GB1412451A - Braking control apparatus - Google Patents

Abstract

1412451 Vehicle braking systems WESTINGHOUSE BRAKE & SIGNAL CO Ltd 8 June 1973 [21 June 1972] 29177/72 Heading F2F A braking control apparatus for a rail vehicle comprises a blending valve 6 responsive to both a D.C. signal from a rectifier 9 having input terminals connected to receive an A.C. signal indicative of the degree of electrodynamic braking and an output braking demand signal from a digital or analogue control valve apparatus 4 whereby the blending valve 6 output pressure signal represents the braking force required to achieve the demanded retardation with the amount of electric braking produced being subtracted from it. In operation, signals appearing in lines 1, 2 and 3 running the length of the train are converted into a pneumatic pressure in a conduit 5 fed to blending valve 6 which also receives a pressure from an electropneumatic converter 8 receiving the D.C. signal. The circuit in Fig. 3 represents rectifier 9. When electrodynamic braking starts an A.C. input is produced at terminals 11, 12 and an e.m.f. appears in windings 17, 15 of a transformer provided with a core 16. A rectifier bridge 18 is caused to conduit to energize transistors 22, 23 whereby current is supplied to converter 8 via terminals 20, 21. A capacitor 30 is also charged and transistor 24 switched on thereby switching off transistors 25, 23, 22. Since the number of turns of winding 17 is half that of winding 15 a doubled output current appears at terminals 20, 21. Thus the amplified dynamic brake signal results in a boosted signal in conduit 7 thereby holding back the rise of pneumatic braking. After a time interval determined by the time constant of capacitor 30 and a resistor 32 the base current to a transistor 24 ceases, the latter then being turned off. Consequently, transistors 25, 23, 22 are rendered conducting and the current supply to terminals 20, 21 is therefore halved. Current produced by a current transformer 13 is rectified via a diode bridge 38 and charges capacitors 42, 40. Thus when the input current at terminals 11, 12 decreases at the end of dynamic braking capacitor 40 discharges via a transistor 27 the latter becoming conducting to render a transistor 26 conducting to carry a current whose magnitude is determined by a Zener diode 36. Transistor 26 thereby becomes a constant current device causing a predetermined amount of current to be diverted from terminals 20, 21. Hence the pneumatic brake is caused to respond more rapidly. A circuit is described, Fig. 4 (not shown), which ensures that the boost circuit does not operate when subjected to a sharp rise in dynamic braking when a smaller value of dynamic brake load resistance is selected by a cam controller controlling the braking current.