Device and method for testing electrical properties of lubricating film of rolling bearing

Abstract

The present application relates to the testing technology of the electric performance of the motor bearing of the motor train unit, in particular to a device and method for testing the electric performance parameters of the lubricating oil film of the rolling bearing. The main contents of the technical scheme of the present application are divided into four parts: first, a test device for simulating multiple working conditions and establishing the lubricating oil film of the rolling bearing, which can simulate the actual operating environment of the motor bearing and establish the lubricating oil film of the bearing under dynamic conditions, and can provide a basis for evaluating the electric performance parameters of the oil film of the motor bearing and the insulation performance of the bearing; second, a structural unit and method for effectively testing the electric performance of the lubricating oil film are provided, which can accurately obtain the electric performance parameters of the lubricating oil film; third, a measurement equivalent circuit based on the insulating coating, bearing and lubricating oil film and a calculation method for the electric performance parameters of the oil film are provided, which can provide input parameters for the state of the oil film under the electrified condition and the design of the insulating bearing; and fourth, a reliability evaluation method for the insulation performance of the bearing is provided, which can provide a basis for product design.

Description

Technical Field

[0001] This invention relates to testing technology for the electrical performance of traction motor bearings in high-speed trains, and to a device and method for testing the electrical performance parameters of lubricating oil film in rolling bearings. Background Technology

[0002] As the service life of traction motor bearings in high-speed trains using DC-AC variable frequency drive systems gradually increases, the risk of bearing failure due to electro-erosion also increases, posing a certain impact on train operation safety. In actual product failure cases, abnormal peeling of bearing rings and rolling elements caused by electro-erosion accounts for the vast majority. Therefore, improving the bearing's resistance to electro-erosion by optimizing the bearing insulation coating is a mainstream technical direction. However, because the bearing insulation coating and the lubricating oil film together form a hybrid equivalent circuit, it is necessary to establish an evaluation method by obtaining the electrical performance parameters of the lubricating oil film to assess the reliability of the bearing insulation performance.

[0003] Because the electrical performance parameters of bearing oil film are directly related to oil film thickness, and oil film thickness is affected by many factors such as bearing raceway condition, load, speed, and temperature, the electrical performance parameters of bearing oil film are difficult to measure accurately. To solve this problem, it is necessary to develop a suitable device and method for testing the electrical performance parameters of rolling bearing lubricating oil film.

[0004] The relevant existing technologies are as follows:

[0005] (1) Test bench and test method for oil film conductivity of grease-lubricated ball bearings. This test machine is only applicable to ball bearings, and the test rolling element parameters and oil film state are significantly different from the actual conditions. It cannot simulate temperature and the conditions of multiple rolling elements in parallel in the load-bearing area, so its applicable scope is limited.

[0006] (2) A testing device and method for testing the lubricating oil film thickness of rolling bearings. This testing device uses ultrasonic sensors attached to the inner surface of the bearing ring to obtain real-time film thickness values ​​at the contact points of the rolling bearing using ultrasonic film thickness measurement technology. This method mainly measures the oil film thickness of the bearing, but cannot test the electrical performance parameters of the oil film.

[0007] (3) Calculation method: Calculate the thickness of the lubricating oil film and the Hertz contact area according to the bearing operating conditions. Then, obtain the resistivity and dielectric constant of the lubricating grease base oil through testing. Finally, calculate the resistance and capacitance of the oil film based on the resistivity, thickness, area and dielectric constant.

[0008] Disadvantages of existing technology

[0009] (1) There is a lack of test equipment that can simulate the oil film state of rolling bearings under actual operating conditions and perform oil film electrical performance tests.

[0010] (2) At present, most of the devices and methods for measuring lubricating oil film are for measuring its thickness, and there is a lack of devices and methods for measuring the electrical performance parameters of lubricating oil film.

[0011] (3) By measuring or calculating parameters such as oil film thickness and Hertzian contact area, and then using the formulas R = ρL / s and C = ε0ε for resistance and capacitance, the method is to calculate these parameters. r A / s is theoretically calculated, but the oil film thickness and Hertz contact area are difficult to calculate accurately, which may lead to a large deviation between the calculation results and the actual results, and it is also impossible to verify them.

[0012] (4) There is currently a lack of methods for assessing the reliability of bearing insulation performance. Summary of the Invention

[0013] To address the problems mentioned in the background art, the present invention provides a device and method for testing the electrical performance parameters of lubricating oil film in rolling bearings.

[0014] The device for testing the electrical performance parameters of lubricating oil film in rolling bearings according to the present invention is implemented by the following technical solution: A device for testing the electrical performance parameters of lubricating oil film in rolling bearings includes a transmission mechanism, a test shaft system, an environmental test chamber, a loading unit, and a hot air blower; the transmission mechanism includes a mounting platform, a drive motor mounted below the mounting platform, a drive wheel mounted on the output shaft of the drive motor, and a driven wheel located above the mounting platform and connected to the drive wheel by a belt;

[0015] The test shaft system includes a test shaft, a pair of bearing seats mounted on a mounting platform via a base, and a pair of bearings installed in the bearing seats; the middle part of the test shaft is supported by two bearings, the part of the test shaft located between the two bearings is positioned by a shaft shoulder, and the part located outside the bearings is axially fixed by a sealing ring and a lock nut.

