Real-time online measurement device and method for thickness of lubricating film of motion friction pair

Abstract

The invention discloses a real-time online measurement device and method for the thickness of a lubricating film of a motion friction pair. The real-time on-line measurement device for the thickness of the lubricating film of the motion friction pair is composed of a friction wear testing machine and a real-time on-line measurement device for the thickness of the lubricating film between surface contact friction pairs in relative motion, and can realize real-time on-line measurement of the thickness and the change rule of the lubricating film between the surface contact friction pairs in relative motion. The principle of the measuring method is based on a contact resistance method, the contact resistance between a friction pair in a mixed lubrication state is measured through a high-precision table type universal meter, and the actual contact area of a lower sample and an upper sample of the friction pair is calculated according to the friction contact theory and a conversion formula of the contact resistance and the contact area. And calculating the thickness value of the lubricating film according to the conversion relation between the actual contact area and the average film thickness. The device transmits an output signal measured by a universal meter in real time into a computer, a current-resistance and lubricating film thickness conversion program is written in the computer according to a film thickness measurement method principle, and a lubricating film thickness value is output in real time.

Description

Technical Field

[0001] This invention relates to the field of lubricating film thickness detection technology, and in particular to a real-time online measurement device and method for the thickness of lubricating film in moving friction pairs. Background Technology

[0002] Measuring the thickness of the lubricating film on friction pairs is an important issue in engineering, particularly in the areas of lubricants, friction materials, and mechanical design. Accurate measurement of lubricating film thickness is crucial for ensuring the reliability of mechanical components, reducing energy loss, and extending equipment lifespan.

[0003] Currently, commonly used methods for measuring lubricating film thickness include optical interferometry, magnetoresistive methods, and capacitance methods, each with its own advantages and disadvantages. For example, optical interferometry provides relatively reliable results, but it can only measure transparent friction pairs and cannot be used to measure the film thickness of actual engineering metal friction pairs. Furthermore, optical interferometry is highly sensitive to environmental conditions; factors such as temperature, air pressure, and vibration can affect the measurement results, requiring strict environmental control. Magnetoresistive methods may experience saturation effects under high magnetic field strength, leading to distorted measurement results. Additionally, magnetoresistive methods typically require maintaining a certain distance from the object being measured, thus demanding high standards in the design and adjustment of the measuring device. Capacitance methods are affected by the surrounding environment; factors such as humidity and temperature can influence the capacitance value. In some applications, special materials may be needed to construct the capacitance sensor, potentially increasing cost and complexity. Especially for moving friction pairs in mixed lubrication states, where rough peaks directly contact the friction interface, measuring lubricating film thickness becomes even more difficult, rendering some traditional methods unsuitable. Furthermore, with the development and application of science and technology and mechanical design, the demand for the lubrication performance and service life of friction pairs is constantly increasing. The complex and variable working conditions of engineering friction pairs greatly increase the probability of them being in a mixed lubrication state. Therefore, how to measure and evaluate the dynamic lubrication film thickness and lubrication performance of friction pairs has important scientific and practical significance and engineering application value.

[0004] To address the aforementioned issues, this paper proposes a device and method for real-time online measurement of the lubricating film thickness of moving friction pairs. This method provides real-time measurement of the lubricating film thickness between friction pairs with different motion patterns under mixed lubrication conditions, enabling continuous monitoring of the lubrication and friction states of the friction pairs. This facilitates the design, development, and performance improvement of key friction pairs in high-end equipment and components. Summary of the Invention

[0005] Purpose of the Invention: To address the shortcomings of existing technologies, the purpose of this invention is to provide a real-time online measurement device and method for the thickness of the lubricating film on a moving friction pair. This method is based on the testing principle of the contact resistance of friction surfaces. A high-precision benchtop multimeter is used to measure the current and resistance of the moving friction pair circuit, and the signals are transmitted to a computer. Based on the measurement method principle, a program for converting current to resistance and lubricating film thickness is written in the computer, and the value of the lubricating film thickness of the friction pair is output in real time.

