GB547041A - Improvements in or relating to liquid pressure braking systems - Google Patents

Abstract

547,041. Hydraulic master cylinders. HYDRAULIC BRAKE CO. Feb. 7, 1941, No. 1667. Convention date, Feb. 7, 1940. [Class 103 (i)] In hydraulic master cylinders, for operating brakes, comprising a relatively large diameter piston effective for moving the brake shoes into contact with the drums and a smaller diameter piston by which the braking pressure is applied, the larger piston is gradually rendered ineffective during an operation by the provision of a restricted passage connecting the chamber in front of the larger piston with the reservoir. Relatively large and small pistons 66, 82 move in chambers 32, 34 of the cylinder 24. In the release position of the pistons, these chambers communicate with the reservoir 10 through ports 38, 28. A chamber 70 between the piston 66 and a head 72 is constantly open to the reservoir through a passage 26. A restricted passage 88 and a passage 86 closed at one end by a plug 92 connects the chambers 32,70. The passage 88 is restricted by a wire inserted therein. During initial movement of the pistons to apply the brake, liquid is displaced by the large piston 66 from chamber 32 through passages 94 in piston 82 past the sealing cup 96 to chamber 34 thence to the brakes by the port 42. Liquid also flows slowly from the chamber 32 at this stage through the passage 88 to the reservoir. A large volume of liquid is thus displaced from chamber 34 but when due to the application of the brake shoes to the drum the pressure of the liquid rises substantially, the flow through the passage 88 increases so that the pressure of the liquid is gradually transferred from the piston 66 to the smaller piston 82. During retraction of the pistons liquid is drawn into the chambers 34, 32 from the reservoir through passages 76, 94 in the pistons and past the sealing cups 78, 96, excess subsequently returning to the reservoir through ports 38, 28.