HK1179691B - Method for detecting the performance of auxiliary power unit - Google Patents

Abstract

The present application discloses a method for detecting performance of an APU, comprising: obtaining EGT (Exhaust Gas Temperature), LCIT (Load Compressor Inlet Temperature), STA (Starting Time), TSR and PT, comparing respectively a difference of EGT and LCIT (i.e., EGT-LCIT), STA, TSR and PT with respective threshold value; assigning a weights to comparison results between the EGT-LCIT, STA, TSR and PT and the respective threshold value; and determining the performance of the APU based on the comparison results considering the weight between the EGT-LCIT, STA, TSR and PT and the respective threshold value.

Description

Performance detection method of auxiliary power unit

Technical Field

The invention relates to a method for detecting the running state of aircraft equipment, in particular to a method for detecting the performance of an onboard auxiliary power unit.

Background

An airborne auxiliary power unit (AirborneAuxiliaryPowerUnit), called auxiliary power unit APU for short, is a small turbine engine installed at the tail of an airplane. The main function of the APU is to provide power and air, and there are also a small number of APUs that can provide additional thrust to the aircraft. Specifically, the APU provides power to start the main engine before the aircraft takes off from the ground, so that ground electric and air source vehicles are not needed to start the aircraft. On the ground, the APU also provides power and compressed air to ensure lighting and air conditioning in the passenger cabin and the cockpit. When the airplane takes off, the APU can be used as a standby power supply. After the aircraft lands, the APU still supplies power for illumination and air conditioning.

The function of the APU determines the stability of its operation directly related to the flight cost and quality of service of the aircraft. Moreover, in the absence of ground power supply and air supply guarantee, once an APU fails, the aircraft can be directly disabled. At present, the fault removal and maintenance of the APU are almost post-processing. However, among aircraft devices, the APU is a relatively expensive maintenance device. In addition, the price of the whole part of the APU is high, the cost of the storage spare parts is high, and the repair sending period is up to 4-5 months after the fault. The post-processing maintenance mode ensures that the stable operation of the APU cannot be guaranteed. Moreover, since the time consumption after the APU repair is long, the time consumption is also long, which directly causes the delay and even the stop of the airplane.

Disclosure of Invention

In view of one or more technical problems in the prior art, according to an aspect of the present invention, a method for detecting performance of an auxiliary power unit APU is provided, including: acquiring an exhaust temperature EGT, a compressor inlet temperature LCIT, a starting time STA, a service time TSR and a bleed air pressure PT of the APU in operation; comparing the difference EGT-LCIT, STA, TSR and PT of the EGT and LCIT with respective thresholds; assigning respective weights to respective comparison results of the EGT-LCIT, STA, TSR and PT with the respective thresholds; and judging the performance of the APU based on the comparison results of the weighted EGT-LCIT, STA, TSR and PT and the respective thresholds.

According to another aspect of the present invention, a method for detecting performance of an APU is provided, including: obtaining APU operating parameters selected from the group consisting of: the method comprises the following steps that (1) the APU operates an exhaust temperature EGT, a starting time STA, a bleed air pressure PT and an IGV angle; judging whether the parameters are changed significantly; determining the performance of the APU based on whether the parameter has changed significantly.

According to another aspect of the present invention, a method for detecting performance of an APU is provided, including: obtaining APU operating parameters selected from the group consisting of: the APU operates an exhaust temperature EGT and a bleed air pressure PT; determining whether the parameter is close to a limit value of the parameter; and determining the performance of the APU based on whether the parameter is close to the limit value of the parameter.

Drawings

Preferred embodiments of the present invention will now be described in further detail with reference to the accompanying drawings, in which:

FIG. 1 is a schematic structural diagram of an aircraft APU according to one embodiment of the present invention;

FIG. 2 is a schematic structural view of an inlet guide vane assembly according to one embodiment of the present disclosure;

FIG. 3 is a schematic view of an inlet guide vane control arrangement according to an embodiment of the present invention;

FIG. 4 is a schematic diagram of an APU performance variation curve according to one embodiment of the present invention;

FIG. 5 is an example of an A13 message for airbus;

FIG. 6 is a flow diagram of a method of detection of APU performance in accordance with one embodiment of the present invention;

FIG. 7 is a flow diagram of a method of detecting APU performance in accordance with another embodiment of the present invention;

FIG. 8 is a flow diagram of a method of detecting APU performance in accordance with another embodiment of the present invention.