[0006] Technical Solution: A real-time online measurement device and method for the lubricating film thickness of a moving friction pair. The real-time online measurement device for the lubricating film thickness of a moving friction pair consists of a high-speed friction and wear testing machine and a real-time online measurement device. The principle of the measurement method is based on the contact resistance method. Using the friction and wear testing machine, the surface contact friction pair is placed under specific working conditions and subjected to relative motion. The loop resistance of the moving friction pair is measured using a high-precision benchtop multimeter, obtaining the contact resistance between the lubricating film of the lower and upper samples of the friction pair in a mixed lubrication state. Based on the friction contact theory and the conversion formula between contact resistance and contact area, the actual contact area of ​​the friction pair is calculated, and the lubricating film thickness is calculated based on the conversion relationship between contact area and average film thickness. This method transmits the electrical signal measured by the multimeter to a computer. Based on the principle of the measurement method, a current-resistance-lubricating film thickness conversion program is written in the computer, outputting the lubricating film thickness value in real time.

[0007] The steps for measuring the lubricating film thickness are as follows: 1) Connect the upper sample of the friction pair to the wire, fix it on the friction and wear testing machine using the upper sample clamp, fix the lower sample of the friction pair on the friction testing machine using the lower sample clamp, and connect it to the real-time online measuring device through the carbon brush connected by the wire. Inject lubricating medium into the oil bath to immerse the surface of the lower sample of the friction pair; 2) Turn on the friction and wear testing machine, set the test load of the friction pair and apply it, turn on the regulated voltage power supply and the high-precision benchtop multimeter, and perform static measurement of the contact resistance of the friction pair to obtain the initial resistance of the circuit; 3) According to the operating conditions of the friction pair, set and adjust the speed and other parameters of the friction and wear testing machine, turn on the friction and wear testing machine to make the friction pair move relative to each other, and simultaneously turn on the real-time online measuring device for lubricating film thickness to perform dynamic measurement of the contact resistance of the friction pair; 4) Import the electrical data collected by the high-precision benchtop multimeter into the computer in real time, use the current-resistance to lubricating film thickness conversion program written in the computer to calculate and output the lubricating film thickness value, and realize the real-time online measurement of the lubricating film thickness of the moving friction pair. The conversion principle and formula between the contact area, contact resistance and lubricating film thickness of the friction pair are as follows:

[0008] If the regulated voltage of the online measuring device is U0, the inherent internal resistance of the circuit in the device is R0, and the measured circuit current after the circuit is turned on is I0 when there is no relative movement between the upper and lower samples of the friction pair, then the total circuit resistance R1 is:

[0009]

[0010] static contact resistance R of friction pair c :

[0011] R c =R1-R0 (2)

[0012] Based on the relationship between contact area and contact resistance:

[0013]

[0014] The derivation leads to:

[0015]

[0016] Where ρ is the resistivity of the friction pair material.

[0017] Combining equations (2) and (3), we get:

[0018]

[0019] When the upper and lower samples of the friction pair move relative to each other, the circuit current measured after the circuit is turned on is I. i The dynamic resistance of the loop is obtained as R. i Similarly, we can obtain:

[0020]

[0021] Among them, A i The dynamic actual contact area during the motion of the friction pair is derived from formula (6):

[0022]

[0023] According to the theory of frictional contact, the actual contact area A of the rough surface of the friction pair is... i It can also be expressed as:

[0024] A i =π 2 ·(λβσ) 2 ·F2(H) (8)

[0025] Where λ is the surface roughness peak density of the friction pair, β is the radius of curvature of the roughness peak, F2(H) is the probability density function of the roughness peak distribution, and σ is the overall surface roughness of the friction pair, calculated by the following formula:

[0026]

[0027] Wherein, σ1 and σ2 are the root mean square roughness of the surfaces of the upper and lower samples of the friction pair, respectively.

[0028] By combining formulas (7) and (8), we can derive the following:

[0029]

[0030] If the surface roughness of the friction pair follows a Gaussian distribution, the probability density function F2(H) of the roughness peak distribution in equation (7) can be expressed as:

[0031]

[0032] Where H is the lubricating film thickness ratio, i.e., the thickness h of the lubricating film of the friction pair. c The ratio of the surface roughness σ to the overall surface roughness.

