Measuring and testing – Frictional resistance – coefficient or characteristics
Reexamination Certificate
2000-07-17
2001-12-18
Williams, Hezron (Department: 2856)
Measuring and testing
Frictional resistance, coefficient or characteristics
C073S007000, C073S121000
Reexamination Certificate
active
06330820
ABSTRACT:
This invention relates to testing apparatus for friction materials used in brakes, clutches and the like and in particular relates to the testing the functioning of such materials within friction couples, that is, when pressed into rubbing engagement with a relatively moving rubbing element.
The invention relates to providing apparatus in which simple tests may be carried out repeatedly with minimal delay in substantially unvarying conditions It furthermore relates to apparatus capable of simulating friction couple operation where low, possibly sub-zero, conditions have to be repeatable and at a rate that also permits tests to be repeated with minimal delay.
It is known to test a friction material for vehicle braking systems prior to specifying its use by subjecting a relatively small sample of the material, typically less than 4 cm
2
in surface area, to a succession of simulated braking operations, within a friction couple, that is, by repeatedly bringing it to bear, under controlled ‘braking pressure’, against a relatively moving rubbing element of the material, usually a metal such as cast iron, used in the vehicle brake itself, to simulate said brake application, the consequential retardation forces it produces and frictional heat it generates. Because of the relatively small area of rubbing contact, the relative speed, braking application (bearing) pressure and retardation forces are correspondingly scaled down, and suitable for testing apparatus us ed within a workshop or laboratory environment.
It will be appreciated that as the frictional rubbing occurs between the friction material and rubbing element, heat is generated which raises the temperature of the rubbing element. Whereas in a vehicle braking system there is usually motion and infrequent brake applications which permit the heat within the rubbing element to dissipate, conditions are not so favourable within the climate of a workshop or laboratory, where the lack of such motion and the ambient temperature may also compromise the ability to simulate braking repeatedly within a practicably short time as the heat generated in each test must be dissipated before the same starting conditions are re-established for each subsequent test with the same friction material or a different friction material for comparative testing; that is, the duration of a test program is directly related to the speed at which initial temperature or hundreds of simulated braking operations, each of which may last only a few seconds, may become impracticable to conduct within a workshop or laboratory with known testing machines.
There also exists a requirement to simulate vehicle braking operation within an operating environment significantly below the freezing point of water. Such vehicle braking thus occurs in an atmosphere that is dry, in the sense that it contains no water in vapour or liquid form. However, this is less than trivial to achieve within the aforesaid workshop or laboratory environment, because of both the relatively high ambient temperature and atmospheric moisture in such environment, and the need to reproduce identical conditions at will.
Thus in respect of testing apparatus that simulates a friction couple by creating rubbing friction in order to test friction materials, whereas the apparatus may be of relatively simple form, the generation of frictional heat creates practical difficulties in reproducing conditions for performing such simulations in a commercially practicable manner. Analogous considerations apply also to friction materials used in non-vehicular brakes and in dry-plate clutch arrangements, and having regard to the above, it is an object of the present invention to provide a friction material testing arrangement of compact and simple construction that permits practicably rapid repetition of frictional rubbing operations with a friction couple. It is furthermore an object of the present invention to provide friction material testing apparatus of compact and simple construction that is capable, within a workshop or laboratory environment, of simulating frictional rubbing with a friction couple in subzero temperatures with commercially practicable repetition.
According to the present invention apparatus for testing the frictional behaviour of dry friction material in a friction couple with a relatively moving rubbing surface against which it is pressed repeatedly comprises the apparatus (i) an element carrier arranged to support a rubbing element of thermally conductive material, having a said rubbing surface, said element carrier being movable in the plane of the rubbing surface, (ii) sample carrier for at least one sample of said friction material, disposed facing said element carrier, one of said element and sample carriers comprising a table that is rotatable within limits of constraint and the other one of said carriers being rotatable with respect to the table, (iii) carrier drive means arranged to move said other one of the carriers and the friction couple component thereon orthogonal or parallel with respect to said table and the friction couple component thereon to make and break rubbing contact between the rubbing surface and each contacting sample and characterised by (iv) measuring means operable to sense the temperature of the rubbing element and, in response to friction between the rubbing surface and friction material, to limit rotation of the table and measure the force applied to said table by way of the rubbing element, (v) control means operable to control the carrier drive means to effect frictional coupling in response to the temperature of the rubbing element being below a predetermined trigger temperature, and (vi) cooling means operable to extract heat forcibly from the rubbing element to reduce it to said predetermined trigger temperature.
The cooling means may comprise heat exchanger means in which a fluid coolant forced to pass over a thermal conductor in a thermal conduction path including the rubbing element. Preferably such heat exchange means comprises a walled container having at least one wall in thermal contact with the rubbing element, inlet and outlet ports operable to admit and remove said fluid coolant and a source of said fluid coolant arranged to deliver it to the container inlet port at a predetermined rate.
The cooling means may also include thermoelectric cooling means having at least one thermoelectric cooling element disposed between, and in thermal contact with, the heat exchanger means and rubbing element, and power supply means arranged to provide a predetermined level of current to each thermoelectric cooling element.
REFERENCES:
patent: 3360977 (1968-01-01), Herman
patent: 3852993 (1974-12-01), Bronovets et al.
patent: 4038863 (1977-08-01), Mellor et al.
patent: 5168750 (1992-12-01), Kurtz
patent: 5685193 (1997-11-01), Hurtubise et al.
patent: 5689058 (1997-11-01), Yuan
patent: 5697472 (1997-12-01), Walker et al.
Cotterill Ronald I
Davenport Alan
Dunning Kenneth
Marshall James B
Baker, Jr. Thomas S.
Federal-Mogul Friction Products Limited
Williams Hezron
Wilson Katina
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