Detailed Description

FIG. 1 is a schematic structural diagram of an aircraft APU, in accordance with one embodiment of the present invention. As shown, the APU100 includes a generator 102, a gearbox 104, a compressor section 106, and a hot section 108. The compressor section 106 includes a front end axial flow centrifugal compressor 105 for generating high pressure gas to supply bleed air to the outside. The hot section portion 108 includes an aft end axial flow centrifugal compressor 107. The rear end axial flow centrifugal compressor 107 is used for providing high-pressure gas to the combustion chamber 120 of the hot section part 108 for combustion in the combustion chamber 120. The fuel system (not shown) of the APU provides fuel to the combustion chamber 120. The combustor 120 generates high-temperature and high-pressure gas by burning fuel, and applies work to the turbine 140 of the hot-section 108, thereby rotating the turbine 140. The turbine 140 drives the front-end axial flow centrifugal compressor 105 through the shaft 103 to generate high-pressure gas, and drives the generator 102 through the gear box 104. The generator 102 generates power and supplies the power to the outside.

APUs are typically part of axial flow centrifugal engines, such as GTCP131-9A, APS3200 model numbers. The largest difference between the APU and the engine of the aircraft is that the APU rotor is constant speed, whereas the rotor of the aircraft engine is variable speed. Therefore, the APU always supplies compressed air to the front end axial flow centrifugal compressor 105 at a constant rotation speed to supply a rear load. The APU has a bleed air control valve therein which controls whether the high-pressure gas is directed to the bleed air load or to the exhaust line. Therefore, the pressure of the bleed air reflects the performance of the front end compressor from the side.

The greater the bleed air load power demand, the greater the resistance to rotation of the front end axial flow centrifugal compressor 105. To maintain a constant rotational speed, the hot leg portion 108 is required to provide a greater torque. The fuel control system of the APU delivers more fuel to the combustion chamber 120 for combustion to provide more heat energy to the turbine 140 to rotate the front end portion at a constant speed. The APU also has a temperature sensing sensor for sensing the exhaust temperature (EGT) of the APU exhaust gases and an Inlet Guide Vane (IGV) assembly.

FIG. 2 is a schematic structural view of an inlet guide vane assembly according to one embodiment of the present invention. As shown, the inlet guide vane assembly 200 is substantially disc-shaped. A plurality of Inlet Guide Vanes (IGVs) are provided on the side near the bottom of the disk. The plurality of inlet guide vanes may be controlled to open at different angles. The inlet guide vanes may have an angle ranging from 15 degrees to 115 degrees. The inlet guide vanes are not fully closed and the vanes are set to the 15 degree position to cool the front end axial flow centrifugal compressor 105.

FIG. 3 is a schematic view of an inlet guide vane control arrangement according to an embodiment of the present invention. As shown, the inlet guide vane control architecture 300 includes an Inlet Guide Vane Actuator (IGVA) 301 and a Linear Variable Differential Transformer (LVDT) 302 connected thereto. The inlet guide vane assembly 200 is mounted to the intake passage of the front end axial flow centrifugal compressor 105. The LVDT is connected to the IGV on the inlet guide vane assembly 200. The IGVA controls the IGVs to open at a proper angle through the LVDT according to the requirement of the aircraft on compressed air.

The EGT temperature detector of the APU detects the exhaust gas temperature EGT of the APU. Due to the material limitations of the APU itself, EGT has a limited value, namely the red line value EGTRedLine. In order to avoid that the APU burns out and is scrapped when the APU is over-temperature, the APU control system generally controls the actual EGT within the red line value EGTRedLine. Thus, when the temperature probe approaches the over temperature red line value, the fuel system of the APU will reduce fuel delivery to lower the exhaust temperature. Meanwhile, as the fuel supply is reduced, the rotation speed is necessarily reduced to drive the original large load. However, since the APU must maintain a constant rotational speed, in order to reduce the load on the front-end compressor, the APU will adjust the angle of the IGV via the IGVA to turn down the inlet, reducing the amount of gas input to the front-end compressor and turn down the front-end compressor. Therefore, the bleed air pressure output by the front-end air compressor is reduced, and the flow is reduced.

FIG. 4 is a schematic diagram of an APU performance variation curve, according to one embodiment of the present invention. As the usage time increases, all APU performance becomes progressively worse, i.e., the fade index increases. When the decay index of the APU performance is stable, the APU performance is in a stable period; when the performance degradation of the APU is gradually accelerated, the performance of the APU enters a degradation period; when a certain threshold value is exceeded, the performance of the APU enters a failure period, and the APU can fail at any time. When the APU enters a fault period, the use of the APU is influenced, and adverse consequences are generated on the service quality and the flight safety; and is easy to cause non-planned maintenance, resulting in flight delay and flight stop. There is no means in the prior art to detect whether the performance of the APU enters the decline period. And certain embodiments of the present invention may implement such detection.

The following benefits are achieved for the detection of the decline period: first, when the APU is in the decline period, the probability of failure is still very low. If the airplane is selected to be overhauled at the moment, the flight safety and the service quality can be guaranteed. Secondly, when detecting that the APU is in a decline period, the airline company can schedule the maintenance of the aircraft in time, thereby avoiding the unscheduled maintenance and reducing the delay of the aircraft. And meanwhile, the waste of maintenance cost caused by maintenance according to hard time limit is avoided. Of course, embodiments of the present invention may also be applicable to the detection of a period of failure.

