GB911096A - Improvements in or relating to liquid pressure braking systems for vehicles - Google Patents

Abstract

911,096. Brakes, fluid-pressure. AUTOMOTIVE PRODUCTS CO. Ltd. Oct. 17, 1960 [Sept. 23, 1959], No. 32406/59. Class 103 (1). A liquid-pressure braking system for a trailer vehicle includes a reducing valve 23 between a trailer mounted master cylinder 10 energized by a vacuum servo 15 controlled from the tractor, and the brake cylinders 11 of the trailer, the valve having a by-pass which is closed to render the valve operative to reduce brake pressure only when a predetermined adjustable pressure is exceeded, thereby avoiding skidding at high brake-pressures. Master cylinder pressure initially reaches a brake cylinder feed-pipe 25 freely through a pipe 21, duct 22, ports 5 and the bore of a sleeve 47, which constitutes the by-pass. When brake cylinder pressure reaches a predetermined value it acts on the larger effective area at the right of a stepped piston 31 which it forces to the left against the bias of a spring 36 adjustable by a hand wheel 41. As the piston 31 moves it takes along the sleeve 47 which then seats on a ball valve 49, thereby closing the by-pass through the sleeve 47. Any further increase in master cylinder pressure is transmitted to the brakes 11 solidly through the piston 31 at a ratio which is reduced in the proportion of the ratio of the effective righthand and left-hand areas of the piston 31. On release of master cylinder pressure seating, pressure is removed from the ball 49, permitting release of brake cylinder pressure, whereupon the spring 36 moves the piston 31 to the right, in the position shown, and a push-piece 51 fully unseats the ball 49.