Method for performing maintenance on an engine

Abstract

A method for performing maintenance on an engine includes: providing an engine maintenance system including a database system having a database and a database management device: providing a first performance parameter stored in the database and characterizes an engine performance before an engine maintenance procedure; providing a maintenance parameter stored in the database and characterizes a scope of a maintenance measure performed on an engine during an engine maintenance procedure; providing a second performance parameter stored in the database and characterizes the engine performance after the engine maintenance procedure; determining, using the database management device, a functional relationship between the maintenance parameter and the contribution of the maintenance parameter to a difference between the first performance parameter and the second performance parameter; outputting the functional relationship via the engine maintenance system; and performing maintenance on the engine taking the functional relationship into account.

Claims

1. A method for performing maintenance on an engine, comprising the steps of: providing an engine maintenance system including a database system having a database and a database management device; providing at least one first performance parameter stored in the database and characterizing an engine performance before an engine maintenance procedure; providing at least one maintenance parameter stored in the database and characterizing a scope of a maintenance measure performed on the engine during the engine maintenance procedure; providing at least one second performance parameter stored in the database and characterizing the engine performance after the engine maintenance procedure; determining, using the database management device, a functional relationship between the maintenance parameter and the contribution of the maintenance parameter to a difference between the first performance parameter and the second performance parameter; outputting the functional relationship via the engine maintenance system; and performing maintenance on the engine taking the functional relationship into account; wherein the functional relationship comprises
Y.sub.model,j=f(X.sub.i,j,a.sub.i) wherein Y.sub.model,j is a difference between the first and second performance parameters for an engine j; wherein X.sub.i,j is a maintenance parameter for a maintenance measure i and the engine j; and wherein a.sub.i is a function parameter for the maintenance measure i.

2. The method as recited in claim 1 wherein the first performance parameter or the second performance parameter is determined using a monitoring system of the engine or using a performance test stand and is stored in the database.

3. The method as recited in claim 2 wherein the first performance parameter or the second performance parameter is determined taking into account at least one parameter selected from the group of height, pressure, temperature, rotational speed, fuel mass flow, flight Mach number, air mass flow, efficiency, capacity, valve position, guide vane angle, clearance-maintaining position and vibrations in the turbine region of the engine or in a compressor of the engine.

4. The method as recited in claim 2 wherein the at least one maintenance parameter characterizes a degree of a change in a feature of a component of the engine resulting from the maintenance measure or a degree of restoration of a feature of a component of the engine resulting from the maintenance measure or is determined taking into account a number of cycles that a component to be serviced of the engine has operated since a previous maintenance of the engine.

5. The method as recited in claim 2 wherein the first performance parameter or the second performance parameter or the maintenance parameter is available in the form of data of an already serviced engine stored in the database or is acquired on the engine to be serviced and stored in the database.

6. The method as recited in claim 2 wherein the first performance parameter or the second performance parameter or the maintenance parameter is provided in relation to a type or a specimen or a stage or a stage cluster of the engine.

7. The method as recited in claim 2 wherein the functional relationship is determining by a compensation calculation.

8. The method as recited in claim 2 wherein the functional relationship is determined for a plurality of maintenance parameters.

9. The engine maintenance system for the method as recited in claim 2, comprising: a database system including: a database adapted to store at least one first performance parameter characterizing an engine performance before an engine maintenance procedure, at least one maintenance parameter characterizing a scope of a maintenance measure performed on an engine during an engine overhaul, and at least one second performance parameter characterizing the engine performance after the engine maintenance procedure; and a database management device adapted to access the database and to determine a functional relationship between the at least one maintenance parameter and the contribution of the maintenance parameter to the difference between the first performance parameter and the second performance parameter; and an output device for outputting the functional relationship determined by the database management device in order for it to be taken into account in the maintenance of the engine.

10. The method as recited in claim 7 wherein the compensation calculation determines the functional relationship, the functional relationship being between a change in a clearance of a blade and an associated increase in engine efficiency.

11. The method as recited in claim 7 wherein the compensation calculation determines a linear relationship between a change in a clearance of a blade and an associated increase in engine efficiency as the functional relationship.

12. The method as recited in claim 10 wherein the linear relationship is approximated using a constant.

13. The method as recited in claim 1 wherein the functional relationship is between a change in clearance of a blade and an associated increase in engine efficiency.

