CN103822600B - The supersonic detection method of thin friction material Rotating fields slide bearing lubricating film thickness - Google Patents

Abstract

The invention discloses an ultrasonic detection method for the lubricating film thickness of a sliding bearing with a thin friction material layer structure. The method is based on the reference reflection echo signal of the bearing bush-air interface which needs to be obtained by the basic stiffness model method. Or theoretically calculate the echo signal amplitude spectrum of the substrate-liner interface, and then respectively obtain the reference echo, the frequency domain amplitude ratio of the superimposed signal and the substrate-liner interface echo at different film thickness echoes, and press Superposition The signal spectrum analysis method obtains the amplitude ratio of the echo component containing film thickness information and the substrate-lining interface echo at a specific frequency, thereby obtaining the reflection coefficient value in film thickness measurement and finally determining the lubricating film thickness value. The invention realizes the measurement of the submicron and micron lubricating film thickness of the fluid lubrication sliding radial and thrust bearings when the reflected echo signals are superimposed.

Description

Ultrasonic testing method for lubricating film thickness of sliding bearing with thin friction material layer structure

【Technical field】

The invention belongs to the fields of industrial equipment operation state monitoring and tribological element design and experimental inspection, and in particular relates to an ultrasonic detection method for the lubricating film thickness of a sliding bearing with a thin friction material layer structure.

【Background technique】

Sliding bearings are widely used in high-speed, precision, heavy-duty and other occasions, and have become important core components in large-scale thermal power, hydropower units, nuclear power plant main circulation pumps, high-speed precision machine tools and other equipment. Fluid lubricated sliding bearings rely on the fluid lubricating film to separate the bearing bush and the journal surface. The characteristics and state of the lubricating film determine the bearing capacity, running stability and life of the sliding bearing. Therefore, the thickness of the fluid lubricating film, etc. The detection of state is of great significance not only for the experimental comparative study of fluid lubrication theory, but also for the monitoring of the running state of sliding bearings.

The lubricating film thickness of sliding bearings is one of the basic parameters of sliding bearings. Usually, in the design and performance calculation of sliding bearings, it is necessary to obtain the minimum lubricating film thickness and thickness distribution of the sliding bearing through physical assumptions and mathematical approximations, and determine other important parameters in the design of sliding bearings, such as lubricating film pressure, Load capacity, aspect ratio, etc. However, the assumptions in the theoretical calculation are not completely consistent with the actual situation, and the factors produced in the bearing manufacturing process and operation process make it difficult to accurately describe the area where the lubricating film exists and its thickness. Therefore, in order to determine the impact of various assumptions and the actual distribution of the lubricant film thickness during operation, it is necessary to study and propose a detection method for the lubricant film thickness.

The lubricating film of a sliding bearing exists between two interfaces in relative motion, and its thickness is usually between submicron to tens of microns, and has the characteristics of real-time change, which makes the measurement of the thickness of the fluid lubricating film very challenging. Traditional lubricating film thickness detection methods based on resistance, capacitance and optical methods need to destroy the surface of the friction pair, or require one side of the friction pair to be a light-transmitting substance. Compared with these methods, the ultrasonic detection method does not need to modify the surface of the friction pair, and its penetrating ability makes up for the lack of light transmission required by the optical method. The detection method based on ultrasonic technology has obvious advantages for the detection of the thickness of the sliding bearing lubricating film. Superiority.

The thin dielectric layer thickness measurement method usually based on the ultrasonic time difference method and the resonance method is restricted by the principle of the measurement model, and its thickness measurement range is generally on the order of tens of microns and above. According to the relationship between the stiffness of the intermediate medium layer and the ultrasonic reflection coefficient, the ultrasonic stiffness model method extends the measurement range of the thickness of the intermediate fluid layer to the order of ten microns to submicrons, laying a theoretical foundation for the practical application of ultrasonic testing of lubricating film thickness. The method of ultrasonic stiffness model provides a specific measurement method for the lubricating film thickness in the three-layer structure of bearing bush-fluid film-journal. This method compares the reflection wave amplitude of the bearing pad-fluid film interface with the reflection wave amplitude of the bearing pad-air interface, and obtains the reflection coefficient value determined by the film thickness, material acoustic parameters, etc., and then according to the relationship between the reflection coefficient and the film thickness The relationship yields a fluid film thickness value.

