Hydraulic brake booster with tubular conduit return spring

Claim 1

In a hydraulic power brake booster having a housing, a bore formed in said housing and having a bore wall, a power piston reciprocably received in said bore and having a dynamic seal reciprocably sealing between said power piston and said bore wall, a power chamber in said bore defined in part by one side of said power piston, a brake fluid reservoir, control valve means in said housing adapted to control hydraulic booster actuating pressure to said power piston, a pump operatively receiving hydraulic fluid from said reservoir and operatively providing hydraulic fluid under pressure to said power chamber under control of said valve means, and connection means for connecting said booster to operatively pressurize at least one of a plurality of brake circuits, the improvement comprising: an annular conduit retainer mounted in said bore on the opposite side of said power piston from said power chamber and forming with said bore wall a first annular chamber about said retainer, first and second retainer seals respectively located on axially opposite sides of said first annular chamber and sealing between said retainer and said bore wall; said power piston having an extension extending axially through said annular conduit retainer and in reciprocable sealing relation therewith to define between said power piston and said annular conduit retainer a reservoir pressure chamber continuously fluid connected to said reservoir, said power piston extension also providing a booster output member; said power piston further having a recess therein defined by a side wall with a control valve reciprocably received therein and forming a part of said control valve means, a second annular chamber formed about said control valve with said side wall of said recess, and first and second control valve seals respectively located on axially opposite sides of said second annular chamber and reciprocably sealing between said control valve and said recess side wall, said first control valve seal being moveable axially into said second annular chamber upon actuating movement of said control valve in said power piston recess to fluidly connect said second annular chamber and said power chamber; said power piston having a third annular chamber formed in said power piston recess about said control valve with the edge of said third annular chamber nearer said power chamber forming a first valve portion; said control valve having a shoulder thereon positioned in said third annular chamber and having the outer edge thereof forming a second valve portion cooperating with said first valve portion to control hydraulic fluid exhaust from said power chamber with axial relative movements of said control valve and said power piston, a passage in said control valve opening at one end into said reservoir pressure chamber and also opening into said third annular chamber on the opposite side of said second valve portion from said power chamber, said passage providing an exhaust from said power chamber to said reservoir via said reservoir pressure chamber; and a resilient pressure hydraulic fluid conduit in said reservoir pressure chamber and having one end sealingly secured to said conduit retainer and continuously fluid connected within said conduit retainer to said first annular chamber, and having the other end sealingly secured to said power piston and continuously fluid connected within said power piston to said second annular chamber, so that no hydraulic pressure differential is exerted across said power piston and particularly across said power piston to said bore wall dynamic seal when said booster is not pressure actuated, said resilient pressure hydraulic fluid conduit also being a spring acting on said conduit retainer and said power piston to provide power piston return spring force continuously urging said power piston to the booster release position.