Ultrasonic measurement method for oil film thickness in center of elastohydrodynamic contact area of high-speed rolling bearing

Abstract

The application relates to a kind of high-speed rolling bearing elastohydrodynamic contact zone center oil film thickness ultrasonic measurement method, belongs to lubricating oil film thickness measurement field.The application aims at the problem that ultrasonic pulse is difficult to act on oil film contact zone center in high-speed rolling bearing, and the accuracy of contact zone film thickness measurement result is poor.The application comprises the following steps: obtaining the trigger signal of each sampling period by the light signal formed in the light absorption area during the rotation of the rolling bearing, the ultrasonic probe emits ultrasonic pulse based on the delay of the trigger signal and forms focused focus spot in the target oil film contact zone of the corresponding test roller;in each sampling period, a certain number of ultrasonic reflection wave signals carrying oil film thickness information are collected;the ultrasonic reflection wave signal closest to the center of the target oil film contact zone is selected from all the ultrasonic reflection wave signals as the target ultrasonic reflection wave signal;the target oil film contact zone center oil film thickness is calculated from the target ultrasonic reflection wave signal.The application is used for the measurement of oil film thickness.

Description

Technical Field

[0001] This invention relates to an ultrasonic method for measuring the thickness of the oil film at the center of the elastohydrodynamic contact zone of a high-speed rolling bearing, and belongs to the field of lubricating oil film thickness measurement. Background Technology

[0002] Rolling bearings play a crucial role in high-end equipment, including rocket and space shuttle engines, wind turbines, high-speed trains, high-precision medical equipment, and satellite gyroscopes, providing essential rotational support. Oil film thickness is a vital indicator for early warning of rolling bearing failure and for monitoring lubrication failure. Therefore, measuring oil film thickness is essential for the maintenance and repair of rolling bearings in high-end equipment and for extending their service life.

[0003] Currently, methods for measuring the thickness of lubricating oil film in rolling bearings mainly include optical, electrical, and ultrasonic methods. Optical methods offer high measurement accuracy, but their application in practical engineering is limited due to the requirement for high material transparency. Electrical methods are affected by conductor effects and various interference factors, making it impossible to directly acquire the resistance and capacitance signals of each contact area, resulting in only an average value of the bearing's lubricating oil film thickness, which contains significant errors. Ultrasonic methods can penetrate solid materials, enabling non-destructive monitoring of the lubricating oil film inside rolling bearings, and have been widely used in low-speed rolling bearings. However, accurate measurement of the contact area film thickness requires capturing the ultrasonic pulse signal at the center of the contact area. In high-speed rolling bearings, limitations such as the hardware pulse emission frequency and the distance between the ultrasonic probe and the oil film being measured make it difficult for the ultrasonic pulse to act on the center of the contact area. Alternatively, the need to collect a large number of continuous pulses significantly increases the cost of equipment for acquisition, transmission, and storage. Summary of the Invention

[0004] To address the problem that ultrasonic pulses are difficult to apply to the center of the oil film contact area in high-speed rolling bearings, resulting in poor accuracy of oil film thickness measurement, this invention provides an ultrasonic measurement method for the center of the elastohydrodynamic contact area of ​​high-speed rolling bearings.

[0005] The present invention provides an ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing, comprising:

[0006] A light-absorbing area is provided on the rolling bearing cage;

[0007] Calculate the contact half-width of the test roller, and set a reference delay time based on the contact half-width. The maximum delay displacement generated by the reference delay time is one-tenth of the contact half-width.

[0008] The duration and number of sampling periods are set. During the rotation of the rolling bearing, the trigger signal for each sampling period is obtained through the light signal formed by the light absorption area. Based on the trigger signal, a delay is applied to make the ultrasonic probe emit ultrasonic pulses and form a focused spot in the target oil film contact area of ​​the corresponding test roller. Within the sequentially changing sampling periods, the delay time generated based on the trigger signal is successively 1, 2, 3 times, ... of the reference delay time. Within each sampling period, a set number of ultrasonic reflected wave signals carrying oil film thickness information are collected. The ultrasonic reflected wave signal closest to the center of the target oil film contact area is selected from all ultrasonic reflected wave signals as the target ultrasonic reflected wave signal.