However, the sliding bearing bush is usually formed by casting or rolling from the matrix and the friction material layer. The friction material layer is usually made of alloy material, which plays the role of reducing friction, embedding abrasive particles, and facilitating maintenance. The friction material layer is also called the bearing lining. The thickness of the lining layer is usually in the range of a few tenths of a millimeter to 6mm. In this way, under the premise of ensuring that the ultrasonic thickness measurement method does not destroy the superiority of the bearing structure, the measurement model of the three-layer structure becomes the bearing shell matrix-lining- Fluid film-journal four-layer structure. Take short-pulse ultrasonic measurement as an example. Generally, the ultrasonic wave occupies a pulse width of more than 3 wavelengths in the tested material. It is about 1mm, and when a 5MHz long pulse transducer is used, this width value becomes 4.6mm. The phenomenon of superposition will occur with the reflection echo of the second interface, which is the meaning of "thin friction material layer" or "thin lining layer" in the present invention. _The ultrasonic reflection echo signals _of "thick lining" and "thin lining" bearing _pads are shown in _Fig . Respectively, the liner-fluid film interface echoes are formed by repeated transmission and reflection between the liners, and _Pm is the superimposed signal of the above echoes in the case of a thin liner. When the reflected echoes are superimposed, the basic stiffness model method can no longer be used to obtain the reflection coefficient of the bearing pad-fluid film interface, so it is difficult to measure the lubricating film thickness of sliding bearings in most cases in practical engineering applications.

【Content of invention】

The object of the present invention is to address the deficiencies in the prior art and provide an ultrasonic detection method for the thickness of the lubricating film of a sliding bearing with a thin friction material layer structure. When the reflection echo containing the film thickness information of the bearing liner-fluid film interface is superimposed on the signal of the reflection echo of the bearing liner matrix-liner interface, the frequency domain analysis is carried out to extract the information related to the change of the fluid film thickness in the echo. Furthermore, the reflection coefficient of the fluid layer interface and the thickness of the lubricating film are obtained.

To achieve the above object, the present invention adopts the following technical solutions:

The ultrasonic detection method for the lubricating film thickness of a sliding bearing with a thin friction material layer structure comprises the following steps:

1) The time-domain echo signal p b (t) of the bearing pad matrix-lining layer interface of the thick friction material layer bearing pad test block of the same material as the thin friction material layer structure sliding bearing is measured by the ultrasonic testing system, and the time domain echo signal p _b (t) is analyzed. Wave signal p _b (t) obtained by fast Fourier transform its frequency domain amplitude spectrum |P _b (ω)|, and then measure the reference echo of the thin friction material layer sliding bearing to be detected at the bearing pad-air interface signal p _a (t), and the superimposed echo signal p _m (t) of the sliding bearing bush-fluid film interface measured with a thin friction material layer, where the thin friction material layer is the bearing bush whose thickness is less than half of the ultrasonic pulse width of the ultrasonic transducer Lining layer, the thick friction material layer is the bearing bush lining whose thickness is greater than or equal to half of the ultrasonic pulse width of the ultrasonic transducer;

2) Fast Fourier transform is performed on the reference echo signal p _a (t) and the superimposed echo signal p _m (t) obtained in step 1), respectively, to obtain the frequency domain amplitude spectrum of the reference echo signal |P _a ( ω)| and the frequency-domain amplitude spectrum of the superimposed echo signal |P _m (ω)|, and the results are then compared with the frequency-domain amplitude spectrum P _b (ω) of the bearing substrate-lining interface obtained in step 1). By comparison, the amplitude ratio Q _a (ω) of the reference echo signal to the substrate-lining interface echo and the amplitude ratio Q _m (ω) of the superimposed echo signal to the substrate-lining interface echo are obtained;

3) Based on the amplitude ratio Q _a (ω) of the reference echo signal obtained in step 2) and the echo of the substrate-lining interface combined with its peak frequency ω _as , calculate the peak frequency ω _as to (1+10%) ω _as The amplitude ratio k _a (ω _a ) of different interface echo components in the reference echo signal in the frequency region and at two endpoints is calculated as follows:

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; cos</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&CenterDot;</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: t ₀ is the time taken for the ultrasonic wave to pass through the thickness of the thin lining, ω _a is the frequency of the reference echo signal in the range from ω _as to (1+10%) ω _as , Q _a (ω _a ) is the reference echo signal Amplitude ratio to the substrate-liner interface echo at ωa _;