[0033] Combining equations (10) and (11), and setting F2(H) in equation (10) to Fi, we can solve equation (11) to obtain the lubricating film thickness ratio H as follows:

[0034]

[0035] The thickness h of the lubricating film of the moving friction pair can be calculated using the film thickness ratio formula. c :

[0036] h c =σ·H (13)

[0037] Finally, the relationship between the contact resistance of the surface contact friction pair and the thickness of the lubricating film can be obtained using the above formula.

[0038] The friction pair measured in this invention must be made of conductive material and involve surface contact with relative motion, while the lubricating medium must be non-conductive. Specifically, by constructing a real-time online measurement circuit for the friction pair fixed on a friction and wear testing machine, the contact resistance of the moving friction pair in a mixed lubrication state is dynamically measured. Through computer-programmed calculations relating contact resistance to lubricating film thickness, the oil film thickness value can be output online in real time.

[0039] Preferred option: In order to better adapt to the changes in the motion form of different friction pairs and to accurately measure the oil film thickness of friction pairs under different motion states, the friction and wear testing machine can be set to the following motion states: reciprocating motion, rotary motion and shaft rotation.

[0040] Preferred option: In order to accurately measure the contact resistance value of the friction pair and stabilize the circuit, and improve its anti-interference ability, a specially made clamp with insulation treatment is used to install and fix the current-conducting carbon brush on the lower sample.

[0041] Preferred option: To make the actual values ​​of electrical parameters in the measurement circuit more accurate, a signal amplifier can be connected in series in the circuit for conditioning and amplification, and then the collected electrical signal and the multimeter value can be transmitted to the computer together.

[0042] Preferred option: In order to improve work efficiency and simplify the workflow, the dynamic change of lubricating film thickness obtained by converting the real-time contact resistance of the friction pair obtained by measurement can be calculated into the oil film thickness value in real time online through computer program design and writing.

[0043] Preferred option: In order to accurately measure the dynamic contact resistance value and ensure circuit stability, the sampling frequency of the multimeter electrical signal in the measurement circuit is consistent with the sampling frequency of the speed sensor and force sensor of the friction and wear testing machine.

[0044] Beneficial Effects: This invention addresses the need for real-time online detection of lubricating film thickness between moving friction pairs by proposing a device and method for real-time measurement of lubricating film thickness. The measurement method is based on the contact resistance method. A high-precision benchtop multimeter measures the contact resistance between friction pairs in a mixed lubrication state. Based on frictional contact theory and the conversion formula between contact resistance and contact area, the actual contact area between the lower and upper samples of the friction pair is calculated. The lubricating film thickness is then calculated based on the conversion relationship between the actual contact area and the average film thickness. The device transmits the output signal obtained from the real-time measurement by the multimeter to a computer. A current-resistance-lubricating film thickness conversion program is written in the computer based on the film thickness measurement method principle, enabling real-time output of the lubricating film thickness value. Attached Figure Description

[0045] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the provided drawings without creative effort.

[0046] Figure 1 Schematic diagram of an online measurement device for the thickness of the lubricating film of a moving friction pair;

[0047] Figure 2 This is a schematic diagram illustrating the principle of online measurement of lubricating film thickness.

[0048] Figure 3 This is a schematic diagram of the contact lubrication region of the rough peaks of the friction pair;

[0049] Figure 4 Schematic diagram of different motion modules of the friction and wear testing machine;

[0050] Figure 5 Flowchart for real-time online conversion of lubricating film thickness. Detailed Implementation

[0051] 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.

[0052] In the description of this invention, it should be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this invention.

[0053] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can include direct contact between the first and second features, or contact between the first and second features through another feature between them. Furthermore, "above," "over," and "on top" of the second feature includes the first feature directly above or diagonally above the second feature, or simply indicates that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature includes the first feature directly below or diagonally below the second feature, or simply indicates that the first feature is at a lower horizontal level than the second feature.

