U.S. patent application number 09/553404 was filed with the patent office on 2002-06-06 for monitoring of bearing performance.
Invention is credited to Care, Ian C.D..
Application Number | 20020066306 09/553404 |
Document ID | / |
Family ID | 10854103 |
Filed Date | 2002-06-06 |
United States Patent
Application |
20020066306 |
Kind Code |
A1 |
Care, Ian C.D. |
June 6, 2002 |
MONITORING OF BEARING PERFORMANCE
Abstract
A method and apparatus for anticipating the onset of or
measurement of a deleterious condition in a bearing comprising
monitoring the bearing for electrostatic activity indicative of the
onset of the condition using one or more electrostatic sensors,
processing signals derived from the sensors and employing same to
activate alarm means, alter bearing loading to reduce or eliminate
the source condition or shut down the equipment to prevent further
bearing damage.
Inventors: |
Care, Ian C.D.; (Derby,
GB) |
Correspondence
Address: |
MANELLI DENISON & SELTER
2000 M STREET NW SUITE 700
WASHINGTON
DC
20036-3307
US
|
Family ID: |
10854103 |
Appl. No.: |
09/553404 |
Filed: |
April 20, 2000 |
Current U.S.
Class: |
73/86 |
Current CPC
Class: |
G01M 13/04 20130101 |
Class at
Publication: |
73/86 |
International
Class: |
G01N 003/62 |
Foreign Application Data
Date |
Code |
Application Number |
May 25, 1999 |
GB |
9912112.1 |
Claims
I claim:
1. A method of anticipating the onset of a deleterious condition in
a mechanical rolling element bearing comprising monitoring the
bearing for electrostatic activity indicative of the onset of
distress of the bearing or its components.
2. A method according to claim 1 including generation of an output
signal responsive to detection of said electrostatic activity.
3. A method according to claim 2 wherein said output signal is
employed to generate a visual warning of the onset of said
condition.
4. A method according to claim 2 wherein said output signal is
employed to generate an audible warning of the onset of said
condition.
5. A method according to claim 2 wherein said signal is employed to
rectify a condition giving rise to stressing or slippage of the
bearing.
6. A method according to claim 5 wherein said output signal is
employed to alter the bearing loading to remove the source of the
deleterious condition.
7. A method according to claim 2 wherein said output signal is
employed to terminate operation of equipment of which the bearing
forms a part to prevent further bearing damage.
8. A method according to claim 2 wherein said output signal is
stored and employed to provide a continuous record of bearing
performance over time.
9. A method according to claim 2 wherein said output signal is
superimposed on a signal generated by the electrostatic charge in
the bearing under static conditions.
10. A method according to claim 2 wherein said output signal
represents the charge in electrostatic activity generated by said
distress alone.
11. A method according to claim 2 in which each rolling element of
the bearing is detected and said output signal related to the
rolling element or elements giving rise to said electrostatic
activity.
12. Apparatus for anticipating the onset of a deleterious condition
in a bearing comprising means for sensing electrostatic activity in
the bearing generated in response to the onset of distress of the
bearing or its components.
13. Apparatus according to claim 12 wherein said means for
measuring electrostatic activity comprises an electrostatic sensor
adapted to be mounted within sensing proximity range of and
external to the bearing and operable to detect changes in
electrostatic charge on components of the bearing.
14. Apparatus according to claim 12 wherein said means for
measuring electrostatic activity comprises an electrostatic sensor
adapted to be mounted within the bearing and operable to detect
changes in electrostatic charge on components of the bearing.
15. Apparatus according to claim 12 including means for generating
a signal in response to said changes in activity and means for
processing said signal to produce an electrical output.
16. Apparatus according to claim 15 including visual alarm means
operable in response to said output to provide a warning of the
onset of said deleterious condition.
17. Apparatus according to claim 15 including audible alarm means
operable in response to said output to provide a warning of the
onset of said deleterious condition.
18. Apparatus according to claim 15 including control means
operable in response to said output to alter the loading on the
bearing.
19. Apparatus according to claim 15 including control means
operable in response to said output to interrupt operation of
equipment of which said bearing forms a part to prevent further
damage to the bearing.
20. Apparatus according to claim 15 including recording means
operable to record and store said output signals to provide a
continuous record of bearing performance over time.
21. Apparatus according to claim 20 wherein said recording means is
operable to predict remaining or used bearing life.
22. Apparatus according to claim 15 wherein said signal processing
means is adapted to produce an initial output signal proportional
to the degree of deleterious condition in the bearing.
23. Apparatus according to claim 22 wherein the output signal
derived from said electrostatic activity is superimposed on said
initial output signal.
24. Apparatus according to claim 15 wherein said output signal
represents the charge in electrostatic activity generated by said
distress alone.
25. Apparatus according to claim 15 including further sensing means
operable to detect each rolling element of the bearing as it moves
past said means for sensing electrostatic activity, whereby the
individual ball or roller element giving rise to said electrostatic
activity may be identified.
