A system and method for measuring the thickness of an oil film of a current-carrying lubricated friction pair based on a capacitive effect

Abstract

This invention discloses a system and method for measuring the thickness of an oil film in a current-carrying lubrication friction pair based on the capacitance effect, belonging to the field of precision measurement technology. It includes a friction pair test bench, a current-carrying control unit, and a voltage acquisition unit. The friction pair test bench includes a tension shaft, a conductive copper ring electrically isolated from the tension shaft, brush bundles symmetrically arranged on both sides of the tension shaft, and a tension adjustment assembly. The current-carrying control unit includes a constant current source, a control board, a relay, and a precision charging resistor. The control board controls the operating mode of the constant current source and switches the circuit to the precision charging resistor via the relay, so that the current-carrying friction pair and the precision charging resistor form an equivalent RC circuit. The voltage acquisition unit includes a digital oscilloscope, which is electrically connected to the brush bundles on both sides, and is used to acquire the voltage rise curve during the oil film charging process. This invention can accurately acquire the oil film charging voltage curve, achieving precise measurement of the oil film thickness of the current-carrying friction pair. It has a simple structure and reliable testing capabilities.

Description

Technical Field

[0001] This invention relates to the field of precision measurement technology, and in particular to a system and method for measuring the thickness of oil film in a current-carrying lubrication friction pair based on the capacitance effect. Background Technology

[0002] Precision conductive slip rings are core components of satellite payload drive systems, responsible for the seamless and stable transmission of power and signals. They are the "lifeline" ensuring continuous power supply and high-quality data transmission for satellite payloads. Precision conductive slip rings rely on the sliding electrical contact between brushes and conductive ring plates to achieve power / signal transmission. During operation, they are prone to problems such as abnormal fluctuations in electrical transmission performance, momentary interruptions, out-of-tolerance issues, and unstable control of wear debris. In the vacuum environment of space, this can further lead to arcing, causing material damage and migration. To overcome the technical bottleneck of low-wear and stable transmission, conductive grease lubrication has become the mainstream technology for improving the lifespan and reliability of conductive slip rings. Grease-lubricated brush bundle-conductive ring current-carrying friction pairs exhibit significant advantages in high-current transmission, wear debris suppression, and signal stability during low-current transmission in high-speed, vacuum environments.

[0003] However, the thickness of the lubricating grease film formed under electromechanical combined loads is a core parameter determining the electrical transmission performance and reliability of grease slip rings: During boundary lubrication, the oil film is thinner, with solid-solid electrical contact as the primary mode, exhibiting resistive electrical properties; during mixed lubrication, solid-solid and solid-liquid contacts coexist, resulting in electrical properties exhibiting both resistive and capacitive properties; during elastohydrodynamic lubrication, the oil film completely separates solid-solid contacts, exhibiting capacitive electrical properties. The oil film thickness directly determines the contact voltage fluctuation, contact surface wear, and oxidation degree of the slip ring. However, currently, there is no reliable technical means to measure the dynamic oil film thickness of grease slip rings, making it impossible to monitor the lubrication reliability and electrical transmission stability of their electrical contact interfaces in real time.

[0004] Existing oil film thickness measurement technologies have significant limitations: the ultrasonic method has specific requirements for the physical state and acoustic characteristics of the oil film, while the optical interferometry method requires the oil film to be transparent and have specific interface reflection characteristics. Neither of these methods can effectively measure the dynamic oil film thickness in the Hertz contact area of ​​the brush filament bundle current-carrying friction pair. Grease-lubricated conductive slip rings typically operate in a mixed lubrication zone, where the oil film thickness is mostly in the submicron range, and the ultrasonic method is not accurate enough in this measurement range. At the same time, all existing measurement methods impose stringent requirements on equipment and installation conditions, making it difficult to achieve in-situ dynamic monitoring. Summary of the Invention

[0005] The purpose of this invention is to provide a system and method for measuring the thickness of oil film in a current-carrying lubrication friction pair based on the capacitance effect, thereby solving the above-mentioned technical problems.