[0054] like Figure 1 As shown, this invention designs a real-time online measurement device and method for the lubricating film thickness of a moving friction pair. The device includes a friction and wear testing machine and a real-time online measurement device. The friction and wear testing machine consists of a vertical load sensor, a horizontal friction force sensor, an upper sample fixture, a lubricating oil tank, a lower sample fixture, a drive module, an upper sample of the friction pair, a lubricating medium, and a lower sample of the friction pair. The real-time online measurement device consists of a computer, a data cable, a high-precision multimeter, carbon brushes, wires, a signal amplifier, and a regulated power supply. The high-precision multimeter is connected in series with the signal amplifier and the regulated power supply via wires, and is connected to the upper sample of the friction pair and the current-conducting carbon brushes fixed on the lower sample of the friction pair, forming a current loop. The computer is connected to the high-precision multimeter via the data cable to collect the current value in the measurement loop of the high-precision multimeter in real time.

[0055] like Figure 2 and Figure 3The diagram shows the circuit schematic and contact principle diagram of the lubricating film thickness of a moving friction pair in real time. The measurement principle is based on the contact resistance method. A high-precision benchtop multimeter is used to measure the real-time current of the circuit. The acquired electrical signal is then processed and amplified by a signal amplifier before being imported into a computer for further data processing and analysis. The contact resistance between the upper and lower samples of the surface contact friction pair is calculated. Based on the friction contact theory and the conversion formula between the contact area of ​​the friction pair rough peak, the contact resistance, and the actual contact area, the actual contact area between the upper and lower samples of the friction pair is calculated. Finally, the film thickness between the friction pairs is calculated based on the conversion relationship between the contact area and the lubricating film thickness.

[0056] like Figure 4 As shown, the friction and wear testing machine can simulate different motion modes of friction pairs, adjust friction parameters under different motion modes, and measure the mechanical state of the friction pairs in real time. The testing machine includes the following three typical motion modes: reciprocating motion, rotary motion, and shaft / ring rotation.

[0057] like Figure 5 As shown, the real-time online conversion program for lubricating film thickness is as follows: 1) Static measurement of friction pair contact resistance; 2) Dynamic measurement of friction pair contact resistance under mixed lubrication conditions; 3) Real-time data acquisition, data preprocessing, and error term elimination on the computer; 5) Input of friction test parameters and friction pair material properties; 6) Data processing and current-resistance-contact area calculation; 7) Calculation of friction pair lubricating film thickness. Through program design and writing in the computer, the relationship between the electrical signals acquired by the online measuring device, friction pair parameters, and lubricating film thickness can be established and calculated. This allows for direct acquisition of the corresponding lubricating film thickness value through changes in loop current-resistance. This real-time online measurement method can provide instant lubricating film thickness data under friction pair operating conditions, aiding in the monitoring and optimization of critical friction pair systems.

[0058] The various embodiments in this specification are described in a progressive manner, with each embodiment focusing on its differences from other embodiments. Similar or identical parts between embodiments can be referred to interchangeably. For the apparatus disclosed in the embodiments, since they correspond to the methods disclosed in the embodiments, the description is relatively simple; relevant parts can be referred to the method section.

[0059] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. An apparatus and method for on-line measurement of thickness of lubricating film of a moving friction pair, characterized by: The device is composed of a high-speed friction and wear testing machine (1) and a real-time online measuring device (2), and the device and method can realize real-time online measurement of the thickness and variation of the lubricating film between the relative moving surface contact friction pairs.

2. High speed tribological tester (1) according to claim 1, characterized in that: The friction and wear testing machine is composed of a vertical load sensor (11), a horizontal friction force sensor (12), an upper sample clamp (13), a lubricating oil pool (14), a lower sample clamp (15), a driving module (16), an upper sample of the friction pair (17), a lubricating medium (18) and a lower sample of the friction pair (19).

3. Drive module (16) of a tribological test rig (1) according to claim 2, characterized in that The friction and wear testing machine (1) can simulate and measure different forms of friction pairs, including the following three forms: reciprocating motion, rotating motion and shaft circle rotation, and can realize real-time online measurement of the lubricating film thickness between the friction pairs in the mixed lubrication state.

