FORM 2
THE PATENTS ACT, 1970
(39 of 1970)
& The Patent Rules, 2003
COMPLETE SPECIFICATION
1.TITLE OF THE INVENTION:
SYSTEM AND METHOD FOR CONTROLLING A SPEED OF ROTATION OF AN
AIRCRAFT TURBINE ENGINE WITH FAULT MANAGEMENT
2. APPLICANT:
Name: SAFRAN AIRCRAFT ENGINES
Nationality: France
Address: 2 boulevard du Général Martial Valin, 75015 PARIS, France.
3. PREAMBLE TO THE DESCRIPTION:
The following specification particularly describes the invention and the manner in
which it is to be performed:
2
DESCRIPTION
5
TECHNICAL FIELD
The invention relates to the field of controlling an aircraft turbine engine and, more
specifically, the field of closed-loop controlling the rotational speed of the turbine engine by
monitoring a fuel metering valve. It concerns a control system and method for an aircraft
10 turbine engine, as well as a turbine engine equipped with the control system.
STATE OF THE PRIOR ART
The speed of rotation of an aircraft turbine engine is generally monitored by a fuel
metering valve comprising a metering slide, whose position determines a volumetric flow rate
15 of fuel injected into the combustion chamber and an actuator arranged to displace the
metering slide depending on a control electric current. For most turbine engines, a closedloop
control of the rotational speed to a speed setpoint is carried out in order to obtain better
performances of the turbine engine, in particular in terms of response to the speed setpoint.
This closed-loop control can in particular be based on a double control loop, namely a global
20 loop controlling the rotational speed of the turbine engine by calculating a position setpoint of
the metering slide, and a local loop controlling the actuator depending on a position of the
metering slide, measured by a position sensor. A drawback of this double control loop is that
in case of failure of the position sensor, all rotational speed control can no longer be carried
out. The loss of the position sensor then leads to a stop of the turbine engine. On a multi25
engine aircraft, this implies a redistribution of the thrust and the electrical energy generation
on the remaining turbine engines. On a single-engine aircraft, the loss of the position sensor is
more critical since it implies not only a total loss of thrust but also a loss of the electrical
energy generation. The position sensor being a critical element for the flight of the aircraft, it
is normally doubled. Each position sensor then provides a position measurement to a
30 corrector of the local loop, which performs the closed-loop control based on an average value
of the two position measurements. Nevertheless, in the presence of two position sensors, a
problem arises in the case of discrepancy between the position measurements. The corrector
is not able to determine which of the position measurements is correct and should be used for
3
the closed-loop control. Thus, even in case of failure of a single measurement sensor, the
closed-loop control of the rotational speed of the turbine engine can be prevented. A fortiori,
the closed-loop control is prevented in the case of loss of the two position sensors.
In view of the above, the aim of the invention is to provide a system 5 for controlling an
aircraft turbine engine allowing closed-loop controlling the rotational speed thereof to a
setpoint even in the case of failure of a position sensor measuring a position of the metering
slide. Another aim of the invention is to provide a control system guaranteeing an operation
of the turbine engine within nominal operating ranges even in the absence of information on
10 the position of the metering slide.
DISCLOSURE OF THE INVENTION
To this end, the invention is based on a closed-loop control of the rotational speed
dispensing with the measurement of position of the metering slide. The actuator is driven
15 directly depending on a deviation between the rotational speed setpoint and the rotational
speed measurement.
More specifically, the invention relates to a control system for an aircraft turbine
engine, the turbine engine comprising:
20  a combustion chamber,
 a fuel metering valve including a metering slide, a position of which determines a
volumetric flow rate of fuel injected into the combustion chamber and an actuator arranged
to displace the metering slide depending on a control electric current,
 a position sensor arranged to measure a position of the metering slide and deliver a
25 position measurement,
 a speed sensor arranged to measure a rotational speed of the turbine engine and
deliver a rotational speed measurement, and
 a monitoring unit arranged to deliver a rotational speed setpoint, to detect a failure
of the position sensor and to deliver a failure signal in the case of detection of a failure of the
30 position sensor.
According to the invention, the control system comprises:
 a nominal-mode processing chain including:
4
- a global corrector arranged to receive the rotational speed setpoint and the
rotational speed measurement and determine a fuel mass flow rate setpoint
depending on the rotational speed setpoint and the rotational speed measurement,
- a conversion module arranged to convert the fuel mass flow rate setpoint into a
position 5 setpoint, and
- a local corrector arranged to receive the position setpoint and the position
measurement and determine a nominal-mode control electric current depending on
the position setpoint and the position measurement,
 a degraded-mode processing chain including a direct corrector arranged to receive
10 the rotational speed setpoint and the rotational speed measurement and determine a
degraded-mode control electric current depending on the rotational speed setpoint and the
rotational speed measurement, and
 a mode management module arranged to receive the failure signal, the nominalmode
control electric current and the degraded-mode control electric current, and to deliver,
15 to the actuator of the fuel metering valve, the nominal-mode control electric current in the
absence of reception of the failure signal and the degraded-mode control electric current in
the case of reception of the failure signal.
