Axial plunger pump internal friction pair wear degree identification method based on leakage coefficient

Abstract

The invention belongs to the technical field of hydraulic elements, and particularly relates to an axial plunger pump internal friction pair wear degree identification method based on a leakage coefficient, the method is combined with the leakage coefficient to solve the leakage rate when oil in a plunger cavity passes through each friction pair gap, and a flow-thermal coupling plunger pump outlet oil pressure model is established; constructing a set of identification algorithm, and identifying a leakage coefficient in the model in combination with monitoring data of pump outlet oil pressure and leakage flow; when the plunger pump operates under a certain working condition, the leakage coefficient represents the overall abrasion degree of the pump, and the overall abrasion degree serves as a quantitative evaluation index of the abrasion degree of the pump: the larger the identified leakage coefficient is, the larger the abrasion degree of the plunger pump is; the leakage coefficient can also be fuzzified into a wear degree label for use. Compared with an existing plunger pump digital-analog fusion driving abrasion fault diagnosis method, the method is small in modeling error, more convenient and easier to implement, has applicability in a quite wide working condition domain and can be used for achieving abrasion fault diagnosis of the industrial plunger pump.

Description

Technical Field

[0001] The invention belongs to the technical field of hydraulic components, and in particular relates to a method for identifying the wear degree of internal friction pairs of an axial piston pump based on a leakage coefficient. Background Art

[0002] As a hydraulic power element, swash plate axial piston pumps (plunger pumps) are widely used in hydraulic transmission systems in various fields, including aerospace, due to their advantages such as high pressure, high power density, and easy variable adjustment. Among the many potential failures of plunger pumps, wear of key friction pairs is particularly prone to occur. Wear and degradation of these key friction pairs can lead to increased leakage and decreased performance, and can even become a decisive factor affecting the operating performance and service life of plunger pumps. Therefore, real-time detection, identification, and diagnosis of wear failures of friction pairs within plunger pumps are crucial for achieving predictive maintenance of plunger pumps.

[0003] Plunger pump fault diagnosis technologies can be categorized into model-based, data-based, and digital-analog fusion. Compared to model-based or data-based fault diagnosis technologies, the data-driven and mechanism-based fusion approach offers both interpretability and high model deployment efficiency, as well as higher model accuracy.

[0004] Existing methods for diagnosing wear faults in piston pumps using digital-analog fusion drive systems all rely on a mechanistic model of the pump outlet oil pressure. These models ignore oil temperature fluctuations and assume uniform friction pair clearances when calculating friction pair leakage. However, thermal effects can affect pump flow properties, and friction pair wear exhibits significant non-uniformity. Consequently, these assumptions and simplifications can lead to significant modeling errors, negatively impacting identification and diagnostic results, such as causing them to exhibit physical inconsistencies. Furthermore, existing methods use physical information neural networks to identify the friction pair clearance parameters in the mechanistic model and then calculate volumetric efficiency as an evaluation metric for pump wear. This approach relies on empirical engineering knowledge of the parameters to be identified (such as the reasonable range of wear friction pair clearances) and a limited amount of sample data for training. Furthermore, it requires the additional calculation of volumetric efficiency as an evaluation metric, making it complex and impractical for practical use. Summary of the Invention

[0005] (1) Technical issues to be solved

[0006] The technical problem to be solved by the present invention is that the current wear fault diagnosis method for axial piston pumps driven by digital-analog fusion has large modeling errors and is relatively complex.

[0007] (2) Technical solution

[0008] To solve the above technical problems, the present invention provides a method for identifying the wear degree of the internal friction pair of an axial piston pump based on the leakage coefficient, the method comprising:

[0009] Step 1: Combined with the leakage coefficient, establish the flow-heat coupling outlet oil pressure mechanism model of the axial piston pump;

[0010] Step 2: Combine the outlet oil pressure and leakage flow monitoring signals of the plunger pump to identify the leakage coefficient in the model; use the leakage coefficient as a quantitative evaluation indicator to identify the degree of wear of the plunger pump: the larger the identified leakage coefficient, the greater the degree of wear of the pump.

[0011] In step 1, the model is constructed based on the lumped parameter method, i.e., the inlet / outlet oil circuits and each plunger cavity of the plunger pump are regarded as cavities, i.e., capacitive elements; the valves and grooves connecting each cavity are regarded as resistive elements; each plunger cavity is connected to the high-pressure / low-pressure oil circuit in sequence through the waist-shaped groove on the distribution plate as the cylinder body rotates; in this way, the plunger pump is abstracted into a multi-cavity interconnected system; for a single plunger cavity, the flow rate of the oil is always in the direction of flowing out of the cavity as the positive direction;

[0012] For the pressure of the oil in each cavity, it is assumed that: the oil flow in the cavity is one-dimensional; the oil properties in the cavity are uniform; heat conduction and radiation within the oil are not considered; the pressure and temperature of the oil in the cavity to be calculated are the average pressure and average temperature of the oil; then, based on the law of conservation of mass, the cavity pressure building equation is obtained as follows:

[0013]

[0014] In the above formula, p is the pressure of the oil in the cavity; t is the time; β is the bulk elastic modulus of the oil in the cavity; V is the volume of the oil in the cavity, that is, the cavity volume; Q i ——Volume flow rate of oil in / out of the cavity. The flow rate into the cavity is set as positive, and vice versa as negative; α p ——Volume expansion coefficient of the oil in the cavity; T——Temperature of the oil in the cavity;

[0015] For the temperature of the oil in each cavity, the following assumptions are made: ignore macroscopic kinetic energy and macroscopic potential energy; do not consider the inlet effect, assume that the temperature of the oil flowing out of the cavity is the same as the average temperature of the oil in the cavity; and assume that the specific enthalpy of the oil flowing out of the cavity is the same as the average specific enthalpy in the cavity; then, according to the law of conservation of energy, the cavity temperature building equation is obtained as follows:

[0016]

[0017] In the above formula: c p ——Isobaric specific heat capacity of oil; m——mass of oil in the cavity; ρ——density of oil; Qin ——Volume flow rate of oil flowing into the cavity; T in ——the temperature of the oil flowing into the cavity; p in ——pressure of the oil flowing into the cavity; h——composite heat transfer coefficient between the cavity and the outside world; A h ——heat exchange area between the cavity and the outside; T a — ambient temperature; —The axial power exchange rate between the cavity and the environment, which represents the energy transferred from the rotating part of the cavity boundary to the outside world in the form of rotational work;

