Patent GB-538554-A (GB)
Title: Improvement in devices for applying power to brake members
IPC: B60T13/24
Filed: 1939-11-03
Abstract: 538,554. Fluid-pressure brake systems. NEW BRITAIN MACHINE CO. Nov. 3, 1939, No. 29331. Convention date, Nov. 8, 1938. [Class 103 (i)] In a fluid-pressure system for operating brakes operation of a hydraulic master cylinder by a pedal first moves the brake shoes into light contact with the brake drums by the foot pressure alone and upon further movement of the pedal a valve is operated by the master cylinder which renders operative a fluid-pressure cylinder to apply effective pressure to the shoes through the hydraulic system. A power unit for a vehicle brake system is shown comprising a pipe connection 21 which leads to a pedal-operated master cylinder (not shown) and which is connected by a pipe 30 to a hydraulic cylinder 34 from which a pipe 115 leads to the brakes. The piston rod 39 of a piston 102 working in a cylinder 99 serves as a plunger for the cylinder 39. A pipe 42 leads from the cylinder 34 through a capillary orifice 42b to a chamber 43 formed in a casting 44 behind a plunger 51 which is connected to a valve 55 adapted to seat on a diaphragm 88 secured to the casting 44. A second diaphragm 95 connected to a diaphragm 88 by a ferrule 91, 93 carries a valve 87 also adapted to seat on the diaphragm 88. Valve chamber 56 is constantly under vacuum through plug 58, check valve 59 apertures 62, and pipe 73 connected to the manifold of the vehicle engine. A plug 63 can be screwed more or less into the plug 58 to adjust the apertures 62 and thus the vacuum. The cylinder 99 is mounted in an airtight casing 80, 109 which is in communication with the vacuum chamber 56 through passages in the casting 44. The cylinder chamber at the right-hand of piston 102 is thus constantly under vacuum through apertures 110 in the end-plate 109 of the cylinder. The cylinder chamber at the left-hand of the piston is also normally under vacuum through the apertured end-wall 100 of the cylinder, the ferrule 93, 91, the valve 55 and chamber 56. When the pedal is depressed liquid is at first forced from the master cylinder through pipes 21, 30, cylinder 34 and pipe 115 to the brake cylinders and brings the brake shoes into contact with the drums. When the hydraulic pressure is transmitted through pipe 42 and the orifice 42b and acting on the plunger 51 is sufficient to overcome the spring 92, the diaphragms 88, 95 are deflected, and valve 87 is unseated, thus admitting air to the left-hand side of piston 102 through a filter 79, passage 83 and ferrule 93. Pressure is thus applied by the piston 102 to the plunger 39 which cuts off the connection between the pipe 30 and the cylinder 34 and applies additional pressure to the liquid in this cylinder and thus to the brakes. The connection between pipes 30, 42 is maintained for the control of the valve. A screw-plug 49 permits escape of air from the 'hydraulic system. A pipe 125c closed by a screw-plug 125b is provided for lubricating the cylinder 99. The construction of the unit is such that it exerts substantially no thrust on the vehicle frame on which it is mounted by U-shaped members 25, 26. A modification is shown for compressed-air operation of the piston 102, the valves 87, 55 being arranged to connect the left-hand side of the piston to the compressed air source and to atmosphere respectively and the right-hand side of the piston being constantly connected to the atmosphere through a pipe and filter. The casing 80 is filled in this case with compressed air. The pressure applied by the piston 102 is dependent upon the foot pressure since this latter pressure is opposed by the pressure in the cylinder 99 acting on the valve 55.