GB1601703A - Measurement of the quality of bearing surfaces - Google Patents

Description

(54) MEASUREMENT OF THE QUALITY OF BEARING SURFACES (71) We, NATIONAL RESEARCH DEVELOP MENT CORPORATION of Kingsgate House, 66-74 Victoria Street, London SW1E 6SL, do hereby declare the invention for which we pray that a patent may be granted to us, and the method by which it is to be performed, to be particularly described in and by the following statement:- This invention relates to the measurement of the quality of bearing surfaces and of the thickness of their lubricating oil films.

It is known that information relating to lubricated bearing surfaces can be obtained by applying a small electrical potential between them and taking measurements of the changes in electrical resistance when the bearings are in rolling or sliding contact.

The electrical resistance fluctuates rapidly as though due to repeatedly making and breaking of physical contact. Two quantities can be measured, these are the number of contacts per unit time, (hereinafter denoted by C) and the fraction of time during which contact is held (hereinafter denoted by y).

The above quantities do not themselves give a direct indication of the quality of the bearing surfaces and quantities which are more relevant are the actual count rate of individual contacts taking into account contacts which overlap in time, the average number of simultaneous contact points and the average duration of an individual contact.

According to the invention apparatus for measuring the quality of bearing surfaces comprises means for providing an electrical supply between two surfaces which bear on each other, means for determining when the contact resistance between such surfaces is high or low, means for deriving the quantities C' and y (both as hereinbefore defined) from such determination, and means for calculating one or more of the quantities C, M and T defined as follows: C = C/(1 M = 7(1-7) T = e/C' Preferably the said determining means includes a hysteresial comparator which provides a high output only when the input thereto has risen above a preset level and which provides a low output only when the input thereto has fallen below a further preset level which is lower than the aforesaid preset level.

Preferably means are provided for indicating the calculated quantities.

It can be shown that the quantity C as calculated above is the actual count rate and that provided there is at least a minimum proportion of sliding contact M and T are the average number of simultaneous contact points and the average duration of an individual contact respectively.

Means may also be provided for calculating the quantities Mr = - ln(lr) Tr= - MrlC together with means for indicating these quantities.

Where the contact is purely a rolling contact and does not include any proportion of sliding contact then the quantities Mr and Tr are the average number of simultaneous contact points and the average duration of an individual contact.

In order that the invention may be more fully understood reference will now be made to the accompanying drawing in which: Figure 1 illustrates a bearing being measured, and Figure 2 illustrates in block diagrammatic form an embodiment of the invention.

Referring now to Figure 1 there is shown therein a bearing comprising a housing 1 supporting a rotatable shaft 2. Lubricating oil is supplied between the shaft and its housing. In order to monitor the bearing an electrical- contact 3 bears on a slip ring on shaft 2 and an electrical potential is supplied to contact 3 from a potential divider comprising resistors Rl and R2 which are connected across a battery 4. One terminal of battery 4 is earthed, as Is housing l. As shaft 2 rotates electrical continuity between the shaft and its housing is continually broken and remade and this will âppear at a terminal 5 connected to contact 3 as a continuous fluctuation between earth potential and the potential of the junction be tween R1 and R2. This fluctuation can be used to give an indication of the quality of the bearing.

Apparatus for processing the signal obtained is shown in Figure 2. The input terminal of the apparatus is connected to terminal 5 and the input signal is fed firstly to a hysteresial comparator 6 to improve the quality of the signal. Comparator 6 operates to be switched on only when the input signal has risen above a predetermined level and remains on until the input signal has fallen below a sceond predetermined level which is lower than the first level. The two switching levels of comparator 6 can be independently adjusted. The pulses emitted from comparator 6 are fed in parallel to a counter 7 and to a coincident gate 8 which is also fed from a high frequency oscillator 9 of say 10 MHz. The output from coincident detector 8 is fed to a second counter 10.

Over a preset time period counter 7 gives the count rate C' at which contact is made and broken while counter 10 gives a count which represents the time integral of the input signal and hence the fraction of time during which contact is absent. From this figure the fraction of time y during which contact is held can be readily derived.

Periodically the two counts C' and 7 are loaded into an arithmetic unit 11 which is set to carry out the following calculations on the input data: C = C'/(1-7) M = 7/(1-7) T = 7/C' Mr = - ln(1 -7) Tr = Mr/C The transfer of the counts to arithmetic unit 11 is controlled by a program counter 13. A display 12 is provided for sequentially displaying the quantities C, M and T or alternatively the quantities C, Mr and Tr.

The sequential display is also controlled by counter 13. Alternatively or in addition a print-out can be provided.

The quantity M or Mr can be simply related to the thickness of the oil lubrication film and the roughness of the lubricated surfaces. In sliding contacts where the oil film is essentially of constant thickness, T is related to the surface roughness and means asperity curvature of the contacting elements.

A term named the wear coefficient has been defined as the probability of an asperity-asperity collision producing a wear particle. Thus the quantity C, which is the actual count or collision rate, taking into account contacts which overlap in time, is important in the study or monitoring of wear.

