Method and an instrument for determining the limiting parameter of a turboshaft engine

• US 20080125931A1
• Filed: 06/07/2007
• Published: 05/29/2008
• Est. Priority Date: 06/16/2006
• Status: Active Grant

• Current Assignee: Airbus Helicopters
• Original Assignee: Eurocopter
• Inventors: Gaulmin, Francois-Xavier, Iraudo, Lionel
• Granted Patent: US 8,121,773 B2
• Time in Patent Office: Days
• US Class Current: 701/29
• CPC Class Codes: F02C 9/00 Controlling gas-turbine plants; Controlling fuel supply in air- breathing jet-propulsion plants controlling air intakes F02C7/057; controlling turbines F01D; controlling compressors F04D27/00; controlling in general G05
• CPC Class Codes: F05D 2260/80 Diagnostics
• CPC Class Codes: G01D 1/18 with arrangements for signalling that a predetermined value of an unspecified parameter has been exceeded G01D1/14 takes precedence

Abstract

The present invention relates to a method and to an instrument for determining the limiting margin of a surveillance parameter of a turboshaft engine. During a preliminary stage, a secondary processor means (11) determines a preliminary comfort margin. Thereafter, during a main stage, it estimates a useful comfort margin from the preliminary comfort margin, and then an apparent difference between the current value and the limit value of the surveillance parameter, and finally the limiting margin by subtracting the useful comfort margin from the apparent difference.

Claims

1. A method of determining the limiting margin between the current value and the limit value of a surveillance parameter for a turboshaft engine operating at a given speed, said surveillance parameter reaching a guaranteed value when the engine is old, the method comprising the following successive steps:

a) during a preliminary stage, determining a preliminary comfort margin from a real difference equal to said current value minus said guaranteed value; and

b) during a main stage;

b1) determining a useful comfort margin from said preliminary comfort margin;

b2) determining the apparent difference between the current value and the limit value of said surveillance parameter; and

b3) determining said limiting margin by subtracting the useful comfort margin from the apparent difference.

2. A method according to claim 1, wherein said main stage is performed continuously while said rotorcraft is in flight.

3. A method according to claim 1, wherein said preliminary stage is implemented solely when performing spot checks on the soundness of the engine.

4. A method according to claim 1, wherein said preliminary comfort margin is equal to said real difference, said useful comfort margin being equal to said preliminary comfort margin.

5. A method according to claim 1, wherein said preliminary comfort margin is estimated with the help of a moving average by adding the real differences determined during the most recent preliminary stages and then dividing the resulting sum by the number of preliminary stages taken into consideration.

6. A method according to claim 1, wherein during step a), a transfer relationship is used to modulate said real difference as a function of outside conditions, i.e. outside temperature (T0) or even outside pressure (P0) depending on the surveillance parameter under consideration, in order to obtain a modulated difference.

7. A method according to claim 6, wherein when the surveillance parameter is the speed of rotation of the gas generator of said turboshaft engine, said transfer relationship is the following first relationship in which “

*”

represents the multiplication symbol and Δ

NG′

, Δ

NG, and T0 represent respectively the modulated difference, the real difference between the current value and the guaranteed minimum value for said speed of rotation, and the temperature outside the rotorcraft;

$\mathrm{\Delta <br><br>}<br><br><br><br>{\mathrm{NG}}^{\mathrm{\prime <br><br>}}=\mathrm{\Delta <br><br>}<br><br><br><br>\mathrm{NG}*\sqrt{\frac{288}{T<br><br><br><br>0}}$

8. A method according to claim 6, wherein when the surveillance parameter is the ejection temperature of the gas at the inlet to the free turbine as developed by said turboshaft engine, said transfer relationship is the following second relationship in which “

*”

represents the multiplication symbol and Δ

T′

, Δ

T, T0, and P0 represent respectively the modulated difference, the real difference between the current value and the guaranteed value of said ejection temperature, and the temperature and the pressure outside the rotorcraft;