In order to realize the detection of the performance of the APU, the operation state of the APU on the airplane needs to be monitored, and relevant data of the operation of the APU are acquired. As aircraft systems become more complex, aircraft data systems also become more powerful. For example, the airliner aircraft compatibility systems (acms) system and the airliner heatheatmonitor (ahm) system from boeing. One feature of these systems is that the operational data of the aircraft can be monitored in real time, and when certain trigger conditions are met, messages containing specific data are automatically generated.

Taking the ACMS system of airbus as an example, the AHM system of boeing corporation can be compared, and the ACMS system includes flight integrated data system (aids). And the data management unit (dmu) is the core of the AIDS system. The DMU has two very important functions:

-collecting, processing and recording a number of parameters on board the aircraft, including data from black boxes. These parameters are stored in the DMU's internal memory or in an external recorder, such as the AIDS digital recorder digital aid recorder (dar);

-generating a system message, which is triggered when the state or system parameters of the aircraft meet the triggering conditions of the message. These messages are stored in the non-volatile memory of the DMU.

According to one embodiment of the invention, the operating data of the APUs may be obtained using an aircraft data system, such as an ACMS or AHM system.

The ACARS system consists of an avionics computer called ACARS Management Unit (MU) and a control display unit (cdu). The MU is used to transmit and receive VHF radio digital messages from the ground. On the ground, the ACARS system consists of a network of ground stations with radio transceiver mechanisms, which can receive or transmit messages (data chain messages). These ground stations are typically owned by various service providers that distribute received messages to servers of different airlines on the network. According to one embodiment of the invention, the acquired operation data of the APU is used for generating the APU message, and the APU message is sent to a server on the ground through the ACARS.

According to an embodiment of the present invention, the APU message may also be transmitted through a communication device or system of an aviation telecommunications network (atn).

In fact, for the existing air data system, performance monitoring of the APU is an existing project, so that a corresponding APU message can be automatically generated and transmitted to the ground through ACARS or ATN. However, these monitored data are not used for the decay period detection of the APU performance.

For example, the A13 message of airbus, i.e. (APUMES/IDLEREPORT), or the APU message of Boeing is an example of such an APU message.

In the following embodiments, a message a13 of airbus is taken as an example for explanation. The Boeing APU messages are processed similarly.

Fig. 5 is an example of an a13 message for airbus. As shown in the figure, the a13 message mainly includes 4 pieces of information, which are: the system comprises a header, APU resume information, operating parameters for starting an aircraft engine and APU starting parameters.

The header consists of CC and C1 sections and mainly comprises flight information of the airplane, a message generation section stage, a bleed valve state, total temperature (namely outside temperature) and other information. The APU resume information is composed of section E1 and comprises information such as APU serial number, operation hour, cycle and the like. The operation parameters for starting the aircraft engine consist of sections N1 to S3; wherein, N1 and S1 represent the operation condition when the first aircraft engine is started, N2 and S2 represent the operation condition when the second aircraft engine is started, and N3 and S3 represent the condition when the APU is slowed down after the APU finishes starting the engine.

The a13 message includes a plurality of parameters related to the operating conditions of the APU. The operation parameters of the starting engine comprise EGT temperature, IGV opening angle, compressor inlet pressure, load compressor inlet temperature, bleed air flow, bleed air pressure, lubricating oil temperature and APU generator load. The parameters of the APU during starting comprise starting time, EGT peak value, rotating speed at the EGT peak value and inlet temperature of a load compressor.

In addition to the parameters in the a13 message, the performance of the APU may be related to other parameters. Taking an airbus A320 airplane as an example, the number of the system data collected by the airplane can be up to 13000. Many of these parameters also reflect APU performance, either directly or indirectly. Therefore, how to select a suitable parameter from a plurality of APU performance parameters and generate a corresponding suitable algorithm to accurately reflect the performance of the APU is one of the problems to be solved by the invention.

FIG. 6 is a flow diagram of a method of detecting APU performance in accordance with one embodiment of the present invention. As shown in the figure, in the method 6000 for detecting the performance of the APU of this embodiment, in step 6100, the following information of the operation of the aircraft APU is obtained: exhaust temperature EGT, compressor inlet temperature LCIT, start-up time STA, service time TSR and bleed air pressure PT. In step 6200, the differences EGT-LCIT, STA, TSR, and PT of EGT and LCIT are compared to respective thresholds. According to one embodiment of the invention, the threshold value is a limit value of the respective parameter. At step 6300, respective weights are assigned for the results of the comparisons of EGT-LCIT, STA, TSR, and PT to the respective thresholds. In step 6400, the results of comparisons of EGT-LCIT, STA, TSR, and PT with respective thresholds after considering the weights are integrated. At step 6510, it is determined whether the integrated result exceeds a first predetermined value. If the integrated result does not exceed the first predetermined value, in step 6520, it is determined that the performance of the APU is good; at step 6610, it is determined whether the integrated result exceeds a second predetermined value. If the second predetermined value is not exceeded, then in step 6620, determining that the performance of the APU is normal; in step 6710, it is determined that the integrated result is greater than a third predetermined value. If the third predetermined value is not exceeded, then it is determined at step 6720 that the APU performance has entered the fade period. If the integrated result exceeds the third predetermined value, then in step 6800, it is determined that the APU performance has entered the failure period.

