Patent Description:
In order to protect an aircraft engine from exceeding operating temperature limits, the maximum temperature in the thermodynamic cycle is quantified and monitored during operation. However, the temperature of certain locations of the aircraft engine are difficult to measure due to instrumentation and material temperature limitations. Consequently, temperature instrumentation at these locations have a tendency to fail in service due to their harsh operating environment. Providing redundancy can help mitigate the consequences of such failures. For instance, the temperature instrumentation can include an array of thermocouples connected in parallel. In this way, when one of the thermocouples fail, the temperature reading provided by the array remains the same, which allows for a longer lifetime. Reference is made in this respect to the disclosure of <CIT>. Although existing temperature instrumentation is satisfactory to a certain degree, there remains room for improvement.

In one aspect, there is provided a method of detecting failure in an array of thermocouples connected in parallel, the method comprising: during an operation mode of the array of thermocouples, measuring a voltage V across the array of thermocouples, the voltage V associated with a temperature T; during a failure detection mode of the array of thermocouples, shunting the array of thermocouples, and measuring a shunt voltage Vs occurring across a resistive element connected in series with the array of thermocouples; comparing the shunt voltage Vs to an expected shunt voltage Vs_exp for the array of thermocouples at the temperature T; and generating a failure signal indicative of a detected failure in the array of thermocouples when the shunt voltage Vs deviates from the expected shunt voltage Vs_exp by more than a deviation threshold.

In another aspect, there is provided a system for detecting failure in an array of thermocouples, the system comprising: a processing unit; and a non-transitory computer-readable medium having stored thereon program instructions executable by the processing unit for: during an operation mode of the array of thermocouples, measuring a voltage V across the array of thermocouples, the voltage V associated with a temperature T; during a failure detection mode of the array of thermocouples, shunting the array of thermocouples, and measuring a shunt voltage Vs occurring across a resistive element connected in series with the array of thermocouples; comparing the shunt voltage Vs to an expected shunt voltage Vs_exp for the array of thermocouples at the temperature T; and generating a failure signal indicative of a detected failure in the array of thermocouples when the shunt voltage Vs deviates from the expected shunt voltage Vs_exp by more than a deviation threshold. In embodiments, the system comprises the array of thermocouples.

In another aspect, there is provided a circuit comprising: an array of thermocouples connected in parallel and defining a first terminal and a second terminal for measurement of a voltage V thereacross, the voltage V associated with a temperature T; a resistive element connected in series between the first terminal and a third terminal; a shunting device connectable across the second terminal and the third terminal; and a controller operatively coupled to the circuit for selective operation thereof in an operation mode and in a failure detection mode, wherein, in the operation mode, the shunting device is in an open state and the controller measures the voltage V across the array of thermocouples and, in the failure detection mode, the array of thermocouples is shunted via the shunting device, and a shunt voltage Vs is measured across the resistive element.

<FIG> illustrated a gas turbine engine <NUM> of a type preferably provided for use in subsonic flight, generally comprising in serial flow communication a fan <NUM> through which ambient air is propelled, a compressor section <NUM> for pressurizing the air, a combustor <NUM> in which the compressed air is mixed with fuel and ignited for generating an annular stream of hot combustion gases, and a turbine section <NUM> for extracting energy from the combustion gases. High pressure rotor(s) <NUM> of the turbine section <NUM> are drivingly engaged to high pressure rotor(s) <NUM> of the compressor section <NUM> through a high pressure shaft <NUM>. Low pressure rotor(s) <NUM> of the turbine section <NUM> are drivingly engaged to the fan <NUM> and to low pressure rotor(s) <NUM> of the compressor section <NUM> through a low pressure shaft <NUM> extending within the high pressure shaft <NUM> and rotating independently therefrom.

Although illustrated as a turbofan engine, the gas turbine engine <NUM> may alternatively be another type of engine, for example a turboshaft engine, also generally comprising in serial flow communication a compressor section, a combustor, and a turbine section, and an output shaft through which power is transferred. A turboprop engine or hybrid engine may also apply. In addition, although the gas turbine engine <NUM> is described herein for flight applications, it should be understood that other uses, such as industrial or the like, may apply.

