Patent GB-495640-A (GB)
Title: Improvements in or relating to hydraulic brake systems for motor vehicles
IPC: B60T11/16
Filed: 1937-04-14
Abstract: 495,640. Hydraulic brakes. CARROLL, E. G. April 14, 1937, No. 10581. Convention date, April 25, 1936. [Class 103 (i)] In a hydraulic brake system for motor vehicles comprising a master cylinder 1 having coaxial bores 2, 3 at least one of which is connected to the wheel brake cylinders 33 and at least one of which is connected to a reservoir of actuating fluid, the compensating ports 12 which connect these bores so as to compensate for temperature changes are arranged so that the same pressure is developed in these ports as is developed in the braking system during the braking movement in order to prevent scoring of the cup gaskets 11 carried by pistons 7 reciprocated in the master cylinder. The master cylinder, Fig. 1, has two bores 2, 3 containing integrally connected pistons 6, 7. The bore 2 communicates by a passage 4 with a connection R leading to the wheel brake cylinder 33. The latter contains opposed pistons 31, 32 which apply the brake shoes 108 to the brake drum 109. The bore 3 which contains a counterspring 39 is connected to a pressure gauge 40 and to a bore 18 in a reservoir 17. When the pistons 6, 7 are in the release position shown, the compensating ports 12 which are connected to the bore 2 by the passages 4 are exposed to the bore 3. The cup gasket 11 is exposed to the same pressure on both sides when covering the compensating ports 12. The piston 6 has a piston ring 49 and two cup gaskets 9, 16 of which the second 16 contains lubricant. The bore 18 of the reservoir 17 has a compensating port 21 and in the bore 18 slides a spring-loaded piston 19 with a gasket 27, the upward movement of the piston being limited by a shoulder on its stem 20 engaging the cover 22. All the cup gaskets of the system may be of oil resistant synthetic rubber so that light petroleum distillates may be used as the operating fluid. To free the system of air, the brake pedal 13 is held by a wedge in the braking position and the reservoir 17 filled with operating fluid. The piston 19 is then reciprocated until the operating fluid flows out past an open needle valve 35. During this operation the gaskets 11, 27 allow fluid to pass in one direction only. When the bleeding is completed, the valve 35 is closed and its cap 37 replaced. The piston 19 is then raised and the pedal 13 released so that the system is under a supercharged pressure which is shown by a handle 23 and by the gauge 40. The latter comprises a spring-loaded piston 42 with a gasket 42a and a rod 43 the end of which co-operates with a scale 44. The supercharged pressure may be obtained automatically during the braking operation as in Fig. 3. The double piston 55, 58 is hollow so that the bore 60, corresponding to the bore 3, Fig. 1, communicates by a passage 70 with a hollow piston 73 working a cylinder 71 and having a ported flange 76 working in a chamber 69. The piston 73 is operated by the brake pedal 78 and engages the piston 55. In the braking operation, the increase in volume of the chamber 69 is greater than the diminution in volume of the bore 60 so that liquid is drawn from the reservoir through the connection Sa. During the return stroke this excess liquid builds up pressure in the bore 18 of the reservoir. As in Fig. 1, a connection Ra leads to the brake cylinders and the bores 60, 63 communicate by compensating ports 64. Air vents 62, 65 are also provided. The piston 58 may have an additional piston at its end so as to form therebetween an annular chamber of constant size. In this case a reservoir open to atmosphere may be used. The dual arrangement in Fig. 2 comprises two double pistons 87, 91 and 88, 92 which sweeps out the same effective volumes. The larger portions 87, 88 of these pistons work in bores 85, 86 having connections R, F to the rear and front brake cylinders respectively. Compensating ports 97, 99 connect these bores with bores 89, 90 respectively, the latter communicating through the double piston 88, 92. An additional piston 103 is provided on the piston 87 so as to form an annular chamber 102 which traps any leakage and is connected to the reservoir 84 by a pipe 105. The bore 90 is connected to the reservoir by the pipe 107.