Patent GB-806823-A (GB)
Title: Improvements in or relating to railway classification systems
IPC: B61L17/02
Filed: 1957-02-19
Abstract: 806,823. Railway classification systems. GENERAL RAILWAY SIGNAL CO. Feb. 19, 1957 [March 29, 1956], No. 5595/57. Class 104 (1). [Also in Group XL (c)] In a railway vehicle classification system for distributing free rolling vehicles by gravity amongst a plurality of classification tracks, means are provided to detect the approach of a slowmoving vehicle and to divert such vehicle into a separate track clear of the classification tracks. A train of vehicles is pushed over the crest of a hump where they are uncoupled and allowed to roll in the direction of the classification tracks. Car retarders below the hump and at the branching tracks are provided with automatic control to ensure that the vehicles pass to their respective classification track at the desired coupling speeds. Slow-moving vehicles which are not likely to reach the classification track are diverted to a set-out track located along an approach track from the hump retarder by a switch actuated before the retarder below the hump is reached. A detector track circuit associated with the set-out track switch includes a relay 2TR which is normally energized when the track circuit is unoccupied and is de-energized and drops away when the detector track circuit is occupied. Before the set-out switch detector track circuit is another track circuit which has associated therewith a track relay 1TR. The de-energization of the relay 1TR determines the instant at which the vehicle speed is to be checked to determine whether it is above or below a preselected value. A directional antennµ 11 positioned between or alongside the rail track and associated with the detector track circuit including the relay 1TR is directed to transmit a beam of high-frequency energy towards the vehicle rolling down the hump. A transmitter receiver 10 supplies a high-frequency signal to this antenna 11 and receives the reflected signal received by the antenna 11 and reflected by a vehicle. The frequency of the reflected signal is, according to the Doppler principle, higher than the transmitted signal by an amount proportional to the vehicle speed. The transmitter-receiver 10 mixes the reflected signal with a portion of the originally transmitted frequency to provide a beat frequency, the frequency of which is directly proportional to the vehicle speed. This beat frequency is applied to a discriminator 12 which selectively controls relays Sand CK. The check relay CK is picked up when the beat frequency signal has an amplitude above a predetermined minimum value and this indicates the proper operation of the speed measuring apparatus. The relay S is selectively actuated in accordance with the vehicle speed so that the relay S is picked up if the beat frequency signal is above a predetermined value and is dropped if below this value. When a vehicle enters the track circuit associated with the relay 1TR this relay drops and at the same time the reflected signal received by the antenna 11 causes the check relay CK to be picked up. If the vehicle speed is below a predetermined value a circuit is completed from +ve, front contact 13 of relay CK, back coritact 14 of relay S, front contact 15 of detector track relay 2TR, back contact 16 of relay 1TR and winding of relay PR to - ve to pick up relay PR. When relay PR is picked up a hold circuit is completed from +ve front, contact 17 of relay 2TR, front contact 18 of relay PR and winding of relay PR to - ve to maintain this relay energized. A switch repeater relay RWP is energized when the switch points to the setout track are in the reverse position while the switch repeater relay NWP is energized when the switch points are in the normal open position. If the switch points are in the normal open position and relay RWP is dropped, the picking up of relay PR completes a circuit from +ve, front contact 19 of relay 2TR, front contact 20 of relay PR, back contact 21 to winding of relay RWR. Relay RWR is then energized to close the circuit from +ve to wire 23 in order to operate the set-out track switch point to the reverse position. Thus, a slow rolling vehicle having a speed below that effective to pick up relay S at the instant relay 1TR drops, results in relay PR being picked up to operate the reverse switch control relay RWR and the switch-machine 24 is thus operated to the reverse position. The track circuit including relay 1TR is made sufficiently long to ensure that there is sufficient time after relay 1TR drops for the set-out switch to operate to the reverse position before the vehicle occupies the set-out switch detector track circuit. If a vehicle at the instant of the dropping of relay 1TR had been travelling at a higher speed so that relay S was picked up the circuit for picking up relay PR would have been open because of the open back contact 14 of relay S and the reverse switch control relay RWR would not have been energized. When a slow rolling car enters the set-out switch detector track circuit the relay 2TR drops to open both the pick-up and hold circuits for relay PR at contacts 15 and 17. The relay PR now drops but a circuit cannot be completed to energize the normal switch control relay NWR through back contact 20 of relay PR since front contact 19 on relay 2TR is still open. As soon as the vehicle clears the detector track circuit so that relay 2TR is re-energized a circuit is completed through contacts 19 and 20 and the now closed back contact 25 of relay NWP and the winding of relay NWR to - ve to energize relay NWR so that energy is supplied through contact 26 and wire 27 to operate the switch-machine 24, thus moving the switch back to its original normal open position. An indicator lamp associated with relay RWP is provided to show an operator that a vehicle has been diverted to the set-out track. Speed measuring equipment other than the Doppler frequency shift radar type may be used.