SHAFT MONITORING SYSTEM

Abstract

A monitoring system for monitoring the axial position of a rotating shaft is provided. The system includes first and second, axially adjacent phonic wheels which are mounted coaxially to the shaft for rotation therewith. The first and second phonic wheels respectively have first and second circumferential rows of detectable features. The system further includes a sensor configured to detect the passage of the first row of detectable features by generating a first alternating measurement signal component, and to detect the passage of the second row of detectable features by generating a second alternating measurement signal component. The first and second rows of detectable features are configured such that the first and second alternating measurement signal components have distinguishably different frequencies and/or such that the first alternating measurement signal component generated by the sensor when the sensor is axially aligned with the first row has a distinguishably different amplitude to the second alternating measurement signal component generated by the sensor when the sensor is axially aligned with the second row. The sensor is positioned relative to the first and second phonic wheels such that axial displacement of the shaft causes the signal generated by sensor to contain less of the first alternating measurement signal component and more of the second alternating measurement signal component whereby the axial position of the shaft can be monitored.

Claims

1. A monitoring system for monitoring the axial position of a rotating shaft, the system including: first and second, axially adjacent, phonic wheels which are formed from respective axially adjacent portions of a unitary annular body and mounted coaxially to the shaft for rotation therewith, the first phonic wheel having a first circumferential row of detectable features, and the second phonic wheel having a second circumferential row of detectable features, wherein the first and second circumferential rows of detectable features are first and second circumferential rows of teeth; and a sensor configured to detect the passage of the first row of detectable features by generating a first alternating measurement signal component, and to detect the passage of the second row of detectable features by generating a second alternating measurement signal component; wherein the first and second rows of detectable features are configured such that the first and second alternating measurement signal components have distinguishably different frequencies and/or such that the first alternating measurement signal component generated by the sensor when the sensor is axially aligned with the first row has a distinguishably different amplitude to the second alternating measurement signal component generated by the sensor when the sensor is axially aligned with the second row; and wherein the sensor is positioned relative to the first and second phonic wheels such that axial displacement of the shaft causes the signal generated by the sensor to contain less of the first alternating measurement signal component and more of the second alternating measurement signal component whereby the axial position of the shaft can be monitored.

2. The monitoring system according to claim 1, wherein the sensor is a magnetic sensor that detects a varying reluctance caused by the passage of the rows of detectable features.

3. The monitoring system according to claim 1, wherein the first and second phonic wheels are initially formed with identical rows of teeth, and the teeth of one of the rows being subsequently machined to reduce the number of teeth and/or change the shape of the teeth.

4. The monitoring system according to claim 1, wherein in a normal operating mode of the shaft, the overall signal substantially contains just the first alternating measurement signal component.

5. The monitoring system according to claim 1, wherein in a failure mode of the shaft, the overall signal substantially contains just the second alternating measurement signal component.

6. A gas turbine engine for an aircraft comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; and a monitoring system according to claim 1 for monitoring the axial position of the core shaft, the first and second, axially adjacent, phonic wheels being mounted coaxially to the core shaft for rotation therewith.

7. A gas turbine engine for an aircraft comprising: an engine core comprising a turbine, a compressor, and a core shaft connecting the turbine to the compressor; a fan located upstream of the engine core, the fan comprising a plurality of fan blades; and a gearbox that receives an input from the core shaft and outputs drive to the fan via an output shaft so as to drive the fan at a lower rotational speed than the core shaft; a thrust shaft that extends through the gearbox to connect the fan to an axial location bearing mounted on the core shaft, thereby relieving the output shaft of responsibility for axially locating the fan relative to the core shaft; and a monitoring system according to claim 1 for monitoring the axial position of the thrust shaft, the first and second, axially adjacent, phonic wheels being mounted coaxially to the thrust shaft for rotation therewith.

