Abstract: A slack adjuster has a non-rotatable fast-threaded output member (19) threadedly engaged by a pair of nuts (20, 21), one of the nuts being a first brake-force-transmitting nut (20) clutchable to prevent rotation thereof and the other being a second adjustment nut (21) clutchable to land. Relative axial movement of these nuts relative to the output member (19) is a measure of "excessive" brake clearance and restoration of the normal spacing between these nuts serves to restore brake clearance to "normal". The nuts (20, 21) are housed in a housing (8) which is non-rotatable but axially movable with respect to the output member (19). The first nut (20) is clutchable to a thrust member (26) resiliently loaded with a force which is overcome only by forces of the magnitude of braking forces transmitted through the slack adjuster.

Abstract: A tread-brake unit copmrises, as a unitary structure, a brake shoe (300) for engaging a vehicle wheel tread, a brake actuator (100) having an output member (19) via which the brake shoe (300) can, firstly, be moved into engagement with the wheel tread and, thereafter, a braking force generated by the actuator (100) can be transmitted to the brake shoe (300), and a slack adjuster (200) by which clearance between the brake shoe (300) and the wheel tread, in the "released" condition of the unit, can be maintained substantially constant. The slack adjuster (200) has a pair of fast-threaded units (20,21), each nut being threadedly engaged with and rotatable on the output member (19) of the actuator (100).

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: A force-applying system is provided which combines a first direct electric actuator and a second, electrically controlled spring-applied actuator. The output force-applying member of the second actuator is operable through a force-transfer device one member of which is operatively loaded by the force-applying spring of the second actuator and another member of which is controlled by a solenoid. The operation is such that when the solenoid is energized, the members are out of engagement and when the solenoid is de-energized, the two members are engaged so as to operatively connect the spring to the output member. The solenoid and the electric motor of the direct actuator are controlled through an electrical circuit which ensures that the electric motor of the direct actuator is de-energized when the solenoid is de-energized.

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 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: 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.

Abstract: The present invention provides an electric actuator having an output member movable from a first variable position to a second variable position; an electric motor operable to control a spring system to exert an output force on the output member when in its second position; a device for generating an electrical signal when the output member is about to leave the second position as it returns to the first position; and a motor-control electrical circuit which recognizes the generation of the electrical signal and thereafter operates the electric motor to a pre-determined degree to move the output member a corresponding pre-determined distance back to the first position so that there is preserved a substantially constant distance between the first and second positions.

Abstract: An electric actuator having an output member movable into and out of a force-exerting position, electric motor means operable both to move the output member to and from its force-exerting position and, when the output member is in that position, to control a spring system to generate a required output force on the output member, and means for withholding the spring system from generating a force on the output member until the output member is determined as being in its force-exerting position.

Abstract: An electric actuator having an electric motor operable to control the output force generated by a spring system of the actuator on an output member of the actuator; measuring means responsive to a characteristic of the spring system which is indicative of the value of the output force; and an electrical circuit by which operation of the electric motor can be initiated and can be terminated when the measuring means detects the characteristic as being indicative of the output force of a required value.

Abstract: A railway vehicle braking system is provided with a "snow brake" control arrangement which is used in freezing temperatures to apply a small brake force for prolonged periods to engage blocks or shoes on the vehicle wheels to reduce icing. The "snow brake" control arrangement itself includes an pneumatic valve system that includes a relay valve unit which, in a first mode, provides "snow brake" operation and, in a second mode, provides for application of brake pressure from the straight air pipe to the brake cylinders. A solenoid valve, actuated responsive to energization of a control solenoid by a snow brake control switch, controls connection of "snow brake" pressure from a supply reservoir to a control chamber of the relay valve. When the straight air pipe is pressurized responsive to call for service or emergency braking, the solenoid is de-energized and the control chamber vents to atmosphere through the solenoid valve.

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 continuous quick service valve arrangement for a direct release brake control system is provided with a sensing valve responsive to reductions of brake pipe pressure in relation to a reference pressure to apply fluid under pressure via a choke to a pulsating device which operates a quick service valve to drive pulses of air out of the brake pipe for as long as the brake pipe pressure continues to reduce for a brake application, the pulsating device is operated by a biassed member which when operated by being displaced in response to attainment of a certain pressure in a volume supplied by the sensing valve presents a greater area to the volume and opens a discharge path for the volume to permit the member to repetitively operate and reset.

Abstract: A piston-cylinder arrangement comprising a cylinder member and piston means mounted slideably therein, the piston means comprising a piston member and a packing member mounted on the piston member for movement therewith, wherein said packing member has first and second axially spaced radially outer surfaces dimensioned such that each contacts slidingly against said cylinder wall and wherein the piston means comprises a lubricant reservoir in communication with the space between said surfaces, which space is substantially closed by said cylinder wall.

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.