Railway switches and signals – Block-signal systems – Automatic
Patent
1992-04-29
1993-09-07
Werner, Frank E.
Railway switches and signals
Block-signal systems
Automatic
246187R, 246194, B61L 1304, B61L 2922
Patent
active
052421368
DESCRIPTION:
BRIEF SUMMARY
This invention relates to railway signalling systems and specifically to the detection of a train within a defined section of track by means of track circuit apparatus utilizing the rails within the section as part of the track circuit.
Such track circuits detect the presence of trains in a track section by detecting the change in the shunt impedance between the running rails of the track circuit. When a train enters the sections, the wheels and axles of the train present a low impedance, henceforth called the train shunt impedance, between the rails and in parallel with the existing shunt resistance formed by the track ballast, henceforth called the ballast resistance. This is illustrated in the accompanying FIGS. 1a and 1b.
FIG. 1a shows a track section defined by insulated joints X at the ends of rails 1 and 2. A source of electricity diagrammatically represented by battery 3 is connected across the rails 1 and 2 at one end of the section and a detector 4 is connected across the rails at the other end of the section to complete the track circuit through the rails. In the condition shown in FIG. 1a the detector 4 would register the voltage applied across the rails, less any losses along the track section through ballast resistance, hence indicating that there is no train in the section.
When a wheel/axle set 5 enters the track section as shown in FIG. 1b and provided that the wheel/axle set 5 makes good electrical contact with the rails 1 and 2, the voltage at the detector 4 falls nearly to zero as a result of the low train shunt impedance. This condition of the track circuit is interpreted as track section occupied by the signalling system.
Present day railway signalling depends on reliable detection of the occupancy of track sections. Decisions made by signalmen or signalling equipment as a result of faulty detection could lead to unsafe situations developing.
The reliable operation of the track circuit depends upon good electrical contact between the wheels and rails and good electrical conductivity of the wheel/axle set so that the train shunt resistance is low enough to provide in effect a short circuit between the rails. Under certain conditions however the rail-wheel-axle-wheel-rail circuit is not as good an electrical conductor as is required for reliable operation of the train detection circuitry. This is mainly caused by the growth of surface films, for example, rust films on the rails from place to place along the rails. This is particularly noticeable in the case of modern designs of multiple unit rolling stock.
The presence of a contaminant such as a rust film between the wheels and rails will form a layer of insulating and/or semiconducting material. To overcome the electrical barrier so formed there are two mechanisms which may be considered, namely: high voltage, and wheel/rail contacts to a working level where the electrical resistance is sufficiently low to permit the track circuit to operate satisfactorily.
It is already known to provide a so-called shunt assist circuit in order to overcome the aforesaid electrical barrier. One such circuit is described in an article entitled "Lightweight Vehicle Track Shunting" by Thomas K. Dyer, Inc. published in April 1981 by the U.S. Department of Commerce National Technical Information Service. In this article is described a shunt assist circuit comprising an excitation circuit which circulates a relatively high amperage 400 cps current from wheel to rail and back to wheel of a train unit. It is stated that this breaks down the rail-wheel resistance and improves the shunting by a wheel/axle set very effectively. The excitation circuit consists basically of a transformer, the turns of the transformer primary being wound around a first axle of a truck or bogie. The power is supplied to the transformer primary from a small on-board alternator. The secondary of the transformer comprises a single turn formed by said first axle a second axle of the train unit spaced from said first axle and the two rails between said first and second axles.
In order to
REFERENCES:
patent: 1302345 (1919-04-01), Finnigan
patent: 1822497 (1931-09-01), Loomis
patent: 2817012 (1957-12-01), Kendall
patent: 3270199 (1966-08-01), Smith
patent: 3387064 (1968-06-01), Joy et al.
patent: 3913874 (1975-10-01), Barpal
patent: 4041448 (1977-08-01), Noens
patent: 4420133 (1983-12-01), Dietrich
patent: 4720067 (1988-01-01), Jaeger
patent: 5170970 (1992-12-01), Ballinger
Thomas K. Dyer, Inc., "Lightweight Vehicle Track Shunting", published in Apr. 1981, by the U.S. Department of Commerce National Technical Information Service, see pp. 33 to 35 Modifications to the Rail Vehicle.
Cribbens Alan H.
Sutton Malcolm S.
British Railways Board
Lowe Scott L.
Werner Frank E.
LandOfFree
Railway signalling systems does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Railway signalling systems, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Railway signalling systems will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-482140