Self-energizing disc brakes

A self-energising disc brake comprising a housing, first and second axially spaced radial surfaces in said housing, radial pilot lugs in said housing, first and second pressure plates centred on said pilot lugs, adjacent faces of said pressure plates being provided with co-operating oppositely inclined angularly spaced recesses, balls or rollers located in complementary pairs of said recesses, a rotatable friction member disposed between each said pressure plate and an adjacent radial surface, each said member comprising a disc, and first and second linings of friction material for engagement with said pressure plate and said radial surface carried by opposite faces of said disc, and means for moving said pressure plates angularly relative to said housing to initiate application of said brake with said pressure plates also moving axially to urge the friction member into engagement with said radial surface due to a tendency for said balls or rollers to ride up ramps defined by said end faces, said pressure plate thereafter being carried round with said friction member to provide a servo action, wherein said means for moving said pressure plates angularly comprises an hydraulic actuator which is located within said housing, and said actuator comprises a cylinder body which has a bore of which the axis is tangential to said plates, and is outside of the plan projection of said plates, and at least one piston for co-operation with a lug on one of said pressure plates working in said bore, the co-operation of said piston with said lug causing said pressure plate to move angularly to initiate application of said brake when hydraulic fluid under pressure is admitted to a pressure space defined in said bore to act on said piston, said engagement of the balls or rollers with said ramps at a predetermined relative angular position between said pressure plates precluding further relative angular movement between said plates in that direction and provides a stop to prevent further movement of said piston in an outward brake-applying direction with respect to said bore, said engagement of said balls or rollers with said ramps to define said stop being chosen to occur at a point before over-application of the brake can cause said piston to travel completely out of said bore, and wherein said ramps are provided with surfaces of different relative slopes so that the input effort required to produce a given braking force increases noticeably towards the fully worn lining condition, thereby providing a wear warning device for the user.