Fail-safe speed control system for railroad trains

Claim 1

In a speed control system for trains moving over a stretch of track divided into sections at preselected wayside locations, each train being equipped for receiving and responding to speed command signals transmitted through the rails of said track, said system including a central control station within said stretch, the combination comprising, a. a track transmitter at each wayside location coupled to said rails for transmitting a distinct speed command signal to control approaching trains and a corresponding signal for train detection into the advance section, b. a track receiver at each wayside location coupled to said rails and responsive only to the detection signal transmitted by the track transmitter at the entrance end of the approach section for recording jointly a section nonoccupied indication and the corresponding speed command signal when a detection signal is received and a section occupied indication when the detection signal is absent, c. a communication system between said central station and each wayside location connected for selectively transmitting speed commands and occupancy indications between said station and said locations, d. a speed command generator at said central location for each wayside location selectively connected to said communication system for transmitting to the corresponding wayside track transmitter a speed command selected in accordance with advance traffic conditions, e. a speed command comparison unit at said central station for each wayside location selectively connected to said communication system for receiving the combined track occupancy and received speed command indication from the corresponding track receiver, 1. each speed command comparison unit also cross connected to the speed command generator for the first wayside location in aPproach for comparing the speed command transmitted to the approach location track transmitter with that received by the corresponding track receiver, f. a safety protection unit at said central station for each track section connected for receiving the occupancy indication from the speed command comparison unit associated with the exit end of the corresponding track section and interconnected with other safety protection units for establishing the advance traffic condition which determines the allowable speed command for a train in the approach section, 1. each speed command comparison unit delivering a nonoccupied indication for the approach track section to the associated safety protection unit when and only when the received speed command indication agrees with the speed command transmitted by the associated speed command generator to the entrance end track transmitter, g. a track relay associated with each safety protection unit and controlled by the associated speed command comparison unit to a first position or a second position as a section nonoccupied or occupied indication, respectively, is supplied to the associated safety protection unit, h. a first circuit at said central station for each track section including a first position contact of the corresponding track relay and interposed in the connections, between said communication system and the entrance end track transmitter, by which the selected speed commands are delivered to that track transmitter, and i. an alternate circuit for each track section including a second position contact of the corresponding track relay and connected for supplying only a restricted speed command direct to the entrance end track transmitter from the associated speed command generator so that a proceed speed command can not be supplied to a following train in the adjoining approach track section.