A method for predicting the early engine change rate of an aeroengine

Abstract

The present invention discloses a method for predicting the early engine change rate of an aeroengine, which includes the following steps carried out in sequence: Step 1, determining the failure rate during the whole-life period of the aeroengine; Step 2, determining the probability of repairable failures under the grass-roots level conditions of the whole aeroengine; Step 3, determining the early engine change rate of the aeroengine without considering the engine change maintenance strategy; Step 4, determining the early engine change rate of the aeroengine when considering the engine change maintenance decision. During the demonstration stage, scheme stage, and early stage of engineering development of the aeroengine, it supports the prediction work of the early engine change rate index, evaluates the feasibility and coordination of the realization of the reliability and supportability design of the aeroengine, provides a basis for the demonstration, scheme design, and engineering design of the reliability and supportability indicators, realizes a method that can support the early prediction of indicators during the demonstration stage, scheme stage, and engineering development stage, and ensures that the index of the early engine change rate meets the requirements through design means.

Description

Technical Field

[0001] The present invention relates to a method for predicting the early engine replacement rate of an aeroengine, belonging to the technical field of aeroengines. Background Art

[0002] As a parameter for measuring the reliability of an aeroengine, the early engine replacement rate (UERR) of an aeroengine is measured by the number of times of early engine replacement caused by engine failures per 1,000 flight hours of the engine. The early engine replacement rate of the engine has long been verified through the statistics and evaluation of field usage data, lacking a method that can support the early prediction of indicators in the demonstration stage, the scheme stage, and the engineering development stage, and it is impossible to ensure the indicator of the early engine replacement rate to meet the requirements through design means.

[0003] The early engine replacement rate of an aeroengine is one of the important indicators affecting the combat readiness integrity of an aircraft. If the early engine replacement rate fails to meet the standard, it will inevitably lead to the situation that the actual deployment quantity of the user's backup engines cannot meet the repair requirements at the grass-roots level of the engines, resulting in insufficient combat readiness integrity of the aircraft due to insufficient available engines. Summary of the Invention

[0004] To solve the above technical problems, the present invention provides a method for predicting the early engine replacement rate of an aeroengine.

[0005] The present invention is achieved through the following technical solutions.

[0006] A method for predicting the early engine replacement rate of an aeroengine provided by the present invention includes the following steps carried out in sequence:

[0007] Step 1, determining the failure rate during the whole-life of the aeroengine;

[0008] Step 2, determining the probability of repairable failures under the grass-roots level conditions of the whole aeroengine;

[0009] Step 3, determining the early engine replacement rate of the aeroengine without considering the engine replacement maintenance strategy;

[0010] Step 4, determining the early engine replacement rate of the aeroengine considering the engine replacement maintenance decision.

[0011] In the step of determining the failure rate during the whole-life of the aeroengine, the failure rate λ of the whole-life of the aeroengine is calculated as:

[0012]

[0013] In the formula:

[0014] T BF —The average time between failures of the whole aeroengine.

[0015] In the step of determining the probability of repairable faults at the grass-roots level of the whole aero-engine, it is mainly divided into the following steps:

[0016] g) Through the analysis of the engine's corrective maintenance tasks, determine the grass-roots corrective maintenance items and maintenance units;

[0017] h) Through reliability allocation and prediction, determine the failure rate λ of the i-th maintenance unit; i ;

[0018] i) Through the failure mode, effects and criticality analysis (FMECA) of the maintenance unit, determine the failure mode and the failure mode frequency ratio of the i-th maintenance unit;

[0019] j) Through the grass-roots maintenance method of the maintenance unit, determine the repairable failure mode and the corresponding failure mode frequency ratio α of the i-th maintenance unit; Rij ;

[0020] k) Based on the repairable failure mode and the corresponding failure mode frequency ratio of the i-th maintenance unit, calculate the probability of repairable faults λ of the i-th maintenance unit; Ri ;

[0021] l) Calculate the probability of repairable faults λ of the whole aero-engine; R .

[0022] The probability of repairable faults λ Ri The calculation formula is as follows:

[0023]

[0024] In the formula:

[0025] λ i —The failure rate of the i-th maintenance unit of the aero-engine, i = 1, 2, 3,..., n, where n is the number of maintenance unit items;

[0026] α Rij —The failure mode frequency ratio of the j-th repairable failure mode of the i-th maintenance unit of the aero-engine, j = 1, 2, 3,..., m, where m is the number of repairable failure mode items of the maintenance unit.