Within the scope of the present invention, a flight parameter of the aircraft
20 corresponds for example to a Mach number or to an altitude of the aircraft. An operating
parameter of the turbine engine corresponds for example to a temperature within the turbine
engine, for example a temperature of the exhaust gases or in the combustion chamber, or to
a pressure within the turbine engine, for example a static pressure at the inlet of the
combustion chamber.
25
According to a particular embodiment, the direct corrector is arranged to further
receive one or more flight parameter(s) of the aircraft and/or one or more operating
parameter(s) of the turbine engine, the degraded-mode control electric current being further
determined depending on the flight parameters of the aircraft and/or the operating
30 parameters of the turbine engine. Advantageously, the direct corrector can be arranged to
receive a Mach number and an altitude of the aircraft and determine the degraded-mode
control electric current depending on these flight parameters.
5
The direct corrector is for example a proportional corrector, an integral corrector, a
derivative corrector or any combination of these correctors. In particular, the direct corrector
may include a corrector of the proportional-integral type. When the direct corrector receives
a flight parameter of the aircraft and/or an operating parameter of the turbine engine, the
gain of the proportional corrector, the integration constant of the proportional 5 corrector
and/or the derivative constant of the derivative corrector can be variables depending on
these parameters.
The degraded-mode processing chain can also be arranged so as to integrate a
10 protection module arranged to limit the operation of the turbine engine in nominal operating
ranges, which correspond to a closed-loop control of the turbine engine by the nominal-mode
processing chain, or even in reduced operating ranges.
In particular, in a first embodiment, the degraded-mode processing chain further
15 includes a gradient limiter arranged to receive the rotational speed setpoint and determine an
acceleration-limited speed setpoint. The acceleration-limited speed setpoint is determined so
as to limit a speed of evolution of the rotational speed setpoint and is used by the direct
corrector instead of the rotational speed setpoint. In practice, the acceleration-limited speed
setpoint is determined so as to follow the rotational speed setpoint with an evolution speed
20 which is less than or equal to a predetermined maximum acceleration threshold.
The gradient limiter can further be arranged to receive one or more flight parameter(s)
of the aircraft and/or one or more operating parameter(s) of the turbine engine, the
predetermined maximum acceleration threshold then being variable depending on the flight
25 parameters and/or the operating parameters of the turbine engine.
In a second embodiment, the degraded-mode processing chain further includes a
limiting circuit arranged to receive the rotational speed setpoint, the rotational speed
measurement and an operating parameter of the turbine engine, and determine a limited
30 speed setpoint, the limited speed setpoint being determined by calculating a difference
between the operating parameter and a predetermined minimum threshold parameter or
between the operating parameter and a predetermined maximum threshold parameter, by
multiplying said difference by a coefficient relating to the operating parameter, by adding the
6
rotational speed measurement to the result of the multiplication, and by taking, as limited
speed setpoint, the maximum between the result of the addition and the rotational speed
setpoint when the difference is calculated relative to a minimum threshold parameter, and
the minimum between the result of the addition and the rotational speed setpoint when the
difference is calculated relative to a maximum threshold 5 parameter.
In particular, the limiting circuit can be arranged to receive, as an operating parameter,
a pressure measurement of the turbine engine, for example a measurement of the static
pressure at the inlet of the combustion chamber, a difference being calculated between the
10 pressure measurement and a predetermined minimum pressure. Alternatively, the limiting
circuit can be arranged to receive, as an operating parameter, a temperature measurement of
the turbine engine, for example a measurement of the temperature of the exhaust gases, a
difference being calculated between the temperature measurement and a predetermined
maximum temperature.
15
The limiting circuit can be arranged to receive several operating parameters of the
turbine engine, each operating parameter being compared to a minimum or maximum
threshold parameter, as previously indicated. In this case, the limited speed setpoint is
determined as being the maximum of the different minima and maxima determined for the
20 operating parameters of the turbine engine.
The invention also relates to a turbine engine for an aircraft comprising:
 a combustion chamber,
 a fuel metering valve including a metering slide, a position of which determines a
25 volumetric flow rate of fuel injected into the combustion chamber and an actuator arranged
to displace the metering slide depending on a control electric current,
 a position sensor arranged to measure a position of the metering slide and deliver a
position measurement,
 a speed sensor arranged to measure a rotational speed of the turbine engine and
30 deliver a rotational speed measurement,
 a monitoring unit arranged to deliver a rotational speed setpoint, to detect a failure
of the position sensor and to deliver a failure signal in the case of detection of a failure of the
position sensor, and
7
 a control system as previously described.
