Patent GB-576132-A (GB)
Title: Improvements relating to railway braking apparatus
IPC: B61K7/12
Filed: 1942-12-30
Abstract: 576,132. Vehicle brakes. TOMLINSON, A. V. (Union Switch & Signal Co.). Dec. 30, 1942, No. 18508. [Class 103 (i)] [Also in Group XXXV] In a system for retarding wagons by apparatus on the permanent way in which the movement off normal of a control lever causes the maximum or a predetermined high pressure to be applied to the braking bars, the pressure being progressively reduced in accordance with the speed of the car and being removed when a desired speed is reached and the circuits being such that should the speed subsequently increase, the braking pressure would be increased again, the speed is measured by counting chains driven by alternating or pulsating current of constant frequency connected up by track relays. The speeds at which the controls come into operation are determined jointly by jumpering at a terminal frame and by the position to which the control lever is set. Two systems are described. First system, Fig. 1a, 1b. When the control lever L is moved off normal, the circuit of a magnetically controlled valve V1 is opened and that of a similar valve V2 is completed to admit pressure fluid to a ram M which controls the application of pressure to braking bars 2, 3, 2a, 3a. On arriving at the retarding section, the wagon energizes the first of a series of track relays 1TR .. 6TR and this completes a series circuit for relays W, 1SU, UX (upper) and the first of a chain of unitinterval counting relays 1U. 1SU energizes the zero relay OM of a series of multiple-interval counting relays OM .. 5M. W connects a source A of A.C. via rectifiers 334 and 35 to a pair of polarized relays PX, NX which interact so as to cause the contact 42 to change over in response to each negative half-cycle and so build up the unit-interval chain. The third relay of this chain causes the change-over of another polarized relay MX whereby, if the relay 6U is operated, the first of the multiple-interval counting relays OM .. 5M is operated. This action proceeds while 1TR is actuated, the time taken for a wagon to traverse the section being indicated by the points to which the chains build up. When the wagon leaves the first section, 1TR falls and 2TR pulls up, the counting relays and 1SU are released, a new circuit is made over W, 2SU, UX (lower) 1U and the time taken to traverse the second section is measured in a similar way. When the time of traverse is sufficiently short, no control of the braking apparatus takes place.. When however the speed has fallen to a point determined jointly by jumpering between contacts of the counting relays and terminals 81 .. 89 and 93 .. 100 and by the position to which the control lever L has been set, a circuit is made over 1SP and 1P 45-55 or 2SP and 2P 45-55 according as an odd or even numbered section is being traversed. These relays in conjunction with a switch P 45-55 controlled by a Bourdon tube control the valves V1, V2 until the pressure in the ram M has fallen to a point between 45 and 55 lbs. per square inch. A further reduction in speed similarly causes a reduction of pressure to between 20 and 30 lbs. per square inch and finally, when a desired speed is reached, the relay 1PO or 2PO reduces the pressure to atmospheric. These relays have locking circuits, which keep them actuated until the end of the period being measured (unless a subsequent relay 1P20-30 is operated), and resistance-condenser circuits which hold them during the measurement of the next period. If the lever is moved to its extreme position, the full braking pressure is applied permanently. Modified system, Figs. 2a and 2b. This is similar to the arrangement just described but has provision for an additional braking pressure and has a switch MS for disabling the automatic control and connecting up an alternative lever L1 whereby the attendant can select any of four braking pressures which are maintained whatever the speed of the wagon. With switch MS in its other position, control is given to lever L. This, in its normal position, energizes valve V1 to relieve the brake bars of pressure and in any off-normal position applies maximum braking pressure or a pressure of 45-55 lbs. per square inch according to the position of a switch MS1. In its positions p1, p2, p3 it selects speeds at which relay 1P is to pull up over contacts of the counting relays. 1P on operating locks over a number of parallel contacts of the units relays and reduces the braking pressure either to 45 to 55 lbs. per square inch or to 20 to 30 lbs. per square inch according to the position of MS1. 1P remains operated until the speed drops enough to energize 1PO which energizes V1 directly to relieve the pressure entirely. In this arrangement there is only a single set of pressure-modifying relays. The time-measuring circuits differ somewhat as regards circuit details from those shown in Fig. 1 but exercise the same functions.