[0027] The calculation of the probability of repairable faults λ of the whole aero-engine R The calculation formula is as follows:

[0028]

[0029] In the formula:

[0030] λ Ri —The repairable failure rate of the i-th maintenance unit of the aero-engine, i = 1, 2, 3,..., n, where n is the number of maintenance unit items.

[0031] The steps for determining the early engine replacement rate of an aero-engine without considering the engine replacement maintenance strategy are as follows: When not considering the aero-engine replacement maintenance strategy and only considering the situation where the aero-engine needs to be replaced in advance due to irreparable failures occurring at the grass-roots level, calculate the early engine replacement rate UERR':

[0032] UERR′ = 1000S(λ - λ R )

[0033] In the formula:

[0034] S — The conversion coefficient between the working time and flight time of the aero-engine;

[0035] λ — The failure rate during the whole-life period of the aero-engine;

[0036] λ R — The probability of repairable failures of the aero-engine for the whole machine.

[0037] The determination of the conversion coefficient between the working time and flight time of the aero-engine is as follows: For aircraft with a short single mission time (1 to 2 hours) and a high sortie rate, the value range of the conversion coefficient is 1.1 < S ≤ 1.2; for aircraft with a long single mission time (more than 2 hours) and a low sortie rate, the value range of the conversion coefficient is 1 < S ≤ 1.1.

[0038] The steps for determining the early engine replacement rate of the aero-engine when considering the engine replacement maintenance decision are determined as follows:

[0039] a) Adopt the average repair time allocation method based on functional complexity to determine the repair time M of the maintenance unit cti ;

[0040] b) Determine the engine replacement time T according to the installation and disassembly requirements of the aero-engine by the aircraft DA ;

[0041] c) Calculate the engine replacement maintenance probability PDA when adopting the engine replacement maintenance decision:

[0042] When: M cti > T DA , λ Rk = λ Ri

[0043]

[0044] In the formula:

[0045] λ Rk—The repairable failure rate of the maintenance unit whose repair time is greater than the engine replacement time, k = 1, 2, 3, …, p, where p is the number of maintenance unit items whose repair time is greater than the engine replacement time;

[0046] λ Ri —The repairable failure rate of the i-th maintenance unit of the aeroengine, i = 1, 2, 3, …, n, where n is the number of maintenance unit items.

[0047] λ R —The repairable failure probability of the whole aeroengine.

[0048] d) Determine the proportion P of the flight time of high-intensity missions within the specified time to the total flight time according to the sortie profile of typical missions of the aircraft HS ;

[0049] e) Calculate the early engine replacement rate UERR of the aeroengine when considering the engine change maintenance decision:

[0050] UERR = 1000S[λ - (1 - P DA P HS )λ R )

[0051] In the formula:

[0052] S—The conversion coefficient between the working time and the flight time of the aeroengine;

[0053] λ—The failure rate during the whole life of the aeroengine;

[0054] λ R —The repairable failure probability of the whole aeroengine;

[0055] P DA —The engine change maintenance probability when adopting the engine change maintenance decision;

[0056] P HS —The proportion of the flight time of high-intensity missions.

[0057] The selection of the average repair time allocation method based on functional complexity includes the following three categories: the allocation method based on failure rate, the equal-proportion allocation method based on similar products, and the allocation method based on functional complexity.

[0058] The beneficial effects of the present invention are as follows: The present invention supports the prediction work of the early engine replacement rate index in the demonstration stage, scheme stage, and early stage of engineering development of aero-engines, evaluates the feasibility and coordination of the realization of the reliability and supportability design of aero-engines, provides a basis for the demonstration, scheme design, and engineering design of reliability and supportability indicators, and realizes a method that can support the early prediction of indicators in the demonstration stage, scheme stage, and engineering development stage. By means of design, the index of the early engine replacement rate is guaranteed to meet the requirements, avoiding the situation where the actual deployment quantity of the user's backup engines cannot meet the repair requirements at the grass-roots level of the engines due to the non-compliance of the engine replacement rate, and the situation where the aircraft combat readiness integrity is insufficient due to the shortage of available engines. Brief Description of the Drawings

[0059] Figure 1 It is a flowchart of the method steps of the present invention. Detailed Embodiment

[0060] The technical solution of the present invention will be further described below, but the scope of protection claimed is not limited thereto.