According to an embodiment of the present invention, the information required in step 6100 may be obtained from an APU message, such as the A13 message. For example, an a13 message of the operation of the aircraft APU can be remotely acquired in real time from an international aviation telecommunication group SITA network control center and an ADCC network control center of a national aviation data communication company, and the message decoder decodes the a13 message of the operation state of the aircraft APU to obtain the operation information of the aircraft APU.

And if the APU running state message is not automatically generated in the aircraft data system, adding corresponding sensors and triggering conditions to generate the required APU message. And if the existing APU message in the aircraft data system does not completely cover one or more of the exhaust temperature EGT, the compressor inlet temperature LCIT, the starting time STA, the use time TSR and the bleed air pressure PT, modifying the generation condition of the APU message and increasing one or more missing measurement parameters. The APU message can be transmitted to the data server of the airline company in real time through the ACARS or ATN system, so that the real-time monitoring of the performance of the APU can be realized. Of course, the message transmission mode can also avoid the high cost and human error of the manual mode.

According to one embodiment of the invention, the information required in step 6100 may be obtained directly from the aircraft data system without generating APU messages.

In step 6200, the difference between EGT and LCIT, EGT-LCIT, is EGT_Readline。EGT_ReadlineIs the EGT red line value of the APU. EGT_ReadlineDepending on the APU model. Different models of APUs have different EGT red line values, which can be obtained by looking up the relevant manual. The threshold of STA is STA_WarningLineIs the STA performance decay value, which also depends on the APU model. The threshold value of TSR is TSR_rtThe term "wing time reliability" means the time corresponding to 70% wing time reliability of an APU of a certain model. The threshold value of PT is PT_MinMeaning the minimum required bleed air pressure for a particular model APU. Alternatively, the threshold value of PT is PT_BaseLineMeaning the lowest inherent bleed air quantity for a certain model APU when it is operating normally. Comparing EGT-LCIT, STA, TSR and PT with respective thresholds can reflect the degree of deviation of the performance of the current APU from the standard performance of the APU, and thus reflect the degree of performance degradation of the APU. EGT_Readline、STA_WarningLineAnd PT_MinOr PT_BaseLineIt can be obtained by looking up the relevant airplane manual or from the manufacturer. Of course, they can also be obtained by actual experiments. However, TSR_rtDue to the influence of other factors such as geography and maintenance environment, the standard value is deviated to a certain extent. The inventor finds that the aging mode of the APU is Poisson distribution through long-term observation and analysis. In order to obtain more accurate TSR_rtData from which the required TSR can be calculated from the actual data by Poisson distribution_rt. For example, the parameters (such as the mean value) of the poisson distribution followed by the actual using time TSR may be first calculated, and then the corresponding using time TSR when the failure rate is 30% (the stability rate is 70%) may be calculated by using the obtained parameters of the poisson distribution followed by actual using time TSR_rt。

The EGT-LCIT, STA, TSR, and PT may be compared with their respective thresholds in a ratio manner or in a difference manner. To facilitate considering the weights of the various parameters, in step 6200, ratios of EGT-LCIT, STA, TSR, and PT to respective thresholds are calculated, in accordance with an embodiment of the present invention.

EGT-LCIT, STA, TSR and PT have different effects on APU performance, so they need to be assigned different weights. In the case of obtaining the ratios of EGT-LCIT, STA, TSR and PT to the respective thresholds, according to an embodiment of the present invention, take R1, R2, R3 and R4 as the respective weights of EGT-LCIT, STA, TSR and PT, and R1+ R2+ R3+ R4= 1. Based on the observation and analysis of the inventors, the effect of TSR was greatest, so R3 was generally greater than 0.25; the influence of EGT-LCIT and STA may be different for different types of APUs; in contrast, the PT effect is small and R4 is minimal. According to one embodiment of the invention, for an APU of APS3200 model, R3=0.35, R2=0.3, R1=0.2, R4= 0.15. For GTCP131-9A model APU, R3=0.35, R1=0.3, R2=0.2, R4= 0.15.