[0006] To achieve the above objectives, this invention provides a system for measuring the oil film thickness of a current-carrying lubricating friction pair based on the capacitance effect, comprising a friction pair test bench, a current-carrying control unit, and a voltage acquisition unit: The friction pair test bench includes a tension shaft, a conductive copper ring electrically isolated from the tension shaft, a bristle bundle symmetrically arranged on both sides of the tension shaft, and a tension adjustment assembly for adjusting the contact pressure between the bristle bundle and the conductive copper ring. The current-carrying control unit includes a constant current source, a control board, a relay, and a precision charging resistor. The control board is responsible for controlling the working mode of the constant current source and connecting the precision charging resistor through the relay switching circuit, so that the current-carrying friction pair and the precision charging resistor form an equivalent RC circuit. The voltage acquisition unit includes a digital oscilloscope, which is electrically connected to the brush bundles on both sides to acquire the voltage rise curve during the oil film charging process.

[0007] Preferably, the friction pair test bench also includes an insulating spacer ring, a support arm, and two swing arms; the insulating spacer ring is coaxially tightened on the tightening shaft, the conductive copper ring is clamped at the bottom of the oil groove of the insulating spacer ring, the two swing arms are connected to the support arm through bearings, and a set of brush filament bundles are fixed at the end of each swing arm through a circuit adapter plate, the brush filament bundles extend into the oil groove and contact the cylindrical surface of the conductive copper ring.

[0008] Preferably, the tension adjustment assembly includes two telescopic rods and a tension sensor. The two ends of the tension sensor are connected to the two swing arms via the telescopic rods, and the contact pressure between the brush filament bundle and the conductive copper ring is changed by adjusting the angle of the swing arms.

[0009] Preferably, an insulating gasket is provided between the circuit adapter plate and the swing arm, and an insulating spacer is used to achieve electrical isolation between the conductive copper ring and the tensioning shaft to prevent the current in the current-carrying friction pair from being conducted to the system's mechanical structure and measurement parts.

[0010] Preferably, the control board controls the constant current source to achieve three working modes: fixed current mode, used to simulate the stable operation of the slip ring and collect the contact voltage; stepped scanning current mode, used to output stepped increasing-decreasing current to study the effect of current change on electrical contact characteristics; and pulse current mode, used to output constant pulse current to charge the oil film.

[0011] Preferably, in pulse current mode, the control board connects to a precision charging resistor through a relay control circuit, the constant current source outputs a constant pulse current, and the digital oscilloscope synchronously acquires the charging voltage rise curve.

[0012] A method for measuring the thickness of an oil film in a current-carrying lubrication friction pair based on the capacitance effect includes the following steps: S1. Assemble the friction pair test bench, adjust the position of the brush filament bundle to allow it to smoothly enter the insulating ring oil groove, adjust the contact pressure between the brush filament bundle and the conductive copper ring to the specified load through the tension adjustment component, inject conductive grease into the oil groove and drive the expansion shaft to rotate and run for a period of time until the conductive grease forms a uniform oil film on the conductive copper ring. S2. The control board switches the constant current source to pulse current mode, and inputs pulse current to the equivalent RC circuit composed of current-carrying friction pair and precision charging resistor to charge the oil film. S3, Calculate the first step related to oil film thickness. n layer m The equivalent total capacitance of the brush filaments connected in parallel and then symmetrically connected in series. Its formula is: ; ; ; ; in, m The number of bristles for each stack layer. For contact capacitance, , These are the vacuum permittivity and the relative permittivity of grease, respectively. This is the ratio of the Hertzian contact area capacitance to the total contact capacitance of the single wire. (.) represents the ratio function of the total contact capacitance. h The oil film thickness in the Hertzian contact area. The Hertzian contact area, These are dimensionless material parameters. For dimensionless load parameters, For dimensionless velocity parameters, For contact geometry parameters, , These are the contact length and minor axis coefficients, respectively, of the contact geometry parameters. , These are the equivalent elastic modulus and the effective composite radius of the monofilament contact, respectively. F To adjust the test load on the friction pair; S4. Based on the equivalent total capacitance combined with the equivalent capacitance model of the brush bundle, the dynamic oil film thickness in the Hertz contact zone of the current-carrying friction pair is obtained. h Its formula is: .

[0013] Preferably, in S2, during the no-current test, the constant current source is activated every preset time interval. Output trigger signal, wait Then apply charging current, charging time Disconnect afterward; during on-load testing, first reduce the constant operating current to zero and wait... After discharging is complete, apply charging current; after charging is complete, switch back to constant operating current mode.

