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 electric actuator having an electric motor operable to determine the output force generated on an output member by a spring; a drive shaft arranged to be driven by the electric motor and having first and second drive means, a non-rotational but axially movable intermediate member which is threadedly engaged with first driven means arranged to be driven by the first drive means; the spring being located between the intermediate member and the output member and arranged so that axial movement of the intermediate member is transmitted to the output member so long as the latter is free to move and, when the output member is restrained from movement, generates the output force on the output member upon continued operation of the electric motor; a stop carried by the intermediate member and positionally adjustable with respect thereto in the direction in which the intermediate member is axially movable, and second driven means with the second drive means, the first driven means being engageable with the stop to

Abstract: An electro-pneumatic brake system in which an electric brake demand signal controls the energization of a stepping motor. The shaft of the motor is threadedly engaged with a captive nut which bears against an abutment carried by a brake controlling valve, the opening of which determines brake actuating pressure downstream of the valve. Rotation of the motor therefore directly controls the brake pressure by movement of the valve.

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: An empty-load railway vehicle braking system wherein the piston-and-cylinder of the empty-load valve operates against the rack of a rack-and-pinion arrangement of which the pinion is drivingly connected to an arresting member the position of which is determined by the loading of the vehicle.

Abstract: An electric actuator having an electric motor operable to determine the output force generated on an output member by a spring system, and an adjustable stop by which can be limited the maximum value of the output force, the position of the adjustable stop being variable in accordance with variation of the required maximum value of the output force to be exerted by the output member.

Abstract: A piston sealing arrangement particularly for pistons used in railway brake cylinders, comprising a flexible piston seal and a multi-function ring in the form of a separate wear band. The wear band is allocated on the pressure side of the piston seal to minimize radial motion of the sealing ring if the piston rocks.In FIG. 1 is shown a pneumatic brake cylinder 10 in which is located a piston 11. Piston 11 has an external flange 14 which backs a piston seal 15. Located on the pressure side of the piston seal 15 is a wear band 16 which is located very close to the piston seal 15 on the pressure side. The rubber piston seal 15, has a sealing lip 18 in contact with the inner wall of the cylinder 10.The wear band is chamfered at 19 so that the portion 20 of the wear band closest to the sealing ring 15 is the part of the wear band that actually contacts the inner wall of the cylinder.

Abstract: An interlocking system comprising a plurality, e.g., three, of parallel sub-systems operating asynchronously to produce identical replicated outputs which are mutually compared to determine the correct output and disqualifying a minority output thereby ensuring high system integrity. Each sub-system includes a similar arrangement for computing the difference between all possible pairs of sub-systems. Comparison of these results with a reference table of all possible difference results and then comparison of the difference equations yields a common factor which is the sub-system producing the error. Action can then be taken to disqualify its output, e.g., by switching-off its power supply. A final output is taken, preferably from one sub-system, with a second as standby.

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: 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.