Bearing sensing arrangement

Abstract

There is disclosed a system for monitoring a bearing. The system comprises one or more acoustic transducers and a processor. The one or more acoustic transducers are configured to: produce a first signal indicative of an active acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and produce a second signal indicative of a passive acoustic wave transmitted through the bearing and received at the one or more acoustic transducers. The processor is configured to: receive the first and second signals; and monitor the bearing based upon the first and second signals.

Description

[0001] Bearing Sensing Arrangement

[0002] The present invention relates to a system for monitoring a bearing, a gas turbine engine, a kit of parts, a method of monitoring a bearing, and a computer-readable medium.

[0003] Bearings are commonplace components across a wide range of different applications and industries. Bearings fall into two main categories: hydrodynamic bearings and elasto-hydrodynamic bearings. In hydrodynamic bearings the stationary and moving surfaces are conformal to one another. In elasto-hydrodynamic bearings the stationary and moving surfaces are non-conformal to one another. This application is focused on elasto-hydrodynamic bearings. Another term for elasto-hydrodynamic bearings is rolling element bearings. Rolling element bearings comprise an inner or top race (e.g. a [typically stationary] inner ring), an outer or bottom race (e.g. a [typically rotatable] outer ring) and a plurality of rolling elements therebetween. The rolling elements facilitate rotation of at least one of the inner and outer race (typically the inner race) relative to the other. The aforementioned races may otherwise be referred to as raceways. One example of a rolling element bearing is a thrust bearing.

[0004] One specific application of bearings is incorporation in engines, such as gas turbine engines. In particular, aeroderivative gas turbine engines comprise many bearings throughout the various compressor and turbine stages. It has been found that the reliability of such gas turbine engines is very heavily dependent on the performance and operation of such bearings. In particular, bearing failure can cause unpredictable outages of the gas turbine engine, leading to undesirable maintenance intervals. Existing instrumentation does not provide reliable or accurate monitoring for such bearings.

[0005] There exists a need to overcome one or more of the disadvantages of existing systems, whether mentioned in this document or otherwise.

[0006] According to a first aspect of the invention there is provided a system for monitoring a bearing, the system comprising: one or more acoustic transducers, the one or more acoustic transducers being configured to: produce a first signal indicative of an active acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and

[0007] 38260609-1 produce a second signal indicative of a passive acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and a processor configured to: receive the first and second signals; and monitor the bearing based upon the first and second signals.

[0008] The term “active acoustic wave” is intended to encompass an acoustic wave which is transmitted into a medium by an acoustic transducer. Active ultrasonic measurements are typically performed in the frequency range of 0.5 to 15 MHz. The component / ultrasonic wave interactions can be considered macroscopic (i.e. relating to geometries of the same order of magnitude as the part).

[0009] The term “passive acoustic wave” is intended to encompass an acoustic wave which is produced by the bearing itself, as opposed to being transmitted into the bearing from an acoustic transducer. In other words, the passive acoustic wave originates in the bearing, whereas an active acoustic wave originates in an acoustic transducer. Passive ultrasonic measurements are typically in the frequency range of 20 to 500 kHz, more preferably 100 to 500 kHz. They may be considered microscopic (i.e. relating to geometries that are one or more magnitudes smaller than the geometry of the part).

[0010] The bearing may be a roller bearing. The (roller) bearing may comprise: an inner race and an outer race; and a plurality of rolling elements disposed between the inner race and the outer race. At least one of the inner race and the outer race is rotatable relative to the other about an axis of rotation. The bearing may be a thrust bearing. The bearing may be a journal bearing. In the case of a journal bearing, the journal bearing may comprise at least a bearing housing configured to receive a shaft. At least the acoustic transducer configured to produce the first signal is preferably mounted to the bearing housing.

[0011] The acoustic transducers may be ultrasonic transducers. The acoustic transducers may operate above the upper audible limit of human hearing, typically above 20 KHz. For example, the acoustic transducers may operate in a frequency range of between around 20 kHz and around 20 GHz. The acoustic waves may be ultrasonic waves, which may be in the frequency range of between around 20 kHz and around 20 GHz.

[0012] 38260609-1 Advantageously, the combination of active and passive acoustic sensing means that a wider range of parameters can be determined, providing a fuller picture of the health (in other words, the condition) of the bearing being monitored. The information from one type of sensor can also advantageously be used to interpret information from another type of sensor. For example, an active acoustic transducer can identify what is happening to that specific bearing. A passive acoustic transducer may be exposed to a much wider range of acoustic (e.g. ultrasonic) sources in the system. Therefore, if the passive acoustic transducer measures a signal, but the active acoustic transducer is not, then it can be determined that the source of that signal is somewhere else and not within the bearing.

[0013] The one or more acoustic transducers may comprise first and second acoustic transducers, and wherein: the first acoustic transducer is configured to produce the first signal; and the second acoustic transducer is configured to produce the second signal.

[0014] The second acoustic transducer may not be mounted to the bearing. Put another way, the second acoustic transducer may be separate from the bearing. The second acoustic transducer may be configured to receive airborne acoustic signals.

[0015] Advantageously, the use of a first acoustic transducer to produce the first signal, and the second acoustic transducer to produce the second signal, means that acoustic transducers which are more effective at different frequencies can be used. Put another way, a dedicated first active acoustic transducer can be used, along with a dedicated second passive acoustic transducer, both having resonant frequencies well matched with the respective uses. For example, the first acoustic transducer (i.e. the transducer which receives the active acoustic wave) may have a relatively high resonant frequency, such that the first acoustic transducer is particularly sensitive to frequencies in a particular frequency range of interest. Conversely, the second acoustic transducer (i.e. the transducer which receives the passive acoustic wave) may have a relatively low resonant frequency, such that the first acoustic transducer is particularly sensitive to frequencies in a different, lower, frequency range of interest.

[0016] The first acoustic transducer may engages the bearing, directly or indirectly, and preferably engages, directly or indirectly, one of the inner race and the outer race.

[0017] 38260609-1 The first acoustic transducer engaging the bearing, directly or indirectly, advantageously provides a transmission path through the bearing, facilitating the transmission of acoustic signals.

[0018] The one or more acoustic transducers may comprise one acoustic transducer, and wherein the acoustic transducer is configured to produce the first signal and the second signal.

[0019] Advantageously, the use of one acoustic transducer which produces both the first and second signals reduces part count and simplifies installation of the monitoring system. In this case, the acoustic transducer is multifunctional, and acts as both an active and passive transducer.

[0020] The acoustic transducer may be configured to produce the first and second signals simultaneously.

[0021] Producing the first and second signals simultaneously provides a higher resolution of monitoring once the signals, at different frequencies, are separated from one another by post-processing.

[0022] The acoustic transducer may be configured to produce the first and second signals at different times.

[0023] Producing the first and second signals at different times (e.g. not simultaneously) is advantageous in reducing the processing otherwise required to separate the signals when they are received simultaneously. The first and second signals being produced at different times may otherwise be described as the first and second signals being produced asynchronously.

[0024] An acoustic transducer configured to produce the first signal may be further configured to emit the active acoustic wave into the bearing.

[0025] 38260609-1 Advantageously, operating the acoustic transducer in pulse-echo mode reduces part count and simplifies installation by alleviating the need for a separate transducer to emit the active acoustic wave.

[0026] An acoustic transducer other than an acoustic transducer configured to produce the first signal may be configured to emit the active acoustic wave into the bearing.

[0027] Advantageously, operating two acoustic transducers in a pitch-catch or through- transmission mode means acoustic signals can be more reliably received in certain instances.

