GB635699A - Improvements in or relating to brake systems - Google Patents

Abstract

635,699. Fluid-pressure-operated brakes. TECALEMIT SOC. ANON. Jan. 2, 1947, No. 195. Convention date, Jan. 2, 1946. [Class 103 (i)] To render the pressure applied to vehicle brakes dependent on the adhesion between the wheels and the track, one wheel or axle is more intensely braked than the others and the looking of this wheel or axle acts to limit the pressure reduction initiated by the driver in a brake control pipe. The braking pressure may be rendered dependent also upon the falling speed by causing the pressure in the control pipe and a centrifugal device to act jointly on a valve which directly controls the pressure in the brake cylinders or which reduces the pressure in a further control pipe connected to triple valves which control the cylinder pressure. Fig. 1 shows an automatic compressed-air system, comprising a main control pipe 15 normally charged from a main reservoir 70 through the driver's valve 16 and charging through a check-valve 49 an auxiliary reservoir 47 for each brake cylinder which is connected to pipe 48. The control pipe and cylinder pressures act respectively through pistons 36, 42 and a lever 37 to operate supply and exhaust valves 45, 45<SP>1</SP> for the cylinders. The fulcrum 38 of the lever 37 is adjustable by a centrifugal device 40 driven from an axle other than the more intenselv braked axle 1. The pressure in the pipe 15 acts through a piston 30 and a lever 23 against a spring 29 whereby this pressure is maintained by the operation of supply and exhaust valves 33 at a value determined by the position of the' fulcrum 22 which is carried by the rod 20 of a piston 19 normally subject to the pressure in pipe 15 acting against a spring 24. Centrifugal devices 3, 4 driven respectively by the more heavily braked axle 1 and another one 2 are connected by a rod 5, a lever 8 pivoted at 9, and a pivoted arm 12 to a slide valve 14 which, as shown, normally connects the pipes 15, 15<SP>1</SP>. The valve 14 carries a locking detent 26 for the rod 20. If with the parts in the running condition shown, the pipe 15, 15<SP>1</SP> is opened to atmosphere by the driver's valve 16 the rod 20 with the fulcrum 22 is moved to the right by spring 24 so that the piston 30 is moved down to exhaust the pipe through the passage 32 also. The pistons 36, 42 are therefore moved by the spring 50 to open the valve 45 to supply the brake cylinders. When the braking pressure is sufficient to lock the axle 1, the force on the rod 5 due to the unbalanced force applied thereto by the devices 3, 4 moves to the right, thus moving the valve 14 to cut off the pipe 15 from the driver's valve 16 and also engaging the detent 26 to lock the fulcrum 22 in its adjusted position. The pressure in the pipe 15 is thus stabilized. When the cylinder pressure acting on piston 42 corresponds to the reduced pressure in the pipe 15 acting on piston 36, the supply valve 45 is closed. A braking action is thus applied to the axles other than the axle 1 at a value which is just short of that which would lock these axles and this value is maintained substantially constant, taking account of the increase of the coefficient of friction with fall of speed, by the centrifugal device 40 which by shifting the fulcrum 38 to the left as the speed falls causes the piston 42 to unseat the exhaust valve 451 to reduce the cylinder pressure. In a modification, instead of a centrifugal device being provided for each brake cylinder as in Fig. 1, the pressure reduction in the pipe 15 effected and stabilized by the means shown in Fig. 1, operates a relay valve to effect a proportional depression in a pipe to which are connected all the triple valves associated each with a brake cylinder. The relay valve comprises a pair of pistons subject respectively to the pressure in the pipe 15 and in the triple valve pipe and acting in opposite senses on the two arms of a lever, the fulcrum of which is adjusted by a centrifugal device such as 40, Fig. 1. Each piston is acted upon by a balancing spring and one of them engages supply and exhaust valves for the triple valve pipe.