[0061] Reference Figure 1 .

[0062] A method for predicting the early engine replacement rate of an aero-engine provided by the present application includes the following steps:

[0063] 1. Determine the failure rate during the whole-life period of the aero-engine

[0064] According to the user requirements, determine the mean time between failures index of the whole aero-engine, and determine the failure rate during the life period of the aero-engine.

[0065] Since the aero-engine belongs to a complex electromechanical product, by means of periodic or condition-based preventive maintenance work to maintain the reliability of the engine at a certain level, the failure distribution of the aero-engine during its life period can be approximated as an exponential distribution. Therefore, calculate the failure rate λ of the whole aero-engine during its life period according to Equation (1):

[0066]

[0067] In the formula:

[0068] T BF —Mean time between failures of the whole aero-engine.

[0069] 2. Determine the probability of repairable failures under the grass-roots level conditions of the whole aero-engine

[0070] The main steps are as follows:

[0071] a) Through the analysis of the engine reparative maintenance tasks, determine the grass-roots level reparative maintenance items and maintenance units;

[0072] b) Determine the failure rate λ of the i-th maintenance unit through reliability allocation and prediction i ;

[0073] c) Determine the failure mode and failure mode frequency ratio of the i-th maintenance unit through Failure Mode, Effects and Criticality Analysis (FMECA) of the maintenance unit

[0074] d) Determine the repairable failure modes of the i-th maintenance unit and the corresponding failure mode frequency ratio α through the grass-roots level maintenance method of the maintenance unit Rij ;

[0075] e) Based on the repairable failure modes of the i-th maintenance unit and the corresponding failure mode frequency ratio, calculate the repairable failure probability λRi of the i-th maintenance unit according to Equation (2)

[0076]

[0077] In the formula:

[0078] λ i — The failure rate of the i-th maintenance unit of the aero-engine, i = 1, 2, 3, …, n, where n is the number of maintenance unit items

[0079] α Rij — The failure mode frequency ratio of the j-th repairable failure mode of the i-th maintenance unit of the aero-engine, j = 1, 2, 3, …, m, where m is the number of repairable failure mode items of the maintenance unit

[0080] f) Calculate the repairable failure probability λ of the whole aero-engine according to Equation (3) R 。

[0081]

[0082] In the formula:

[0083] λ Ri — The repairable failure rate of the i-th maintenance unit of the aero-engine, i = 1, 2, 3, …, n, where n is the number of maintenance unit items

[0084] The grass-roots level maintenance unit, maintenance method and repairable failure mode of the aero-engine

[0085] To ensure that the early engine replacement rate meets the requirements, it is necessary to improve the repairable ability of the aero-engine at the grass-roots level. Therefore, it is necessary to analyze the maintenance unit, failure mode and maintenance method to determine the maintenance unit that needs to be repaired at the grass-roots level and its failure mode. According to the structural characteristics of aero-engines such as turbojet, turbofan, turboprop, and turboshaft, the grass-roots level repairable units and failure modes are determined as follows

[0086] a) LRU / LRM

[0087] The main objects of maintenance are Line Replaceable Units (LRUs) and Line Replaceable Modules (LRMs). The main maintenance method is the replacement of LRUs / LRMs. When the maintenance of LRUs / LRMs can be completed by replacement under grass-roots level conditions, the repairable fault modes of LRUs / LRMs cover all fault modes of LRUs / LRMs, and the frequency ratio of repairable fault modes is the sum of the frequency ratios of all fault modes of LRUs / LRMs, that is, equal to 1.

[0088] b) External structural parts

[0089] The main maintenance units are independent external pipelines, brackets, pipe joints, sealing rings, fasteners, clamps and other components. The main maintenance method is replacement. Fault modes such as deformation, scratches, indentations, and paint layer peeling can be repaired by simple structural repairs such as correction, grinding, and spraying. When the maintenance of external structural parts can be completed by replacement under grass-roots level conditions, the repairable fault modes of external structural parts cover all fault modes of external structural parts. When the grass-roots level conditions only allow the maintenance of external structural parts by simple structural repairs, the repairable fault modes only include deformation, scratches, indentations, and paint layer peeling, etc.