[0028] For example, one frequency can be transmitted (e.g. a high frequency acoustic wave that is preferred for focusing or directing) and another frequency be received (e.g. in the case of a low frequency transducer that can receive both high frequency active acoustic waves and low frequency passive acoustic waves). Or the inverse can be used: a low frequency transmitted for beam spread, and a high frequency received to isolate high frequency reflected acoustic waves.

[0029] The electronics and control circuitry may also be simpler. A receive active channel may be similar to a receive passive channel, albeit a different frequency bandwidth (or a wide bandwidth to cover both).

[0030] Reflecting acoustic waves off of one or more internal surfaces can also be utilised with such arrangements.

[0031] At least one of the one or more acoustic transducers may be configured to emit the active acoustic wave parallel to the axis of rotation, preferably through an outer race of the bearing.

[0032] Advantageously, transmitting the active acoustic wave parallel to the axis of rotation is beneficial for more reliably being able to detect a temperature of the bearing.

[0033] At least one of the one or more acoustic transducers may be configured to emit the active acoustic wave towards a surface of an inner race, or outer race, of the bearing, the

[0034] 38260609-1 surface being engaged by a plurality of rolling elements of the bearing, the active acoustic wave preferably being reflected by multiple internal surfaces.

[0035] Advantageously, transmitting the active acoustic wave towards the surface of the inner race, or outer race, engaged by the plurality of rolling elements means that parameters of the rolling elements can be determined.

[0036] The (active) acoustic wave may be one or more of: angled, steered, focused, spread, split, or otherwise towards the surface. This may be achieved by one or more of: a wedge, lens, size of piezo ceramic, shape of piezo ceramic, distance through the part, frequency of piezo ceramic, or otherwise. These all facilitate the (active) acoustic wave being directed to (e.g. impinging) the surface to be monitored.

[0037] The acoustic transducer configured to emit the active acoustic wave may be angled towards the surface.

[0038] As used herein, “angling” a transducer (and similar terms) means that the transducer is oriented in such a way that it emits and / or receives acoustic waves in a direction towards which the transducer is said to be angled. The angling towards a surface may otherwise be described as non-parallel, and / or non-perpendicular, to the axis of rotation. The acoustic transducer configured to produce the first signal may be the same, or different, acoustic transducer to that configured to emit the active acoustic wave.

[0039] Advantageously, angling the acoustic transducer configured to produce the first signal towards the surface means that the active acoustic wave is reliably directed towards the surface.

[0040] The acoustic transducer may be angled using a bracket.

[0041] Advantageously, the use of the bracket provides a repeatable way of being able to angle the acoustic transducer without necessarily having to alter the geometry of the acoustic transducer itself.

[0042] The acoustic transducer configured to emit the active acoustic wave may comprise an angled surface.

[0043] 38260609-1 Advantageously, the acoustic transducer comprising an angled surface means that the active acoustic wave can be reliably directed towards the surface.

[0044] The acoustic transducer configured to emit the active acoustic wave may be angled towards the surface by a wedge that interposes the acoustic transducer and the bearing.

[0045] The use of the wedge between the acoustic transducer and bearing is an advantageous way of being able to angle the active acoustic wave towards the surface.

[0046] An acoustic transducer of the one or more acoustic transducers may be mounted to the bearing, preferably mounted on a chamfered surface of the bearing.

[0047] Mounting the acoustic transducer on a chamfered surface of the bearing utilises an existing surface of the bearing for providing the angled mounting. It has been found to be advantageous that a first, active transducer be mounted to the bearing.

[0048] The one or more acoustic transducers may form part of an array of acoustic transducers, the array of acoustic transducers comprising a plurality of acoustic transducers; and / or the one or more acoustic transducers may comprise a plurality of acoustic transducers disposed at different positions around the bearing.

[0049] Multifunctional active / passive acoustic transducers may be used. Dedicated separate active / passive acoustic transducers may be used. A combination of multifunctional and dedicated separate acoustic transducers may be used.

[0050] Advantageously, the use of an array of acoustic transducers means that a higher resolution of monitoring, by using the multiple acoustic transducers, can occur.

[0051] Advantageously, disposing the plurality of acoustic transducers at different positions around the bearing means that the bearing can be monitored at a wider range of spatial positions.

[0052] Monitoring the bearing may comprise determining one or more of: a temperature of the bearing;

[0053] 38260609-1 a rolling element to rolling element timing of the bearing; a lubrication state of an inner race and / or an outer race of the bearing; a thickness of a lubricant film between the inner race and / or outer race and a rolling element of the bearing; a loading of the bearing; a presence of a defect in the bearing; a presence of debris in the bearing; and a rotational speed of the bearing.

[0054] The aforementioned parameters are all useful data outputs and the monitoring of the bearing.

[0055] Monitoring the bearing may comprise detecting one or more changes in the bearing operating conditions and / or comparing a determined parameter with an operational model of the bearing.

[0056] Advantageously, detecting one or more changes in the bearing, and / or comparing a determined parameter with an operational model of the bearing, are desirable data outputs for use in the monitoring of the bearing.

[0057] Monitoring the bearing may comprise detecting changes in an amplitude and / or frequency of the active acoustic wave, indicative of a rolling element of the bearing passing the one or more acoustic transducers; optionally wherein monitoring the bearing further comprises detecting slippage of the bearing by comparing a rolling element to rolling element frequency with a frequency of rotation of a rotatable one of an inner or outer race of the bearing.

[0058] Advantageously, the monitoring can be used to determine a rolling element to rolling element frequency.

[0059] Advantageously, any detected mismatch between the aforementioned frequencies is indicative of one or more rolling elements slipping, as opposed to smoothly rolling, on the inner or outer race, which can be indicative of a failure of the bearing.

[0060] 38260609-1 Variations in the amplitude of the active acoustic wave, indicative of the passage of rolling elements, may be indicative of an uneven loading of the bearing.

[0061] Advantageously, variations between peak-to-peak amplitudes, or any other measure of signal amplitude or energy (e.g. root-mean square, RMS), for the rolling elements can be used to infer an uneven loading of the bearing.

[0062] Monitoring the bearing may comprise detecting changes in an amplitude and / or frequency of the passive acoustic wave, indicative of a rolling element of the bearing passing the one or more acoustic transducers

[0063] The processor may be located remotely from the one or more acoustic transducers.

[0064] The processor may be configured to communicate with the one or more acoustic processors via a communication network. The network may be a local area network (LAN) or a wide area network (WAN). The WAN may use the internet. In one particular implementation, the processor may be a cloud-based processor.

[0065] Advantageously, the processor being located remotely from the one or more acoustic transducers means the signals can be processed over the cloud, for example.

[0066] Alternatively, the processor may be a local processor. In other words, the processor may be co-located with the one or more acoustic transducers and, optionally, the bearing. In this example, the processor may be directly connected to the one or more acoustic transducers, e.g., by electrical cables or wires, without using a communication network.

[0067] According to a second aspect of the invention there is provided a gas turbine engine comprising a plurality of systems according to the first aspect of the invention, the gas turbine engine further comprising a processor configured to: receive monitoring data from the plurality of systems; and monitor the gas turbine engine based upon the monitoring data from the plurality of systems.

[0068] 38260609-1 The gas turbine may comprise between 10 to 20 bearings. The gas turbine may comprise a corresponding number of systems (e.g. monitored bearings). Alternatively, only a subset of constituent bearings may be monitored.

[0069] Advantageously, the overall gas turbine engine health can be monitored based upon monitoring data from the constituent plurality of bearing systems. An overall asset health can therefore be determined.

[0070] According to a third aspect of the invention there is provided a kit of parts for monitoring a bearing, the kit of parts comprising: one or more acoustic transducers, the one or more acoustic transducers being configured to: produce a first signal indicative of an active acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and produce a second signal indicative of a passive acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and a processor connectable to the one or more acoustic transducers, the processor being configured to: receive the first and second signals; and monitor the bearing based upon the first and second signals.

