Parking brake assembly for railway vehicle brake system

A parking brake actuator for a railway vehicle brake rigging being in fluid communication with a fluid pressure carrying brake pipe of the railway vehicle, the brake rigging having at least a push rod mounted for movement therewithin, the push rod is responsive to a reduction of the fluid pressure in the brake pipe to move in a first direction causing the brake rigging to apply brakes and responsive to an increase of the fluid pressure in the brake pipe to move in an opposed second direction causing the brake rigging to release brakes, said parking brake actuator comprising:

• (a) a hollow housing engageable with a predetermined portion of the brake rigging, said housing having a first end and an opposed second end, said first end having means for mounting said parking brake actuator to a portion of the brake rigging, said second end having an opening axially formed therethrough;
• (b) a piston assembly mounted for a longitudinal movement within said housing and dividing said housing into a pressurized portion disposed intermediate said first end of said housing and a first end of said piston assembly and a non-pressurized portion disposed adjacent said second end of said housing;
• (c) a piston rod secured at a first end thereof to a second end of said piston assembly and capable of extending through said axial opening in said second end of said housing responsive to the supply of fluid pressure, said piston rod securable at a second end thereof to a first end of the push rod, whereby said piston rod and said piston assembly move longitudinally with the push rod in the first and second directions;
• (d) means for preventing rotation of said piston rod during its longitudinal movement within said housing;
• (e) a spring member disposed in said non-pressurized portion of said housing and caged between an inner surface of said second end of said housing and said second end of said piston assembly, said spring member being capable of exerting a force against said piston assembly upon release of said spring member responsive to a loss of the fluid pressure in said pressurized portion of said housing and causing said longitudinal movement of said piston assembly within said housing in the second direction to accordingly retract said piston rod thereinto;
• (f) a fluid communication means in fluid communication with said pressurized portion of said housing and with the brake pipe for supplying the fluid pressure to said parking brake actuator during brake application of the railway vehicle brake rigging resulting in said longitudinal movement of said piston assembly and said piston rod in the first direction and in compression of said spring member, said fluid communication means for evacuating the fluid pressure from said pressurized portion of said housing during brake release resulting in said longitudinal movement of said piston assembly and said piston rod in the second direction due to said force exerted by said released spring member;
• (g) a first elongated thread formed on at least a portion of said piston rod movable through said non-pressurized portion of said housing;
• (h) a ratchet mounted within said non-pressurized portion of said housing for rotation about a longitudinal axis of said piston rod;
• (i) an aperture axially formed through said ratchet;
• (j) a second thread formed on a surface of said axial aperture for operable engagement with said first thread;
• (k) a shaft mounted for rotation in a spaced relationship with said ratchet, wherein a rotational axis of said shaft is substantially parallel to a rotational axis of said ratchet, said shaft having a first end thereof disposed within said non-pressurized portion of said housing and having a second end thereof extending through an aperture formed through said second end of said housing past an outer surface thereof;
• and
• (l) a holding pawl disposed within said non-pressurized portion of said housing and secured to said shaft for rotation therewith, said holding pawl rotateable in a first rotational direction for engagement with said ratchet teeth when a first rotational force is applied to said second end of said shaft due to the fluid pressure in the brake pipe being reduced to a predetermined level, said engagement preventing movement of the push rod in the second direction, said holding pawl rotateable in a second rotational direction for disengaging said ratchet teeth and permitting the push rod to move in the second direction when a second rotational force is applied to at least one of said second end of said shaft and said holding pawl due to the increase of the fluid pressure in the brake pipe.