[0009] The thickness of the oil film at the center of the target oil film contact area is calculated from the target ultrasonic reflected wave signal.

[0010] According to the ultrasonic measurement method for the center oil film thickness of the elastohydrodynamic contact zone of a high-speed rolling bearing of the present invention, the light-absorbing zone is formed by spraying paint.

[0011] According to the ultrasonic measurement method for the center oil film thickness of the elastohydrodynamic contact area of ​​a high-speed rolling bearing of the present invention, the optical signal formed in the light absorption area is triggered by the electrical signal generated by the photoelectric sensor to generate a high-level signal. The high-level signal is delayed by the delay designer to trigger the signal generator. The signal generator emits a square wave pulse to control the ultrasonic pulse generator receiver to emit a negative sharp pulse signal of a specified frequency to excite the ultrasonic probe to emit an ultrasonic pulse. The ultrasonic reflected wave signal carrying the oil film thickness information is received by the ultrasonic pulse generator receiver and transmitted to the acquisition, storage and analysis system for processing to obtain the center oil film thickness of the oil film contact area.

[0012] According to the ultrasonic measurement method for the center oil film thickness of the elastohydrodynamic contact zone of a high-speed rolling bearing of the present invention, the reference delay time is expressed as Δt:

[0013]

[0014] In the formula D p The delay displacement is the reference delay duration, and v is the velocity of the oil film contact area passing under the ultrasonic probe:

[0015]

[0016] In the formula, b is the contact half-width;

[0017]

[0018] In the formula n c R is the rotational speed of the rolling bearing cage, d is the inner diameter of the rolling bearing, D is the outer diameter of the rolling bearing, and R is the outer diameter of the rolling bearing. r Where is the roller radius;

[0019]

[0020] In the formula n i This refers to the rotational speed of the inner ring of the rolling bearing.

[0021] According to the ultrasonic measurement method for the center oil film thickness of the elastohydrodynamic contact area of ​​a high-speed rolling bearing of the present invention, the target oil film contact area is the oil film contact area of ​​the selected test roller;

[0022] The number of ultrasonic pulses emitted by the ultrasonic probe recorded in each sampling period is N. p 2 to 4 times:

[0023]

[0024] In the formula L o L is the distance between the centers of adjacent oil film contact areas. p The distance between adjacent ultrasound pulses:

[0025]

[0026] L p =v / f max ,

[0027] In the formula N r f is the number of rollers in a rolling bearing. max This is the maximum pulse transmission frequency of the ultrasonic pulse generator receiver;

[0028] The number of ultrasonic pulses N p for:

[0029]

[0030] According to the ultrasonic measurement method for the center oil film thickness of the elastohydrodynamic contact zone of a high-speed rolling bearing of the present invention, the number of sampling cycles is a multiple of the test base.

[0031] The test base is represented as N test :

[0032]

[0033] Transforming equation (7), we get:

[0034]

[0035] The ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing according to the present invention uses the following method for selecting the target ultrasonic reflected wave signal:

[0036] A fast Fourier transform is performed on all ultrasonic reflected wave signals to obtain the frequency domain amplitude of the corresponding ultrasonic probe center frequency. Based on the principle of minimizing the amplitude of the central axis, the ultrasonic reflected wave signal corresponding to the center of the target oil film contact area is selected as the target ultrasonic reflected wave signal.

[0037] According to the ultrasonic measurement method for the center oil film thickness of the elastohydrodynamic contact zone of a high-speed rolling bearing of the present invention, the method for calculating the center oil film thickness of the target oil film contact zone includes calculating the reflection coefficient, which is calculated based on the frequency domain amplitude of the center frequency of the ultrasonic probe corresponding to the target ultrasonic reflected wave signal.

[0038]

[0039] In the formula |R(f c | represents the center frequency f of the ultrasonic probe corresponding to the target ultrasonic reflected wave signal. c The amplitude of the reflection coefficient at point A oil A is the average amplitude value of the non-rolling element region of the rolling bearing obtained by measurement. min r represents the frequency domain amplitude corresponding to the target ultrasonic reflected wave signal. oil This is a reference coefficient for the steel-oil interface.

