Abstract: A railway signalling system includes a plurality of trackside equipments (11,12) and means (1,2,3,4,6, 15,16) for transmitting control information to the equipments and receiving status information therefrom, each of the trackside equipments being provided with a respective microprocessor (13 or 14) via which such control information is transmitted from the said means to the equipment and via which such status information is received by said means from the equipment.

Abstract: A circuit arrangement for providing in a fail-safe manner an alternating output signal to a load, e.g. in a railway signalling system. The load is connected across a first winding of a transformer, to opposite ends of a second winding of which transformer is connected a bi-directional current switching circuit. First and second modulated signal sources are connected to the bi-directional switching circuit. Each of the signal sources modulates a carrier signal with a modulation signal, the outputs of the signal sources being out of phase with respect to each other. The bi-directional switching circuit is operative to switch current through the second winding alternately in opposite directions at the frequency of the modulation signal. The circuit arrangement is such that if any of its components fails to operate correctly, the output appearing across the first winding is no greater than a threshold level.

Abstract: In a railway vehicle safety system, a frequency modulated signal is transmitted to a vehicle informing, inter alia, of a safe maximum speed, the said speed being represented by the carrier modulation frequency. In addition, the frequency of the carrier may possess one of a number of alternative frequencies. Apparatus for analysing received signals to identify the carrier frequency and the modulation frequency employs a fast Fourier transform processor. In order to save computation time by eliminating useless calculations, a received signal is heterodyned by a local signal selected according to the carrier frequency identified and the base-band components are analysed to identify the modulation frequency.

Abstract: A contact arrangement for a semiconductor device (typically a GTO thyristor), in which a disc-shaped first connector electrically connects one region of the semiconductor element with its associated contact. The first connector having therein apertures through which pass resiliently-loaded electrical connections to a second region of the element, the surface of that second region lying below the surface(s) of the first region. The various parts of the device may be so shaped as to ensure correct relative positioning of the parts during assembly and the maintenance of that positioning during subsequent handling.

Abstract: A brake control system for a multiple unit train of mixed motor cars and trailer cars--of the type usually to be found operating as metro or mass transit trains--and in which the motor cars have dynamic brakes operation of which is blended with, but given preference over, the friction brakes of all units. A brake demand signal calling for a given level of train retardation is weighted on each vehicle, according to the load of the vehicle, and the level of dynamic braking effort invoked on each motor car is limited in accordance with a maximum adhesion level calculated n proportion to the measured load of that car. In a modified arrangement the adhesion level is calculated in accordance with the load of the lightest loaded motor car. Signals representing the amount of dynamic brake effort achieved by each motor car is supplied to a trailer car and subtracted from the load weighted braking effort for the trailer car and the result used to actuate the friction brakes of the trailer.

Abstract: An electrically-controlled force-exerting actuator comprising a force-applying power spring arranged to exert a force on an output member, a force-applying control spring arranged with respect to the power spring such that the force exerted by the control spring is detracted from the force exerted by the power spring to determine the residual force exerted on the output member by the power spring, and an electric motor operable to vary the detractive force exerted by the control spring.

Abstract: An F.M. demodulator of the phase quadrature type is adapted for fail-safe operation and in particular for use in a railway signalling system. A Bessel band-pass filter is chosen for the design basis of the phase delay arm, its characteristics, failure modes and resulting effects are considered and the design adaptations required to avoid the potentially unsafe effects of failures are determined. Due to loss of failure in the unmodified filter design the slope of the phase characteristic can increase effectively broadening the filter bandwidth and reducing attenuation of out-of-band signals which could, as a result, provide a false output. The demodulator may be combined with a fiber-optic link to form part of a complete signaling transmission system.

Abstract: An arrangement for checking the integrity and operability of a semiconductive device including a control circuit for injecting test signals into a normal control signal to induce a momentary change of the operating condition of the semiconductive device, a sensing circuit connected in parallel with the semiconductive device sensitive to an induced change to produce an output indicating the induced change, and a correlation circuit operative to correlate the test pulses with the sensed response which is arranged to carry out predetermined action in the event that the correlation circuit determines a state of inoperability of the semiconductive device.