[0018] Considering the accuracy and efficiency of the model, the heat transfer term hA between the cavity and the outside world in the temperature building equation is ignored. h (TT a ), ignoring the changes in oil properties with temperature and pressure, and considering the pressure and temperature of the oil in the inlet oil channel cavity as constant values;

[0019] Furthermore, based on the pressure building equation and the temperature building equation, combined with the oil flow relationship of the outlet oil circuit cavity, an outlet oil circuit oil state model is established; the outlet oil circuit pressure building equation is:

[0020]

[0021] Where N is the total number of plunger pairs, p H is the plunger pump discharge pressure, V hpipe is the volume of the pump outlet cavity, is the flow rate of oil from the i-th plunger cavity to the outlet oil circuit, T H is the temperature of the oil in the outlet oil circuit; Q load is the flow rate of oil in the outlet oil circuit flowing out through the loading throttle valve, calculated by the following formula:

[0022]

[0023] Where C d is the flow coefficient of thin-walled holes, A load is the opening area of ​​the loading throttle valve; the temperature equation of the oil in the outlet oil circuit is:

[0024]

[0025] Where, It represents the temperature of the oil flowing from the i-th plunger cavity to the outlet oil circuit, that is, the temperature of the oil in the i-th plunger cavity; is the pressure of the oil flowing from the i-th plunger chamber to the outlet oil circuit, that is, the pressure of the oil in the i-th plunger chamber; m1 is the mass of the oil in the outlet oil circuit chamber; is the flow direction judgment coefficient. When the oil in the i-th plunger cavity flows into the high-pressure oil circuit, that is, hour, otherwise

[0026] Furthermore, based on the pressure building equation and the temperature building equation, combined with the oil flow relationship of the plunger cavity, the plunger cavity oil state model is established; when the cylinder body rotates, each plunger will rotate around the cylinder body axis under the constraint of the swash plate while making reciprocating linear motion along the plunger hole, causing the volume of the plunger cavity to change, generating a volume flow At the same time, as the plunger cavity rotates, the plunger cavity will be connected and closed with the high-pressure waist-shaped groove and the low-pressure waist-shaped groove in turn, generating flow to the high-pressure waist-shaped groove respectively. and the flow to the low-pressure waist trough In addition, the plunger cavity continuously leaks outward through each friction pair, generating leakage flow The pressure building equation of the plunger cavity is:

[0027]

[0028] Where, Represents the pressure of the oil in the i-th plunger cavity; V pc is the volume of the plunger cavity at any moment, that is:

[0029]

[0030] V pc0 Indicates the maximum volume of the plunger cavity, d p Indicates the plunger diameter, z i represents the displacement of the i-th plunger at any moment and is calculated by the following formula:

[0031]

[0032] Where z i The positive direction is from the valve plate to the swash plate, α represents the swash plate inclination angle, R p Indicates the radius of the cylinder plunger hole distribution circle; is the cylinder body angle, the i=1 plunger is the cylinder body angle The plunger is at the outer dead center and is numbered against the direction of cylinder rotation;

[0033] From this we can get the volume flow for:

[0034]

[0035] Flow rate from the i-th plunger cavity to the high-pressure waist-shaped groove for:

[0036]

[0037] Where, is the connection area between the plunger cavity and the high-pressure waist groove; sgn(x) is the sign judgment function used to determine the direction of flow, which is defined as:

[0038]

[0039] The flow rate of the i-th plunger cavity entering the low-pressure area for:

[0040]

[0041] Where, is the connection area between the plunger cavity and the high-pressure waist groove; the flow rate of the i-th plunger cavity leaking outward through the friction pair is:

[0042]

[0043] Where p a is the shell pressure, K ou is the plunger cavity leakage coefficient; the sum of the leakage flow of each plunger cavity is the overall leakage flow of the plunger pump, that is:

[0044]

[0045] The temperature building equation of the plunger cavity is:

[0046]

[0047] Where m2 is the mass of the oil in the plunger cavity; and is the flow direction judgment coefficient. When the oil flows into the i-th plunger cavity, that is, and hour, and Take 1; otherwise take 0;

[0048] Furthermore, in the model, the connection area between the plunger cavity and the waist groove is calculated. and It is believed that the plunger cavity and the high-pressure waist-shaped groove and low-pressure waist-shaped groove of the valve plate form a flow area that varies with the cylinder body rotation angle. Dynamically changing variable thin-wall throttle; Represents the connection area between the i-th plunger cavity and the high-pressure waist-shaped groove, let represents the connection area between the i-th plunger cavity and the low-pressure waist-shaped groove; define θ' as the dead zone wrap angle of the valve plate, and θ0 as the wrap angle of the bean-shaped hole at the end of the plunger cavity; first, it is deduced that the cylinder body rotates from a specific angle [-π-(θ'-θ0) / 2] to [π-(θ'-θ0) / 2], that is, in a complete rotation cycle, the connection area between the first plunger cavity and the high-pressure waist-shaped groove is The piecewise calculation function is as follows:

[0049]

[0050] Where,

[0051]

[0052] Further calculate the flow area of ​​the i-th plunger cavity and the high-pressure waist groove for

[0053]

[0054] Further calculate the flow area of ​​the i-th plunger cavity and the low-pressure waist groove for

[0055]

[0056] are all periodic functions of 2π, so we have:

[0057]

[0058] Wherein, in step 2, the leakage coefficient K in the model is ou The identification problem is refined into a two-parameter optimization problem as shown below, namely:

[0059]

[0060] Among them, A load is the load throttle valve opening area, error represents the error function between the simulation value and the experimental value of the pump outlet pressure and leakage flow, that is, the optimization objective function; error is defined as follows:

[0061]

[0062] In the above formula, mean(x) represents the mean of x; p exq and p sim Respectively express the test value and simulation value of the pump outlet pressure, q exp and q sim represent the test value and simulation value of the pump leakage flow respectively; λ1 and λ2 are weight coefficients, λ1+λ2=1, which are used to coordinate the weights of the two sub-optimization objectives; at the same time, the simplex search method is used to solve the two-parameter optimization problem;

[0063] The leakage coefficient K is identified by combining the monitoring data of the real-time outlet oil pressure and leakage flow signal of the plunger pump. ou After obtaining the real-time value, the piston pump internal wear degree is quantitatively identified using this as an evaluation index: the identified leakage coefficient K ouThe larger it is, the more serious the overall wear of the plunger pump is. The leakage coefficient value can also be fuzzy converted into a wear degree label for wear fault diagnosis.

