GB2260815A - Condition monitoring systems - Google Patents

Abstract

The presence of high frequency vibration pulses is used to monitor conditions at surfaces of components in rolling and/or sliding contact, e.g. a pair of gear wheels 33, 34. Signals output by accelerometers 31, 32 are merged and high frequency components, e.g. in the range 20kHz to 200kHz, are enhanced by a signal enhancer 38 and processed by a signal processor 39 to detect vibration pulses emitted due to contact at the interface. A warning signal is output by a go/no go indicator 40 if processed parameters exceed acceptable limits. The system may be used to detect direct surface contact due to failure of oil supply or indirect contact arising from the presence of debris particles in the oil. <IMAGE>

Description

Description of Invention CONDITION MONITORING SYSTEMS This invention relates to systems for monitoring conditions at interfaces of components which are in rolling and/or sliding contact, and is particularly, although not exclusively, concerned with conditioning monitoring rotating components such as meshing gear wheels and shaft bearing interfaces.

It is known that when the surfaces of two components are in rolling and/or sliding contact vibration occurs and vibration patterns can be sensed using suitable sensors such as, for example, accelerometers.

US-A-3,699,806 discloses a system for detecting damage to a rolling element in a pair of engaging rolling elements such as a bearing or gear assembly. Vibrations repeating with a frequency equal to or close to the rotation rate or periodicity of a gear are sensed and converted to an electrical signal which is processed by signal averaging to provide an indication of surface defects or incipient surface breakdown. Thus this system extracts and analyses low frequency vibration to detect surface damage and does not provide an indication of circumstances which may result in surface breakdown such as lack of lubricant at the interface of the surfaces or the presence of debris in the lubricant following running-in.

In tests carried out to measure vibration patterns emitted by meshing gear wheels the inventor has identified the presence of high frequency vibration pulses typically in the range 20 kHz to 200 kHz. These high frequency vibration pulses do not appear to be caused by known normal factors. It is believed they arise from direct or indirect contact at the interface of the meshing gear teeth. Direct contact may result from a failure of the oil supply or from a breakdown of the oil film under load (i.e. scuffing). Indirect contact may occur in the presence of debris particles resulting from wear at the interface or transported from elsewhere through the lubricant to this interface. It is suggested that particularly at high torques, e.g. 40Nm, there may be instantaneous contact of the surfaces which results in a high frequency wave front being generated.

The inventor proposes to use the presence of these high frequency vibration pulses to monitor conditions at surfaces of components in rolling and/or sliding contact, such as meshing gear wheels, and thereby to ascertain the health of the components or of systems of which they form part.

Accordingly, in one aspect the present invention provides a method of monitoring conditions at interfaces of components in rolling and/or sliding contact, comprising the steps of: a. sensing vibrations emitted by the components; b. outputting a signal representative of the sensed vibrations; c. processing high frequency components of the signal to detect vibration pulses emitted due to contact at the interface; and d. generating a warning signal if processed parameters of the high frequency components exceed acceptable limits.

Preferably Step c. comprises processing signal frequency components in the range 20kHz to 200kHz.

In another aspect the present invention provides a system for monitoring conditions at interfaces of components in rolling and/or sliding contact, comprising sensor means for sensing vibrations emitted by the components and for outputting a signal representative of the sensed vibrations, processing means adapted for processing high frequency components of the signal to detect vibration pulses emitted due to contact at the interface of the components, and means for generating a warning signal if processed parameters of the high frequency components exceed acceptable limits.

Warning signals may be fed to a go/no go indicator which may give a visual and/or audible warning.

The sensor means may be mounted on one or more moving components or on a stationary component associated with the moving component to sense vibrations emitted by the moving component.

The sensor means may comprise one or more accelerometers.

In an embodiment of the invention two or more accelerometers are tangentially mounted on the moving component and the signals output by the accelerometers merged by amplifier means to obtain a torsional acceleration signal.

In another embodiment of the invention signals output by the high frequency signal processing means are fed to an analogue to digital converter and digital signals are input to pattern recognition means which enable the cause of the high frequency vibration pulses to be determined, such causes being, for example, surface wear, lack of oil or presence of unacceptable debris particles at the interface of the components.

A method and system in accordance with the present invention are particularly suited for use in condition monitoring transmission drive systems, in particular gear boxes, and can be used to advantage in a system monitoring the health of a helicopter gearbox.

Accelerometers may be mounted on rotating members or stationary parts of the gearbox assembly to detect high frequency vibration pulses, say in the range 20 to 200 kHz, resulting from gear tooth contact.

Accelerometers having high natural frequency may be coupled with amplifiers which give an output proportional to the third differential of displacement, i.e. rate of change of acceleration, to detect high frequency vibration pulses generated by metallic contact.

The high frequency vibration pulses may be used to detect contact between gear teeth either directly or indirectly via debris particles.

Thus, the high frequency vibration pulses may be used to detect the presence of debris particles in the oil passing through a gear mesh.

The high frequency vibration pulses may also be used to detect failure of the oil supply to a gear mesh.

When such problems occur there is an increase in the amplitude and length of time of occurrence of the high frequency vibration pulses and sensed signals can be processed and analysed to generate warning signals.

The invention will now be further described by way of example only and with reference to the accompanying drawings in which: Figures 1 and 2 are vibration traces showing the filtered high frequency component of two meshing gears; and Figure 3 is a block diagram of a condition monitoring system in accordance with one embodiment of the invention.

Trace 10 in Figure 1 is a filtered high frequency component of vibration sensed in tests carried out by the inventor with two meshing gear wheels at a torque of 20Nm and at 200 Hz tooth frequency, trace 11 being a once per tooth marker provided for reference.

