Master brake cylinder for two-circuit braking system

Claim 1

In a master brake cylinder for a first and second brake circuit forming a two circuit braking system including a housing; a brake fluid reservoir; a brake fluid pressure source; an auxiliary piston having a pedal-actuated side and which together with the housing defines a first main cylinder; a control piston sliding within the auxiliary piston; a brake control valve means; and a second main cylinder and piston for the second brake circuit having a control chamber, the brake control valve means including a portion being actuated by the control piston for establishing fluid communication between the brake fluid pressure source and the first brake circuit and the control chamber of the second main cylinder, the portion of said brake control valve means being exposed to the pressure in the first brake circuit and the control piston having means for engaging and carrying along the auxiliary piston after a predetermined amount of axial travel, the improvement comprising, auxiliary piston extension means for actuating said piston in said second main cylinder when said auxiliary piston and said control piston approach within a predetermined distance of said second main cylinder piston, wherein said auxiliary piston is exposed on the side remote from said pedal-actuated side to the pressure of the brake fluid pressure source, and wherein said portion of said brake control valve means is disposed within said auxiliary piston, secondary piston means and pin means sliding therein, said secondary piston means being exposed to the pressure in said second main cylinder and varying the extension of said pin means into said second main cylinder by sliding displacement with respect to said secondary piston means and further including electric switch means actuated by the relative approach of said pin means and said secondary piston means and wherein said piston in said second main cylinder has a tapered wall capable of displacing said pin means relative to said secondary piston means, thereby actuating said switch means when insufficient pressure exists in said second main cylinder for causing said secondary piston means and said pin means to move away from said tapered surface.