14. The method as recited in claim 1 wherein the functional relationship is determined as a polynomial model, exponential model or is based on a stochastic model.

15. The method as recited in claim 1, wherein the maintenance parameter is a change in a tip clearance, a change in a surface roughness, a change in a leading edge radius or a change in a chord length of a blade resulting from the engine maintenance procedure.

16. The method as recited in claim 4, wherein the maintenance parameter is a change in a tip clearance, a change in a surface roughness, a change in a leading edge radius or a change in a chord length of a blade resulting from the engine maintenance procedure.

17. The method as recited in claim 1, wherein the maintenance parameter includes information that a certain portion of a plurality of rotor blades of the engine were or are to be polished during the engine maintenance procedure.

18. The method as recited in claim 4, wherein the maintenance parameter includes information that a certain portion of a plurality of rotor blades of the engine were or are to be polished during the engine maintenance procedure.

19. The method as recited in claim 16, wherein the at least one first performance parameter characterizing an engine performance before an engine maintenance procedure is fuel mass flow before the engine maintenance procedure and wherein the at least one second performance parameter characterizing the engine performance after the engine maintenance procedure is fuel mass flow after the engine maintenance procedure.

20. A method for performing maintenance on an engine, comprising the steps of: providing an engine maintenance system including a database system having a database and a database management device; providing at least one first performance parameter stored in the database and characterizing an engine performance before an engine maintenance procedure; providing at least one maintenance parameter stored in the database and characterizing a scope of a maintenance measure performed on the engine during the engine maintenance procedure; providing at least one second performance parameter stored in the database and characterizing the engine performance after the engine maintenance procedure; determining, using the database management device, a functional relationship between the maintenance parameter and the contribution of the maintenance parameter to a difference between the first performance parameter and the second performance parameter; outputting the functional relationship via the engine maintenance system; and performing maintenance on the engine taking the functional relationship into account; wherein the at least one maintenance parameter characterizes a degree of a change in a feature of a component of the engine resulting from the maintenance measure or a degree of restoration of a feature of a component of the engine resulting from the maintenance measure or is determined taking into account a number of cycles that a component to be serviced of the engine has operated since a previous maintenance of the engine; wherein the maintenance parameter is a change in a tip clearance, a change in a surface roughness, a change in a leading edge radius or a change in a chord length of a blade resulting from the engine maintenance procedure; wherein the at least one first performance parameter characterizing an engine performance before an engine maintenance procedure is exhaust gas temperature before the engine maintenance procedure; and wherein the at least one second performance parameter characterizing the engine performance after the engine maintenance procedure is fuel exhaust gas temperature after the engine maintenance procedure.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Other features of the present invention will become apparent from the claims, the exemplary embodiments, and from the drawings. The aforementioned features and feature combinations, as well as the features and feature combinations mentioned in the exemplary embodiments, may be used not only in the particular stated combination, but also in other combinations, without departing from the scope of the present invention. In the drawing,

(2) FIG. 1 shows a schematic cross section through an engine on which different parameters are measured for determining a first and a second performance parameter;

(3) FIG. 2 shows a flow chart for determining a functional relationship between different maintenance parameters and their respective contribution to a difference between an engine performance before an engine maintenance procedure and an engine performance after an engine maintenance procedure.

(4) FIG. 3 shows an alternative flow chart for determining a functional relationship between different maintenance parameters and their respective contribution to a difference between an engine performance before an engine maintenance procedure and an engine performance after a maintenance procedure.

(5) FIG. 4 shows a diagram in which the potential of two maintenance measures for engine performance improvement is plotted as a function of a number of cycles of a component; and

(6) FIG. 5 shows a comparison between measured changes in efficiency of serviced engines and efficiency changes which were calculated based on the determined functional relationship.

DETAILED DESCRIPTION

(7) FIG. 1 shows a schematic cross section through a generally known aircraft engine 10 on which different parameters are measured for determining a first performance parameter Y.sub.pre and a second performance parameter Y.sub.post. First performance parameter Y.sub.pre characterizes an engine performance before an engine maintenance procedure, while second performance parameter Y.sub.post characterizes an engine performance after an engine maintenance procedure. These performance parameters Y.sub.pre, Y.sub.post may be determined based on on-wing data collected by a monitoring system 12 (monitoring tool) of engine 10 during the operation of engine 10. This data includes performance-relevant parameters, such as pressures, temperatures, rotational speeds, flight Mach number, fuel mass flow, and the like. Alternatively or additionally, it is possible to use data from a test stand, for example when the engine has been removed from a wing of an aircraft or from a helicopter. After maintenance, second performance parameter Y.sub.post is determined during an acceptance test which is mandatory in order to document the maintenance result. If the on-wing data is not available or not sufficiently accurate, an additional test run may be scheduled to be performed before maintenance for data generation purposes in order to determine performance parameter Y.sub.pre. The recorded parameters are basically the same as in the on-wing case; only the air mass flow of engine 10 is measured instead of the flight Mach number.

