Patent GB-602485-A (GB)
Title: Improvements in fluid-pressure braking apparatus for trailer vehicles
IPC: B60T13/36
Filed: 1945-07-16
Abstract: 602,485. Fluid-pressure controlled brakes. SERVO-FREIN DEWANDRE SOC. ANON. July 16, 1945, No. 18163. Convention date, June 19, 1942. [Class 103 (i)] A driver's valve for an automatic compressed air-brake system for trailer vehicles comprises a valve-operating piston subject on its opposite faces respectively to the pressure in the main reservoir and the brake pipe, a spring being interposed between the piston and the pedal to obtain a self-lapping action. The control valve on the trailer which supplies the brake cylinders from the auxiliary reservoir comprises pistons subject to the brake pipe and cylinder pressures acting against the controlling brake pipe pressure. The system shown comprises a drivers valve, Fig. 2, on the tractor, connected by pipe 16 to the main reservoir and by brake pipe 17 to the control valve 21, Fig. 5, on the trailer. The auxiliary reservoir is supplied from the pipe 17 through a non-return valve. The driver's valve comprises a piston 29 connected to the pedal 9 by a spring 35 and levers 33, 32 and subject on opposite sides respectively to main reservoir pressure through pipe 16 and to the pressure in the control pipe 17. Normally the piston is held in the position shown by a spring 34 in which an escape valve 26 closes an atmosphere outlet 38 and. a supply valve 28 is unseated to connect the main reservoir to the control pipe 17. Operation of the pedal moves the piston to close the valve 28 and, when lost-motion provided at 39 is taken up, to open the valve 26, thus venting the pipe 17 and operating the control valve 21, Fig. 5, to apply the brakes. If the pedal is held, the piston returns sufficiently to seat the valve 38. The pressure drop in the pipe 17 is thus dependent upon the position of the pedal and it reacts through the piston on the pedal and the driver's foot. The lost-motion provided at 39 between the valves by permitting slight movement of the pedal when the valves are both closed without opening either of them conduces to the stabilizing of the pressure in the pipe 17 when the pedal is held. The control valve 21 comprises chambers 47, 50 connected at 49, 51 respectively to the auxiliary reservoir and to pipe 17 and separated by a piston 40 upon which bears the rod of a piston 41 which separates chambers 52, 53 connected respectively to atmosphere and, at 54, to the trailer brake cylinders. Normally, the pressure in chambers 47, 50 being equal, the pistons are held in the position shown by the spring 42 so that the valve 43 is held from its seat on the piston 41 and the brake cylinders are thus connected to atmosphere through the chamber 52. When by operation of the driver's valve the pressure falls in the pipe 17, the pistons are moved to seat the valve 43 and, after lostmotion provided at 55 has been taken up, to open the valve 45, thus connecting the auxiliary reservoir to the brake cylinders by chambers 47, 53 and passage 48. When the brake cylinder pressure acting on piston 41 is equal to the pressure difference acting on piston 40, the pistons return sufficiently to close the valve 45. The brake cylinder pressure is thus dependent upon the pressure drop in pipe 17 and since this pressure drop reacts on the pedal 9, the force which must be applied to the pedal is a measure of the braking action.