8. The gas turbine engine according to claim 7, wherein: the turbine is a first turbine, the compressor is a first compressor, and the core shaft is a first core shaft; the engine core further comprises a second turbine, a second compressor, and a second core shaft connecting the second turbine to the second compressor; and the second turbine, second compressor, and second core shaft are arranged to rotate at a higher rotational speed than the first core shaft.

9. The gas turbine engine according to claim 7, further comprising: an engine electronic controller which is operatively connected to the monitoring system to receive the overall signal and is configured to monitor therefrom the axial position of the shaft to which the first and second phonic wheels are mounted.

10. The gas turbine engine according to claim 9, wherein the first and second rows are configured such that the first and second alternating measurement signal components have distinguishably different frequencies, and the engine electronic controller converts the overall signal into a shaft speed, the engine electronic controller monitoring the axial position of the shaft to which the first and second phonic wheels are mounted on the basis of an apparent change in speed of the shaft.

11. Use of the monitoring system of claim 1 for monitoring the axial position of a rotating shaft to which the first and second phonic wheels are mounted.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0061] Embodiments will now be described by way of example only, with reference to the Figures, in which:

[0062] FIG. 1 is a sectional side view of a gas turbine engine;

[0063] FIG. 2 is a close up sectional side view of an upstream portion of a gas turbine engine;

[0064] FIG. 3 is a partially cut-away view of a gearbox for a gas turbine engine;

[0065] FIG. 4 shows an example of a unitary annular body providing first and second phonic wheels;

[0066] FIG. 5 shows how the output signal generated by a probe varies depending on the relative position of the probe and the phonic wheels of FIG. 4;

[0067] FIG. 6 shows a variant example of a unitary annular body providing first and second phonic wheels;

[0068] FIG. 7 shows how the output signal generated by a probe varies depending on the relative position of the probe and the phonic wheels of FIG. 6;

[0069] FIG. 8 shows schematically the front end of an interconnecting shaft joining the low pressure turbine to the fan of a non-geared turbofan; and

[0070] FIG. 9 shows schematically a conventional phonic wheel having a circumferential row of teeth, and a variable reluctance sensor.

DETAILED DESCRIPTION OF THE DISCLOSURE

[0071] FIG. 1 illustrates a gas turbine engine 10 having a principal rotational axis 9. The engine 10 comprises an air intake 12 and a propulsive fan 23 that generates two airflows: a core airflow A and a bypass airflow B. The gas turbine engine 10 comprises a core 11 that receives the core airflow A. The engine core 11 comprises, in axial flow series, a low pressure compressor 14, a high-pressure compressor 15, combustion equipment 16, a high-pressure turbine 17, a low pressure turbine 19 and a core exhaust nozzle 20. A nacelle 21 surrounds the gas turbine engine 10 and defines a bypass duct 22 and a bypass exhaust nozzle 18. The bypass airflow B flows through the bypass duct 22. The fan 23 is attached to and driven by the low pressure turbine 19 via a shaft 26 and an epicyclic gearbox 30.

[0072] In use, the core airflow A is accelerated and compressed by the low pressure compressor 14 and directed into the high pressure compressor 15 where further compression takes place. The compressed air exhausted from the high pressure compressor 15 is directed into the combustion equipment 16 where it is mixed with fuel and the mixture is combusted. The resultant hot combustion products then expand through, and thereby drive, the high pressure and low pressure turbines 17, 19 before being exhausted through the nozzle 20 to provide some propulsive thrust. The high pressure turbine 17 drives the high pressure compressor 15 by a suitable interconnecting shaft 27. The fan 23 generally provides the majority of the propulsive thrust. The epicyclic gearbox 30 is a reduction gearbox.

[0073] An exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2. The low pressure turbine 19 (see FIG. 1) drives the shaft 26, which is coupled to a sun wheel, or sun gear, 28 of the epicyclic gear arrangement 30. Radially outwardly of the sun gear 28 and intermeshing therewith is a plurality of planet gears 32 that are coupled together by a planet carrier 34. The planet carrier 34 constrains the planet gears 32 to precess around the sun gear 28 in synchronicity whilst enabling each planet gear 32 to rotate about its own axis. The planet carrier 34 is coupled via linkages 36 to the fan 23 in order to drive its rotation about the engine axis 9. Radially outwardly of the planet gears 32 and intermeshing therewith is an annulus or ring gear 38 that is coupled, via linkages 40, to a stationary supporting structure 24.