[0016] The environmental test chamber is fixed on the mounting platform and is equipped with a temperature sensor. The drive end of the test shaft is fixedly connected to the driven wheel, while the non-drive end extends into the environmental test chamber through a hole in the side wall for installing the oil film electrical performance test unit. The environmental test chamber is equipped with an air inlet and an air outlet. The air inlet and air outlet are connected to the air outlet and air inlet of the hot air blower to form a circulation pipeline.

[0017] The loading unit is located at the top of the environmental test chamber; it is used to apply radial load to the oil film electrical performance test unit.

[0018] The formation and state of the oil film in rolling bearings are mainly affected by factors such as bearing type, rotational speed, temperature, and load. This device designs a test apparatus that uses a modular design of bearing units to adjust the rotational speed, ambient temperature, and load to simulate the oil film state under specific conditions. During the test, a drive motor and pulley rotate the driven wheel and the test shaft. The right end of the test shaft is placed inside an environmental simulation test chamber. The chamber is heated by a hot air blower and ventilation ducts. A PT100 temperature sensing element is installed inside the chamber to monitor and provide feedback on the ambient temperature. A pressure sensor and a loading unit are installed at the upper end of the test chamber. The loading unit applies radial load to the bearing unit.

[0019] Furthermore, the oil film electrical performance testing unit includes a test bearing unit, insulating paper, a digital bridge, a loading positioning sleeve, and an axial adjustment device. The test bearing unit consists of inner and outer bearing covers and a test bearing located inside the inner and outer bearing covers. The inner side of the inner and outer bearing covers is provided with an annular oil reservoir for storing lubricating grease. The lower ends of the inner and outer bearing covers are connected by bolts. An insulating paper is placed between the top of the test bearing and the inner wall of the top of the inner and outer bearing covers. The bottom of the loading positioning sleeve is provided with a groove to hold the inner and outer bearing covers in place, and the top is provided with a vertical groove. The front end of the loading unit extends into the vertical groove. The axial adjustment device includes a nylon seat, a carbon brush, an axial adjustment screw, and a fixing plate installed on the outer wall of the environmental test chamber. The fixing plate has a screw hole, and the end of the nylon seat also has a screw hole. The axial adjustment screw passes through the screw hole on the fixing plate and extends into the screw hole at the end of the nylon seat. The front end of the nylon seat has a hole that is confined within the carbon brush hole. The end of the carbon brush is connected to the nylon seat by a spring, and the front end of the carbon brush presses against the non-transmission end face of the test shaft. The outer ring of the test bearing is connected to the spring by a wire and connected in series with a digital bridge.

[0020] Oil film electrical performance testing mainly includes measuring oil film resistance, capacitance, and breakdown voltage. The inner and outer bearing covers form a sealed lubrication unit with the test bearing, simulating the product bearing unit. An axial loading device is fixed to the test chamber housing, and the carbon brush position is adjusted axially by rotating a screw to ensure good contact between the carbon brush and the shaft end. Additionally, a loading positioning sleeve is provided between the bearing unit and the radial loading head to ensure effective transmission of radial load and axial limitation of the bearing unit.

[0021] The operating conditions are simulated and an oil film formation device and an oil film electrical performance testing unit are used to form an oil film. The oil film resistance, capacitance and breakdown voltage are tested using a digital bridge and a DC regulated power supply.

[0022] This invention also discloses a method for testing the electrical performance parameters of lubricating oil films in rolling bearings. The method utilizes a testing device suitable for testing the electrical performance parameters of lubricating oil films in rolling bearings to test the resistance and capacitance of the oil film, and includes the following steps:

[0023] First, lubricating grease is loaded into the oil reservoirs of the test bearing and its inner and outer covers. The test bearing is then heat-fitted onto the test shaft, and the inner and outer covers are installed and axially tightened with screws to ensure good sealing at both ends of the test bearing. Next, the positive terminal of the digital bridge is connected to the outer ring of the test bearing, and a loading unit is used to apply load. At the same time, the axial adjustment device is used to ensure good contact between the carbon brush and the end of the test shaft. Finally, the test is conducted according to the required speed, load, and ambient temperature. After the speed, temperature, and load stabilize, the oil film resistance and capacitance values ​​of the test bearing under different working conditions are measured in real time using the digital bridge.

[0024] This invention also discloses a method for calculating electrical performance parameters. This method calculates the electrical performance of bearing oil film through equivalent circuits of different types of bearing oil film, provides input parameters for oil film state under energized conditions and insulated bearing design, and compares them with test values.

[0025] Rolling bearings are divided into insulated bearings and non-insulated bearings; insulated bearings are insulated bearings with coatings on the inner and outer rings; ①a. In the equivalent circuit of a non-insulated bearing, the total resistance includes the bearing outer ring resistance, bearing inner ring resistance, total rolling element resistance, total oil film resistance outside the rolling elements, and total oil film resistance inside the rolling elements, which are connected in series. The total oil film resistance outside the rolling elements is formed by all the oil film resistances outside the rolling elements in parallel, and the total oil film resistance inside the rolling elements is formed by all the oil film resistances inside the rolling elements in parallel.

[0026] b. In the equivalent circuit of a non-insulated bearing, the total capacitance includes the total capacitance of the oil film outside the rolling body and the total capacitance of the oil film inside the rolling body connected in series; the total capacitance of the oil film outside the rolling body is formed by all the oil film capacitances outside the rolling body connected in parallel, and the total capacitance of the oil film inside the rolling body is formed by all the oil film capacitances inside the rolling body connected in parallel.