[0014] Preferably, the formula for the equivalent total capacitance based on the oil film charging curve is: ; ; ; ; in, This is the charging voltage. Due to voltage limitations, For the current moment, The charging time constant. The oil film charging voltage corresponding to the first sampling time. The oil film charging voltage corresponding to the second sampling time. The saturation voltage for charging the oil film. This is the equivalent total resistance. This is the standard resistance value for a precision charging resistor. This is the steady-state contact voltage.

[0015] Preferably, the test process simulates the actual rotational speed change of the slip ring. The rotational speed is switched in a preset order for each group. The stable test is performed for a preset duration at each rotational speed. An oil film charging test is performed every preset time interval. The charging curve and oil film distribution morphology are collected simultaneously. All the above test conditions are repeated at least 3 times.

[0016] Therefore, the present invention employs the above-mentioned system and method for measuring the oil film thickness of a current-carrying lubrication friction pair based on the capacitance effect, which has the following beneficial effects: 1. Filling the technical gap in oil film thickness measurement in specific scenarios: This invention achieves thickness measurement based on the interfacial capacitance characteristics of grease-lubricated current-carrying friction pairs, breaking through the application limitations of existing ultrasonic and optical interferometry methods, realizing reliable measurement of oil film thickness of this type of current-carrying friction pair, and providing core technical means for the study of electrical contact interface of grease-lubricated conductive slip rings.

[0017] 2. Achieved high-precision measurement of submicron oil film thickness: The capacitor charge-discharge effect thickness measurement method adopted in this invention is not limited by the submicron range. Combined with the microsecond-level time resolution and microvolt-level voltage resolution of the high-frequency digital oscilloscope, it can accurately capture the voltage change during the oil film charging process, realize high-precision dynamic measurement of submicron oil film thickness, and accurately reflect the small fluctuations in oil film thickness under mixed lubrication conditions.

[0018] 3. Advantages of in-situ, non-invasive, and low installation requirements: This invention utilizes the interfacial capacitance characteristics of the grease-lubricated current-carrying friction pair itself as the measurement basis in situ. There is no need to add additional sensors or modify the original structure in the contact area of ​​the friction pair. Real-time dynamic monitoring of oil film thickness can be achieved simply by connecting an external constant current source, control board, and digital oscilloscope. It is easy to install, low in cost, and will not interfere with the normal operation of the slip ring. It can be directly applied to bench testing and in-service health status monitoring of slip rings.

[0019] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0020] Figure 1 This is a schematic diagram of an oil film thickness measurement system for a current-carrying lubrication friction pair based on the capacitance effect according to the present invention. Figure 2 For the present invention Figure 1 Enlarged view of point A in the middle; Figure 3 This is a schematic diagram illustrating the composition and function of the control board of the present invention; Figure 4 To illustrate the principle of oil film thickness measurement based on the capacitor charging effect of this invention, (a) is the electrical equivalent diagram of the brush bundle-conductive ring current-carrying friction pair, (b) is the equivalent RC circuit of the grease lubrication current-carrying friction pair circuit, and (c) is the oil film charging curve. Figure 5 The diagram shows the timing control of oil film charging according to the present invention. (a) is the timing diagram of oil film charging test without current carrying capacity, and (b) is the timing diagram of oil film charging test with current carrying capacity.

[0021] Figure Labels 1. Tensioning shaft; 2. Conductive copper ring; 3. Brush filament bundle; 4. Insulating spacer ring; 5. Conductive grease; 6. Control board; 7. Circuit adapter board; 8. Constant current source; 9. Digital oscilloscope; 10. Telescopic rod; 11. Tension sensor; 12. Bearing; 13. Support arm; 14. Swing arm. Detailed Implementation

[0022] To make the objectives, technical solutions, and advantages disclosed in the embodiments of the present invention clearer, the embodiments of the present invention will be further described in detail below with reference to the accompanying drawings and examples. It should be understood that the specific embodiments described herein are only used to explain the embodiments of the present invention and are not intended to limit the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the embodiments of the present invention without creative effort are within the scope of protection of this application. Examples of the embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout.

[0023] It should be noted that the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion, such as a process, method, system, product, or server that includes a series of steps or units, not necessarily limited to those steps or units explicitly listed, but may include other steps or units not explicitly listed or inherent to such process, method, product, or device.

[0024] The embodiments of the present invention will now be described in detail with reference to the accompanying drawings.

