Real-time testing method for bending and torsional strain of water-lubricated bearings under operating conditions

Abstract

This invention proposes a real-time monitoring method for bearing operating conditions based on bending and torsional strain testing technology. This method monitors the bending moment and torque on the journal section near the bearing under actual operating conditions. Based on a shaft system mechanics analysis model, it calculates the dynamic load and frictional torque borne by the bearing in real-time, obtaining the bearing friction coefficient under real-time conditions. This allows for the monitoring and evaluation of the bearing's real-time operating condition. Its advantages include obtaining the real-time operating condition of the bearing under actual operating conditions, solving the technical problem of difficulty in real-time monitoring and evaluation of the operating condition of water-lubricated bearings, and being applicable to the simultaneous evaluation of the operating condition of multiple bearings in a shaft system.

Description

Technical Field

[0001] This invention relates to the field of testing and analysis technology for the operating conditions of water-lubricated bearings, and in particular to a real-time testing method for the bending and torsional strain of water-lubricated bearings under operating conditions. Background Technology

[0002] Water-lubricated bearings are critical components in marine and other power systems, playing a vital role in supporting drive shafts and rotating parts. A water film exists between the drive shaft and the bearing, separating them and reducing friction. Once this water film is disrupted or becomes too thin, dry friction occurs between the shaft and the bearing, deteriorating the bearing's operating condition and leading to significant vibration, noise, and fatigue damage. Statistics show that friction-related failures account for more than one-third of bearing failures. Bearing failure severely impacts the safe operation of machinery. Monitoring, analyzing, and evaluating the operating condition of water-lubricated bearings is beneficial for preventing bearing wear failure and ensuring and extending their service life.

[0003] Bearings experience varying working loads, speeds, lubricating medium temperatures, and bearing deformations under different operating conditions, resulting in diverse working states, including dry friction, boundary friction, and hydrodynamic lubrication. These varying working states are difficult to analyze through calculation or experimentation alone. Therefore, the testing, analysis, and evaluation of the working state of water-lubricated bearings are best conducted under actual operating conditions of the power system. This necessitates a testing method capable of real-time testing and analysis of the water-lubricated working state under real-world operating conditions. This is the current development trend in this technical field, and corresponding real-time detection devices and evaluation methods are receiving increasing attention.

[0004] Existing related methods and technologies:

[0005] (1) Calculation method. The bearing friction torque is affected by many factors, including the properties of the materials of the two contact surfaces and the lubrication medium. It also varies with the working conditions and environmental conditions of the friction pair. To date, there is no theoretical formula that can accurately calculate it.

[0006] (2) Friction tests were conducted using various types of friction and wear testing machines, and the friction coefficient was obtained. The test load was applied by a ball screw driven by a motor. When the pin and the disc moved relative to each other, the frictional force generated between the two pairs of friction surfaces was measured by a force sensor fixed to the side of the lever arm. This method is mainly used to determine the frictional characteristics of friction pair test specimens and cannot be used for testing real water-lubricated bearings.

[0007] (3) Bearing test bench testing. Loading is achieved by applying tension to the test bearing through a tie rod mounted on the loading ring. When the test shaft rotates, the frictional force between the shaft and the test bearing is measured by a tension sensor, and the friction factor is calculated based on the radial force and frictional force. This method is used to test the friction and lubrication characteristics of the test bearing under different linear velocities and loads. Some test benches measure the radial loading force using a weighing sensor mounted directly below the radial loading cylinder, measure the swing angle using an angle sensor mounted on the bearing swing rod to obtain the swing speed, and measure the frictional torque between the test bearing and the pin shaft. This type of method can only be used for test bench research and cannot be used to monitor and evaluate the frictional state of the bearing under different operating conditions in actual installation. Due to structural limitations, radial load interference is unavoidable when collecting circumferential frictional force, and its influence needs to be eliminated through special devices or measurement methods, such as using a rolling bearing with a friction coefficient 1 to 2 orders of magnitude smaller than that of a sliding bearing for radial loading to solve the frictional torque measurement error.

[0008] (4) Acoustic emission monitoring method. This method uses acoustic emission sensors to collect sound signals emitted by the friction pair, thereby analyzing the friction state of the sliding bearing. However, this method is highly susceptible to environmental noise interference, and the equipment is expensive.

