Patent GB-1439921-A (GB)
Title: Master cylinder devices for fluid pressure braking systems and  to fluid pressure braking systems
IPC: B60T13/60
Filed: 1972-06-22
Abstract: 1439921 Braking systems; master cylinders AUTOMOTIVE PRODUCTS Ltd 21 June 1973 [22 June 1972] 29284/72 Heading F2F A hydraulic braking system comprises a master cylinder device 12 with a piston 30 operable by a push rod 31 to supply liquid to a port 20 of an intermediate tandem slave cylinder 18; movement of piston 30 also causes actuation of a valve device 57 which is thereby caused to bring about actuation of a vacuum-suspended servomotor 66 having a plunger 68 connected to the tandem slave cylinder 18. Thus a thrust is applied to an annular piston 74 of slave cylinder 18 comprising the sum of the thrust produced by movement of plunger 68 and thrust produced by displacement of liquid from master cyinder device 12. The master cylinder device 12 shown in Fig. 2 comprises a stepped plunger 25 slidably engaged within a through bore 27 of an annular plug 24, the plunger 25 being operable upon the valve device 57. The piston 30 carries a probe 34 having larger diameter end portions 35, 36. Portion 35 is slidable in an axial bore 33 in piston 30. A coil spring 42 acting on piston 30 takes its abutment on a top-hat metal pressing 38 retained on piston 30 and urges a plate 44 into abutment with end portion 36. The master cylinder device 12 has a port 50 and a recouperation port 51 connected by a pipe 13 to one compartment 11 of a reservoir 10 and has an outlet port 29 connected to part 20 of intermediate tandem slave cylinder 18. A pair of radially extending levers 52 positioned in the master cylinder device 12 have their inner ends in engagement with plunger 25 and their outer ends in engagement with respective fulcrums 53 defined by the annular plug 24. Intermediate their ends the levers 52 are engaged by a radial flange 56 on a tubular plunger 55. The valve device 57 comprises a hollow casing 58 divided by a diaphragm 61 into two compartments 59, 60. The diaphragm 61 carriers a normally open valve 62 which places compartments 59, 60 in communication when open and casing 58 carries a normally closed valve 63 operable to connect compartment 59 to atmosphere when operated. Compartment 60 is connected to the inlet manifold of the vehicle engine by a pipe 64 and the compartment 59 is connected to a compartment 65 of the servomotor 66, the other compartment 69 of which is connected to the inlet manifold by a pipe 71. The intermediate tandem slave cylinder 18 has ports 15, 16 connected to a compartment 14 of reservoir 10, and has outlet ports 72, 73 connected to rear brakes and front brakes respectively. In operation of the braking system, piston 30 is moved to close off the recouperation port 51 and to bring end portion 36 of probe 34 into contact with plunger 25. Subsequent movement of piston 30 is transmitted to the plunger 25 through the coil spring 42 whilst liquid is displaced through port 29 to port 20 of slave cylinder 20, and the movement of plunger 25 operates the valve device 57 to cause actuation of servomotor 66. This causes leftward movement of movable wall 70 which brings plunger 68 into engagement with the annular piston 74 in slave cylinder 18 to close the central aperture thereof. Thereafter the piston 74 is acted on by the combined thrust of the servomotor 66 and the liquid displaced from the master cylinder device 12 and braking pressure is applied to operate the brakes via ports 72, 73-a floating piston 75 is arranged between ports 72, 73. The valve device 57 is arranged so that with a liquid pressure sufficient to apply the brakes, the pressure in chamber 59 acts via valve 62 against plunger 25 to cause spring 42 to collapse: thereafter the piston 30 moves towards plunger 25 to increase pressure in bore 23. In the event of failure of pressure in the master cylinder device 12 the piston 30 engages plunger 55 to actuate the valve device 57. In the embodiment of the master cylinder device 12 shown in Fig. 3 the plunger 25 has a closed end bore 76 to receive an axial projection 79 on a member 77 which also incorporates a radial flange 78, abutting plunger 25, and a stepped stem. The end portion 80 of the stepped stem slides within bore 33 of piston 30. In the modification of Fig. 4 (not shown) the member 77 is replaced by an annular member (84) and a stem (85) which is slidable within the annular member (84).