Patent GB-1333050-A (GB)
Title: Boosted hydraulic braking systems
IPC: B60T13/14
Filed: 1969-12-19
Abstract: 1333050 Master cylinders; full power systems CLAYTON DEWANDRE CO Ltd 15 Dec 1970 [19 Dec 1969] 62006/69 Heading F2F A vehicle brake hydraulic control system includes a pedal operated master cylinder 1 and actuation of the piston 12 thereof causes a valve 19 to open and to admit hydraulic pressure to an outlet port 23 and also to a servo cylinder 8 to actuate a servo piston 9; a supplementary hydraulic cylinder 4 includes a piston 5 operable by the servo piston 9 and also responsive to the pressure generated by the master cylinder 1 and the output of the cylinder 4 is delivered from an outlet port 6 and in the event of loss of servo power the fluid delivered by the master cylinder 1 by-passes the piston 5 and flows directly to the port 6. As particularly described, the port 23 communicates with the rear brakes and the port 6 communicates with the front brakes of the vehicle. As shown in Fig. 1 the valve 19 is opened by movement of a control piston 21 in response to pressure developed by the piston 12 of the master cylinder, but if the master cylinder hydraulic system fails the control piston 21 is moved by a push-rod 28. When the valve 19 is opened, i.e. lifted from its seating at one end of a tubular valve guide 18, the hydraulic pressure to operate the servo piston 9 passes through the valve 19 from a full power hydraulic system incorporating a reservoir, a pump and an accumulator; this hydraulic pressure enters the housing 7 by an inlet port 16 and leaves via a return port 17 and there is a relief valve 29 therebetween. The piston 5 is a floating piston incorporating a by-pass passage 14 which is closable by a seal 15 at the end of the servo piston 9. When the full power system operates properly the passage 14 will be closed when the servo piston 9 is moved but in the event of failure of the full power system the passage 14 remains open to allow direct communication between the master cylinder 1 and the outlet port 6. In the modification of Fig. 2 (not shown) the control piston (21a) is displaced mechanically, when the master cylinder is actuated, by means of a preloaded captive spring (32) which is located between the control piston (21a) and an abutment (33) on a rod (34) slidable in a bore in the control piston (21a). In the modification of Fig. 3 the servo piston 9a is integral with the piston 36 in the supplementary cylinder and the arrangement includes a tappet valve 40 which closes when the servo piston 9a is actuated to thereby shut off direct communication between the master cylinder and the outlet port. In the embodiment of Fig. 4 (not shown), the outlet port (6b) is at the left hand end of the housing and fluid from the master cylinder is conducted through an axial bore (46) in the servo piston (9b); this bore (46) is closable by a valve (47) when the servo piston (9b) is actuated. In the embodiment of Fig. 5 the supplementary piston 5c is formed on a hollow fitting 49 the interior of which can communicate with port 6c via ports 51 and via the master cylinder with ports 50; when the servo piston 9c is actuated a valve element 53, 54 is moved to shut off communication between ports 50 and 51.