[0027] ②a. In the equivalent circuit of an insulated bearing with coatings on the inner and outer rings, the total resistance includes the resistance of the insulation coating, the resistance of the outer ring of the bearing, the resistance of the inner ring of the bearing, the total resistance of the rolling elements, the total resistance of the oil film outside the rolling elements, and the total resistance of the oil film inside the rolling elements, which are connected in series. The total resistance of the oil film outside the rolling elements is formed by all the oil film resistances outside the rolling elements in parallel, and the total resistance of the oil film inside the rolling elements is formed by all the oil film resistances inside the rolling elements in parallel.

[0028] b. In the equivalent circuit of an insulated bearing with coatings on the inner and outer rings, the total capacitance includes the capacitance of the insulating coating, the total capacitance of the oil film outside the rolling rings, and the total capacitance of the oil film inside the rolling rings connected in series; the total capacitance of the oil film outside the rolling rings is formed by all the oil film capacitors outside the rolling rings connected in parallel, and the total capacitance of the oil film inside the rolling rings is formed by all the oil film capacitors inside the rolling rings connected in parallel.

[0029] Based on the above equivalent circuit calculations, the resistance and capacitance of the insulated bearing and the non-insulated bearing can be calculated.

[0030] This invention also discloses a method for evaluating the reliability of bearing insulation performance: PSCAD simulation software is used to analyze the equivalent circuit of the insulated bearing and oil film. The equivalent circuit model consists of the bearing insulation coating, oil film, and rolling elements. Power supply parameters are set and input according to measured shaft voltage, frequency, du / dt, etc., and then the voltage division values ​​of the coating and oil film are calculated separately. Only when the voltage division value of the oil film is less than its breakdown voltage will the oil film not be broken down, thus preventing discharge and ensuring that the bearing raceway surface is not eroded by electrolytic corrosion, and confirming that the bearing insulation coating design meets the requirements.

[0031] This invention solves the following technical problems:

[0032] (1) The present invention has developed a test device that can simulate the lubricating oil film of rolling bearings under multiple working conditions, and can realize the test device for load, speed, temperature and open bearing unit lubrication cavity structure changes.

[0033] (2) The present invention provides a device for testing the multi-parameter electrical properties of rolling bearing oil film under multiple working conditions.

[0034] (3) Establish a model of the equivalent circuit of the insulated bearing and the lubricating oil film and a method for calculating the electrical performance parameters. (4) This invention establishes a method for evaluating the reliability of the bearing insulation performance.

[0035] (5) The present invention solves the problem that the state of the lubricating oil film of rolling bearings is difficult to be accurately simulated and that there is a lack of devices and methods for measuring its electrical performance parameters. Attached Figure Description

[0036] Figure 1 A schematic diagram of the testing device described in this invention.

[0037] Figure 2 Schematic diagram of the electrical performance testing unit.

[0038] Figure 3 Equivalent circuit of non-insulated bearing oil film

[0039] Figure 4 Equivalent circuit of bearing oil film with insulating coating on inner and outer rings

[0040] Figure 5 A schematic diagram of the planar projection of the rolling element within the raceway.

[0041] Figure 6 One of the three-dimensional projection diagrams of the rolling elements within the raceway (S NoHz ).

[0042] Figure 7 Schematic diagram of the three-dimensional projection of the rolling element in the raceway (S) Hz ).

[0043] 1—Drive motor; 2—Driving pulley; 3—Belt; 4—Mounting platform; 5—Driven pulley;

[0044] 6—Bearing housing; 7—Locking nut; 8—Outer sealing ring; 9—Ceramic ball bearing; 10—Base;

[0045] 11—Loading wrench; 12—Spring; 13—Washer; 14—Loading rod; 15—Test shaft; 16—Pressure sensor; 17—PT100 temperature sensor; 18—Environmental test chamber; 19—Test bearing outer cover; 20—Test bearing; 21—Insulating pad; 22—Loading positioning sleeve; 23—Digital bridge; 24—Connecting plate; 25—Fixing plate; 26—Carbon brush; 27—Nylon seat; 28—Axial adjustment screw; 29—Oil groove; 30—Hot air blower. Detailed Implementation

[0046] Example 1

[0047] A device for testing electrical performance parameters of lubricating oil film in rolling bearings includes a transmission mechanism, a test shaft system, an environmental test chamber, a loading unit, and a hot air blower 30; the transmission mechanism includes a mounting platform 4, a drive motor 1 mounted below the mounting platform 4, a drive wheel 2 mounted on the output shaft of the drive motor 1, and a driven wheel 5 located above the mounting platform 4 and connected to the drive wheel 2 via a belt 3;

[0048] The test shaft system includes a test shaft 15, a pair of bearing seats 6 mounted on the mounting platform 4 via a base 10, and a pair of ceramic ball bearings 9 installed in the bearing seats 6; the middle part of the test shaft 15 is supported by two ceramic ball bearings 9, the part of the test shaft 15 located between the two ceramic ball bearings 9 is positioned by a shaft shoulder, and the part located outside the ceramic ball bearings 9 is axially fixed by an outer sealing ring 8 and a locking nut 7.

[0049] The environmental test chamber 18 is fixed on the mounting platform 4 and is equipped with a temperature sensor 17. The transmission end of the test shaft 15 is fixedly connected to the driven wheel 5, while the non-transmission end extends into the environmental test chamber 18 through a hole in the side wall for installing the oil film electrical performance test unit. The environmental test chamber 18 is provided with an air inlet and an air outlet. The air inlet and air outlet are connected to the air outlet and air inlet of the hot air blower 30 to form a circulation pipeline. The loading unit is located at the top of the environmental test chamber 18 and is used to apply a radial load to the oil film electrical performance test unit.

