Method of stopping a rotorcraft engine in overspeed, and a system and a rotorcraft associated therewith

Patent metadata

Field	Value
Publication number	US-10150569-B2
Application number	US-201514867464-A
Country	US
Kind code	B2
Filing date	Sep 28, 2015
Priority date	Sep 26, 2014
Publication date	Dec 11, 2018
Grant date	Dec 11, 2018

Abstract

A method of stopping an engine of a rotorcraft in overspeed, the engine comprising a gas generator and a power assembly. When the engine is in operation, a relationship is established giving a limit derivative that varies as a function of the speed of rotation of the power assembly. The speed of rotation, referred to as the “current speed”, reached by the power assembly is measured and the time derivative of the speed of rotation is determined and referred to as the “current derivative”. The engine is stopped automatically when the limit derivative corresponding to the current speed as determined by the relationship is less than or equal to the current derivative.

First claim

What is claimed is:

1. A method of stopping an engine of a rotorcraft when the engine is in overspeed, the engine including a gas generator and a power assembly, the power assembly having a power turbine set in rotation by gas coming from the gas generator and a power shaft constrained to rotate with the power turbine, the power assembly being rotatable about a longitudinal axis at a speed of rotation, the method comprising:
prior to a flight of the rotorcraft, establishing a relationship that provides a limit derivative threshold over a range of speeds of rotation, the limit derivative threshold according to the relationship having a non-constant value varying over the range of speeds of rotation as a function of speed of rotation values within the range of speeds of rotation; and
during a flight of the rotorcraft:
measuring a current speed of rotation of the power assembly;
determining a time derivative of the current speed of rotation, wherein the time derivative of the current speed of rotation is referred to as a current derivative; and
determining that the current speed of rotation is in the range of speeds of rotation specified by the relationship and that the limit derivative threshold corresponding to the current speed of rotation in application of the relationship is less than or equal to the current derivative and automatically stopping the engine in response to the current speed of rotation being in the range of speeds of rotation specified by the relationship and the limit derivative threshold corresponding to the current speed of rotation in application of the relationship being less than or equal to the current derivative.

2. The method according to claim 1 , wherein the gas generator is fed by a fuel metering device, the fuel metering device is set between a minimum limit inducing a minimum fuel flow rate and a maximum limit inducing a maximum fuel flow rate, and wherein automatically stopping the engine is performed by setting the fuel metering device of the engine at the minimum limit.

3. The method according to claim 1 , wherein the engine includes a cock on a fuel pipe, and wherein automatically stopping the engine is performed by closing the cock.

4. The method according to claim 1 , wherein the engine is fed with fuel by a pump, and the pump is shut down following automatic stopping of the engine.

5. The method according to claim 1 , wherein the limit derivative threshold decreases between:
an intermediate value reached for an intermediate speed of rotation value; and
a minimum value reached for a maximum acceptable speed of rotation value, the maximum acceptable speed of rotation value being greater than the intermediate speed of rotation value, the minimum value of the limit derivative threshold being less than the intermediate value of the limit derivative threshold.

6. The method according to claim 5 , wherein the minimum value of the limit derivative threshold is zero.

7. The method according to claim 5 , further comprising not automatically stopping the engine when the speed of rotation is less than the intermediate speed of rotation value, whatever the current derivative.

8. The method according to claim 5 , further comprising automatically stopping the engine when the speed of rotation is greater than the maximum acceptable speed of rotation value, whatever the current derivative.

9. The method according to claim 5 , wherein the limit derivative threshold decreases linearly between the intermediate value and the minimum value.

10. The method according to claim 1 , wherein in a phase diagram plotting the speed of rotation along the abscissa axis and the time derivative of the speed of rotation up the ordinate axis, the relationship providing the limit derivative threshold over the range of speeds of rotation takes the form of a curve that is not parallel to the ordinate axis, the curve splitting the plane of the phase diagram into an authorized sector of operation that does not require the engine to be stopped and an unauthorized sector of operation that does require the engine to be stopped, the unauthorized sector being located downstream from the curve in the direction of increasing abscissa values, the engine to be stopped when an operating point corresponding to the current derivative and to the current speed is located in the unauthorized sector.

11. An overspeed safety system for an engine of a rotorcraft, the engine including a gas generator and a power assembly, the power assembly having a power turbine set in rotation by the gas generator and a power shaft constrained to rotate with the power turbine, the power assembly being rotatable about a longitudinal axis at a speed of rotation, the overspeed safety system comprising:
a shutdown system for stopping operation of the engine;
a processor unit connected to the shutdown system;
a speed sensor for measuring the speed of rotation of the power assembly;
the processor unit being connected to the speed sensor, the processor unit being configured to
store a relationship, established prior to a flight of the rotorcraft, that provides a limit derivative threshold over a range of speeds of rotation, the limit derivative threshold according to the relationship having a non-constant value varying over the range of speeds of rotation as a function of speed of rotation values within the range of speeds of rotation; and
during a flight of the rotorcraft:
use the speed sensor to measure a current speed of rotation of the power assembly;
determine a time derivative of the current speed of rotation, wherein the time derivative of the current speed of rotation is referred to as a current derivative; and
determine that the current speed of rotation is in the range of speeds of rotation specified by the relationship and that the limit derivative threshold corresponding to the current speed of rotation in application of the relationship is less than or equal to the current derivative and use the shutdown system to automatically stop the engine in response to the current speed of rotation being in the range of speeds of rotation specified by the relationship and the limit derivative threshold corresponding to the current speed of rotation in application of the relationship being less than or equal to the current derivative.

12. The overspeed safety system according to claim 11 , wherein the shutdown system includes a fuel-metering device conveying fuel to the gas generator.

13. The overspeed safety system according to claim 11 , wherein the shutdown system includes a pump conveying fuel to the gas generator.

14. The overspeed safety system according to claim 11 further comprising a shield ring surrounding the power turbine, the power turbine further having a plurality of blades, each blade being fastened to a fuse member.

15. The overspeed safety system according to claim 11 , wherein the processor unit is a full authority digital engine controller (FADEC) of the engine.

16. A rotorcraft comprising a rotor and at least one engine, each engine of the at least one engine driving a power transmission train connected to the rotor, wherein the rotorcraft further includes at least one overspeed safety system according to claim 11 , each overspeed safety system of the at least one overspeed system being connected to an engine of the at least one engine.

Assignees

• Airbus Helicopters

Inventors

• Certain Bernard

Classifications

• F02C9/46

  Emergency fuel control · CPC title

• B64D27/10

  of gas-turbine type  (jet aircraft B64D27/16) · CPC title

• F02C9/28

  Regulating systems responsive to plant or ambient parameters, e.g. temperature, pressure, rotor speed (F02C9/30 - F02C9/38, F02C9/44 take precedence) · CPC title

• F05D2270/042

  by keeping it below damagingly high values · CPC title

• F05D2270/304

  Spool rotational speed · CPC title