An improved brake for relatively rotating first and second members of the type which includes a housing having a cylindrical portion and a backing plate, said cylindrical portion being secured to said backing plate and said backing plate being secured to said first member;
- a plurality of brake discs carried by said housing for relative rotation therewith and axial movement therein, a plurality of reaction plates carried by said second member for relative rotation therewith and axial movement thereon, said discs and said plates being intervened in alternating fashion to define a pack;
- said housing having a central bore defined by a radially, inwardly extending annular wall of said backing plate and an interior cylindrical surface of said cylindrical portion;
- a first piston having a tubular portion with a cylindrical outer surface and a radially, outwardly extending wall having an annular surface extending outwardly from said cylindrical outer surface, said first piston being axially, slidably mounted in said bore with said annular wall, said interior cylindrical surface, said exterior cylindrical surface and said annular surface defining a first expandable chamber between said bore and said first piston;
- a first generally U-shaped expandable seal in said first chamber being seated against said annular wall of said bore and having a pair of lips capable of respectively making sliding, sealing contact with said interior cylindrical surface and said exterior cylindrical surface;
- a second generally U-shaped expandable seal in said first chamber being seated against said annular surface of said first piston and having a pair of lips capable of respectively making sliding, sealing contact with said interior cylindrical surface and said exterior cylindrical surface;
- means for selectively introducing hydraulic fluid to and discharging said hydraulic fluid from an intermediate region of said first chamber between said first and said second seals, said hydraulic fluid being sealingly retained therein by said first and said second seals and capable of acting on said first piston for selective movement of said first piston axially relative to said bore;
- and said tubular portion of said first piston having an end remote from said annular wall of said bore including a radially inwardly extending shoulder which is aligned with said pack to provide compressive braking force thereto when said first piston is moved axially toward said pack by said introduction of said hydraulic fluid to said first chamber, said improvement comprising:
- said backing plate having an annular cavity therein open toward an interior of said housing, said cavity being defined by an inwardly facing cylindrical surface and an inwardly extending flange at an end thereof toward said interior of said housing;
- a second piston being axially, slidably mounted within said cavity and having an outwardly facing cylindrical surface and an outwardly extending flange thereof at an end thereof remote from said interior of said housing;
- said inwardly extending flange, said inwardly facing cylindrical surface, said outwardly facing cylindrical surface, and said outwardly extending flange defining a second expandable chamber between said cavity and said second piston;
- axially extending means on said second piston extending into said interior of said housing in alignment with said radially inwardly extending shoulder of said first piston;
- means for biasing said second piston toward said pack to cause said axially extending means to contact said radially inwardy extending shoulder which is capable of providing said compressive braking force to said pack;
- a third generally U-shaped expandable seal in said second chamber being seated against said inwardly extending flange of said backing plate, a fourth generally U-shaped expandable seal in said second chamber being seated against said outwardly extending flange of said second piston, said third and said fourth seals each having a pair of lips capable of respectively making sliding, sealing contact with said inwardly facing cylindrical surface and said outwardly facing cylindrical surface;
- means for the selective introduction of hydraulic fluid to and discharge of hydraulic fluid from said second chamber between said third and said fourth seals, said introduction of said hydraulic fluid being capable of axially moving said second piston away from said pack in opposition to said means for biasing;
- and
- said discharge to said hydraulic fluid allowing said means for biasing to produce said compressive braking force to said pack.