[0064] The method combines the leakage coefficient to solve the leakage amount of oil in the plunger cavity when passing through the gaps of each friction pair, and establishes a flow-heat coupling plunger pump outlet oil pressure model; constructs a set of identification algorithms, and identifies the leakage coefficient in the model in combination with the monitoring data of the pump outlet oil pressure and leakage flow; when the plunger pump operates under certain working conditions, the leakage coefficient characterizes the overall wear degree of the pump, and uses this as a quantitative evaluation indicator of the pump wear degree: the larger the identified leakage coefficient, the greater the wear degree of the plunger pump; the leakage coefficient can also be fuzzy converted into a wear degree label for use.

[0065] Among them, compared with the existing plunger pump digital-analog fusion drive wear fault diagnosis method, the method has smaller modeling error and is more convenient and easy to implement.

[0066] The method is applicable in a wide range of working conditions.

[0067] The method can be used to implement wear fault diagnosis of industrial plunger pumps.

[0068] (3) Beneficial effects

[0069] Compared with the existing plunger pump digital-analog fusion wear fault diagnosis method, the plunger pump wear degree identification method based on leakage coefficient proposed in the present invention has the following beneficial effects: (1) Small modeling error. The leakage coefficient is used to solve the leakage amount of oil in the plunger cavity through each friction pair, and considering the thermal effect, a flow-heat coupling model of the oil pressure at the outlet of the plunger pump that is more in line with reality is established; (2) Convenient and direct, easier to implement. The method proposed in the present invention does not rely on engineering experience and training sample data, and the leakage coefficient can be directly used as a diagnostic indicator of the pump wear degree. BRIEF DESCRIPTION OF THE DRAWINGS

[0070] Figure 1 Schematic diagram of the plunger pump throttling loading system.

[0071] Figure 2 It is a lumped parameter model of a piston pump.

[0072] Figure 3 The flow relationship of a single plunger cavity.

[0073] Figure 4 Cylinder angle And the plunger number diagram; n p Is the spindle speed, ODC represents the outer dead point (ODC) of the plunger pump, and IDC represents the inner dead point (IDC) of the plunger pump.

[0074] Figure 5 It is a schematic diagram of the connection and disconnection between the plunger cavity and the high / low pressure waist groove.

[0075] Figure 6 It is a distribution plate structure.

[0076] Figure 7 Flowchart of the proposed wear degree identification method.

[0077] Figure 8a-Figure 8b is the leakage coefficient of the pump with different wear degrees under various setting conditions; Figure 8a In the form of a three-dimensional scatter plot, Figure 8b It is in the form of a two-dimensional scatter plot. DETAILED DESCRIPTION

[0078] In order to make the purpose, content, and advantages of the present invention more clear, the specific implementation methods of the present invention are further described in detail below with reference to the accompanying drawings and examples.

[0079] Example 1

[0080] In this embodiment, it includes:

[0081] Step 1: Establish the flow-heat coupling outlet pressure mechanism model of the axial piston pump.

[0082] Without loss of generality, this paper uses a throttling-loaded plunger pump as a model to illustrate the modeling method. The modeling is based on the lumped parameter method, which treats the plunger pump's inlet / outlet oil circuits and each plunger chamber as a cavities, or capacitive elements; the valves and grooves connecting the cavities are considered resistive elements; and as the cylinder rotates, each plunger chamber is connected to the high-pressure / low-pressure oil circuits through the waist-shaped grooves on the distribution plate. This allows the plunger pump to be abstracted as a multi-cavity interconnected system. For a single plunger chamber, the oil flow rate is always in the direction out of the chamber as the positive direction.

[0083] For the oil pressure in each cavity, we assume that: the oil flow within the cavity is one-dimensional; the oil properties within the cavity are uniform; heat conduction and radiation within the oil are not considered; and the pressure and temperature of the oil within the cavity to be calculated are the average pressure and average temperature of the oil. Then, based on the law of conservation of mass, we can obtain the cavity pressure buildup equation shown below:

[0084]

[0085] In the above formula, p is the pressure of the oil in the cavity; t is the time; β is the bulk elastic modulus of the oil in the cavity; V is the volume of the oil in the cavity, that is, the cavity volume; Q i ——Volume flow rate of oil in / out of the cavity. The flow rate into the cavity is set as positive, and vice versa as negative; α p——Volume expansion coefficient of the oil in the cavity; T——Temperature of the oil in the cavity.

[0086] For the temperature of the oil in each cavity, we assume that: the macroscopic kinetic energy and macroscopic potential energy are ignored; the inlet effect is not considered, and the temperature of the oil flowing out of the cavity is assumed to be the same as the average temperature of the oil in the cavity; and the specific enthalpy of the oil flowing out of the cavity is assumed to be the same as the average specific enthalpy in the cavity. Then, according to the law of conservation of energy, the cavity temperature equation can be obtained as shown below:

[0087]

[0088] In the above formula: c p ——Isobaric specific heat capacity of oil; m——mass of oil in the cavity; ρ——density of oil; Q in ——Volume flow rate of oil flowing into the cavity; T in ——the temperature of the oil flowing into the cavity; p in ——pressure of the oil flowing into the cavity; h——composite heat transfer coefficient between the cavity and the outside world; A h ——heat exchange area between the cavity and the outside; T a — ambient temperature; ——The axial power exchange flow between the cavity and the environment, which represents the energy transferred to the outside world by the rotating part of the cavity boundary in the form of rotational work.

[0089] Considering the accuracy and computational efficiency of the model, the heat transfer term hA between the cavity and the outside world in the temperature building equation is ignored. h (TT a ), ignoring the changes in oil properties with temperature and pressure, and considering the pressure and temperature of the oil in the inlet oil circuit cavity as constant values.