[0071] According to a fourth aspect of the invention there is provided a method of monitoring a bearing, the method comprising: receiving a first signal, from one or more acoustic transducers, indicative of an active acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; receiving a second signal, from the one or more acoustic transducers, indicative of a passive acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and processing the first and second signals to monitor the bearing.

[0072] Advantageously, the combination of active and passive acoustic sensing means that a wider range of parameters can be determined, providing a fuller picture of the health of the bearing being monitored.

[0073] 38260609-1 The method may further comprise causing the acoustic transducer which receives the first signal to emit the acoustic wave into the bearing.

[0074] According to a fifth aspect of the invention there is provided a computer program comprising instructions which, when executed by a processor, cause a system incorporating the processor to carry out the method of the fourth aspect of the invention.

[0075] According to a sixth aspect of the invention there is provided a computer-readable medium comprising instructions which, when executed by a processor, cause a system incorporating the processor to carry out a method in accordance with the fourth aspect of the invention.

[0076] The computer-readable medium may be transitory or non-transitory.

[0077] Optional and / or preferred features as set out herein may be used either individually or in combination with each other where appropriate and particularly in the combinations as set out in the accompanying claims. The optional and / or preferred features for each aspect of the invention set out herein are also applicable to any other aspects of the invention, where appropriate. For example, optional features set out in connection with the first aspect of the invention may be combined with any of the second to sixth aspects of the invention. The first, second or third aspects of the invention may be used to carry out the method of the fourth aspect of the invention.

[0078] Embodiments will now be described, purely by way of example, with reference to the accompanying drawings, in which like features are denoted by like reference signs, and in which:

[0079] Figure 1 shows a part-cutaway perspective view of a bearing;

[0080] Figure 2 is a schematic illustration of a system in accordance with an embodiment of the invention;

[0081] Figure 3 is a schematic illustration of a system according to another embodiment;

[0082] Figure 4 is a flow diagram of a method of monitoring a bearing according to an embodiment;

[0083] Figures 5 and 6 are graphs showing plots of data illustrating how one or more ‘active’ measurements of a bearing can be monitored;

[0084] 38260609-1 Figure 7 is a graph showing plots of data illustrating how a "passive’ measurement of a bearing can be monitored; and

[0085] Figures 8 to 13 are schematic illustrations of bearings according to different embodiments of the invention.

[0086] Figure 1 shows a part-cutaway perspective view of a bearing 2. The bearing 2 is a ball bearing (an example of a rolling element bearing) but, as will be described below, the invention can be worked with a variety of other kinds of bearing (e.g. roller, needle, taper etc.). The bearing 2 comprises an inner race 4, an outer race 6 and a plurality of rolling elements 8 therebetween. At least one of the inner race 4 and outer race 6 is rotatable, with respect to the other, about an axis of rotation 10. Although not shown, the bearing 2 will typically be mounted on a shaft which is configured to rotate about the axis of rotation 10. It will be appreciated that in some examples the outer race 6 may be configured to rotate relative to a stationary inner race, or both the inner race 4 and outer race 6 may each be configured to rotate, for example, in an inter-shaft bearing.

[0087] Each race 4, 6 includes a surface (e.g. a contact surface) for contacting the rolling elements 8. Put another way, each of the inner and outer races 4, 6 has a surface which is engaged by the rolling elements 8. The inner race 4 has a radially outwardly facing contact surface 12 which is engaged by the rolling elements 8. The outer race 14 has a radially inwards facing contact surface 14 which is engaged by the rolling elements 8. As shown in Figure 1 , the contact surfaces 12, 14 may be defined by grooves in which the rolling elements 16 are located and retained. The grooves may have a shape which corresponds to the opposing contact surface of the rolling elements 8. Hence, as shown, there is provided an annular groove which extends around the axis of rotation 10 and which is arcuate in an axially extending cross-section.

[0088] The bearing 2 may be lubricated so as to have at least a film of lubricant between the rolling elements 8 and the contact surfaces 12, 14 of the respective races 4, 6. The bearing 2 may also be sealed or shielded with a barrier located within a gap between the inner and outer races 4, 6.

[0089] The rolling elements 8 shown in Figure 1 are in the form of ball bearings which are evenly distributed around the axis of rotation 8. A cage 16 may be used to control the relative spacing of the rolling elements 8. Although Figure 1 shows rolling elements 8 in the form

[0090] 38260609-1 of ball bearings, it will be appreciated that the invention may be applied to any variety of elasto-hydrodynamic bearings comprising linear, cylindrical, needle, spherical, tapered or other rolling elements. It will also be appreciated that the invention may be applied to hydrodynamic radial, thrust, linear and journal bearings. Other examples of other suitable bearings may exist. Further, the invention may find application in bearings other than rolling element bearings or other structures which are configured to rotate relative to one another. Further still, in the broadest sense, the invention may find application in any rotating component where ultrasonic interrogation of the rotating component is required. Any references to the outer race throughout this document may be generalised to a stationary part of the bearing, such as a bearing housing (e.g. for a journal bearing), in light of the multitude of different bearings the invention can be worked with.

[0091] Turning to Figure 2, a schematic illustration of a system 20 in accordance with an embodiment of the invention is provided. The system 20 is for monitoring the bearing 2.

[0092] Figure 2 schematically illustrates the inner and outer races 4, 6 of the bearing 2. One rolling element 8 is shown between the inner and outer races 4, 6, the rolling element 8 being engaged by cage 16. An axis of rotation 17, about which one or more of the inner and outer races 4, 6 rotates, is also schematically indicated. Figure 2 also shows one or more acoustic transducers, comprising first and second acoustic transducers 22, 24. In this embodiment the first acoustic transducer 22 is an active acoustic transducer. In this embodiment the second acoustic transducer 24 is a passive acoustic transducer.

[0093] An active acoustic transducer refers to an acoustic transducer which receives an (active) acoustic wave, transmitted through a medium, the acoustic wave having been emitted by either the same acoustic transducer (in the case of a pulse-echo arrangement) or a different acoustic transducer (in the case of a pitch-catch or through-transmission arrangement). The active acoustic wave being transmitted through the medium may otherwise be described as the active acoustic wave being transmitted into the medium. For the avoidance of doubt, the active acoustic wave being transmitted through a medium may occur by way of a pulse-echo, pitch-catch or through-transmission arrangement.

[0094] Pulse-echo refers to an arrangement in which an acoustic transducer (e.g. a single acoustic transducer) both emits an active acoustic wave and receives the reflected active

[0095] 38260609-1 acoustic wave. In pitch-catch and through-transmission arrangements, separate (active) acoustic transducers emit, and receive, the (active) acoustic wave. Pitch-catch refers to an arrangement whereby a transmission point of an (active) acoustic wave into a medium is not on the same axis as a reception point of the (acoustic) acoustic wave. Put another way, the two (active) acoustic transducers do not directly oppose each other (e.g. are not provided at the same position on different sides of a component). The (active) acoustic wave may thus reflect off of one or more internal surfaces within the component between the (active) acoustic transducers which emit, and receive, the (active) acoustic wave. In through-transmission arrangements, the emitting and receiving (active) acoustic transducers typically oppose one another (e.g. are provided at the same position on different sides of a component).

[0096] Active acoustic (ultrasonic) measurements are typically performed in the frequency range of 0.5 to 15 MHz. The component / acoustic wave interactions can be considered macroscopic (i.e. relating to geometries of the same order of magnitude as the part).

