Patent GB-914687-A (GB)
Title: Improvements in or relating to vacuum-assisted braking systems
Inventor: BALLARD DONALD HENRY
IPC: B60T13/24
Filed: 1959-05-04
Abstract: 914,687. Fluid-pressure brakes. CLAYTON DEWANDRE CO. Ltd. April 27, 1960 [May 4, 1959], No. 15218/59. Class 103 (1). [Also in Group XXIX] In a vacuum-assisted braking system for road vehicles of the kind in which the output of the servomotor is transmitted through an hydraulic system to the wheel brakes, the servomotor is of the vacuum-suspended, piston and cylinder type, the cylinder being longer than the stroke of the piston to provide a vacuum reservoir 3 and means 5, 7, 22 extend through one end of the servo cylinder for transmitting the thrust of the brake pedal to the servo piston 2 and for actuating valve means 30, 32 carried by the piston and controlling operation of the ssrvo, means 18 being connected to the opposite side of the servo piston and operable to transmit the manual effort and the servo output to a concentricallydisposed master cylinder 8 mounted on the other end of the servo cylinder, the thrust of the servo piston 2 being transmitted by a piston-rod 18 which extends into the master cylinder and constitutes one of the pistons or displacement members in the master cylinder. In the inoperative position shown, the servo piston 2 is located in the forward end of the servo motor with interconnecting valves 30, 32 in their closed and open positions respectively, such that atmospheric connection 26, 27 is sealed-off and vacuum, from a vacuum source via connection 4, is established on both sides of the piston 2. The servo piston 2 is formed to provide an internal chamber 19 across which extends a flexible annular diaphragm 20 clamped at its inner edge to a carrier 21 secured at its centre to a slidable axially-displaceable stud 22 which abuts the rear face of a plunger 7 actuated by a thrust rod 5. Upon actuation of the brake pedal, the thrust rod 5 moves the piston 7 and the stud 22 rearwardly so displacing the diaphragm carrier 21 to close valve 32 and close the connection between the front side of the piston and the rear side of the diaphragm. Continued movement of the thrust rod displaces the valve assembly 30, 32, so lifting the atmospheric valve 30 and permitting air to flow to the space ahead of the piston to effect displacement of the piston 2 and associated rod 18 to actuate a tandem master cylinder to apply hydraulic pressure to the brakes of the vehicle. Should the source of vacuum fail, manual effort will displace the thrust rod 5 and associated plunger 7 until the latter reaches the limit of its movement in the servo piston extension 2a and thereafter the effort will be transmitted mechanically through the piston and piston-rod 18 to the master cylinder. The tandem master cylinder comprises two working spaces 9, 10 connected respectively to separate reservoirs 11, 12, by tiltable replenishing valves 13. The rear piston 15 is supported for axial movement in a transverse wall structure 17 whilst the front piston 16 is constituted by the rear end of a rod 18 which is socketed into an extension 2b in the rear side of the servo piston and extends into the forward end of the master cylinder, the piston 15 being actuated mechanically by the piston 16 in the event of failure of the hydraulic system incorporating working space 9.