Patent GB-588970-A (GB)
Title: A fluid pressure system for actuating brakes
IPC: B60T13/24
Filed: 1943-09-20
Abstract: 588,970. Fluid-pressure-operated brakes. SCHNELL, S. Sept. 20, 1943, No. 15417. [Class 103 (i)] [Also in Group XXIX] Brake operating means comprises two hydraulic master cylinders connected to the same brake and operated respectively directly by a manual member and by power means controlled by the manual member, a relief valve being provided to limit the pressure developed in the power operated cylinder. As shown, the power is pneumatic and is controlled by a follow-up valve device so that the master pistons move together and which enables both pistons to be manually operated if the power fails. The master cylinders A, B, are slidable to a limited extent within a reservoir casing 1 and are supported by a fixed part 11 so that normally the cylinders are connected to the reservoir by passages 22 which are closed by engagement of the cylinder extensions with seals 23 upon initial movement of the master pistons 14 The piston rod 16 of cylinder B is connected to the piston 38 of a cylinder 37 mounted on the base plate 31 and connected to the induction pipe of the vehicle engine. The pressure in the chamber c at the other side of the piston 38 is controlled by a valve comprising a disc 47 integral with a rod 48 slidable in the piston rod 16 and adapted to engage a seat 45 on a bell-shaped member 43 integral with a tubular rod 42. The rod 48 is coupled by rods 49, 50 to a crank arm on a pedal operated shaft which carries a second crank arm connected by rod 36 to the piston rod 16 of cylinder A. Normally the disc 47 is seated by spring 51 and holes (not shown) in piston 38 are uncovered by valve element 44 carried by member 43 so that vacuum exists on both sides of the piston. Upon movement of the pedal, element 44 is seated on the piston to cut off chamber c from chamber d and thus from the vacuum source and disc 47 is then unseated to connect chamber c to atmosphere through passages 44<1>, the rod 42, the boot 52 and an air cleaner 53. The piston 38 with master piston 14 of cylinder B are thus moved by air pressure and the piston 14 of cylinder A is moved directly by the pedal to apply the brakes. If the pedal movement ceases, the piston 38 and member 43 advances slightly to re-seat the disc 47. The movement of both master pistons thus corresponds to the pedal movement. When the pressure in cylinder B reaches a predetermined value, a relief valve 28 opens to permit liquid in that cylinder to flow into the reservoir 1 through passage 27 so that further pressure is applied only by the cylinder A, the cylinder B being cut off by a non-return valve 24. If the vacuum fails, the piston 14 of cylinder B is operated directly by the pedal by engagement of the valve disc 47 with the piston rod 16. During brake application cylinders A, B are maintained in position to close passages 22 by the pressure on the cylinder end walls 18 and upon return of the pedal cylinder B returns to open the passages 22 thereof upon initial movement of the piston since this cylinder is cut off from the pipe line, but cylinder A returns only when the piston 14 thereof reaches its initial position.