Adjustment means for double diaphragm spring brake chamber actuator

Claim 1

In a brake mechanism, a housing having side walls and having a rear wall with a substantially planar exterior surface, a diaphragm positioned within and peripherally held by said housing, air pressure inlet means in said housing communicating with one side of said diaphragm, a piston positioned in said housing on the opposite side of said diaphragm said piston being of suitable dimensions for reciprocating motion within said housing without engaging said side walls and having a generally conical, hollow hub extending away from said diaphragm, said piston including an annular rib disposed at the base of said hub, said housing having an inwardly-directed projection including a generally conical inner surface for receiving said hub, said projection extending inwardly of said housing from said rear wall a distance approximating the extension of said hub from said piston with the axial depth of said conical inner surface being greater than the extension of said hub beyond said annular rib, said projection being of such other dimensions as to engage said annular rib without engaging any part of said hub when said hub is received within said projection and the axes of said conical hub and said conical inner surface are colinear, whereby an unobstructed air passage about the entire surface of said hub within said projection is provided, spring means in said housing for normally urging said piston and diaphragm in a brake operating direction, limiting means for limiting the travel of said piston in said brake operating direction in response to said spring means including a threaded rod, said threaded rod including threads along substantially its entire length and having a portion extending outwardly from said housing and a portion telescopically arranged within said hollow piston hub through a passage in said hub along an axis generally aligned with said brake operating direction, said passage in said hub being suitable for sliding motion of said rod therethrough, said threaded rod extending outwardly of said housing through a passage in said housing suitable for permitting sliding motion of said threaded rod therethrough, and said limiting means further including first means at one end of said rod within said hub and second means disposed along the length of said rod beyond the outer wall of said housing for limiting the piston travel to be generally equal to or less than the outwardlyextending and telescopically arranged threaded rod portions between said first and second means, said first means being effective to prevent complete rEmoval of said rod from said hub and cooperatively operating with the inner surface of said hub to prevent rotation of said threaded rod, said second means being of dimensions sufficient to prevent its movement through said passage in said housing such that said second means cooperatively operates with said threaded rod and said first means to change the limit of travel of said piston when said second means is manually rotated, said hub extending from said piston substantially less than the maximum travel of said piston such that said threaded rod extends substantially beyond said housing when said spring means is compressed, whereby said second means is maintained substantially in the plane of said exterior surface of said housing or outwardly of that plane at all positions of said piston, and cap means of dimensions sufficient to accommodate the maximum extension of said threaded rod beyond said exterior surface, and mounting means on said exterior surface for removably mounting said cap over said extending threaded rod portion.