4) Based on the amplitude ratio Q _m (ω) of the superimposed signal echo obtained in step 2) and the echo of the substrate-lining interface combined with its peak frequency ω _ms , calculate the different interfaces in the superimposed echo signal at the peak frequency ω _ms Echo component amplitude ratio km ( _{ω ms} ), its calculation formula is as follows:

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula: Q _m (ω _ms ) is the amplitude ratio of the superimposed signal echo to the substrate-lining interface echo amplitude ratio Q _m (ω) at the peak frequency ω _ms ;

5) The amplitude ratios of different interface echo components in the superimposed echo signal obtained in step 4) k _m (ω _ms ) and the amplitude ratios of different interface echo components in the reference echo signal obtained in step 3) k _a (ω _ms ) at the frequency ω _ms to obtain the reflection coefficient R of the echo signal when measuring the lubricant film thickness, and finally according to the film thickness formula of the basic stiffness model method combined with the reflection coefficient R to obtain the lubricating film thickness of the thin friction material layer structure sliding bearing h.

Further improvement of the present invention is that, in step 5), the film thickness formula of the basic stiffness model method is:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&rho;c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula: ρ is the density of fluid medium, the unit is kg/m ³ ;

c is the sound velocity of the fluid medium, in m/s;

z ₁ is the acoustic impedance of the bearing lining material, in kg/(m ² ·s);

z ₂ is the acoustic impedance of the journal material, in kg/(m ² ·s);

ω is the angular frequency of the ultrasonic reflected wave, in rad/s.

Compared with the prior art, the present invention has the following technical effects:

The invention discloses an ultrasonic detection method for the lubricating film thickness of a sliding bearing with a thin friction material layer structure. The method analyzes the superimposed echo reflection signal during the ultrasonic measurement of the lubricating film thickness of a sliding bearing with a thin friction material layer structure, and obtains the film thickness The amplitude ratio of the liner-lubricating film interface echo component of the information to the unchanged substrate-liner interface echo component is compared with the amplitude ratio of the reference echo signal to obtain the film thickness measurement The results of echo reflection coefficient and film thickness at time. The invention solves the problem of measuring the lubricating film thickness of the micron-level and sub-micron-level lubricating film of the thin friction material layer structure commonly used in engineering applications, and expands the application range of the method for measuring the thickness of the ultrasonic lubricating film.

【Description of drawings】

Fig. 1 Time-domain signal diagram of ultrasonic reflection echo of sliding bearing with thick friction material layer;

Fig. 2 Time-domain signal diagram of ultrasonic reflection echo of sliding bearing with thin friction material layer;

Figure 3 Babbitt alloy-oil film-steel medium film thickness and reflection coefficient relationship curve;

Fig. 4 The time-domain signal diagram of the echo time domain of the thick lining bearing pad test block matrix-lining interface;

Fig. 5 Spectrum of the echo signal amplitude of the thick lining bearing pad test block matrix-lining interface;

Fig. 6 Comparison diagram of time-domain signals of reference echo and superimposed echo of different film thicknesses for sliding bearings with thin lining;

Fig.7 The reference echo of the thin liner sliding bearing and the amplitude spectrum of the superimposed echo signal at different film thicknesses;

Fig. 8 The reference echo of the thin lining sliding bearing and the ratio of the superimposed echo signal to the echo amplitude of the substrate-lining interface at different film thicknesses;

Fig.9 The results of multiple measurements of the amplitude ratio of the liner-lubricating film interface echo and the substrate-liner interface echo amplitude ratio when the thin liner sliding bearing has different film thicknesses;

Fig. 10 The reference echo signal of the thin-lined sliding bearing is compared with the multiple measurement results of the liner-air interface echo and the matrix-liner interface echo amplitude ratio;

Fig. 11 The reflection coefficient measurement results of sliding bearings with thin friction material layer with different film thicknesses;

Fig. 12 Comparison diagram of detection results and set thickness of lubricating film thickness of sliding bearing with thin friction material layer.

Among them: 1 is the echo P _b of the bearing shell matrix-lining layer interface; 2 is the primary echo P ₁ of the lining layer-fluid film interface; 3 is the secondary echo P ₂ of the lining layer-fluid film interface; 4 is the lining layer-fluid film interface The third echo of the interface P ₃ ; 5 is the fourth echo P ₄ of the liner-fluid film interface; 6 is the superposition signal P _m of the echo of the bearing bush matrix-liner interface and the multiple echoes of the liner-fluid film interface; 7 is the reference echo Wave; 8 is the increasing direction of film thickness.

