Tandem master cylinder

Claim 1

In a tandem master cylinder for a split brake system including: a housing having a main bore; a primary piston slidably disposed in said main bore and having a secondary bore coaxial with said main bore; a secondary piston slidably disposed in said secondary bore and cooperative with said secondary bore to form a first pressure chamber situated on one axial side of said secondary piston and also cooperative with said main bore and a part of said secondary bore to form a second pressure chamber situated on the other axial side of said secondary piston, said secondary piston being responsive to the pressure difference between said first and second pressure chambers and movable to reduce said pressure difference; a spring disposed within said first pressure chamber for urging said secondary piston to a set position; a return spring disposed within said second pressure chamber for urging said primary piston to a rest position; first conduit means for selectively hydraulically connecting said first and second chambers to two independent hydraulic sources respectively in accordance with the position of said primary piston; second conduit means for separately discharging therethrough the hydraulic pressures developed in said first and second pressure chambers; and limiting means for limiting the movement of said secondary piston away from said set position thereof within a predetermined range; the improvement comprising: said secondary piston being in the form of a spool to have an annular recess intermediate between the axial ends thereof; and said first conduit means including first and second passageway arrangements which respectively establish communication between said hydraulic sources and said first and second pressure chambers upon quick return of said primary piston to said rest position; said first passageway arrangement including a first port inlet formed in said housing and constantly in hydraulic communication with one of said hydraulic sources, an annular chamber defined between said secondary bore and said annular recess formed in said secondary piston and constantly in hydraulic communication with said first port inlet, a plurality of apertures formed in said secondary piston for selectively providing communication between said annular chamber and said first pressure chamber, and an annular seal mounted on said secondary piston and operatively connected to said apertures, said annular seal being adapted to regulate selective communication from said annular chamber to said first pressure chamber through said apertures in response to the pressure difference between said annular chamber and said first pressure chamber; and said second passageway arrangement including a second port inlet formed in said housing and constantly in hydraulic communication with the other of said hydraulic sources, a plurality of openings formed in said housing for selectively providing communication between said second port inlet and said second pressure chamber, and an annular seal mounted on said housing and operatively connected to said openings, said second named annular seal being adapted to regulate selective communication from said second port inlet to said second pressure chamber through said openings in response to the pressure difference between said second port inlet and said second pressure chamber.