Brake apply and release mechanism

Claim 1

A parking and service brake comprising: a rotatable element to be braked and friction braking means for friction braking engagement therewith; a brake actuating and release mechanism; a selectively actuated master cylinder having a fluid pressurizing chamber and a fluid reservoir; a first fluid conduit fluidly connecting said master cylinder fluid reservoir and said brake actuating and release mechanism; a second fluid conduit fluidly connecting said master cylinder fluid pressurizing chamber and said brake actuating and release mechanism; said brake actuating and release mechanism including a housing having a cylinder bore therein, a fixed wall dividing said cylinder bore into first and second fluid pressure chambers, first and second pistons reciprocably received in said cylinder bore on opposite sides of said fixed wall and respectively defining movable end walls of said first and second chambers, said second piston operatively engaging said friction braking means to exert braking forces thereon as said second piston is urged in the brake applying direction away from said fixed wall, an axially movable push rod sealingly extending through an aperture in said fixed wall and engageable by said pistons to transmit forces only in compression between said pistons, a pre-loaded compression spring in said cylinder bore engaging said first piston and continually urging said first piston toward said push rod and said second piston, said spring exerting a brake apply force compressibly therethrough in one condition of operation, and first and second fluid passages in said housing respectively connecting with said first and second chambers and having a check valve therebetween permitting fluid flow and pressure communication only from said second fluid passage to said first fluid passage, said first passage having an outlet port fluidly connected with said first fluid conduit and a normally closed but selectively opened valve fluidly intermediate said outlet port and the connection of said first passage and said check valve, said second passage having a port fluidly connected with said second fluid conduit to receive fluid delivered under pressure from said master cylinder pressurizing chamber and deliver the same to said second fluid pressure chamber at desired brake actuating pressure levels when said master cylinder is actuated; said master cylinder also delivering fluid under pressure from said fluid pressurizing chamber to said second passage and through said check valve and said first passage to said first fluid pressure chamber to urge said first piston away from said fixed wall and compress said spring to store force therein, said check valve and said normally closed valve holding fluid pressure in said first fluid pressure chember and said first passage upon release of fluid pressure in said second fluid chamber and said second passage to keep force stored in said spring by compression thereof and to permit said second piston to move toward said fixed wall to release the brake; and means controlled independently of actuation of said master cylinder to open said normally closed valve to communicate said first fluid pressure chamber and said first passage to said reservoir through said first fluid conduit to release the pressurized fluid in said first fluid pressure chamber and said passage, thereby releasing the force stored in said spring to move said first piston against said push rod and to move said push rod against said second piston to exert the force released from said spring to cause said friction braking means to engage said rotatable element in friction braking relation, said check valve acting when said normally closed valve is open and fluid pressure is being delivered to said second passage to permit fluid flow therethrough from said second passage into said first passage and thence through said open normally closed valve and said first fluid conduit to said fluid reservoir to return any fluid displaced through said second passage under these conditions to said fluid reservoir.