According to a particular embodiment, the position sensor comprises a first sensitive
element and a second sensitive element, the first sensitive element being arranged to
measure a position of the metering slide and deliver a first position measurement, 5 the second
sensitive element being arranged to measure a position of the metering slide and deliver a
second position measurement, the monitoring unit being arranged to detect a failure of the
position sensor in the case of a deviation between the first position measurement and the
second position measurement which is greater than a predetermined threshold or in the
10 absence of reception of the first position measurement and of the second position
measurement.
Finally, the invention relates to a control method for an aircraft turbine engine, the
turbine engine comprising:
15  a combustion chamber,
 a fuel metering valve including a metering slide, a position of which determines a
volumetric flow rate of fuel injected into the combustion chamber and an actuator arranged
to displace the metering slide depending on a control electric current,
 a position sensor arranged to measure a position of the metering slide and deliver a
20 position measurement,
 a speed sensor arranged to measure a rotational speed of the turbine engine and
deliver a rotational speed measurement, and
 a monitoring unit arranged to deliver a rotational speed setpoint, to detect a failure
of the position sensor and to deliver a failure signal in the case of detection of a failure of the
25 position sensor.
According to the invention, the control method comprises the steps consisting of in:
 supervising a failure of the position sensor,
 in the absence of failure of the position sensor,
- determining a fuel mass flow rate setpoint depending on the rotational speed
30 setpoint and the rotational speed measurement,
- converting the fuel mass flow rate setpoint into a position setpoint,
- determining a nominal-mode control electric current depending on the position
setpoint and the position measurement, and
8
- delivering, to the actuator of the fuel metering valve, the nominal-mode control
electric current,
 in the case of a failure of the position sensor,
- determining a degraded-mode control electric current depending on the
rotational speed setpoint and the rotational speed 5 measurement, and
- delivering, to the actuator of the fuel metering valve, the degraded-mode control
electric current.
BRIEF DESCRIPTION OF THE DRAWINGS
10 Other features, details and advantages of the invention will become apparent on
reading the following description, given only by way of example and with reference to the
appended drawings in which:
- Figure 1 represents, in block diagram form, an example of a turbine engine of an
aircraft and a control system with double control loop for the turbine engine;
15 - Figure 2 represents, in block diagram form, an example of a turbine engine of an
aircraft and of a control system according to the invention for the turbine engine, said control
system comprising a nominal-mode processing chain and a degraded-mode processing chain;
- Figure 3 represents a closed-loop control carried out using the degraded-mode
processing chain;
20 - Figure 4 represents a protection module equipping the degraded-mode processing
chain;
- Figure 5 represents an example of a control method according to the invention.
DETAILED DESCRIPTION
25 Figure 1 represents, in block diagram form, an example of a turbine engine of an aircraft
and of a control system for the turbine engine based on a double control loop. The turbine
engine 10 comprises in particular a servo valve 11, a metering slide 12, a combustion chamber
and a set of rotating elements, generally designated by the term “engine” 13, a position
sensor 14 and a speed sensor 15. The servo valve 11 and the metering slide 12 form a fuel
30 metering valve. The metering slide 12 is arranged to be able to be displaced into different
positions by the servo valve 11, each position, denoted “Pos” corresponding to a volumetric
flow rate of fuel, denoted “WF”, which is injected into the combustion chamber. The
combustion of this volume of fuel drives in rotation rotating elements of the turbine engine,
9
in particular a compressor and a turbine. For a double-body turbine engine, the rotating
elements comprise a low-pressure body and a high-pressure body, each body comprising a
compressor, a turbine and a connecting shaft between the compressor and the turbine. The
rotational speed of one of the rotating elements is measured by the speed sensor 15. For the
remainder of the description, it is considered that the speed sensor 5 15 measures the
rotational speed of the low pressure body XNBP, the measurement being denoted “M_XNBP”.
Moreover, the position Pos of the metering slide 12 is measured by the position sensor 14,
the position measurement being denoted “M_Pos”. The position sensor 14 may include two
sensitive elements, each sensitive element being arranged to measure the position of the
10 metering slide 12 and deliver a position measurement. The position sensor 14 is for example a
sensor of the “Linear Variable Differential Transformer” LVDT type.