[0090] c) Maintenance unit body / flow path structural parts

[0091] For engines designed with maintenance unit bodies, according to the division of maintenance unit bodies, taking a turbofan engine with an afterburner as an example, generally includes: fan, core engine, low-pressure turbine, afterburner, adjustable nozzle, etc. The main maintenance method of the maintenance unit body is replacement. Fault modes such as scratches, indentations, and paint layer peeling can be repaired by simple structural repairs such as grinding and spraying; for engines not designed with maintenance unit bodies, generally only the maintenance of the fan inlet fairing, the first-stage rotor blades of the fan, the afterburner diffuser, and the adjustable tail nozzle is carried out. The main maintenance method is replacement, and some fault modes can be repaired by simple structural repairs such as correction, grinding, and spraying. When the maintenance can be completed by replacing the engine maintenance unit body and the flow path components under grass-roots level conditions, the repairable fault modes of the maintenance unit body / flow path structural parts cover all fault modes of the maintenance unit body / flow path structural parts. When the grass-roots level conditions only allow the maintenance of the maintenance unit body / flow path structural parts by simple structural repairs, the repairable fault modes only include scratches, indentations, and paint layer peeling, etc.

[0092] 3. Determine the early engine replacement rate of an aeroengine when the engine replacement maintenance strategy is not considered

[0093] When not considering the engine replacement maintenance strategy for aero-engines and only considering the situation where the aero-engine needs to be replaced in advance due to an irreparable fault occurring at the grass-roots level, the aero-engine early replacement rate UERR' is calculated according to Equation (4):

[0094] UERR′=1000S(λ - λ R )……………………(4)

[0095] Where:

[0096] S—The conversion coefficient between the working time and flight time of the aero-engine;

[0097] λ—The failure rate during the whole-life period of the aero-engine;

[0098] λ R —The probability of repairable faults of the whole aero-engine.

[0099] The grass-roots level engine replacement maintenance decision for the aero-engine

[0100] The grass-roots level engine replacement maintenance decision for the aero-engine needs to be determined according to the demand of the flight mission for the aircraft sortie rate. When the flight mission is heavy and the demand for the aircraft sortie rate is high, if a fault that needs to be repaired occurs, an engine replacement maintenance decision may be required. When the engine replacement maintenance time is less than the maintenance time of the corrective maintenance items, the backup engine can be activated to replace the faulty engine in advance. After the faulty engine is replaced and repaired in the maintenance workshop or returned to the repair factory, it is redeployed as a backup engine again.

[0101] Determination of the conversion coefficient between the working time and flight time of the aero-engine

[0102] Due to reasons such as ground taxiing, usage support, and maintenance support, the actual working time of the aero-engine is generally higher than the flight time, and its conversion coefficient is mainly affected by the following factors:

[0103] a) The average flight time of the aircraft per mission. The shorter the average flight time per mission, the greater the proportion of the ground working time of the engine required for ground taxiing, usage support, and maintenance support, and the greater the conversion coefficient. Conversely, the conversion coefficient is smaller;

[0104] b) The preventive maintenance frequency of the engine. The greater the preventive maintenance frequency of the engine, the more preventive maintenance times of the engine within the life period, the greater the proportion of the ground working time of the engine required for maintenance operation, and the greater the conversion coefficient. Conversely, the conversion coefficient is smaller;

[0105] c) Mean time between failures of the engine. The shorter the mean time between failures of the engine, the more times of corrective maintenance of the engine within the service life, the greater the proportion of the ground working time of the engine required for maintenance operation, and the greater the conversion coefficient. Conversely, the conversion coefficient is smaller.

[0106] The conversion coefficient can be determined by calculating the working time and flight time consumed by the engine on the ground within the service life. According to the statistical data, for aircraft with short single - mission time (1 to 2 hours) and high sortie rate, the value range of the conversion coefficient is 1.1 < S ≤ 1.2; for aircraft with long single - mission time (more than 2 hours) and low sortie rate, the value range of the conversion coefficient is 1 < S ≤ 1.1.