[0097] A passive acoustic transducer refers to an acoustic transducer which receives a (passive) acoustic wave generated or produced by the bearing itself. That is to say, the passive acoustic wave is not emitted by an acoustic transducer. Passive acoustic (ultrasonic) measurements are typically in the frequency range 20 to 500 kHz, often more particularly 100 to 500 kHz. They may be considered microscopic (i.e. relating to geometries that are one or more magnitudes smaller than the geometry of the part).

[0098] The system 20 further comprises a controller 26. The controller 26 comprises a processor 28, a memory 30, an analogue-to-digital converter (ADC) and a digital-to- analogue converter (DAC). The ADC and DAC are collectively represented by block 32. The DAC is an optional component. In some embodiments a pulser may instead use a switch to a high voltage source. Said switching may be configured to provide a top hat, or negative top hat, pulse; a square wave; or a capacitive discharge to the one or more acoustic transducers.

[0099] The processor 28 can be any suitable type of data processing device, such as a microprocessor, microcontroller, digital signal processor or application specific integrated circuit (ASIC). The processor 28 is communicatively coupled to the memory 30. The memory 30 can include a volatile memory, a non volatile memory, or both

[0100] 38260609-1 volatile and non-volatile memories. The memory 30 stores a control program (not shown in Figure 1). The control program includes processor-executable instructions that, when executed by the processor 28, cause the system 20 to perform the method described below with reference to Figure 4.

[0101] The ADC and DAC 32 are communicatively coupled to each of the first and second acoustic transducers 22, 24. The ADC and DAC are typically coupled to the acoustic transducers 22, 24 by an electrical connection (e.g., using one or more electrically- conducting cables). The DAC converts a digital output from the processor 28 into an analogue electrical signal (e.g., a voltage signal), which is supplied to the acoustic transducers 22, 24. The analogue electrical signal produced by the DAC energises at least the first acoustic transducer 22, causing it to emit (active) acoustic wave 34 into the bearing 2. In this example, the active acoustic wave 34 is specifically emitted into the outer race 6 of the bearing 2, but this is a non-limiting example. In this example, the active acoustic wave 34 is also emitted parallel to the axis of rotation 17. However, in other embodiments, and as will be described below, the active acoustic wave may be emitted towards one or more of the surfaces 12, 14, or perpendicular (e.g. substantially perpendicular) to the axis of rotation 17. It is advantageous that the active acoustic wave impinge the surfaces 12, 14 for a number of reasons. Not least the arcuate, recessed nature of these surfaces 12, 14 means a wave will readily reflect off of these surfaces 12, 14.

[0102] The first acoustic transducer 22 generates analogue electrical signals when it receives reflected (active) acoustic wave 36 transmitted through the bearing 2. The first acoustic transducer 22 thus produces a first signal indicative of the active acoustic wave 36 transmitted through the bearing 2 and received at the first acoustic transducer 22.

[0103] Each of the first and second acoustic transducers 22, 24 is thus connected to the processor 28. The connection may be by way of a wired connection or a wireless connection (as will be described below). The processor 28 is configured to receive first and second signals, produced by the first and second acoustic transducers 22, 24 respectively, and monitor the bearing 2 based upon the first and second signals. In other embodiments, the system may comprise a plurality of processors. Each of the first and second acoustic transducers may be connected to separate processors.

[0104] 38260609-1 In the illustrated example, and as mentioned above, the first acoustic transducer 22 is an active acoustic transducer, whereas the second acoustic transducer 24 is a passive acoustic transducer. As such, unlike the first acoustic transducer 22, the second acoustic transducer 24 does not emit an acoustic wave. Instead, the second acoustic transducer 24 only receives a (passive) acoustic wave, schematically indicated 38 in Figure 2. Passive acoustic waves are generated in a component (such as bearing 2) due to microstructural defects or deformations, or due to multi-component impacts (e.g. debris on the surfaces 12, 14 of the inner and outer races 4, 6). The second acoustic transducer 24 generates analogue electrical signals when it receives (passive) acoustic wave 38 transmitted through the bearing 2. The second acoustic transducer 24 thus produces a second signal indicative of the passive acoustic wave 38 transmitted through the bearing 2 and received at the second acoustic transducer 24.

[0105] As the active and passive acoustic transducers (e.g. first and second acoustic transducers 22, 24 respectively) have different frequency content, of one order of magnitude difference or more, the circuit (e.g. one or more components of the controller 26) is preferably configured for each separately. This may mean there is a separate channel for the first / second acoustic transducers 22, 24. Alternatively, if one transducer is configured to receive both passive and active acoustic waves (e.g. as will be described in connection with Figure 3), then there may be a switched circuit for improved electronic receiving performance (e.g. the circuit switching between active / passive modes). Further alternatively, if one transducer is configured to receive both passive and active acoustic waves, there may be one circuit, for simplicity, which provides ample performance for both active and passive acoustic wave measurement.

[0106] The ADC 32 receives an analogue electrical signal from each of the acoustic transducers 22, 24, and produces a digital representation of each analogue signal. More specifically, the ADC outputs a series of digital samples, which are supplied to the processor 28 whereupon they are processed to monitor the bearing 2.

[0107] Propagation of the emitted and received acoustic waves 34, 36, 38 through the bearing 2 will be affected by the physical properties, and conditions, of the bearing 2. For example, the speed at which the acoustic waves 34, 36, 38 propagate, the amount of attenuation experienced by the acoustic waves 34, 36, 38 as they propagate, and the amount of reflection experienced by the emitted acoustic wave 22 may be affected by

[0108] 38260609-1 properties and / or conditions of the bearing 2. Examples of the properties / conditions of the bearing which can affect these criteria (for which more detail will be provided later in this document) include:

[0109] • a temperature of the bearing;

[0110] • a rolling element to rolling element timing of the bearing (e.g. the time between successive rolling elements of the bearing passing a transducer);

[0111] • a lubrication state of the inner race and / an outer race of the bearing;

[0112] • a thickness of a lubricant film between the inner race and / or outer race and a rolling element of the bearing;

[0113] • a loading of the bearing;

[0114] • the presence of defects in the bearing;

[0115] • the presence of debris in the bearing; and

[0116] • a rotational speed of the bearing.

[0117] Advantageously, the combination of active and passive acoustic sensing means that a wider range of parameters can be determined, providing a fuller picture of the health of the bearing 2 being monitored. The information from one type of sensor can also advantageously be used to interpret information from another type of sensor. For example, the first (active) acoustic transducer 22 can identify what is happening to the bearing 2 to which it is mounted. The second (passive) acoustic transducer 24 may be exposed to a much wider range of acoustic (e.g. ultrasonic) sources in the wider system (e.g. a gas turbine, comprising a plurality of bearings). Therefore, if the second acoustic transducer is reporting a signal but the first acoustic transducer is not, it can be determined that the bearing 2 is not the source of the acoustic emissions. The combination of active and passive acoustic sensing thus facilitates interpretation of historically challenging passive acoustic signals.

[0118] In an alternative embodiment to that shown in Figure 2, the system processes the received signals remotely. In said system, the ADC and DAC are not physically colocated with the controller. Instead, the ADC and DAC exchange data with the controller via a network. The network may comprise a local area network (LAN), a wide area network (WAN) or a combination thereof. The ADC and DAC and the controller may each be communicatively coupled to the network by a respective network interface. The network interfaces may be wired or wireless interfaces, and may use any suitable communication protocol(s).

[0119] 38260609-1 Returning to Figure 2, the first acoustic transducer 22 operates in pulse-echo mode. That is to say, the first acoustic transducer 22 both emits active acoustic wave 34 and receives reflected active acoustic wave 36. In alternative embodiments, a pitch-catch or through- transmission arrangement may be used in which a corresponding first acoustic transducer (only) receives an active acoustic wave which is emitted by a different, separate active acoustic transducer.