As air passes through the gas turbine engine <NUM>, it undergoes numerous pressure and temperature changes along the way. The path along which air flows is referred to as the "gas path. " Example temperature measurement points for the airflow along the gas path are illustrated in <FIG>. T1 refers to an inlet temperature, taken just as the air enters through the fan rotor <NUM>. T2 refers to a low pressure compressor inlet temperature, taken before the low pressure rotors <NUM> of the compressor section <NUM>. T3 refers to a high pressure compressor delivery temperature, taken after the high pressure rotors <NUM> of the compressor section <NUM>. T4 refers to a combustor outlet temperature, taken before the high pressure rotors <NUM> of the turbine section. T5 refers to the turbine outlet temperature, taken after the low pressure rotors <NUM> of the turbine section <NUM>. In some other embodiments, the temperature measurement points can differ from the ones illustrated in <FIG>.

In order to protect the gas turbine engine <NUM> from exceeding operating temperature limits, the maximum temperature in the thermodynamic cycle of the gas turbine engine <NUM> is quantified and monitored during operation. The maximum temperature usually occurs at location T4, which can be very difficult to measure due to instrumentation and material temperature limitations. Instead, the temperature at location T4 may be correlated with a temperature measured downstream from location T4, where the temperature is cooler, such as location T4. <NUM>, which is sometimes referred to as an inter-turbine or indicated turbine temperature (ITT) and is taken between the high pressure rotors <NUM> and low pressure rotors <NUM> of the turbine section <NUM>. <NUM> correlations can be determined during the development phase of the gas turbine engine <NUM>, and can be implemented in the engine control system.

In some embodiments, the temperature at any location of gas turbine engine <NUM>, for example at location T4. <NUM>, is measured using an array of thermocouples. The array can have a number N of thermocouples. The array of thermocouples may be disposed independently or may be supported by a harness having a given geometry. An example array of thermocouples mounted on a harness is illustrated in <FIG>. In this example, a harness <NUM> has a circular geometry and holds N=<NUM> thermocouples <NUM><NUM>-<NUM><NUM> to form the array <NUM>. Other geometries for the harness <NUM> may also be used, such as ellipsoid, oval, rectangular, square, and the like, such that a circumference of the gas turbine engine <NUM> is surrounded by the harness <NUM>. Although shown as closed, the harness <NUM> may also be open, for example in a U-shape, a V-shape, curvilinear or linear. Other harness geometries may also apply, depending on practical implementation. The number N of thermocouples and their location on the harness <NUM> may vary, depending on practical implementation.

<FIG> shows an example circuit <NUM> having an array <NUM> of thermocouples TCN connected in parallel. As shown, there is a number N of thermocouples TCN in the array <NUM>, where the number N is an integer greater than unity. For instance, the number N can be <NUM>, <NUM>, <NUM> and the like. Each of the thermocouples TCN has two different electrically conducting materials connected to one another to form a hot junction and a cold junction. As per the Seebeck effect, an electromotive force develops across the two junctions when a temperature difference exists between the hot junction and the cold junction of the thermocouple. The electromotive force creates a difference of potential across each thermocouple, and this difference of potential, or voltage Vi, is proportional to the temperature difference. The thermocouples TCN are connected in parallel between a first terminal A and a second terminal B. Accordingly, the voltage measured across the first and second terminals A and B, i.e., VAB, is indicative of an average of the individual voltages VN, i.e., the sum of the individual voltages VN divided by the number N of thermocouples in the array <NUM>: <MAT>.

Accordingly, a single voltage measurement can factor in all of the individual voltages VN at the same time. The voltage VAB can then be processed to obtain the temperature T surrounding the array <NUM> of thermocouples TCN: <MAT>.

In some embodiments, all of the thermocouples TCN of the array <NUM> are disposed in a common area <NUM> of a gas turbine engine of a given temperature T. As such, V<NUM> ≅ V<NUM> ≅ ··· ≅ VN, and equation (<NUM>) becomes: <MAT>.

When one thermocouple TCN fails, an open circuit is created for that broken thermocouple, and one of the individual voltages VN goes to zero as no current can flow across the open circuit. In this situation, the reading of the voltage VAB may not indicate any anomaly even if one or more of the thermocouples TCN has failed. A thermocouple failure would thus be undetectable solely based on the reading of the voltage VAB, unless all of the thermocouples TCN fail which would yield a null voltage VAB. Equation (<NUM>) thus remains true even if one or more of the thermocouples, but not all, of the thermocouples fail. The circuit <NUM> is provided to detect the failure of one or more thermocouple TCN of the array <NUM>.