[0040] According to the ultrasonic measurement method for the center oil film thickness of the elastohydrodynamic contact zone of a high-speed rolling bearing of the present invention, the center oil film thickness of the target oil film contact zone is calculated based on the reflection coefficient:

[0041]

[0042] In the formula h center ρ represents the thickness of the oil film at the center of the target oil film contact area. oP c is the corrected density of the lubricating oil under the Hertzian contact mean pressure P. oP ρ is the corrected sound velocity of the lubricating oil under the Hertzian contact mean pressure P. s c is the density of the outer ring of the rolling bearing. s This refers to the sound velocity of the outer ring of the rolling bearing.

[0043] According to the ultrasonic measurement method for the center oil film thickness of the elastohydrodynamic contact zone of a high-speed rolling bearing of the present invention, the axis of the ultrasonic probe is perpendicular to the arc of the outer ring of the rolling bearing at its location, and the focused spot is located at the interface between the outer ring of the rolling bearing and the oil film.

[0044] The beneficial effects of the present invention are as follows: The method of the present invention is based on delay design to realize the measurement of the oil film thickness at the center of the contact area. By designing a series of delay pulses that match the working conditions, the ultrasonic pulse can accurately act on the center of the bearing contact area and obtain its reflection signal. Then, the oil film thickness at the center of the contact area is obtained through algorithm processing.

[0045] The method of this invention only requires collecting a small number of continuous pulses within one sampling period, and then proceeds to the next recording after the data transmission is completed. This greatly reduces the cost of data transmission and storage.

[0046] The method of the present invention scans the contact area by controlling the emission time of ultrasonic pulses with equally spaced delay signals in different sampling periods, so that at least one ultrasonic pulse signal acts on the center of the contact area, thereby achieving accurate measurement of the oil film thickness at the center of the contact area. Attached Figure Description

[0047] Figure 1 This is a schematic diagram of the measurement state of the ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing as described in this invention;

[0048] Figure 2 This is a schematic diagram illustrating the method for measuring the film thickness at the center of the elastohydrodynamic contact zone of a high-speed rolling bearing under ultrasonic pulse application positions with different delay durations; in the diagram, T represents the corresponding f. max The cycle;

[0049] Figure 3 This is a schematic diagram illustrating the interaction between an ultrasonic pulse and two consecutive oil film cycles.

[0050] Figure 4 This is a time-domain ultrasonic pulse signal amplitude diagram recorded in the first test of the specific embodiment;

[0051] Figure 5 This is a time-domain ultrasonic pulse signal amplitude diagram recorded in the second test of Specific Embodiment 1;

[0052] Figure 6 This is a diagram of a single ultrasonic pulse signal in Specific Embodiment 1;

[0053] Figure 7 This is a graph showing the amplitude change corresponding to the center frequency of the probe during the first test in Specific Embodiment 1;

[0054] Figure 8 This is a graph showing the amplitude change corresponding to the center frequency of the probe during the first test in Specific Embodiment 1. Detailed Implementation

[0055] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0056] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0057] The present invention will be further described below with reference to the accompanying drawings and specific embodiments, but this is not intended to limit the scope of the invention.

[0058] Specific Implementation Method 1: Combination Figures 1 to 3 As shown, this invention provides an ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing, comprising:

[0059] A light-absorbing area is provided on the rolling bearing cage;

[0060] Calculate the contact half-width of the test roller, and set a reference delay time based on the contact half-width. The maximum delay displacement generated by the reference delay time is one-tenth of the contact half-width.

[0061] The duration and number of sampling periods are set. During the rotation of the rolling bearing, the trigger signal for each sampling period is obtained through the light signal formed by the light absorption area. Based on the trigger signal, a delay is applied to make the ultrasonic probe emit ultrasonic pulses and form a focused spot in the target oil film contact area of ​​the corresponding test roller. Within the sequentially changing sampling periods, the delay time generated based on the trigger signal is successively 1, 2, 3 times, ... of the reference delay time. Within each sampling period, a set number of ultrasonic reflected wave signals carrying oil film thickness information are collected. The ultrasonic reflected wave signal closest to the center of the target oil film contact area is selected from all ultrasonic reflected wave signals as the target ultrasonic reflected wave signal.

[0062] The thickness of the oil film at the center of the target oil film contact area is calculated from the target ultrasonic reflected wave signal.

[0063] As an example, combined Figure 1 As shown, the light-absorbing area is formed by spraying paint.

