MONITORING A LEAK-FREE VALVE IN A BILLING DRIVE

Description

Technical field

[0001] The present invention relates generally to the lubrication system of a turbojet engine. It relates more particularly to the monitoring of an anti-leak valve of an oil supply circuit between an oil reservoir and elements to be lubricated of a turbojet engine. State of the prior art

[0002] A turbojet engine has a lubrication system, directly mounted on the accessory gearbox (also called AGB) of the turbojet engine. The lubrication system includes an oil reservoir, an oil supply circuit to distribute the oil to the turbojet engine components to be lubricated and an oil recovery circuit to ensure the oil returns to the reservoir. A set of pumps, actuators and sensors allow the circulation of oil from the reservoir to the turbojet engine components to be lubricated via the supply circuit and vice versa from the turbojet engine to the reservoir via the recovery circuit.

[0003] The two main functions of the lubrication system are, on the one hand, to lubricate and cool the turbojet components and, on the other hand, to maintain the oil temperature at an acceptable level. The overall monitoring of the lubrication system is carried out by control software that acquires data from an oil pressure and temperature sensor located at the accessory box and an oil level sensor located in the oil tank.

[0004] The oil supply circuit between the oil tank and the turbojet engine components to be lubricated includes an anti-leak valve, known as ALV. The anti-leak valve is an all-or-nothing type: it opens depending on the operating conditions and is not controlled by the turbojet engine computer. The anti-leak valve's function is to prevent the oil in the tank from emptying by gravity into the turbojet engine's accessory box when the turbojet engine is stopped.

[0005] If the anti-leak valve malfunctions, it no longer fulfills its function, which can have a negative impact on the turbojet engine.

[0006] Indeed, the various pumps in the lubrication system's supply and recovery circuits do not operate when the turbojet engine is stopped, and without the anti-leak valve, the oil drains from the oil tank into the turbojet engine's accessory box. This poses problems, including a risk that the empty tank could be filled with oil during a maintenance operation, which would lead to an overflow of oil in the turbojet engine. However, an overflow of oil has harmful effects on the turbojet engine.

[0007] There is therefore a need to monitor the anti-leak valve of the oil supply circuit between the oil tank and the elements to be lubricated in the turbojet engine, in order to be able to detect a failure of the anti-leak valve. FR2958911 A1 describes an example of monitoring the level of oil contained in the tank of a turbojet engine. Statement of the invention

[0008] The invention aims to solve the problems of the prior art by providing a method for monitoring an anti-leak valve of an oil supply circuit between an oil reservoir and elements to be lubricated of a turbojet, characterized in that it comprises steps of: Command for measuring oil level values ​​in the tank, respectively at the beginning and at the end of the turbojet engine startup, Calculation of the difference between the oil level values ​​in the tank at the beginning and at the end of the turbojet engine startup, to form a measured change in the oil level in the tank, Command for measuring an oil temperature value, Determination of an estimated change in the oil level in the tank, depending on the oil temperature value, Calculation of the difference between the measured change in the oil level in the tank and the estimated change in the oil level in the tank for the measured temperature value, Comparison of the calculated difference with a detection threshold, Activation of an alarm if the calculated difference is lower than the detection threshold.

[0009] Thanks to the invention, it is possible to monitor the anti-leak valve of the oil supply circuit between the oil tank and the elements to be lubricated of the turbojet without installing a position sensor on the anti-leak valve. Such a sensor would have an impact on the mass, cost and complexity of the product.

[0010] The invention also avoids preventive maintenance operations to ensure the proper functioning of the anti-leak valve, which would significantly increase maintenance constraints and which are not part of an operationally feasible solution.

[0011] According to a preferred feature, the start and end of the turbojet engine start are detected based on a speed measurement of a high pressure shaft of the turbojet engine. According to a preferred feature, the alarm is activated if the result of the comparison is less than the detection threshold for a first predetermined number of turbojet engine starts among a second predetermined number of the last turbojet engine starts.