Trace 12 in Figure 2 is a filtered high frequency component of vibration sensed in similar tests carried out by the inventor at 40Nm torque and 200 Hz tooth frequency, trace 13 again being a reference once per tooth marker.

It will be seen that whilst at the lower torque the trace 10 shows very little vibration activity, at the higher torque the trace 12 shows a significant number of bursts of vibration, spaced at once per tooth.

As previously discussed these are believed to be due to touching of opposed surfaces of the meshing gear teeth at that point in the mesh where the oil film is at its thinnest, as evidenced by markings present on the gear teeth after the test run at the higher torque.

The inventor proposes that condition monitoring of meshing gear wheels and other rotating components which have surfaces in rolling and/or sliding contact, such as shaft bearing interfaces, be carried out by a method which comprises sensing vibrations emitted by the components and outputting a signal representative of the sensed vibrations to signal processing means which filters out low frequency components and processes, high frequency components by any of a number of standard methods such as, for example, total power, peak values, averaging or Kurtosis, to detect and analyse high frequency vibration pulses emitted due to surface contact at the interface, and to generate a go/no go signal which may provide a visual and/or audible warning.

Referring to Figure 3, a condition monitoring system 30 in accordance with one embodiment of the invention comprises a pair of accelerometers 31, 32 sensing vibrations emitted by a gear wheel 33 meshing with a gear wheel 34 at an interface 35. Whilst in this embodiment the accelerometers are mounted on the gear wheel 33 in a non-illustrated embodiment they are mounted on a rotating component connected with the gear wheel, such as, for example, a drive shaft (not shown). Signals output by the accelerometers 31, 32 are passed to an amplifier 36 where they are merged and a resultant signal is fed to low frequency filter means 37.The low frequency filter means 37 filters out the low frequency components of the signal, e.g. frequencies below 20 kHz, and allows the high frequency components to pass to signal enhancement means 38, which may comprise an envelope diode, for enhancement of the high frequency components. The enhanced high frequency components are then passed to signal processing means 39 which may use any of the standard techniques mentioned above to analyse the high frequency components and to generate a signal which is output to a go/no go indicator 40.

In this embodiment the enhanced high frequency components are passed also to an analogue to digital converter 41 and digital signals are input to pattern recognition means 42. The pattern recognition means processes the digital signals to obtain timing and magnitude patterns for high frequency vibration pulses which patterns are compared with tooth contact timing.

The amplitude and frequency of the high frequency vibration pulses is used to generate a warning and the pattern of timing and magnitude of the pulses is compared with tooth contact timing to determine the cause of the occurrence of the high frequency vibration pulses, such as loss of oil, breakdown of the oil film, and presence of debris particles at the interface.

It should be appreciated that the system hereinbefore described with reference to Figure 3 is by way of example only and that certain of the processing functions may be integrated. Thus, for example, the low frequency filtering and enhancement of the high frequency components of the signal may be integrated in a single circuit rather than being performed by separate circuits.

In a non-illustrated embodiment of the invention the sensor means comprise accelerometers having high natural frequency. These accelerometers are coupled with amplifiers which give an output proportional to the third differential of displacement to detect high frequency vibration pulses generated by metallic contact at the interface of the components. In this embodiment the low frequency filter means is not required.

In another non-illustrated embodiment of the invention the enhanced high frequency components of the signal are fed only to the signal processing means 39, the analogue to digital converter 41 and pattern recognition means 42 being omitted from the system.

Claims (12)

1. A method of monitoring conditions at interfaces of components in rolling and/or sliding contact, comprising the steps of: a. sensing vibrations emitted by the components; b. outputting a signal representative of the sensed vibrations; c. processing high frequency components of the signal to detect vibration pulses emitted due to contact at the interface; and d. generating a warning signal if processed parameters of the high frequency components exceed acceptable limits.

2. A method as claimed in Claim 1, wherein step c. comprises processing signal frequency components in the range 20kHz to 200kHz.

3. A system for monitoring conditions at interfaces of components in rolling and/or sliding contact, comprising sensor means for sensing vibrations emitted by the components and for outputting a signal representative of the sensed vibrations, processing means adapted for processing high frequency components of the signal to detect vibration pulses emitted due to contact at the interface of the components and means for generating a warning signal if processed parameters of the high frequency components exceed acceptable limits.

4. A system as claimed in Claim 3, wherein the processing means is adapted for processing signal frequency components in the range 20kHz to 200kHz.

5. A system as claimed in Claim 3 or Claim 4, wherein the sensor means are mounted on one or more of the moving components.

6. A system as claimed in Claim 3 or Claim 4, wherein the sensor means are mounted on a stationary component associated with the moving components.

7. A system as claimed in Claim 5 or Claim 6, wherein the sensor means comprise one or more accelerometers.

8. A system as claimed in any one of Claims 4 to 7, wherein signals output by the high frequency signal processing means are fed to an analogue to digital converter and digital signals are input to pattern recognition means which enable the cause of the high frequency pulses to be determined.

9. A system as claimed in Claim 4, wherein the sensing means comprise accelerometers having high natural frequency, the accelerometers being coupled with amplifiers which give an output proportional to the third differential of displacement.

10. A helicopter gearbox having a health monitoring system comprising a system in accordance with any one of Claims 4 to 9.

11. A condition monitoring system substantially as hereinbefore described with reference to and as shown in Figure 3 of the accompanying drawings.

12. Any new or improved features, combinations and arrangements described, shown and mentioned or any of them together or separately.