[0025] like Figures 1-5 As shown, this invention provides a system and method for measuring the thickness of an oil film in a current-carrying lubrication friction pair based on the capacitance effect. The system includes a friction pair test bench, a current-carrying control unit, and a voltage acquisition unit. The friction pair test bench includes a tensioning shaft 1, a conductive copper ring 2 electrically isolated from the tensioning shaft 1, brush filament bundles 3 symmetrically arranged on both sides of the tensioning shaft 1, and a tension adjustment component for adjusting the contact pressure between the brush filament bundles 3 and the conductive copper ring 2. The friction pair test bench also includes an insulating spacer ring 4, a support arm 13, and two swing arms 14. The insulating spacer ring 4 is coaxially tensioned on the tensioning shaft 1 and has an oil groove for accommodating conductive grease 5. The conductive copper ring 2 is clamped at the bottom of the oil groove, achieving electrical isolation from the tensioning shaft 1 through the insulating spacer ring 4. The two swing arms 14 are swayably connected to the support arm 13 via bearings 12. Each swing arm 14 has a set of brush filament bundles 3 fixed at its end via a circuit adapter plate 7. The brush filament bundles 3 extend into the oil groove and contact the cylindrical surface of the conductive copper ring 2. The circuit adapter plate 7 and the swing arms... An insulating gasket is provided between 14. The conductive copper ring 2 and the tensioning shaft 1 are electrically isolated by an insulating spacer 4 to prevent the current in the current-carrying friction pair from being conducted to the mechanical structure and measurement part of the system. The tension adjustment assembly includes two telescopic rods 10 and a tension sensor 11. The two ends of the tension sensor 11 are connected to the two swing arms 14 via the telescopic rods 10 respectively. Before the test, the length of the telescopic rods 10 is adjusted so that the two swing arms 14 swing towards each other or away from each other, thereby driving the two symmetrically arranged brush filament bundles 3 to close or open on both sides of the tensioning shaft 1. The position of the brush filament bundles 3 is adjusted so that they can smoothly enter the oil groove of the insulating spacer 4 and contact the cylindrical surface of the conductive copper ring 2. The contact pressure between the brush filament bundles 3 and the conductive copper ring 2 is changed by adjusting the angle of the swing arm 14 so that they form a friction pair under the specified test load. Then, a specified amount of conductive grease 5 is injected into the oil groove and the tensioning shaft 1 is driven to rotate so that the friction pair runs for a period of time until the conductive grease 5 forms a uniform oil film on the conductive ring.

[0026] The current-carrying control unit includes a constant current source 8, a control board 6, a relay, and a precision charging resistor. The constant current source 8 is a multi-functional integrated test unit for the brush filament-conductive ring current-carrying friction process, including current supply, contact resistance measurement, and oil film capacitor charging. It supports automatic switching between connecting to a source meter for small currents and a large current source for large currents. The minimum resolution for voltage measurement is 1μV, and the minimum resolution for resistance measurement is 1mΩ. The positive and negative terminals of the constant current source 8 are connected to the circuit adapter boards 7 on both sides, respectively. Current is output from the constant current source 8, transmitted through the control board 6 to the brush filament bundle 3, flows through the brush filament bundle 3-conductive copper ring 2 current-carrying friction pair, and then returns to the constant current source 8 along another path of the brush filament bundle 3. The control board 6 is communicatively connected to the constant current source 8, responsible for controlling the power supply of the constant current source 8 to the current-carrying friction pair in the circuit. It also handles communication between the constant current source 8 and the host computer, and switches the operating mode and data acquisition mode of the constant current source 8 via a relay. The control board 6 can connect a 3Ω precision charging resistor through a relay switching circuit, so that the current-carrying friction pair and the precision charging resistor form an equivalent RC circuit. The host computer communicates with the control board 6 to realize real-time storage, preliminary processing and standardized management of all collected data, and to build a test dataset.

[0027] The voltage acquisition unit includes a digital oscilloscope 9, and the voltage measurement interface of the digital oscilloscope 9 is directly connected to the wires of the brush bundles 3 on both sides to acquire the charging voltage data of the lubricating oil film of the current-carrying friction pair at high frequency.