[0120] In Figure 2 the first acoustic transducer 22 is shown mounted to (e.g. engaged with) the bearing 2, specifically to the outer race 6 thereof. As will be described in detail below, there are various other mounting options for at least the first acoustic transducer 22, and particularly for directing the acoustic wave 34 towards the surface 14. The first acoustic transducer 22 may be mounted, directly or indirectly, to the bearing 2, and specifically to the outer race 6. One or more components may interpose the first acoustic transducer 22 and the outer race 6, as long as there remains a transmission pathway between the transducer 22 and the bearing to, preferably the outer race 6 thereof.

[0121] In Figure 2 the second acoustic transducer 24 is shown not mounted to the bearing 2. Put another way, the second acoustic transducer 24 is schematically illustrated being separated from the bearing 2. The second acoustic transducer 24, which it will be recalled is a passive acoustic transducer, can thus be used for airborne acoustic sensing. In other embodiments, the second acoustic transducer 24 (e.g. passive acoustic transducer) could be mounted to the bearing 2.

[0122] Turning to Figure 3, a schematic illustration of a system 40 according to another embodiment is provided. The system 40 shares many features in common with the system 20 shown in Figure 2, and so only the differences will be described in detail for brevity.

[0123] The system 40 comprises one acoustic transducer 42 that is configured to produce both the first and second signals. Put another way, the acoustic transducer 42 provides the functionality of both the first and second transducers 22, 24 for the system 20 shown in figure 2. Described another way still, the acoustic transducer 42 provides both an active and passive transducer functionality. As such, like in the previous embodiment, the acoustic transducer 42 emits active acoustic wave 34, and then receives reflected active

[0124] 38260609-1 acoustic wave 36. However, the acoustic transducer 42 also receives the passive acoustic wave 38 produced by the bearing 2. The acoustic transducer 42 in the illustrated embodiment may therefore be described as a multipurpose, multifunctional, acoustic transducer. The acoustic transducer 42 thus produces: i) a first signal indicative of the active acoustic wave 36 transmitted through the bearing 2 and received at the acoustic transducer 42; and ii) a second signal indicative of the passive acoustic wave 38 transmitted through the bearing 2 and received at the acoustic transducer 42.

[0125] The inventors have found that the use of an active acoustic transducer can provide both the functionality of emitting and receiving active acoustic waves, and receiving passive acoustic waves, obviating the need for a separate, dedicated passive acoustic transducer.

[0126] By mounting the acoustic transducer 42 to the bearing 2, and specifically to the outer race 6 thereof, the comparative lack of sensitivity of the acoustic transducer 42 for receiving passive acoustic waves, compared to that of a dedicated passive acoustic transducer (e.g. 24 in Figure 2), is mitigated. The sensitivity is related to the geometry of the piezo ceramic and corresponding resonant frequency of the piezo. The sensitivity is also related to the design and integration of any related components for improving the acoustic wave transmission and / or receiving performance (e.g. the use of a delay line).

[0127] The first and second signals produced by the acoustic transducer 42 may be produced simultaneously. That is to say, active and passive acoustic monitoring may occur simultaneously. Owing to the active acoustic waves being emitted at a frequency of around 5 MHz, and the passive acoustic waves being emitted at around 0.2 MHz, it is possible to separate the overlaid signals that correspond to the active and passive waves respectively. The separation can occur in post processing / filtering of the signals.

[0128] Alternatively, the first and second signals may be produced by the acoustic transducer 42 asynchronously. Put another way, the first and second signals are not produced simultaneously. In such examples the acoustic transducer 42 still acts as both an active and passive acoustic transducer, but switches between the two functionalities.

[0129] For either of the systems 20, 40 shown in Figures 2 and 3 respectively, the one or more acoustic transducers may form part of an array of acoustic transducers. The array of

[0130] 38260609-1 acoustic transducers may thus comprise a plurality of acoustic transducers. The array of acoustic transducers may provide for multiple measurement locations. That is to say, the constituent acoustic transducers may be disposed at a plurality of different positions around the bearing. The array of acoustic transducers may comprise acoustic transducers having a range of different specifications. That is to say, some may be (for example) high-frequency, some (for example) low-frequency, and some medium frequency (for example). The array comprising a plurality of transducers having different specifications advantageously extends the frequency range of the overall array. The array of acoustic transducers may thus comprise a mixture of different acoustic transducers, or may comprise a plurality of same-variety acoustic transducer. It also follows that the array of acoustic transducers may comprise a plurality of multipurpose transducers such as the transducer 42 of Figure 3. Accordingly, the transducer 42 shown in Figure 3 may not be the only transducer in the system 40, or in a wider system (e.g. a gas turbine engine) of which the system 40 forms part.

[0131] Figure 4 is a flow diagram of a method 48 of monitoring a bearing. The method 48 can be carried out using the systems 20, 40 of either of Figures 2 or 3.

[0132] The method 48 begins at operation 50, in which the processor 28 causes the one or more (active) acoustic transducers to emit an (active) acoustic wave 34 into the bearing 2. The processor 28 may cause the one or more acoustic transducers to emit the active acoustic wave 34 by outputting digital values to the DAC. The digital values represent an excitation waveform which, after digital-to-analogue conversion by the DAC, is received by the one or more acoustic transducers. The excitation waveform causes the one or more acoustic transducers to emit the active acoustic wave 34 into the bearing, whereupon it propagates through the bearing 2. The excitation waveform may be any of a pulse wave, continuous wave, swept frequency wave, or a toneburst excitation.

[0133] With reference to Figures 2 and 3, the acoustic wave 34 propagates through the bearing 2, specifically the outer race 6 thereof, until it reaches second outer wall 6b. The acoustic wave 34 is reflected by the second outer wall 6b, such that it propagates back towards the first outer wall 6a. A portion of the reflection 36 of the acoustic wave 34 is received by the one or more acoustic transducers, referred to as the first received active acoustic wave 36. The first received active acoustic wave 36 causes the one or more acoustic transducers to produce an analogue electrical signal.

[0134] 38260609-1 At operation 52, the processor 28 receives a first signal that is indicative of the first received active acoustic wave 36. For example, the processor 28 may receive a digital signal from the ADC, wherein the digital signal is a digital representation of the analogue electrical signal produced by the one or more acoustic transducers in response to the first received active acoustic wave 36. The processor 28 may store the first signal in the memory 30, such that the stored signal can be processed later to monitor the bearing 2 as described in more detail in connection with operation 58.

[0135] Operation 54 is substantially the same as operation 52, but is performed with respect to a passive acoustic wave 38. As explained in connection with Figures 2 and 3, where dedicated (separate) active and passive acoustic transducers are used, a first acoustic transducer may emit and receive the active acoustic wave, whilst a second acoustic transducer receives the passive acoustic wave. Where one, multifunctional acoustic transducer is used, that acoustic transducer may emit and receive the active acoustic wave and receive the passive acoustic wave.

[0136] With reference to Figures 2 and 3, the passive acoustic wave 38 propagates through the bearing 2. At least a portion of the passive acoustic wave is received by the one or more acoustic transducers, referred to as the second received acoustic wave. The second received acoustic wave 38 causes the one or more acoustic transducers to produce an analogue electrical signal.

[0137] At operation 54, the processor 28 receives a second signal that is indicative of the second received acoustic wave 38. For example, the processor 28 may receive a digital signal from the ADC, wherein the digital signal is a digital representation of the analogue electrical signal produced by the one or more acoustic transducers in response to the second received acoustic wave 38. The processor 28 may store the second signal in the memory 30, such that it can be processed later to monitor the bearing 2.