According to one embodiment of the invention, the performance of the APU is evaluated using the following formula:

wherein, the PDI (Performance DetectionIndex) performance detection index is a parameter reflecting the performance of the APU. According to the inventors' observation and analysis, if the PDI is less than 0.7, the APU performs well; if the PDI is greater than 0.7 and less than 0.85, the performance of the APU is normally available; if the PDI is greater than 0.85, the APU performance is poor and the fade period has been entered. If the PDI is close to 1, e.g., greater than 0.95, this indicates that the APU has entered a failure period and is likely to fail at any time. Thus, one example of the first predetermined value in step 6510 is 0.7, and one example of the second predetermined value in step 6610 is 0.85; one example of the third predetermined value in step 6710 is 0.95.

The method of the above embodiment of the present invention is further illustrated below by 2 examples.

Example 1: the relevant information for an APU of APS3200 model is as follows: EGT_ReadlineIs 682; STA (station)_WarningLineIs 90; PT_MinIs 3; TSR_rtIt was 5000. The weighting parameters R1=0.2, R2=0.3, R3=0.35, R4=0.15 are taken.

The method comprises the steps of remotely acquiring an aircraft APU message from an SITA network control center or an ADCC network control center in real time, decoding the aircraft APU message through an ACARS message decoder to obtain aircraft APU operation information, and comprises the following steps: the exhaust temperature EGT is 629, the compressor inlet temperature LCIT is 33, the start time STA is 59, the on wing time TSR is 4883 and the bleed air pressure PT is 3.66, by the following equation:

the PDI value was calculated to be 0.85. And judging that the performance of the APU enters a decline period, and planning to maintain the APU of the airplane.

Example 2: the relevant information for the APU of GTCP131-9A model is as follows: EGT_ReadlineIs 642; STA (station)_WarningLineIs 60; PT_MinIs 3.5; TSR_rtIt was 5000. The weighting parameters R1=0.3, R2=0.2, R3=0.35, R4=0.15 are taken.

The method comprises the steps of remotely acquiring an aircraft APU message from an SITA network control center or an ADCC network control center in real time, decoding the aircraft APU message through an ACARS message decoder to obtain aircraft APU operation information, and comprises the following steps: an exhaust temperature EGT of 544, a compressor inlet temperature LCIT of 31, a start time STA of 48, an on wing time TSR of 2642 and a bleed air pressure PT of 3.76, by means of the formula

The PDI value was calculated to be 0.72. And judging that the performance of the APU is normal and the APU can still be normally used.

Compared with the prior art, the embodiment of the invention obtains the PDI value by real-time acquisition of the exhaust temperature EGT, the inlet temperature LCIT of the compressor, the starting time STA, the wing time TSR and the bleed air pressure PT of the APU, and calculates according to the formula (1), and then the accurate detection of the performance of the APU is limited according to the comparison of the PDI value and the preset value. In addition, the ACARS message of the operation state of the aircraft APU is remotely acquired in real time, so that the workload of manual acquisition is reduced, and the working efficiency is improved.

The measurement of EGT and PT is affected by differences in altitude and temperature. According to one embodiment of the invention, the measured EGT and PT are compared to a standard state to remove the effect of altitude and ambient temperature for more accurate detection of APU performance. For example, an altitude of 0 m and a temperature of 50 ℃ may be selected as the standard state, and other altitudes and temperatures may be selected as the standard state.

According to one embodiment of the present invention, the atmosphere correction formula for PT under the standard condition of 0 m altitude and 50 ℃ temperature is

Wherein PT_stdIs the pressure at an altitude of 0 m, ALT is the altitude or standard altitude, TAT is the ambient or total temperature, m is the air mass, which can be taken to be 29. g takes 10 m/s²And R is an adjusting parameter and can take a value of 8.51.

The altitude pressure correction coefficient can thus be derived:

considering the influence of temperature, the final PT correction formula is

Wherein PT_corIs the corrected bleed air pressure, Δ PT is a temperature-dependent function, which can be calculated using the following formula:

ΔPT＝a1TAT²+b1TAT+c1（4）

wherein TAT is ambient temperature; a1, b1, and c1 are adjustment coefficients. a1, b1 and c1 can be obtained by experimental measurement. According to one embodiment of the invention, a1 has a range of 10^-5Of order, b1 is 10^-2And c1 is between 0 and-1.

After a1, b1 and c1 are experimentally measured, the measured PT can be converted into a corrected PT in a standard state according to equation (3)_cor。

The correction formula for EGT is as follows:

wherein EGT_corIs EGT in the normal state, Δ EGT is a function dependent on temperature, PT_ReqI.e. PT_minIs the lowest bleed pressure required at engine start, and p1 and p2 are adjustment factors. According to one embodiment of the invention, the value range of p1 is 20-60, and the value range of p2 is 70-100. Specific values for p1 and p2 can be obtained experimentally. For example, at different sea level barometric altitudes, different EGTs were measured while maintaining a temperature of 50 degrees, maintaining a certain power output. Then, the change of the EGT is compared with the EGT of 50-degree sea level air pressure, and the change of the EGT and the temperature are regressed, so that the adjusting coefficient in the correction formula can be obtained.

