GB605465A - Improvements in fluid pressure systems - Google Patents

Abstract

605,465. Fluid-pressure brakes. SCHNELL, S. July 5, 1945, No. 17205. [Class 103 (i)] In a fluid-pressure actuating system, particularly for a brake, in which a pressure " booster " comprising pistons of different diameter is interposed in a conduit connecting a source of fluid pressure, e.g. a master cylinder, with the fluid motor to be actuated, e.g. a brake cylinder, the conduit is normally closed by a valve which opens only when the pressure from the source attains a predetermined value to admit pressure fluid to the " booster," and a second conduit which normally establishes direct communication between the source and the fluid motor contains a normally open valve which is moved to a closed position when the first-mentioned valve is opened. As shown in Figs. 1 and 2, a pedal-operated master cylinder 11 supplies pressure fluid directly to the brake cylinders 10 through a pipe 3 and a pipe 6 controlled by a valve 38 carried by a piston 36. The master cylinder is also connected through pipes 2 and 4 to a cylinder 20 containing a piston 22 integral with a smaller piston 21 which works in a cylinder 19 connected to the brake cylinders by a pipe 5. The area of piston 21 is half that of piston 22, and the pistons are urged to the right by a light spring 25. The pipe 2 is normally closed by a valve 31 carried by a piston 32 urged to the right by a spring 34 which seats on a plate 35. When the master cylinder pedal is depressed, fluid is supplied to the brake cylinders through the pipes 3 and 6 until the pressure rise is sufficient to unseat the valve 31, whereafter fluid is supplied to the cylinder 20 to move the pistons 21, 22 to the left and thus boost the pressure in the brake cylinders. As the piston 32 moves to the left to unseat the valve 31, it engages a projection 42 on the piston 36 and seats the valve 38. The areas of pistons 32 and 36 are so chosen that the pressure on piston 32 is sufficient to hold the valve 38 seated against the pressure in pipe 6 (twice the master cylinder pressure), the pressure on piston 36 and the force of the spring 34. When the pedal is released, the piston 32 moves to the right sufficiently to allow the valve 38 to be unseated, and fluid is returned to the master cylinder via pipes 6 and 3. At the same time, pistons 21 and 22 are moved to the right by the pressure on piston 21 and the force of the spring 25, and fluid in the cylinder 20 is returned to the master cylinder via pipes 4 and 2 and the valve 31 which does not close completely until the pistons 21, 22 are in their retracted positions. To prevent premature opening of the valve 31 by rapid operation of the master cylinder, a restriction 44 is provided in the passage leading to the pipe 2. Fig. 3 shows a modification in which the valve seat 52 of the valve 31 is formed on a piston 48 integral with a larger piston 49 working in a chamber to which the pipe 2 is connected, the pipe 2 communicating with the valve through a passage 50 in the pistons provided with a restriction 56. If the master cylinder pressure rises to some predetermined high value after the valve 31 has been unseated, the pressure on piston 49 moves the pistons to the left against the action of a spring 55 to reseat the valve and thus limit the pressure which can be established in the brake cylinders.