Patent GB-365717-A (GB)
Title: Improvements in or relating to servo brake operating mechanism
IPC: B60T13/24
Filed: 1930-11-28
Abstract: 365,717. Fluid-pressure brakes. BLACKLOCK, C. T., Crossways, Beaumont Fee, and CLAYTON DEWANDRE CO., Ltd., Titanic Works, both in Lincoln. Nov. 28, 1930, No. 35899. [Class 103 (i).] A brake system comprises two hydraulic transmission systems connected to separate groups of brakes, the cylinders of these systems being mounted on a vacuum or fluid pressure power cylinder containing a pair of pistons one of which is directly connected to one of the hydraulic pistons while the other is connected to the second hydraulic piston through mechanism which is connected also to the control valve of the power cylinder and to the brake pedal or lever whereby manual effort is applied to the second hydraulic piston while the vacuum or pressure in the power cylinder is maintained proportional to the manual effort. The system shown in Fig. 1 comprises a pair of pistons 14, 31 arranged to be subject to engine suction and connected respectively to the master pistons 10, 8 of separate hydraulic systems connected each to one group of brakes. The piston 14 is connected to the piston 10 by the parts 11, 12, 13. The piston 31 is connected to one arm of a crank lever 26, 27 mounted on the end of a balance lever 5, the other arm being connected to the valve device. The lever 5 is pivoted at 6 on a lever 2 turning on a fixed pivot 3 between which and a boss on the end of the lever 5, limited play is provided. The lever 5 is connected by link 9 to the piston 8 and the lever 2 is connected by a rod 4 to the pedal or may be extended as at 2<1> for direct actuation. The valve device comprises suction and inlet valves 19, 20 seated by a spring 21, lever 22 abutting on the ends 30, 28 respectively of a tubular part on the valve 20 and a rod 29 connected to the valve 19. When to apply the brakes, the lever 2 is rocked by the rod 4, the piston 8 is first moved inwardly by the lever 5 until there is sufficient reaction in the link 9 to cause the lower end of this lever to move outwardly to unseat the suction valve 19 and apply suction to the piston 31. When the suction on the piston 31 is sufficient to balance the manual pressure on the rod 4 the suction valve re-closes. The pressure due to the suction also acts through the piston 14 on the hydraulic piston 10 to apply the group of brakes operated thereby, this pressure as also that on the piston 31 being proportional to the pressure applied to the rod 4. If the pressure on the rod 4 is relieved, the valve 20 is opened until the suction is correspondingly reduced. In the event of failure of the hydraulic system comprising the piston 8, this piston is moved until it meets a stop and the valve will then be operated so that the pistons 14, 10 will still be effective. If the engine suction fails, the engagement of the boss of the lever 5 with the pivot 3 enables this lever to actuate the piston 8 and the brakes associated with it by manual force applied to the lever 2. Figs. 2 and 3 show modified control mechanism comprising a balance lever 40 pivoted at 41 on a lever 42 rocking on a pivot 43, which passes through a boss 44 on the lever 40 with limited clearance. The lever 40 is connected to the piston 48 by a rod 50 to the pedal and by lever 46 and rod 39 to the valve device 38. The lever 42 is connected by link 43a to the hydraulic piston 49. This device operates in a similar manner to that shown in Fig. 1, the effort applied to the brakes by the piston 48 being balanced by and proportional to the manual effort. Pneumatic and hydraulic pistons corresponding to the pistons 14, 10, Fig. 1, are arranged at the other end of the apparatus.