[0107] 4. Determine the early engine replacement rate of an aero - engine when considering the engine replacement maintenance decision

[0108] During the actual in - field use of an aero - engine, when a fault that requires maintenance occurs, due to tight flight tasks, the engine replacement maintenance decision may be adopted to repair the fault by directly replacing the engine. At this time, it is necessary to consider the proportion of the time of high - intensity sortie missions of the aircraft within the specified time in the total flight time, and judge the probability of adopting engine replacement maintenance when the engine replacement time is less than the repair time of the corrective maintenance items. The early engine replacement rate of an aero - engine when considering the engine replacement maintenance decision is determined according to the following steps:

[0109] a) Adopt the average repair time allocation method based on functional complexity to determine the repair time M of the maintenance unit cti ;

[0110] b) Determine the engine replacement time T according to the installation and disassembly requirements of the aero - engine by the aircraft DA ;

[0111] c) Calculate the engine replacement maintenance probability PDA when adopting the engine replacement maintenance decision according to Equation (5): When: M cti >T DA λ Rk =λ Ri

[0112]

[0113] In the formula:

[0114] λ Rk — The repairable failure rate of the maintenance unit whose repair time is greater than the engine replacement time, k = 1, 2, 3, …, p, where p is the number of maintenance unit items whose repair time is greater than the engine replacement time;

[0115] λ Ri — The repairable failure rate of the i - th maintenance unit of the aero - engine, i = 1, 2, 3, …, n, where n is the number of maintenance unit items.

[0116] λ R — The repairable fault probability of the whole aero-engine.

[0117] d) Determine the proportion P of the flight time of high-intensity missions within the specified time to the total flight time according to the sortie profile of typical aircraft missions HS ;

[0118] e) Calculate the early engine replacement rate UERR considering the engine replacement maintenance decision according to Equation (6):

[0119] UERR = 1000S[λ - (1 - P DA P HS )λ R ………………(6)

[0120] In the formula:

[0121] S — The conversion coefficient between the working time and flight time of the aero-engine;

[0122] λ — The failure rate during the whole-life period of the aero-engine;

[0123] λ R — The repairable fault probability of the whole aero-engine;

[0124] P DA — The engine replacement maintenance probability when adopting the engine replacement maintenance decision;

[0125] P HS — The proportion of the flight time of high-intensity missions.

[0126] The selection of the average repair time allocation method based on function complexity

[0127] The allocation of the average repair time mainly includes the following three categories:

[0128] a) The allocation method based on the failure rate, that is, the less repair time is allocated to the maintenance unit with a higher failure rate, and the more repair time is allocated to the maintenance unit with a lower failure rate.

[0129] b) The equal-proportion allocation method based on similar products, that is, based on the repair time proportion relationship of the maintenance units of similar products, the average repair time is allocated by the analogy method.

[0130] c) The allocation method based on function complexity, that is, considering the relationship between the function of the maintenance unit and the maintenance interface, fault detection and isolation, inspection and debugging. The more complex the function, the more maintenance interfaces, and the more complex the fault detection and isolation, inspection and debugging, the more repair time is allocated. On the contrary, the less repair time is allocated.

[0131] The method of allocating indicators with failure rate as the main factor ignores factors such as the type and quantity of maintenance interfaces determined by the functional complexity and functional implementation approach of work units. That is, the more maintenance interfaces, the higher the quantitative maintainability indicator should be. Also, since work units with higher functional complexity often have higher failure rates, the allocated maintainability indicators are lower, which leads to a serious deviation between the allocation results of maintainability indicators with failure rate as the main factor and the actual engineering data. Especially when there is an order-of-magnitude difference in the failure rates of work units, this situation is particularly serious. This makes the traditional method of allocating the quantitative indicator of mean time to repair with failure rate as the main factor unable to be used in engineering practice. For newly developed products in forward development, due to the lack of data support from similar products, it is difficult to adopt the proportional allocation method based on similar products. Therefore, this method recommends using the mean time to repair allocation method based on functional complexity. By determining the maintenance complexity through the functional items and functional categories allocated to the maintenance units, and then allocating the repair time based on the maintenance complexity factor, the repair time of the maintenance units can be determined more accurately.

[0132] For example, the specific indicator parameters of a certain type of aero-engine installed on a certain fighter are as follows: The mean time to repair (MTTR) of the whole engine is 180 min, the mean time between failures (MTBF) of the whole engine is 210 h, and the disassembly and installation time T DA of the engine is 240 min.

