Measuring and testing – By abrasion – milling – rubbing – or scuffing
Reexamination Certificate
2003-02-06
2004-11-09
Garber, Charles D. (Department: 2856)
Measuring and testing
By abrasion, milling, rubbing, or scuffing
Reexamination Certificate
active
06813926
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to the determination of wear of a surface of a body and in particular relates to wear of a rubbing or frictional engagement surface of a friction couple such as a brake or clutch for a vehicle or like machine.
A friction couple is defined, for the purpose of this specification, as comprising a rubbing member having a rubbing surface and a friction material member capable of coupled motion relative to the rubbing surface when pressed into frictional engagement therewith substantially normally to the direction of said coupled motion such that a frictional engagement region extends along, and transversely to, said coupled motion direction.
An arrangement for measuring wear in a rubbing surface of a friction couple is described in WO9/17072 and the contents thereof are incorporated herein by reference. However, to facilitate a clearer understanding of the invention with regard to the friction coupling and rubbing surface, FIGS.
1
(
a
) and
1
(
b
) of that application are reproduced here as FIGS.
1
(
a
) and
1
(
b
) respectively. Referring to FIGS.
1
(
a
) and
1
(
b
) a wheel
10
for a rail vehicle comprises an axle
11
that defines a rotation axis
12
and a rim
13
spaced therefrom by radially extending spokes
14
. The spokes are faced, on at least one axial facing side thereof, by a flat annular brake disc
15
of cast iron or steel having surface
16
against which brake pads
17
of friction material can be pressed by respective pivoted levers
18
to effect braking in conventional manner. The brake disc and pads comprise a friction couple of which the disc
15
is a rubbing member, having rubbing surface
16
, and each pad
17
comprises a friction material capable of coupled motion relative to the rubbing surface, by virtue of rotational motion of the latter, when pressed into frictional engagement substantially normally to the direction of coupled motion, defining a frictional engagement region
19
of the rubbing surface which extends along, and transversely to, the coupled motion direction, that is, the swept area of the brake disc. The frictional engagement region may extend for the full radial width of the disc or less than the full width, as indicated by margins
19
′.
It will be appreciated that in operation and as a result of successive braking operations on the vehicle, the components of the friction couple will wear. The rubbing surface of the disc, within the frictional engagement region
19
will normally wear to a much lesser extent than the friction material of the pads and any wear that does occur will normally be uniform in the direction of the coupled motion, that is, in the circumferential direction along the frictional engagement region, but may vary across the regions in a direction inclined to the coupled motion direction due to variations in the properties of, and/or braking forces exerted on, the pads of friction material.
From FIG.
1
(
b
) it will be seen that insofar as wear is substantially uniform in the circumferential direction of coupled motion, then wear across the rubbing surface may be measured at any inclination to the coupled motion direction and not just transversely thereto (radially). It will be appreciated that if the surface wear is mapped in a truly radial direction then it will be of little consequence if successive measurements are made at different circumferential positions, for example radial paths
20
and
21
, whereas if an initial mapping measurement is made along a chord
22
defined between arbitrary points x—x then subsequent measurements will need to be made along the same chord or sufficiently closely thereto to be correlated with the first measurement.
It will be seen from FIG.
1
(
a
) that in a typical situation in which rubbing surface wear is to be measured, the rubbing surface is not only vertically orientated but also there is limited access for placing, as well as aligning, any measuring arrangement.
There is described in the aforementioned publication an arrangement particularly suited for measuring wear in such a rubbing surface of a railway vehicle disc brake, the arrangement including a transducer having a probe, a transducer carrier member to support it such that the probe interfaces with the rubbing surface and to scan the probe across the rubbing surface
16
along a track, such as that
22
, and non-wearing lands defined in the margins
19
′ beyond the frictional engagement region, and releasable attachment means to permit the carrier member to be positioned periodically with respect to the same part of the rubbing surface to monitor long term wear by way of the scanned transducer probe. The margin lands, which may be referred to as datum lands, define a datum plane relative to which the frictional engagement region of the rubbing surface wears. The transducer carrier is supported on such lands and scanning means define a temporary scan plane offset from the datum plane so that the transducer signals derived from scanning the lands and the frictional engagement region between the lands, representing distance of the probe-surface interface from the temporary scan plane, can be referred to the datum plane of the unworn rubbing surface.
Because of the nature of the rubbing surface, and in practice the difficulty of unimpeded access to it, the described arrangement includes an alignment template fordisposition against the rubbing surface, initially to create a pair of location recesses in rubbing surface margins outside the frictional engagement region by which the template can be re-positioned on subsequent occasions, and to define by said positioning and re-positioning a scan track against which the arrangement carder can be positioned prior to removal of the template, leaving the transducer probe to scan along the track between limits of scan denoted by the recesses.
Such an arrangement is found to work satisfactorily where there is sufficient access for both alignmenttemplate and carrier member in side-by-side relationship and where a frictional engagement region of the rubbing area is contained between surface margins that define a datum plane in which said location recesses are effected and scan track defined. That is, in operation of the above described arrangement, each scan of the transducer probe encompasses a non-wearing surface land adjacent each location recess which land acts to define a reference or datum plane when the wearing frictional engagement region is scanned.
Thus notwithstanding any difficulty in repositioning the carrier member accurately, the ability to position it against such non-wearing margins of a rubbing surface and to refer transducer probe measurements to such a non-wearing datum permits signals derived at different times to be correlated and a wear pattern established.
However, there are situations when it is difficult to obtain repeatability of positioning and correlation of measurements, such as when the frictional engagement region extends for the full width of the surface and there are no non-wearing regions and for access is restricted. Even if the transducer carrier can be positioned such that the transducer probe scans along the same track, the transducer signals, which relate the instantaneous surface position to the temporary scan plane defined by attaching the transducercarrierto that surface, become less easy to correlate with those for other attachments of the carrier.
Also, when access to the rubbing surface is limited, the ability to separately attach both an alignment template and the carrier member relative thereto may be impaired. There is difficulty in ensuring that the transducer carrier and/or alignment template is re-positioned accurately if the surface wears unevenly, notwithstanding the inherent tolerances to positioning accuracy associated with the components and operating situation.
BRIEF SUMMARY OF THE INVENTION
It is an object of the present invention to provide a method of determining wear of a rubbing surface of a friction couple of the type hereinbefore defined that is le
Cotterill Ronald Ian
Dunning Kenneth
Lomas David Michael
Federal-Mogul Friction Products Limited
Garber Charles D.
Reising Ethington Barnes Kisselle P.C.
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