As depicted, the circuit <NUM> has a resistive element <NUM> connected in series between a first terminal A and a third terminal C, a shunting device <NUM> connectable across the second terminal B and the third terminal C, and a controller <NUM> for selective operation of the circuit <NUM> in an operation mode and in a failure detection mode. The resistive element <NUM> can be provided in the form of any component suitable for providing an electrical resistance, including, but not limited to, a resistor of resistivity R. The shunting device <NUM> may be an electrical switch, as illustrated, or any other component suitable for connecting second terminal B to third terminal C so as to form a path for current to travel across the resistive element <NUM> and into/out of the array <NUM>.

In the operation mode, the shunting device <NUM> is in an open state and the controller <NUM> measures the voltage VAB across the array <NUM> of thermocouples TCN. The measured voltage VAB is associated with a temperature T, as the voltage across the array <NUM> of thermocouples TCN is dependent on the temperature of the area <NUM> in which lay the thermocouples TCN. The temperature T is indicative of the temperature surrounding the array of thermocouples at the time the voltage measurement is made. In the failure detection mode, the array <NUM> of thermocouples TCN is shunted via the shunting device <NUM>, and a shunt voltage VAC is measured across the resistive element <NUM> connected in series with the array <NUM> of thermocouples TCN.

It is expected that since the thermocouples TCN produce corresponding individual voltages Vi, they also produce individual currents ii as per Ohm's Law. In the illustrated circuit <NUM>, the individual currents ii merge together to flow across the resistive element <NUM> when the array <NUM> of thermocouples TCN is shunted: <MAT>.

With the resistive element <NUM> providing a resistivity R, and Ohm's Law, equation (<NUM>) becomes: <MAT> when the N thermocouples function properly, and because the thermocouples are generally at the same temperature T, accordingly I<NUM> ≅ I<NUM> ≅ ··· ≅ IN and equation (<NUM>) becomes: <MAT>.

If a number Nf of the N thermocouples has failed, N becomes N-Nf in equation (<NUM>): <MAT> with VAC' denoting the shunt voltage VAC when at least one of the thermocouples has failed. If all of the thermocouples have failed, then N = Nf and the voltage VAC' goes to zero as discussed above. However, if <NUM> < Nf < N, the measured voltage VAC' will deviate from an expected value for the shunt voltage VAC when all of the thermocouples are working at the temperature T. As each of the thermocouples TCN produce the same amount of individual current ii at the same temperature T, each thermocouple failure will incur an incremental drop ΔVAC' to the shunt voltage VAC, the incremental drop corresponding to ΔVAC' ≅ R · IN. By monitoring the shunt voltage VAC and comparing it to an expected shunt voltage VAC_exp at the temperature T, a thermocouple failure may be detected.

<FIG> shows an example of a method <NUM> for detecting a failure in an array of thermocouples connected in parallel. The method <NUM> can be performed by the circuit <NUM> described above with reference to <FIG>.

At step <NUM>, during an operation mode of the array of thermocouples, a voltage V across the array of thermocouples is measured. The voltage V is associated with a temperature T. In some embodiments, a voltage V<NUM> is associated to a temperature T<NUM>, a voltage V<NUM> is associated to a temperature T<NUM>, a voltage Vs is associated to a temperature T<NUM>, and so forth.

At step <NUM>, during a failure detection mode of the array of thermocouples, the array of thermocouples is shunted and a shunt voltage occurring across a resistive element connected in series with the array of thermocouples is measured.

At step <NUM>, the shunt voltage Vs is compared to an expected shunt voltage Vs_exp for the array of thermocouples at the temperature T. For instance, if the temperature is determined to be temperature T1, the expected shunt voltage Vs_exp,<NUM> may be used.

At step <NUM>, a signal indicative of a detected failure in the array of thermocouples is generated when the shunt voltage Vs deviates from the expected shunt voltage Vs_exp by more than a deviation threshold D. In other words, the signal can be generated upon determining that: <MAT>.

The deviation threshold D is set to a value that takes into account an acceptable difference between the measured voltage Vs and the expected voltage Vs_exp, for example due to the precision of the measurement equipment. In some embodiments, the deviation threshold D is set to a value that corresponds to an expected voltage drop when one thermocouple TCN of the array has failed. The deviation threshold D may be determined through testing, simulation, modeling and the like. In some embodiments, the deviation threshold D can be of about <NUM> mV, preferably about <NUM> mV and most preferably about <NUM> mV.

The signal issued at step <NUM> may be used to set a maintenance flag, trigger a warning, or any other form of alert indicative of the failure.

