Patent GB-592419-A (GB)
Title: Improvements in hydraulic brake mechanism
IPC: B60T13/24
Filed: 1944-10-17
Abstract: 592,419. Fluid-pressure brakes. EMPIRE ELECTRIC BRAKE CO. Oct. 17, 1944, No. 20080. Convention date, Sept. 30, 1943. [Class 103 (i)] In a hydraulic brake system comprising a manually operated master cylinder controlling a pneumatically operated booster the diaphragm of which acts on a piston to force liquid to the brake cylinders, the control valves of the booster are carried by the diaphragm thus giving a follow-up action. Liquid from the master cylinder flows initially to the brake cylinders and subsequently operates the valves through a piston upon which the brake cylinder pressure reacts so that the operator is made aware of this pressure. The booster diaphragm is operated by the master cylinder pressure if the pneumatic pressure fails. The booster casing comprises identical stampings 18, 19 held together by a split ring 23 joined at its ends by a tightening bolt 25. The diaphragm comprises a flexible part 22 clamped at its outer edge between the stampings 18, 19 and at its inner edge between a plate 41 and an annular disc 42 welded to the plate which is secured to a tubular part 59 abutting on an annular piston 60 slidable in a cylinder 35 connected by pipe 16 to the brake cylinders. The piston 60 is secured to a tubular part 58 within which slides one part of a plunger 47 the other part of which carries a piston ring 79 slidable in a cylinder 29 connected. by pipe 14 to a pedal-operated master cylinder. The cylinders 29, 35 normally communicate through a bore in the piston 47 past a ball-valve 54 held unseated by a rod 52 normally abutting, as shown, on a stop 34. A valve 87 housed in a cavity 81 formed in the plate 41 is normally seated on a flange 84 to cut off the chamber A of the booster from the atmosphere to which the cavity is open through a goose-neck 91 and pipes 96, 99. A valve 100 housed in a second cavity 82 formed in the plate 41 is normally open to connect the booster chambers A, B together through openings 106 and since chamber B is constantly connected to a source of vacuum by pipe 120, both chambers are normally under vacuum. The valves are engaged by a floating lever 110 which is supported by pins slidable in slots in a P-shaped bracket 68 secured to the diaphragm plate 41, the lever being branched to straddle a reduced part 64 of the piston 47 so as to be engaged thereby. When the master cylinder is operated liquid flows initially therefrom through the cylinders 29, 35 and the bore in the piston 47 to the brake cylinders moving the brake shoes towards or into contact with the brake drums, until the pressure acting on the differential end areas of the piston 47 moves it to the right. The lever 110 is thus actuated and as the spring of the air valve 87 is stronger than that of the vacuum valve 100, the lever first pivots on the valve 87 to close the valve 100 and then pivots on the valve 100 to open the valve 87 causing the diaphragm 22, 41 to apply pressure through piston 60, to the liquid in cylinder 35 the pressure in which reacts through the piston 47 on the pedal. If the pedal movement ceases the diaphragm moves farther slightly until. the air valve is re-closed. If the booster fails, the diaphragm is moved to apply the brakes by engagement of the shoulder 66 of the piston 47 with the bracket 68. Compressed air may be used instead of vacuum, the pipes 99, 120 being then connected respectively to the supply and to atmosphere.. U.S.A. Specifications 2,260,490, 2,260,491 and 2,260,492 are referred to.