Patent GB-473410-A (GB)
Title: Improvements in or relating to vehicle brakes
IPC: B60T8/20
Filed: 1937-04-13
Abstract: 473,410. Vehicle brakes. BROWALL, B. H., and SVENSKA AKTIEBOLAGET BROMSREGULATOR. April 13, 1937, No. 10454. [Class 103 (i)] In vehicle brakes especially railway-car brakes, the braking - apparatus is automatically shifted from one to the other of two braking effort stages by a member movable between two end positions according as to whether the load exceeds or is below a predetermined limit, the movable member being urged to one end position by a force varying with the load and to the other end position by a practically constant force corresponding to the predetermined load limit. As shown in Fig. 1, the movable member is formed as a lever 2 pivoted on a spring suspension bracket 3 and movable between abutments 4, 5 under the action of a weight 7 and a component of the supporting spring pressure transmitted by a link 1. The lever actuates a valve 6 for cutting in or out an additional brake cylinder or otherwise changing over from one braking effort stage to the other. The weight 7 is adjustable on the lever to change the predetermined load limit. Fig. 2 shows a bellcrank lever 2 connected to the spring link 1 and to a piston 9 movable between the ends of a cylinder 10 connected to a source of constant fluid pressure. In the case of an automatic fluid-pressure operated brake, the cylinder is connected to the pressure fluid conduit 11 of the brake through a non-return valve or a valve 12 closed by the brake cylinder pressure acting in a cylinder 13 when the braking operation is performed. This form has the advantage of suiting the load limit to the charging pressure of the system. The cylinder 10 is connected to an equalizing reservoir 14 and the lever 2 by a rod 15 to the means for changing over the braking effort stage. In a further modification the lever 2 is pressed by a rod loaded by compression springs, the movement of the rod being so limited by abutments that the pressure of the springs is substantially constant. The rod may control the change-over mechanism directly or by a mechanical interconnection or by a servomotor the interconnected valves of which are operated directly by the rod. In the latter arrangement the pressure on the inlet valve besides that of the springs has initially to be overcome by the lever so that the change-over mechanism is held steadily in one or other position. The loadresponsive lever 2, Fig. 4, is straddled by a piston rod 39 connected to the differential diaphragm-pistons 41, 50 enclosing a chamber 42 supplied with pressure fluid at 43. The rod 39 operates a slide valve 45 controlling ports 47, 46 48 leading respectively to a servomotor, the atmosphere, and a chamber 51 beneath the diaphragm 50. In the unloaded position of the lever shown, the servomotor is vented and the lower diaphragm balanced due to the connection of the chambers 42, 51 by the port 48. When the valve 45 descends, the chamber 51 is cut off from the chamber 42 and then vented so that the force opposing the load is reduced as the change over takes place. Simultaneously the port 47 is opened to the chamber 42 and the servomotor operates the change-over mechanism. In another form, a single diaphragm on which the load lever presses, encloses a liquid-filled chamber communicating by a restricted tube with a second chamber connected above the liquid level to a source of pressure. The diaphragm actuates a pair of valves interconnected by a lever for controlling a servomotor, the valves being so disposed that the force opposing the load is reduced after the inlet valve is opened. This latter form as well as the arrangement involving compression springs may be utilized in the arrangement shown in Fig. 5 in which levers 2a, 2b responsive to the load on the front and back axles a, b respectively operate control valves 35a, 35b in such manner that the servomotor 34 controlling the change-over mechanism is vented and lower braking effort stage operative unless the load limit is exceeded at both axles. The levers move between abutments 4a, 5a and 4b, 5b respectively, and as shown the constant forces opposing the loads are exerted by pistons 9a, 9b supplied with pressure fluid by a conduit 30 connected to the servomotor conduit 33 which is in turn connected to the brake conduit 11 by a passage containing a check valve 32. In a modification of this arrangement, the two load levers are connected to the ends of a floating lever which is connected intermediately to a piston exposed to a constant pressure. The piston rod is formed as the control valve of the servomotor and its passages are arranged so that changeover takes place only when the load limit is exceeded at both axles.