Patent GB-308329-A (GB)
Title: Improvements in brakes
IPC: B60T13/74
Filed: 1927-12-20
Abstract: 308,329. Lomonossoff, G. V., and Kapitza, P. Dec. 20, 1927. Electromagnets.-In brakes particularly for vehicles of the kind that are applied by springs or similar means and held off by electromagnets, the armature of the magnet is arranged to be in contact, or substantially so, with the magnet core in the release position whereby the remanent magnetism is utilized to permit the use of a reduced current for holding off the brakes. Means are provided for supplying a current of larger value to the magnets immediately upon cutting off the holding-off current to prevent the sudden application of the brakes at full pressure. As shown in Fig. 1, a pair of magnets 1 have their armatures 2 each connected by a lever 4, link 6, lever 8 and adjustable link 11 to a beam 25 carrying brake blocks 26. Application springs 13 extend from a fixed point 14 to the levers 8. The magnets may comprise a core 1 with a coil 31 and an armature having a flange 32 received in an annular slot in the core. The force for withdrawing the brake blocks is mainly exerted on this flange through which the magnetic field passes transversely. The flange is so shaped as to obtain the desired relation between increments of armature movement and increments of brake pressure so as, for instance, to compensate for variations in the obliquity of the levers during the stroke. The magnetic cores may be provided with a separate smaller coil for the holding-off current, the main coil 31 being in this case deenergized after the withdrawal of the shoes. The electric control system comprises an operating arm 35 carrying contact plates 37, 38 and fixed plates 39, 45 connected to the magnet coils 50. to release the brakes, the switch 61 is closed and the arm 35 is placed in the position shown so that current is supplied to the coils 50 from the battery B through the leads 51, 57 and the fixed contacts 40, 46, thereby causing the armatures 2 to move into contact with the cores 1. The switch 61 is then opened so that the current is reduced by flowing through the resistance 60. In applying the brakes, the arm 35 is quickly moved to place the plate 37 into contact with the contact 41 and the plate 38 into contact with the plate 47.The coils 50 are thus short-circuited through the plates 45, 47, a relay coil 65, switch 68, 69, lead 52, and plates 37, 39. The back EMF set up by the movement of the armatures 2 causes a current to flow through the relay coil 65 which causes the switch arm 68 to move over on to contact 70 and thus to establish a circuit through the coils 50 from the battery through the resistance 72. This current is sufficient to permit the springs 13 to apply the brake shoes to the wheels but without appreciable pressure. The main switch arm 35 may now be successively moved over the contacts 42, 43, 44 to include increasing resistances 62, 63, 64 and thus to reduce gradually the current in the coils 50 and increase the effective pressure of the springs 13 on the brake shoes. An air spring or a vacuum device may be substituted for the metallic springs 13. Specifications 310,093, [Class 103 (i), Brakes &c.]. and 312,259 are referred to.