Patent GB-592406-A (GB)
Title: Improvements in or relating to fluid pressure control systems
IPC: B60T11/224
Filed: 1944-05-12
Abstract: 592,406. Hydraulic brakes. SCHNELL, S. May 12, 1944, No. 9144. [Class 103 (i)] [Also in Group XXVIII] A fluid pressure system suitable for operating brakes of the type in which a master cylinder directly supplies the brake or other operating cylinder and also controls a pump or other power-operated means which also supplies the operating cylinder includes a device which enables the power-produced pressure in the cylinder to be reduced and re-established independently of operation of the power-operated means, in accordance with variations of the pressure produced by the master cylinder. The pedal-operated master cylinder 2 is connected by pipe 10 to the control means of a pump P which delivers by pipe 11 to brake-operating cylinder 13. An auxiliary pressure control device C which includes an exhaust valve for the cylinders 13 is connected by pipes 15, 16 to the pipes 10, 11 and by pipes 17, 18, 19 to the reservoirs 8, 20 of the master cylinder and the pump which comprises a swash plate 26 connected to pumping units 27 and actuated by a ring 25 on a driving member 24 driven by a pulley 23 from, for example, an electric motor or a vehicle driving engine. Each pumping unit 27 comprises a piston 31 having a ball-and-socket 'connection 32 with the swash plate, an inlet valve 36 controlling a passage 35 and a delivery valve 38. Each unit 27 delivers to the pipe 11 through passages 39, 45, 49 and past a packing-cup 47 provided on a stepped piston 42 which has a ball-and-socket connection 44 with the swash plate. The device C comprises pistons 54, 55 of unequal diameter carrying respectively a valve 60 and its seat 61 and movable apart to an extent determined by the extension 58 of piston 55 so that the valve is normally open to exhaust the cylinders 13 by connecting the pipe 16 to the reservoir pipe 17. The pistons are normally held in the extreme position shown by a spring 64. Pressure liquid supplied to pipe 15 when the master piston 3 is operated closes the valve 60 and that supplied to pipe 10 initially flows past the packing-cup 51 of piston 42 to pipe 11 to supply the cylinders 13 until the brake shoes contact the drums. The piston 42 is at the same time moved to the right to tilt the swash plate 26, thus bringing the pump into action to supply liquid to pipe 11. The effective area of the piston 42 that is subject to the master cylinder pressure may be double that exposed to the pump pressure so that when the pressure built up in the cylinders 13 is double that in the master cylinder the piston 42 is returned, thus rendering the pump inoperative. The ratio of the effective areas of the pistons 54, 55 is the same as that of the areas of piston 42 so that the pistons 54, 55 remain in the position shown, but if the master cylinder pressure is reduced the pistons 54, 55 will move to the right until the increase in volume of the space at the left hand of piston 55 effects a corresponding reduction of the pressure in the cylinders 13. The pressure in the cylinders 13 may similarly be restored by restoring the master cylinder pressure. When this pressure is reduced to a low value determined by the spring 64 the valve 60 will be forced off its seat by the pressure in the cylinders 13, thus connecting the cylinders to the exhaust pipe 17.