Abstract: A railway signalling receiver in which a signal carried by the railway lines is sensed and the sensed signal is sampled, digitized and subjected to a discrete Fourier transform operation which transform the time domain samples into the frequency domain. The frequency content of the signal may then be examined in order to identify the original signal or to decode the information carried. The signal may be a frequency shift keyed carrier signal. A technique of maintaining the safety of the system by discriminating against potentially confusingly similar ASK signals, which can arise spontaneously in electric traction territories, is described. A technique of digitally heterodyning down a carrier signal so that the transform operates on the lower sidebands frequencies in order to maximize efficiency of the transform calculations is also described. The receiver is useful as a jointless track circuit receiver and also in a part of the train borne equipment of an automatic train protection system.

Abstract: Vital transmission checking apparatus is disclosed for a communication channel which transmits quasi-static signals representing several alternative states of a function, e.g., the control function for a signal in a railway control system, one of which states is potentially unsafe. Each function channel transmits a digital signature code of predetermined length which is continuously repeated in a selected form, e.g., non-inverted, inverted, or alternately inverted and non-inverted, to represent the different states of the function. To provide a check of proper transmission, the repeated signature code is periodically corrupted in accordance with a predetermined error pattern which is repeated at a lower repition frequency than the code. The channel receiver is so designed that its output can only be held in the selected state when both the signature code and the error pattern in the received signal are correct. If a fault is detected, the receiver output is shifted to the most safe state of the function.

Abstract: This invention relates to a valve assembly for a railway braking system, including a brake cylinder pressure-maintaining valve which, during brake application, takes air from the brake pipe and feeds it into the brake cylinder until it reaches minimum brake pressure. To avoid the need for an extra valve, the brake cylinder pressure-maintaining valve is used as a quick service bulb exhaust valve during brake release and member are provided to ensure that the brake cylinder pressure maintaining valve opens immediately on brake release. Once the brakes have been applied, pressure in the brake cylinder is maintained from the quick service bulb 59. Brake cylinder exhaust pressure taken from a point 124 after the brake cylinder exhaust valve 50, but before the brake cylinder exhaust choke 70, is directed to chamber G above the inshot and brake cylinder-maintaining valve diaphragm 131. Since the pressure in port 124 upstream of the brake cylinder exhaust choke 70 attains a pressure well within 10 p.s.i.

Abstract: This invention relates to a railway braking system in which a drop in brake pipe pressure calling for brake application initiates a pilot pressure and this pilot pressure is used to operate other valves pneumatically to effect braking. In this system, during the initial part of a brake application, air flows to atmosphere through a pilot exhaust choke. To avoid problems during release of the braking, it is proposed to isolate or restrict this pilot exhaust choke during at least the initial part of the brake application stage. To achieve this, an interlock valve is introduced into a passage between a release ball valve and a pilot exhaust choke. The interlock valve is operated by a diaphragm biassed by a spring and separating two chambers. Brake pipe pressure is applied to the first chamber and auxiliary reservoir pressure to the second chamber. A very small drop in brake pipe pressure closes the valve and cuts off connection between the release ball valve and the pilot exhaust choke.

Abstract: A contact shim for insertion between an electrode internal contact member and a contact surface of a semiconductor element in a semiconductor device assembly. The shim has a generally continuous body (2) provided with a number of apertures (4, 5, 6, 7) having a land (1) or finger extending at least partially thereacross, preferably a land comprises a bar which bisects an aperture (4, 5, 6, 7). The apertures and bisecting lands may be used as visual guides in aligning the shim with reference marks on the contact surface of the semiconductor element and, the means of attaching the shim to the element may be applied to the lands in order that any distortion consequent upon attachment is confined to the lands leaving the body of the shim undistorted.