(8) Depending on the type and configuration of engine 10, different parameters may be measured to determine first performance parameter Y.sub.pre and second performance parameter Y.sub.post. Preferably, at least the following measurement values are used to determine first performance parameter Y.sub.pre and second performance parameter Y.sub.post:

(9) N1, N2 rotational speeds of the low-pressure and high-pressure compressor shafts

(10) WF, TF: fuel mass flow and fuel temperature

(11) EGT: exhaust gas temperature, measured upstream and downstream of the low-pressure turbine (depending on the engine type).

(12) In the case of the present engine 10, the following parameters may additionally be measured, either alone or in any combination, in order to determine first performance parameter Y.sub.pre and second performance parameter Y.sub.post even more accurately:

(13) P2, T2: pressure and temperature at the engine inlet (upstream of the fan)

(14) P25, T25: pressure and temperature between the low-pressure compressor/booster and the high-pressure compressor

(15) PS3, T3: static pressure and total temperature between the high-pressure compressor and the combustion chamber

(16) P125: pressure downstream of the fan

(17) P49: pressure downstream of the low-pressure turbine

(18) VBV: position of the variable bleed valve

(19) VGV: position of the variable guide vanes

(20) ECBV: position of the environmental control bleed valve

(21) HPT ACC, LPT ACC: active clearance control position for the high pressure turbine and the low pressure turbine

(22) N1 VIB, N2 VIB: vibration measurement at the low-pressure and high-pressure compressor shafts

(23) Toil, Poil: temperature and pressure in the oil system of the engine

(24) Further parameters which concern the aircraft associated with engine 10 and may, in principle, also be taken into account in the determination are:

(25) PALT (pressure altitude)

(26) TAT (total air temperature)

(27) MN (flight Mach number).

(28) In the case of an off-wing measurement on a performance test stand, the air mass flow is measured instead of the flight Mach number as a parameter. It is preferred to use basically the same parameters for determining first performance parameter Y.sub.pre and second performance parameter Y.sub.post, at least for a particular maintenance procedure.

(29) During an engine maintenance procedure, it is possible, in principle, to perform different maintenance and repair measures which, depending on their type and scope, provide different contributions to an overall improvement in engine performance, which manifests itself by a difference between first performance parameter Y.sub.pre and second performance parameter Y.sub.post. The difference between first performance parameter Y.sub.pre and second performance parameter Y.sub.post may be expressed, for example, as a change in efficiency of the engine resulting from the maintenance measures performed. In order to be able to determine, prior to the maintenance of engine 10, the maintenance measures that are necessary, for example, to achieve or restore a specific minimum engine performance, a functional relationship between individual maintenance measures and their respective potential for increasing the engine performance is determined The type and scope of a specific maintenance measure performed on engine 10 during engine maintenance are characterized by an associated maintenance parameter X or X

(30) Depending on the maintenance measure, maintenance parameter X or X may characterize the change in a feature, such as, for example, the change in a tip clearance, in a surface roughness, in a leading edge radius, or in a chord length of a blade resulting from the maintenance. Furthermore, maintenance parameter X may characterize measures for restoring features. For example, maintenance parameter X may characterize the information that a certain portion (e.g. 50%) of the rotor blades of the 2nd stage of engine 10 were or are to be polished. The number of cycles that a component has operated since the previous maintenance may also be used for the description of the condition of engine 10 before maintenance in order to determine maintenance parameter or parameters X.

(31) In order to determine the functional relationship between a particular maintenance parameter X or X and the contribution of maintenance parameter X or X to a difference between first performance parameter Y.sub.pre and second performance parameter Y.sub.post, it is possible to use mathematical functions which are based on physical considerations. For example, the functional relationship between a change in clearance (X=c) and a resulting change in efficiency may be linearly approximated using a constant c.sub.clearance:
=c.sub.clearance*c

(32) Alternatively, more complex functional relationships may also be used, depending on the maintenance measure. It may also be provided that the functional relationship between a particular maintenance measure and its effect on the turbine performance be determined, for example without hypotheses, as a polynomial model, as an exponential model, or based on a stochastic model.

