Patent GB-506733-A (GB)
Title: Variable speed control of brake pressure
IPC: B60T8/32
Filed: 1937-11-26
Abstract: 506,733. Fluid - pressure brakes; electric control systems. HUDD, A. E. Nov. 26, 1937, No. 32592. [Class 103 (i)] [Also in Group XXXVIII] The effect of pneumatic pressure or vacuum on a brake member is governed in accordance with the speed of a vehicle through an auxiliary valve which reduces the action of the pressure or vacuum by the force of an electromagnet energized by an electric generator having a permanent magnet rotor and driven from the vehicle wheels so that it is driven at a speed which varies with the speed of the vehicle. A spring of selected strength may also operate on the valve to maintain a minimum brake pressure at low speeds. In the case of a train with a number of coaches each with brake cylinders operated by a pneumatic pressure or vacuum system energized from a common source, each coach has a separate generator driven from the wheels or axles to control the auxiliary valve. Each generator comprises a permanent magnet rotor and a rectifier, preferably a metal oxide rectifier, in circuit with the stator. Where each coach has a lighting dynamo, the rotor may be mounted on its armature shaft. As applied to a vacuum brake control system. Fig. 1, a brake cylinder may comprise a piston 11 in a cylinder 10, connected to brake shoes 3. One end of the cylinder 10 communicates with a vacuum pipe line 8 having a main control valve 6 for releasing the vacuum in the line which may be generated by a steam ejector 7. The other end of the cylinder communicates through a vacuum reservoir 15 and an auxiliary valve 19 with the pipe line 8 or with atmosphere. The auxiliary valve 19 is operated by a diaphragm 22 carrying an armature 29 and a plunger 21 which is controlled by an electromagnet 25, 27 energized by a motor generator through a full wave rectifier 32. The generator comprises a fixed field coil 33 surrounding a soft iron core 34 between the poles of a rotating permanent magnet 35 secured to the armature shaft 36 of an existing lighting dynamo. The diaphragm 22 divides a chamber into two compartments 23, 24, one of which 23 communicates with the vacuum reservoir 15 and also through the auxiliary valve 19 with pipe line 8 and atmosphere, and the other 24 directly with the pipe line. To ensure that deceleration at low speeds may not be objectionable to travellers, change of brake pressure may be graded in relation to change of speed. By adjusting the air gap in the electromagnet 25, 27, the braking effect at low speeds may be varied. In a pressure controlled system Fig. 6, a brake cylinder 87 may be brought into communication with a pressure reservoir 90 through a relay valve mechanism under the control of the driver through a triple valve 89 and with the atmosphere through an auxiliary valve 118 subjected to pressure in the brake cylinder 87 and to an electromagnet 122, 125. The relay valve mechanism may comprise two relay valves 89, 106 in series between the reservoir 90 and brake cylinder 87, the valve 106 nearer to the cylinder being arranged to remain open and the other 89 closed when the brakes come off, the latter valve being opened under the control of the driver and the former valve 106 closed when a pro-determined pressure is built up in the brake cylinder. The auxiliary valve 118 controls direct communication between the brake cylinder 87 and atmosphere and is urged in one direction by pressure in a passage 120 leading from the brake cylinder 87, and in the other direction by the electromagnet 122, 125. An armature 126 energized by the electromagnet operates the auxiliary valve 118 with the assistance of a spring 129, the strength of which is selected so that the valve 118 cannot close until a predetermined maximum pressure is built up in the brake cylinder. The relay valve 106 may also be subjected to opposed forces provided by the pressure in the cylinder 87 and the force of an electromagnet 108, 109 energized by a generator 113 which energizes the coil 128 of the electromagnet 122, 125 and with which the coil winding 112 is in series. Material sold under the Registered Trade Mark " Ferodo " is preferably employed for the brake shoes.