Abstract: Scraper rings are known which are mounted in the back plate of a hydraulic cylinder to scrape a hydraulic piston rod. Known scrapers are not very suitable for applications where the piston rod is liable to movement and vibration e.g. in pneumatic pistons and cylinders. The present invention provides a shaft scraper ring arrangement in which the scraper ring is so supported so as to be movable, to a limited extent, in a plane transverse to the shaft or rod which is to be scraped. Cylinder 1 contains a piston 2 and a back plate 3. Supported centrally in the back plate 3 is a housing 4 which supports a plate 5 carrying a rod scraper 5a. Piston 2 is supported by a piston rod 2a which is scraped by the rod scraper. A seal 10 located on the rod scraper plate 5 bears against the rod 2a. Rod scraper plate 5 has limited freedom for movement in a plane transverse to the rod 2a. The plate 5 is loosely carried by the housing 4 being located between two felt oil retaining annular rings 8.

Abstract: A plug door for a vehicle, such as a railway carriage, is carried and driven by a swinging lever which has a sliding fulcrum mechanism the effect of which is to flatten the arc through which the door is carried. The edge of the door which trails in an opening movement is guided either by means of a relatively long pivot arm or by a curved or straight track. The alternative guide means give different trajectories to the leading edge of the door, the long pivot arm guide keeps the door closest to the side of the vehicle during opening. A duplicate swinging lever with sliding fulcrum mechanism as a guide for the trailing edge will move the door parallel to the side of the vehicle and the sliding fulcrums will substantially reduce the outward excursion. By mounting the driving swinging lever over-center, i.e. closer to the trailing edge of the door the plug action is provided for so that a closed door may be flush with the vehicle skin.

Abstract: When the forward load current through a thyristor is commutated it does not immediately recover its availability to block forward current flow due to re-applied forward voltage, the time taken for this blocking ability to return is known as the thyristor turn-off time. Hitherto a low valued current has been passed through the thyristor immediately after commutation in the reverse direction to achieve reduction of the turn-off time. The present invention operates to achieve a greater reduction of the turn-off time by passing a low-valued current through the thyristor in a forward direction immediately after commutation. Several alternative circuit arrangements and operating configurations for supplying the forward recovery current are described.

Abstract: A computer based railway interlocking control system, having triple parallel redundant control computers (FIG. 2) provides greater system reliability as compared to a single computer system. The railway traffic control devices, e.g. points and signals, are arranged to be controlled by signals in one of two possible steady states, the interlocking control means (30, 31, 32, FIG. 2) is arranged to produce control signals in the steady state for de-energized or "safe" device settings and in an alternating state for energized or potentially "unsafe" settings. The alternating control signals (33, 34, 35 or 38) must be converted to the corresponding steady state to operate the devices thus, the converting or restoring circuit discriminates against dormant wrong side failures, i.e. "unsafe" signals to increase the inherent safety of the system.

Abstract: The invention concerns an electrically assisted pneumatic train braking system. In a normal emergency/service pneumatic braking system a pneumatic pressure change must propagate along the train braking system from car to car. The present system includes two valves which are connected to each end of the brake pipe of each car, the first is responsive to a pressure change in the brake pipe to produce an electrical signal and the second being responsive to the electrical signal to produce a pressure change in the brake pipe. Thus, the propagation time for the whole braking system is reduced to little more than that for the total length of the couplings between cars.

Abstract: A slack adjuster for railway brakes has an input member to which a brake force is applied and an output member movable coaxially therewith, a coupling element via which a brake force is transmissible between the two members and which is positively engaged with one of the members via a cooperating helical engagement means and is engageable with the other member via clutching faces which are retained in force transmitting engagement by the reaction forces produced by the helical engagement means when a force is transmitted between the members for a brake application, the clutching faces being disengageable when such reaction forces are removed to permit relative rotation of the members and enable wear or slack in the brake rigging to be taken up.

Abstract: An electric actuator which comprises an electric motor operable to a varying degree correspondingly to cause a spring to generate on an output member an output force which varies in accordance with the varying degree of operation of the electric motor.