(33) For further illustration, FIG. 2 shows a flow chart for determining a functional relationship between different maintenance parameters X.sub.i,j and their respective contribution to a difference between an engine performance before an engine maintenance procedure and an engine performance after an engine maintenance procedure. Depending on the associated maintenance measure, the maintenance parameter may characterize a scope of a particular maintenance measure and, accordingly, may also be referred to as X.sub.i,j.

(34) Initially, an engine maintenance system 14 is provided which includes a database system 16 having a database 18 and a database management device 20. In FIG. 2,

(35) Y.sub.pre: denotes the performance parameter before maintenance

(36) Y.sub.post: denotes the performance parameter after maintenance

(37) X: designates a maintenance/condition parameter

(38) a.sub.i: denotes a function parameter

(39) i: is a running index denoting different maintenance measures

(40) j: is a running index for different engines in the database.

(41) Database 18 contains on-wing and/or test stand data 22, which is measured on engine 10 prior to performing the maintenance and used for determining first performance parameter Y.sub.pre,j for the present engine j. Database 18 further contains data 24 characterizing the scope of maintenance. The scope of maintenance may be described by the degree of restoration of a feature or component of a stage of engine 10 according to the following formula:

(42) ${}_{j,k}=\frac{\underset{m}{.Math.}{N}_{j,k,m}}{N_{j,\mathrm{tot}}}$
where:
: denotes the scope of maintenance
j: designates the engine stage
k: denotes the feature/component
m designates the maintenance measure (repair/replacement)
N: is the number of parts

(43) For the sake of simplification, the scope of maintenance may be determined for a plurality of stages of an engine 10 together; i.e., as a cluster, according to the following formula:

(44) ${}_k=\frac{\underset{j}{\overset{n}{.Math.}}=1{}_{j,k}}{n}.$
where n denotes the number of engine stages.

(45) Possible data sources for determining the scope of maintenance are, for example, planning records of previous maintenance scopes, records of the spare parts that were needed for previous maintenance procedures, records of the manufacturing data of engine 10, or data from modification tracking systems. Moreover, database 18 contains on-wing and/or test stand data 26 of engine 10 after completion of the maintenance procedure, from which second performance parameter Y.sub.post,j is determined for the present engine j. With reference to engine j, maintenance parameters X.sub.i,j (X.sub.i,j) are determined from data 24 for each of the maintenance measures and used by database management device 20 to determine a functional relationship
Y.sub.model,j=f(X.sub.i,j,a.sub.i)
between the individual maintenance parameters X.sub.i,j (X.sub.i,j) and the contribution of each maintenance parameter X.sub.i,j (X.sub.i,j) to a difference Y.sub.model,j between first performance parameter Y.sub.pre and second performance parameter Y.sub.post. Subsequently, database management device 20 performs a compensation calculation in which a differenceY.sub.meas,j=Y.sub.post,jY.sub.pre,j between performance parameters Y.sub.pre,j, Y.sub.post,j. is determined for engine j. This difference Y.sub.meas,j is then used to perform a compensation calculation in which all coefficients a.sub.i of the computed functional relationship Y.sub.model,j are optimized in such a way that it holds that:

(46) $\mathrm{.Math.}=\underset{j}{.Math.}{Y}_{\mathrm{meas},j}-Y_{\mathrm{model},j}\stackrel{!}{->}\min$

(47) This may be done using, for example, the method of least squares. The result may then be output to maintenance personnel via an output device 28, and taken into account accordingly in the maintenance of future engines 10.