The control system 20 comprises a global corrector 21, a converter 22 and a local
corrector 23. The global corrector 21 receives the rotational speed measurement M_XNBP
15 and a speed setpoint, denoted “C_XNBP”, provided by a unit for monitoring the aircraft. This
setpoint is for example determined depending on the thrust required by a pilot of the aircraft
or an automatic pilot. Depending on the speed setpoint C_XNBP and the rotational speed
measurement M_XNBP, the global corrector 21 determines a fuel mass flow rate setpoint,
denoted “C_WF”. The converter 22 is arranged to receive this setpoint C_WF and determine
20 an associated position setpoint C_Pos for the metering slide 12. The converter 22 can in
particular determine the position setpoint C_Pos depending on one or more parameter(s), for
example a temperature of the fuel upstream of the metering slide 12. The position setpoint
C_Pos is delivered to the local corrector 23, which also receives the position measurement
M_Pos. The local corrector 23 is arranged to determine a control electric current I_com
25 depending on the position setpoint C_Pos and the position measurement M_Pos. When the
position sensor 14 provides several position measurements, the local corrector 23 considers
for example an average value of the position measurements. The control electric current
I_com is delivered to the servo valve 11, such that the actuation thereof displaces the
metering slide into the desired position. The global corrector 21 and the local corrector 23 are
30 for example PID (proportional, integral, derivative) correctors.
The control system 20 thus includes a double control loop, namely a local loop BL,
formed by the local corrector 23, the servo valve 11 and the position sensor 14, and a global
10
loop BG, formed by the global corrector 21, the converter 22, the local corrector 23, the servo
valve 11, the position sensor 14, the metering slide 12, the engine 13 and the speed sensor
15. It emerges from this arrangement that in the case of absence of reception of the position
measurement M_Pos by the local corrector 23, or of a significant deviation between the
position measurements by several sensitive elements, the local loop 5 BL is no longer
operational, which also leads to prevent the operation of the global loop BG. In the absence of
any closed-loop control, the turbine engine is automatically or manually stopped.
In order to avoid a loss of control of the turbine engine, and therefore of the turbine
10 engine itself, the invention proposes a control system comprising, in addition to the double
control loop which is described above, a loop for controlling the rotational speed of the
turbine engine which does not take into account the position measurement M_Pos and which
can be used in the case of unavailability or failure of this position measurement M_Pos. This
control loop is called a “degraded-mode failure loop”.
15
Figure 2 represents, in block diagram form, an example of a turbine engine of an aircraft
and a control system according to the invention for the turbine engine. The turbine engine 10
comprises, like the turbine engine of Figure 1, a servo valve 11, a metering slide 12, an engine
13 including a combustion chamber and rotating elements, a position sensor 14 and a speed
20 sensor 15. Furthermore, the turbine engine 10 comprises a monitoring unit 16, a temperature
sensor 17 arranged to measure a temperature within the turbine engine and a pressure
sensor 18 arranged to measure a pressure within the turbine engine. The monitoring unit 16 is
arranged to provide the speed setpoint C_XNBP and various flight and/or operating
parameters of the turbine engine 10, as indicated hereinafter. In this exemplary embodiment,
25 the temperature sensor 17 is arranged to determine a measurement of the temperature of
the exhaust gases M_TM49 and the pressure sensor 18 is arranged to determine a
measurement of the static pressure at the inlet of the combustion chamber M_PS32. The
temperature sensor 17 could nevertheless measure any other temperature of the turbine
engine necessary for the regulation thereof. The control system 100 comprises a nominal30
mode processing chain 110, a degraded-mode processing chain 120 and a mode management
module 130.
11
The nominal-mode processing chain 110 includes, in a manner identical to the control
system 20 of Figure 1, a global corrector 21, a converter 22 and a local corrector 23. In
addition, it includes a C/P limiter 111, a protection corrector 112 and a correction
management module 113. The C/P limiter 111 receives, from the monitoring unit 16, flight
parameters and operating parameters of the turbine engine, and determines 5 minimum and
maximum limits of fuel flow rate depending on these parameters. The flight parameters
comprise, for example, a Mach number and an altitude of the aircraft and the operating
parameters of the turbine engine comprise, for example, a measurement of the temperature
of the exhaust gases M_TM49 and a measurement of the static pressure at the inlet of the
10 combustion chamber M_PS32. The protection corrector 112 also receives flight parameters
and operating parameters of the turbine engine. From these parameters, the protection
corrector 112 calculates a fuel mass flow rate setpoint C_WFps allowing meeting the
threshold parameters, for example a maximum exhaust gas temperature TM49_MAX and a
minimum static pressure at the inlet of the combustion chamber PS32_MIN. Of course, other
15 parameters can be taken into account by the protection corrector 112. In practice, the
protection corrector 112 can include an individual protection corrector for each parameter to
be supervised. The global corrector 21 determines the fuel mass flow rate setpoint C_WF
depending on the speed setpoint C_XNBP and the rotational speed measurement M_XNBP.