26. A gas turbine engine incorporating apparatus for anticipating
the onset of a deleterious condition in a bearing according to
claims 15.
Description
[0001] The present invention relates to a method and means for
monitoring the performance of mechanical bearings.
[0002] Mechanical bearings, such as ball or roller bearings, are
designed to operate under predetermined load conditions. When
correctly loaded bearings work well. However at loads approaching
zero, slippage can occur between components of the bearing. With
changing loads the bearing races can move out of their correct
optimum positions. Vibration and impact can also damage bearing
components. Hitherto it has been difficult to sense the onset of
slippage or other conditions giving rise to bearing damage with the
result that bearings are generally over-engineered relative to the
loading and other conditions under which they are designed to
operate.
[0003] When a mechanical rolling element bearing operates correctly
the surface rotation speed of the rolling elements of the bearing
are the same as the differential speed between the inner and outer
races. The bearing elements will appear to rotate at around half
the differential speed of the inner and outer components of the
bearing. If a bearing slips, overheating and damage can result. The
surface speed of the rolling elements will reduce and the speed of
the cage in which they are mounted will be less than the
differential speed of the inner and outer races. Detection of these
conditions therefore provides early warning of potential bearing
failure.
[0004] Hitherto sensing of slippage or other stress conditions in
such bearings has been relatively complex. Previous proposals
include the use of thermal sensors to detect overheating of the
lubricant film in which the bearing operates or have required
incorporation of radioactive tracers in the bearing components
themselves. Such systems are complex. In addition they operate by
detecting slippage and cannot detect overstressing of bearings
through other causes. Previous proposals have also included
proximity sensors operative to detect the speed of rotation of
bearing rolling elements and races.
[0005] It is an object of the present invention to provide an
improved method and apparatus for monitoring bearing
performance.
[0006] We have found that bearings subject to stress or slippage
generate a significant electrostatic charge proportional to the
degree of stress and a change of charge distribution under
slippage. Thus it is possible to sense the condition of a bearing
by sensing the resultant change and pattern of electrostatic
activity. Accordingly the invention provides a method of
anticipating the onset of a deleterious condition in a bearing
comprising monitoring the bearing for electrostatic activity
indicative of the onset of distress of the bearing or its
components.
[0007] Preferably the method includes generation of an output
signal responsive to detection of said change in electrostatic
activity. Said output signal may be employed to actuate indicator
or alarm means providing a visual and/or audible warning of the
onset of the said condition. Alternatively or in addition said
signal may be employed to rectify a condition giving rise to
stressing or slippage of the bearing. Thus the output signal may be
employed to alter the bearing loading to remove the source of the
deleterious condition. Alternatively said output signal may be
employed to terminate operation of equipment of which the bearing
forms a part to prevent further bearing damage, or to limit the
`life` or further running of the bearing to prevent failure.
[0008] The invention also provides apparatus for anticipating the
onset of a deleterious condition in a bearing comprising means for
sensing electrostatic activity in the bearing generated in response
to the onset of distress of the bearing or its components.
[0009] Preferably said means for measuring electrostatic activity
comprises an electrostatic sensor adapted to be mounted within
sensing proximity range outwith the bearing or within the bearing
structure and operable to detect changes in electrostatic charge on
components of the bearing.
[0010] Preferably also the apparatus includes means for generating
a signal in response to said changes in activity and means for
processing said signal to produce an electrical output.
[0011] The apparatus may also optionally include means for
detecting individual bearing elements and for processing of
signal(s) derived therefrom.
[0012] The apparatus may include visual or audible alarm means
operable in response to said output to provide a warning of the
onset of said deleterious condition. Alternatively or in addition
the apparatus may include means operable in response to said output
to alter the loading on the bearing to reduce or eliminate said
condition. The apparatus may alternatively include means operable
in response to said output to interrupt operation of equipment of
which said bearing forms a part to prevent further damage to the
bearing.
[0013] The output signal may be recorded or stored to show events
in the bearing life/performance as part of an engine/shaft/bearing
health management system. In this way a continuous record of
bearing performance over time may be produced and may be employed
to predict remaining or used bearing life.
[0014] An embodiment of the invention will now be described, by way
of example only, with reference to the accompanying drawings, in
which:
[0015] FIG. 1 is a diagrammatic cross-section through part of a gas
turbine engine incorporating means for monitoring bearing
performance according to the invention;
[0016] FIG. 2a is a diagram of the signal produced by a bearing
under normal operating conditions; and
[0017] FIG. 2b is a similar diagram showing the signal produced
from a bearing undergoing or about to undergo slip.