[0012] The invention also relates to a device for monitoring an anti-leak valve of an oil supply circuit between an oil reservoir and elements to be lubricated of a turbojet, characterized in that it comprises: A sensor capable of measuring oil level values ​​in the tank, respectively at the start and at the end of the turbojet engine startup, A sensor capable of measuring an oil temperature value, A computer capable of calculating the difference between the oil level values ​​in the tank at the start and at the end of the turbojet engine startup to form a measured change in the oil level in the tank, determining an estimated change in the oil level in the tank as a function of the oil temperature value, calculating the difference between the measured change in the oil level in the tank and the estimated change in the oil level in the tank for the measured temperature value, comparing the calculated difference with a detection threshold, and activating an alarm if the calculated difference is lower than the detection threshold.

[0013] The invention also relates to a turbojet engine equipped with a device for monitoring an anti-leak valve of an oil supply circuit between an oil reservoir and elements to be lubricated of the turbojet engine, as previously presented.

[0014] The invention also relates to an aircraft equipped with a turbojet engine as previously presented.

[0015] The device, the turbojet and the aircraft have advantages similar to those previously presented.

[0016] In a particular embodiment, the steps of the method according to the invention are implemented by computer program instructions.

[0017] Consequently, the invention also relates to a computer program on an information medium, this program being capable of being implemented in a computer, this program comprising instructions adapted to the implementation of the steps of a method as described above.

[0018] The invention also relates to an information medium readable by a computer, and comprising computer program instructions adapted to the implementation of the steps of a method as described above. Brief description of the drawings

[0019] Other characteristics and advantages will appear on reading the following description of a preferred embodiment given by way of non-limiting example, described with reference to the figures in which: [ Fig. 1 ] illustrates a turbojet engine equipped with a monitoring circuit for the anti-leak valve of the lubrication system supply circuit, according to one embodiment of the invention, [ Fig. 2 ] illustrates a method for monitoring the anti-leak valve of the lubrication system supply circuit, according to one embodiment of the invention, [ Fig. 3 ] illustrates the evolution of the oil level in the tank during the start-up of the turbojet, [ Fig. 4 ] illustrates the oil level in the tank during turbojet start-up as a function of oil temperature, [ Fig. 5 ] illustrates an indicator formed according to the invention, as a function of the oil temperature, [ Fig. 6 ] illustrates the distribution of the indicator represented in the Figure 5 , [ Fig. 7 ] illustrates indicators determined for turbojet starts and the distribution of these indicators.

[0020] Identical, similar or equivalent parts of different figures bear the same numerical references so as to facilitate the transition from one figure to another.

[0021] The different parts represented in the figures are not necessarily on a uniform scale, to make the figures more readable.

[0022] The different possibilities (variants and embodiments) must be understood as not being mutually exclusive and can be combined with each other. Detailed description of specific embodiments

[0023] According to a preferred embodiment, shown in figure 1 , a turbojet engine comprises a lubrication system 1 for a set 2 of turbojet engine components to be lubricated.

[0024] The lubrication system comprises an oil reservoir 10, an oil supply circuit 11 for distributing the oil to the turbojet engine components to be lubricated and an oil recovery circuit 12 for ensuring the return of oil to the reservoir. The turbojet engine also comprises an accessory box, not shown.

[0025] We are particularly interested in an anti-leak valve 110, called ALV from the English “Anti Leak Valve”, of the oil supply circuit 11, arranged between the reservoir 10 and the set 2 of organs to be lubricated.

[0026] The anti-leak valve is an all-or-nothing type. The anti-leak valve's function is to prevent the oil in the tank from emptying by gravity into the turbojet's accessory box when the turbojet is stopped.

[0027] The turbojet engine comprises sensors, in particular an oil temperature sensor 3 placed in the accessory box, a high pressure shaft speed sensor 4 of the turbojet engine and an oil level sensor 5 placed in the oil tank 10. Only the elements useful for understanding the invention are described, and the other elements of the turbojet engine and its lubrication system are known to those skilled in the art and will not be detailed here.