【detailed description】

The present invention is described in further detail below in conjunction with accompanying drawing:

Referring to Figures 3 to 12, the ultrasonic detection method for the lubricating film thickness of a sliding bearing with a thin friction material layer structure according to the present invention includes the following steps:

Step 1) Measure the time domain echo signal p _b (t) of the bearing pad base-lining interface of the thick friction material layer bearing pad test block of the same material as the thin friction material layer structure sliding bearing by the ultrasonic testing system, and compare the time domain The frequency domain amplitude spectrum |P _b (ω)| of the echo signal p _b (t) obtained by fast Fourier transform, and then measure the reference return of the sliding bearing with a thin friction material layer to be detected at the bearing bush-air interface wave signal p _a (t), and the superimposed echo signal p _m (t) measured at the interface of the sliding bearing bush-fluid film of the thin friction material layer, wherein the thin friction material layer has a thickness less than half of the ultrasonic pulse width of the ultrasonic transducer Bearing liner, the thick friction material layer is the bearing liner whose thickness is greater than or equal to half of the ultrasonic pulse width of the ultrasonic transducer;

2) Fast Fourier transform is performed on the reference echo signal p _a (t) and the superimposed echo signal p _m (t) obtained in step 1), respectively, to obtain the frequency domain amplitude spectrum of the reference echo signal |P _a ( ω)| and the frequency domain amplitude spectrum |P _m (ω ₎ | )|compared, the amplitude ratio Q _a (ω) of the reference echo signal to the substrate-lining interface echo and the amplitude ratio Q _m (ω) of the superimposed echo signal to the substrate-lining interface echo are obtained;

3) Based on the amplitude ratio Q _a (ω) of the reference echo signal obtained in step 2) and the echo of the substrate-lining interface combined with its peak frequency ω _as , calculate the peak frequency ω _as to (1+10%) ω _as The amplitude ratio k _a (ω _a ) of different interface echo components in the reference echo signal in the frequency region and at two endpoints is calculated as follows:

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; cos</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$

In the formula: t ₀ is the time taken for the ultrasonic wave to pass through the thickness of the thin lining, ω _a is the frequency of the reference echo signal in the range from ω _as to (1+10%) ω _as , Q _a (ω _a ) is the reference echo signal Amplitude ratio to the substrate-liner interface echo at ωa _;

4) Based on the amplitude ratio Q _m (ω) of the superimposed signal echo obtained in step 2) and the echo of the substrate-lining interface combined with its peak frequency ω _ms , calculate the different interfaces in the superimposed echo signal at the peak frequency ω _ms Echo component amplitude ratio km ( _{ω ms} ), its calculation formula is as follows:

${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$

In the formula: Q _m (ω _ms ) is the amplitude ratio of the superimposed signal echo to the substrate-lining interface echo amplitude ratio Q _m (ω) at the peak frequency ω _ms ;

5) The amplitude ratios of different interface echo components in the superimposed echo signal obtained in step 4) k _m (ω _ms ) and the amplitude ratios of different interface echo components in the reference echo signal obtained in step 3) k _a (ω _ms ) at the frequency ω _ms to obtain the reflection coefficient R of the echo signal when measuring the lubricant film thickness, and finally according to the film thickness formula of the basic stiffness model method combined with the reflection coefficient R to obtain the lubricating film thickness of the thin friction material layer structure sliding bearing h.

Wherein, in step 5), the basic stiffness model method film thickness formula is:

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&rho;c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

In the formula: ρ is the density of fluid medium, the unit is kg/m ³ ;

c is the sound velocity of the fluid medium, in m/s;

z ₁ is the acoustic impedance of the bearing lining material, in kg/(m ² ·s);

z ₂ is the acoustic impedance of the journal material, in kg/(m ² ·s);

ω is the angular frequency of the ultrasonic reflected wave, in rad/s.

In order to further understand the present invention, it is now described in further detail.

