GB624485A - Improvements relating to control systems for track braking apparatus - Google Patents

Abstract

624,485. Track brakes for vehicles. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. April 1, 1947, No. 8816. Convention date, April 23, 1946. [Class 103 (i)] Relates to track brakes for vehicles of the kind described in Specification 391,463, comprising brake bars arranged to grip the sides of the wheels and to control systems therefor in which the fluid pressure by which the bars are applied is determined in accordance with the setting of a hand lever. The invention consists in the provision of a valve device which by restricting the escape of pressure fluid from the brake cylinders when the bars have been set, allows the separation of the bars by the entry of the wheels between them to increase the pressure. In the system shown the device is operative only at the higher operating pressures. Brake cylinders 1, 1<SP>1</SP> operating respectively a pair of brake bars for each rail are connected to a main control valve 4 through a valve device 2 connected by ports 5, 6 respectively to the pipe 3 and the cylinders. The device 2 comprises non-return valves 8, 10, the valve 8 carrying a piston 9, the upper face of which is subject either to the pressure in pipe 3 or to atmosphere according as a magnet 14 is or is not energized to move valves 12, 24 to the position shown or to an upper position. Thus, if the pipe 3 is supplied by the valve device 4 with the magnets 14 de-energized, the pressure fluid flows past valve 10 to the cylinders 1 1<SP>1</SP>, and the pressure in the cylinders when it tends to rise due to the separation of the brake bars by the entry between them of the wheels, is not relieved since the valve 10 is held closed by the pressure in the pipe 3 acting upon the valve and piston 9. The valve 8 opens to reduce the cylinder pressure when the pressure in pipe 3 is reduced by the valve device 4. If the magnets 14 are de-energized, the piston 9 being subject to atmospheric pressure at both faces, the devices 2 are ineffective to permit an increase of pressure in the cylinders 1, 1<SP>1</SP> above that in the pipe 3. In the control system shown in Fig. 4, the main valve device 4 comprises magnet-operated exhaust and supply valves 16, 18 controlled by switches s1, s2, s3, s4, operated successively by a hand lever 15 to supply the cylinders 1, 1<SP>1</SP> at increasing pressures. The hand lever operates the switch d also to open the exhaust valve 16. When the switch s3 is closed the valve 18 is energized to supply the cylinders 1, 11 until at a predetermined pressure, the pressure responsive switch 17 breaks the valve circuit. With the circuit of valve 18 closed through switches s3, 17, the circuit of a relay 20 is closed through the rectifier 22 to energize the magnets 14 of the. valve devices 2 through switch 20a and to close a holding circuit for this relay through switch 20b and rectifier 21. The valve devices 2 are thus effective to permit increase of pressure in cylinders 1, 1<SP>1</SP> by the separation of the brake bars. If the switches s2, s or d are then closed the circuit of a relay 19 is closed to de-energize the magnets 14 by opening switch 19a so that the cylinder pressure equalizes with that in the pipe 3 the pressure in which is determined by the corresponding device 17 or when switch d is energized is reduced to normal. The circuit of the magnets 14 is broken also at contacts 20a when the holding circuit for relay 20 is broken at switch s3. The valve devices 2 are effective also when the brake is affixed by closing the switch s4. In a modification of the valve device 2, the magnet 14 and valves 12, 24 by which the device may be rendered ineffective are dispensed with.