Patent GB-1207721-A (GB)
Title: Automatic braking system and apparatus for use therein
IPC: G01S13/931
Filed: 1968-01-04
Abstract: 1,207,721. Vehicle control system. AMBAC INDUSTRIES Inc. 4 Jan., 1968 [5 Jan., 1967], No. 652/68. Heading B7N. [Also in Divisions F2 and H4] In an arrangement for braking a free running rail vehicle in a classification or hump yard to a speed at which it couples safely to a preceding vehicle in a classification siding, each vehicle is provided with a control system including an ultra-sonic, pulse reflection ranging apparatus whereby a vehicle is braked if (a) its speed is in excess of a set value e.g. 4 m.p.h.; (b) a signal from an object in advance is repeatedly received initially during a " late gate " period (range 25-60 ft.); and (c) the signal indicates that the object detected is closing at above a set rate. Alternator 52 coupled to vehicle wheel 50 provides via rectifier 54 a D.C. voltage for operation of the apparatus and an indication of the vehicle speed via ground speed sensor 55. The alternator is also associated with a direction sensor which via switch 67 ensures that only the leading one of the ranging equipments provided at each end of the vehicle is brought into operation. On decoupling of the vehicle from a train for classification the normal brake control system 80-is disabled and the brakes 72 are now operated by pressurized air from reservoir 100 only when a solenoid 101 is operated by the control system. When the speed of the free rolling vehicle exceeds 4 m.p.h., D.C. power is applied via pressure-operated switch 66 and speed operated switch 60 to the leading ranging and control apparatus. The P.R.F. of the ranging apparatus is determined by square wave oscillator 102 which is set at a value which allows the ultrasonic signals to be reflected from objects at a maximum range of 60 ft. The positive and negativegoing portions of the square wave output signal define " early " and " late " gate intervals to be referred to later. The leading edge of the positive-going portion of the signal triggers a monostable circuit 103 to provide a short-duration pulse which controls ultra-sonic oscillator 104. The U.S. pulse is amplified and applied via duplexer 106 to radiator 108, 109. The received pulses are applied via duplexer 106 and amplifier 110 to detector 118. The detected pulses are applied via a blanking circuit 120, which removes the initial pulse produced by the transmitter, to a Schmitt trigger circuit having a threshold such that only pulses in excess of a set amplitude are passed via amplifier 124 to differentiator 126. Pulses other than those occurring in the late gate interval (range 25-60 ft.) are excluded by gate 128 and the differentiated signal after clipping triggers a bistable circuit 132 which is then returned to its initial state by the following transmit trigger pulse. The bi-stable output pulse, having a width inversely proportional to range, then triggers a sawtooth generator providing pulses having an amplitude inversely proportional to range. These are applied to a sensor circuit 140 which supplies corresponding square wave output pulses only if the object is closing at. a predetermined rate. The pulses are applied via gate 142 to trigger a monostable circuit connected to an integrator and if the signal repeatedly occurs the integrator charges to a value above the threshold of the Schmitt trigger circuit and this supplies an output to coil 101 of the brake operation solenoid. If the output of the Schmitt trigger persists, hold circuit 152 comes into operation to ensure that the trigger supplies an output until the vehicle speed drops to a set value e.g. 3 m.p.h. when the speed sensor 55 switches off the D.C. supply to the apparatus and the brakes are released. Signals from buffer amplifier 124 are also applied to differentiator 160 and if these occur during the early gate interval (10-25 ft. they are clipped and trigger a bi-stable circuit 166 which is returned to its initial stateby the transmit-trigger pulse. The bi-stable circuit provides an output which shorts out the signals present in the sawtooth circuit 136 and sensor circuit 140 thus preventing the occurrence of a braking signal. However the hold circuit 152 prevents switch off of a brake signal produced by an object detected during the late gate interval which subsequently is detected during the early gate interval.