[0074] Note that the terms low pressure turbine and low pressure compressor as used herein may be taken to mean the lowest pressure turbine stages and lowest pressure compressor stages (i.e. not including the fan 23) respectively and/or the turbine and compressor stages that are connected together by the interconnecting shaft 26 with the lowest rotational speed in the engine (i.e. not including the gearbox output shaft that drives the fan 23). In some literature, the low pressure turbine and low pressure compressor referred to herein may alternatively be known as the intermediate pressure turbine and intermediate pressure compressor. Where such alternative nomenclature is used, the fan 23 may be referred to as a first, or lowest pressure, compression stage.

[0075] The epicyclic gearbox 30 is shown by way of example in greater detail in FIG. 3. Each of the sun gear 28, planet gears 32 and ring gear 38 comprise teeth about their periphery to intermesh with the other gears. However, for clarity only exemplary portions of the teeth are illustrated in FIG. 3. There are four planet gears 32 illustrated, although it will be apparent to the skilled reader that more or fewer planet gears 32 may be provided within the scope of the claimed invention. Practical applications of a planetary epicyclic gearbox 30 generally comprise at least three planet gears 32.

[0076] The epicyclic gearbox 30 illustrated by way of example in FIGS. 2 and 3 is of the planetary type, in that the planet carrier 34 is coupled to an output shaft via linkages 36, with the ring gear 38 fixed. However, any other suitable type of epicyclic gearbox 30 may be used. By way of further example, the epicyclic gearbox 30 may be a star arrangement, in which the planet carrier 34 is held fixed, with the ring (or annulus) gear 38 allowed to rotate. In such an arrangement the fan 23 is driven by the ring gear 38. By way of further alternative example, the gearbox 30 may be a differential gearbox in which the ring gear 38 and the planet carrier 34 are both allowed to rotate.

[0077] It will be appreciated that the arrangement shown in FIGS. 2 and 3 is by way of example only, and various alternatives are within the scope of the present disclosure. Purely by way of example, any suitable arrangement may be used for locating the gearbox 30 in the engine 10 and/or for connecting the gearbox 30 to the engine 10. By way of further example, the connections (such as the linkages 36, 40 in the FIG. 2 example) between the gearbox 30 and other parts of the engine 10 (such as the input shaft 26, the output shaft and the fixed structure 24) may have any desired degree of stiffness or flexibility. By way of further example, any suitable arrangement of the bearings between rotating and stationary parts of the engine (for example between the input and output shafts from the gearbox and the fixed structures, such as the gearbox casing) may be used, and the disclosure is not limited to the exemplary arrangement of FIG. 2. For example, where the gearbox 30 has a star arrangement (described above), the skilled person would readily understand that the arrangement of output and support linkages and bearing locations would typically be different to that shown by way of example in FIG. 2.

[0078] Accordingly, the present disclosure extends to a gas turbine engine having any arrangement of gearbox styles (for example star or planetary), support structures, input and output shaft arrangement, and bearing locations.

[0079] Optionally, the gearbox may drive additional and/or alternative components (e.g. the intermediate pressure compressor and/or a booster compressor).