[0050] Example 2

[0051] The oil film electrical performance testing unit includes a test bearing unit, insulating paper, a digital bridge, a loading positioning sleeve, and an axial adjustment device. The test bearing unit consists of inner and outer bearing covers and a test bearing 20 located inside the inner and outer bearing covers. The inner side of the inner and outer bearing covers is provided with an annular oil reservoir 29 for storing lubricating grease. The lower ends of the inner and outer bearing covers are connected by bolts. An insulating paper 21 is placed between the top of the test bearing and the inner wall of the top of the inner and outer bearing covers. The bottom of the loading positioning sleeve 22 is provided with a groove to hold the inner and outer bearing covers in place, and the top is provided with a vertical groove. The front end of the loading rod 14 extends into the vertical groove. The axial adjustment device includes a nylon seat 27, a carbon brush 26, an axial adjustment screw 28, and a fixing plate 25 mounted on the outer wall of the environmental test chamber. The fixing plate 25 has screw holes, and the nylon seat 27 also has screw holes at its end. The axial adjustment screw 28 passes through the screw holes on the fixing plate 25 and extends into the screw hole at the end of the nylon seat 27. The front end of the nylon seat 27 has a hole that confines the carbon brush within the hole. The end of the carbon brush is connected to the nylon seat by a spring, and the front end of the carbon brush presses against the non-transmission end face of the test shaft. The outer ring of the test bearing is connected to the spring by a wire and a digital bridge 23 is connected in series. The axial adjustment screw 28 is typically rotated only half a turn during adjustment, which will not affect the wires.

[0052] Example 3

[0053] The loading unit includes a washer 13 with internal threads installed on the top of the environmental test chamber, a loading rod 14 that is spirally connected to the washer 13 via external threads, a pressure sensor 16 and a spring 12 fitted on the loading rod 14, and a loading wrench 11 fitted on the loading rod via an internal quadrature or internal hexagonal structure above the spring.

[0054] The present invention will be further described below with reference to the accompanying drawings.

[0055] The main contents of this invention are divided into four parts: first, a test device for multi-condition simulation and establishment of lubricating oil film in rolling bearings; second, a structural unit and method for effectively testing the electrical performance of lubricating oil film; third, a measurement equivalent circuit based on insulating coating, bearing, and lubricating oil film, and a method for calculating the electrical performance parameters of oil film; and fourth, a method for evaluating the reliability of bearing insulation performance.

[0056] (1) Test apparatus for multi-condition simulation and establishment of lubricating oil film in rolling bearings

[0057] The device mainly consists of a test shaft system, a transmission mechanism, an environmental test chamber, a loading unit, and a hot air blower. See details below. Figure 1The drive motor is suspended and fixed below the test bench. A drive wheel is installed at the motor output, and a driven wheel is mounted on the test shaft. The drive wheel drives the driven wheel and the shaft to rotate via a belt. Two ceramic rolling element bearings are used as support bearings in the middle of the test shaft. The inner side of the support bearings is positioned by a shaft shoulder, and the outer side is axially fixed by a sealing ring and a lock nut. The bearing housings are bolted to the base. The non-drive end of the shaft extends into the test chamber, and the test bearing unit is installed at the non-drive end of the shaft. Hot circulating air can be introduced into the chamber to simulate a high-temperature environment.

[0058] The loading unit consists of a loading nut, a pressure sensor, a washer, and a loading head. During loading, radial pressure is generated by compressing the spring by tightening the loading wrench. The magnitude of the radial force is determined by the pressure sensor installed in the housing, and is finally applied to the outer ring of the test bearing through the loading head.

[0059] Main technical specifications of the test device

[0060] Maximum spindle speed of the testing machine: 8000 r / min, steady-state error ≤ ±2%FS;

[0061] The testable bearing diameter range is 50-120mm, including deep groove ball bearings and cylindrical roller bearings;

[0062] The rotation speed and temperature can be controlled, displayed, and recorded, and it can operate according to the set acceleration and deceleration curves;

[0063] Preloading method for testing machine: manual loading; load values ​​can be displayed and recorded in the software interface; maximum radial preload on the testing machine spindle: 3kN;

[0064] The hot air blower has a power of 5kW and a maximum heating temperature of 180℃.

[0065] (2) Oil film electrical performance test unit and test method

[0066] Electrical performance testing unit

[0067] Oil film electrical performance testing mainly includes measuring oil film resistance, capacitance, and breakdown voltage. This test unit primarily consists of a test bearing unit, insulating paper, a digital bridge, a loading positioning sleeve, a nylon seat, carbon brushes, and an axial adjustment device, etc. See details... Figure 2 The inner and outer bearing covers form a sealed lubrication unit with the test bearing, simulating the sealed lubrication structure of a bearing unit. The inner and outer covers are designed with annular oil reservoirs that can be filled with grease before the test begins. During the test, they can be replenished interactively with the grease inside the bearing. The inner and outer bearing covers are connected by screws, and insulating material is used to insulate the inner and outer bearing covers from the radial loading mechanism.