[0009] (5) Wear debris analysis method. This method analyzes the degree of friction by collecting the amount of wear debris on the inner surface of the bearing. However, this method can only detect wear after the bearing has worn to a certain extent, resulting in poor real-time performance.

[0010] (6) Oil Film Voltage Measurement Method. An oil film measurement circuit is constructed, with one end of a wire connected to the bearing bush and the other end to the shaft. A voltmeter is used to measure the pressure drop of the lubricating oil film between the sliding bearing and the main shaft. The changes in oil film voltage are analyzed to understand the oil film condition and, consequently, the degree of bearing wear. Different sliding bearing materials result in different circuit resistances, affecting the oil film voltage value. Therefore, the oil film voltage drop ratio needs to be calculated. The voltage drop ratio is the ratio between the oil film voltage and the total circuit voltage, reflecting the variation of the oil film voltage throughout the circuit.

[0011] Assuming the lubricating oil film pressure drop is V1 and the total circuit voltage drop is V2, the pressure drop ratio q, which reflects the lubrication state during the friction process of the sliding bearing, is:

[0012] q = V1 / V2

[0013] If q = 1, the clearance between the sliding bearing and the main shaft is conducted by lubricating oil. At this time, the total circuit voltage drop is all provided by the circuit power supply V2, and the sliding bearing is in the full fluid lubrication stage. On the contrary, if q = 0, the lubricating oil between the inner ring of the sliding bearing and the shaft diameter surface is exhausted, and the two contact surfaces are completely in contact. At this time, the oil film thickness is 0, and the sliding bearing is in the dry friction stage; if 0 < q < 1, there is insufficient lubricating oil between the sliding bearing and the shaft diameter, or the lubricating oil cannot be evenly spread on the two contact surfaces due to pressure concentration. At this time, the sliding bearing is in the boundary friction or partial fluid lubrication stage. Limited by the actual use of lubricating oil, the theoretical value range of q is between 0 and 1, but does not include 0 and 1. In actual use, the sensitivity of this method is not high and is greatly affected by the quality of the oil.

[0014] (7) Motor current signal feature analysis method. Analyze the working state of the sliding bearing by collecting the current signal at the stator end of the motor. As the energy input source for the operation of mechanical components, in addition to performing mechanical work, the output torque of the motor also needs to overcome the frictional work. Therefore, the output torque of the motor is in a balance process of generation and elimination. Once the frictional torque at the output end changes, it will be directly reflected in the motor current signal, resulting in corresponding changes in the amplitude or phase of the current signal. Keeping the motor unloaded and at a constant speed, the sliding frictional torque of the bearing directly affects the change of the current signal. Therefore, accurately extracting the frictional energy value in the motor current signal becomes the monitoring focus. The motor current signal feature analysis was initially used to diagnose the broken rotor bar fault of the motor. In recent years, the motor current signal feature analysis method has been widely applied to diagnose the external load fault of the motor. Since the friction characteristic frequency is close to the fundamental frequency of the current sampling signal and is easily covered by the fundamental frequency, and the sampling signal is also easily interfered by environmental noise, the main problem to be solved for monitoring the friction state with the motor current is to separate the friction characteristic frequency and the fundamental frequency to highlight the friction characteristic frequency and minimize the influence of environmental noise on the separation process. This method is only effective when the bearing friction is severe to a certain extent, and the sensitivity to the early friction state assessment is poor.

[0015] (8) Journal center position change judgment method. Analyze the formation of the water film in the bearing by monitoring the change of the journal center position and the floating height of the journal center during operation, and evaluate the working state of the bearing accordingly. This method requires installing 2 displacement sensors on the journal, and knowing the output values of the displacement sensors at zero speed and actual working speed, as well as geometric parameter values such as the bearing clearance. Water lubricated bearings usually use rubber materials, and the rubber will deform under dynamic loads, which has a greater impact on the measurement results of the journal center position.

