Control valve for a vacuum brake booster

In a brake booster having a housing with a cavity therein, a wall located in said housing for dividing said cavity into first and second chambers, said wall having a hub member with a bore therein, said hub member having a first passage connected to said first chamber and separated from a second passage connected to said second chamber by an annular seat, a control valve located in said bore and selectively positionable in a rest position with respect to said annular seat to allow vacuum present in said first chamber to be freely communicated to said second chamber by way of said first and second passages and a portion of said bore and in an operational position with said annular seat to interrupt vacuum communication through said first passage and initiate communication of air from the surrounding environment by way of said bore and second passage to said second chamber to create an operational pressure differential across said wall, said operational pressure differential acting on said wall and overcoming a return spring to produce an output force in response to an input force, the improvement in said control valve comprising:

• a plunger located in said bore and having a cylindrical body with a shoulder located between a first end and a second end, and first end receiving a reaction force corresponding to said output force;
• a sleeve member concentric to said cylindrical body;
• a first resilient member acting on and urging said sleeve member toward said shoulder on said plunger;
• a poppet member located in said bore and having a first end secured to said hub and a second end free to move within said bore;
• an input member connected to said second end of said plunger;
• stop means located in said second passage having a first end and a second end, said first end engaging said sleeve;
• and
• second resilient means for urging said free end of said poppet member into engagement with said second end of said plunger in said rest position and into engagement with said annular seat during said operation position and on termination of said input force, said first resilient member and said reaction force acting on said shoulder and first end of said plunger, respectively, to move said second end of said plunger into engagement with said free end of said poppet member and said free end of the poppet member away from said annular seat to define a first gap between said free end and annular seat to allow said vacuum in said first chamber to evacuate air from said second chamber, said stop means moving in said second passage and engaging said hub to limit the movement of said sleeve within said bore by said first resilient means while said reaction force continues to move said plunger to establish said first gap, said first gap being sustained by the reaction force until said operational pressure differential and reaction force terminates, said air from the environment present in said bore and vacuum present in said portion of said bore creating a static pressure differential across said poppet member, static pressure differential producing a force that acts on said poppet member and plunger to thereafter move said plunger into engagement with said sleeve and thereby define said rest position for said control valve.