$\mathrm{\Delta <br><br>}<br><br><br><br>T^{\mathrm{\prime <br><br>}}=\mathrm{\Delta <br><br>}<br><br><br><br>T*\left({\left(\frac{1013.25}{P<br><br><br><br>0}\right)}^{\mathrm{\beta <br><br>}<br><br><br><br>1}*{\left(\frac{288.15}{T<br><br><br><br>0}\right)}^{\mathrm{\beta <br><br>}<br><br><br><br>2}\right)$

9. A method according to claim 6, wherein when the surveillance parameter is torque developed by said turboshaft engine, said transfer relationship is the following third relationship in which “

*”

represents the multiplication symbol and Δ

C′

, Δ

C, T0, and P0 represent respectively the modulated difference, the real difference between the current value and the guaranteed minimum value of said torque, and the temperature and the pressure outside the rotorcraft;

$\mathrm{\Delta <br><br>}<br><br><br><br>C^{\mathrm{\prime <br><br>}}=\mathrm{\Delta <br><br>}<br><br><br><br>C*\left({\left(\frac{1013.25}{P<br><br><br><br>0}\right)}^{\mathrm{\alpha <br><br>}<br><br><br><br>1}*{\left(\frac{288.15}{T<br><br><br><br>0}\right)}^{\mathrm{\alpha <br><br>}<br><br><br><br>2}\right)$

10. A method according to claim 6, wherein said preliminary comfort margin is equal to said modulated difference.

11. A method according to claim 6, wherein the preliminary comfort margin is estimated using a moving average, adding the modulated differences determined during the most recent preliminary stages and dividing the resulting sum by the number of preliminary stages taken into consideration.

12. A method according to claim 5, wherein said number of preliminary stages taken into consideration lies in the range five to fifteen.

13. A method according to claim 6, wherein when the preliminary comfort margin is determined by means of a modulated difference, during step b1), the useful comfort margin is estimated by replacing the preliminary comfort margin in the flying conditions of the rotorcraft using said transfer relationship.

14. A method according to claim 1, wherein when the surveillance parameter is the speed of rotation of the gas generator of the turboshaft engine, said guaranteed value corresponds to the value that would be reached by said speed of rotation if the engine were an old engine.

15. A method according to claim 1, wherein when the surveillance parameter is the ejection temperature of the gas at the inlet to the free turbine of the turboshaft engine, said guaranteed value corresponds to the value that said temperature would reach if the engine were an old engine.

16. A method according to claim 1, wherein when the surveillance parameter is the torque of the turboshaft engine, said guaranteed value corresponds to the limit value of said torque at the operating speed of the engine.

17. A first limitation instrument (10) for a rotorcraft (G) provided with at least one turboshaft engine (M), said instrument (10) comprising firstly acquisition sensors (1) for acquiring the current values of a plurality of surveillance parameters of said engine (M), and secondly main processor means (12) for determining a limiting parameter, namely the surveillance parameter having the smallest limiting margin, said instrument (10) being provided with display means (13) presenting the display value of said limiting parameter on a display screen (13′

), the instrument including secondary processor means (11) that;

a) during a preliminary stage, determining for each surveillance parameter, a preliminary comfort margin from a real difference equal to said current value minus said guaranteed value; and

b) during a main stage, determining in succession;

b1) a useful comfort margin from said preliminary comfort margin;

b2) the apparent difference between the current value and the limit value of said surveillance parameter; and

b3) said limiting margin by subtracting the useful comfort margin from the apparent difference.

18. A first limitation instrument according to claim 17, wherein said secondary processor means (11) is integrated in the main processor means (12).

19. A first limitation instrument according to claim 17, including secondary sensors measuring outside conditions, namely the outside pressure and temperature in order in particular to ensure that the secondary processor means (12) determines a modulated difference of said real difference as a function of outside conditions (P0, T0).

20. A first limitation instrument according to claim 17, wherein said secondary processor means (11) is provided with a memory (11′

) suitable for storing the most recently determined modulated differences in order to take a moving average thereof.

21. A first limitation instrument according to claim 17, wherein said display value corresponds to said limiting margin of said limiting parameter converted into a power margin by said main processor means (12).

22. A first limitation instrument according to claim 17, wherein said display value corresponds to said limiting margin of said limiting parameter converted into a pitch margin by said main processor means (12).