Railway service and parking brake actuator

A brake actuator for a railway brake to provide both service and parking braking, comprising

• a cylinder having a cylindrical operating cavity with open and closed ends,
• a cylindrical piston assembly extending through the open end of the cylinder into sealing engagement with the cavity and having a reaction surface adjacent the cylinder closed end, a stepped bore including a second and a smaller third cavities,
• means connecting the actuator to the brake such that extension of the piston from the cylinder applies the brake and retraction of the piston within the cylinder releases the brake,
• a first hydraulic supply for admitting pressurized hydraulic fluid through the cylinder into the operating cavity between the closed end thereof and the piston assembly reaction surface to exert a first hydraulic extension force which extends the piston assembly and applies the brake to provide a service brake,
• first spring means exerting a retracting force smaller than the hydraulic extension force on the piston assembly,
• a hollow parking brake piston having an inner surface and a cylindrical outer surface sealingly received within the second cavity,
• a second hydraulic supply for admitting pressurized hydraulic fluid through the piston assembly into the second cavity to extend the parking brake piston to react against the cylinder closed end to extend the piston assembly with a second hydraulic extension force and apply the brake to provide a parking brake,
• a mechanical lock for locking the parking brake piston to maintain the parking brake applied upon removal of hydraulic pressure, comprising
• a carrier member attached to the piston assembly for movement therewith and located within the second cavity,
• a plurality of circumferentially-spaced ramps formed on the carrier member and tapered inwardly toward the direction of parking brake piston extension,
• a rotary locking member wedged between the parking brake piston inner surface and each ramp, and
• second spring means biasing the rotary locking members into wedged position to lock the parking brake piston against retraction but permit its extension,
• a third hydraulic supply for admitting pressurized hydraulic fluid through the piston assembly to the third cavity, and
• an unlocking member including an operating piston sealingly received in the third cavity and responsive to pressurized hydraulic fluid to force the rotary locking members out of wedged position which unlocks the piston and enables retraction of the parking brake piston within the piston assembly.

A brake actuator for operating a railway brake to provide both service and parking braking, comprising

• a cylinder having an operating cavity with open and closed ends,
• a piston assembly extending through the open end into the cavity and having a reaction surface adjacent the cylinder closed end,
• means connecting the actuator to the brake such that extension of the piston from the cylinder applies the brake and retraction of the piston within the cylinder releases the brake,
• a first hydraulic supply for admitting pressurized hydraulic fluid into the operating cavity between the closed end and the reaction surface to exert a first hydraulic extension force which extends the piston assembly and applies the brake to provide a service brake,
• spring means exerting a retracting force smaller than the hydraulic force on the piston assembly,
• a second cavity formed in the piston assembly,
• a parking brake piston received within the second cavity, a second hydraulic supply for admitting pressurized hydraulic fluid into the second cavity to extend the parking brake piston which extends the piston assembly with a second hydraulic extension force and applies the brake to provide a parking brake,
• a mechanical lock for locking the parking brake piston extended to maintain the parking brake applied upon removal of hydraulic pressure, and
• unlocking means for unlocking the parking brake piston which enables the spring means to retract the piston assembly and release the parking brake.

A parking brake actuator having a cylinder, a piston carried by the cylinder, a hydraulic supply for admitting pressurized hydraulic fluid to the cylinder to extend the piston from the cylinder to apply a parking brake, spring means for retracting the piston within the cylinder upon removal of hydraulic pressure to release the parking brake, a mechanical lock for locking the piston in extended position to maintain the parking brake applied upon removal of hydraulic pressure, and unlocking means for disabling the mechanical lock to unlock the piston and enable retraction of the piston, characterized by the mechanical lock comprising

• an inner cylindrical surface carried by the piston,
• a carrier member carried within the piston and attached to the cylinder for movement therewith,
• a ramp formed on the carrier member and tapered inwardly toward the direction of extension,
• a rotary locking member wedged between the piston inner cylindrical surface and the ramp, and
• second spring means biasing the rotary locking member into wedged position to prevent retraction of the piston but permit its extension, and further characterized by the unlocking means comprising
• an unlocking member movable relative to the carrier member to move the rotary locking member out of wedged position, and
• second hydraulic supply means for supplying pressurized hydraulic fluid to cause the unlocking member to force the rotary locking member out of wedged position which enables the first spring means to retract the piston to release the brake.