[0080] Other gas turbine engines to which the present disclosure may be applied may have alternative configurations. For example, such engines may have an alternative number of compressors and/or turbines and/or an alternative number of interconnecting shafts. By way of further example, the gas turbine engine shown in FIG. 1 has a split flow nozzle 18, 20 meaning that the flow through the bypass duct 22 has its own nozzle 18 that is separate to and radially outside the core engine nozzle 20. However, this is not limiting, and any aspect of the present disclosure may also apply to engines in which the flow through the bypass duct 22 and the flow through the core 11 are mixed, or combined, before (or upstream of) a single nozzle, which may be referred to as a mixed flow nozzle. One or both nozzles (whether mixed or split flow) may have a fixed or variable area. Whilst the described example relates to a turbofan engine, the disclosure may apply, for example, to any type of gas turbine engine, such as an open rotor (in which the fan stage is not surrounded by a nacelle) or turboprop engine, for example. In some arrangements, the gas turbine engine 10 may not comprise a gearbox 30.

[0081] The geometry of the gas turbine engine 10, and components thereof, is defined by a conventional axis system, comprising an axial direction (which is aligned with the rotational axis 9), a radial direction (in the bottom-to-top direction in FIG. 1), and a circumferential direction (perpendicular to the page in the FIG. 1 view). The axial, radial and circumferential directions are mutually perpendicular.

[0082] In the exemplary arrangement for a geared fan gas turbine engine 10 is shown in FIG. 2, the output shaft 50 from the epicyclic gear arrangement 30 is radially located at each end by sets of roller bearings 52. These allow the shaft to transmit torque to the fan 23, but not provide significant axial retention functionality. To axially retain the output shaft 50 and the fan 23, a separate thrust shaft 54 extends from a set of ball bearings 56 attached to the interconnecting shaft 26, through the centre of the sun gear 28 to join to the output shaft 50. Thus torque transmission and axial retention responsibilities are split between the output shaft 50 and the thrust shaft 54.

[0083] Failure of the thrust shaft 54 or the ball bearings 56 can endanger the engine, and thus it is desirable to have early detection of any axial displacement of the shaft 54. Accordingly, the engine also has a monitoring system for monitoring the axial position of the shaft. This system comprises first 56 and second 58 axially adjacent phonic wheels. Conveniently these can be mounted at the front of the output shaft 50 coaxially with the thrust shaft 54. At this location they co-rotate with the entire assembly of the fan 23, output shaft 50 and thrust shaft 54.

[0084] FIG. 4 shows an example of the first 56 and second 58 phonic wheels in more detail. Conveniently, they can be part of a unitary annular body. Each wheel has a circumferential row of detectable features, which in this case are teeth, the second row of the second phonic wheel 58 having twice as many teeth as the first row of the first phonic wheel 56. Also, as drawn, the height of the teeth in the second row is lower than that in the first row, although this height difference could be the other way round or there could be no height difference. The system further has a sensor for detecting the passage of the teeth in form of a reluctance probe 60 which is mounted to a stationary structure of the engine.

[0085] FIG. 5 shows how the output signal generated by the probe 60 varies depending on the relative position of the probe and the wheels 56, 58 of FIG. 4. In normal operation of the thrust shaft 54, the probe sits centrally above the first row of teeth of the first phonic wheel 56. This corresponds to zero axial displacement of the shaft 54. The signal is substantially formed by just a first alternating measurement signal component whose frequency and amplitude is determined by the number and height of the teeth in the first row. At maximum forward axial displacement, due to failure of the shaft 54 or the bearings 56, the probe sits centrally above the second row of teeth of the second phonic wheel 58, and the signal is substantially formed (i.e. is dominated) by just a second alternating measurement signal component whose doubled frequency and reduced amplitude is determined by the number and height of the teeth in the second row. The signal is typically received by an engine electronic controller (EEC) of the engine, which can use the signal as a measure of the rotational speed of the assembly of the fan 23, output shaft 50 and thrust shaft 54. As a doubling of the speed of the assembly relative to e.g. the speed of the corresponding low pressure turbine 19 is physically impossible, the detection of such an event by the EEC can be used to alert the crew of thrust shaft failure or to initiate an automatic response so that appropriate engine management actions are taken.