[0090] Furthermore, based on the pressure buildup equation and temperature buildup equation, combined with the oil flow relationship of the outlet oil circuit chamber, an outlet oil circuit state model was established. The outlet oil circuit of the plunger pump is connected to each plunger chamber through the high-pressure waist-shaped groove of the distribution plate on one side and to the loading throttle valve on the other side. Each plunger chamber passes through the high-pressure waist-shaped groove in turn, discharges oil into the outlet oil circuit, and then flows into the oil tank through the loading throttle valve. Therefore, the pressure buildup equation of the outlet oil circuit is:

[0091]

[0092] Where N is the total number of plunger pairs, p H is the plunger pump discharge pressure, V hpipe is the volume of the pump outlet cavity, is the flow rate of oil from the i-th plunger cavity to the outlet oil circuit, T H is the temperature of the oil in the outlet oil circuit; Q loadis the flow rate of oil in the outlet oil circuit flowing out through the loading throttle valve, which can be calculated by the following formula:

[0093]

[0094] Where C d is the flow coefficient of thin-walled holes, A load is the opening area of ​​the loading throttle valve. The temperature equation of the oil in the outlet oil circuit is:

[0095]

[0096] Where, It represents the temperature of the oil flowing from the i-th plunger cavity to the outlet oil circuit, that is, the temperature of the oil in the i-th plunger cavity; is the pressure of the oil flowing from the i-th plunger chamber to the outlet oil circuit, that is, the pressure of the oil in the i-th plunger chamber; m1 is the mass of the oil in the outlet oil circuit cavity. is the flow direction judgment coefficient. When the oil in the i-th plunger cavity flows into the high-pressure oil circuit, that is, hour, otherwise

[0097] Furthermore, based on the pressure and temperature building equations, combined with the oil flow relationship of the plunger cavity, a plunger cavity oil state model is established. When the cylinder rotates, each plunger will rotate around the cylinder axis under the constraint of the swash plate while making reciprocating linear motion along the plunger hole, causing the volume of the plunger cavity to change, generating a volume flow rate. At the same time, as the plunger cavity rotates, the plunger cavity will be connected and closed with the high-pressure waist-shaped groove and the low-pressure waist-shaped groove in turn, generating flow to the high-pressure waist-shaped groove respectively. and the flow to the low-pressure waist trough In addition, the plunger cavity continuously leaks outward through each friction pair, generating leakage flow Therefore, the pressure building equation of the plunger cavity is:

[0098]

[0099] Where, Represents the pressure of the oil in the i-th plunger cavity; V pc is the volume of the plunger cavity at any moment, that is:

[0100]

[0101] V pc0 Indicates the maximum volume of the plunger cavity, d p Indicates the plunger diameter, z i represents the displacement of the i-th plunger at any moment and is calculated by the following formula:

[0102]

[0103] Where z i The positive direction is from the valve plate to the swash plate, α represents the swash plate inclination angle, R p Indicates the radius of the cylinder plunger hole distribution circle. is the cylinder body angle, the i=1 plunger is the cylinder body angle The plunger is at the outer dead center when the cylinder is rotated.

[0104] From this we can get the volume flow for:

[0105]

[0106] Flow rate from the i-th plunger cavity to the high-pressure waist-shaped groove for:

[0107]

[0108] Where, is the connection area between the plunger cavity and the high-pressure waist groove; sgn(x) is the sign judgment function used to determine the direction of flow, which is defined as:

[0109]

[0110] The flow rate of the i-th plunger cavity entering the low-pressure area for:

[0111]

[0112] Where, is the connection area between the plunger cavity and the high-pressure waist groove. The flow rate of the i-th plunger cavity leaking outward through the friction pair is

[0113]

[0114] Where p a is the shell pressure, K ou is the plunger cavity leakage coefficient, which reflects the degree of oil leakage in the plunger cavity under a certain pressure. The sum of the leakage flow of each plunger cavity is the overall leakage flow of the plunger pump, that is:

[0115]

[0116] The temperature building equation of the plunger cavity is:

[0117]

[0118] Where m2 is the mass of oil in the plunger cavity. and is the flow direction judgment coefficient. When the oil flows into the i-th plunger cavity, that is, and hour, and Takes 1; otherwise takes 0.

[0119] Furthermore, in the calculation process, the connection area between the plunger cavity and the waist groove is required. and When the cylinder body rotates relative to the valve plate, the plunger cavity in the cylinder body will be connected and disconnected with the high-pressure waist-shaped groove and low-pressure waist-shaped groove of the valve plate through the bean-shaped hole at the tail end. It can be considered that the plunger cavity and the high-pressure waist-shaped groove and low-pressure waist-shaped groove of the valve plate form a flow area that changes with the rotation angle of the cylinder body. Dynamically changing variable thin-wall throttle. Represents the connection area between the i-th plunger cavity and the high-pressure waist-shaped groove, let represents the connection area between the i-th plunger cavity and the low-pressure waist-shaped groove; define θ' as the dead zone wrap angle of the valve plate, and θ0 as the wrap angle of the bean-shaped hole at the end of the plunger cavity. First, it is deduced that the cylinder body rotates from a specific angle [-π-(θ'-θ0) / 2] to [π-(θ'-θ0) / 2], that is, in a complete rotation cycle, the connection area between the first plunger cavity and the high-pressure waist-shaped groove is The piecewise calculation function is as follows:

[0120]

[0121] Where,

[0122]

[0123]

[0124] At the same time, since the flow area of ​​other plunger cavities and high-pressure waist-shaped grooves changes with the cylinder body angle in exactly the same way, there is only a phase difference. Based on the above characteristics, the flow area of ​​the i-th plunger cavity and the high-pressure waist-shaped groove can be further calculated. for

[0125]

[0126] Since the waist-shaped grooves in the high and low pressure areas of the distribution plate are symmetrical relative to the y-axis, the flow area between the i-th plunger cavity and the low pressure waist-shaped groove can be further calculated. for

[0127]

[0128] Flow area of ​​each plunger cavity are all periodic functions of 2π, and we have:

[0129]

[0130] Step 2: Identification of leakage coefficient and wear degree

[0131] When the plunger pump works under certain working conditions, the leakage degree and leakage coefficient K of the plunger pump ou It is positively correlated with the degree of wear. Therefore, the leakage coefficient can be used as an evaluation index to quantitatively identify the degree of wear of the plunger pump.

[0132] The leakage coefficient of the plunger pump is obtained by real-time identification by combining the monitoring data of the pump external characteristic signal. In the established model, the load throttle valve opening area A load In practice, it is difficult to measure in real time, and it will also affect the outlet pressure of the pump. Therefore, the leakage coefficient K ou The identification of the leakage coefficient K is actually ou and load throttle valve opening area A load In summary, the leakage coefficient K in the model ou The identification problem can be refined into a two-parameter optimization problem as shown below, namely:

[0133]

[0134] Here, error represents the error function between the simulated and experimental values ​​of the pump outlet pressure and leakage flow, i.e., the optimization objective function. The value of this error function should be related to both the error in the pump outlet pressure and the error in the leakage flow, so that during the optimization process, the error function value error is sufficiently small if and only if both the error in the outlet pressure and the error in the leakage flow are sufficiently small. Here, error is defined as follows:

[0135]

[0136] In the above formula, mean(x) represents the mean of x; p exq and p sim Respectively express the test value and simulation value of the pump outlet pressure, q exp and q sim where λ1 and λ2 represent the measured and simulated values ​​of the pump leakage flow, respectively; λ1 and λ2 are weight coefficients, λ1 + λ2 = 1, used to coordinate the weights of the two sub-optimization objectives. Meanwhile, the simplex search method is used to solve the dual-parameter optimization problem.