[0068] The axial adjustment device consists of a fixed plate, a screw, and a nylon block. The nylon block and the fixed plate have threaded holes at their ends. The screw is screwed into the threaded hole in the fixed plate and then connected to the nylon block through its end threaded hole. Axial adjustment is achieved by rotating the screw. The positive terminal of the digital bridge is connected to the bearing cover, and the negative terminal is connected to the carbon brush, forming a test circuit.

[0069] Test methods

[0070] The oil film resistance and capacitance were tested using a multi-condition simulation and oil film establishment device and an oil film electrical performance testing unit. The specific steps are as follows:

[0071] First, lubricating grease is filled into the bearing and the oil reservoirs of the inner and outer bearing covers. The bearing is then heat-fitted onto the shaft, and the inner and outer bearing covers are installed and axially tightened with screws to ensure a good seal at both ends of the bearing. Next, the positive terminal of the digital bridge is connected to the outer ring of the bearing, and a radial loading rod is used to apply load. Simultaneously, the carbon brush axial adjustment device in the test unit is adjusted to ensure good contact between the carbon brush and the end of the shaft. Finally, the test is conducted according to the required speed, load, and ambient temperature. After the speed, temperature, and load stabilize, the oil film resistance and capacitance values ​​under different operating conditions are measured in real time using the digital bridge.

[0072] Breakdown voltage test method: First, obtain the reference limit for the breakdown voltage of the oil film of a certain thickness through theoretical calculation. Select a suitable DC regulated power supply, and establish the oil film under the test condition according to the method described above for testing resistors. Then, connect the DC regulated power supply in series with the test circuit formed by the oil film, bearings, carbon brushes, and other components. During measurement, gradually increase the voltage. When the voltage suddenly drops, the voltage value is the breakdown voltage value of the oil film of that thickness.

[0073] (3) Calculation method of equivalent circuit and electrical performance parameters

[0074] Equivalent circuit model

[0075] The equivalent circuit of bearing oil film can be divided into two types according to whether the bearing is insulated or not. Insulated bearings can be further divided into insulated bearings with coatings on both the inner and outer rings. The circuit mainly consists of coated capacitors, coated resistors, bearing steel resistors, inner and outer ring oil film resistors and capacitors, etc. The equivalent circuits of oil film for various types of bearings are as follows: Figure 3 , 4 .

[0076] 1) Equivalent circuit of non-insulated bearing oil film

[0077] ①a. In the equivalent circuit of a non-insulated bearing, the total resistance includes the bearing outer ring resistance, bearing inner ring resistance, total rolling element resistance, total oil film resistance outside the rolling elements, and total oil film resistance inside the rolling elements, which are connected in series. The total oil film resistance outside the rolling elements is formed by all the oil film resistances outside the rolling elements in parallel, and the total oil film resistance inside the rolling elements is formed by all the oil film resistances inside the rolling elements in parallel.

[0078] b. In the equivalent circuit of a non-insulated bearing, the total capacitance includes the total capacitance of the oil film outside the rolling body and the total capacitance of the oil film inside the rolling body connected in series; the total capacitance of the oil film outside the rolling body is formed by all the oil film capacitances outside the rolling body connected in parallel, and the total capacitance of the oil film inside the rolling body is formed by all the oil film capacitances inside the rolling body connected in parallel.

[0079] 2) Equivalent circuit of bearing oil film with insulating coating on inner and outer rings

[0080] ②a. In the equivalent circuit of an insulated bearing with coatings on the inner and outer rings, the total resistance includes the resistance of the insulation coating, the resistance of the outer ring of the bearing, the resistance of the inner ring of the bearing, the total resistance of the rolling elements, the total resistance of the oil film outside the rolling elements, and the total resistance of the oil film inside the rolling elements, which are connected in series. The total resistance of the oil film outside the rolling elements is formed by all the oil film resistances outside the rolling elements in parallel, and the total resistance of the oil film inside the rolling elements is formed by all the oil film resistances inside the rolling elements in parallel.

[0081] b. In the equivalent circuit of an insulated bearing with coatings on the inner and outer rings, the total capacitance includes the capacitance of the insulating coating, the total capacitance of the oil film outside the rolling rings, and the total capacitance of the oil film inside the rolling rings connected in series; the total capacitance of the oil film outside the rolling rings is formed by all the oil film capacitors outside the rolling rings connected in parallel, and the total capacitance of the oil film inside the rolling rings is formed by all the oil film capacitors inside the rolling rings connected in parallel.

[0082] Electrical performance parameter calculation method

[0083] The method for calculating the capacitance of the insulating coating is as follows:

[0084] C 涂层 =ε0ε r A / d (1)

[0085] ε0 — vacuum permittivity

[0086] ε r —Relative permittivity

[0087] A – Area of ​​both end faces of the bearing + Area of ​​the outer diameter of the bearing

[0088] d—Thickness of insulating coating

[0089] The calculation method for oil film capacitance is as follows:

[0090] Oil film capacitors are divided into Hertzian contact region capacitors and non-Hertzian region capacitors. Hertzian contact capacitors are categorized by C... H This indicates that the non-Hertz contact capacitance is expressed as C No This indicates that, since the bearing load-bearing area is generally supported by multiple rolling elements, the oil film capacitance of a single rolling element unit is analyzed first:

[0091] Hertz contact capacitance C H单When elastic deformation occurs between the rolling element and the raceway surface, an oil film forms a capacitance at the contact area, which is considered a parallel plate capacitor. The Hertzian contact capacitance C of the oil film between the inner and outer rings of the bearing can be calculated according to equations (2) and (3), respectively. H单外 C H单内 The total Hertz capacitance of a single rolling element C H单 According to formula (4), since the relative gap between the rolling elements and the raceway surface in the non-load-bearing area is relatively large, it does not need to be considered.

