Patent GB-1456821-A (GB)
Title: Brake control apparatus
IPC: B60T8/88
Filed: 1973-02-27
Abstract: 1456821 Electro-pneumatic brake control apparatus; load-responsive braking WESTING- HOUSE BRAKE & SIGNAL CO Ltd 14 Feb 1974 [27 Feb 1973] 9631/73 Heading F2F Brake control apparatus for a car of a railway train is connected to a D.C. control line or circuit 1 and an emergency and A.C. line or circuit 2 which provides the power supply for the control signalling processing apparatus; an output braking signal is adjustable in dependence upon a control signal on the line 1 and a dynamic braking input signal to actuate an electropneumatic converter 9 to control the braking pressure in brake cylinders. In the absence of a signal on the line 2 the apparatus becomes totally unresponsive to the control signal and the apparatus fails safe to a braking condition. In the embodiment of Fig. 1 a D.C. control analogue signal circuit 1 is coupled to a D.C. transformer 3, the supply to which is derived from an isolating and regulating transformer 14 which is normally energized from the A.C. line 2. A further A.C. output from transformer 4 supplies a rectifier 5, and another output provides an excitation over a connection 16 to a dynamic brake sensing unit. The A.C. output from tranformer 3 is applied to a rectifier 7 which provides a command input D.C. signal to the converter 8 sealed to correspond to the required braking effort for a fully loaded vehicle. The converter has two further inputs viz. at 9 a dynamic brake torque feed-back signal and at 10 an input from an amplifier demodulator 11 corresponding to the amount by which the output of the converter 8 is to be reduced to correspond to the actual degree of loading of the vehicle. For this purpose, the rectifier 7 supplies a D.C. signal to an inverter and amplitude modulator 6 which is also connected to rectifier 5 and transformer 4, and the A.C. output from 6 which is the 'inversion' of the D.C. input corresponding to the fully loaded command signal is applied to a pressure transducer 12. This receives an input pressure from the vehicle suspension via a pipe 13 and proportions an output signal applied to demodulator 11 to the difference between a set full load condition and the actual load condition of the vehicle, and the input on line 10 is similarly proportioned. The output from converter 8 is applied to a load cutoff valve 14 and thence to a relay valve 15. The load cut-off valve 14 is controlled by the suspension pressure and limits the maximum braking pressure under all loading conditions. In the event of the train braking or a power supply failure therefore the apparatus fails to a full braking condition governed only by the suspension pressure. The embodiment of Fig. 3 has a command signal train line 3, an emergency line 4 and a brake release train line 5. The input on line 3 is constituted by a variable mark-to-space ratio D.C. signal which is A.C. coupled via an isolating stage 8 to an inversion circuit 9 the output of which is applied to a power gate circuit 10, which derives A.C. power via a transformer 11 from the line 4. The output from circuit 10 is rectified and applied via a low current relay 19 to an electropneumatic converter 21. A further output from transformer 11 is applied to the output of circuit 10 via a connection 12, and combined with the output from the rectifier is the output from an amplifier 13 whose input is a load-weighed A.C. input derived from a load-weighing transducer 15. The converter 21 is connected via a load cut-off valve 23 to a relay valve 24, the valve 23 being provided with a crush-loaded car reference spring 22. The signal applied to line 3 is an energizeapply signal but passage through circuit 9 converts it to an energize-to-release signal, as load increases the current applied to converter 21 decreases to have the effect of increasing the brake forces but as a D.C. dynamic brake feedback signal in a line D.B. increases the current is supplemented to have the effect of reducing the brake forces. The release line 5 may be energized from the line 4 by means coupled to the driver's brake handle to effect release of the brake in circumstances where it is not releaseable by the control line 3: an audible or visible warning to the driver is given. Should a fault develop which stops the analogue blending unit 1 producing brake release the absence of current in relay 19 operates relay contacts 20 and the release line 5 is directly connected to converter 21 to give brake release and isolates subsequent units on other cars of the train from the release line current. Fig. 6 shows the electropneumatic converter 21 in conjunction with the pressure transducer 15 connected to the air suspension, the load cutoff valve 23, the relay valve 24 and a combined strainer and check valve 42 with built-in isolating valve which is manually operable to isolate the unit from the main reservoir at 50 and vent the unit. The converter 21 consists a spring- mounted valve member 44 the thrust upon which towards its valve seat is adjustable by means of a current applied to a coil 45 of an armature mounted in the field of a magnetic yoke 46. The converter 21 has a small associated relay valve having a pressure responsive member 47 for operating a valve member 48 against the thrust of a bias spring 49. The relay valve relays pressure from a brake supply reservoir (charged from the main reservoir via the combined strainer and check valve) to the load cut-off valve 23, which permits a pressure dependent on the load to pass to relay valve 24. The cut-off valve 23 which is connected to the air suspension has pressure responsive members 51, 52, 53. The unit also includes a pressure limiting valve 56 and a filter 57.