Patent GB-887233-A (GB)
Title: Fluid-pressure system
Inventor: DEWAR DOUGLAS
IPC: B64C25/42
Filed: 1957-05-15
Abstract: 887,233. Hydraulic braking systems. DUNLOP RUBBER CO. Ltd. May 1, 1958 [May 15, 1957], No. 15352/57. Class 103 (1). In a fluid pressure braking system the supply of pressure fluid in a main pressure conduit is cut off on admission of pressure to an emergency pressure conduit. A control valve 1 as described in Specification 687,358, is operable by pedals 13 or 15, which are duplicated, to supply hydraulic pressure from a main source 19 and main pipe 6 through valve units 2 or 4 to pipes 8 or 8a and brake 10 or 12 through anti-skid devices 11 or 11a respectively. Should a pressure failure occur in this main system indicated by gauge 31 connected to conduits 6, 8 and 8a, the operator moves a lever 28 to an emergency position to operate a valve 26 by a cable 27 to supply pressure from emergency reservoir 25 to valve 1 which has been operated by cable 29, to supply fluid from pipe 7 through valve units 3, 5 to the brakes via pipes 9 or 9a; pressure in conduit 7 causes a plunger in a relay valve 24 to pressurize fluid in a conduit 23 to cause a relay valve 17 in conduit 6 to close conduit 6 and divert pressure therein to an exhaust reservoir via connection 21. On pressurization of pipe 9 due to emergency application, a piston in shuttle valve 34 closes port 36 and supplies pressure direct to the brake by-passing the units 11, 11a. The relay valves 17 and 26 reducing the source pressure from 3,000 p.s.i. to 1,500 p.s.i. comprise an inlet valve 40, Fig. 2, biased by spring 41 to close passage 42 from inlet 18 and an exhaust valve cap 43 urged against a slidable seat 44 by a cradle 45 against which spring 41 acts, the cap 43 being held firmly on its seat by a plunger 46 under the influence of a spring 47. In valve 17 the spring 47 is pre-adjusted by shims 55 between a guide 53 and a cap 54 in which the plunger 46 sliding through a guide block 57. A piston-rod 59, sliding in a flange 56 on which bears the spring 47, has a head 60 within the spring guide 53 and spaced from a flange 61 of the guide. Piston 66 on rod 59 is spaced from flange 56 by an element 62 having a peripheral groove 63 communicating with emergency connection 22 to valve 24 and axial passages 65, the piston being biased against element 62 by a spring 68 bearing against closure caps 69 having a venting port 70. In normal operation, the springs 41, 47 are so calibrated that operating pressure of, say, 1,500 p.s.i. in chamber 49 permits spring 41 to close inlet valve 40, for a greater pressure the saddle 40 is also moved to exhaust the excess pressure through port 21 and for less pressure the pressure from source can overcome spring 41 and flow passed the valve 40, for example during brake application. In valve 26 the spring 47 is manually adjustable and engages a lever 48 engaging the upper part of plunger 46; in emergency operation the cable 27 pivots the lever 48 to increase the pressure of spring 47 on plunger 46, exhaust valve 43 and cradle 45 to open inlet valve 40 to supply pressure through the conduit 7 to the valve units 3 and 5. The pressure fluid in conduit 7 causes relay valve 24 to pressurize fluid in pipe 23 which through connection 22 and axial ports 65 in element 62 moves piston 66 against spring 68, causing the rod head 60 to engage flange 61 and relieve the spring 47 on plunger 46 allowing the spring 41 to move the cradle 45, seat 44, exhaust valve cap 43 and inlet valve 40 to close the passage 6 between the valve 17 and control valve 1 and to exhaust pressure in this passage via chamber 49 and exhaust valve 43, 44. Should lever 28 be moved to a "parking position," the plunger 46 in valve 26 is depressed further to build up a greater pressure in conduits 7, 9, 9a and the brakes are more firmly applied, the valve 17 operating as in an emergency application. Specifications 676,708, 687,308 and 701,973 are referred to.