[0086] FIG. 5 also shows the output signal generated by the probe 60 for intermediate axial displacements. Thus at a displacement in which the probe is still above but at the edge of the first row, the signal is substantially formed by just the first alternating measurement signal component. Similarly at a larger displacement in which the probe is above but at the edge of the second row, the signal is substantially formed by just the second alternating measurement signal component. However, at an intermediate displacement in which the probe is above a small gap that separates the first row from the second row, the signal is a combination of the two components. In other words, for displacements which are greater than this intermediate displacement, the second component dominates and an additional zero crossing occurs, and thus the probe effectively provides a binary output as regards detection of axial displacement of the shaft 54.

[0087] FIG. 6 shows in detail a variant example of the first 56 and second 58 phonic wheels. Again the wheels are part of unitary annular body, and each wheel has a circumferential row of teeth. However, now the second row of the second phonic wheel 58 having half the number of teeth as the first row of the first phonic wheel 56, and the height of the teeth in the second row is the same as that in the first row. This variant has advantages in terms of ease of manufacture. In particular, the body can initially be machined to have a single row of teeth extending across both wheels. One of the wheels (in this example the second wheel) can then be machined (e.g. milled) to remove every other tooth. This combination of operations (machining to form teeth, and milling to remove teeth) is simpler to perform than two separate machining operation to form to two different rows of teeth.

[0088] FIG. 7 shows how the output signal generated by the probe 60 varies depending on the relative position of the probe and the wheels 56, 58 of FIG. 6. In this case, when the probe is over the second row, the number of zero crossings halves, which can be detected by EEC as a reduction in speed of the assembly of the fan 23, output shaft 50 and thrust shaft 54.

[0089] In the above examples, the number of zero crossings (i.e. change in frequency) in the output signal is measured to monitor shaft axial position. However, another possibility in the example of FIGS. 4 and 5 is to measure output signal amplitude, with the axial displacement being detected when a step change in amplitude (in this case a halving) occurs.

[0090] Although described above for monitoring the axial position of the assembly of the fan 23, output shaft 50 and thrust shaft 54, the monitoring system has wider applicability in gas turbine engines, and is not limited to use in geared fan gas turbine engine. For example, it can be used to monitoring the axial position of any interconnecting shaft by which a turbine drives a compressor (e.g. interconnecting shafts 26, 27 in FIG. 1). Typically these interconnecting shafts have a set of ball bearings and a set of roller bearings. FIG. 8 shows schematically the front end of the interconnecting shaft 62 joining the low pressure turbine to the fan of a non-geared turbofan. A front set of roller bearings 64 radially locates the shaft and a rear set of ball bearings (off to the right and thus not shown in FIG. 8) axially locates the shaft. The axially adjacent phonic wheels 56, 58 of the monitoring system are mounted coaxially to the shaft from an extension to the inner case of the roller bearings, and the reluctance probe 60 is mounted to a stationary structure of the engine above the first wheel 56. The thrust load on the ball bearings is rearwards and thus failure of the bearings causes the shaft 62 to move in that direction such that the shaft moves rearwards. As a result, the reluctance probe 60 arrives above the second wheel 58, and the change in the output signal of the probe is detected by the engine's EEC.

[0091] In other engine configurations, the thrust load on the ball bearings can be forwards. In such cases, the second wheel phonic 58 wheel can be arranged on the other side of the first phonic wheel 56.

[0092] A suitably adapted monitoring system can also be used to detect failure of the interconnecting shaft 62, although that may not be necessary if the engine has other systems for detecting loss of torque-transmission capability in the shaft.

[0093] Although described above in relation to monitoring a thrust shaft (FIGS. 1 to 7) and the fan/compressor end of an interconnecting shaft (FIG. 8), the monitoring system may also be used at other locations in the engine, e.g. for monitoring the axial position of an interconnecting shaft at its turbine section end.

[0094] It will be understood that the invention is not limited to the embodiments above-described and various modifications and improvements can be made without departing from the concepts described herein. Except where mutually exclusive, any of the features may be employed separately or in combination with any other features and the disclosure extends to and includes all combinations and sub-combinations of one or more features described herein.