[0028] The turbojet engine includes a circuit 6 for monitoring the anti-leak valve 110 of the oil supply circuit. The anti-leak valve monitoring circuit may be a dedicated computer or a subset of a computer which performs overall monitoring of the oil circuit via regulation software which receives data from sensors.

[0029] The monitoring circuit 6 has the general structure of a computer. It comprises in particular a processor 60 executing a computer program implementing the method according to the invention, a memory 61, an input interface 62 and an output interface 63.

[0030] These different elements are traditionally connected by a 65 bus.

[0031] The input interface 62 is connected to respective outputs of the sensors 3, 4 and 5 and is intended to receive the quantities measured by these sensors.

[0032] The processor 60 executes the processing operations described below. These processing operations are carried out in the form of computer program code instructions which are stored in the memory 61 before being executed by the processor 60.

[0033] Memory 61 stores measured values ​​and calculated values.

[0034] The output interface 63 is connected to an alarm system 7, integrated or not into the monitoring circuit 6 and which is activated depending on the result of the monitoring. The alarm system 7 is conventional and includes an interface intended for an operator to deliver an alarm to him.

[0035] There figure 2 represents an embodiment of a method for monitoring the anti-leak valve 110 of the oil supply circuit 11 of the turbojet engine. This method comprises steps E0 to E9 implemented by the monitoring circuit 6 during start-up of the turbojet engine.

[0036] Step E0 is a waiting step, in which the turbojet engine is stopped. The following steps E1 to E9 are carried out when a turbojet engine start is initiated.

[0037] When starting the turbojet engine in the absence of a leak from the anti-leak valve 110 of the oil supply circuit 11, the change in the quantity of oil present in the set 2 of components of the turbojet engine to be lubricated is a reproducible phenomenon where only the variability in oil temperature from one flight to another leads to a slight dispersion.

[0038] In the event of a leak from the anti-leak valve 110 of the oil supply circuit 11, oil flows between the tank and the accessory box when the turbojet engine is stopped. This causes an abnormally high quantity of oil in the set 2 of turbojet engine components to be lubricated just before start-up and at the beginning of start-up. In this case, during start-up of the turbojet engine, the change in the quantity of oil present in the set 2 of turbojet engine components to be lubricated will therefore be different from the change normally encountered.

[0039] Step E1 is a command to measure the EOL stop oil level in the tank 10 at the start of the turbojet engine startup. The oil level in the tank 10 is measured by the sensor 5. The overall quantity of oil in the turbojet engine is substantially equal to the sum of the quantity of oil present in the tank 10 and the quantity of oil present in the set 2 of components of the turbojet engine to be lubricated. The measurement of the oil level in the tank 10 is therefore an indicator of the quantity of oil present in the set 2 of components of the turbojet engine to be lubricated.

[0040] The turbojet engine start is identified by the N2 speed of the turbojet engine's high-pressure shaft. Indeed, during turbojet engine start, the N2 speed of the turbojet engine's high-pressure shaft varies between zero at the start of start and a speed characteristic of an idle speed at the end of start. The characteristic speed of an idle speed is, for example, equal to 70% of the turbojet engine's maximum speed. The N2 speed of the high-pressure shaft is measured by sensor 4.

[0041] The start of the turbojet engine startup is identified by the N2 speed of the turbojet engine's high pressure shaft which is zero.

[0042] The result of step E1 is the measured EOL stop value of the oil level in tank 10 at the start of turbojet engine startup.

[0043] The next step E2 is an oil temperature measurement command performed by the oil temperature sensor 3.

[0044] The result of step E2 is a measured EOT start temperature value during turbojet engine start-up.

[0045] The next step E3 is a command to measure the idle EOL oil level in the tank 10 at the end of the turbojet engine start. Here too, the oil level in the tank is measured by the sensor 5 and is characteristic of the quantity of oil present in the set 2 of turbojet engine components to be lubricated.