[0016] Most existing methods require calculations or experiments on friction and wear testing machines and test benches, primarily studying the frictional properties between bearing friction pairs. These methods are difficult to apply to real-time monitoring and evaluation of the actual working condition of water-lubricated bearings under operating conditions. Acoustic emission methods are significantly affected by noise and have low reliability. Methods such as wear debris monitoring, current monitoring, and oil film voltage monitoring are greatly affected by operating conditions and are difficult to use for early wear monitoring. Journal center position monitoring is significantly affected by factors such as the deformation of the rubber material in water-lubricated bearings, resulting in large testing errors and significant errors in judging the bearing's working condition. Summary of the Invention

[0017] The purpose of this invention is to provide a real-time testing method for bending and torsional strain of water-lubricated bearings under operating conditions, enabling real-time testing, analysis, and evaluation of the operating condition of water-lubricated bearings under actual operating conditions, and solving the technical difficulties in bearing condition testing and analysis under operating conditions.

[0018] The technical solution of this invention is: to provide a method for real-time testing of bending and torsional strain of water-lubricated bearings under operating conditions, comprising the following steps:

[0019] S1. Monitor the bending moment and torque on the journal section near the bearing under real operating conditions. Based on the shaft system mechanical analysis model, calculate the dynamic load and friction torque borne by the bearing under real-time conditions, and obtain the bearing friction coefficient under real-time conditions.

[0020] S2. Based on the friction coefficient corresponding to different working states of the bearing, define a fuzzy membership function to transform the friction coefficient value into a membership value within [-1,1].

[0021] S3. Monitor and evaluate the real-time working status of the bearing based on the membership value: if the membership value is <0, the bearing is in normal working condition; if the membership value is >0, the bearing is in deteriorated working condition; the larger the membership value, the more severe the deterioration of the bearing's working condition.

[0022] Furthermore, the water-lubricated bearing model to be tested consists of a rotating shaft, multiple discs, a pair of wheels, a motor, and bearings; the water-lubricated bearing model contains n bearings, bearing 1 is located at the free end, bearing n is located at the motor end, and bearings 2, bearing 3, ..., bearing n-1 are located between the first and last bearings.

[0023] Furthermore, in step S1, the bending strain and torsional strain measurement sections are selected, starting from the first bearing, and one measurement section is selected for every other bearing;

[0024] Bending and torsional strain gauges are arranged on the selected measurement cross section. To improve the measurement accuracy of bending and torsional strain signals, the bending and torsional strain tests of the cross section are arranged in a full-bridge manner. Under the condition of shaft rotation, the strain signals are tested by wireless transmission and reception methods.

[0025] Furthermore, in step S1, a bending mechanics analysis model of the shaft system is established, and the wheel is simplified into lumped masses, namely: U1, U2, ..., U n The loads borne by each bearing are: F1, F2, ..., F n The bending moments obtained at each strain measurement section are: M1, M2, ..., M n The shear force obtained at each strain measurement section is: Q1, Q2, ..., Q n ;

[0026] Based on the structural characteristics of the shaft system, the bending mechanics analysis model of the shaft system is decomposed into a first section and an intermediate section; for the first section, according to the force and moment balance theory, the load F1 borne by the first bearing can be obtained:

[0027]

[0028] Where M1 is the bending moment at strain measurement section 1, measured by a strain gauge; q is the uniformly distributed mass of the shaft segment between the first measurement section and the first bearing; l1 is the distance from the first measurement section to the first bearing; and the shear force Q1 at the first strain measurement section is:

[0029]

[0030] For any segment in the middle, taking the i-th segment as an example, given the bending moment and shear force on the left side and the bending moment on the right side, the load F borne by the i-th bearing can be obtained according to the theory of force and moment balance. i :

[0031]

[0032] Among them, M i M i+1 Q represents the bending moments at both sides of the i-th segment, measured by a strain gauge. i The shear force on the left side of the i-th segment is calculated from the mechanical model of the (i-1)-th segment, U. i Let q be the concentrated mass of this segment, and q be the uniformly distributed mass of the i-th axis segment; l 1i Let l be the length of the i-th axis segment. 2i Let l be the distance from the concentrated mass within shaft segment i to the left end section. 3i The distance from the bearing inside shaft segment i to the left end section;

[0033] Shear force Q on the right side section of the i-th axis segment i+1 :

[0034] Q i+1 =Q i +F i -U i -ql1i ;

[0035] By following this pattern from left to right, the dynamic load borne by each bearing part can be obtained.