[0138] At operation 56, the processor 28 monitors the bearing 2 based upon the first and second signals. As mentioned above, examples of the properties / conditions of the bearing 2 which can be monitored include:

[0139] • a temperature of the bearing;

[0140] 38260609-1 • a rolling element to rolling element timing of the bearing (e.g. the time between successive rolling elements of the bearing passing a transducer);

[0141] • a lubrication state of the inner race and / an outer race of the bearing;

[0142] • a thickness of a lubricant film between the inner race and / or outer race and a rolling element of the bearing;

[0143] • a loading of the bearing;

[0144] • the presence of defects in the bearing;

[0145] • the presence of debris in the bearing; and

[0146] • a rotational speed of the bearing.

[0147] The operations of the method 48 need not be performed in exactly the order shown in Figure 4, but can be performed in a different order that achieves substantially the same result. For example, operations 52 and 54 can be performed at substantially the same time (that is, signals can be received from the one or more acoustic transducers at substantially the same time). As mentioned above, for the system 20 of Figure 2, operations 52 and 54 can be carried out by the first and second acoustic transducers 22, 24 respectively. For the system 40 of Figure 3, operations 52 and 54 are carried out by the (one) acoustic transducer 42. As such, for the system 40, operations 52 and 54 can either be carried out at the same time (i.e. simultaneously) or asynchronously (e.g. the acoustic transducer 42 switching sequentially between active / passive operations). Operation 50 is optional, in the sense that it does not form an essential feature of the subject-matter for which protection is sought.

[0148] The ways in which the first and second signals can be used to monitor the bearing will now be described in connection with the following figures.

[0149] Beginning with Figure 5, a graph is provided with a temperature (° centigrade) on the x- axis, and a time-of-f light (nanoseconds) measurement shown on the y-axis. Data points are plotted on the graph, with a best fit line overlaid. Figure 5 demonstrates how, for a test bearing placed in an oven and subjected to a ramped temperature, the time-of-flight measurement for an active acoustic wave transmitted through the bearing tracks the temperature. That is to say, there is a correlation between the time-of-flight of the active acoustic wave and the temperature of the bearing. Figure 5 thus demonstrates that at least an active acoustic wave received by a transducer can be used to determine a temperature of the bearing. This is desirable for reasons of being able to detect whether

[0150] 38260609-1 a bearing is operating outside of an allowable temperature range, and being able to determine what range of temperatures the bearing generally operates at.

[0151] Turning to Figure 6, a graph is provided with a measurement time (seconds) on the x- axis and an amplitude (bits) of received active acoustic waves on the y-axis. The data points of Figure 6 are experimental data from an unloaded test bearing having a similar geometry to that shown in Figures 2 and 3. The repeating reductions in amplitudes of the active acoustic waves (e.g. 60, 62, 64, 66, 68, 70) are due to the passage of a rolling element of the bearing. The variations in the amplitude of the cyclical reductions in amplitude are due to the bearing being unloaded (e.g. amplitude of 62 vs 70).

[0152] The data presented in Figure 6 can advantageously be used to determine a rolling element to rolling element timing of the bearing. That is to say, the data shown in Figure 6 can be used to determine how much time passes between successive rolling elements passing the active transducer. This is advantageous for at least the reason that the rolling element to rolling element timing of the bearing can be used to determine a rolling element to rolling element frequency. The rolling element to rolling element frequency can be compared to a theoretical passing frequency derived from an RPM measurement of a shaft received by the bearing and / or an RPM measurement derived from the passive acoustic transducer. By comparing these two frequencies, it is possible to determine whether the rolling elements are rolling as desired, or are dragging along a surface of the inner race or outer race, reducing the working life of the bearing.

[0153] As also mentioned above in connection with Figure 6, the variations in the amplitude of the reductions are owing to the bearing being loaded / unloaded. The data presented in Figure 6 can therefore also be used to determine an undesirable uneven loading of the bearing, leading to a reduction in the working life of the bearing. The data presented in Figure 6 can also be used to determine an operational performance of a wider system (e.g. equipment) the bearing forms part of (e.g. a gas turbine engine).

[0154] The examples presented in connection with Figures 5 and 6 are all active measurements corresponding to signals produced by an acoustic transducer that receives an active acoustic wave.

[0155] 38260609-1 Other examples of active measurements that can be used to monitor bearing are set out below.

[0156] As has been mentioned, temperature can be determined by transmitting an active acoustic wave through the bearing, preferably the outer race, preferably parallel to the axis of rotation. A change in the time of flight (ToF) of the active acoustic wave is observed due to changes in temperature.

[0157] Following on from the above, it may be that the acoustic transducer sensor emits the acoustic wave through the outer race without the acoustic wave hitting the rolling element / race interface. This may be due to the size or frequency of the acoustic transducer and / or the geometry of the bearing and / or the location of the acoustic transducer on the bearing. This is useful for the temperature measurement outlined above (e.g. ensuring no interference from the change in signal due to the rolling elements passing the acoustic transducer).

[0158] Rolling element detection is another alternative. Transmitting an active acoustic wave through the bearing, preferably the outer race, preferably parallel to the axis of rotation may result in some of the wave impinging the rolling element / race interface (e.g. [contact] surfaces 12, 14 of Figure 1) when the rolling element is aligned with the acoustic transducer. This results in some of the acoustic wave being transmitted across the rolling element / raceway interface, resulting in a decrease in the amount of reflected energy to the acoustic transducer.

[0159] As will be described in detail below, for rolling element detection (among others) it may be desirable to direct the acoustic wave at an angle into the outer race to reflect multiple times (e.g. from multiple internal surfaces) within the outer race way before being reflected back to the acoustic transducer.

[0160] This angling of the acoustic transducer may be achieved by way of a lens or wedge on / in / between the acoustic transducer and the bearing to direct the acoustic wave. Alternatively, or in combination, the angling may be achieved by using the bearing geometry to achieve the same outcome. For example, the acoustic transducer could be mounted to a chamfer on the bearing (e.g. on the outer race thereof).

[0161] 38260609-1 Rolling element to rolling element timing is another useful output. Rolling element to rolling element timing can be used to determine the passing frequency of the rolling elements with respect to the acoustic transducer, which could then be compared to a frequency of rotation of a shaft to determine whether the rolling elements are being dragged (e.g. not rotating fully).

[0162] A lubrication state of the contact surfaces of the inner race and outer race can also be determined. The acoustic wave that reflects from the surface acquires information on the amount of lubricant on the surface. Changes to lubricant on the surface affect the reflected acoustic wave received at the acoustic transducer.

[0163] Lubricant film between the rolling element and the contact surfaces can also be measured. The amount of ultrasound (for example) transmitted into the rolling element is a function of the thickness of the lubricant film between the rolling element and the contact surface.

[0164] Load on the bearing can also be determined. The amount of load on the bearing will impact the film thickness between the rolling element and the contact surfaces. This will present as a change in the lubricant film thickness between the rolling element and the raceway. The following can also be determined:

[0165] • The load on an individual rolling element by monitoring the amplitude of the reflected active acoustic wave;

[0166] • The load on successive rolling elements, and variation thereof, and thereby the load variation / fluctuation in the turbine (where, for example, the bearing forms part of a turbine, optionally in a gas turbine engine; and.

[0167] • The load vector by using multiple transducers around a circumference of the bearing to sense the load at multiple locations around the bearing.

[0168] It will be appreciated that one or more of the aforementioned active measurements may be used (e.g. monitored) in combination with one another, or in isolation of one another.

