Brakes – Wheel – Axially movable brake element or housing therefor
Patent
1998-07-30
2000-11-07
Schwartz, Christopher P.
Brakes
Wheel
Axially movable brake element or housing therefor
188250B, 188250E, F16D 6538
Patent
active
061422630
DESCRIPTION:
BRIEF SUMMARY
This invention relates to brake elements particularly useful for railway braking applications.
It is known from PCT/GB94/01964 (WO95/07418) that modern high speed train systems routinely impose extremely severe loading on the brake pads, especially on disk brake pads. This is due to the substantial amounts of energy which have to be dissipated every time the brakes are applied, resulting in the attainment of extremely high working temperatures, typically well in excess of 1000.degree. C. WO95/07418 discloses a friction pad composition suitable for this type of heavy duty braking service.
It is also known from PCT/GB92/02055 (WO93/10370) to interpose a layer of a relatively soft elastomeric material between a layer of friction material and a backing plate in order to confer a degree of resilience onto the assembly, thereby enabling the working face of the friction lining to conform more uniformly to the confronting surface of the moving element of the system which is to be braked. The elastomer material should exhibit a Rockwell hardness value below that of the friction lining in order to ensure satisfactory conformability.
In relatively moderate braking applications the technique disclosed in WO93/10370 has proved valuable in considerably extending brake element working life.
Unfortunately, attempts to apply the concept of WO/93/10370 to severe duty braking applications of the kind addressed by WO95/07418 have not proved successful, due to the extremely high temperatures developed in use.
According to the present invention a brake element comprising a friction material lining and a backing plate, together with a relatively soft layer of elastomeric material being interposed between said friction material lining and said backing plate, is characterised in that a further layer of elastomeric material of relatively low thermal conductivity and relatively high resistance to thermal degradation is interposed between the friction material lining and the relatively soft layer of elastomeric material. The further layer is preferably semi-conformable relative to the soft underlayer. That is to say it is more conformable than the friction layer, but less conformable than the underlayer.
It has bee n found that the incorporation of the further elastomeric material layer with relatively poor thermal conductivity allied to high resistance to thermal degradation makes it possible to utilise the technique of WO93/10370 to very considerably enhance the useful service life of severe duty disk brake pads of the kind disclosed in WO95/07418. In a typical case the service life may be extended from an unacceptable 1.5 months to as much as 10 or 11 months before replacement is necessary. The further layer apparently serves to protect the soft elastomeric material layer from the heat generated in the top layer of friction material.
The further layer is preferably formulated to have a thermal conductivity on t he order of only 8-12% of that of the friction layer. Th is will normally be greater than that of the relatively soft elastomeric material layer. All three layers are preferably formulated so as to avoid or at least minimise interface shear stresses due to thermal expansion developed in response to the temperatures attained in braking service. This may be done by appropriate choice of materials such as fillers and/or metallic ingredients for the two elastomeric material layers. For practical purposes it has proved sufficient to formulate the elastomer material layers for a thermal expansion of the order of 0.01 mm to 0.05 mm, over a temperature range of, say, ambient to 200.degree. C. and determined in accordance with the test method described below, using a sample length of 8 mm.
Advantageously, the longitudinal and/or transverse grooving of WO95/07418 is employed, but with the grooves extending through both the friction material layer and through the further elastomeric material layer to the interface between the latter and the relatively soft elastomeric material layer. This has been found to enhance the conformability o
REFERENCES:
patent: 4373615 (1983-02-01), Melinat
patent: 5099962 (1992-03-01), Furusu et al.
patent: 5407034 (1995-04-01), Vydra et al.
Ferodo Limited
Schwartz Christopher P.
Siconolfi Robert A.
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