[0036] Furthermore, in step S1, a torsional mechanics analysis model of the shaft system is established, where T1, T2, ..., T n The torques at n measurement sections are obtained by strain gauges; τ1, τ2, ..., τ n This refers to the frictional torque borne by each bearing;

[0037] Determined from the torque balance of the shaft segment:

[0038]

[0039] Calculate the real-time friction coefficient μ of each bearing under its operating conditions. i :

[0040]

[0041] In the formula, r is the bearing radius.

[0042] Furthermore, in step S2, the ideal working state is a full water film lubrication state, where μ = 0.001-0.01. As the working state deteriorates, the bearing progresses from a semi-liquid friction state (μ = 0.01-0.1) to a boundary lubrication state (μ ≤ 0.15-0.3), a semi-dry friction state (μ = 0.1-0.5), and a dry friction state (μ = 0.6-0.9 for rubber against other materials).

[0043] Define fuzzy membership functions:

[0044]

[0045] In the formula, k and c are coefficients, k = 6, c = 0.01; as the friction state deteriorates from the full water film lubrication state to the dry friction state, the friction coefficient value becomes larger and larger, and the corresponding membership value becomes larger and larger, indicating that the working state tends to deteriorate; based on the membership value obtained by real-time monitoring, the actual working state of the water-lubricated bearing is monitored and evaluated.

[0046] The beneficial effects of the real-time testing method for bending and torsional strain of water-lubricated bearings under operating conditions provided by this invention are as follows:

[0047] The water-lubricated bearing working condition monitoring method proposed in this invention applies bending strain and torsional strain testing technology to obtain the real-time working condition of the bearing under actual operating conditions, and can be used to carry out real-time monitoring and evaluation of the bearing working condition.

[0048] This invention differs from existing monitoring methods such as acoustic emission, oil film voltage, and motor current. It provides a new strain-based testing method for assessing the working condition of bearings, solving the technical problem of real-time monitoring and assessment of the working condition of water-lubricated bearings.

[0049] This method can be applied simultaneously to assess the working condition of multiple bearings in a shaft system. Attached Figure Description

[0050] The invention will be further described below with reference to the accompanying drawings:

[0051] Figure 1 A schematic diagram of the bearing and shaft system model;

[0052] Figure 2 To select the measurement sections for bending strain and torsional strain;

[0053] Figure 3 To arrange bending and torsional strain gauges on the selected measurement section;

[0054] Figure 4 This is a full-bridge measurement method for bending strain;

[0055] Figure 5 This is a full-bridge measurement method for torsional strain;

[0056] Figure 6 A model for analyzing the bending mechanics of the shaft system;

[0057] Figure 7 A schematic diagram showing the disassembly of the shaft system mechanical model into the first and middle sections;

[0058] Figure 8 This is a model for analyzing the torsional mechanics of the shaft system.

[0059] Figure 9 The curve represents the fuzzy membership function. Detailed Implementation

[0060] The following detailed description, in conjunction with the accompanying drawings and specific embodiments, further illustrates the real-time testing method for bending and torsional strain of water-lubricated bearings under operating conditions proposed in this invention. The advantages and features of this invention will become clearer from the following description and claims. It should be noted that the accompanying drawings are all in a very simplified form and use non-precise ratios, and are only used to facilitate and clarify the illustration of the embodiments of this invention.

[0061] The core idea of ​​this invention is to propose a real-time monitoring method for bearing operating conditions based on bending and torsional strain testing technology. This method monitors the bending moment and torque on the journal section near the bearing under actual operating conditions. Based on a shaft system mechanics analysis model, it calculates the dynamic load and frictional torque borne by the bearing in real-time, obtaining the bearing friction coefficient under real-time conditions. Based on the friction coefficients corresponding to different bearing operating states, a fuzzy membership function is defined to transform the friction coefficient values ​​into membership values ​​within the range [-1, 1]. The real-time operating state of the bearing is monitored and evaluated based on the membership values. A membership value < 0 indicates normal bearing operating conditions; a membership value > 0 indicates deteriorated bearing operating conditions. The larger the membership value, the more severe the deterioration of the bearing operating conditions.

[0062] Example 1

[0063] by Figure 1 The bearing and shaft system model shown is used as an example for introduction. This model consists of a rotating shaft, multiple discs, couplings, a motor, and bearings, including n bearings. Bearing 1 is located at the free end, bearing n is located at the motor end, and bearings 2, 3, ..., n-1 are located between the first and last bearings. This model is representative.

