Air operated spring brake

Claim 1

In a spring brake assembly of the type that includes a housing defined by a generally cylindrical side wall and forward and rearward end pieces, a transverse pratition that divides the interior of said housing into first and second confined spaces, longitudinally aligned openings in said partition and forward end wall, a transverse resilient diaphragm in said first confined space that divides the latter into first and second compartments, a first transverse pressure plate in said first compartment bonded to said diaphragm, a push rod secured to said first pressure plate and extending therefrom through an opening in said forward end piece to actuate a brake on a wheel as said push rod moves from a first towards a second position, a source of compress air from which first and second conduits extend, means for controlling the flow of air from said source to said second compartment, first spring means in said first compartment that at all times tend to maintain said first pressure plate and push rod in a first position, a piston in said second confined space in slidable sealing contact with the interior of said housing, said piston dividing said second confined space into third and fourth compartments, the improvement for operating said spring brake assembly in such a manner that foreign material cannot enter said second, third or fourth compartments from the ambient atmosphere, and said spring brake assembly actuates said brake gradually to bring said wheel with which it is associated to a stop upon a failure of said source of compressed air, said improvement comprising: a. second spring means in said fourth compartment that is of greater strength than said first spring means; b. valve means in communication with said second conduit and said third compartment, said valve means allowing said compressed air to flow into said third compartment for said piston to move from a first to a second position and compress said second spring means, but said valve means upon a failure of said source of compressed air allowing air in said third compartment to escape therefrom at a modulated rate, with said rate determining the rapidity with which said push rod will move from said first towards said second position to apply an increasing force to said brake to tend to stop the rotation of said wheel; c. a second pressure plate in said second compartment; d. an elongate actuator extending from said piston through said opening in said partition and supporting said second pressure plate in said second compartment in a position to exert a force on said first pressure plate and push rod as said piston moves from said second towards said first position; e. first sealing means on said partition for slidably engaging said actuator and preventing the flow of air between said second and third compartments; f. air passage means that are at all times in communication with saiD fourth compartment, but which establish communication between said fourth compartment and said second compartment to equalize the air pressure therein only when there is a failure of said source of compressed air, and said piston moves from said second position towards said first position as said second spring means expand to move said actuator and second pressure plate from said first towards said second position to gradually set said brake; and g. manually operable means on said brake assembly that may be used to move said piston to said second position after said brake has been set after a failure of said source of compressed air, with said piston when moved to said second position concurrently moving said actuator and second pressure plate longitudinally in said housing to the extent that said first spring means returns said first pressure plate and push rod to said first position thereof.