Patent Application
20050200349
This invention relates to the field of gas turbine engines. More precisely, this invention concerns the determination of a gas turbine engine shaft speed.
Sensors are crucial in operating rotating gas turbine engines. Among those sensors is the turbine shaft rotation speed sensor, sometimes called the “N2 sensor” which provides data regarding the rotation speed of the low spool shaft, typically, and which is a primary input variable necessary for the control logic of the gas turbine engine. In the prior art, such sensors are typically mechanical and located near the shaft to directly collect data on the rotation speed of the shaft. However, the prior art is costly, heavy and suffers from reliability concerns, as do all mechanical devices.
There is therefore a need for a sensing method and apparatus for providing a gas turbine shaft speed.
According to a first broad aspect of the invention, there is provided a method of determining a turbine shaft speed of a gas turbine engine, the engine having a turbine shaft drivingly connected to an alternator, the alternator adapted to generate electricity for a first purpose, said method comprising receiving a frequency signal from the alternator, and determining said gas turbine shaft speed using said signal.
According to another broad aspect of the invention, there is provided an apparatus for determining a speed of a turbine shaft of a gas turbine engine, said apparatus comprising input means for receiving a rotation signal from an alternator driven by the turbine shaft, the alternator adapted to generate electricity for a first purpose, and a processing unit for determining said gas turbine shaft speed using said signal.
According to another broad aspect of the invention, there is provided an apparatus of operating a gas turbine engine, the engine having a turbine shaft drivingly connected to a permanent magnet alternator, the method comprising the steps of operating the engine to rotate the turbine shaft and thereby rotate the alternator, extracting generated electricity from the alternator to thereby provide operational electrical power to at least a first piece of equipment, extracting from the generated electricity a frequency indicative of alternator rotation speed, determining a rotation speed of the turbine shaft using said frequency, and providing the determined rotation speed to an engine controller for use in controlling operation of the gas turbine engine.
Further features and advantages of the present invention will become apparent from the following detailed description, taken in combination with the appended drawings, in which:
It will be noted that throughout the appended drawings, like features are identified by like reference numerals.
Now referring to
Prior to describing step 32 in more detail, a preferred embodiment of an apparatus 17 for determining the shaft 20 speed will be described in conjunction with
In
As mentioned, in a preferred embodiment of the invention, the signal from the PMA is a voltage signal and the conditioning unit 42 extracts a frequency component N from the alternator signal. The alternator signal is an AC signal which has a frequency which is proportional to the rotation speed of the PMA 24 and also proportional to the speed to the gas turbine shaft 20. Frequency and PMA rotation are related by a ratio R1, determined by the internal construction (e.g. number of magnetic poles, etc.) of the alternator (i.e. it is the number of AC cycles produced by the alternator for each revolution of the device), while PMA 24 rotation and shaft 20 rotation are related by a gear ratio R2, determined by the gearing ratio (if any) between the driving and driven shafts. Other ratios, collectively referred to herein as Rn, may also be pertinent to relate shaft 20 rotation speed to output frequency.
The processing unit 44 receives the conditioned alternator signal and provides the shaft speed signal. The processing unit 44 also receives ratio information R1, R2, . . . Rn preferably from memory 46. In a preferred embodiment, the appropriate rotation ratio R is pre-determined and thus pre-stored in memory 46 at manufacturing. Memory 46 need not be “memory” per se, as is used in the electronics or computing sense, but rather may be performed by any suitable electronic, mechanical or other device.
Now referring to
According to step 30, an alternator signal is received from the permanent magnet alternator 40 by the signal conditioning unit 42 of the purpose of determining 17 the speed of shaft 20.
According to step 32, the received alternator signal is conditioned by the signal conditioning unit 42. As explained above, the signal conditioning unit 42 performs a signal conditioning of the alternator signal and extracts a frequency component N of the alternator signal. Filtering and conditioning of the alternator signal may be also be provided to improve signal quality.
According to step 36, the cumulative ratio R between the rotation speed of the shaft and the frequency of the alternator signal is provided, where R=R1*R2*Rn. In a preferred embodiment the rotation ratio R is retrieved from the memory 46 where it is stored. According to step 38, the shaft speed Ω, expressed in Hz or rotation/s, is computed as Ω=R*N, where N, expressed in Hz, is the frequency of the alternator signal.
In an alternate embodiment, the shaft speed Ω may be computed using a lookup table (not shown) comprising a relation between a given signal frequency N and a corresponding shaft speed Ω. Such a lookup table may be implemented in memory 46. Optionally, an interpolation may be performed in order to limit the size of the lookup table. Ideally, interpolation would be performed by processing unit 44 using at least two values from the lookup table.
Unlike the prior art sensors, the present apparatus determines the shaft speed using existing equipment and data provided on the engine 10. Furthermore, in the preferred embodiment where the EEC PMA is used, failure mitigation is provided against the eventuality of a power supply interruption.
The embodiments of the invention described above are intended to be exemplary only, and modifications are available without departing from the scope of the invention disclosed. For example, although the use of a PMA is preferred, any alternator or other alternating current generating device in which the frequency is related to the rotation of a shaft of interest may be used. Still other modifications will be apparent to the skilled reader in light of the present disclosure. The scope of the invention is therefore intended to be limited solely by the scope of the appended claims.