(48) FIG. 3 shows an alternative flow chart for determining a functional relationship Y.sub.model between different maintenance parameters X.sub.i,j (X.sub.i,j) and their respective contribution to a difference Y.sub.meas,j between an engine performance before an engine maintenance procedure and an engine performance after a maintenance procedure. In contrast to the preceding exemplary embodiment, database 18 includes above-described data 22, 24, 26 from previous maintenance procedures on the same or other engines 10. In addition, database 18 includes data 22, 24, 26 obtained based on the engine 10 that is currently to be serviced. Based on the historical data 22, 24, 26 and the currently determined data 22 and 24, database management device 20 determines the effects of individual maintenance measures on the expected overall effect on the engine performance, and outputs the same to maintenance personnel via output device 28. This enables selective planning and performing of the scope of maintenance, because it is possible to select only the most efficient maintenance measures which, considering, for example, the costs of the individual maintenance measures, provide the best cost/performance ratio for restoring a minimum engine performance. Alternatively or additionally, further aspects, such as, for example, the expected number of cycles of certain components, ensuring a minimum engine performance up to a certain point in time, and the like, may be taken into account in the planning and performance of maintenance. The data 22, 24 determined before maintenance and the data 26 determined after maintenance are also stored in database 18, so that the data content of database 18 is continuously increased and a self-learning prediction model is obtained.

(49) As mentioned earlier, different mathematical models may be used as a basis for characterizing individual maintenance measures. For example, based on literature data, a mathematical model of the deterioration of a feature can be described according to the formula
X.sub.k=a.sub.k*t.sup.1/.sup.k

(50) Together with the following formula:
.sub.k=b.sub.k*X.sub.k
for describing the effect of this feature on the engine's efficiency, the following formula can be derived:
.sub.k=.sub.k=10*.sub.k*max(t/1000t0.sub.k;0).sup.1/.sup.k
where:
a: coefficient for the rate of deterioration
: coefficient for the deterioration curve (qualitative)
: coefficient for the rate of performance loss
t0: beginning of the decrease in performance (in cycles or flight hours)

(51) Based on this formula, it is possible to predict the number of cycles (t) after which, starting from the base value or the beginning of the decrease in performance (t0), aging; i.e., a deterioration in engine efficiency, is to be expected due to the respective feature/component. By adding up all features for all considered engine stages according to the formula

(52) ${}_{\mathrm{tot}}=\underset{k}{.Math.}{}_k$
it is possible to predict and plan the overall maintenance requirements of the engine. Table 1 exemplarily shows optimized correlation factors regarding the efficiency of different maintenance measures on components of a high-pressure compressor with respect to the resulting increase in engine efficiency. It can be seen that different maintenance measures differ in their effectiveness for the improvement in efficiency.

(53) TABLE-US-00001 TABLE 1 Restoration of the . . . blade clearance by a blade clearance by a maintenance measure maintenance measure on on the blade tip(s) the casing liner (tip clearance, blade tip) (tip clearance, casing liner) blade contour surface roughness front rear Front rear front rear front rear 0.53 0.27 0.03 0.34 0.58 0.09 1.00 0.38 t0 0.30 0.70 0.30 0.08 0.27 0.68 0.19 0.41 5.62 5.84 7.63 7.33 6.10 5.21 6.17 6.62

(54) FIG. 4 shows a diagram in which the potential of two maintenance measures for engine performance improvement is plotted as a function of a number of cycles of a blade of engine 10. The number of cycles of the blade is plotted on the axis of abscissas, while the difference between the engine performance before and after maintenance is plotted on the axis of ordinates. The dot-dash line describes the effect of the maintenance measure restore blade clearance, while the dashed line describes the effect of the maintenance measure restore desired surface roughness on the engine performance as a function of the number of cycles of the blade. The solid line represents the combined overall potential of both maintenance measures. It can be seen that the effects of the two maintenance measures on the improvement of the engine performance vary as a function of the number of cycles, and that for higher numbers of cycles, the maintenance measure restore blade clearance has greater effects on the efficiency than the maintenance measure restore desired surface roughness.

(55) FIG. 5 shows a diagram in which measured efficiency changes of serviced engines are plotted in percent on the ordinate and the efficiency changes .sub.pred of serviced engines which are calculated based on determined functional relationships of individual maintenance measures are plotted in percent on the abscissa. Solid line VIa represents a fit with a linear relationship of the data points shown as triangles. Dotted line VIb illustrates the relationship as a linear trend model, while dashed lines VIc bound the confidence interval for the analysis of the performance parameters (95% probability). The high predictive power of the determined functional relationships is readily apparent.

(56) The parameter values given in the documents for defining process and measurement conditions for the characterization of specific properties of the subject matter of the present invention are to be considered as within the scope of the present invention, even in the context of deviations, e.g., due to measurement errors, system errors, weighing errors, DIN tolerances, and the like.