The fuel mass flow rate setpoints C_WF and C_WFps, and the minimum and maximum limits
20 of fuel flow rate are provided to the correction management module 113, which checks that
the fuel mass flow rate setpoint C_WF complies with the minimum and maximum limits of
fuel flow rate and with the setpoint C_WFps, and provides at the output a thresholded fuel
mass flow rate setpoint C_WFOK. Said setpoint C_WFOK is converted by the converter 22 into
a position setpoint C_Pos for the metering slide 12. In a similar manner to the control system
25 of Figure 1, the position setpoint C_Pos is provided to the local corrector 23 in order to carry
out a closed-loop control on the position of the metering slide 12. The local corrector 23
determines a nominal-mode control electric current I_nom which corresponds, in the absence
of action of the C/P limiter 111 and of the protection corrector 112, to the control electric
current I_com of the control system 20.
30
The degraded-mode processing chain 120 includes a protection module 121 and a
direct corrector 122. The protection module 121 is arranged to fulfil functions which are
similar to those of the C/P limiter 111 and of the protection corrector 112. It receives flight
12
parameters and operating parameters of the turbine engine 10 from the monitoring unit 16,
the temperature sensor 17 and the pressure sensor 18. The protection module 121 further
receives the speed setpoint C_XNBP and determines a safe speed setpoint C_XNBPOK. An
exemplary embodiment of the protection module 121 will be described in detail with
reference to Figure 4. The direct corrector 122 receives the safe speed 5 setpoint C_XNBPOK
and the rotational speed measurement M_XNBP, and determines a degraded-mode control
electric current I_deg depending on this safe speed setpoint C_XNBPOK and this rotational
speed measurement M_XNBP. The direct corrector 122 is for example a PI (proportional,
integral) corrector.
10
The mode management module 130 receives the nominal-mode control electric current
I_nom and the degraded-mode control electric current I_deg and delivers a control electric
current I_com for the servo valve 11. The mode management module 130 is arranged to
deliver, as control electric current I_com, the nominal-mode control electric current I_nom in
15 the absence of a failure in the measurement of the position of the metering slide 12, and the
degraded-mode control electric current I_deg in the case of a failure. To this end, the mode
management module can receive a failure signal Sd generated in the case of a failure of the
position sensor 14. The failure signal Sd is for example generated by the monitoring unit 16.
Alternatively, the mode management module 130 can receive the position measurement of
20 each of the sensitive elements from the position sensor 14 and deduce a failure therefrom, in
particular in the case of a deviation between the two position measurements. Thus,
depending on the control electric current selected by the mode management module, the
control system 100 performs a closed-loop control of the rotational speed XNBP either using
the nominal-mode processing chain 110, or using the degraded-mode processing chain 120. In
25 this case, when the nominal-mode control electric current I_nom is selected, a local closedloop
control is performed through the local corrector 23, the servo valve 11 and the position
sensor 14, and a global closed-loop control is performed concomitantly by the global corrector
21, the converter 22, the local corrector 23, the servo valve 11, the metering slide 12, the
engine 13 and the speed sensor 15.
30
Figure 3 represents the closed-loop control carried out using the degraded-mode
processing chain 120 when the degraded-mode control electric current I_deg is selected. A
single closed-loop control loop is formed by the direct corrector 122, the servo valve 11, the
13
metering slide 12, the engine 13 and the speed sensor 15. The closed-loop control can be
qualified as “direct” insofar as it does not use the position measurement M_Pos of the
metering slide 12. It should be noted that the direct corrector 122 can directly receive the
speed setpoint C_XNBP, as represented in Figure 3, in the absence of a protection module
5 121.
Figure 4 represents the protection module 121 of the degraded-mode processing chain
120. The protection module 121 comprises a limiting circuit 30 and a gradient limiter 40. The
limiting circuit 30 comprises a first subtracter 31, a first amplifier 32, a first adder 33, a MIN
10 operator 34, a second subtracter 35, a second amplifier 36, a second adder 37 and a MAX
operator 38. It is arranged to receive the rotational speed setpoint C_XNBP, the rotational
speed measurement M_XNBP, the measurement of the temperature of the exhaust gases
M_TM49 and the measurement of the static pressure at the inlet of the combustion chamber
M_PS32, and to deliver a limited speed setpoint C_XNBPlim. The subtracter 31 subtracts the
15 measurement of the exhaust gas temperature M_TM49 from a maximum temperature
TM49_MAX (TM49_MAX - M_TM49); the amplifier 32 calculates a value E_TM49 by
multiplying the result of the subtraction by a temperature coefficient K_TM49 (E_TM49 =
K_TM49 x (TM49_MAX - M_TM49)); the adder 33 adds the result of this multiplication to the
rotational speed measurement M_XNBP: K_TM49 x (TM49_MAX - M_TM49) + M_XNBP; and
20 the MIN operator 34 compares the result of this addition with the rotational speed setpoint
C_XNBP and retains the minimum value. In parallel, the subtracter 35 subtracts the pressure
measurement M_PS32 from a minimum pressure PS32_MIN (PS32_MIN - M_PS32); the
amplifier 36 calculates a value E_PS32 by multiplying the result of the subtraction by a
pressure coefficient K_PS32 (E_PS32 = K_PS32 x (PS32_MIN - M_PS32)); the adder 37 adds the
25 result of this multiplication to the rotational speed measurement M_XNBP (K_PS32 x
(PS32_MIN - M_PS32) + M_XNBP); and the MAX operator 38 compares the result of this
addition to the minimum value retained by the MIN operator 34 and retains the maximum
value. This maximum value corresponds to the limited speed setpoint C_XNBPlim.