[0133] 1. Determine the failure rate during the whole life of the aero-engine

[0134] Calculate the failure rate λ = 0.0047619 of the aero-engine during its whole life according to Equation (1).

[0135] 2. Determine the repairable failure probability under the grass-roots level conditions of the whole aero-engine

[0136] Through the analysis of corrective maintenance tasks, determine the grass-roots level corrective maintenance items and maintenance units; according to the reliability allocation and prediction report, determine the failure rate λi of the maintenance units; through the failure mode, effects and criticality analysis (FMECA) of the maintenance units, determine the failure modes and failure mode frequency ratios of the maintenance units; according to the grass-roots level maintenance methods of the maintenance units, determine the repairable failure modes and the corresponding failure mode frequency ratios α Rij of the maintenance units; based on the repairable failure modes and the corresponding failure mode frequency ratios of the maintenance units, calculate the repairable failure probability λ of the maintenance units according to Equation (2) Ri ;

[0137] The data of the name, failure rate, repairable failure mode frequency ratio, repairable failure probability and mean time to repair of each grass-roots level maintenance unit are shown in Table 1 below.

[0138] Table 1 Calculation Table of Repairable Fault Data for Grassroots-Level Maintenance Units

[0139]

[0140] Calculate the repairable fault probability λ of the entire aero-engine according to Equation (3) R It is 0.0042724.

[0141] 3. Determine the early engine replacement rate of the aero-engine without considering the engine replacement maintenance strategy

[0142] When not considering the aero-engine replacement maintenance strategy and only considering the situation where the aero-engine needs to be replaced in advance due to irreparable faults at the grassroots level, and at the same time considering the aircraft equipped with this type of engine with a short single mission time and a high sortie rate, through the prediction of the ground working time and flight time of the engine during its life, calculate and determine that the conversion coefficient S between the engine working time and the flight time is 1.12, and calculate the early engine replacement rate UERR' of the aero-engine according to Equation (4):

[0143] UERR' = 1000×1.12×(0.0047619 - 0.0042724) = 0.55 times / 1000 flight hours

[0144] 4. Determine the early engine replacement rate of the aero-engine when considering the engine replacement maintenance decision

[0145] Adopt the average repair time allocation method based on functional complexity, and use the average repair time of the entire engine (MTTR = 180 min) as the input to determine the average repair time M of each maintenance unit cti ; Determine the engine replacement time T according to the installation and disassembly requirements of the aero-engine by the aircraft DA It is 240 min.

[0146] Determine the repairable fault rate λ of the maintenance units with a maintenance time longer than the engine replacement time Rk , specifically the λ of each maintenance unit Rk See Table 2, and then calculate the engine replacement maintenance probability P when adopting the engine replacement maintenance decision according to Equation (5) DA It is 0.5838.

[0147] Table 2 Calculation Table of Early Engine Replacement Rate

[0148]

[0149] According to the typical mission sortie profile of the equipped aircraft, determine the proportion P of the flight time of high-intensity missions HS It is 0.2418.

[0150] The early engine replacement rate UERR considering the engine replacement and maintenance decision is calculated according to Equation (6) as

[0151] UERR = 1000 × 1.12 × [0.0047619 - (1 - 0.5838 × 0.2418) × 0.0042724] = 1.22 times per 1000 flight hours