(1) general idea of the present invention

For the time-domain echo signals superimposed in the four-layer structure of the bearing pad matrix-lining layer-fluid film-journal, since the change of the film thickness does not affect the echo amplitude of the bearing pad matrix-lining layer interface, that is, when the film thickness is measured The p _b component in the superimposed echo signal obtained in is fixed and is determined by the material parameters. In this way, the amplitude ratio of the liner-fluid film interface echo component containing film thickness information in the superimposed echo signal to p _b is obtained, and then the amplitude ratio of the liner-air interface echo to p _b is obtained as the reference amplitude The value ratio, the reflection coefficient at different film thicknesses can be determined from the amplitude ratio of the above two and p _b , and the film thickness value can be obtained according to the basic stiffness model method.

(2) Calculation of the amplitude ratio of superimposed signal echo and substrate interface echo

For ultrasonic detection of lubricating film thickness when the lining is thin, the superimposed echo signal p _m (t) is composed of the echo signal p _b (t) of the substrate-lining interface and the multiple reflection echo signal of the lining-lubricating film interface p ₁ (t), p ₂ (t), p ₃ (t), etc. are superimposed. The time interval between these echoes is determined by the thickness of the lining and its material properties. Let the time it takes for the ultrasonic wave to pass through the thickness of the lining to be t ₀ , then the time interval between the echoes formed by the back and forth alloy lining is 2t ₀ . Due to the different parameters of the first and second interface materials, and the influence of different lubricating film thicknesses on the echo amplitude of the second interface, there is a certain amplitude difference between p ₁ (t) and p _b (t), while p ₁ (t), p ₂ (t), p ₃ (t) etc. The amplitude difference among the echoes is formed by the different attenuation caused by the different times of passing through the alloy layers. First, ignore the influence of echoes such as p ₂ (t), p ₃ (t) on p _m (t), let p _m (t) _consist of two echo signals p _b (t+t ₀ ) and p ₁ (tt ₀ ), and the Fourier transform of the substrate-lining interface echo signal p _b (t) is p _b (ω), according to the relevant theorems of Fourier transform, we can get

$\begin{array}{c}<span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>\mathrm{<span\; class="notranslate">\; f</span>}<span\; class="notranslate">\; \&lsqb;</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; p</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; t</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; |</span>\\ <span\; class="notranslate">\; =</span><span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{{\mathrm{<span\; class="notranslate">\; j\&omega;t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; e</span>}}^{<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; j\&omega;t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>\end{array}$

$<span\; class="notranslate">\; =</span>\sqrt{{<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; cos</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}<span\; class="notranslate">\; )</span>$

Among them, k(ω) is the amplitude ratio of the two pulse components at different frequencies in the frequency domain. Then the amplitude ratio Q(ω) of p _m (t) and p _b (t) in the frequency domain is

$\mathrm{<span\; class="notranslate">\; Q</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}{<span\; class="notranslate">\; |</span>{\mathrm{<span\; class="notranslate">\; P</span>}}_{\mathrm{<span\; class="notranslate">\; b</span>}}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; |</span>}<span\; class="notranslate">\; =</span>\sqrt{{<span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 4</span>}\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; \&omega;</span>}<span\; class="notranslate">\; )</span>{\mathrm{<span\; class="notranslate">\; cos</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 5</span>}<span\; class="notranslate">\; )</span>$

(3) Solving the amplitude ratio of different interface echo components when superimposing signals

If |P _m (ω)| can be obtained in advance, Q(ω) can be obtained through the ratio of the amplitude spectrum of the thin lining echo p _m (t) to |P _b (ω)|, and then by solving the formula ( 5) equation to obtain the frequency domain amplitude ratio k(ω) of p ₁ (t) and p _b (t) at different film thicknesses, and then compare it with the reference amplitude ratio obtained from the liner-air interface to obtain the reflection Coefficients and film thickness values. In this way, it is necessary to obtain the substrate-lining interface echo _pb by processing the thick-lined bearing bush test block of the same material and using the same ultrasonic testing system before testing the thin-lined lubricating film thickness (as shown in Figure 1 ), which is usually easy to realize, and can also be obtained through theoretical calculation of material acoustic parameters |P _b (ω ₎ | Accuracy, but does not affect the monitoring of film thickness variation trend.