[0092] C H单外 =ε0ε r A 外 / H c外 (2)

[0093] C H单内 =ε0ε r A 内 / H c内 (3)

[0094] C H单 =C H单外 C H单内 / (C H单外 +C H单内 (4)

[0095] A 外 —The Hertzian contact area between the outer ring and the rolling element;

[0096] A 内 —The Hertzian contact area between the inner ring and the rolling element;

[0097] H c外 —The thickness of the oil film between the outer ring and the rolling elements;

[0098] H c内 —The thickness of the oil film between the inner ring and the rolling elements;

[0099] ε0 is the vacuum permittivity of the material.

[0100] ε r The relative permittivity of the material;

[0101] C H单 —The sum of the Hertzian contact capacitances of the inner and outer ring oil films of a single rolling element.

[0102] Non-Hertz contact capacitor: A spherical capacitor composed of rolling elements, a non-Hertz contact area oil film, and raceways within a certain region, as shown in the following planar projection. Figure 5 , 6 As shown in Figure 7. It is known that the farther away from the contact point, the greater the distance between the two plates, and the smaller the non-Hertz contact capacitance. The non-Hertz contact region includes S1 and S2. NoHzWhen calculating the capacitance of the non-Hertz contact region, the radial direction of the bearing is taken as the x-axis and the axial direction as the y-axis. The area outside r′ in the axial and radial directions of the bearing is ignored. The calculation deviation can be less than 10%, so only the capacitance within r′ is calculated. The capacitance within r′ consists of two parts, one of which is… Figure 5 Part C of S1 s单 The second is S NoHz Capacitance C within the region NoHz Region S1 is the area of ​​the circle formed with radius b of the major semi-axis of the rolling contact ellipse, minus the area of ​​the circle formed with radius a of the minor semi-axis (i.e., S1 is the circle with radius b minus the Hertzian contact area S). Hz (partial), S NoHz The region is defined by the origin of the coordinate system, extending outwards along the gap between the bearing outer ring raceway and the rolling element spherical surface to r′, forming two boundary lines. Within this region, the area of ​​the gap between the bearing outer ring raceway and the rolling element spherical surface is (…). Figure 5 , 6 (as shown in the figure); its calculation formula is shown in (5)(6).

[0103]

[0104]

[0105] C No单总 =C s单 +C NoHz (7)

[0106] a——Minor semi-axis of the rolling element Hertzian contact ellipse;

[0107] b—the major semi-axis of the Hertzian contact ellipse of the rolling element;

[0108] r—radius of the rolling element;

[0109] r0—Outer raceway radius;

[0110] r′——The thickness of the gap between the roller and the raceway is 100H. c At that time, the distance projected onto the contact point from the raceway surface;

[0111] S Hz —Hertz contact area;

[0112] S1, S NoHz —All are non-Hertz contact areas;

[0113] ε0 — vacuum permittivity;

[0114] ε r —Relative permittivity;

[0115] H c —Oil film thickness;

[0116] Hertz contact capacitance C of each rolling element H单 Non-Hertz contact capacitance C H单 If the rolling elements are connected in parallel, and the oil film capacitance of the multiple rolling elements in the bearing area is also connected in parallel, then the total capacitance of each rolling element and the total capacitance of the oil film in the bearing area are considered.

[0117] Therefore, the total capacitance of a single rolling element is:

[0118] C 单总 =C H单 +C NO单总 (8)

[0119] The total capacitance of the rolling elements within the bearing area is:

[0120] C 总 =C 1单总+ ...+C NO单总 (9)

[0121] (4) Reliability assessment of bearing insulation performance

[0122] PSCAD software can be used to simulate and analyze the equivalent circuit of insulated bearings and oil films. The equivalent circuit model consists of the bearing insulation coating, oil film, and rolling elements. Power supply parameters are set according to the measured peak shaft voltage, frequency, and pulse waveform rise time (du / dt). The voltage division values ​​of the insulation coating and oil film are calculated separately. These values ​​are then compared with the measured oil film breakdown voltage to confirm whether the oil film has broken down. If the oil film voltage division is less than its breakdown voltage, discharge and electrolytic corrosion will not occur, and the insulation coating design meets the requirements.

[0123] Beneficial effects of the technical solution of this invention

[0124] (1) This invention constructs a device that can simulate the actual operating environment of motor bearings and establish a bearing lubricating oil film under dynamic conditions, which can provide a basis for evaluating the electrical performance parameters of motor bearing oil film and the insulation performance of bearings. (2) This invention proposes a test method for testing the resistance, capacitance and breakdown voltage of bearing lubricating oil film under dynamic conditions, which can accurately obtain the electrical performance parameters of lubricating oil film.

[0125] (3) This invention proposes a theoretical method for calculating bearing oil film capacitance, which can provide input parameters for oil film state under energized conditions and design of insulated bearings.

[0126] (4) This invention proposes a method for evaluating the effectiveness of bearing insulation performance, which can provide a basis for product design.