The results obtained from the apparatus of Figure 2 thus have application as follows: (1) to provide a quantitative measure of oil film thickness or surface roughness changes in lubricated contacts. (2) to provide information relating to changes in mean surface roughness and asperity radius in sliding contacts where the oil fiIm is of constant thickness.

(3) to provide an estimate of the number of individual asperity-asperity collisions for wear monitoring.

WHAT WE CLAIM IS: 1. Apparatus for measuring the quality of bearing surfaces comprising means for providing an electrical supply between two surfaces which bear on each other, means for determining when the contact resistance between such surfaces is high or low, means for deriving the quantities C' and y (both as hereinbefore defined) from such determination, and means for calculating one or more of the quantities C. M and T defined as follows: C = Ct/(1y) M = 7(1-7) T = 7/C' 2. Apparatus as claimed in claim 1 in which the said determining means includes a hysteresial comparator which provides a high output only when the input thereto has risen above a preset level and which provides a low output only when the input thereto has fallen below a further preset level which is lower than the aforesaid preset level.

3. The apparatus as claimed in either one of the preceding claims in which means are provided for indicating the calculated quantities.

4. The apparatus as claimed in any one of the preceding claims in which means are provided for calculating the quantities Mr = -ln(l-) Tr = -Mr/C together with means for indicating these quantities.

5. Apparatus for measuring the quality of bearing surfaces substantially as described herein with reference to the accompanying drawing.

**WARNING** end of DESC field may overlap start of CLMS **.

Claims (5)

**WARNING** start of CLMS field may overlap end of DESC **. tween R1 and R2. This fluctuation can be used to give an indication of the quality of the bearing. Apparatus for processing the signal obtained is shown in Figure 2. The input terminal of the apparatus is connected to terminal 5 and the input signal is fed firstly to a hysteresial comparator 6 to improve the quality of the signal. Comparator 6 operates to be switched on only when the input signal has risen above a predetermined level and remains on until the input signal has fallen below a sceond predetermined level which is lower than the first level. The two switching levels of comparator 6 can be independently adjusted. The pulses emitted from comparator 6 are fed in parallel to a counter 7 and to a coincident gate 8 which is also fed from a high frequency oscillator 9 of say 10 MHz. The output from coincident detector 8 is fed to a second counter 10. Over a preset time period counter 7 gives the count rate C' at which contact is made and broken while counter 10 gives a count which represents the time integral of the input signal and hence the fraction of time during which contact is absent. From this figure the fraction of time y during which contact is held can be readily derived. Periodically the two counts C' and 7 are loaded into an arithmetic unit 11 which is set to carry out the following calculations on the input data: C = C'/(1-7) M = 7/(1-7) T = 7/C' Mr = - ln(1 -7) Tr = Mr/C The transfer of the counts to arithmetic unit 11 is controlled by a program counter 13. A display 12 is provided for sequentially displaying the quantities C, M and T or alternatively the quantities C, Mr and Tr. The sequential display is also controlled by counter 13. Alternatively or in addition a print-out can be provided. The quantity M or Mr can be simply related to the thickness of the oil lubrication film and the roughness of the lubricated surfaces. In sliding contacts where the oil film is essentially of constant thickness, T is related to the surface roughness and means asperity curvature of the contacting elements. A term named the wear coefficient has been defined as the probability of an asperity-asperity collision producing a wear particle. Thus the quantity C, which is the actual count or collision rate, taking into account contacts which overlap in time, is important in the study or monitoring of wear. The results obtained from the apparatus of Figure 2 thus have application as follows: (1) to provide a quantitative measure of oil film thickness or surface roughness changes in lubricated contacts. (2) to provide information relating to changes in mean surface roughness and asperity radius in sliding contacts where the oil fiIm is of constant thickness. (3) to provide an estimate of the number of individual asperity-asperity collisions for wear monitoring. WHAT WE CLAIM IS:

1. Apparatus for measuring the quality of bearing surfaces comprising means for providing an electrical supply between two surfaces which bear on each other, means for determining when the contact resistance between such surfaces is high or low, means for deriving the quantities C' and y (both as hereinbefore defined) from such determination, and means for calculating one or more of the quantities C. M and T defined as follows: C = Ct/(1y) M = 7(1-7) T = 7/C'

2. Apparatus as claimed in claim 1 in which the said determining means includes a hysteresial comparator which provides a high output only when the input thereto has risen above a preset level and which provides a low output only when the input thereto has fallen below a further preset level which is lower than the aforesaid preset level.

3. The apparatus as claimed in either one of the preceding claims in which means are provided for indicating the calculated quantities.

4. The apparatus as claimed in any one of the preceding claims in which means are provided for calculating the quantities Mr = -ln(l-) Tr = -Mr/C together with means for indicating these quantities.

5. Apparatus for measuring the quality of bearing surfaces substantially as described herein with reference to the accompanying drawing.