After obtaining Q(ω), Equation (5) becomes the following equation including k(ω).

k ² (ω)+(4cos ² ωt ₀ -2)·k(ω)+[1-Q ² (ω _s )]＝0 (6)

It can be seen from formula (5) that Q(ω) is a positive value curve that fluctuates with frequency in a cosine manner, and the peak value of Q(ω) near the ultrasonic echo center frequency is Q(ω _s ), and ω _s is Q(ω s ). (ω) peak frequency, then the above formula becomes

k ² (ω _s )+2k(ω _s )+[1-Q ² (ω _s )]＝0 (7)

The amplitude ratio k(ω _s ) of p ₁ (t) containing film thickness information and p _b (t) kept unchanged at ω _s frequency can be obtained from formula (7).

(4) Solution of ultrasonic echo reflection coefficient and film thickness when superimposing signals

Since the reflection coefficient of ultrasonic waves at the bearing bush-air interface is close to 1 (R=0.999982 when the bearing bush is steel, and R=0.999961 when it is Babbitt alloy), it is necessary to obtain the reflected echo at the bearing bush-air condition at the measuring point as the reference echo signal, and then compare the echo signal obtained during the actual film thickness detection with the reference echo signal to obtain an approximate reflection coefficient. The specific method is as follows.

From the previously detected reference echo signal p _a (t) of the thin liner bush-air interface, according to formula (5) and formula (7), it can be obtained that p ₁ (t) and p _b (t) at ω Amplitude ratio _ka (ω _s ) at frequency _s . Then the reflection coefficient of the echo at ω _s at different film thicknesses is

$\mathrm{<span\; class="notranslate">\; R</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; k</span>}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}{{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 8</span>}<span\; class="notranslate">\; )</span>$

In fact, echo components such as p ₂ (t) and p ₃ (t) in p _m (t) have a slight influence on |P _m (ω)|, that is, the amplitude of Q(ω), while at the same time The obtained k _a (ω _s ) also includes the influence of multiple echoes p ₂ (t), p ₃ (t) in the liner-air interface, and the final ratio R(ω _s ) eliminates the The impact of these factors on the final film thickness results. In this way, after obtaining R(ω _s ), the thickness value of the lubricating film of the thin lining sliding bearing can be obtained according to the following basic stiffness model method formula.

$\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&rho;c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$

Among them, the acoustic impedance z ₁ of the bearing material and the acoustic impedance z ₂ of the journal material corresponding to both sides of the lubricating film, as well as the fluid layer density ρ and the sound velocity c are determined by the material properties. According to formula (3), the theoretical relationship curve between film thickness and reflection coefficient of Babbitt alloy-oil film-steel medium is shown in Figure 3, which can be used as a guide for the selection of measurement frequency and an auxiliary inspection of film thickness measurement results.

Referring to Figures 4-10, the technical solution of the present invention mainly includes the acquisition of the separable matrix-lining interface echo signal, the acquisition of the reference echo signal of the thin lining bearing bush-air interface, and the solution to the superimposed signal echo during implementation. There are some steps such as the amplitude ratio of the interface echo with the substrate, the amplitude ratio of different interface echo components in the superimposed signal, the reflection coefficient of the ultrasonic echo and the solution of the film thickness. Taking the detection of an ultrasonic transducer with a center frequency of 10MHz as an example, the main steps are as follows.

1) The time-domain waveform p _b (t) is obtained from the test block of thick lining bearing pad (as shown in Fig. 4), and its amplitude spectrum |P _b (ω)| obtained by fast Fourier transform (as shown in Fig. 5 Show). Secondly, measure the reference echo signal of the thin-lined sliding bearing to be detected at the bearing bush-air interface, as well as the echo signal p _m (t) at different lubricating film thicknesses, the reference echo signal and the Echo signal (as shown in Figure 6).

2) Perform fast Fourier transform on the reference echo signal and echo signals with different film thicknesses (as shown in Figure 7), and compare with |P _b (ω)| shown in Figure 5 according to formula (5) , get the ratio Q(ω) curve shown in Figure 8.

3) After obtaining the Q(ω) ratio curve, the k(ω _s ) value of different thickness lubricating films can be obtained from formula (7) (as shown in Figure 9). Similarly, the Q(ω) of the reference echo The value of the reference echo k _a (ω _s ) is shown in Figure 10, and its peak frequency ω _s is 10.4MHz, and it can be seen from Figure 8 that the ω _s near the center frequency of 10MHz at different film thicknesses is not the same as that of the reference echo The ω _s of the waves coincide completely, so in order to obtain the accurate reflection coefficient at the peak frequency ω _s at different film thicknesses, the k value of the reference echo in the frequency range near its ω _s is determined by formula (6), and the results of multiple measurements It shows that the echo component of the reference signal liner-air interface and |P _b (ω)| have a relatively stable k value in this frequency range.

