Patent GB-1187211-A (GB)
Title: Electric controlled Brake System for Railway Cars
IPC: B60T8/18
Filed: 1967-07-03
Abstract: 1,187,211. Transistor circuits, WESTING- HOUSE AIR BRAKE CO. 3 July, 1967 [14 Sept., 1966], No. 30534/67. Heading H3T. [Also in Divisions F2 and H2] In an electrically controlled braking system for a vehicle (Division F2), a wire P carries a control signal varying from zero to a predetermined level (e.g. 0À5 amp.) to effect proportional brake control and above that level (e.g. in the range 0À5 to 1À0 amp.) the control calls for propulsion, the signal at zero level calling for full braking and the signal at the predetermined level for no braking, a power amplifier being provided which is responsive to the signal to provide output current in proportion to the control signal, the brake being a spring-applied friction brake which is torque motor released, means applying the output current to the torque motor on each of the truck brake units 57, 62, the braking system also including a dynamic brake means for modulating the control signal according to the load on the vehicle and according to the degree of dynamic braking applied by the dynamic braking. In part of the circuit arrangement shown in Fig. 1B the control signal conductor P controls the output of the magnetic amplifier MA and an A.C. power supply lead 10, a rectifying bridge 11 and a 250 ohm load 12 is in series with the latter. A brake transfer circuit 15 transfers operation from brake to propulsion when a voltage of slightly more than 4 volts D.C. appears across a resistance 12 and back to brake when the voltage is reduced to below 4 volts D.C. so long as the voltage at point 16 of the bridge 11 proportional to the conductor wire P current of 0À52 amp. or above the brake transfer relay BT is held in and as the conductor wire P current drops below 0À48 amp. the brake transfer relay BT drops out and the braking system is then brought into operation. In the brake transfer circuit (shown in Fig. 2) the current in the conductor P is applied to the input terminal 130 and a voltage passes through the capacitor 131 and is clipped by the diode 132 and a series resistance 133 to remove negative-going portions thereof. The positive portions of the input signal are applied to a resistance 134 to the base of an NPN transistor 135 the base of which is biased negatively by voltage supply through a switch 137 from a slider 138 of a potentiometer 139 having a negative voltage supply 140. So long as the input signal does not overcome the bias provided from the slider 138 the transistor 135 will not turn on. The output from the transistor 135 is passed on through a capacitor 141 through a resistance 142 to Zener diodes 143, 144 in series with each other and to the base of an NPN transistor 145. The collector of the transistor 145 is connected to a positive voltage terminal 146 through a primary winding 147 of a transformer 148. Connected from the highpotential side of the resistance 149 is the collector of an NPN transistor 150. The transistor 145 is normally non-conductive and will not turn on until the transistor 135 is nearly full on due to the fact that Zener diodes 143, 144 isolate the base of the transistor 145 from input current until they are rendered conductive. When the transistor 135 becomes sufficiently conductive the Zener diodes 143, 144 conduct and the transistor 145 becomes conductive which in turn renders the transistors 150 conductive and the current passes through the primary winding 147. The transistors switch on and off with the magnetic amplifier output providing a fail-safe voltage to the relay BTD which is energized from the secondary winding 151 of the transformer 148 through a rectifying bridge 152. Accordingly the relay BTD is energized when current passes through the transformer 148. When the BTD relay picks up it shifts the contacts of the armatures 155 and 156 so that the bias on the base of the transistor 135 is shifted since the contact 158 is connected to the slider 160 on the potentiometer 161. The armature 155 then pulls to the right completing a circuit to the contact 163 and thereby applying current from supply terminal 164 for the relay BT. The condenser 167 and the resistance 168 connected across the relay BT prevents unstable operation of that relay. As the current in the conductor P reduces to 0À48 ampere the BTD relay drops the input back to the higher negative bias ensuring that the brake relay BT will drop out. The sliders 138 and 160 may be adjusted so that the BTD relay pulls in on 0À52 amp. but drops out again when the P wire conductor current falls to 0À48 amp.