Δ EGT can be calculated using the following equation:

ΔEGT＝a2TAT²+b2TAT+c2（6）

wherein TAT is ambient temperature; a2, b2, and c2 are tuning parameters. a2, b2 and c2 can be obtained by experimental measurement. According to one embodiment of the invention, a2 ranges from 0.005 to 0.02, b2 ranges from 0.5 to 2.5, and c2 ranges from 60 to 100.

After the modified EGT and PT are used, equation (1) can be rewritten as:

according to one embodiment of the invention, for the corrected PDI, if the PDI is less than 0.7, the APU performs well; if the PDI is more than 0.7 and less than 0.8, the performance of the APU is normally available; if the PDI is greater than 0.8, the APU performance is poor and the fade period has been entered. If the PDI is greater than 0.85, it indicates that the APU has entered a failure period. Thus, one example of the first predetermined value in step 6510 is 0.7, and one example of the second predetermined value in step 6610 is 0.8; one example of the third predetermined value in step 6710 is 0.85.

FIG. 7 is a flow diagram of a method of detecting APU performance in accordance with another embodiment of the present invention. As shown, in the APU performance detection method 700, at step 710, one or more of an aircraft APU operating exhaust temperature EGT, a start time STA, a bleed air pressure PT, and an IGV angle are obtained. The method for acquiring the performance parameters of the APU described in the embodiment of fig. 6 may be applied to this embodiment.

According to the principles of APU operation, one important parameter reflecting the performance of the APU is EGT, i.e., the APU exhaust temperature. Because the EGT directly reflects the heat energy conversion efficiency of the whole APU when the APU runs at a constant rotating speed. The lower the APU thermal energy conversion efficiency, the higher the value of EGT. Because the control system of the APU can operate the fuel flow valve and the IGV inlet angle to ensure no overtemperature, when the APU is in a state close to the overtemperature and needs to prevent the overtemperature, the PT and IGV angles in the parameters of the APU can reflect the change. STA is a parameter that reflects the overall performance of the APU, including the performance of the starter motor, the performance of the gearbox, and the efficiency of the compressor unit and the power unit (i.e., one compressor and two stages of turbines). By monitoring the four key parameters EGT, IGV, STA and PT, the current performance of the APU and the change trend thereof can be reflected. Moreover, the respective detection of the parameters also facilitates the fault source judgment of the APU and the discovery of the hidden fault.

At step 720, it is determined whether a significant change in one or more of the exhaust temperature EGT, the start time STA, the bleed air pressure PT, and the IGV angle has occurred. And if one parameter of the exhaust temperature EGT, the starting time STA, the bleed air pressure PT and the IGV angle is changed obviously, judging that the parameter is bad.

For EGT and PT, EGT in the above-described embodiments can be applied_corAnd PT_corInstead of directly obtained EGT and PT, to eliminate the influence of altitude and temperature and obtain more accurate results.

As usage time increases, APU performance also gradually deteriorates. This attribute of the APU performance parameter may be reflected by the following formula:

X=β0+β1t₀（8）

wherein X is any one of the parameters of exhaust temperature EGT, start time STA, bleed air pressure PT and IGV angle, t₀Is the installation time of the APU, β 0 and β 1 are fitting parameters, whereβ 1 is a slope term that reflects the trend of the parameter.

According to one embodiment of the invention, a plurality of values of one of EGT, STA, PT and IGV taken over a period of time are fitted to yield a slope term β 1. Comparing β 1 with the slope term as a reference, if the slope terms are significantly different, it is judged that the one of EGT, STA, PT, and IGV has significantly changed. The slope term used as a reference is calculated by using the data of the APU with good working state, and the slope term can be the data after the initial installation of the same APU, and can also be the data of other APUs with good working state of the same type.

According to one embodiment of the invention, after the parameters of the APU installation and the APU are initialized, the initial recorded parameters are averaged to obtain the initial value of each parameter as the respective reference value. The number of the plurality of records is generally greater than or equal to 10 records.

And comparing the subsequent parameters with the reference value to obtain the change value of the self. These change values also conform to equation (8). Their slope terms may also reflect the trend of change of the APU parameters. Therefore, in the present embodiment, the slope term of one of the EGT, STA, PT, and IGV with respect to the change value of the reference value is compared with the slope term of the change value as a reference, and if the slope terms are significantly different, it is determined that the one of the EGT, STA, PT, and IGV has significantly changed. This parameter becomes worse.

According to one embodiment of the invention, the parameter values of one of the EGT, STA, PT and IGV in the consecutive equal-length time periods are compared with independent samples, and if the parameter values of the EGT, STA, PT and IGV are obviously changed, the one of the EGT, STA, PT and IGV is judged to be obviously changed. This parameter becomes worse.

