Brakes – Elements – Shoes
Patent
1996-03-06
1998-03-10
Schwartz, Chris
Brakes
Elements
Shoes
188250B, F16D 6900
Patent
active
057250774
DESCRIPTION:
BRIEF SUMMARY
The present invention relates to a friction pad for use in a brake assembly.
In particular the present invention relates to a friction pad for use in a very high performance disc brake system wherein a large mass is required to be stopped on a large number of occasions from a relatively high speed, for example, a high speed passenger train.
BACKGROUND OF THE INVENTION
Generally high performance brake systems, particular railway brakes, fall into two basic categories. One category covers high speed installations with a low braked mass and relatively infrequent applications. The French TGV system falls into this category, general parameters being a speed of 300 Km/hr and a mass to be braked of 4000 Kgs. The required braking time is about 78 seconds with a peak braking power of 730 Kw/m.sup.2, for the disc and 6 Mw/m.sup.2 for the pad, the total energy absorbed being 14 mega Joules. The other category covers low speed installations with a high braked mass and frequent applications. Light rail and trams fall into this category, general parameters being a speed of 80 Km/hr and a braked mass of 9000 Kgs. The peak braking power is 770 Kw/m.sup.2 for the disc and 3-5 Mw/m.sup.2 for the pad, the total energy absorbed being 2.3 mega Joules. A typical stopping time for this category is about 23 seconds.
Friction pads for use in disc brakes generally take the form of a substantially planar backing plate to which a pad of friction material is secured. In operation, the pad is urged against the brake disc causing frictional engagement, the effect of which increases with the applied braking pressure. As a result, the friction material and the disc are subjected to heating. Where the frictional engagement is high and the relative rotational speed of the disc over the pad is also high, there is the possibility that the pad material will be prematurely worn away. Damage such as stress cracking due to the sequential heating and cooling of the braking disc may occur, especially where hot spots occur due to physical/chemical unstable interaction at the interface between the friction pad and braking disc, this being dependent upon the disc, pad and installation design. An additional factor is the rate of wear of the brake disc itself. Attempts to re-formulate the friction material to reduce the rate of wear of the pad often have the effect of greatly increasing the rate of wear of the brake disc. This is particularly the case where the formulation includes increased levels of abrasive material intended to increase pad life. Accordingly, to dissipate the heat generated over a larger area of the brake disc and to thus reduce the likelihood of hot spots and attendant stress cracking, it has been proposed to utilize a brake disc with a ceramic surface, one such brake disc being disclosed in published PCT Patent Specification WO92/08909.
It is also known from DE-11-9114265 to employ barytes and magnesium oxide in powder form, together with up to 40 wt % of iron as ingredients of a non-asbestos friction material formulation.
Whilst a braking disc having a ceramic surface of this kind increases the performance of the brake disc as compared to conventional steel and/or sintered brake discs, as regards thermo-mechanical fatigue cracking defects, and whilst known friction pads can be used therewith, such known friction pads tend to prematurely wear away and do not provide the desired performance due to increased temperatures at the interface between the friction pad and the ceramic surface of the disc, as compared to the interface temperature between such a friction pad and a plain steel or an aluminium metal matrix composite disc.
It is a particular object of the present invention to provide a friction pad for use in a disc brake assembly wherein the brake disc has a ceramic material braking surface, the friction pad providing improved performance in respect of pad life and frictional grip on the ceramic surface brake disc.
DESCRIPTION OF THE INVENTION
According to the present invention a friction pad for use in a brake assembly c
REFERENCES:
patent: 3434998 (1969-03-01), Alduch et al.
patent: 3891595 (1975-06-01), Birchall
patent: 3896075 (1975-07-01), Longley
patent: 4438004 (1984-03-01), Myers
patent: 4461643 (1984-07-01), Kaufman
patent: 4465796 (1984-08-01), Leroy et al.
patent: 4735975 (1988-04-01), Iwata et al.
patent: 5122550 (1992-06-01), Schmitt
patent: 5145888 (1992-09-01), Gong et al.
Hubbard David A.
Lotfipour Mahmoud
Taylor Alfred J.
Taylor Susan K.
Ferodo Limited
Sab Wabco (Bromborough) Limited
Schwartz Chris
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