[0064] In this embodiment, the light-absorbing region serves as the reference point for generating the trigger signal, ensuring that the sampling signals of all sampling periods have the same starting point.

[0065] Furthermore, combined with Figure 1 As shown, when the light-absorbing area on the rolling bearing cage passes the photoelectric sensor, the light signal generated by the light-absorbing area triggers the high-level signal through the electrical signal generated by the photoelectric sensor. The high-level signal is then delayed by the delay designer to trigger the signal generator. The signal generator then sends a square wave pulse to control the ultrasonic pulse generator receiver to send a negative spike pulse signal of a specified frequency to excite the ultrasonic probe to send an ultrasonic pulse. Then, the ultrasonic reflected wave signal carrying the oil film thickness information is received by the ultrasonic pulse generator receiver and transmitted to the acquisition, storage and analysis system for processing to obtain the oil film thickness at the center of the oil film contact area.

[0066] The number of bearing revolutions per sampling period is related to the operating speed of the data acquisition, storage, and analysis system. If data storage can be completed within one revolution of the bearing, a one-week sampling period can be chosen; otherwise, a two- or three-week sampling period can be selected. For sampling periods longer than one week, ultrasonic pulse emission can be avoided by signal suppression when the light-absorbing area passes through the photoelectric sensor. Therefore, there are no strict requirements for storage speed, reducing data storage costs; ordinary memory can be used.

[0067] Combination Figure 2 As shown, the upper left subplot represents the positional relationship between the ultrasonic focusing focal spot and the contact area without time delay. Due to the increase in bearing speed, the ultrasonic focusing focal spot may not be able to interact with the center of the contact area or even the entire contact area. However, after a series of tiny time delays, as shown... Figure 2 The lower left and right sub-images ensure that at least one of the series of focused ultrasound spots accurately interacts with the center of the contact area.

[0068] The oil film thickness obtained by applying an ultrasonic pulse to a radius of one-tenth of the contact half-width centered at the contact area center is closest to the true value. To ensure that an ultrasonic pulse is sufficiently close to the contact center, the maximum value of the displacement caused by the delay is set to one-tenth of the contact half-width. For higher accuracy, a smaller delay displacement can be set.

[0069] The reference delay duration is expressed as Δt:

[0070]

[0071] In the formula D p The delay displacement is the reference delay duration, and v is the velocity of the oil film contact area passing under the ultrasonic probe:

[0072]

[0073] In the formula, b is the contact half-width;

[0074] For bearings, without considering slippage and other effects, v can be approximated as:

[0075]

[0076] In the formula n c R is the rotational speed of the rolling bearing cage, d is the inner diameter of the rolling bearing, D is the outer diameter of the rolling bearing, and R is the outer diameter of the rolling bearing. r Where is the roller radius;

[0077]

[0078] In the formula n i This refers to the rotational speed of the inner ring of the rolling bearing.

[0079] Combination Figure 3 As shown, since only the film thickness at the center of the contact area corresponding to a single roller needs to be measured, it is only necessary to record the continuously emitted ultrasonic pulses covering two oil film contact areas; in actual testing, the continuously emitted ultrasonic pulses of three oil film contact areas can also be recorded as needed.

[0080] The target oil film contact area is the oil film contact area of ​​the selected test roller;

[0081] The number of ultrasonic pulses emitted by the ultrasonic probe that needs to be recorded in each sampling period is N. p 2 to 4 times:

[0082]

[0083] In the formula L o L is the distance between the centers of adjacent oil film contact areas, which can be approximated as the distance between the contact points of adjacent rollers on the outer ring; p The distance between adjacent ultrasound pulses:

[0084]

[0085] L p =v / f max ,

[0086] In the formula N r f is the number of rollers in a rolling bearing. max This is the maximum pulse transmission frequency of the ultrasonic pulse generator receiver;

[0087] The number of ultrasonic pulses N p for:

[0088]

[0089] Obviously, as the cage rotational speed increases, the number of pulses recorded in a single operation will decrease. The maximum transmission frequency of ultrasonic pulses is typically 20kHz. For a bearing with 14 rolling elements and a cage rotational speed of 15000rpm, the number of pulses recorded, N, will be... p The cost is only 6. This obviously greatly reduces the requirements for data transmission and storage at high speeds, thereby reducing costs.