[0064] like Figure 2 As shown, the selected sections for measuring bending strain and torsional strain are shown. Figure 1 Taking the model as an example, starting from the first bearing, a measurement section is selected for every other bearing. Figure 2 There are n bearings and n measurement sections are set.

[0065] like Figure 3 As shown, bending and torsional strain gauges are arranged on the selected measurement cross-section. To improve the measurement accuracy of bending and torsional strain signals, the cross-section bending and torsional strain tests are arranged in a full-bridge configuration. Figure 4 and Figure 5 The full-bridge measurement methods for bending and torsional strain are presented respectively. With the shaft rotating, strain signals can be measured using wireless transmission and reception methods.

[0066] Establish a bending mechanics analysis model for the shaft system, such as Figure 6 As shown. The roulette wheel is simplified into lumped masses, namely: U1, U2, ..., U n The loads borne by each bearing are: F1, F2, ..., F n The bending moments obtained at each strain measurement section are: M1, M2, ..., M n The shear force obtained at each strain measurement section is: Q1, Q2, ..., Q n .

[0067] Based on the characteristics of the shaft system structure, Figure 6 The model shown is broken down into a first segment and a middle segment, as follows: Figure 7 As shown.

[0068] For the first segment, according to the theory of force and torque balance, the load F1 borne by the first bearing can be obtained:

[0069]

[0070] Where M1 is the bending moment at strain measurement section 1, measured by a strain gauge; q is the uniformly distributed mass of the shaft segment between the first measurement section and the first bearing; l1 is the distance from the first measurement section to the first bearing. Shear force Q1 at the first strain measurement section:

[0071]

[0072] For any segment in the middle, taking the i-th segment as an example, given the bending moment and shear force on the left side and the bending moment on the right side, the load F borne by the i-th bearing can be obtained according to the theory of force and moment balance. i :

[0073]

[0074] Among them, M i M i+1 Q represents the bending moments at both sides of the i-th segment, measured by a strain gauge. i The shear force on the left side of the i-th segment is calculated from the mechanical model of the (i-1)-th segment, U. i Let q be the concentrated mass of this segment, and q be the uniformly distributed mass of the i-th axis segment; l 1i Let l be the length of the i-th axis segment. 2i Let l be the distance from the concentrated mass within shaft segment i to the left end section. 3i The distance from the bearing inside shaft segment i to the left end section is given.

[0075] Shear force Q on the right side section of the i-th axis segment i+1 :

[0076] Q i+1 =Q i +F i -U i -ql 1i

[0077] By following this pattern from left to right, the dynamic load borne by each bearing part can be obtained.

[0078] Establish a torsional mechanical analysis model for the shaft system, such as Figure 8 As shown in the figure. T1, T2, ..., T n The torques at n measurement sections are obtained by strain gauges. τ1, τ2, ..., τ n This refers to the frictional torque borne by each bearing.

[0079] It can be obtained from the torque balance of the shaft segments:

[0080]

[0081] Calculate the real-time friction coefficient μ of each bearing under its operating conditions. i :

[0082]

[0083] In the formula, r is the bearing radius.

[0084] The ideal operating condition is full water film lubrication, where μ = 0.001-0.01. As the operating condition deteriorates, the bearing evolves from a semi-liquid friction state (μ = 0.01-0.1) to a boundary lubrication state (μ ≤ 0.15-0.3), a semi-dry friction state (μ = 0.1-0.5), and a dry friction state (0.6-0.9 for rubber compared to other materials).

[0085] Define fuzzy membership functions:

[0086]

[0087] In the formula, k and c are coefficients, k = 6, c = 0.01. Figure 9 The table also indicates the membership intervals corresponding to different friction states. As the friction state deteriorates from a fully wet film lubrication state to a dry friction state, the friction coefficient value increases, and the corresponding membership value also increases, indicating that the working condition tends to deteriorate. A membership value < 0 indicates that the bearing is in good working condition, while a membership value > 0 indicates that the bearing is in poor working condition. The larger the membership value, the more severe the deterioration.