In some embodiments, and as provided at step <NUM>, a number Nf of failed thermocouples is determined based on a difference between the shunt voltage Vs and the expected shunt voltage Vs_exp at the temperature T. More specifically, the number Nf of failed thermocouples can be given by a mathematical equation equivalent to the following equation: <MAT> as per equations (<NUM>) and (<NUM>). In some embodiments, the method <NUM> includes a step of a generating an alert signal upon determining that the number Nf of thermocouple failures is above a given threshold number. For instance, the given threshold number can be <NUM>, <NUM> or more depending on the embodiment. In some embodiments, such an alert signal is generated when two or fewer of the thermocouples are still working, indicating that maintenance should be performed to avoid misreadings at the location of the array. This alert signal may be the same or different from the signal generated at step <NUM> of the method <NUM>. In some embodiments, the method <NUM> includes a step of generating an alert signal upon determining that the number of working thermocouples is below a given threshold number. In some embodiments, the signal(s) generated by the controller is(are) stored in a non-transitory memory system, communicated to a network, or both.

In some embodiments, a signal indicative that the array of thermocouples is fully functional is generated upon determining that the measured shunt voltage Vs does not deviate from the expected shunt voltage Vs_exp by more than the deviation threshold D.

In some embodiments, step <NUM> comprises activating a shunting device, such as an electrical switch connecting the resistive element in series with the array of thermocouple, upon initiation of the failure detection mode and de-activating the shunting device upon termination of the failure detection mode. In some embodiments, the method <NUM> further comprises a step of monitoring failures in the array of thermocouples by initiating the failure detection mode at a given frequency. For instance, the failure detection mode can be performed at a frequency of <NUM> minute, <NUM> hour or <NUM> day depending on the embodiment. The failure detection mode can also be performed on demand in some embodiments, or at every start-up and/or shutdown of the engine. Various commands used for operation of the engine <NUM> may be used to trigger the failure detection mode of the circuit <NUM>.

It is intended that the array of thermocouples is disposed in a hot area of an aircraft engine in some embodiments. In embodiments where the aircraft engine is a gas turbine engine, the array of thermocouples can circumferentially surround a turbine section of the gas turbine engine. In embodiments where the aircraft engine is a gas-electricity hybrid engine, the array of thermocouples can surround a battery pack of the gas-electricity hybrid engine.

The controller <NUM> shown in <FIG> can be provided as a combination of hardware and software components. The software components of the controller <NUM> can be implemented in the form of a controller application <NUM>, an example of which is described with reference to <FIG>. Moreover, the hardware components of the controller <NUM> can be implemented in the form of a computing device <NUM>, an example of which is shown in <FIG>. In some embodiments, the controller <NUM> can be implemented as part of a fullauthority digital engine controls (FADEC) or other similar device, including electronic engine control (EEC), engine control unit (ECU), and the like.

Referring now to <FIG>, the controller application <NUM> is configured to receive, in the operation mode of the circuit <NUM>, the measured voltage VAB which can be associated with the temperature T surrounding the array of thermocouples at the moment the voltage VAB was measured, as per equation (<NUM>). As per equation (<NUM>), the measured voltage VAB is converted into temperature T using a known relationship between VAB and T. In the failure detection mode, the controller application <NUM> is configured to receive the shunt voltage Vs measured across the resistive element when the array of thermocouple is shunted via the shunting device. As depicted, the controller application <NUM> has access to a storage medium <NUM> including expected shunt voltages Vs_ref,i for different temperatures Ti. Table <NUM> below shows an example.

For instance, in an exemplary scenario in which an array of <NUM> thermocouples is used, the measured voltage VAB corresponds to temperature T2 and the shunt voltage Vs is measured to be <NUM> mV. In this scenario, the controller application <NUM> detects a deviation of the shunt voltage Vs from the expected shunt voltage Vs_exp,<NUM>=<NUM> mV by more than the deviation threshold D. In this embodiments, a deviation threshold D of about <NUM> mV was found convenient. Accordingly, the controller application <NUM> generates a signal indicative of a detected failure in the array of thermocouples. The number Nf of failed thermocouples can be determined using equation (<NUM>) above. For instance: <MAT>.

Alternatively, using the data shown in Table <NUM>, the controller application <NUM> may also determine the number Nf of failed thermocouples. In this case, as the shunt voltage Vs is <NUM> mV, the controller application can deduce that the number of failed thermocouples is <NUM>. Accordingly, the controller application <NUM> may determine the number Nf of failed thermocouples by using a mathematical formula (or known relationship) or by using a look-up table. Other embodiments may also apply. In this specific example, a shunt voltage Vs of <NUM> mV would not have deviated from the expected shunt voltage Vs_exp,<NUM> by more than the deviation threshold D and no such signal would have been generated.