Claims

1. A method for testing the electrical performance parameters of lubricating oil film in rolling bearings, comprising using a testing device for testing the electrical performance parameters of lubricating oil film in rolling bearings to test the resistance and capacitance of the oil film, wherein the testing device includes a transmission mechanism, a test shaft system, an environmental test chamber, a loading unit, and a hot air blower; the transmission mechanism includes a mounting platform, a drive motor mounted below the mounting platform, a drive wheel mounted on the output shaft of the drive motor, and a driven wheel located above the mounting platform and connected to the drive wheel by a belt; The test shaft system includes a test shaft, a pair of bearing seats mounted on a mounting platform via a base, and a pair of bearings installed in the bearing seats; the middle part of the test shaft is supported by two bearings, the part of the test shaft located between the two bearings is positioned by a shaft shoulder, and the part located outside the bearings is axially fixed by a sealing ring and a lock nut. The environmental test chamber is fixed on the mounting platform and is equipped with a temperature sensor. The drive end of the test shaft is fixedly connected to the driven wheel, while the non-drive end extends into the environmental test chamber through a hole in the side wall for installing the oil film electrical performance test unit. The environmental test chamber is equipped with an air inlet and an air outlet. The air inlet and air outlet are connected to the air outlet and air inlet of the hot air blower to form a circulation pipeline. The loading unit is located at the top of the environmental test chamber; it is used to apply a radial load to the oil film electrical performance testing unit. The oil film electrical performance testing unit includes a test bearing unit, insulating paper, a digital bridge, a loading positioning sleeve, and an axial adjustment device. The test bearing unit consists of inner and outer bearing covers and a test bearing located inside the inner and outer bearing covers. The inner side of the inner and outer bearing covers is provided with an annular oil reservoir for storing grease. The lower ends of the inner and outer bearing covers are connected by bolts. An insulating paper is placed between the top of the test bearing and the inner wall of the top of the inner and outer bearing covers. The bottom of the loading positioning sleeve is provided with a groove to hold the inner and outer bearing covers in place, and the top is provided with a vertical groove. The loading unit extends into the vertical groove. The axial adjustment device includes a nylon seat, a carbon brush, and an axial adjustment screw. A fixed plate is installed on the outer wall of the environmental test chamber. The fixed plate has screw holes, and the end of the nylon seat also has screw holes. The axial adjustment screw passes through the screw holes on the fixed plate and extends into the screw hole at the end of the nylon seat. The front end of the nylon seat has a hole, and the carbon brush is confined in the hole. The end of the carbon brush is connected to the nylon seat by a spring. The front end of the carbon brush abuts against the non-transmission end face of the test shaft. The outer ring of the test bearing is connected to the spring by a wire and a digital bridge is connected in series. The loading unit includes a washer with internal threads installed on the top of the environmental test chamber, a loading rod that is screwed to the washer by external threads, a pressure sensor and a spring fitted on the loading rod, and a loading wrench fitted on the loading rod by an internal square or internal hexagon structure above the spring. Its features are, The testing method includes the following steps: First, lubricating grease is loaded into the oil reservoirs of the test bearing and its inner and outer covers. The test bearing is then heat-fitted onto the test shaft, and the inner and outer covers are installed and axially tightened with screws to ensure good sealing at both ends of the test bearing. Next, the positive terminal of the digital bridge is connected to the outer ring of the test bearing, and a loading unit is used to apply load. At the same time, the axial adjustment device is used to ensure good contact between the carbon brush and the end of the test shaft. Finally, the test is conducted according to the required speed, load, and ambient temperature. After the speed, temperature, and load stabilize, the oil film resistance and capacitance values ​​of the test bearing under different working conditions are measured in real time using the digital bridge. It also includes a method for calculating electrical performance parameters. This method calculates the electrical performance of bearing oil film through equivalent circuits of different types of bearing oil film, provides input parameters for oil film state under energized conditions and design of insulated bearings, and compares them with test values. Rolling bearings are divided into insulated bearings and non-insulated bearings; insulated bearings are insulated bearings with coatings on both the inner and outer rings. ①a. In the equivalent circuit of a non-insulated bearing, the total resistance includes the bearing outer ring resistance, bearing inner ring resistance, total rolling element resistance, total oil film resistance outside the rolling elements, and total oil film resistance inside the rolling elements, which are connected in series. The total oil film resistance outside the rolling elements is formed by all the oil film resistances outside the rolling elements in parallel, and the total oil film resistance inside the rolling elements is formed by all the oil film resistances inside the rolling elements in parallel. b. In the equivalent circuit of a non-insulated bearing, the total capacitance includes the total capacitance of the oil film outside the rolling body and the total capacitance of the oil film inside the rolling body, which are connected in series. The total capacitance of the external oil film of the rolling mill is formed by the parallel connection of all external oil film capacitances of the rolling mill, and the total capacitance of the internal oil film of the rolling mill is formed by the parallel connection of all internal oil film capacitances of the rolling mill. ②a. In the equivalent circuit of an insulated bearing with coatings on the inner and outer rings, the total resistance includes the resistance of the insulation coating, the resistance of the outer ring of the bearing, the resistance of the inner ring of the bearing, the total resistance of the rolling elements, the total resistance of the oil film outside the rolling elements, and the total resistance of the oil film inside the rolling elements, which are