IMPROVEMENTS RELATING TO INTERNAL SHOE-DRUM BRAKES FOR VEHICLES

1,253,586. Internal shoe drum brakes; slave cylinders; spring applied, fluid pressure released brakes. GIRLING Ltd. 5 Aug., 1970 [12 Aug., 1969], No. 40156/69. Headings F2E and F2F. An internal shoe-drum brake has two shoes 10, 11 which are separated to apply the brake by opposed pistons 14, 15 and 19, 20 movable in respective double-ended hydraulic cylinders 16 and 18: for service braking the pistons 14, 15 and 19, 20 are urged apart by hydraulic pressure but for parking or emergency braking the pistons 19, 20 are moved apart mechanically by a wedge 26, the wedge 26 being actuated by a spring (in the form of Bellville washers 35 or a compression spring) which is normally held inoperative by fluid pressure. As shown, the cylinder 18 contains a third piston 21 and in service braking hydraulic pressure is introduced through on inlet 42 into a chamber 23 between pistons 20 and 21, whereby piston 20 is moved directly and piston 19 is moved through piston 21. In parking or emergency braking the wedge 26 is movable in slots 24, 25 in the pistons 19, 21 with the interposition of free running rollers 27, 28 retained in cages on the wedge 26 and the piston 19 is moved directly and the piston 20 is moved through piston 21. The wedge 26 is mounted on a rod 29 coupled by a swivelling joint 31 to a piston 32 working in a bore 33. To release and apply the brake by the wedge 26 fluid pressure is introduced into and evacuated from an annular chamber 37. Automatic adjusters 17, 171 are provided for both shoes 10, 11.