Patent GB-1197789-A (GB)
Title: Braking Systems for Vehicles.
IPC: B60T8/18
Filed: 1967-07-03
Abstract: 1,197,789. Brake alarm signals. WESTINGHOUSE AIR BRAKE CO. 3 July, 1967 [14 Sept., 1966], No. 30535/67. Heading B7N. [Also in Divisions F2, G1, H3] In a vehicle braking system where a command signal representing a desired braking level controls electronic circuitry to provide an actual braking level corresponding to the desired level, means are provided to detect any one of a plurality of malfunctions in the electronic circuitry and to apply the brake as a result thereof. In Fig. 1, a command signal for a railway brake is applied at 1 and after amplification at 3 is combined in a further amplifier 11 with a signal, derived at 5, representing the loading at each end of the vehicle. The output of amplifier 11 is applied in parallel to two further amplifiers 13, 14 in each of which it is combined with further signals representing the degree of dynamic braking and (from transducers TX, TY) the brake-cylinder pressure or the brake-shoe retarding force. The amplifiers 13, 14 (which saturate on small signals) give outputs which are the algebraic sums of their inputs, and the output will be positive or negative depending on whether less or more braking is called for. A negative output operates relays A1D, A2D which control further relays A1, A2, these in turn releasing normally operated electromagnetic valves A1X, A2Y and allowing air to flow from reservoirs MR to the brake cylinders BC. A positive output from amplifiers 13, 14 operates relays RID, R2D which control further relays R1, R2, these in turn operating electromagnetic valves R1X, R2Y to release air from the brake cylinders. Safety provisions.-Failure of electrical power will cause the valves A1X, A2Y to operate to pass air to the brake cylinders. The above-described release of valves A1X, A2Y and the operation of valves R1X, R2Y depends on closure of the lower contacts of relay EO. This relay is normally held on by latching contacts EO1 and conduction of transistor Q1, an indicator lamp LEO being simultaneously lit. The relay can be de-energized by a manualemergency switch PE or by cutting off of transistor Q1; after clearance of faults it can be reset by switch RST. Transistor Q1 will be cut off if transistor Q2 conducts as a result of conduction in any one of diodes AA-EE. Diodes AA and BB are sensitive to amplifiers 3 and 11 operating outside their normal ranges of voltage, detected by circuits A and B (Figs. 3 and 4, not shown). Diodes CC and DD conduct if relays A1 and A2 or R1 and R2 remain in a different state from one another for a longer time than necessary to charge the corresponding capacitor 28b. Diode FE conducts if switch LPS closes, indicating abnormally low air pressure in the main reservoirs. In addition, the brakes can be operated manually by moving switch 30 to the right, transferring control of valves A1X, R1X, A2Y, R2Y to auxiliary voltage sources Am and Rm. Modifications.-The amplifiers 3 and 5 may be replaced by a single parallel-fed stage feeding amplifiers 13 and 14 respectively through loadweighting potentiometers (Fig. 5, not shown). Since there is now one less phase-reversing stage, the A1 and A2 relays (now operated directly by the amplifier outputs) are connected to negative potential sources to be operated by positive output signals. Similarly the R1 and R2 relays are operated when the amplifier outputs go negative. The signals from the transducers TX and TY are applied via differentiating amplifiers to sharpen the response to change in air pressure and slow down the response as the correct point is reached, to prevent overshoot. In Fig. 6 (not shown) there is described a simpler system with only two input parameters, a command signal (at 50) and a signal from a transducer (53) fed back via a differentiating amplifier (52).