[0137] The leakage coefficient K is identified by combining the monitoring data of the real-time outlet oil pressure and leakage flow signal of the plunger pump. ou After obtaining the real-time value of the piston pump, it can be used as an evaluation index to quantitatively identify the degree of internal wear of the piston pump: the identified leakage coefficient K ou The larger it is, the more serious the overall wear of the plunger pump is.

[0138] Example 2

[0139] In this embodiment, it includes:

[0140] Step 1: Establish the flow-heat coupling outlet pressure mechanism model of the axial piston pump.

[0141] The throttling loaded plunger pump is used as the model to illustrate the modeling method. The system principle is as follows: Figure 1 As shown. The modeling is based on the idea of ​​lumped parameter method, that is, the inlet / outlet oil circuits and each plunger cavity of the plunger pump are regarded as cavities, that is, capacitive elements; the valves and grooves connecting each cavity are regarded as resistive elements; each plunger cavity is connected to the high-pressure / low-pressure oil circuit through the waist-shaped groove on the distribution plate in turn as the cylinder rotates. In this way, the plunger pump can be abstracted into a Figure 2 The multi-cavity interconnected system shown in Figure 1. For a single plunger cavity, the oil flow relationship is as follows: Figure 3 As shown in the figure, the flow rate of oil in the plunger cavity is in the direction of flowing out of the cavity as the positive direction.

[0142] For the oil pressure in each cavity, we assume that: the oil flow within the cavity is one-dimensional; the oil properties within the cavity are uniform; heat conduction and radiation within the oil are not considered; and the pressure and temperature of the oil within the cavity to be calculated are the average pressure and average temperature of the oil. Then, based on the law of conservation of mass, we can obtain the cavity pressure buildup equation shown below:

[0143]

[0144] In the above formula, p is the pressure of the oil in the cavity; t is the time; β is the bulk elastic modulus of the oil in the cavity; V is the volume of the oil in the cavity, that is, the cavity volume; Q i ——Volume flow rate of oil in / out of the cavity. The flow rate into the cavity is set as positive, and vice versa as negative; α p ——Volume expansion coefficient of the oil in the cavity; T——Temperature of the oil in the cavity.

[0145] For the temperature of the oil in each cavity, we assume that: the macroscopic kinetic energy and macroscopic potential energy are ignored; the inlet effect is not considered, and the temperature of the oil flowing out of the cavity is assumed to be the same as the average temperature of the oil in the cavity; and the specific enthalpy of the oil flowing out of the cavity is assumed to be the same as the average specific enthalpy in the cavity. Then, according to the law of conservation of energy, the cavity temperature equation can be obtained as shown below:

[0146]

[0147] In the above formula: c p ——Isobaric specific heat capacity of oil; m——mass of oil in the cavity; ρ——density of oil; Q in ——Volume flow rate of oil flowing into the cavity; T in ——the temperature of the oil flowing into the cavity; pin ——pressure of the oil flowing into the cavity; h——composite heat transfer coefficient between the cavity and the outside world; A h ——heat exchange area between the cavity and the outside; T a — ambient temperature; ——The axial power exchange flow between the cavity and the environment, which represents the energy transferred to the outside world by the rotating part of the cavity boundary in the form of rotational work.

[0148] Considering the accuracy and efficiency of the model comprehensively, the heat transfer term hA between the cavity and the outside world is ignored in the temperature building equation. h (TT a ), ignoring the changes in oil properties with temperature and pressure, and considering the pressure and temperature of the oil in the inlet oil circuit cavity as constant values.

[0149] Furthermore, based on the pressure buildup equation and temperature buildup equation, combined with the oil flow relationship of the outlet oil circuit chamber, an outlet oil circuit state model was established. The outlet oil circuit of the plunger pump is connected to each plunger chamber through the high-pressure waist-shaped groove of the distribution plate on one side and to the loading throttle valve on the other side. Each plunger chamber passes through the high-pressure waist-shaped groove in turn, discharges oil into the outlet oil circuit, and then flows into the oil tank through the loading throttle valve. Therefore, the pressure buildup equation of the outlet oil circuit is:

[0150]

[0151] Where N is the total number of plunger pairs, p H is the plunger pump discharge pressure, V hpipe is the volume of the pump outlet cavity, is the flow rate of oil from the i-th plunger cavity to the outlet oil circuit, T H is the temperature of the oil in the outlet oil circuit; Q load is the flow rate of oil in the outlet oil circuit flowing out through the loading throttle valve, which can be calculated by the following formula:

[0152]

[0153] Where C d is the flow coefficient of thin-walled holes, A load is the opening area of ​​the loading throttle valve. The temperature equation of the oil in the outlet oil circuit is:

[0154]

[0155] Where, It represents the temperature of the oil flowing from the i-th plunger cavity to the outlet oil circuit, that is, the temperature of the oil in the i-th plunger cavity; is the pressure of the oil flowing from the i-th plunger chamber to the outlet oil circuit, that is, the pressure of the oil in the i-th plunger chamber; m1 is the mass of the oil in the outlet oil circuit cavity. is the flow direction judgment coefficient. When the oil in the i-th plunger cavity flows into the high-pressure oil circuit, that is, hour, otherwise

[0156] Furthermore, based on the pressure and temperature building equations, combined with the oil flow relationship of the plunger cavity, a plunger cavity oil state model is established. When the cylinder rotates, each plunger will rotate around the cylinder axis under the constraint of the swash plate while making reciprocating linear motion along the plunger hole, causing the volume of the plunger cavity to change, generating a volume flow rate. At the same time, as the plunger cavity rotates, the plunger cavity will be connected and closed with the high-pressure waist-shaped groove and the low-pressure waist-shaped groove in turn, generating flow to the high-pressure waist-shaped groove respectively. and the flow to the low-pressure waist trough In addition, the plunger cavity continuously leaks outward through each friction pair, generating leakage flow Therefore, the pressure building equation of the plunger cavity is:

[0157]

[0158] Where, Represents the pressure of the oil in the i-th plunger cavity; V pc is the volume of the plunger cavity at any moment, that is:

[0159]

[0160] V pc0 Indicates the maximum volume of the plunger cavity, d p Indicates the plunger diameter, z i represents the displacement of the i-th plunger at any moment and is calculated by the following formula:

[0161]

[0162] Where z i The positive direction is from the valve plate to the swash plate, α represents the swash plate inclination angle, R p Indicates the radius of the cylinder plunger hole distribution circle. is the cylinder body angle, the i=1 plunger is the cylinder body angle The plunger is at the outer dead center and is marked against the direction of cylinder rotation, such as Figure 4 shown.