[0046] The end of turbojet start is identified by the N2 speed of the turbojet high pressure shaft, which is equal to the turbojet idle speed.

[0047] The result of step E3 is the measured EOL idle oil level value in tank 10 at the end of turbojet engine startup.

[0048] Alternatively, the measurement times during start-up are different and determined by other N2 speed values ​​of the high pressure shaft of the turbojet.

[0049] There figure 3 represents the evolution of the EOL oil level in tank 10 during the start of the turbojet engine, i.e. from the beginning to the end of the start, as a function of the N2 speed of the high pressure shaft of the turbojet engine. figure 3 represents a nominal operating case, when the anti-leak valve 110 operates normally.

[0050] The N2 speed of the turbojet's high pressure shaft varies between zero speed and idle speed, and is expressed as a percentage of the turbojet's maximum speed.

[0051] In the event of a leak from the anti-leak valve 110, it is recalled that there is an excess of oil in the set 2 of turbojet components to be lubricated and consequently an abnormal distribution of the oil in the turbojet, at the start of the start. At the end of the start, the behavior will be stabilized since recovery pumps of the oil recovery circuit will have recovered all or part of the oil initially stored in the set 2 of turbojet components to be lubricated.

[0052] The next step E4 is a calculation of an indicator equal to the difference of the measured value EOL stop of oil level in the tank at the beginning of the turbojet engine start and the measured value EOL idle of oil level in the tank at the end of the turbojet engine start: EOL Mesure = EOL stop − EOL ralenti

[0053] This indicator forms a measured change in the oil level in the reservoir. Its function is to detect any abnormal behavior of the anti-leak valve 110 during start-up, based on the variation in the oil level in the reservoir between the start of start-up (zero engine speed) and the end of start-up (engine idle reached). The result of step E4 is therefore the value of the EOL Measure indicator.

[0054] In parallel with step E4, or following step E4, step E5 is a calculation of an estimated change in the oil level in the tank 10 as a function of the oil temperature at start-up of the turbojet engine. The oil temperature is measured by the sensor 3.

[0055] The inventors found that the variation observed in the oil level in the tank at turbojet start-up is mainly related to the oil temperature. To improve the accuracy of the above indicator, the oil temperature is taken into account to gain precision.

[0056] There figure 4 represents the EOL oil level in tank 10 during turbojet start-up as a function of oil temperature.

[0057] There is a significant correlation between the magnitude of the oil level in the tank at turbojet startup and the oil temperature at startup.

[0058] Thus, it is possible to model the variations in oil temperature at startup by creating a model of the oil level in the tank at turbojet startup in the form: EOL Mod è le = a × EOT start + b

[0059] Where EOT start represents the oil temperature at turbojet start and a and b are constants.

[0060] The result of step E5 is therefore the estimated EOL value Oil level model in tank 10 for the EOT start oil temperature measured at turbojet start.

[0061] Steps E4 and E5 are followed by step E6 in which the difference ΔEOL between the EOL Measurement value calculated in step E4 and the model EOL value calculated in step E5 is calculated: Δ EOL = EOL Mesure − EOL Mod è le

[0062] The ΔEOL difference is an indicator in which the influence of temperature is removed.

[0063] The result of step E6 is therefore the value of the ΔEOL indicator.

[0064] There Figure 5 represents the difference ΔEOL as a function of oil temperature over a series of measurements made with a given turbojet. By comparing the Figure 5 with

[0065] there figure 4, we see that this indicator is centered on zero, whatever the temperature in an operating range.

[0066] There figure 6 represents the distribution of the ΔEOL indicator over the series of measurements made with a given turbojet. This distribution can be approximated by a relatively little dispersed Gaussian.

[0067] The next step E7 is a detection to determine whether the oil level in the tank is normal or not, that is, whether the anti-leakage valve is working normally or not.

[0068] To do this, the value of the ΔEOL indicator determined in the previous step is compared to a detection threshold, for example equal to -2 as shown in figure 7 The result of the comparison is stored.

