Patent GB-1186136-A (GB)
Title: Dual Master Cylinder.
IPC: B60T11/20
Filed: 1968-10-16
Abstract: 1,186,136. Brake master cylinders. FORD MOTOR CO. Ltd. 16 Oct., 1968 [17 Oct., 1967], No. 49078/68. Heading F2F. A master cylinder has a first pressure chamber defined in part by a first piston, and a second pressure chamber defined in part by a second piston, one of the pistons being formed with an axially-extending stem portion, the other of the pistons being formed with an axial recess receiving the stem portion, and spring means being positioned along the stem portion and caged within the axial recess, the spring means biasing the first and second pistons into an axially normal relative position, and the pistons being movable to increase and decrease the axial lengths of the chambers. As shown, the first pressure chamber is constituted by the chamber 26, Fig. 1, defined by part of a bore 21, the end 24 of the bore, and the first piston 22; it communicates at 35, 38 with the front wheel brakes of the vehicle. The second pressure chamber 28, is defined by part of a larger bore 18, the first piston 22, and the second piston 19; it communicates with the rear wheel brakes at 39, 41, 42. The first piston 22 has an axially-extending stem portion 44 carrying a lock nut 47 and located within a recess 48 provided in the second piston 19. The distance between the inner face of lock nut 47 and shoulder 46 (see Fig. 3) of the first piston 22 is equal to the distance between a shoulder 51 (see Fig. 3) in the recess 48 and a snap ring 49 inserted near the outer end of the recess 48. Thus, in the normal position, Fig. 1 (brakes not applied), a cup-shaped washer 53 abuts shoulder 46 and snap ring 49, while another cup-shaped washer 54 abuts lock nut 47 and shoulder 51, these washers being held apart by a compression spring 52. A front reservoir chamber 12 communicates with the first pressure chamber 26 by passage 33, orifice 34, and normally open plunger valve 59, while a rear reservoir chamber 13 communicates with the second pressure chamber 28 by port 36. In operation, the piston assembly is moved to the left by a push rod (not shown) located in a blind bore 66 of piston 19 and connected to the brake pedal. Relative to each other, the pistons are maintained in their positions by the spring 52, except that the spring yields sufficiently to compensate for imbalance of pressures in chambers 26, 28, when necessary. As soon as the pistons move, port 36 is covered by piston seal 29, and the increased pressure in chamber 26 causes closing of orifice 34 by valve 59. Should an hydraulic line failure occur in the primary portion of the split system during braking, the pressure in the secondary chamber 28 will overcome the forces of the springs 52 and 56 and move piston 22 leftwardly relative to piston 19 until cup washers 53 and 54 are brought together and against snap ring 49 by nut 47, as shown in Fig. 3. Should an hydraulic line failure occur in the secondary portion, the pressure in primary chamber 26 and the push rod force acting on piston 19 will cause piston 22 to move rightwardly relative to piston 19 until cup washers 53 and 54 are compressed between shoulders 46 and 51, (Fig. 2, not shown).