[0090] Furthermore, the number of sampling periods is a multiple of the test base.

[0091] The test baseline depends on the displacement D caused by the delay. p The distance L between adjacent pulses p , represented as N test :

[0092]

[0093] Transforming equation (7), we get:

[0094]

[0095] Due to the complexity of the actual testing process, N test This is only the minimum base number. More test counts can be set according to the actual situation, but generally it will not exceed 10 times the base number.

[0096] In this embodiment, the above method enables at least one ultrasonic pulse to act on the center of the contact area at a low cost. The method for selecting the target ultrasonic reflected wave signal is as follows:

[0097] A fast Fourier transform is performed on all ultrasonic reflected wave signals to obtain the frequency domain amplitude of the corresponding ultrasonic probe center frequency. Based on the principle of minimizing the amplitude of the central axis, the ultrasonic reflected wave signal corresponding to the center of the target oil film contact area is selected as the target ultrasonic reflected wave signal.

[0098] The method for calculating the thickness of the oil film at the center of the target oil film contact area includes calculating the reflection coefficient, which is calculated based on the frequency domain amplitude of the ultrasonic probe's center frequency corresponding to the target ultrasonic reflected wave signal.

[0099]

[0100] In the formula |R(f c | represents the center frequency f of the ultrasonic probe corresponding to the target ultrasonic reflected wave signal. c The amplitude of the reflection coefficient at point A oil A is the average amplitude value of the non-rolling element region of the rolling bearing obtained by measurement. min r represents the frequency domain amplitude corresponding to the target ultrasonic reflected wave signal. oil This is a reference coefficient for the steel-oil interface, with a value of 0.94.

[0101] Then, calculate the oil film thickness at the center of the target oil film contact area based on the reflection coefficient:

[0102]

[0103] In the formula h center ρ represents the thickness of the oil film at the center of the target oil film contact area. oP c is the corrected density of the lubricating oil under the Hertzian contact mean pressure P. oP ρ is the corrected sound velocity of the lubricating oil under the Hertzian contact mean pressure P. s c is the density of the outer ring of the rolling bearing. s This refers to the sound velocity of the outer ring of the rolling bearing.

[0104] Combination Figure 1As shown, in this embodiment, the axis of the ultrasonic probe is perpendicular to the outer ring arc of the rolling bearing at its location, and the focused spot is located at the interface between the outer ring of the rolling bearing and the oil film. Specific Implementation Example 1:

[0106] Based on the above principle, taking a bearing of model Nu208 under the condition of 10000N load and 30000rpm inner ring speed as an example, the steps of the method of the present invention are described in detail.

[0107] 1. Install the ultrasonic probe using a clamp and adjust its angle so that its axis is perpendicular to the outer ring arc of the bearing. Adjust its position so that the focused spot is located at the outer ring-oil film interface.

[0108] 2. Based on the geometric dimensions, operating speed, and load of the rolling bearing, calculate the contact half-width b and average contact pressure P of the maximum load-bearing roller (test roller), and determine the corresponding lubricating oil parameters.

[0109] 3. Based on the ultrasonic measurement method for the oil film thickness in the elastohydrodynamic contact zone of high-speed rolling bearings with time delay design, a series of time delays Δt and N are determined. test In practice, 10N was selected. test .

[0110] 4. Set the sampling period duration according to the storage speed of the field equipment, control the activation state of the trigger, and based on the determined 10N... test Determine the number of sampling periods.

[0111] 5. After the bearing has stabilized, begin the ultrasonic film thickness measurement test, acquiring continuous pulse signals to meet the set acquisition requirements. The ultrasonic pulse signals recorded between two consecutive tests are shown below. Figure 4 and Figure 5 As shown, Figure 6 A magnified image of a single time-domain ultrasonic pulse signal.

[0112] 6. Perform a fast Fourier transform on the obtained ultrasonic reflection wave signal of the oil film layer to obtain the frequency domain amplitude of the corresponding probe center frequency. Figure 7 and Figure 8 The changes in frequency domain amplitude corresponding to the center frequency of the probe in two consecutive tests are shown.

