Device for discontinuing and automatically restoring the operational function of a spring brake actuator

Claim 1

In a device for discontinuing and automatically restoring the operational function of a spring brake actuator with a spring compressed by fluid pressure in the brake system, preferably arranged in series with a service brake actuator and comprising a cylinder with a fluid pressure operated piston movable therein to operate a brake push rod and having a spring actuating the piston in an operation direction forward for brake application at the fall of fluid pressure acting on the piston, the combination comprising, a conveying mechanism carried by the push rod, which mechanism at the piston movement forward is arranged to convey the push rod but is disconnectable for making possible a return of the push rod alone when said fluid pressure falls and is arranged to return automatically to a position for again conveying the push rod after the fluid pressure returns, wherein the conveying mechanism consists of a nut in non-self-locking engagement with screw-threads on the push rod, a clutch movable with the piston for holding the nut from rotation, manually operable means extending external to said piston for disengaging the clutch until reengaged by movement of said piston when the fluid pressure returns the piston to its return position with brakes disengaged to thereby permit the nut to rotate in response to relative movement between said piston and said push rod thereby comprising means mechanically connected to said piston causing return movement by said piston automatically to rotate said nut with said clutch in disengaged position and including structure re-engaging said clutch to convey said push rod by rotating said nut under the influence of the forces transmitted by the moving piston to engage the clutch for a braking stroke when the fluid pressure moves said piston to the end of its return stroke said clutch comprising ratchet teeth on said nut and means engaging them, the nut being rotatably journalled in the piston and said means for disengaging the clutch comprises a control arm pivoted on the piston and held in engagement actuating the clutch and constituting a pawl mating with said ratchet teeth on the nut thereby registering with said control arm to engage said clutch, and having a manually accessible member for pivoting the control arm to release said clutch and permit said nut to rotate on said rod while out of engagement with said control arm in a direction otherwise held from rotation by said control arm.