Claims

1. A method for predicting the early engine change rate of an aeroengine, characterized in that, It includes the following steps carried out in sequence: Step 1, determine the failure rate during the whole-life of the aero-engine; Step 2, determine the repairable failure probability under the grass-roots level conditions of the whole aero-engine; In the step of determining the repairable failure probability under the grass-roots level conditions of the whole aero-engine, it is mainly divided into the following steps: a) Through the analysis of the engine reparative maintenance tasks, determine the grass-roots level reparative maintenance items and maintenance units; b) Determine the failure rate λ of the i-th maintenance unit through reliability allocation and prediction i ; c) Through the Failure Mode, Effects and Criticality Analysis (FMECA) of the maintenance units, determine the failure mode and the failure mode frequency ratio of the i-th maintenance unit; d) Determine the repairable failure modes of the i-th maintenance unit and the corresponding failure mode frequency ratio α through the grass-roots level maintenance method of the maintenance unit Rij ; e) Calculate the repairable fault probability λ of the i-th maintenance unit based on the repairable fault modes of the i-th maintenance unit and the corresponding frequency ratios of the fault modes Ri ; f) Calculate the repairable fault probability λ of the entire aero-engine R ; Step 3, determine the early engine change rate of the aero-engine without considering the engine change maintenance strategy; The step of determining the early engine change rate of the aero-engine without considering the engine change maintenance strategy is to calculate the early engine change rate UERR': UERR′ = 1000S(λ - λ R ) In the formula: S — conversion coefficient between the working time and the flight time of the aero-engine; λ — failure rate during the whole-life of the aero-engine; λ R — Probability of repairable faults in the whole aero-engine; Step 4, determine the early engine change rate of the aero-engine considering the engine change maintenance decision; The step of determining the early engine change rate of the aero-engine considering the engine change maintenance decision is determined by the following steps: a) Adopt the average repair time allocation method based on functional complexity to determine the repair time M of the maintenance unit cti ; b) Determine the engine replacement time T according to the installation and removal requirements of the aircraft for the aero-engine DA ; c) Calculate the engine change maintenance probability PDA when adopting the engine change maintenance decision; When: M cti > T DA , λ Rk = λ Ri In the formula: λ Rk — The repairable failure rate of the maintenance unit whose repair time is greater than the engine replacement time, k = 1, 2, 3, …, p, where p is the number of maintenance unit items whose repair time is greater than the engine replacement time; λ Ri — The repairable failure rate of the i-th maintenance unit of the aero-engine, where i = 1, 2, 3, …, n and n is the number of maintenance unit items; λ R — Probability of repairable faults in the whole aero-engine; d) Determine the proportion P of the flight time of high-intensity missions within the specified time to the total flight time according to the sortie profile of typical aircraft missions. HS ; e) Calculate the early engine change rate UERR of the aero-engine considering the engine change maintenance decision; UERR = 1000S[λ - (1 - P DA P HS )λ R ​ In the formula: S — conversion coefficient between the working time and the flight time of the aero-engine; λ — failure rate during the whole-life of the aero-engine; λ R — Probability of repairable faults of the entire aero-engine; P DA — Probability of engine replacement maintenance when adopting engine replacement maintenance decision; P HS — Proportion of flight time for high-intensity tasks.

2. The method for predicting the early engine change rate of an aeroengine according to claim 1, wherein In the step of determining the failure rate during the whole-life of the aero-engine, calculate the failure rate λ during the whole-life of the aero-engine as: In the formula: T BF — Mean time between failures of the entire aero-engine.

3. The method for predicting the early engine change rate of the aero-engine according to claim 1, characterized in that The repairable fault probability λ Ri The calculation formula is as follows: In the formula: λ i — Failure rate of the i-th maintenance unit of the aero-engine, where i = 1, 2, 3, …, n, and n is the number of maintenance unit items; α Rij — The failure mode frequency ratio of the i-th maintenance unit and the j-th repairable failure mode of the aero-engine, where j = 1, 2, 3, …, m and m is the number of items of the repairable failure modes of the maintenance unit.

4. The method for predicting the early engine change rate of the aero-engine according to claim 1, characterized in that Calculating the repairable fault probability λ of the entire aero-engine R The calculation formula is as follows: In the formula: λ Ri — The repairable failure rate of the i-th maintenance unit of the aero-engine, where i = 1, 2, 3, …, n, and n is the number of maintenance units.

5. The method for predicting the early engine change rate of an aeroengine according to claim 1, characterized in that The determination of the conversion coefficient between the working time and the flight time of the aero-engine is as follows: for an aircraft with a short single mission time of 1 to 2 hours and a high sortie rate, the value range of the conversion coefficient is 1.1 < S ≤ 1.2; for an aircraft with a long single mission time of more than 2 hours and a low sortie rate, the value range of the conversion coefficient is 1 < S ≤ 1.

1.

6. The prediction method for the early engine change rate of an aero-engine according to claim 1, characterized in that: The selection of the average repair time allocation method based on function complexity includes the following three categories: the allocation method based on failure rate, the equal-proportion allocation method based on similar products, and the allocation method based on function complexity.

Images