And smoothing the parameter values of the EGT, the STA, the PT and the IGV which are actually measured in order to reduce the interference of fluctuation. According to one embodiment of the invention, the parameter values are smoothed by means of a multipoint smooth average rolling mean. The number of the dots is 3 or more. According to another embodiment of the invention, the parameters are smoothed using the following formula:

X_new=C1X_smooth+C2X_old（9）

wherein, X_oldIs a value before smoothing, i.e. a value actually measured; x_newIs the smoothed value; x_smoothIs a smoothed value, which may be a smoothed value of a neighboring point (e.g., a previous point) or an average value of several nearby points (regardless of the current point); c1 and C2 are weight values, C1 is greater than C2, e.g., C1 = 0.8, C2= 0.2.

In step 730, a determination is made as to whether the performance of the APU is degraded, taking into account, in combination, whether one or more of the exhaust temperature EGT, the start time STA, the bleed air pressure PT, and the IGV angle has changed significantly.

According to one embodiment of the invention, if any one of EGT, PT, STA and IGV is deteriorated, the performance of the APU is judged to be deteriorated, and the fading period is entered. According to another embodiment of the invention, if the STA is bad, the performance of the APU is judged to be bad, and the decay period is entered. According to another embodiment of the invention, if any two of EGT, PT, STA and IGV go bad, the performance of APU is judged to be deteriorated, and the decay period is entered. According to another embodiment of the invention, if both EGT and PT are deteriorated, the performance of APU is judged to be deteriorated, and the decay period is entered.

The embodiments of fig. 6 and 7 may be used simultaneously to more accurately detect the performance of the APU.

FIG. 8 is a flow diagram of a method of detecting APU performance in accordance with another embodiment of the present invention. As shown, in the APU performance detection method 800, at step 810, one or both of an aircraft APU operating exhaust temperature EGT and a bleed air pressure PT are obtained. The method for acquiring the performance parameters of the APU described in the above embodiment may be applied to the present embodiment.

In step 820, the exhaust gas temperature EGT and the bleed air pressure PT are compared with their respective limit values. Specifically, EGT may be related to EGT red line value EGT_RedLineComparing; the bleed air pressure PT may be equal to the lowest bleed air pressure PT required at engine start-up_ReqAnd (6) comparing.

In step 830, it is determined that one of the exhaust gas temperature EGT and the bleed air pressure PT is approaching its limit value. According to one embodiment of the invention, the performance of the APU is judged to enter a decline period if one of the exhaust gas temperature EGT and the bleed air pressure PT deteriorates. According to another embodiment of the invention, the performance of the APU is judged to enter a decline period if both the exhaust gas temperature EGT and the bleed air pressure PT are deteriorating.

According to one embodiment of the invention, the following formula may be used for EGT:

EGT_Tolerance=EGT_RedLine-EGT_cor（10）

wherein, EGT_ToleranceIndicating margin of EGT, i.e. EGT from red line value EGT_RedLineThe distance of (c). Since the APU control system will prevent the EGT from over-warming, when the control mechanism is active, it is an indication that the APU is no longer able to obtain more power by increasing the fueling. The power of the APU is gradually decreased with the increase of the usage time, which indicates that the APU enters the decline phase. Therefore, when EGT is used_ToleranceApproaching 0, indicates that the APU enters the decline phase.

PT is an important observed parameter when the APU enters the decline phase.

According to one embodiment of the invention, the following formula may be used for PT:

PT_Tolerance=PT_cor-PT_Req（11）

wherein PT_ToleranceThe margin for PT, i.e. the distance of PT from the lowest bleed pressure required at engine start-up, is indicated. PT_ToleranceReflects the operation condition of the APU in the decline stage. When PT_ToleranceNear 0, the APU should be replaced.

Example 3: exhaust gas derived from messagesCalculating the data of temperature EGT, external temperature TAT, altitude ALT and PT to obtain EGT_cor=654.49，PT_cor = 3.27. According to the inquiry, the lowest bleed air pressure PT of the air passenger A319 aircraft engine start_Req= 3.2. Long-term experiment verifies that the red line value EGT of APS3200 model APU_RedLine= 645. From the above performance evaluation formula, one can derive: EGT_Tolerance= 9.49, a value of 9.49/645 close to 0, about 1.4%; PT_Tolerance0.07, the approximation to the 0 value was 0.07/3.2, about 2.2%. Therefore, the EGT and PT parameters are both deteriorated, and the APU enters the decline period and should be replaced in time.

The methods of fig. 6-8 may be used simultaneously to more accurately detect the performance of the APU.