[0169] Turning to Figure 7, a graph is provided with a measurement time (seconds) on the (common) x-axis, an amplitude measurement (Volts) shown on the a first y-axis 72, and a rotations per minute (RPM) value shown on a second y-axis 74. The RPM value corresponds to a rotational speed of a shaft placed in a bearing during testing. As

[0170] 38260609-1 indicated by the horizontal bars (e.g. 76 [300 RPM], 78 [-800 RPM] etc.), this testing occurred at different shaft speeds. The time period over which the horizontal bars extend is indicative of the time period of the testing at that shaft speed.

[0171] Figure 7 demonstrates illustrates how, in the time domain, there are visible differences in the amplitude of passive acoustic waves received by a transducer depending upon the RPM value of the shaft rotated within a bearing. This passive monitoring can thus be used to determine a speed of the bearing, and specifically a rotational speed of a rotating part of the bearing.

[0172] The example presented in connection with Figure 7 is a passive measurement corresponding to signals produced by an acoustic transducer that receives a passive acoustic wave generated by the bearing.

[0173] Other examples of passive measurements that can be used to monitor bearing are set out below:

[0174] • Defect detection. Microscopic defects, such as rolling contact fatigue and microscopic cracking, will generate detectable acoustic emission events;

[0175] • Debris detection. Debris in the rolling interface (e.g. contact surface) will cause the rolling elements to impact the surface and cause detectable acoustic emissions;

[0176] • Lubrication monitoring. Lubrication levels will impact the amplitudes of acoustic emissions that are emitted from the bearing;

[0177] • Speed monitoring. As the rolling elements roll in the bearing there will be a cyclic generation of acoustic emissions. By acquiring these ultrasonic waveforms, the frequency content can be ascertained and the rolling speed determined; and

[0178] • Load variation / fluctuation. As the rolling elements experience a change in load they will emit a variable / fluctuating amplitude of acoustic emissions. These acoustic emissions, emitted from the bearing, will be correlated to the load on the bearing.

[0179] It will be appreciated that one or more of the aforementioned passive measurements may be used (e.g. monitored) in combination with one another, or in isolation of one another. It will be also appreciated that one or more of the aforementioned passive

[0180] 38260609-1 measurements may be used (e.g. monitored) in combination with one or more of the active measurements mentioned earlier in this document.

[0181] Advantageously, multiple active and passive measurements can be used to build an operational model, and / or detect changes in the operating conditions, and / or detect changes in the health, of the bearing, or a wider system or component the bearing forms part of. For example, where the bearing is incorporated in a turbine, the multiple active and passive measurements for the bearing can be used to detect changes in the overall turbine operating conditions (e.g. speed, load). Where the turbine forms part of a gas turbine engine, the multiple active and passive measurements for the bearing can also be used to detect changes in the overall gas turbine engine operating conditions (e.g. speed, load). Similarly, data obtained from the bearing system (e.g. subsystem) may be combined with other such bearing systems (e.g. subsystems) with the data combined to be able to determine the state of the overall turbine and / or gas turbine engine. This may comprise building an operational model of the turbine and / or gas turbine engine. It may be possible to use the active and / or passive measurements to determine a parameter, and compare that parameter with an operational model of the bearing. The parameter falling outside of an allowable threshold may be indicative of a fault within the bearing or wider system. For example, if a temperature has, at any one time, exceeded a maximum recommended temperature, it may be determined that the bearing health is below an expected level for that scenario. For example, if an average temperature exceeds a maximum recommended average temperature, it may be determined that the bearing health is below an expected level for that scenario.

[0182] Advantageously, the aforementioned monitoring can be used to not only monitor the bearing, and wider system, but also to improve the reliability of the maintenance schedule bearing and wider system (e.g. by way of predictive maintenance and / or avoiding unexpected downtime).

[0183] Figure 8 shows a schematic cross-section view of part of a bearing 120 according to another embodiment. The bearing 120 comprises: an inner race 122, an outer race 124, and a plurality of rolling elements 126. An acoustic transducer 130 is also shown. The acoustic transducer 130 engages the bearing 120 directly, specifically a chamfered surface 134 of the outer race 124. In the illustrated embodiment the acoustic transducer

[0184] 38260609-1 130 is mounted to the bearing 120 by a bracket 132. The bracket 132 is coupled to a retaining ring 134. The retaining ring 134 is, for the purposes of this document, considered to form a part of the bearing 120 by virtue of being directly engaged with the outer race 124. The bracket 132 is coupled to the retaining ring 136 by the fastener 134. Advantageously, by mounting the transducer in engagement with the chamfered surface 134 of the outer race 124, the active acoustic waves emitted by the acoustic transducer 130 can be reflected by internal surfaces within the outer race 124 to be transmitted through a surface engaged by the plurality of rolling elements, or through the plurality of rolling elements.

[0185] Turning to Figure 9, a schematic illustration of part of a cross-section of a bearing 140 according to another embodiment is provided. Like the preceding embodiments, the bearing 120 comprises an inner race (not shown in Figure 9), an outer race 122 and a plurality of rolling elements (one of which is shown labelled 124). The axis of rotation 17, about one or more of which the inner and outer races 122 rotate, is also shown. An acoustic transducer 126 is also shown engaged with, and mounted to, the outer race 122.

[0186] An active acoustic wave 128 emitted by the acoustic transducer 126 is also schematically indicated. Unlike the active acoustic waves 34 shown emitted in Figures 2 and 3, in Figure 9 the active acoustic wave 128 is emitted in a direction non-parallel to the axis of rotation 17. This advantageously means that the active acoustic wave 128 is reflected off of the surface 130 of the outer race 122 which is contacted by the plurality of rolling elements 124. Useful information about the bearing can then be ascertained from the reflective acoustic wave, once the signal is processed. This directionality of the emitted acoustic wave can be achieved in a number of different ways, some of which will be described throughout the following figures. However, in connection with Figure 9, the directionality of the acoustic wave 128 is achieved by the incorporation of a lens 132 forming part of, or coupled to, the acoustic transducer 126. Despite the acoustic transducer 126 being mounted to a flat surface of the outer race 122, perpendicular to the axis of rotation 17, incorporation of the lens 132 redirects, or steers, the active acoustic wave 128 towards surface 130.

[0187] In an alternative embodiment shown in Figure 10, which shares many features in common with Figure 9, a bearing 140 is illustrated. In the Figure 10 embodiment the

[0188] 38260609-1 steering of the active acoustic wave 128 occurs in a different way. In Figure 10 an active acoustic transducer 142 incorporates an angled surface 144. The angled surface 144 engages, directly in the illustrated embodiment, a surface 146 of the outer race 122 which is perpendicular to the axis of rotation 17. When the active acoustic wave 128 is emitted, it is emitted in a direction towards the surface 130.

[0189] In an alternative embodiment shown in Figure 11 , which shares many features in common with Figures 9 and 10, a bearing 150 is illustrated. In the Figure 11 embodiment the steering of the active acoustic wave 128 occurs in a different way. In Figure 11 an active acoustic transducer 152 is indirectly mounted to the outer race 122 by an interposing wedge 154. As such, the wedge 154 defines an angled surface 156 which engages, directly in the illustrated embodiment, the surface 146 of the outer race 122 which is perpendicular to the axis of rotation 17. When the active acoustic wave 128 is emitted, it is emitted in a direction towards the surface 130.

