Patent GB-1480410-A (GB)
Title: Brake booster and master cylinder assembly
IPC: B60T13/24
Filed: 1974-12-20
Abstract: 1480410 Brake booster and master cylinder assembly GENERAL MOTORS CORP 20 Dec 1974 [11 Feb 1974] 55286/74 Heading F2F A brake booster and master cylinder assembly 16 incorporates both a differential air pressure operated booster section 44 and an hydraulic fluid pressure operated booster section 46 for operation of a master cylinder section 48; a manually operable push rod 58 controls sequential power operation of the booster sections 44, 46 and also provides for manual operation of the master cylinder section 48. In the embodiment of Fig. 3 the booster section 44 is a vacuum suspended booster incorporating the push rod 58 which is operable by a brake pedal assembly 54 to operate valves 90, 92, 100 to control the pressure in a chamber 72 on one side of a movable power wall 68. When the push rod 58 is actuated valve 92 engages valve 100 to shut off chamber 72 from a chamber 70 on the other side of wall 68 which chamber 70 is permanently connected to vacuum: further movement disengages valve 90 from valve 92 to admit atmospheric air to chamber 72 creating a pressure differential across power wall 68 to move it leftwardly. Feel is provided to the operator lever reaction mechanism including a lever reaction plate 104 and reaction levers 106. The output mechanism of the booster section 44 comprises a sleeve 118 and a plunger 128 slidably received in sleeve 118, and the sleeve 118 and plunger 128 extend into hydraulic booster section 46. The hydraulic booster section 46 includes a power piston 154 reciprocable in a bore 148 and provided with a valve element 158 co-operable with a valve element 160 on the end of plunger 128 to provide a valve of the open centre type for the hydraulic booster section 46.  An input port 36 of the booster section 46 connects via a conduit 32, a power steering gear 24 and a conduit 26 with a pump 22. The port 36 connects with a power chamber 166 via a passage 174 and a passage 176 mounting a pressure relief valve 178 connects passage 174 and an exhaust chamber 164. A port 38 connects with the exhaust chamber 164 and the port 38 is connected via a conduit 40 with a reservoir section 42 of pump 22.  When the vacuum booster section 44 is power operated, sleeve 118 and plunger 128 are moved leftwardly together, and in this circumstance the valve elements 158, 160 do not change their relationship and hydraulic fluid continues to be circulated through the hydraulic booster section 46. However should the output of booster section 44 not be sufficient to meet the demand force then the valve element 90 will engage plunger 128 to move it leftwardly relative to sleeve 118; valve element 160 moves towards valve element 158 to cause a pressure build-up in chamber 166 which pressure acts on the piston 154. The piston 154 acts on a primary piston 194 of the master cylinder section 48 which also includes a secondary piston 196, the pistons 194, 196 controlling respective brake conduits 52, 50. In the modification of Fig. 4, the master cylinder reservoir 214 acts as a reservoir for the brake circuits and also for the power steering gear and power steering pump. The primary piston 194 is integral with or an extension of power piston 154 and the pistons are mounted in a common housing. In this arrangement conduit 40 is connected to reservoir 214 through a port 278 in the reservoir wall rather than with port 38. Different reaction ratios may be utilized in the two booster sections.