Patent GB-1410865-A (GB)
Title: Method of and apparatus for braking railway vehicles
IPC: B61H5/00
Filed: 1973-11-09
Abstract: 1410865 Electromagnetic track brakes; speedresponsive disc brakes; drum brakes Y DUBREUCQ 9 Nov 1973 [10 Nov 1972 15 May 1973 13 Sept 1973] 52198/73 Heading F2E A method of and apparatus for eddy-current braking of a vehicle or machine having wheels of magnetic material running on a track of magnetic material comprises passing current through an excitation winding carried by the vehicle or machine to create a magnetic flux in a magnetic circuit including two adjacent wheels and the track on which the wheels run, thereby generating braking eddy currents in the adjacent wheels. As shown in Fig. 3, an excitation winding 36, &c., is located around the lower half of each wheel 8, &c., and for braking, direct current is passed through each winding in such a direction that a closed flux path extends along one axle 4, down through wheel 8, along running rail 16, up through wheel 10, along axle 6, down through wheel 12, along rail 18, up through wheel 14 and along axle 4. The windings shown may be supplemented or replaced by winding around the axles 4, 6. Each excitation winding may be a coil of aluminium strip 9, Fig. 6, the strip being oxidized on its surface, and the coil being held inside a suspended casing 7 by a filling of resin 13. The energizing current may be obtained indirectly from an alternator 11 coupled to the end of axle 4. In the control circuit of Fig. 7, when braking is required, contact 17 is closed. Relay 19 is thereby energized, and thereupon closes contact 19-1 to energize the excitation circuit of the alternator 11; contact 19-2 is opened but this is not significant above a certain vehicle speed (see below). If the vehicle speed is sufficiently high for the frequency of the output of alternator 11 to energize a frequency-responsive relay 23, contact 23-1 is closed and thus maintains an electrically-operated valve 15 energized, despite the opening of contact 19-2. As long as valve 15  is energized, the compressed air actuator of a disc brake of which disc 8A, Fig. 6, forms part is vented to atmosphere and the brake is not applied. Part of the output of alternator 11 is rectified at 25 and fed to the excitation windings 9 of the eddy current brake, which is thereby applied. As the vehicle speed falls to a certain value, relay 31 is de-energized, whereupon contact 23-1 re-opens, and since contact 19-2 is still open, valve 15 is de-energized, so the disc brake is applied. Both brakes continue in operation until the vehicle stops. If the alternator fails to operate, contact 23-1 remains open, so the disc brake is automatically applied as an emergency brake. Before re-starting, the operator opens contact 77. In a more elaborate circuit (Fig. 8, not shown) the alternator is replaced by a static converterrectifier fed by H.T. The eddy-current brake is applied immediately contact 17 is closed, as before, but the disc brake is applied additionally on energization of a time-lag relay after a predetermined interval. After a further interval, both brakes are released by the energization of a further time-lag relay. A more elaborate mounting for an excitation winding is depicted in Figs. 9 to 11 (not shown), and another in Figs. 12, 13 (not shown); in both cases the winding is located between horizontal plates held together by bolts, and the lower plate may be removed to permit removal of the winding without disturbance of any other components; the upper plate is so arranged as not to interfere with removal of the wheel. In Fig. 1 a magnetic circuit is produced on one side of a vehicle bogie by an excitation winding 24 surrounding a chassis element 20 of magnetic material; small "rotary" air gaps occur between each wheel 8 or 10 and the adjacent element 20. An analogous circuit is produced at the other side of the bogie. In Fig. 2 the "rotary" air gaps are eliminated by providing pneumatically operated spring- released brake shoes 28, 30 between element 20 and wheels 8, 10, respectively. In Fig. 5 (not shown) part of the flux path is along transverse members separated from the wheels by "rotary" air gaps: the axles are not used for this purpose (compare Fig. 3).