[0018] Referring to FIG. 1, there is shown the rear bearing
compartment of a gas turbine aircraft engine incorporating a
compartment housing cap 5 within which a hollow compressor shaft 6
is supported at its rear end in a mechanical rolling element
bearing 7 mounted in the cap structure 5. The bearing 7 comprises a
plurality of rolling elements 7a in the form of balls or rollers
retained between inner and outer races 7b and 7c. Lubricating oil
is supplied to the bearing through oil inlet and outlet pipes 8 and
9 housed within fixed support members 10 by means of which the cap
structure 5 is mounted within a surrounding plug assembly (not
shown). The components of the bearing may be metallic, non-metallic
or a combination of metallic and non-metallic components.
[0019] An electrostatic sensor 12 is mounted in a fixed position
adjacent the bearing 7 and is connected in an electrical circuit 13
with a processor 14 operable to generate a signal in response to
changes in electrostatic charge sensed by the sensor 12. Any
suitable form of electrostatic sensor may be employed, for example,
sensors of the type disclosed in International Patent Specification
No. WO92/02886 or U.K. Patent Specification No. 2302593.
[0020] Under static conditions the sensor measures ball or roller
distress which bears a relationship to contact load. If the bearing
7 is subjected to overload or slippage resulting in changes of
relatively speed and/or direction of movement of the rolling
elements of the bearing in relation to the bearing races in which
they run, a measurable change of electrostatic charge is generated
in the components of the bearing and sensed by the sensor 12. This
change in electrostatic charge arises as stress or slippage
conditions are approached and the sensor 12 thus generates a signal
indicative of the onset of such a condition. The signal is
transmitted to the processor 14 which generates an output which may
be used to perform any of a number of functions.
[0021] FIGS. 2a, 2b are illustrative of the signal produced from a
bearing under normal and stressed conditions respectively. The
signal generated under normal operation is of generally sinusoidal
form. Under stress a narrow and increased positive peak is
generated as shown in FIG. 2b, the amplitude of which is
proportional to the degree of stress in the bearing. During initial
setting up, the sensor may be adjusted to measure the electrostatic
charge under static conditions (and hence the initial level of ball
or roller distress) on to which the variable change is then
superimposed. Alternatively the sensor may be adjusted to zero
reading under static conditions so as to measure only the variable
electrostatic charge generated under operating conditions.
[0022] In one arrangement the output from the processor 14 may be
employed to energise an audible or visual warning device 15 to warn
of the onset of the adverse condition in the bearing.
Alternatively, or in addition the processor 14 may be connected to
a control unit 16 operable to alter the operating conditions of the
engine in a manner to remove the source of the stress or slippage
as disclosed for example in our co-pending United Kingdom Patent
Application No. 9912108.9. In such cases restoration of
satisfactory loading conditions will restore charge levels being
detected by the sensor 12 and processor 14 to normal and thereby
remove the corrective action once optimum operating conditions have
been restored. In this way the sensor 12 forms part of a continuous
monitoring and control system serving to sense the onset of
slippage or overstressing of the bearing and operable to reduce or
eliminate the source condition and thereby minimise wear or damage
of the bearing and increase bearing life.
[0023] By virtue of the use of an electrostatic sensor positioned
in close proximity to the bearing to be monitored, the method and
apparatus are non-invasive and less complex than techniques
proposed hitherto. Moreover by sensing changes in electrostatic
charge generated within the bearing components as a result of the
onset of a deleterious condition, the arrangement described is
effective not only to sense the onset of slippage, but also other
stress conditions within the bearing not hitherto detectable by
previously proposed techniques. The output signal from the
processor 14 may be recorded and stored in a recording device 17 to
show events in the bearing life/performance as part of an
engine/shaft/bearing health management system. In this way a
continuous record of bearing performance over time may be produced
and may be employed to predict remaining or used bearing life.
[0024] Various modifications may be made without departing from the
invention. For example while the invention has been described by
reference to a shaft bearing in a gas turbine engine, it may be
employed in any situation where mechanical bearings are employed in
order to continuously monitor bearing performance and provide early
warning of stress or slippage and, where appropriate, initiate
corrective action to reduce or eliminate the source of the problem.
In some cases the signal generated by the sensor or processor may
be employed through a control unit such as the unit 16 to shut down
equipment of which the bearing forms a part in order to prevent
further or accelerated damage. It will be appreciated also that in
the case of gas turbine engines a similar sensing system may be
employed in association with any or all of the bearings on which
the various shafts incorporated in such engines are rotatably
mounted.
[0025] In a further modification an additional sensor 20 may be
located adjacent to the bearing to detect the presence of each
rolling element as it moves past the sensor. By correlating signals
from both sensors, the individual ball, roller or like bearing
element giving rise to a stress or slippage signal may be
identified.
[0026] Whilst endeavouring in the foregoing specification to draw
attention to those features of the invention believed to be of
particular importance it should be understood that the Applicant
claims protection in respect of any patentable feature or
combination of features hereinbefore referred to and/or shown in
the drawings whether or not particular emphasis has been placed
thereon.
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