30 The limiting circuit 30 allows preventing the turbine engine 10 from operating with an
exhaust gas temperature which is greater than the maximum temperature TM49_MAX and/or
with a static pressure at the inlet of the combustion chamber which is lower than the
minimum pressure PS32_MIN. Indeed, when the temperature measurement M_TM49
14
approaches the maximum temperature TM49_MAX, the sum of the value E_TM49 and the
rotational speed measurement M_XNBP (E_TM49 + M_XNBP) becomes less than the
rotational speed setpoint C_XNBP. It is then this sum which is used as the limited speed
setpoint C_XNBPlim instead of the rotational speed setpoint C_XNBP. It can be noticed that if
the temperature measurement M_TM49 is equal to the maximum temperature 5 TM49_MAX,
the limited speed setpoint C_XNBPlim is equal to the rotational speed measurement M_XNBP.
Likewise, when the pressure measurement M_PS32 approaches the minimum pressure
PS32_MIN, the sum of the value E_PS32 and the rotational speed measurement M_XNBP
becomes greater than the rotational speed setpoint C_XNBP. It is then this sum which is used
10 as a limited speed setpoint C_XNBPlim instead of the rotational speed setpoint C_XNBP. In
this exemplary embodiment, only two operators 34, 38 are used. Nevertheless, the result of
the addition at the output of the adder 37 could be compared to the rotational speed setpoint
C_XNBP by a first MAX operator, a second MAX operator comparing the values from this first
MAX operator and from the MIN operator 34. Moreover, more than two parameters can be
15 taken into account to determine the limited speed setpoint C_XNBPlim. In this case, each of
these parameters is compared to a minimum or maximum threshold parameter, as described
for the pressure PS32 and the temperature TM49. The setpoint C_XNBPlim then results from
the maximum of the values from the different operators each associated to a parameter.
20 The gradient limiter 40 receives the limited speed setpoint C_XNBPlim and determines
an acceleration-limited speed setpoint, corresponding to the safe speed setpoint C_XNBPOK.
This acceleration-limited speed setpoint C_XNBPOK is determined so as to follow the limited
speed setpoint C_XNBPlim with an evolution speed which is less than or equal to a
predetermined maximum acceleration threshold. The gradient limiter 40 thus allows slowing
25 down the dynamics of the turbine engine and avoiding generating fuel flow rate to pressure
ratios outside the nominal operating ranges. The gradient limiter 40 can receive one or more
flight parameter(s) of the aircraft and/or one or more operating parameter(s) of the turbine
engine, and adapt the maximum acceleration threshold as depending on these parameters. In
particular, the maximum acceleration threshold can be variable depending on the Mach
30 number and the altitude of the aircraft, as well as the static pressure upstream of the
combustion chamber PS32.
15
The temperature coefficient K_TM49 can be determined by comparing, using a turbine
engine model, the effects of an increase in the rotational speed XNBP on the exhaust gas
temperature TM49. The pressure coefficient K_PS32 can be analogously determined. The
predetermined maximum acceleration threshold of the gradient limiter 40 can be determined
using a simulation of a turbine engine model regulated using the nominal-5 mode processing
chain. It may correspond to the acceleration from which the fuel flow rate exceeds the
maximum limit of the C/P limiter 111.
The control system 100 can have a purely hardware architecture, or a software
10 architecture capable of executing a computer program. This is, for example, a field
programmable gate array (FPGA), a processor, a microprocessor, or a microcontroller.
Moreover, the functional configuration of the elements of the control system 100 in no way
limits the hardware configuration of these elements. Thus, by way of example, two elements
presented as being distinct can in practice be formed by the same electrical or electronic
15 component, or the functions thereof which are executed by the same processor.