It is noted that the expected shunt voltages Vs_exp depend on the temperature of the array of thermocouple. If for instance the measured voltage V would have corresponded to temperature T1, then no deviation would have been observed between the shunt voltage Vs of <NUM> mV and the expected shunt voltage Vs_exp,<NUM>- 800mV at temperature T1.

Referring to <FIG>, the computing device <NUM> can have a processor <NUM>, a memory <NUM>, and I/O interface <NUM>. Instructions <NUM> for performing the operation mode, the failure detection mode or any step described above can be stored on the memory <NUM> and accessible by the processor <NUM>.

The processor <NUM> can be, for example, a general-purpose microprocessor or microcontroller, a digital signal processing (DSP) processor, an integrated circuit, a field programmable gate array (FPGA), a reconfigurable processor, a programmable read-only memory (PROM), or any combination thereof.

The memory <NUM> can include a suitable combination of any type of computer-readable memory that is located either internally or externally such as, for example, random-access memory (RAM), read-only memory (ROM), compact disc read-only memory (CDROM), electro-optical memory, magneto-optical memory, erasable programmable read-only memory (EPROM), and electrically-erasable programmable read-only memory (EEPROM), Ferroelectric RAM (FRAM) or the like.

Each I/O interface <NUM> enables the computing device <NUM> to interconnect with one or more input devices, such as the circuit, the shunting device, or with one or more output devices such as an accessible memory system and external network.

Each I/O interface <NUM> enables the controller <NUM> to communicate with other components, to exchange data with other components, to access and connect to network resources, to server applications, and perform other computing applications by connecting to a network (or multiple networks) capable of carrying data including the Internet, Ethernet, plain old telephone service (POTS) line, public switch telephone network (PSTN), integrated services digital network (ISDN), digital subscriber line (DSL), coaxial cable, fiber optics, satellite, mobile, wireless (e.g. Wi-Fi, WiMAX), SS7 signaling network, fixed line, local area network, wide area network, and others, including any combination of these.

It is noted that the controller application <NUM> is stored on the memory <NUM> and accessible by the processor <NUM> of the computing device <NUM>. The computing device <NUM> and the controller application <NUM> described above are meant to be examples only. Other suitable embodiments of the controller <NUM> can also be provided, as it will be apparent to the skilled reader.

The methods described herein may be implemented in a high level procedural or object oriented programming or scripting language, or a combination thereof, to communicate with or assist in the operation of a computer system, for example the computing device <NUM>. Alternatively, the methods may be implemented in assembly or machine language. The language may be a compiled or interpreted language. Program code for implementing the methods may be stored on a storage media or a device, for example a ROM, a magnetic disk, an optical disc, a flash drive, or any other suitable storage media or device. The program code may be readable by a general or specialpurpose programmable computer for configuring and operating the computer when the storage media or device is read by the computer to perform the procedures described herein. Embodiments of the methods may also be considered to be implemented by way of a non-transitory computer-readable storage medium having a computer program stored thereon. The computer program may comprise computer-readable instructions which cause a computer, or more specifically the processor <NUM> of the computing device <NUM>, to operate in a specific and predefined manner to perform the functions described herein, for example those described in the method <NUM>.

Claim 1:
A method (<NUM>) of detecting failure in an array (<NUM>; <NUM>) of thermocouples (<NUM>; TCN) connected in parallel, the method comprising:
during an operation mode of the array (<NUM>; <NUM>) of thermocouples (<NUM>; TCN), measuring (<NUM>) a voltage V across the array (<NUM>; <NUM>) of thermocouples (<NUM>; TCN), the voltage (V) associated with a temperature (T);
during a failure detection mode of the array (<NUM>; <NUM>) of thermocouples (<NUM>; TCN), shunting (<NUM>) the array (<NUM>; <NUM>) of thermocouples (<NUM>; TCN), and measuring a shunt voltage (Vs) occurring across a resistive element (<NUM>) connected in series with the array (<NUM>; <NUM>) of thermocouples (<NUM>; TCN);
comparing (<NUM>) the shunt voltage (Vs) to an expected shunt voltage (Vs_exp) for the array (<NUM>; <NUM>) of thermocouples (<NUM>; TCN) at the temperature (T); and
generating (<NUM>) a failure signal indicative of a detected failure in the array (<NUM>; <NUM>) of thermocouples (<NUM>; TCN) when the shunt voltage (Vs) deviates from the expected shunt voltage (Vs_exp) by more than a deviation threshold.