 0.4-0.5 mm.

4. The method for ultrasonically measuring lubricating oil film thickness with temperature compensation function according to claim 1, characterized in that: The height of the permanent magnet A and the permanent magnet B is 20-40 mm.

5. The method for ultrasonically measuring lubricating oil film thickness with temperature compensation function according to claim 1, characterized in that: The bottom surfaces of the permanent magnets A and B are covered with copper foil.

6. The method for ultrasonically measuring lubricating oil film thickness with temperature compensation function according to claim 1, characterized in that: The specific process of step 1 includes: Ignore the scattering attenuation of transverse waves and longitudinal waves, and define the attenuation coefficients of transverse waves and longitudinal waves as K′ respectively. S and K′ L , the absorption attenuation coefficients of transverse waves and longitudinal waves are a and aS and a aL ,but: From formulas (4)-(7), we can get: Where x is the propagation distance, f S is the frequency of the shear wave, f L is the frequency of the longitudinal wave, C S is the sound velocity of the transverse wave, C L is the sound velocity of the longitudinal wave, w is the ultrasonic angular frequency, ρ is the density of the object being measured, η′ is the shear viscosity coefficient of the material being measured, k c is the thermal conductivity of the material being tested, c V is the specific heat at constant volume, c P is the constant pressure specific heat, η″ is the low-frequency variable viscosity coefficient caused by the i-th relaxation process, τ i is the relaxation time of the i-th relaxation process; When the ratio in the above formula (8) is constant, the temperature change has no effect on it, so the formula (8) needs to satisfy: The relationship between the speed of sound of transverse waves and longitudinal waves in a material is: From formulas (9) and (11), we can get: Here, σ is Poisson’s ratio.

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