[0163] From this we can get the volume flow for:

[0164]

[0165] Flow rate from the i-th plunger cavity to the high-pressure waist-shaped groove for:

[0166]

[0167] Where, is the connection area between the plunger cavity and the high-pressure waist groove; sgn(x) is the sign judgment function used to determine the direction of flow, which is defined as:

[0168]

[0169] The flow rate of the i-th plunger cavity entering the low-pressure area for:

[0170]

[0171] Where, is the connection area between the plunger cavity and the high-pressure waist groove. The flow rate of the i-th plunger cavity leaking outward through the friction pair is

[0172]

[0173] Where p a is the shell pressure, K ou is the plunger cavity leakage coefficient, which reflects the degree of oil leakage in the plunger cavity under a certain pressure. The sum of the leakage flow of each plunger cavity is the overall leakage flow of the plunger pump, that is:

[0174]

[0175] The temperature building equation of the plunger cavity is:

[0176]

[0177] Where m2 is the mass of oil in the plunger cavity. and is the flow direction judgment coefficient. When the oil flows into the i-th plunger cavity, that is, and hour, and Takes 1; otherwise takes 0.

[0178] Furthermore, in the calculation process, the connection area between the plunger cavity and the waist groove is required. and When the cylinder body rotates relative to the valve plate, the plunger cavity in the cylinder body will be connected and disconnected with the high-pressure waist-shaped groove and low-pressure waist-shaped groove of the valve plate in sequence through the bean-shaped hole at the tail end. Figure 5 It can be considered that the plunger cavity and the high-pressure waist-shaped groove and low-pressure waist-shaped groove of the distribution plate form a flow area that changes with the cylinder body angle. Dynamically changing variable thin-wall throttle. Represents the connection area between the i-th plunger cavity and the high-pressure waist-shaped groove, let Represents the connection area between the i-th plunger cavity and the low-pressure waist-shaped groove; the structure of the distribution plate is as follows Figure 6 First, it is deduced that the cylinder rotates from a specific angle [-π-(θ'-θ0) / 2] to [π-(θ'-θ0) / 2], that is, the connection area between the first plunger cavity and the high-pressure waist groove in a complete rotation cycle is The piecewise calculation function is as follows:

[0179]

[0180] Where,

[0181]

[0182] At the same time, since the flow area of ​​other plunger cavities and high-pressure waist-shaped grooves changes with the cylinder body angle in exactly the same way, there is only a phase difference. Based on the above characteristics, the flow area of ​​the i-th plunger cavity and the high-pressure waist-shaped groove can be further calculated. for

[0183]

[0184] Since the waist-shaped grooves in the high and low pressure areas of the distribution plate are symmetrical relative to the y-axis, the flow area between the i-th plunger cavity and the low pressure waist-shaped groove can be further calculated. for

[0185]

[0186] Flow area of ​​the plunger cavity are all periodic functions of 2π, so we have:

[0187]

[0188] Step 2: Identification of leakage coefficient and wear degree.

[0189] When the plunger pump works under certain working conditions, the leakage degree and leakage coefficient K of the plunger pump ou It is positively correlated with the degree of wear. Therefore, the leakage coefficient can be used as an evaluation index to quantitatively identify the degree of wear of the plunger pump.

[0190] The leakage coefficient of the plunger pump is obtained by real-time identification by combining the monitoring data of the pump external characteristic signal. In the established model, the load throttle valve opening area A load In practice, it is difficult to measure in real time, and it will also affect the outlet pressure of the pump. Therefore, the leakage coefficient K ou The identification of the leakage coefficient K is actually ou and load throttle valve opening area A load In summary, the leakage coefficient K in the modelou The identification problem can be refined into a two-parameter optimization problem as shown below, namely:

[0191]

[0192] Where error represents the error function between the simulated and experimental values ​​of the pump outlet pressure and leakage flow, i.e., the optimization objective function. The value of this error function should be related to both the error in the pump outlet pressure and the error in the leakage flow, so that during the optimization process, the error function value error is sufficiently small if and only if both the error in the outlet pressure and the error in the leakage flow are sufficiently small. Define error as follows:

[0193]

[0194] In the above formula, mean(x) represents the mean value of x in a certain period of time; p exq and p sim Respectively express the test value and simulation value of the pump outlet pressure, q exp and q sim Represent the test value and simulation value of the pump leakage flow respectively; λ1 and λ2 are weight coefficients, λ1+λ2=1, which are used to coordinate the weights of the two sub-optimization objectives. At the same time, the simplex search method is used to solve the two-parameter optimization problem, and the termination tolerance of the function value and the termination tolerance of the variable are both set to 10 -2 .

[0195] The leakage coefficient K is identified by combining the monitoring data of the real-time outlet oil pressure and leakage flow signal of the plunger pump. ou After obtaining the real-time value of the piston pump, it can be used as an evaluation index to quantitatively identify the degree of internal wear of the piston pump: the identified leakage coefficient K ou The larger the value is, the more serious the overall wear of the plunger pump is. The process of the proposed wear identification method is as follows: Figure 7 shown.

[0196] In this embodiment, by replacing some of the plunger pairs in the healthy plunger pair group with worn plunger pairs, different degrees of wear faults are injected into the healthy plunger pump. Fault injection is performed on a certain type of 9-plunger axial piston pump with a displacement of 71ml / r, and three types of pumps with different degrees of wear are set, which are recorded as slight wear, moderate wear and severe wear. The outlet oil pressure and leakage flow signal test experiments are carried out on the healthy pump and the three types of pumps with different degrees of wear. The pump speed n in the experiment is p The speeds are set to 500 rpm, 1000 rpm and 1500 rpm respectively, and the pressure p HThe pressures were set to 10 MPa, 15 MPa, and 20 MPa, for a total of nine operating condition combinations. For each plunger pump, 1-minute outlet oil pressure and leakage flow rate signal tests were conducted under these nine operating conditions, resulting in 36 sets of data. After obtaining the signal monitoring data, the sliding window method was used to reduce noise on the collected signal data. The proposed method was then used to identify the leakage coefficient of pumps with various degrees of wear under each operating condition.