Figure 5 represents an example of a control method implementing the turbine engine
and the control system of Figure 2. The method 50 comprises a supervising step 51 in which a
failure of the position sensor 14 is supervised. This supervising step 51 is preferably
20 performed continuously or at regular time intervals. It consists for example in determining an
absence of position measurement or a deviation between two position measurements greater
than a predetermined threshold. In the absence of failure of the position sensor 14, the
method continues to a step 52 of determining a fuel flow rate setpoint. In this step 52, a fuel
mass flow rate setpoint C_WF is determined depending on the rotational speed setpoint
25 C_XNBP and the rotational speed measurement M_XNBP. Step 52 is carried out by the global
corrector 21, the C/P limiter 111, the protection corrector 112 and the correction
management module 113. Then, in a conversion step 53, the fuel mass flow rate setpoint
C_WF is converted into a position setpoint C_Pos. This step 53 is carried out by the converter
22. In a step 54 of determining a nominal-mode control current, a nominal-mode control
30 electric current I_nom is determined depending on the position setpoint C_Pos and the
position measurement M_Pos. In an actuation step 55, the nominal-mode control electric
current I_nom is delivered to the servo valve 11 so as to displace the metering slide 12 into
the desired position. When, during the supervising step 51, a failure of the position sensor 14
16
is detected, the method switches to a step 56 of determining a safe speed setpoint. This step
56 is carried out by the protection module 121. It consists in determining the safe speed
setpoint C_XNBPOK from the rotational speed setpoint C_XNBP, flight parameters and
operating parameters of the turbine engine. The control method then includes a step 57 of
determining a degraded-mode control current. In this step 57, carried out 5 by the degradedmode
processing chain 120, a degraded-mode control electric current I_deg is determined
depending on the safe speed setpoint C_XNBPOK and the rotational speed measurement
M_XNBP. Then, in an actuation step 58, the degraded-mode control electric current I_deg is
delivered to the servo valve 11 so as to displace the metering slide 12 into the desired
10 position.
17
We claim:
1. A control system for an aircraft turbine engine, the turbine engine (10) comprising:
 a combustion chamber (13),
 a fuel metering valve including a metering slide (12), a position of 5 which determines a
volumetric flow rate of fuel injected into the combustion chamber and an actuator (11)
arranged to displace the metering slide depending on a control electric current (I_com),
 a position sensor (14) arranged to measure a position of the metering slide and
deliver a position measurement (M_Pos),
10  a speed sensor (15) arranged to measure a rotational speed of the turbine engine and
deliver a rotational speed measurement (M_XNBP), and
 a monitoring unit (16) arranged to deliver a rotational speed setpoint (C_XNBP), to
detect a failure of the position sensor and to deliver a failure signal (Sd) in the case of
detection of a failure of the position sensor,
15 the control system (100) comprising:
 a nominal-mode processing chain (110) including:
- a global corrector (21) arranged to receive the rotational speed setpoint (C_XNBP)
and the rotational speed measurement (M_XNBP) and determine a fuel mass flow
rate setpoint (C_WF) depending on the rotational speed setpoint (C_XNBP) and the
20 rotational speed measurement (M_XNBP),
- a converter (22) arranged to convert the fuel mass flow rate setpoint (C_WF) into
a position setpoint (C_Pos), and
- a local corrector (23) arranged to receive the position setpoint (C_Pos) and the
position measurement (M_Pos) and determine a nominal-mode control electric
25 current (I_nom) depending on the position setpoint (C_Pos) and the position
measurement (M_Pos),
 a degraded-mode processing chain (120) including a direct corrector (122) arranged
to receive the rotational speed setpoint (C_XNBP) and the rotational speed measurement
(M_XNBP) and determine a degraded-mode control electric current (I_deg) depending on the
30 rotational speed setpoint (C_XNBP) and the rotational speed measurement (M_XNBP), and
 a mode management module (130) arranged to receive the failure signal (Sd), the
nominal-mode control electric current (I_nom) and the degraded-mode control electric
current (I_deg), and to deliver, to the actuator (11) of the fuel metering valve, the nominal18
mode control electric current (I_nom) in the absence of reception of the failure signal and the
degraded-mode control electric current (I_deg) in the case of reception of the failure signal.
2. The control system according to claim 1, wherein the direct corrector (122) is
arranged to further receive one or more flight parameter(s) of the aircraft 5 and/or one or more
operating parameter(s) of the turbine engine, the degraded-mode control electric current
(I_deg) being further determined depending on the flight parameters of the aircraft and/or
the operating parameters of the turbine engine.
10 3. The control system according to one of claims 1 and 2, wherein the degraded-mode
processing chain (120) further includes a gradient limiter (40) arranged to receive the
rotational speed setpoint (C_XNBP) and determine an acceleration-limited speed setpoint
(C_XNBPOK), the acceleration-limited speed setpoint being determined so as to limit a speed
of evolution of the rotational speed setpoint, the acceleration-limited speed setpoint
15 (C_XNBPOK) being used by the direct corrector (122) instead of the rotational speed setpoint
(C_XNBP).
4. The control system according to claim 3, wherein the gradient limiter (40) is further
arranged to receive one or more flight parameter(s) of the aircraft and/or one or more
20 operating parameter(s) of the turbine engine, the predetermined maximum acceleration
threshold being variable depending on the flight parameters and/or the operating parameters
of the turbine engine.
