GB1309217A - Fluid pressure operable brakes - Google Patents

Abstract

1309217 Brake actuators; slack-adjusting; disc brakes PONT-A-MOUSSON SA 10 Dec 1971 [12 Feb 1971] 57373/71 Heading F2E A fluid-pressure brake actuator comprises a cylinder 2, a piston 3 for carrying a brake lining 5, a member 9 of plate form constructed to return the piston by magnetic action, slidably disposed in the cylinder behind the piston and having a pressure-equalizing aperture 10, and a projection 7 extending from the back of the piston through the member 9 with limited axial play corresponding to the normal working stroke of the piston, whereby, when the normal stroke is exceeded as a result of lining wear, the piston entrains member 9 to adjust the working stroke. As shown and described, the following forces or resistances are listed in decreasing order of magnitude: the force on the piston due to fluid pressure introduced at 6 for operation, the resistance of resilient seal 11, the magnetic attraction of member 9 on piston 3, and the resistance of piston seal 15. Member 9 is a permanent magnet. In operation, in the absence of wear, fluid pressure forces piston 3 away from magnet 9 through a distance a (see parts 1, 5 and 9, 13). On release, magnet 9 retracts piston 3 to its former position. On wear occurring, necessitating movement of piston 3 through distance b, the fluid pressure forces it first through distance a, after which the continuing fluid pressure causes the piston to entrain magnet 9 by means of split ring 13 and overcome the resistance of seal 11, moving the assembly a further distance (b-a). On release, seal 11 holds magnet 9 in its new position while the magnetic force withdraws piston 3 a distance a once more. In Fig. 2 (not shown) member 9 is an electromagnet fed from an external source. The fluid may be hydraulic or pneumatic. The invention is applicable also to drum brakes with appropriate change of shape of pad 5.