[0190] In an alternative embodiment shown in Figure 12, which shares many features in common with Figures 9 to 11 , a bearing 160 is illustrated. In the Figure 12 embodiment the steering of the active acoustic wave 128 occurs in a further different way. In Figure 12 an active acoustic transducer 162 is indirectly mounted to the outer race 122 by an interposing wedge assembly 164. Unlike the wedge of Figure 11 , the wedge assembly 164 comprises a wedge 166 and a lens 168. The wedge assembly 164 defines an angled surface 170 which engages, directly in the illustrated embodiment, the surface 146 of the outer race 122 which is perpendicular to the axis of rotation 17. When the active acoustic wave 128 is emitted, it is emitted in a direction towards the surface 130, but not directly at. As the acoustic wave 128 propagates through the lens 168, it is steered directly towards the surface 130. Put another way, the wedge assembly 164 directs the acoustic wave 128 to the surface 130. The surface 130 may be described as a focal point of the lens 168. The purpose of the lens 168 is to focus the acoustic wave 128. By focusing the acoustic wave 128, responsiveness is improved, as well as improved wave steering. It is a means of advantageously arranging the acoustic wave to improve sensitivity.

[0191] In Figure 13, which shares many features in common with Figures 9 to 12, a bearing 180 is illustrated in which a geometry of the bearing 180, specifically the outer race 182 thereof, is modified to accommodate the acoustic transducer 162. In this embodiment the outer race 182 facilitates the direction and / or modification of the active acoustic wave

[0192] 38260609-1 128. This advantageous provides improved sensitivity, and a resulting improved measurement.

[0193] The bearings shown in Figures 8 to 13 may otherwise be referred to as systems. The bearings of Figures 8 to 13 may be used in combination with one another. The bearings of Figures 8 to 13 may be used in combination with one or more of the systems shown in Figures 2 and 3. The bearings of Figures 8 to 13 may be used in exchange of (e.g. in place of) the bearings shown in the systems of Figures 2 and 3. The method set out at Figure 4 may be carried out by any one of the systems and / or bearings described throughout this document.

[0194] Throughout this document, the active acoustic waves emitted may comprise one or more of the following: longitudinal waves, shear waves, Rayleigh waves, or other type of pressure waves.

[0195] The method 48 can be implemented by instructions stored on a processor-readable medium. The processor-readable medium may be: a read-only memory (including a PROM, EPROM or EEPROM); a random access memory; a flash memory; an electrical, electromagnetic or optical signal; a magnetic, optical or magneto-optical storage medium; one or more registers of a processor; or any other type of processor-readable medium. The method 48 and / or the functionality of the processor 28 can be implemented by hardware, firmware, software or any combination thereof. Such hardware may include one or more application-specific integrated circuits or appropriately connected discrete logic gates. A hardware description language can be used to implement the method 48 and / or the functionality of the processor 28 with dedicated hardware.

[0196] It will be understood that the invention has been described above purely by way of example, and that modifications of detail can be made within the scope of the claims.

[0197] 38260609-1

Claims

CLAIMS:

1. A system for monitoring a bearing, the system comprising: one or more acoustic transducers, the one or more acoustic transducers being configured to: produce a first signal indicative of an active acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and produce a second signal indicative of a passive acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and a processor configured to: receive the first and second signals; and monitor the bearing based upon the first and second signals.

2. The system of claim 1 , wherein the one or more acoustic transducers comprises first and second acoustic transducers, and wherein: the first acoustic transducer is configured to produce the first signal; and the second acoustic transducer is configured to produce the second signal.

3. The system of claim 2, wherein the first acoustic transducer engages the bearing, directly or indirectly, and preferably engages, directly or indirectly, one of the inner race and the outer race.

4. The system of claim 1 , wherein the one or more acoustic transducers comprises one acoustic transducer, and wherein the acoustic transducer is configured to produce the first signal and the second signal.

5. The system of claim 4, wherein the acoustic transducer is configured to produce the first and second signals simultaneously.

6. The system of claim 4, wherein the acoustic transducer is configured to produce the first and second signals at different times.

7. The system of any preceding claim, wherein an acoustic transducer configured to produce the first signal is further configured to emit the active acoustic wave into the bearing.38260609-18. The system of any one of claims 1 to 6, wherein an acoustic transducer other than an acoustic transducer configured to produce the first signal is configured to emit the active acoustic wave into the bearing.

9. The system of any preceding claim, wherein at least one of the one or more acoustic transducers is configured to emit the active acoustic wave parallel to the axis of rotation, preferably through an outer race of the bearing.

10. The system of any preceding claim, wherein at least one of the one or more acoustic transducers is configured to emit the active acoustic wave towards a surface of an inner race, or outer race, of the bearing, the surface being engaged by a plurality of rolling elements of the bearing, the active acoustic wave preferably being reflected by multiple internal surfaces.11 . The system of claim 10, wherein the acoustic transducer configured to emit the active acoustic wave is angled towards the surface.

12. The system of claim 11 , wherein the acoustic transducer configured to emit the active acoustic wave comprises an angled surface.

13. The system of either of claims 11 or 12, wherein the acoustic transducer configured to emit the active acoustic wave is angled towards the surface by a wedge that interposes the acoustic transducer and the bearing.

14. The system of any preceding claim, wherein an acoustic transducer of the one or more acoustic transducers is mounted to the bearing, preferably mounted on a chamfered surface of the bearing.

15. The system of any preceding claim, wherein the one or more acoustic transducers form part of an array of acoustic transducers, the array of acoustic transducers comprising a plurality of acoustic transducers; and / or wherein the one or more acoustic transducers comprises a plurality of acoustic transducers disposed at different positions around the bearing.38260609-116. The system of any preceding claim, wherein monitoring the bearing comprises determining one or more of: a temperature of the bearing; a rolling element to rolling element timing of the bearing; a lubrication state of an inner race and / or an outer race of the bearing; a thickness of a lubricant film between the inner race and / or outer race and a rolling element of the bearing; a loading of the bearing; a presence of a defect in the bearing; a presence of debris in the bearing; and a rotational speed of the bearing.

17. The system of any preceding claim, wherein monitoring the bearing comprises detecting one or more changes in the bearing operating conditions and / or comparing a determined parameter with an operational model of the bearing.

18. The system of any preceding claim, wherein monitoring the bearing comprises detecting changes in an amplitude and / or frequency of the active acoustic wave, indicative of a rolling element of the bearing passing the one or more acoustic transducers; optionally wherein monitoring the bearing further comprises detecting slippage of the bearing by comparing a rolling element to rolling element frequency with a frequency of rotation of a rotatable one of an inner or outer race of the bearing.

19. The system of claims 18, wherein variations in the amplitude of the active acoustic wave, indicative of the passage of rolling elements, is indicative of an uneven loading of the bearing.

20. The system of any preceding claim, wherein monitoring the bearing comprises detecting changes in an amplitude and / or frequency of the passive acoustic wave, indicative of a rolling element of the bearing passing the one or more acoustic transducers21. The system of any preceding claim, wherein the processor is located remotely from the one or more acoustic transducers.38260609-122. A gas turbine engine comprising a plurality of systems according to any preceding claim, the gas turbine engine further comprising a processor configured to: receive monitoring data from the plurality of systems; and monitor the gas turbine engine based upon the monitoring data from the plurality of systems.

23. A kit of parts for monitoring a bearing, the kit of parts comprising: one or more acoustic transducers, the one or more acoustic transducers being configured to: produce a first signal indicative of an active acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and produce a second signal indicative of a passive acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and a processor connectable to the one or more acoustic transducers, the processor being configured to: receive the first and second signals; and monitor the bearing based upon the first and second signals.

24. A method of monitoring a bearing, the method comprising: receiving a first signal, from one or more acoustic transducers, indicative of an active acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; receiving a second signal, from the one or more acoustic transducers, indicative of a passive acoustic wave transmitted through the bearing and received at the one or more acoustic transducers; and processing the first and second signals to monitor the bearing.

25. A computer-readable medium comprising instructions which, when executed by a processor, cause a system incorporating the processor to carry out a method according to claim 24.38260609-1

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