Patent GB-1166481-A (GB)
Title: Improvements relating to Aircraft Braking Systems
Inventor: HARVEY SAMUEL ERIC
IPC: B64C25/44
Filed: 1966-01-14
Abstract: 1,166,481. Hydraulic braking systems; valves. DUNLOP CO. Ltd. 12 Jan., 1967 [14 Jan., 1966], No. 1804/66. Headings F2F and F2V. An hydraulic distribution valve, for use in an aircraft including at least two alternative braking systems, includes a spool 32, Fig. 2, held in a first position by pressure in a first braking system and displaced to a second position when the pressure drops in which position a connection is established between a first pressure source and a second braking system, the spool being mechanically connected to a second spool 33 for manual displacement together, the second spool establishing communication between a second pressure source and the second braking system in the displaced position. Individual sets of wheels 13, Fig. 1, are separately controlled by pedals 10 which on normal actuation operate a solenoid valve 11 by an electric switch (not shown) to supply pressure fluid to brakes 12. The valve 11 has main and first emergency supplies selected by a failure-operated automatic change-over valve 14. The latter also feeds a distribution valve 15 which (when lever 21 is in normal position " A ") automatically connects the first emergency supply and pump 16 to control valves 17, 18 whereupon the pedals 10 give a " kickback " signal to the pilot. Thereafter braking is under pedal control from master cylinders 24 via hydraulic links 19, control valves 17, 18 and circuits 20. When lever 21 is in position " B ", a pressure accumulator 22 is connected to the system and in position " C " the pressure accumulator is also connected to the control valves 17, 18 for parking purposes as later described. The distribution valve 15 has connections to the main and first emergency systems at 40, Fig. 2, to a fluid reservoir at 36 via a oneway valve 37, to the pump 16 at 41, to the pressure accumulator 22 at 42 and to a first position on the brake control valves 17, 18 (see Fig. 3) at 43 and to a second position at 44. Spools 32, 33 are moved by lever 21 through rocker 55, a switch 30 being actuated by plunger 54 to close the solenoid valve 11 to signal the pilot. An outer spring of a coil spring assembly 61 urges spool 32, plunger 54 and rod 52 downwards against the main or first emergency fluid pressure in chamber 50. The latter pressure holds the distribution valve 15 closed in the figure 2 position. When pressure falls in chamber 50 the distribution valve 15 is opened by the outer spring 61 so that spool 32 establishes communication between the pump 16 and the brake control valves 17, 18 via port 41, radial bores (not shown), liner waist 71, spool waist 70, liner waist 72 to transfer passage 73, passages 74, 75 spool waist 76 and bore 77. When lever 21 is in position " B " the pressure accumulator 22 is connected to the two positions of the brake control valves 17, 18 and the pump 16 is isolated from the system as follows: the inner end plate 62 moves plunger 54 within passage 53 whilst spool 33 abuts piston 51 until the latter abuts the end wall of chamber 50. Spool waist 76 is now aligned with bores 77 and 80. In lever position C (for parking) fluid is admitted to chamber 140 from the pressure accumulator and acts on the end of spool 116 to hold the brakes on independently of pedal actuation. In all positions of lever 21 when rod 52 is spring-displaced switch 30 is actuated to isolate the main system from the brakes. When spool 32 is spring-displaced rod 52 is displaced downwardly by reservoir pressure (from spring chamber 38) communicated via bore 100. During lever-driven movement of plunger 54 fluid in passage exhausts via bore 100. Each of the brake control valves 17 or 18 has connections to the master cylinder 24, Fig. 1 at 110, to the fluid reservoir at 131, to the brakes at 121 and 122, to the fluid pressure supply at 119. When slave piston 111, plunger 112 and rod 113 are moved upwards to select brake pressure the movement is transmitted by overload spring 114 to spool 116 against the action of spring 115 which gives load " feed ". Spool 116 first disconnects ports 121, 122 from the exhaust chamber 131 by closing porting between piston waist 123 and spool recess 147. Further movement opens porting between spool recess 148 and piston waist 123 and connects fluid supply through ports 119, 120, spool recess 148, piston waist 123, ports 122 and 121 to the brakes. The brake fluid pressure is supplied from piston waist 123 via restrictor 135 and passage 136 to move piston 118 upwards against springs 130 until porting between piston waist 123 and spool recess 148 is closed thus disconnecting brake fluid pressure from supply. Further upward movement of spool 116 similarly increases the brake fluid pressure, the maximum pressure being controlled by an adjustable stop 132. Partial release of the master cylinder 24 allows spring 115 to move slave piston 111, plunger 112, rod 113 and spool 116 downwards, brake pressure being ported to the exhaust chamber through ports 121, 122, piston waist 123 and spool recess 167. Fluid pressure at jet 135 falls and a reduced pressure at the brakes is determined by the new position of spool 116. When a pressure drop causes distribution valve 15 to supply fluid from another source to port 119, fluid from the same source is also applied to chamber 125 and thence is communicated through port 126 to act on shoulder 128 to give the " kick-back " signal. When lever 21 is in position " B " the valve operation is the same with a different fluid source. To prevent a pressure trap when master cylinders 24 are held depressed when lever 21 is being returned to position " A " a non-return valve 139 connects passage 136 with spool recess 148. Hydraulic links 19 are fed via port 142 closed by a non-return valve 141. Chamber 145 is connected to a fluid reservoir to assist in equalizing the pressures acting on the valve. In another embodiment the distribution valve 15 may have the two spools aligned coaxially and possibly integrally.