[0069] On the left side of the figure 7, each point above the detection threshold is a ΔEOL indicator value corresponding to a turbojet engine start-up carried out with a healthy anti-leak valve, while each point below the detection threshold is a ΔEOL indicator value corresponding to a turbojet engine start-up carried out with a faulty anti-leak valve. The right part of the figure represents the distribution of the different points in the left part of the figure.

[0070] If the ΔEOL indicator value is higher than the detection threshold, then the oil level is normal and step E7 is followed by step E0 already described.

[0071] If, on the contrary, the value of the indicator ΔEOL is lower than the detection threshold, then the oil level is abnormal and step E7 is followed by step E8 which is a test to determine whether N, where N is a first predetermined number, for example equal to three, of detections of abnormal oil level, among the M, where M is a second predetermined number greater than N and for example equal to five, last starts of the turbojet engine have been detected.

[0072] If the answer is negative, then step E8 is followed by step E0 already described.

[0073] If, on the other hand, the answer is positive, this means that the detection of an abnormal oil level is a recurring phenomenon. Step E8 is then followed by step E9, at which an alarm is triggered. The alarm is, for example, a message intended for a turbojet maintenance operator.

Claims

1. Method for monitoring an anti-leak valve (110) of a circuit (11) for supplying oil between an oil reservoir (10) and elements (2) to be lubricated of a jet engine, characterised in that it comprises steps of: - Controlling the measurement (E1, E3) of oil level values (EOLstop, EOLidle) in the reservoir, respectively at the start and at the end of the jet engine start-up, - Calculating (E4) the difference (EOLMeasurement) between the oil level values in the reservoir at the start and at the end of the jet engine start-up, to form a measured change in the oil level in the reservoir, - Controlling the measurement (E2) of an oil temperature value (EOTstart), - Determining (E5) an estimated change (EOLModel) of the oil level in the reservoir, depending on the oil temperature value, - Calculating (E6) the difference (ΔEOL) between the measured change in the oil level in the reservoir and the estimated change in the oil level in the reservoir for the measured temperature value, - Comparing (E7) the calculated difference with a detection threshold, - Activating (E9) an alarm if the calculated difference is lower than the detection threshold.

2. Method for monitoring an anti-leak valve according to claim 1, wherein the start and the end of the jet engine start-up are detected on the basis of a speed measurement (N2) of a high pressure shaft of the jet engine.

3. Method for monitoring an anti-leak valve according to claim 1 or 2, wherein the alarm is activated if the result of the comparison is lower than the detection threshold for a first predetermined number (N) of jet engine start-ups from a second predetermined number (M) of recent jet engine start-ups, higher than the first predetermined number.

4. Device for monitoring an anti-leak valve (110) of a circuit (11) for supplying oil between an oil reservoir (10) and elements (2) to be lubricated of a jet engine, characterised in that it comprises: - A sensor (5) capable of measuring oil level values in the reservoir (10), respectively at the start and at the end of the jet engine start-up, - A sensor (3) capable of measuring an oil temperature value, - A calculator (6) capable of calculating the difference between the oil level values in the reservoir at the start and at the end of the jet engine start-up, to form a measured change in the oil level in the reservoir, determining an estimated change of the oil level in the reservoir depending on the oil temperature value, calculating the difference between the measured change in the oil level in the reservoir and the estimated change of the oil level in the reservoir for the measured temperature value, comparing the difference calculated with a detection threshold, and activating an alarm if the calculated difference is lower than the detection threshold.

5. Jet engine equipped with a device for monitoring an anti-leak valve of a circuit for supplying oil between an oil reservoir and elements to be lubricated of the jet engine, according to claim 4.

6. Aircraft equipped with a jet engine according to claim 5.

7. Computer program comprising instructions for executing steps of a method according to any one of claims 1 to 3 when said program is executed by a computer.

8. Recording medium that can be read by a computer on which is saved a computer program comprising instructions for executing steps of the method according to any one of claims 1 to 3.