4) The reflection coefficient of the echo signal at different film thicknesses is obtained from formula (8), and then, according to the reflection coefficient result, the detection result of the lubricating film thickness of the thin lining bearing bush is obtained from formula (3). As shown in Figure 3, when the film thickness is small, the measurement resolution and accuracy of this method are high. Due to the influence of the surface roughness of the bearing pad and the characteristics of the lubricant, the actual detection process can obtain sub-micron film thickness results, and can be infinitely close to the zero film thickness value, and there is no zero film thickness value. In this method, the reflection coefficient value is gradually close to 1 near the thicker film thickness of 10 μm, and the larger film thickness change is reflected by a small reflection coefficient change, which is caused by the noise and spectrum analysis errors in the detection process. The film thickness resolution in a range is low, which is determined by the principle of the basic stiffness model method. When the film thickness reaches 7.5 μm or more, although the single film thickness measurement result cannot reflect the actual film thickness state due to the fluctuation of the error, the distribution trend and the average value of the multiple measurement results can better reflect the thickness of the film within this range. The change of thickness and its thickness value make this method applicable to the detection of micron and submicron lubricating film thickness. Among them, the basic stiffness model method determines that the resolution of film thickness measurement in the range of larger film thickness or close to 10 μm film thickness is low, and the noise interference and spectrum analysis error in the detection process make the film thickness results in this range fluctuate larger. The film thickness in this range is measured multiple times quickly, and the distribution trend and average value of the multiple measurement results reflect the change of film thickness and its thickness value in this range.

Example:

Taking the actual measurement of the lubricating film thickness of a thrust sliding bearing with a 0.5mm thick Babbitt alloy lining as an example, a film thickness simulation device is designed, and a high-precision piezoelectric actuator with closed-loop control is used to generate lubricating film layers of different thicknesses , the film thickness measurement results obtained by the method of the present invention are compared with the feedback thickness of the piezoelectric actuator, which illustrates the effectiveness of the ultrasonic detection method of the present invention. The measured reflection coefficients of the echo signals at different film thicknesses are shown in Figure 11, and the set film thickness in the figure is the film thickness value displayed by the readings of the closed-loop piezoelectric actuator. According to the reflection coefficient result, the comparison of the film thickness measurement result obtained from formula (3) and the set film thickness is shown in Fig. 12 . When the film thickness is large, the measurement results fluctuate greatly, which is caused by measurement noise and spectrum analysis errors, and is also determined by the basic stiffness model method principle, although a single measurement result cannot accurately reflect the actual film thickness state , but the distribution trend and its average value of multiple measurement results better reflect the change of film thickness and its thickness value. The multiple measurement results in the figure reflect the correctness of the method of the present invention.

The above content is a further detailed description of the present invention in conjunction with specific preferred embodiments. It cannot be determined that the specific embodiments of the present invention are limited thereto. Under the present invention, some simple deduction or replacement can also be made, all of which should be regarded as belonging to the scope of patent protection determined by the submitted claims of the present invention.

Claims (2)