[0113] 7. In the completed N test In this experiment, the frequency domain amplitude corresponding to the central axis region of the oil film in the contact area was selected based on the principle of minimizing the amplitude along the central axis. The minimum frequency domain amplitude obtained was 0.735.

[0114] 8. The reference incident signal amplitude is determined to be 0.94 based on the average amplitude of the frequency domain outside the rolling body area below the probe.

[0115] 9. The reflection coefficient is calculated to be 0.782 according to formula (9).

[0116] 10. The thickness of the oil film at the center of the oil film contact area is calculated to be 3.10 μm according to formula (10).

[0117] 11. Repeat the measurement 6 times and calculate the mean.

[0118] To verify the beneficial effects of the method of the present invention, Table 1 presents the comparison results between the theoretical values ​​and the method of the present invention and existing methods.

[0119] Table 1 (Unit: μm)

[0120] Method of the present invention 3.10 3.15 3.14 3.11 3.05 3.15 3.12 Existing methods 4.10 5.12 3.51 3.58 4.98 4.2 4.25 Theoretical value 3.11 3.11 3.11 3.11 3.11 3.11 3.11

[0121] Specific embodiment 2: The bearing model is Nu208, the test load is 10000N, the test inner ring speed is 250rpm, the measurement result of the film thickness at the center of the contact area by the method of the present invention is 0.113μm, the theoretical value is 0.112μm, and the existing method is 0.131μm.

[0122] Specific embodiment 3: The bearing model is Nu208, the test load is 10000N, the test inner ring speed is 5000rpm, the measurement result of the film thickness at the center of the contact area by the method of the present invention is 0.875μm, the theoretical value is 0.897μm, and the existing method is 1.3μm.

[0123] Specific Implementation Example 4: The bearing model is Nu208, the test load is 10000N, the test inner ring speed is 10000rpm, and the measurement result of the film thickness at the center of the contact area by the method of the present invention is 1.465μm, the theoretical value is 1.456μm, and the existing method is 2.26μm.

[0124] Specific Implementation Example 5: The bearing model is Nu208, the test load is 10000N, the test inner ring speed is 20000rpm, and the measured film thickness at the center of the contact area is 2.31μm, the theoretical value is 2.35μm, and the existing method is 3.65μm.

[0125] Specific Implementation Example 6: The bearing model is Nu208, the test load is 10000N, the test inner ring speed is 20000rpm, and the measured film thickness at the center of the contact area is 3.12μm, the theoretical value is 3.11μm, and the existing method is 4.25μm.

[0126] In the above embodiments, compared with existing low-speed bearing film thickness measurement methods, the method of the present invention yields test results close to those of existing methods at low speeds and both conform to theoretical values. As the rotational speed increases, the measurement results of the method of the present invention approach the theoretical values, while existing methods deviate significantly from the theoretical values. This indicates that the method of the present invention is suitable for measuring the film thickness of high-speed bearings in county towns.

[0127] While the invention has been described herein with reference to specific embodiments, it should be understood that these embodiments are merely examples of the principles and applications of the invention. Therefore, it should be understood that many modifications can be made to the exemplary embodiments, and other arrangements can be designed without departing from the spirit and scope of the invention as defined by the appended claims. It should be understood that different dependent claims and features described herein can be combined in ways different from those described in the original claims. It is also understood that features described in conjunction with individual embodiments can be used in other described embodiments.

Claims

1. An ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing, characterized in that... include, A light-absorbing area is provided on the rolling bearing cage; Calculate the contact half-width of the test roller, and set a reference delay time based on the contact half-width. The maximum delay displacement generated by the reference delay time is one-tenth of the contact half-width. Set the duration of the sampling period and the number of sampling periods; During the rotation of the rolling bearing, the trigger signal for each sampling cycle is obtained through the light signal formed by the light absorption area. Based on the trigger signal, a delay is made so that the ultrasonic probe emits an ultrasonic pulse and forms a focused spot in the target oil film contact area of ​​the corresponding test roller. Within the sequentially changing sampling period, the delay duration generated by the trigger signal is an integer multiple of the reference delay duration; a set number of ultrasonic reflected wave signals carrying oil film thickness information are acquired in each sampling period; the ultrasonic reflected wave signal closest to the center of the target oil film contact area is selected from all ultrasonic reflected wave signals as the target ultrasonic reflected wave signal; The thickness of the oil film at the center of the target oil film contact area is calculated from the target ultrasonic reflected wave signal.