connected in series. The total resistance of the oil film outside the rolling elements is formed by all the oil film resistances outside the rolling elements connected in parallel, and the total resistance of the oil film inside the rolling elements is formed by all the oil film resistances inside the rolling elements connected in parallel. b. In the equivalent circuit of an insulated bearing with coatings on the inner and outer rings, the total capacitance includes the capacitance of the insulating coating connected in series, the total capacitance of the oil film outside the rolling elements, and the total capacitance of the oil film inside the rolling elements. The total capacitance of the external oil film of the rolling mill is formed by the parallel connection of all external oil film capacitances of the rolling mill, and the total capacitance of the internal oil film of the rolling mill is formed by the parallel connection of all internal oil film capacitances of the rolling mill. The calculation method for the capacitance of the insulating coating in the electrical performance parameter calculation method is as follows: C 涂层 = ε 0 ε r A / d （1） ε 0 — Vacuum permittivity ε r —Relative permittivity A —Area of ​​both end faces of the bearing + Area of ​​the outer diameter of the bearing d -- Insulating coating thickness The calculation method for oil film capacitance is as follows: Oil film capacitors are divided into Hertz contact capacitors and non-Hertz capacitors. Hertz contact capacitors are... C H This indicates that the non-Hertz contact capacitance is... C No This indicates an analysis of the oil film capacitance of a single rolling element unit. Hertz contact capacitor C H单 When the rolling element comes into contact with the raceway surface and undergoes elastic deformation, an oil film forms a capacitance at the contact area, which is considered as a parallel plate capacitor; calculate the Hertz contact capacitance of the oil film on the inner and outer rings of the bearing according to equations (2) and (3) respectively. C H单外 , C H单内 The total Hertz capacitance of a single rolling element C H单 Calculate according to formula (4); C H单外 = ε 0 ε r A 外 / H c外 （2） C H单内 = ε 0 ε r A 内 / H c内 （3） C H单 =C H单外 C H单内 / (C H单外 +C H单内 ) (4) A 外 —The Hertzian contact area between the outer ring and the rolling element; A 内 —The Hertzian contact area between the inner ring and the rolling element; H c外 —The thickness of the oil film between the outer ring and the rolling elements; H c内 —The thickness of the oil film between the inner ring and the rolling elements; Ɛ 0 The vacuum permittivity of the material is . Ɛ r The relative permittivity of the material; C H单 —The sum of the Hertzian contact capacitances of the inner and outer ring oil films of a single rolling element; Non-Hertz contact capacitor: A spherical capacitor consisting of rolling elements, a non-Hertz contact area oil film, and raceways within a certain region. The non-Hertz contact area includes... S 1 and S NOHz The sum of the areas of the two parts; when calculating the capacitance of the non-Hertz contact region, the radial direction of the bearing is taken as... x The axis, the axial direction is y Shaft, neglecting the axial and radial directions of the bearing. r Areas outside of ′; r The capacitor inside the ' is composed of two parts, one of which is S 1 part C s单 The second is S NoHz Capacitance within the region C NoHz ; S 1 The region is the area where the rolling element contacts the major semi-axis of the ellipse. b The area of ​​the circle formed by the radius, minus the area of ​​the circle with the minor semi-axis. a The difference in area of ​​the circles formed by the radii. S NoHz The region is a circle centered at the origin of the coordinate system, extending outwards along the gap between the outer raceway surface of the bearing and the spherical surface of the rolling elements. r Two boundary lines are formed after the boundary lines are formed. The area of ​​the gap between the outer ring raceway surface of the bearing and the spherical surface of the rolling element in this region is calculated as shown in (5) and (6). （5） （6） （7） In equations (5) and (6): a —The rolling element Hertz contacts the minor semi-axis of the ellipse; b —The rolling element Hertz contacts the major semi-axis of the ellipse; r —Rolling element radius; r 0 —Outer raceway radius; r — The thickness of the gap between the roller and the raceway is 100. H c At that time, the distance projected onto the contact point from the raceway surface; S Hz —Hertz contact area; S 1 , S NoHz —All are non-Hertz contact areas; ε 0 — Vacuum permittivity ε r —Relative permittivity; H c —Oil film thickness; Hertz contact capacitance of each rolling element C H单 Non-Hertz contact capacitors C NO单总 The oil film capacitances of multiple rolling elements in the bearing area are also connected in parallel, so the total oil film capacitance of a single rolling element is: C 单总 = C H单 +C NO单总 （8） The total capacitance of the oil film on the rolling elements within the bearing area is: C 总 =C 1单总+ ...+C N单总 （9）。 2. The method for testing the electrical performance parameters of lubricating oil film in rolling bearings as described in claim 1, characterized in that, It also includes a breakdown voltage test method: First, obtain the reference limit value of the breakdown voltage of the oil film of a certain thickness through theoretical calculation, select a suitable DC regulated power supply, establish the oil film under the test condition according to the above method of testing the resistor, and then connect the DC regulated power supply in series to the test circuit formed by the oil film, the test bearing, and the carbon brush parts; during measurement, gradually increase the voltage, and when the voltage suddenly drops, the value of the suddenly dropped voltage is the breakdown voltage value of the oil film of that thickness.

3. The method for testing the electrical performance parameters of lubricating oil film in rolling bearings as described in claim 1, characterized in that, The equivalent circuit of the insulated bearing and oil film was simulated and analyzed using PSCAD software. The equivalent circuit model consists of the bearing insulation coating, oil film, and rolling elements of the bearing ring. The power supply parameters are based on the measured shaft voltage peak voltage, frequency, and pulse waveform rise time. du / dt The settings are configured, and the voltage division values ​​of the insulating coating and oil film are calculated respectively. Then, they are compared with the measured oil film breakdown voltage to confirm whether the oil film has broken down. If the oil film voltage division value is less than its breakdown voltage, then there will be no discharge and electro-erosion, and the insulating coating design meets the requirements.

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