4. The on-line lubricating film thickness measuring device (2) according to claim 1, characterized in that: The real-time online measuring device (2) is composed of a computer (21), a data line (22), a high-precision multimeter (23), a carbon brush (24), a wire (25), a signal amplifier (26) and a stabilized power supply (27). The high-precision multimeter (23) is connected in series with the signal amplifier (26) and the stabilized power supply (27) through the wire (25), and is connected with the upper sample of the friction pair (17) and the current-conducting carbon brush (24) fixed on the lower sample of the friction pair (19), thereby forming a current loop. The computer (21) is connected with the high-precision multimeter (23) through the data line (22), and can collect the current value in the measuring loop of the high-precision multimeter (23) in real time.

5. The friction pair lubrication film thickness real-time on-line measuring device (2) according to claim 4, characterized in that: The carbon brush (23) is fixed on the lower sample of the friction pair (19) by using a special designed clamp, so that the carbon brush (23) can keep contact with the lower sample during the movement of the friction pair.

6. The apparatus for real-time on-line measurement of the thickness of the lubricating film of a friction pair according to claim 1, characterized in that: The assembly surface of the friction and wear testing machine (1) and the upper sample clamp (13) and the lower sample clamp (15) is insulated, or the upper sample clamp (13) and the lower sample clamp (15) are made of insulating materials.

7. The method of claim 1, wherein the method is an on-line measurement method. The principle of the measuring method is based on the contact resistance method. The real-time current in the loop is measured by the high-precision multimeter (23), the contact resistance between the upper sample (17) and the lower sample (19) of the friction pair is calculated, the actual contact area between the upper sample (17) and the lower sample (19) of the friction pair is calculated according to the friction contact theory and the conversion formula of the contact resistance and the actual contact area, and the film thickness value between the friction pairs is calculated according to the conversion relationship between the contact area and the lubricating film thickness.

8. The method of claim 7, wherein the method is an on-line method of measuring the thickness of the lubricating film of a moving friction pair. The loop electrical signal measured by the high-precision multimeter (23) is transmitted into the computer (21), the conversion program of the current-resistance and the lubricating film thickness is written in the computer (21) according to the principle of the measuring method, the lubricating film thickness value is calculated and output in real time.

9. The method of claim (7) and (8), wherein: The sampling frequency of the high-precision multimeter (23) in the measuring device (2) is consistent with the sampling frequency of the horizontal friction force sensor (12) in the friction testing machine (1), so that the measured value of the lubricating film thickness corresponds to the operating condition of the friction pair.

10. The method of claim (7) and (8), wherein the method is characterized by: The measuring method comprises the following steps: S1: connecting the upper sample (17) and the lead wire (25), fixing the upper sample on the friction and wear testing machine (1) through the upper sample clamp (13), fixing the lower sample (19) on the friction and wear testing machine (1) through the lower sample clamp (15), and connecting the real-time online measurement device (2) through the carbon brush (24) connected by the lead wire, injecting the lubricating medium into the oil pool (14) to immerse the surface of the lower sample (19); S2: opening the friction and wear testing machine (1), setting the test load of the friction pair and loading, opening the constant voltage power supply (27) and the high-precision bench multimeter (23), and performing static determination of the contact resistance of the friction pair to obtain the initial resistance of the loop; S3: according to the operating conditions of the object friction pair, setting and adjusting the speed and other parameters of the friction and wear testing machine, starting the friction and wear testing machine (1) to make the friction pair move relatively, and synchronously starting the real-time online measurement device (2) for the thickness of the lubricating film, and performing dynamic measurement of the contact resistance of the friction pair; S4: real-time importing the electrical data collected by the high-precision bench multimeter (23) into the computer (21), calculating and outputting the thickness of the lubricating film by using the conversion program of current-resistance and lubricating film thickness written in the computer (21), and realizing real-time online measurement of the thickness of the lubricating film of the moving friction pair.

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