Compared with the prior art, the method provided by the embodiment of the invention can realize the performance detection of the APU by acquiring parameters such as the exhaust temperature EGT of the APU, the inlet temperature LCIT of the compressor, the starting time STA, the wing time TSR, the bleed air pressure PT, the angle of the inlet guide vane IGV and the like in real time, and can judge whether the performance of the APU enters the decline period or not, thereby providing good support for an engineer to maintain the APU, ensuring the use of the APU and avoiding the delay and the stop of the airplane caused by the use of the APU. Meanwhile, maintenance and operation control can be carried out in a targeted manner by evaluating the performance of the APU, so that the maintenance cost is greatly reduced.

The above embodiments are provided only for illustrating the present invention and not for limiting the present invention, and those skilled in the art can make various changes and modifications without departing from the scope of the present invention, and therefore, all equivalent technical solutions should fall within the scope of the present invention.

Claims (13)

1. A method for detecting the performance of an Auxiliary Power Unit (APU) comprises the following steps:

acquiring an exhaust temperature EGT, a compressor inlet temperature LCIT, a starting time STA, a service time TSR and a bleed air pressure PT of the APU in operation;

comparing the difference EGT-LCIT, STA, TSR and PT of the EGT and LCIT with respective thresholds;

assigning respective weights to respective comparison results of the EGT-LCIT, STA, TSR and PT with the respective thresholds; and

judging the performance of the APU based on the comparison results of the weighted EGT-LCIT, STA, TSR and PT and the respective thresholds;

wherein the step of determining the performance of the APU comprises determining based on the following formula:

wherein, PDI is a performance detection index which reflects the performance of the APU; r1, R2, R3 and R4 are the respective weights of the EGT-LCIT, STA, TSR and PT;

wherein the threshold value of the EGT-LCIT is the EGT red line value EGT of the APU_Redline；

Wherein the threshold of the STA is a STA performance degradation value (STA)_WarningLine；

Wherein the TSR threshold is a time TSR corresponding to 70% of the APU's on-wing time reliability_rt；

Wherein the threshold value of the PT is the minimum bleed air pressure PT of the APU_Min。

2. The method of claim 1, wherein the weight of TSR is greatest and the weight of PT is least.

3. The method of claim 1, wherein assuming R1, R2, R3 and R4 are the respective weights of said EGT-LCIT, STA, TSR and PT, if said APU is APS3200 model, R1 is 0.2, R2 is 0.3, R3 is 0.35, and R4 is 0.15.

4. The method of claim 1, wherein assuming R1, R2, R3 and R4 as weights for each of said EGT-LCIT, STA, TSR and PT, if said APU is model GTCP131-9A, R1 is 0.3, R2 is 0.2, R3 is 0.35 and R4 is 0.15.

5. The method of claim 1, further comprising: if the PDI is less than a first predetermined value, the APU performs well; if PDI is greater than the first predetermined value and less than a second predetermined value, the performance of the APU is normally available; if PDI is greater than the second predetermined value, the APU performance is poor; the larger the PDI, the worse the APU performance.

6. The method of claim 5, wherein the first predetermined value is 0.7; the second predetermined value is 0.85.

7. The method of claim 1, wherein the PT_MinBy PT_BaseLineInstead, the threshold value for PT is the inherent minimum bleed air quantity PT for normal operation of the APU_BaseLine。

8. The method according to claim 1, wherein the EGT-LCIT is replaced by EGT_corThe PT is replaced by PT_cor(ii) a Wherein, EGT_corIs EGT, PT in the Standard State_corIs the bleed air pressure in the normal state,

wherein the PT_corCalculated according to the following formula:

where Δ PT is a temperature-dependent function, and is an altitude pressure correction coefficient, calculated according to the following formula:

wherein ALT is altitude or standard altitude, TAT is ambient temperature or total temperature, m is air mass, and is 29, and g is 10 m/s²And R is an adjustment parameter.

9. The method of claim 8, further comprising: if the PDI is less than a first predetermined value, the APU performs well; if PDI is greater than the first predetermined value and less than a second predetermined value, the performance of the APU is normally available; if PDI is greater than the second predetermined value, the APU has entered a decline period; if the PDI is greater than a third predetermined value, the APU has entered a failure period.

10. The method of claim 9, wherein the first predetermined value is 0.7; the second predetermined value is 0.8; the third predetermined value is 0.85.

11. The method according to claim 8, wherein the EGT is_corIs calculated according to the following formula:

where Δ EGT is a temperature-dependent function, PT_ReqIs the lowest suction pressure required at engine start, and p1 and p2 are correction factors.

12. The method of claim 8 wherein the step of deriving an exhaust gas temperature EGT, a compressor inlet temperature LCIT, a start time STA, a use time TSR, and a bleed air pressure PT at which said APU is operating comprises deriving said EGT, LCIT, STA, TSR, and PT from APU messages.

13. The method of claim 8 further comprising generating APU messages containing said EGT, LCIT, STA, TSR and PT information for operation by said APU.