Brake pedal 1 is linked through tie-rod 2 to lever 3, the upper end of which is loosely fitted, with a large clearance, on pin A, and the lower end is linked to piston 4. Piston 4 reciprocates in vacuum cylinder 5. The position shown in Fig. a is the inoperative state of the mechanism, in which pusher a of the pedal does not contact the rod of piston 6 in hydraulic cylinder 7 and valve 8 connects vacuum cylinder 5 to the atmosphere. When pedal 1 is depressed (Fig. b), pusher a moves piston 6 to the right. At the same time, the upper end of lever 3 is moved to its opposite extreme position and valve 8 is closed. Further depression of pedal 1 produces the working pressure in main hydraulic cylinder 7, and hydraulic fluid under pressure is delivered through port d to the front wheel brakes and through port b to the rear wheel brakes. This pressure is intensified by the opening of vacuum valve 9, connected to the suction line of the engine. As a result, the vacuum is increased in the vacuum pump and piston 4 is moved to the right, turning lever 3 counterclockwise. Holding the pedal at any position maintains a constant braking force, because moving piston 4 of the vacuum cylinder moves the upper end of lever 3 to its central position with respect to pin A (see Fig. c). This closes both valves and the piston remains in an equilibrium position.
$4295$CHP,Br$