Railway car truck brake apparatus

Claim 1

A brake rigging for a four-wheel type of railway vehicle truck having a transverse axis and a longitudinal axis perpendicular thereto, which brake rigging comprises the combination of two brake beams extending in spaced substantially parallel relation to the transverse axis of the car truck and guidably supported at the ends thereof on the truck for bodily movement longitudinally of the truck, brakeshoe means carried inboard of and adjacent to each guidably supported end of each brake beam for causing a braking effect to be exerted on the corresponding wheel of the truck, a pair of brake cylinder casings each of which is secured to a corresponding one of said two brake beams inboard of one of said brakeshoe means on Opposite sides of and in symmetrically spaced relation to the longitudinal axis of the truck along the length of said corresponding brake beam, a piston operable in each said brake cylinder casing and having a lost-motion connection with one end of a piston rod that at its opposite end is anchored to the other of said two brake beams at corresponding opposite sides of and in symmetrically spaced relation to the longitudinal axis of the truck, each of said brake cylinder casings having a pressure chamber to which fluid under pressure may be supplied, wherein the improvement comprises: a. a double-acting slack adjuster mechanism interposed between and operatively connecting each respective piston and said one end of the corresponding piston rod, to form said lost-motion connection, each of said double-acting slack adjuster mechanism comprising: i. a double-clutch mechanism having: 1. a first clutch element constituting a brake rod having a pair of axially spaced clutch faces formed adjacent one end and being provided with external non-self-locking screw threads adjacent the other, 2. a second clutch element carried by said piston in coaxial relation to said first clutch element and having a pair of axially spaced clutch faces for respective cooperation with said clutch faces on said annular clutch element, 3. said piston rod constituting a nut member having internal non-self-locking screw threads engaging the external nonself-locking screw threads on said brake rod whereby said brake rod is rotatably mounted in said piston rod, ii. a first spring disposed between said piston and said brake rod for exerting a force in a brake applying direction on said brake rod via said first clutch element and said second clutch element independently of said piston, and being yieldable upon further movement of said piston in a brake applying direction, subsequent to movement of said brakeshoe means into braking contact with a corresponding pair of wheels of the truck, to provide disengagement of said first and second clutch elements and apply a force causing rotation in one direction of said first clutch element and brake rod relative to said piston rod to decrease the effective length of said piston rod, and iii. a pair of spring seats formed respectively on said piston rod and said brake rod, iv. a second spring having less strength than said first spring and being interposed and compressed between said pair of spring seats, and v. means including said second spring being effective upon movement of said piston in a brake releasing direction, subsequent to movement of said piston in a brake applying direction a distance greater than a chosen distance incidental to brakeshoe wear to disengage said first and said second clutch means to cause rotation of said first clutch element and brake rod in an opposite direction of said one direction relative to said piston rod to increase the effective length of said piston rod.