[0028] Control board 6 controls constant current source 8 to achieve three operating modes: fixed current mode, used for long-term constant current friction tests to simulate the actual stable energized condition of the slip ring; the test process can run continuously, and the system stores voltage-time curves in real time for calculating contact resistance and analyzing current-carrying stability; the test process supports emergency stop function, and historical data is not lost after power failure; stepped scanning current mode, used to study the influence of current changes on contact characteristics, realizing current gradient loading; the microcontroller control loop outputs a stepped increasing-decreasing current, starting from 0mA and gradually increasing to the maximum value according to the set step height. The current then gradually decreases back to 0mA, with each step held for 30–60 seconds. The system synchronously collects voltage data at each current level to obtain contact resistance, temperature rise, and interface state changes at different current levels. The pulse current mode is mainly used for oil film charging tests to obtain contact capacitance and oil film thickness. During the test, the microcontroller controls the circuit to connect a 3Ω precision charging resistor, and the source meter outputs a constant 50mA pulse current to charge the oil film capacitor. The pulse duration is about 1 second, and the voltage rise curve is synchronously captured by the oscilloscope during the charging process, providing raw data for subsequent calculation of oil film thickness based on RC circuit principles.

[0029] Since the control board 6 controls the constant current source 8 to output a constant pulse current at specified intervals to charge the oil film, the oil film thickness can be dynamically monitored by the capacitor based on the RC circuit charging curve acquired by the oscilloscope. The specific measurement principle of the oil film thickness of the current-carrying friction pair of the brush filament bundle 3-conductive copper ring 2 in oil film lubrication is as follows: Assume that the number of layers of brush filament bundle 3 accumulated in the oil tank is . n Each floor m Each brush bristle generates an elastic pressure of [number] bristles. N Therefore, the pressure on each bristle in each layer is... nN That is, the top layer and the bottom layer are respectively N and nN The pressure of the brush filament bundle 3 on the conductive ring is mnN Adjust the test load of the friction pair as follows: F The pressure exerted by each brush bristle on the conductive ring at the top and bottom layers are respectively F / (mn) and F / m If the single-filament lubricated current-carrying friction pair is considered as a parallel-plate capacitor, then the brush filament bundle-conductive ring current-carrying friction pair can be equivalent to... Figure 4 The electrical diagram is shown in (a). Since the load on a single brush bristle is consistent within the same layer, and increases progressively from the top to the bottom layer, it can be considered as... m One layer capacitor C i After parallel connection, then n The parallel capacitors are connected in series layer by layer, and the thickness of the oil film is determined by the first one. n For a single filament in a lubricated state, the contact capacitance of a layered brush bristle is... Then, calculations as shown in S3 can be performed.

[0030] Based on the above system, the present invention also provides a method for measuring the thickness of the oil film in a current-carrying lubrication friction pair based on the capacitance effect, comprising the following steps: S1. Assemble the friction pair test bench, adjust the position of the brush filament bundle 3 so that it can smoothly enter the oil groove of the insulating ring 4, adjust the contact pressure between the brush filament bundle 3 and the conductive copper ring 2 to the specified load through the tension adjustment component, inject conductive grease 5 into the oil groove and drive the expansion shaft 1 to rotate and run for a period of time until the conductive grease 5 forms a uniform oil film on the conductive copper ring 2. S2, control board 6 switches constant current source 8 to pulse current mode, inputs pulse current to the equivalent RC circuit composed of current-carrying friction pair and precision charging resistor to charge the oil film. S3, Calculate the first step related to oil film thickness. n layer m The equivalent total capacitance of the brush filaments connected in parallel and then symmetrically connected in series. Its formula is: ; ; ; ; in, m The number of bristles for each stack layer. , These are the vacuum permittivity and the relative permittivity of grease, respectively. This is the ratio of the Hertzian contact area capacitance to the total contact capacitance of the single wire. (.) represents the ratio function of the total contact capacitance. h The oil film thickness in the Hertzian contact area. The Hertzian contact area can be calculated using Hertzian contact theory. These are dimensionless material parameters. For dimensionless load parameters, The velocity parameter is dimensionless and can be obtained by solving the coupled Reynolds equations. For contact geometry parameters, , These are the contact length and minor axis coefficients, respectively, of the contact geometry parameters. , These are the equivalent elastic modulus and the effective composite radius of the monofilament contact, respectively. F To adjust the test load on the friction pair; S4. Based on the equivalent total capacitance combined with the equivalent capacitance model of brush bundle 3, the dynamic oil film thickness in the Hertz contact zone of the current-carrying friction pair is obtained. h Its formula is: .

