Spreading type disc brakes for vehicles

Abstract

In a disc brake the application of the brake is initiated by angular movement of at least one pressure plate with respect to a reaction member to cause the pressure plate to move axially into engagement with a friction disc which, in turn, is urged into engagement with a surface in a stationary housing. The angular movement is effected hydraulically by an actuator comprising a piston working in a bore of a cylinder, the axis of which is substantially at right angles to that of the brake. The piston acts through a part-spherical rocking thrust coupling associated with a pull-rod passing through the actuator with a substantial clearance, the inner end of the pull-rod being pivotally coupled to a lug on the pressure plate, and the outer end being adapted for connection to a hand lever by which the pull-rod can be moved in a brake-applying direction. A thrust member is disposed between the piston and the spherical rocking coupling and is engagable with a thrust transmitting face on the piston for sliding movement in a transverse direction with respect to the axis of the cylinder to accommodate angular movement of the pull-rod when the brake is applied. The thrust member and the coupling are biassed towards each other by a compression spring so that the thrust member is restrained from moving radially with respect to the coupling when the brake application is effected by the hand lever. In another construction the spring is omitted and the biassing is achieved by the inherent resilience of a boot for sealing the outer end of the cylinder.