[0197] The leakage coefficient identification results of pumps with various wear levels under various setting conditions are as follows: Figure 8a-Figure 8b The results under the working conditions of 1000rpm and 15MPa are shown in Table 1:

[0198] Table 1 Identification results of leakage coefficient (n p =1000rpm,p H =15MPa)

[0199]

[0200] from Figure 8a As can be seen from Table 1, for a plunger pump operating under certain operating conditions, its leakage coefficient increases significantly as the pump wear increases. The identified leakage coefficient not only has a positive correlation with the pump wear level but is also very sensitive to changes in wear level. This demonstrates that the proposed wear identification method is effective.

[0201] At the same time from Figure 8a-Figure 8b It can also be seen that since the leakage coefficient represents the leakage degree of the pump, it is affected by both the working conditions and the degree of wear. When the working conditions change, even if the degree of wear of the pump remains unchanged, the leakage coefficient will also change. Figure 8a and Figure 8b As can be seen in the figure, the leakage coefficient does not vary significantly with operating conditions. Figure 8(b) clearly demonstrates that, for the specified operating conditions and wear levels, while the leakage coefficients of pumps with the same wear level vary under different operating conditions, the fluctuations are small, demonstrating a clear clustering pattern. Furthermore, the leakage coefficient clusters for pumps with different wear levels under different operating conditions do not intersect. This demonstrates that the proposed method of using leakage coefficient as an indicator for evaluating pump wear is applicable across a wide range of operating conditions.

[0202] In practical applications, the leakage coefficient value can be fuzzyized into a wear degree label. For example, in this embodiment, the leakage coefficient K can be set ou ∈(0,8.4] is a healthy pump, K ou ∈(8.4,68.7] is slight wear, K ou ∈(68.7,150.0] is moderate wear, K ou∈(150,∞] is severe wear, which is used to diagnose wear failure of plunger pump; the unit of leakage coefficient is [×10 -14 m 3 / (s·Pa)].

[0203] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the technical principles of the present invention. These improvements and modifications should also be regarded as the scope of protection of the present invention.

Claims

1. A method for identifying the wear degree of the internal friction pair of an axial piston pump based on leakage coefficient, characterized in that: The method comprises: Step 1: Combined with the leakage coefficient, establish the flow-heat coupling outlet oil pressure mechanism model of the axial piston pump; Step 2: Combine the outlet oil pressure and leakage flow monitoring signals of the plunger pump to identify the leakage coefficient in the model; use the leakage coefficient as a quantitative evaluation indicator to identify the degree of wear of the plunger pump: the larger the identified leakage coefficient, the greater the degree of wear of the pump.

2. The method for identifying the wear degree of the internal friction pair of an axial piston pump based on the leakage coefficient according to claim 1, characterized in that: In step 1, the model is constructed based on the lumped parameter method. The inlet / outlet oil circuits and each plunger cavity of the plunger pump are regarded as cavities, i.e., capacitive elements. The valves and grooves connecting the cavities are regarded as resistive elements. As the cylinder rotates, each plunger cavity is connected to the high-pressure / low-pressure oil circuit through the waist-shaped groove on the distribution plate. In this way, the plunger pump is abstracted into a multi-cavity interconnected system. For a single plunger cavity, the flow rate of the oil is always in the direction of outflow from the cavity as the positive direction. For the pressure of the oil in each cavity, it is assumed that: the oil flow in the cavity is one-dimensional; the oil properties in the cavity are uniform; heat conduction and radiation within the oil are not considered; the pressure and temperature of the oil in the cavity to be calculated are the average pressure and average temperature of the oil; then, based on the law of conservation of mass, the cavity pressure building equation is obtained as follows: In the above formula, p is the pressure of the oil in the cavity; t is the time; β is the bulk elastic modulus of the oil in the cavity; V is the volume of the oil in the cavity, that is, the cavity volume; Q i ——Volume flow rate of oil in / out of the cavity. The flow rate into the cavity is set as positive, and vice versa as negative; α p ——Volume expansion coefficient of the oil in the cavity; T——Temperature of the oil in the cavity; For the temperature of the oil in each cavity, the following assumptions are made: ignore macroscopic kinetic energy and macroscopic potential energy; do not consider the inlet effect, assume that the temperature of the oil flowing out of the cavity is the same as the average temperature of the oil in the cavity; and assume that the specific enthalpy of the oil flowing out of the cavity is the same as the average specific enthalpy in the cavity; then, according to the law of conservation of energy, the cavity temperature building equation is obtained as follows: In the above formula: c p ——Isobaric specific heat capacity of oil; m——mass of oil in the cavity; ρ——density of oil; Q in ——Volume flow rate of oil flowing into the cavity; T in ——the temperature of the oil flowing into the cavity; p in ——pressure of the oil flowing into the cavity; h——composite heat transfer coefficient between the cavity and the outside world; A h ——heat exchange area between the cavity and the outside; T a — ambient temperature; —The axial power exchange rate between the cavity and the environment, which represents the energy transferred from the rotating part of the cavity boundary to the outside world in the form of rotational work; Considering the accuracy and efficiency of the model, the heat transfer term hA between the cavity and the outside world in the temperature building equation is ignored. h (TT a ), ignoring the changes in oil properties with temperature and pressure, and considering the pressure and temperature of the oil in the inlet oil channel cavity as constant values; Furthermore, based on the pressure building equation and the temperature building equation, combined with the oil flow relationship of the outlet oil circuit cavity, an outlet oil circuit oil state model is established; the outlet oil circuit pressure building equation is: Where N is the total number of plunger pairs, p H is the plunger pump discharge pressure, V hpipe is the volume of the pump outlet cavity, is the flow rate of oil from the i-th plunger cavity to the outlet oil circuit, T H is the temperature of the oil in the outlet oil circuit; Q load is the flow rate of oil in the outlet oil circuit flowing out through the loading throttle valve, calculated by the following formula: Where C d is the flow coefficient of thin-walled holes, A load is the opening area of ​​the loading throttle valve; the temperature equation of the oil in the outlet oil circuit is: Where, It represents the temperature of the oil flowing from the i-th plunger cavity to the outlet oil circuit, that is, the temperature of the oil in the i-th plunger cavity; is the pressure of the oil flowing from the i-th plunger chamber to the outlet oil circuit, that is, the pressure of the oil in the i-th plunger chamber; m1 is the mass of the oil in the outlet oil circuit chamber; is the flow direction judgment coefficient. When the oil in the i-th plunger cavity flows into the high-pressure oil circuit, that is, hour, otherwise Furthermore, based on the pressure building equation and the temperature building equation, combined with the oil flow relationship of the plunger cavity, the plunger cavity oil state model is established; when the cylinder body rotates, each plunger will rotate around the cylinder body axis under the constraint of the swash plate while making reciprocating linear motion along the plunger hole, causing the volume of the plunger cavity to change, generating a volume flow At the same time, as the plunger cavity rotates, the plunger cavity will be connected and closed with the high-pressure waist-shaped groove and the low-pressure waist-shaped groove in turn, generating flow to the high-pressure waist-shaped groove respectively. and the flow to the low-pressure waist trough In addition, the plunger cavity continuously leaks outward through each friction pair, generating leakage flow The pressure building equation of the plunger cavity is: Where, Represents the pressure of the oil in the i-th plunger cavity; V pc is the volume of the plunger cavity at any moment, that is: V pc0 Indicates the maximum volume of the plunger cavity, d p Indicates the plunger diameter, z i represents the displacement of the i-th plunger at any moment and is calculated by the following formula: Where z i The positive direction is from the valve plate to the swash plate, α represents the swash plate inclination angle, R p Indicates the radius of the cylinder plunger hole distribution circle; is the cylinder body angle, the i=1 plunger is the cylinder body angle The plunger is at the outer dead center and is numbered against the direction of cylinder rotation; From this we can get the volume flow for: Flow rate from the i-th plunger cavity to the high-pressure waist-shaped groove for: Where, is the connection area between the plunger cavity and the high-pressure waist groove; sgn(x) is the sign judgment function used to determine the direction of flow, which is defined as: The flow rate of the i-th plunger cavity entering the low-pressure area for: Where, is the connection area between the plunger cavity and the high-pressure waist groove; the flow rate of the i-th plunger cavity leaking outward through the friction pair is: Where p a is the shell pressure, K ou is the plunger cavity leakage coefficient; the sum of the leakage flow of each plunger cavity is the overall leakage flow of the plunger pump, that is: The temperature building equation of the plunger cavity is: Where m2 is the mass of the oil in the plunger cavity; and is the flow direction judgment coefficient. When the oil flows into the i-th plunger cavity, that is, and hour, and Take 1; otherwise take 0; Furthermore, in the model, the connection area between the plunger cavity and the waist groove is calculated. and It is believed that the plunger cavity and the high-pressure waist-shaped groove and low-pressure waist-shaped groove of the valve plate form a flow area that varies with the cylinder body rotation angle. Dynamically changing variable thin-wall throttle; Represents the connection area between the i-th plunger cavity and the high-pressure waist-shaped groove, let represents the connection area between the i-th plunger cavity and the low-pressure waist-shaped groove; define θ' as the dead zone wrap angle of the valve plate, and θ0 as the wrap angle of the bean-shaped hole at the end of the plunger cavity; first, it is deduced that the cylinder body rotates from a specific angle [-π-(θ'-θ0) / 2] to [π-(θ'-θ0) / 2], that is, in a complete rotation cycle, the connection area between the first plunger cavity and the high-pressure waist-shaped groove is The piecewise calculation function is as follows: Where, Further calculate the flow area of ​​the i-th plunger cavity and the high-pressure waist groove for Further calculate the flow area of ​​the i-th plunger cavity and the low-pressure waist groove for are all periodic functions of 2π, so we have:

3. The method for identifying the wear degree of the internal friction pair of an axial piston pump based on the leakage coefficient according to claim 2, characterized in that: In step 2, the leakage coefficient K in the model is ou The identification problem is refined into a two-parameter optimization problem as shown below, namely: Among them, A load is the load throttle valve opening area, error represents the error function between the simulation value and the experimental value of the pump outlet pressure and leakage flow, that is, the optimization objective function; error is defined as follows: In the above formula, mean(x) represents the mean of x; p exq and p sim Respectively express the test value and simulation value of the pump outlet pressure, q exp and q sim represent the test value and simulation value of the pump leakage flow respectively; λ1 and λ2 are weight coefficients, λ1+λ2=1, which are used to coordinate the weights of the two sub-optimization objectives; at the same time, the simplex search method is used to solve the two-parameter optimization problem; The leakage coefficient K is identified by combining the monitoring data of the real-time outlet oil pressure and leakage flow signal of the plunger pump. ou After obtaining the real-time value, the piston pump internal wear degree is quantitatively identified using this as an evaluation index: the identified leakage coefficient K ou The larger it is, the more serious the overall wear of the plunger pump is.

4. The method for identifying the wear degree of the internal friction pair of an axial piston pump based on the leakage coefficient according to claim 3, characterized in that: In step 2, the leakage coefficient value may also be fuzzified into a wear degree label for wear fault diagnosis.

5. The method for identifying the wear degree of the internal friction pair of an axial piston pump based on the leakage coefficient according to claim 3, characterized in that: The method combines the leakage coefficient to solve the leakage amount of oil in the plunger cavity when passing through the clearances of each friction pair, and establishes a fluid-thermal coupling plunger pump outlet oil pressure model; constructs a set of identification algorithms, and identifies the leakage coefficient in the model by combining monitoring data of the pump outlet oil pressure and leakage flow; when the plunger pump operates under certain working conditions, the leakage coefficient represents the overall wear degree of the pump, and is used as a quantitative evaluation index of the pump wear degree: the larger the identified leakage coefficient, the greater the wear degree of the plunger pump; the leakage coefficient can also be fuzzy converted into a wear degree label for use.

6. The method for identifying the wear degree of the internal friction pair of an axial piston pump based on the leakage coefficient according to claim 3, characterized in that: Compared with the existing plunger pump digital-analog fusion drive wear fault diagnosis method, the method has smaller modeling error and is more convenient and easy to implement.

7. The method for identifying the wear degree of the internal friction pair of an axial piston pump based on the leakage coefficient according to claim 3, characterized in that: The method is applicable in a wide range of working conditions.

8. The method for identifying the wear degree of the internal friction pair of an axial piston pump based on the leakage coefficient according to claim 3, characterized in that: The method can be used to implement wear fault diagnosis of industrial plunger pumps.

9. The method for identifying the wear degree of the internal friction pair of an axial piston pump based on the leakage coefficient according to claim 3, characterized in that: The method belongs to the technical field of hydraulic components.

10. The method for identifying the wear degree of the internal friction pair of an axial piston pump based on leakage coefficient according to claim 3, characterized in that: The modeling error of the method is small. The leakage coefficient is used to solve the leakage of oil in the plunger cavity through each friction pair. Taking thermal effects into consideration, a fluid-thermal coupling model of the oil pressure at the outlet of the plunger pump that is more in line with reality is established.

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