[0031] like Figure 5 As shown in S2, during the no-current test, the constant current source 8 operates at preset intervals. Output trigger signal, wait A microampere-level charging current is then applied, and a voltage limit is set. Charging time Record the charging voltage during this period. After charging is complete, the power supply is quickly disconnected, and no current flows through the system until the next trigger signal. During the current-carrying test, the friction pair has a constant current before the trigger signal. I 0 passed, constant current source 8 every preset time When outputting the trigger signal, first reduce the constant operating current to zero and wait. After discharging is complete, apply a microampere-level charging current and set the voltage limit to [value missing]. At this point, the oil film is charged, and the charging voltage during this period is recorded. After charging is complete, the system switches back to constant current mode, at which point the constant current flowing through the oil film is... I 0, and continues until the next trigger signal.

[0032] When testing the grease-lubricated brush filament bundle-conductive ring in operation, the control board 6 controls the process to... Figure 1 When a precision charging resistor is connected to the grease-lubricated current-carrying friction pair circuit, the circuit can be equivalent to an RC circuit, such as... Figure 4 As shown in (b), the constant current source 8 continuously inputs the equivalent RC circuit as shown in [the diagram]. Figure 5 The current pulse signal shown i 0 charges the oil film capacitor, with a pulse duration of During the charging process, the rising edge curve of the charging voltage is continuously and dynamically captured, acquired, and stored by the oscilloscope, resulting in an oil film charging curve as shown below. Figure 4 As shown in (c), the formula for the equivalent total capacitance based on the oil film charging curve is: ; ; ; ; in, This is the charging voltage. For the current moment, The charging time constant. The oil film charging voltage corresponding to the first sampling time. The oil film charging voltage corresponding to the second sampling time. The saturation voltage for charging the oil film. This is the equivalent total resistance. This is the standard resistance value for a precision charging resistor. This is the steady-state contact voltage.

[0033] To simulate the speed changes during actual service, the speed of each group was switched in a preset sequence of 50 r / min → 120 r / min → 200 r / min → 120 r / min → 50 r / min. The stable test was conducted for 1 hour at each speed, and an oil film charging test was performed every 10 minutes. The charging curve and oil film distribution morphology were collected simultaneously. All the above test conditions were repeated at least 3 times to ensure the reliability and repeatability of the experimental data.

[0034] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and not to limit them. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the technical solutions of the present invention, and these modifications or equivalent substitutions cannot cause the modified technical solutions to deviate from the spirit and scope of the technical solutions of the present invention.

Claims

1. A system for measuring the thickness of an oil film in a current-carrying lubrication friction pair based on the capacitance effect, characterized in that: Includes a friction pair test bench, a current-carrying control unit, and a voltage acquisition unit: The friction pair test bench includes a tension shaft, a conductive copper ring electrically isolated from the tension shaft, a bristle bundle symmetrically arranged on both sides of the tension shaft, and a tension adjustment assembly for adjusting the contact pressure between the bristle bundle and the conductive copper ring. The current-carrying control unit includes a constant current source, a control board, a relay, and a precision charging resistor. The control board is responsible for controlling the working mode of the constant current source and connecting the precision charging resistor through the relay switching circuit, so that the current-carrying friction pair and the precision charging resistor form an equivalent RC circuit. The voltage acquisition unit includes a digital oscilloscope, which is electrically connected to the brush bundles on both sides to acquire the voltage rise curve during the oil film charging process.

2. The oil film thickness measurement system for current-carrying lubrication friction pairs based on capacitance effect according to claim 1, characterized in that: The friction pair test bench also includes an insulating spacer, a support arm, and two swing arms. The insulating spacer is coaxially tightened on the tightening shaft, and the conductive copper ring is clamped at the bottom of the oil groove of the insulating spacer. The two swing arms are connected to the support arm through bearings. A set of brush filaments is fixed at the end of each swing arm through a circuit adapter plate. The brush filaments extend into the oil groove and contact the cylindrical surface of the conductive copper ring.

3. The system for measuring the oil film thickness of a current-carrying lubrication friction pair based on the capacitance effect according to claim 2, characterized in that: The tension adjustment assembly includes two telescopic rods and a tension sensor. The two ends of the tension sensor are connected to the two swing arms via the telescopic rods. The contact pressure between the brush filament bundle and the conductive copper ring is changed by adjusting the angle of the swing arms.