2. The ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing according to claim 1, characterized in that, The light-absorbing area is formed by spraying paint.

3. The ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing according to claim 1, characterized in that, The light signal generated in the light absorption area triggers a high-level signal through the electrical signal generated by the photoelectric sensor. The high-level signal is then delayed by the delay designer to trigger the signal generator. The signal generator outputs a square wave pulse to control the ultrasonic pulse generator receiver to output a negative spike pulse signal of a specified frequency to excite the ultrasonic probe to output an ultrasonic pulse. The ultrasonic reflected wave signal carrying oil film thickness information is received by the ultrasonic pulse generator receiver and then transmitted to the acquisition, storage and analysis system for processing to obtain the oil film thickness at the center of the oil film contact area.

4. The ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing according to claim 1, characterized in that, The reference delay duration is expressed as ∆t: （1）， In the formula D p The delay displacement generated by the reference delay duration, The velocity of the oil film in the contact area passing under the ultrasonic probe: （2）， In the formula For contact half-width; （3）， In the formula R is the rotational speed of the rolling bearing cage, d is the inner diameter of the rolling bearing, D is the outer diameter of the rolling bearing, and R is the outer diameter of the rolling bearing. r Where is the roller radius; （4）， In the formula This refers to the rotational speed of the inner ring of the rolling bearing.

5. The ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing according to claim 4, characterized in that, The target oil film contact area is the oil film contact area of ​​the selected test roller; The number of ultrasonic pulses emitted by the ultrasonic probe recorded in each sampling period is the number of ultrasonic pulses in each oil film cycle. 2 to 4 times: （5）， In the formula L o L is the distance between the centers of adjacent oil film contact areas. p The distance between adjacent ultrasound pulses: ， ， In the formula f is the number of rollers in a rolling bearing. max This is the maximum pulse transmission frequency of the ultrasonic pulse generator receiver; but for: （6）。 6. The ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing according to claim 5, characterized in that, The number of sampling periods is a multiple of the test base. The test base is expressed as : （7）， Transforming equation (7), we get: （8）。 7. The ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing according to claim 6, characterized in that, The method for selecting the target ultrasonic reflected wave signal is as follows: A fast Fourier transform is performed on all ultrasonic reflected wave signals to obtain the frequency domain amplitude of the corresponding ultrasonic probe center frequency. Based on the principle of minimizing the amplitude of the central axis, the ultrasonic reflected wave signal corresponding to the center of the target oil film contact area is selected as the target ultrasonic reflected wave signal.

8. The ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing according to claim 7, characterized in that, The method for calculating the thickness of the oil film at the center of the target oil film contact area includes calculating the reflection coefficient, which is calculated based on the frequency domain amplitude of the ultrasonic probe's center frequency corresponding to the target ultrasonic reflected wave signal. （9）， In the formula |R(f c | represents the center frequency f of the ultrasonic probe corresponding to the target ultrasonic reflected wave signal. c The amplitude of the reflection coefficient at point A oil A is the average amplitude value of the non-rolling element region of the rolling bearing obtained by measurement. min r represents the frequency domain amplitude corresponding to the target ultrasonic reflected wave signal. oil This is a reference coefficient for the steel-oil interface.

9. The ultrasonic measurement method for the center oil film thickness in the elastohydrodynamic contact zone of a high-speed rolling bearing according to claim 8, characterized in that, Calculation of oil film thickness at the center of the target oil film contact area based on reflection coefficient: （10）， In the formula h center ρ represents the thickness of the oil film at the center of the target oil film contact area. oP c is the corrected density of the lubricating oil under the Hertzian contact mean pressure P. oP ρ is the corrected sound velocity of the lubricating oil under the Hertzian contact mean pressure P. s c is the density of the outer ring of the rolling bearing. s This refers to the sound velocity of the outer ring of the rolling bearing.

10. The ultrasonic measurement method for the center oil film thickness of the elastohydrodynamic contact zone of a high-speed rolling bearing according to claim 9, characterized in that, The axis of the ultrasonic probe is perpendicular to the outer arc of the rolling bearing at its location, and the focused spot is located at the interface between the outer ring of the rolling bearing and the oil film.

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