1. The ultrasonic detection method of the lubricating film thickness of the thin friction material layer structure sliding bearing, is characterized in that, comprises the following steps: 1) The time-domain echo signal p b (t) of the bearing pad matrix-lining layer interface of the thick friction material layer bearing pad test block of the same material as the thin friction material layer structure sliding bearing is measured by the ultrasonic testing system, and the time domain echo signal p _b (t) is analyzed. Wave signal p _b (t) obtained by fast Fourier transform its frequency domain amplitude spectrum |P _b (ω)|, and then measure the reference echo of the thin friction material layer sliding bearing to be detected at the bearing pad-air interface signal p _a (t), and the superimposed echo signal p _m (t) of the sliding bearing bush-fluid film interface measured with a thin friction material layer, where the thin friction material layer is the bearing bush whose thickness is less than half of the ultrasonic pulse width of the ultrasonic transducer Lining layer, the thick friction material layer is the bearing bush lining whose thickness is greater than or equal to half of the ultrasonic pulse width of the ultrasonic transducer; 2) Fast Fourier transform is performed on the reference echo signal p _a (t) and the superimposed echo signal p _m (t) obtained in step 1), respectively, to obtain the frequency domain amplitude spectrum of the reference echo signal |P _a ( ω)| and the frequency domain amplitude spectrum |P _m (ω ₎ | )|compared, the amplitude ratio Q _a (ω) of the reference echo signal to the substrate-lining interface echo and the amplitude ratio Q _m (ω) of the superimposed echo signal to the substrate-lining interface echo are obtained; 3) Based on the amplitude ratio Q _a (ω) of the reference echo signal obtained in step 2) and the echo of the substrate-lining interface combined with its peak frequency ω _as , calculate the peak frequency ω _as to (1+10%) ω _as The amplitude ratio k _a (ω _a ) of different interface echo components in the reference echo signal in the frequency region and at two endpoints is calculated as follows: ${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 4</span>}{\mathrm{<span\; class="notranslate">\; cos</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}{\mathrm{<span\; class="notranslate">\; t</span>}}_{\mathrm{<span\; class="notranslate">\; 0</span>}}<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&Center\; Dot;</span>{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; a</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; )</span>$ In the formula: t ₀ is the time taken for the ultrasonic wave to pass through the thickness of the thin lining, ω _a is the frequency of the reference echo signal in the range from ω _as to (1+10%) ω _as , Q _a (ω _a ) is the reference echo signal Amplitude ratio to the substrate-liner interface echo at ωa _; 4) Based on the amplitude ratio Q _m (ω) of the superimposed signal echo obtained in step 2) and the echo of the substrate-lining interface combined with its peak frequency ω _ms , calculate the different interfaces in the superimposed echo signal at the peak frequency ω _ms Echo component amplitude ratio km ( _{ω ms} ), its calculation formula is as follows: ${\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span>\mathrm{<span\; class="notranslate">\; 2</span>}{\mathrm{<span\; class="notranslate">\; k</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; +</span><span\; class="notranslate">\; \&lsqb;</span>\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; Q</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; \&omega;</span>}}_{\mathrm{<span\; class="notranslate">\; m</span>}\mathrm{<span\; class="notranslate">\; the\; s</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&rsqb;</span><span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 0</span>}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 2</span>}<span\; class="notranslate">\; )</span>$ In the formula: Q _m (ω _ms ) is the amplitude ratio of the superimposed signal echo to the substrate-lining interface echo amplitude ratio Q _m (ω) at the peak frequency ω _ms ; 5) The amplitude ratios of different interface echo components in the superimposed echo signal obtained in step 4) k _m (ω _ms ) and the amplitude ratios of different interface echo components in the reference echo signal obtained in step 3) k _a (ω _a ) Compared with the value at the frequency ω _ms , the reflection coefficient R of the echo signal when measuring the lubrication film thickness is obtained, and finally, according to the film thickness formula of the basic stiffness model method combined with the reflection coefficient R, the lubrication film thickness of the sliding bearing with a thin friction material layer structure is obtained h. 2. the ultrasonic testing method of thin friction material layer structure sliding bearing lubricating film thickness as claimed in claim 1, is characterized in that, in step 5), basic stiffness model method film thickness formula is: $\mathrm{<span\; class="notranslate">\; h</span>}<span\; class="notranslate">\; =</span>\frac{{\mathrm{<span\; class="notranslate">\; \&rho;c</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{{\mathrm{<span\; class="notranslate">\; \&omega;z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}}\sqrt{\frac{{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; +</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; -</span>{<span\; class="notranslate">\; (</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 1</span>}}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; z</span>}}_{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span>}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}{\mathrm{<span\; class="notranslate">\; 1</span>}<span\; class="notranslate">\; -</span>{\mathrm{<span\; class="notranslate">\; R</span>}}^{\mathrm{<span\; class="notranslate">\; 2</span>}}}}<span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; -</span><span\; class="notranslate">\; (</span>\mathrm{<span\; class="notranslate">\; 3</span>}<span\; class="notranslate">\; )</span>$ In the formula: ρ is the density of fluid medium, the unit is kg/m ³ ; c is the sound velocity of the fluid medium, in m/s; z ₁ is the acoustic impedance of the bearing lining material, in kg/(m ² ·s); z ₂ is the acoustic impedance of the journal material, in kg/(m ² ·s); ω is the angular frequency of the ultrasonic reflected wave, in rad/s.