4. The oil film thickness measurement system for current-carrying lubrication friction pairs based on capacitance effect according to claim 2, characterized in that: An insulating gasket is provided between the circuit adapter board and the swing arm, and an insulating spacer is used to achieve electrical isolation between the conductive copper ring and the tensioning shaft to prevent the current in the current-carrying friction pair from being conducted to the system's mechanical structure and measurement parts.

5. The oil film thickness measurement system for current-carrying lubrication friction pairs based on capacitance effect according to claim 1, characterized in that: The control board controls the constant current source to achieve three working modes: fixed current mode, used to simulate the stable operation of the slip ring and collect the contact voltage; stepped scanning current mode, used to output stepped increasing-decreasing current to study the effect of current changes on electrical contact characteristics; Pulse current mode is used to output a constant pulse current to charge the oil film.

6. The oil film thickness measurement system for current-carrying lubrication friction pairs based on capacitance effect according to claim 5, characterized in that: In pulse current mode, the control board connects to a precision charging resistor through a relay control circuit, and the constant current source outputs a constant pulse current. The digital oscilloscope simultaneously acquires the rising edge curve of the charging voltage.

7. A method for measuring the thickness of an oil film in a current-carrying lubrication friction pair based on the capacitance effect, applied to the system described in any one of claims 1-6, characterized in that, Includes the following steps: S1. Assemble the friction pair test bench, adjust the position of the brush filament bundle to allow it to smoothly enter the insulating ring oil groove, adjust the contact pressure between the brush filament bundle and the conductive copper ring to the specified load through the tension adjustment component, inject conductive grease into the oil groove and drive the expansion shaft to rotate and run for a period of time until the conductive grease forms a uniform oil film on the conductive copper ring. S2. The control board switches the constant current source to pulse current mode, and inputs pulse current to the equivalent RC circuit composed of current-carrying friction pair and precision charging resistor to charge the oil film. S3, Calculate the first step related to oil film thickness. n layer m The equivalent total capacitance of the brush filaments connected in parallel and then symmetrically connected in series. Its formula is: ； ； ； ； in, m The number of bristles for each stack layer. For contact capacitance, , These are the vacuum permittivity and the relative permittivity of grease, respectively. This is the ratio of the Hertzian contact area capacitance to the total contact capacitance of the single wire. f (.) represents the ratio function of the total contact capacitance. h The oil film thickness in the Hertzian contact area. The Hertzian contact area, These are dimensionless material parameters. For dimensionless load parameters, For dimensionless velocity parameters, For contact geometry parameters, , These are the contact length and minor axis coefficients, respectively, of the contact geometry parameters. , These are the equivalent elastic modulus and the effective composite radius of the monofilament contact, respectively. F To adjust the test load on the friction pair; S4. Based on the equivalent total capacitance combined with the equivalent capacitance model of the brush bundle, the dynamic oil film thickness in the Hertz contact zone of the current-carrying friction pair is obtained. h Its formula is: 。 8. The method for measuring the oil film thickness of a current-carrying lubrication friction pair based on the capacitance effect according to claim 7, characterized in that: In S2, during the no-current test, the constant current source is applied at preset intervals. Output trigger signal, wait Then apply charging current, charging time Disconnect afterward; during on-load testing, first reduce the constant operating current to zero and wait... After discharging is complete, apply charging current; after charging is complete, switch back to constant operating current mode.

9. The method for measuring the thickness of an oil film in a current-carrying lubrication friction pair based on the capacitance effect according to claim 8, characterized in that: The formula for the equivalent total capacitance based on the oil film charging curve is: ； ； ； ； in, This is the charging voltage. Due to voltage limitations, For the current moment, The charging time constant. The oil film charging voltage corresponding to the first sampling time. The oil film charging voltage corresponding to the second sampling time. The saturation voltage required to charge the oil film. This is the equivalent total resistance. This is the standard resistance value for a precision charging resistor. This is the steady-state contact voltage.

10. The method for measuring the thickness of an oil film in a current-carrying lubrication friction pair based on the capacitance effect according to claim 9, characterized in that: The test process simulates the actual rotational speed change of the slip ring. The rotational speed is switched in a preset order for each group. The stability test is performed for a preset duration at each rotational speed. An oil film charging test is performed every preset time interval. The charging curve and oil film distribution morphology are collected simultaneously. All the above test conditions are repeated at least 3 times.

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