5. The control system according to one of claims 1 to 4, wherein the degraded-mode
25 processing chain (120) further includes a limiting circuit (30) arranged to receive the rotational
speed setpoint (C_XNBP), the rotational speed measurement (M_XNBP) and an operating
parameter of the turbine engine (M_TM49, M_PS32), and determine a limited speed setpoint
(C_XNBPlim), the limited speed setpoint (C_XNBPlim) being determined by calculating a
difference between the operating parameter (M_PS32) and a predetermined minimum
30 threshold parameter (PS32_MIN) or between the operating parameter (M_TM49) and a
predetermined maximum threshold parameter (TM49_MAX), by multiplying said difference
by a coefficient relating to the operating parameter (K_TM49, K_PS32), by adding the
rotational speed measurement (M_XNBP) to the result of the multiplication, and by taking, as
19
limited speed setpoint (C_XNBPlim), the maximum between the result of the addition and the
rotational speed setpoint when the difference is calculated relative to a minimum threshold
parameter, and the minimum between the result of the addition and the rotational speed
setpoint when the difference is calculated relative to a maximum threshold parameter .
5
6. The control system according to claim 5, wherein the limiting circuit (30) is arranged
to receive, as an operating parameter, a pressure measurement of the turbine engine
(M_PS32), a difference being calculated between the pressure measurement and a
predetermined minimum pressure (PS32_MIN), and/or the limiting circuit (30) is arranged to
10 receive, as an operating parameter, a temperature measurement of the turbine engine
(TM_49), a difference being calculated between the temperature measurement and a
predetermined maximum temperature (TM49_MAX).
7. A turbine engine for an aircraft comprising:
15  a combustion chamber (13),
 a fuel metering valve including a metering slide (12), a position of which determines a
volumetric flow rate of fuel injected into the combustion chamber and an actuator (11)
arranged to displace the metering slide depending on a control electric current (I_com),
 a position sensor (14) arranged to measure a position of the metering slide and
20 deliver a position measurement (M_Pos),
 a speed sensor (15) arranged to measure a rotational speed of the turbine engine and
deliver a rotational speed measurement (M_XNBP),
 a monitoring unit (16) arranged to deliver a rotational speed setpoint (C_XNBP), to
detect a failure of the position sensor and to deliver a failure signal (Sd) in the case of
25 detection of a failure of the position sensor, and
 a control system (100) according to one of claims 1 to 6.
8. The turbine engine according to claim 7, wherein the position sensor (14) comprises a
first sensitive element and a second sensitive element, the first sensitive element being
30 arranged to measure a position of the metering slide and deliver a first position
measurement, the second sensitive element being arranged to measure a position of the
metering slide and deliver a second position measurement, the monitoring unit (16) being
arranged to detect a failure of the position sensor in the case of a deviation between the first
20
position measurement and the second position measurement which is greater than a
predetermined threshold or in the absence of reception of the first position measurement and
of the second position measurement.
9. A control method for an aircraft turbine engine, the turbine engine 5 (10) comprising:
 a combustion chamber (13),
 a fuel metering valve including a metering slide (12), a position of which determines a
volumetric flow rate of fuel injected into the combustion chamber and an actuator (11)
arranged to displace the metering slide depending on a control electric current (I_com),
10  a position sensor (14) arranged to measure a position of the metering slide and
deliver a position measurement (M_Pos),
 a speed sensor (15) arranged to measure a rotational speed of the turbine engine and
deliver a rotational speed measurement (M_XNBP), and
 a monitoring unit (16) arranged to deliver a rotational speed setpoint (C_XNBP), to
15 detect a failure of the position sensor and to deliver a failure signal (Sd) in the case of
detection of a failure of the position sensor,
the control method comprising the steps consisting of:
 supervising (51) a failure of the position sensor (14),
 in the absence of failure of the position sensor,
20 - determining (52) a fuel mass flow rate setpoint (C_WF) depending on the
rotational speed setpoint (C_XNBP) and the rotational speed measurement
(M_XNBP),
- converting (53) the fuel mass flow rate setpoint (C_WF) into a position setpoint
(C_Pos),
25 - determining (54) a nominal-mode control electric current (54) depending on the
position setpoint (C_Pos) and the position measurement (M_Pos), and
- delivering (55), to the actuator (11) of the fuel metering valve, the nominal-mode
control electric current (I_nom),
 in the case of a failure of the position sensor,
30 - determining (57) a degraded-mode control electric current (I_deg) depending on
the rotational speed setpoint (C_XNBP) and the rotational speed measurement
(M_XNBP), and
21
- delivering (58), to the actuator (11) of the fuel metering valve, the degradedmode
control electric current (I_deg).