Patent GB-578630-A (GB)
Title: Improvements relating to brake control systems
IPC: B60T8/32
Filed: 1943-11-18
Abstract: 578,630. Brakes. WESTINGHOUSE BRAKE & SIGNAL CO., Ltd. (Westinghouse Air Brake Co.). Nov. 18, 1943, No. 19269. [Class 103 (i)] In a brake control system wherein the brake cylinder pressure is reduced if a wheel slips, the reduction being initiated by the discharge of a condenser normally charged by a generator revolving with the wheel, the duration of the reduction is controlled by a relay having a contact in the energizing circuit of a magnet valve which, when energized, vents the brake cylinder, the contact of the said relay being arranged to be opened at a predetermined time after the operation of the magnet valve. As shown in Fig. 1, the brake cylinders 14 for each of the wheel trucks 11 are controlled by a magnet valve 19, a pressure-operated switch 26 being connected with the supply pipe 15a. The switch 26 closes, by snap action, when the applied pressure exceeds; say, 15 lbs. per square inch, and opens by snap action when the pressure falls. Application of the brakes, therefore, closes the switch 26 and energizes the magnet 23 to an extent insufficient to operate the double beat valve 21, and energizes also the high-resistance relay 34 to pick up the contact b. Direct current generators 28a and 28b are associated with the wheel axles and maintain condensers 30a, 30b in charged condition. The charging-currents pass through windings p of relays 29a, 29b but in the wrong direction for picking up the contacts c, d. If the wheels 28a slip, the rapid deceleration of the wheels causes a rapid reduction in the generated voltage, and leads to a discharge of the condenser 30a through the winding p of the relay 29a, sufficient to cause the relay 29a to pick up the contacts c, d, the former completing the circuit between the battery bus-wires 37, 41 through the low resistance winding h of the relay 29a and the magnet 23. This fully energizes the magnet and moves the valve 21 to the right to vent the cylinders 14 and relieve the braking pressure to allow the wheels. to accelerate to non-slip speed. The pressure drop causes the switch 26 to snap open and break the circuits containing the relays 29a, 34, the contacts c, d dropping out and the brake relief system becomes ineffective as the brakes are re-applied by the de-energizing of the magnet 23 allowing the valve 21 to move again to the left. If the switch 26 fails to open as the pressure falls, a condenser 35 shunted across the relay 34 is provided to prevent complete venting of the cylinders 14. The condenser 35 is charged from the battery wires 37, 41 when the contact is dropped out as shown in Fig. 1. When the contacts c, d are picked up by the relay 29a, and are kept so by the batterysupplied retaining-winding h, the condenser discharges gradually through the relay 34 and keeps the contacts b picked up for a time slightly longer than the normal duration of closure of the switch 26, after which the contact b drops out and de-energizes the magnet 23. If the wheels 28b slip, the cylinders 14 are vented by an identical sequence of events, and provision is made for reversal of direction of carriage motion by a reversing-relay 33 which picks up contacts b, c on reversal. In a modification, Fig. 2, one relay 29c only is used. The windings p<1>.p<2> are so designed that the ampere turns of both windings during normal deceleration are insufficient to pick up the contacts a, b, but that the ampere turns caused by slip of one or both wheel units causes the pick-up. If the right hand wheels 13 slip, the contact b completes the battery circuit through the magnet 23 and vents the cylinders 14. The contact a breaks the generator' circuit and. completes a local condenser-discharge: circuit through the resistor r and windings p<2>. This keeps the contacts a, b picked up for a period of time sufficient to allow the wheels to return to vehicle speed. The contacts a, b then drop out and the brakes are re-applied. A condenser 46 stops sparking at the contact b. If the left hand wheels slip, the operation is similar, except that as the winding p<1> remains energized by a current charging the condenser 30a as the slipping wheel accelerates, the relay 29c remains picked up for a slightly shorter time than when the right hand wheels slip.