[0088] Based on the membership values ​​obtained from real-time monitoring, the actual working condition of water-lubricated bearings can be monitored and evaluated.

[0089] The contents not described in detail in this specification are prior art known to those skilled in the art. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the invention can be implemented in other specific forms without departing from its spirit or essential characteristics. Therefore, the embodiments should be considered in all respects as exemplary and non-limiting, and the scope of the invention is defined by the appended claims rather than the foregoing description. Thus, it is intended that all variations falling within the meaning and scope of equivalents of the claims be included within the present invention.

Claims

1. A method for real-time testing of the working state bending and torsional strain of a water-lubricated bearing under operating conditions, characterized in that, Includes the following steps: S1. Monitor the bending moment and torque on the journal section near the bearing under real operating conditions. Based on the shaft system mechanical analysis model, calculate the dynamic load and friction torque borne by the bearing under real-time conditions, and obtain the bearing friction coefficient under real-time conditions. S2. Based on the friction coefficient corresponding to different working states of the bearing, define a fuzzy membership function to transform the friction coefficient value into a membership value within [-1,1]. S3. Monitor and evaluate the real-time working status of the bearing based on the membership value: if the membership value is <0, the bearing is in normal working condition; if the membership value is >0, the bearing is in deteriorated working condition; the larger the membership value, the more severe the deterioration of the bearing's working condition.

2. The method for real-time testing of the bending and torsion strain of a water-lubricated bearing in operation according to claim 1, characterized in that, The water-lubricated bearing model under test consists of a rotating shaft, multiple discs, coupling wheels, a motor, and bearings. The water-lubricated bearing model contains n bearings, with bearing 1 located at the free end, bearing n located at the motor end, and bearings 2, 3, ..., n-1 located between the first and last bearings.

3. The method for real-time testing of bending and torsional strain of water-lubricated bearings under operating conditions as described in claim 2, characterized in that, In step S1, the bending strain and torsional strain measurement sections are selected, starting from the first bearing, and one measurement section is selected for each bearing; Bending and torsional strain gauges are arranged on the selected measurement cross section. To improve the measurement accuracy of bending and torsional strain signals, the bending and torsional strain tests of the cross section are arranged in a full-bridge manner. Under the condition of shaft rotation, the strain signals are tested by wireless transmission and reception methods.

4. The method for real-time testing of bending and torsional strain of water-lubricated bearings under operating conditions as described in claim 3, characterized in that... In step S1, a bending mechanics analysis model of the shaft system is established, and the wheel is simplified into a lumped mass, as follows: The load borne by each bearing is: The bending moment obtained at each strain measurement section is: The shear force obtained at each strain measurement section is: ; Based on the structural characteristics of the shaft system, the bending mechanics analysis model of the shaft system is decomposed into a first section and an intermediate section; for the first section, according to the force and moment balance theory, the load borne by the first bearing is obtained. : in, The bending moment at section 1 of the strain measurement unit was measured by a strain gauge. The mass is uniformly distributed across the shaft segment between the first measurement section and the first bearing. The distance from the first measurement section to the first bearing; the shear force at the first strain measurement section. : For any segment in the middle, taking the i-th segment as an example, given the bending moment and shear force on the left side and the bending moment on the right side, the load borne by the i-th bearing can be obtained according to the theory of force and moment balance. : in, The bending moments of the two sides of the i-th segment are measured by a strain gauge. The shear force at the left cross section of segment i is calculated from the mechanical model of segment (i-1). For the concentrated quality of this section, Let the mass be the uniformly distributed mass of the i-th axis segment; Let i be the length of the i-th axis segment. Let be the distance from the concentrated mass within shaft segment i to the left-end section. The distance from the bearing inside shaft segment i to the left end section; Shear force on the right side section of the i-th axis segment : ； By repeating this process from left to right, we can obtain the dynamic load borne by each bearing component.

5. The method for real-time testing of bending and torsional strain of water-lubricated bearings under operating conditions as described in claim 4, characterized in that, In step S1, a torsional mechanical analysis model of the shaft system is established. The torque at n measurement sections is obtained by a strain gauge; This refers to the frictional torque borne by each bearing; Determined from the torque balance of the shaft segment: Calculate the real-time friction coefficient of each bearing under its operating conditions. : In the formula, r is the bearing radius.

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