GB1263999A - Improvements in or relating to brakes for vehicles - Google Patents

Abstract

1,263,999. Parking brakes. AUTOMOTIVE PRODUCTS CO. Ltd. 10 March, 1970 [25 March, 1969], No. 15576/69. Heading F2E. A parking brake for a vehicle including a brake shoe or a brake pad, an operating piston 21, mechanical means by which said operating piston is associated with said brake shoe or said brake pad so that said brake shoe is moved into frictional engagement with a corresponding brake drum, or said brake pad is moved into frictional engagement with a corresponding brake disc, by movement of said operating piston in one direction, said operating piston being connected mechanically to a member 28 which is separate from said mechanical means and which moves with any brake applying or releasing movement of said operating piston, and a releasable one-way holding device 30, 39 which co-operates operatively with said connecting member so as to hold said operating piston in any position to which it is moved in said one direction, the arrangement being such that the parking brake can be applied by the application of fluid pressure to said piston and is held mechanically in the brake applied condition by the action of said releasable one-way holding device acting upon said brake shoe or said brake pad through said connecting member, said operating piston and said mechanical means. As shown, a wedge member 17 is mounted between pistons 11, 12 in a wheel cylinder 10 and is engaged by the stem 23 of the piston 21, the latter being held against rotation by a wire clip 24 and having a screw-threaded bore 25 engaged by a stem 28 which is provided with a flange formed with ratchet teeth 30 that are engaged by a pawl 39. A piston 34 mounted in the larger bore 20 of the housing 18 is urged by Bellville washers 35 or other mechanical means towards the end wall 23 of the smaller bore 19. Liquid or air pressure is admitted through a port 40 into the cylinders 19, 20 and between the pistons 21, 34 so that the piston 21 is urged towards the wheel cylinder 10 whereby the member 17 moves the pistons 11, 12 to apply the brake shoes to the drum, the stem 28 being rotated by the interaction of the screw-thread thereof and the screw-thread 27 of the piston 21 while the pawl 29 rides idly over the ratched teeth 30; when the brake is applied the pawl 39 holds the stem 28 againstrotation in the opposite direction. To release the brake, the pawl 39 is disengaged from the teeth leaving the stem free to rotate and allow movement of the piston 21 and member 17 away from the wheel cylinder 10.